npl report eng 57 final report to the cct on key ...npl report eng 57 final report to the cct on key...

NPL REPORT ENG 57 Final report to the CCT on key comparison CCT-K6 – Comparison of local realisations of dew-point temperature scales in the range -50 °C to +20 °C S Bell, M Stevens, H Abe, R Benyon, R Bosma, V Fernicola M Heinonen, P Huang, H Kitano, Z Li, J Nielsen, N Ochi, O A Podmurnaya, G Scace, D Smorgon, T Vicente, A F Vinge, L Wang, H Yi April 2015

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Final report to the CCT on key comparison CCT-K6 – Comparison of local realisations of dew-point temperature scales in the

range -50 °C to +20 °C

S Bell1, M Stevens2, H Abe3, R Benyon4, R Bosma5, V Fernicola6, M Heinonen7, P Huang8, H Kitano3, Z Li9, J Nielsen10, N Ochi3, O A Podmurnaya11, G Scace8, D Smorgon6, T Vicente4, A F Vinge11, L Wang12, H Yi9 1 Engineering Measurement Division, National Physical Laboratory (NPL), Teddington, UK 2 United Kingdom Accreditation Service (UKAS), Feltham, UK 3 National Metrology Institute of Japan (NMIJ), Tsukuba, Japan 4 Instituto Nacional de Técnica Aeroespacial (INTA), Madrid, Spain 5 Van Swinden Laboratorium (VSL), Delft, The Netherlands 6 Istituto Nazionale di Ricerca Metrologica (INRIM), Turin, Italy 7 Centre for Metrology and Accreditation (MIKES), Espoo, Finland 8 National Institute for Standards and Technology ( NIST), Gaithersburg, USA 9 National Institute of Metrology (NIM), Beijing, China 10 Danish Technological Institute (DTI), Århus, Denmark 11 National Scientific and Russian Research Institute for Physical, Technical and Radiotechnical Measurements – East Siberia Branch (VNIIFTRI-ESB), Irkutsk, Russia 12 National Metrology Centre, Agency for Science, Technology and Research (NMC), Singapore

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Queen’s Printer and Controller of HMSO, 2015

ISSN 1754-2987

National Physical Laboratory Hampton Road, Teddington, Middlesex, TW11 0LW

Extracts from this report may be reproduced provided the source is acknowledged and the extract is not taken out of context.

Approved on behalf of NPLML by Teresa Goodman,

Optical Measurement Group

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CONTENTS

1 INTRODUCTION ........................................................................................................................ 6

2 ORGANISATION OF THE COMPARISON ........................................................................... 7

2.1 PARTICIPANTS, AND STANDARDS USED IN THE COMPARISON ............................... 8

2.1.1 INRIM ................................................................................................................................ 8

2.1.2 INTA .................................................................................................................................. 9

2.1.3 MIKES ............................................................................................................................... 9

2.1.4 NIM ................................................................................................................................. 10

2.1.5 NIST................................................................................................................................. 10

2.1.6 NMC ................................................................................................................................ 11

2.1.7 NMIJ ................................................................................................................................ 11

2.1.8 NPL ................................................................................................................................. 11

2.1.9 VNIIFTRI......................................................................................................................... 12

2.1.10 VSL .............................................................................................................................. 12

2.2 COMPARISON SCHEME ...................................................................................................... 13

2.3 COMPARISON SCHEDULE ................................................................................................. 13

3. COMPARISON METHOD ....................................................................................................... 15

3.1 TRANSFER STANDARDS .................................................................................................... 15

3.2 REPORTING ........................................................................................................................... 15

3.3 IMPARTIALITY ..................................................................................................................... 16

3.4 COMPLIANCE WITH OTHER REQUIREMENTS .............................................................. 17

4 PERFORMANCE OF THE TRANSFER STANDARDS....................................................... 17

4.1 PROBLEMS WITH THE TRANSFER STANDARDS .......................................................... 18

4.2 CHECKS OF SAFE TRANSPORTATION ............................................................................ 21

4.3 CONSISTENCY OF PERFORMANCE OF INSTRUMENTS THROUGHOUT THE

COMPARISON ................................................................................................................................ 22

4.4 STABILITY OF EACH HYGROMETER .............................................................................. 23

4.4.1 Pilot measurements ......................................................................................................... 23

4.4.2 INTA measurements of Hyg2........................................................................................... 24

4.4.3 Drift estimates and discussion......................................................................................... 26

5 PARTICIPANT RESULTS ....................................................................................................... 31

6 BILATERAL EQUIVALENCE ................................................................................................ 34

7 KEY COMPARISON REFERENCE VALUES (KCRV) ...................................................... 44

7.1 CALCULATION OF KCRV ................................................................................................... 44

7.2 CHI-SQUARED TEST ............................................................................................................ 45

7.3 COMPARISON RESULTS PRESENTED IN TERMS OF KCRV ........................................ 46

8 DISCUSSION ............................................................................................................................. 49

9. CONCLUSION ........................................................................................................................... 50

10. ACKNOWLEDGEMENTS ....................................................................................................... 50

REFERENCES .................................................................................................................................... 50

APPENDIX 1: TECHNICAL PROTOCOL ..................................................................................... 53

APPENDIX 2: RESULTS REPORTED BY THE PARTICIPANTS ............................................ 71

APPENDIX 3: UNCERTAINTY ANALYSES OF PARTICIPANTS ......................................... 104

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1 INTRODUCTION

At the 19th

(1996) meeting of the International Bureau of Weights and Measures (BIPM)

Consultative Committee for Thermometry (CCT), the Working Group on Humidity

Measurements (CCT/WG6) was formed. The Working Group was charged with organising

an international comparison in the field of humidity standards. Preparations for a key

comparison began with an initial protocol drafted by NIST and reviewed by CCT WG7 (key

comparisons).

At its 2001 meeting, the CCT appointed NPL as pilot, and NMIJ as assistant pilot. It was seen

that the time-consuming nature of comparison measurements in this field would require that

the number of participants be limited in order to keep the duration of the comparison within

reasonable limits. The CCT agreed a limit of 10 participants. The balance of representation

between Regional Metrology Organisations (RMOs) was proposed by the CCT based on the

level of humidity standard activity within the RMOs.

During 2002, RMOs nominated institutes to participate, and the comparison protocol was

revised and agreed with participants. At this time, the role of pilot for EUROMET.T-K6 was

transferred from NPL to MIKES (Finland), and the CCT-K6 and EUROMET.T-K6 protocols

and reporting templates were developed in close alignment.

The CCT-K6 protocol was reviewed by WG6 when they met in September 2002, approved

by K6 participants in March 2003, with agreed minor changes arising from comments from

CCT WG7 who approved the protocol in July 2003.

At the start of preparations, measurement comparison methods in the field of humidity were

not well established, so in-depth trials of (initially) three travelling standards were carried

out. In consultation with participants, two preferred instruments were identified for use.

In late 2002 NPL performed the initial pilot set of comparison measurements using the

travelling standards, marking the effective start of the comparison. Measurements by

participants proceeded until 2009, interspersed by a large number of delays, repairs,

additional checks and participant changes, which all contributed to extending the duration of

the comparison. The details of the incidents and checks are given in Section 3. Despite the

extended timescale and several minor repairs to the instruments, the checks of consistency

and drift of the instruments provide satisfactory evidence that the results are reliable enough

for the purpose of the comparison, as discussed in Section 4.

By the time of conclusion of CCT-K6, the corresponding RMO comparisons APMP.T-K6 [1]

and EUROMET.T-K6 [2] had already been completed, and results were in use to support

claims of calibration and measurement capability (CMCs) of NMIs involved. These

comparisons are therefore available for linkage via common participants, limited only by the

continuity of the realisations at those institutes.

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2 ORGANISATION OF THE COMPARISON

The purpose of the comparison was to establish the degree of equivalence between

realisations of local scales of dew/frost-point temperature of humid gas, in the range -50 °C

to +20 °C, among the participating national measurement institutes.

The key comparison is a comparison of the measurand “realisation of local scale of dew-point

temperature” at the participating national institutes. The dew-point scale comprises dew

points and (below the freezing point of water) frost points.

The comparison was designed to provide

Estimates of bilateral equivalence between every pair of participants at each measured

dew point

A key comparison reference value (KCRV) for each nominal value of dew/frost point

in the comparison.

Estimates of equivalence of each participant to the KCRV

The technical protocol for the comparison is shown in Appendix 1. The comparison was

made by circulation of a pair of travelling transfer standards. Each transfer standard was used

to independently measure dew/frost-point temperature of a sample of moist gas (air or

nitrogen) produced by a participant's standard generator using the same measuring process.

Measurements were made at dew point nominal values of -50 °C, -30 °C, -10 °C, +1 °C and

+20 °C. The points were chosen to test the main range of interest, covering frost and dew

regions. The nominal value of +1 °C represents the range near 0 °C while being far enough

above it to avoid ambiguities that can arise around the freezing point of water.

The comparison took the form of a closed circulation in two consecutive loops. There was

one pair of hygrometers, which were at all times measured nominally simultaneously.

Simultaneous measurements using a pair of standards gives information about the within-

laboratory consistency of the measurements, the reproducibility of the instrument

performance, and continuous feedback about the successful transport of the instruments

without any major shift in performance.

The values of dew-point temperature reported for the travelling standards are “arbitrary”

values calculated from the measured resistance output. The travelling standards are used

simply as comparators.

Further below, values of Key Comparison Reference value (KCRV) are calculated, but it is

important to note that any KCRV in this comparison has no absolute significance – it does

not represent a reference value in the SI, only a comparison parameter.

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2.1 PARTICIPANTS, AND STANDARDS USED IN THE COMPARISON

A list of the participants is given in Table 1, including concise indication of their standard

generator types, and references to publications.

Table 2.1 List of participants. (Institute current names and abbreviations are given – at the start of the

comparison several of them were known by other names). The type of standard is also given, as two-

pressure (2-P), or single-pressure (1-P).

Participant Acronym Standard

type

Centre for Metrology and Accreditation (Finland) [3] MIKES 1-P

Instituto Nacional de Technica Aeroespacial (Spain) [4,5,6,7] INTA 2-P

Istituto Nazionale di Ricerca Metrologica (Italy) 1 [8,9] INRIM 1-P

National Institute of Metrology (China) 1 [10,11] NIM 2-P

National Institute for Standards and Technology (USA) [12,13] NIST 2-P

National Metrology Centre, Agency for Science, Technology and

Research (Singapore) 1 [14, 15]

NMC 2-P

National Measurement Institute of Japan (Japan) [16,17] NMIJ 2-P

National Physical Laboratory (UK) [18,19]] NPL 1-P

National Research Institute for Physicotechnical and Radio

Engineering Measurements (Russia) – East Siberia Branch 2 [20]

VNIIFTRI

ESB

2-P

Van Swinden Laboratorium (Netherlands) 1 [21, 22] VSL 1-P

Details of participant facilities used for the comparison are given in the following

subsections.

Participants have confirmed that no significant changes have been made to their dew point

standards between the time of measurement and the time of reporting. This ensures that the

results of any participant can form a valid link to the KCRV through other comparisons up to

the date of this publication at least. The only exceptions to this are NIST and VSL. The NIST

Low Frost Point Generator used for the -50 °C and -30 °C points in this comparison was

significantly modified after the comparison measurements (as discussed in Section 7.1). The

VSL generator used here for CCT-K6 was used also for EUROMET.T-K6 [2], but since then

has been replaced with a newly constructed standard [23, 24].

2.1.1 INRIM

The INRIM primary standards used in the comparison were INRIM-designed single-pressure

generators [8, 9]. For the comparison values -50 °C, -30 °C and -10 °C, the IMGC02 (now

INRIM 02) standard frost-point generator was used, and and at +1 °C and +20°C the

IMGC01 (now INRIM 01) standard dew point generator was used.

1 At the start of planning the comparison, several participant institutes were known by previous names: INRIM

was IMGC, NIM was NRC-CRM, NMC was SPRING, and VSL was NMi. Throughout this report, current

names of institutes are used.

2 Initially, VNIIM was the planned participant for Russia, but later VNIIFTRI was nominated.

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In the INRIM 02 generator, a stream of N2 gas flows through a heat exchanger and, then, over

a surface of ice inside an isothermal saturator held in a temperature bath. The gas is re-

circulated many times over the isothermal surface, achieving an equilibrium saturation whose

temperature is monitored with two PRTs installed at the outlet of the saturator in the ice layer

and in the air flow. The system was constructed with vacuum-grade fittings and

electropolished tubing. A centrifugal pump is used to re-circulate the carrier gas (N2) at any

flow value between 3 L min-1

and 10 L min-1

. A hygrometer in calibration is connected in a

branch of the main loop with gas flow rate to be set between 0.5 Lmin-1

and 1.5 L min-1

.

The INRIM 01 generator is a recirculating-type generator to cover the dew/frost point range

from -15 °C to +90 °C. The carrier gas can be N2 or air. It is designed to accommodate the

hygrometer in calibration either into an isothermal chamber (closed-circuit mode) or in a

secondary branch with a draw-off flow up to 1.5 L min-1

(open-circuit mode). The saturating

unit consists of a box where the air is forced to flow over a surface of water or ice for a length

of 1.2 m. The temperature is monitored at three different sections of the saturator by means of

three pairs of platinum resistance thermometers (PRTs): one thermometer is located

immediately underneath the water surface (the water depth never exceeds 10 mm) and the

other is placed in the gas, immediately above the first one. One pair of PRTs is at the outlet

where the saturator temperature is defined.

The traceability of the realisation is in terms of temperature through the calibration of the

saturator platinum resistance thermometers with traceability to the SI (ITS-90) via INRIM

temperature standards. Supporting electrical and pressure measurements are traceable through

calibrations at INRIM.

2.1.2 INTA

In the range from -50 °C to -10 °C, the INTA Low-range standard humidity generator is a

modified Thunder Scientific model 4500 two-pressure generator with saturation performed

with respect to ice. In the range from 1 °C to 20 °C the INTA High-range standard humidity

generator is a modified Thunder Scientific model 9000 two-pressure generator used with

saturation with respect to water. The generators were operated in two-pressure mode at

nominal flow rates of 2.7 and 50 L/min, respectively and with a saturator pressure below

300 kPa. The realised frost/dew-point temperatures in both cases were determined from

independent temperature and pressure measurements using standard platinum resistance

thermometers calibrated at the ITS-90 fixed points, precision resistance bridges (1 mA / 75

Hz) and low AC/DC difference standard resistors and precision digital absolute pressure

gauges. Temperature and pressure measurements are traceable to CEM and DC resistance,

AC/DC difference and voltage ratio are traceable to CEM, NPL and PTB, respectively. Both

generators were run on CO2-free air obtained from oil-free compressors fitted with heat

regenerated molecular sieve adsorption driers, and using high-purity deionized water of

nominal resistivity 18 M-cm [4,5,6,7].

2.1.3 MIKES

MIKES used the MIKES Dew/Frost-point Generator (MDFG) as the dew-point temperature

standard in this comparison [3]. The generator comprises three saturators: LRS2 (-80 °C to

+15 °C), LRS1 (-60 °C to +15 °C) and HRS (0 °C to +90 °C). In this comparison, LRS1 was

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used at measurement points -50 °C, -30 °C and -10 °C. HRS was used for measuring the

points +1 °C and +20 °C. All three saturators operate on the same principle. Air flowing at a

rate of typically less than 2 l/min is saturated with water vapour by a single pass through a

precision saturator located in a temperature-controlled liquid bath. A pre-saturator ensures

that the dew-point temperature of air entering a main saturator is slightly higher than the main

saturator temperature. Thus, condensation takes place in the inlet heat exchanger tube of the

main saturator. Saturation with respect to plane water or ice layer is completed by forcing air

flow on water or ice surface in a saturation chamber connected to the outlet of the heat

exchanger tube. Saturated air flows through an internally electropolished tubing to the

hygrometer under calibration. The tubing is heated when needed to prevent any water

condensation in it. The generated dew-point temperature is determined from the measured

saturator temperature, the saturator pressure and the air pressure in the hygrometer under

calibration. Being the primary realisation for dew-point temperature, MDFG provides

traceability to the SI through traceable temperature and pressure measurements. The

traceability of these measurements is established through calibrations at MIKES within its

CMCs published at the BIPM website.

2.1.4 NIM

A two-pressure generator constructed by NIM [10,11] was used for this comparison at the

comparison values -50 °C, -30 °C, -10 °C, +1 °C and +20°C. The two pressure generator

involves saturating a continuous stream of carrier gas with water vapour at a known

temperature and pressure. The uncertainty of the device is determined by the uncertainty of

the temperature and pressure measurements. The two-pressure generator consists of the heat

exchanger, the saturator and the test chamber. All pipe lines were constructed by the use of

internally polished tubing. The carrier gas flow rate range is 0.1 L/min to 2 L/min. The dew-

point/frost-point range is -75 °C to +25 °C. The temperature and pressure measurements are

traceable to NIM’s temperature and pressure standards.

2.1.5 NIST

The NIST primary standards used in the K6 comparison were NIST-designed thermodynamic

generators For the comparison values -10 °C, +1 °C, and +20°C the NIST Hybrid Humidity

Generator (HHG) [12] was used, and at -50 °C and -30 °C the NIST Low Frost-point

Generator (LFPG) [13] was used. The HHG was operated using the two-pressure principle.

When the HHG is operated this way, air flowing at a rate of typically 30 l/min is saturated

with water vapour by a single pass through a temperature-controlled saturator. Saturation

takes place with respect to the surface of water by vapour diffusion and mixing at a measured

controlled pressure that is often elevated. The generated amount fraction (mole fraction) is

determined using the temperature and pressure at the location immediately before the outlet

of the saturator. The generated dew/frost point is calculated using the generated amount

fraction and the pressure at the location of interest. The LFPG operates in a similar manner

as the HHG, except that 1) the operating gas is nitrogen, 2) the flow rate through the saturator

is 2 l/min, 3) the saturator contains ice, 4) the pressure difference Δp between the saturator

and the location of interest is very small, and 5) the frost-point temperature at the location of

interest is determined as the measured saturator temperature with a small correction for Δp.

Also, the LFPG uses internally electropolished tubing in its construction to minimize

adsorption/desorption on the surface of the tubing. The SI traceability of the realisation is in

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terms of temperature and pressure. The traceability of the temperature measurement is

through the calibration of the saturator’s standard platinum resistance thermometer using

ITS-90 fixed points maintained at NIST. The SPRT resistance measurements make use of

standard resistors calibrated at NIST. The calibrations of the two pressure gauges are

traceable to NIST pressure standards.

2.1.6 NMC

Two humidity generators were used as references to compare with the traveling standards

[14,15]. Both are Thunder Scientific products. The Model 4500 frost generator is based on

two-pressure and two-temperature principle and uses nitrogen as working gas. It was used for

the comparison at -50, -30 and -10 °C frost points. Nitrogen flow of 1.5 litres per minute was

used for all measurement points. The Model 2500 humidity generator is based on two-

pressure principle and uses air as working gas. It was used for comparison at -10, +1 and

+20 °C frost/dew points. Air flow of 10 to 20 litres per minute was used instead. The two

transfer standards were connected to each generator in parallel with a leaking valve in

between the generator and the transfer standards. Each standard had a flow approximately 0.5

litres per minute as given by the flow indicator of the standard and the leaking valve released

the extra gas from the generator. The system accuracy affecting parameters of the two

generators, such as pressure transducers and thermometers are regularly calibrated against

reference standards maintained at NMC/A*STAR, Singapore.

2.1.7 NMIJ

Two generators, frost-point generator (FPG) [16] and two-pressure generator (2PG) [17],

both of which were designed by NMIJ, were used for the NMIJ primary humidity standards

in the comparison. The FPG and 2PG were used for the comparison ranges of -50 °C

to -10 °C and +1 °C to +20 °C, respectively. The principle of the two generators is on the

basis of the generation of saturated water vapour using ice or water maintained at constant

temperature. Nitrogen and air were used as matrix gases for the FPG and 2PG, respectively.

The flow rates of the gases passing through the FPG and 2PG were 3 L/min and 20 L/min,

respectively. SUS316L stainless-steel tubes with an outer diameter of 6.35 mm (1/4”) whose

inner surfaces were electropolished were used to connect transfer standards to the FPG. The

pressure and temperature of the saturated gases were measured using pressure gauges and

platinum resistance thermometers, which are traceable to the International System of Units

(SI) using calibrations services at NMIJ or at calibration laboratories accredited by IA Japan.

2.1.8 NPL

The NPL primary standards used in the comparison were NPL-designed single-pressure

generators [18,19]. For the comparison values -50 °C, -30 °C and -10 °C the “NPL Low

Frost-point Generator” (LFG) was used, and at +1 °C and 20 °C the “Standard Humidity

Generator” (SHG2) was used. Both generators operate on the same principle: air flowing at a

rate of typically 0.5 l/min to 1 l/min is saturated with water vapour by a single pass through a

precision saturator located in a temperature-controlled liquid bath. Saturation takes place

with respect to surfaces of water or (below 0 °C) ice, by vapour diffusion and mixing, at

measured controlled pressure close to atmospheric pressure. The LFG is specialised for low-

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range operation by the use of internally electropolished tubing in its construction. The SHG2

is specialised for high-range operation by the use of an initial pre-saturation stage, and trace

heating for condensation protection. The “generated dew-point” is defined by the measured

temperature of the saturated flowing gas at the final stage within the saturator. The

traceability of the realisation is in terms of temperature through the calibration of the

saturator platinum resistance thermometer with traceability to the SI (ITS-90) via NPL

temperature standards. Supporting electrical and pressure measurements are traceable through

calibrations at NPL or at UKAS accredited laboratories in the UK.

2.1.9 VNIIFTRI

The Russian national humidity standard comprises two humidity generators with working

range from 5 °C to 90 °C and from -60 °C to +15 °C respectively. The humidity quantities of

relative humidity, dew/frost-point temperature, mole fraction are disseminated. Ordinary

hygrometers are traceable to the national primary standard in accordance with the state

hierarchical chain for measuring means of gas humidity. The common working range (dew

points from 5 °C to 15 °C) allows comparison of the generators. The generators use the phase

equilibrium method to generate humid gas defined in terms of dew/frost-point temperature

from -79 °C to +90 °C. The expanded uncertainty in dew/frost-point temperature is no more

than 0.12 °C.

2.1.10 VSL

The VSL humidity generator used for the comparison was a dew-point generator of the

circulating single-temperature, single-pressure type [22]. A pump recirculates air or nitrogen

gas over two saturators immersed in temperature-controlled liquid baths in which the

temperature is measured using platinum resistance thermometers, and this determines the

realised value of dew point for the saturated gas. One or other saturator can be selected,

depending on the temperature range within an overall envelope of −60 °C to +70 °C.

Circulation is controlled by means of a centrifugal impeller and switching valves to select the

flow path. Traceability of dew point is provided by calibration of the thermometers by

comparison against standards calibrated to ITS-90.

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2.2 COMPARISON SCHEME

The comparison scheme is illustrated in Figure 2.1. It is shown in two geographical loops

(Europe and rest-of-world) separated by pilot measurements. However the loops ware made

in series, not concurrently, and therefore for purpose of analysis the comparison was

functionally a single loop. Additional intermediate checks were also made (discussed further

below in Section 4).

Figure 2.1 Scheme of the comparison in two geographical loops (Europe and rest-of world) made in series,

separated by pilot measurements. Loops were sequential, not concurrent.

The comparison can be linked to EUROMET.T-K6 through INRIM, INTA, MIKES, NPL

and VSL. A link to APMP.T-K6 is available through NMIJ, NIM and NMC. NIST provides a

link to SIM, and VNIIFTRI provides a link to COOMET. CCT bilateral comparisons will

link to CCT-K6 via key comparison participants.

2.3 COMPARISON SCHEDULE

The approximate measurement dates for the comparison are shown in Table 2.2. Each

laboratory initially proposed an estimated duration of measurements and shipping (typically 8

weeks). Although many participants complied with these estimates, there were many and

frequent disruptions to the schedule, mainly due to instrument breakdowns and repairs, and

consequent need for extra measurement checks by the pilot and others. The outcome of these

repairs is not believed to affect the instrument readings. More detailed discussion of this is in

NPL

NMIJ

Pilot

Assistant Pilot

Participants

INRIM

MIKES

NIST VSL

NIM

NMC

VNIIFTRI

INTA

Loop 1 Loop 2

NPL

14

Section 4. However the simple fact of extending the comparison due to multiple delays

requires a particularly careful consideration of the impact of any possible long-term drift in

the instruments.

NIST obtained agreement to make two sets of measurements, against two different humidity

generators, but afterwards agreed to submit results for just one of these to the comparison.

The 2006 measurements by NMIJ were intended to provide an extra mid-comparison check

of instrument stability. However these were not reported or used, due to a number of extra

checks made by NPL and INTA.

Table 2.2 Approximate measurement dates of the comparison.

Measurement

start

Measurement

finish

NPL Jul-02 Jul-03

NMIJ Sep-03 Oct-03

VSL Oct-03 Dec-03

MIKES Jan-04 Mar-04

INTA Mar-05 Apr-05

INRIM May-05 Jul-05

NPL Sep-05 Feb-06

NMIJ Mar-06 Jul-06

NIST1 Nov-06 Dec-06

NIST2 Jan-07 Feb-07

NMC Mar-07 Apr-07

NIM Oct-07 Dec-07

NPL Feb -08 Mar 08

VNIIFTRI Dec-08 Mar 09

NPL Apr-09 May 09

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3. COMPARISON METHOD

3.1 TRANSFER STANDARDS

After some discussion and trials of several hygrometers, the participants agreed on the use of

two transfer-standard condensation-principle dew-point hygrometers – one Michell

Series 4000 serial number 92-0319, owned by NPL (identified as Hyg1) and one MBW

model DP 3DSH III K-1806, serial number 114155 / 91527, owned by INTA (identified as

Hyg2). Further details of the instruments are given in the protocol in Appendix 1.

These individual instruments were selected because they had the resolution required for the

comparison, and in both cases had an established history of reliability, minimal drift, and

established operating conditions in terms of supplementary cooling, flow rate, short-term

stability, etc. The hygrometers contained integral refrigeration units to provide reproducible

supplementary cooling.

No additional changes in the instruments were made for the comparison. No specific separate

calibrations were made of key components (such as the mirror PRT). (Although this can in

modern instruments provide extra confidence and scope for checking, it was considered

sufficient to treat the instrument “as a whole”).

Towards the end of the comparison, transit data loggers were transported with the

hygrometers to monitor both temperature and mechanical shock during transportation. No

significant events were recorded.

For the purpose of establishing instrument history, past calibration data for Hyg2 were

supplied to the pilot by INTA in confidence, not revealed to other participants, and did not

compromise the “blindness” of comparison measurements by INTA or other participants.

3.2 REPORTING

Each laboratory realised and reported:

5 dew/frost points

each dew/frost point separately reproduced 4 times

each realisation measured using two travelling standards simultaneously, resulting in

40 individual transfer standard results (20 per transfer standard).

Participants were instructed to re-form the condensate layer for every separate measurement.

Participants realised and measured values within 0.5 °C of the comparison nominal values.

Participants reported:

applied dew/frost point from the participant standard generator

measured values (both travelling standards simultaneously)

difference (applied dew point minus – measured dew point) for both travelling

standards

uncertainties associated with these (including short-term standard deviation of

travelling standards)

Difference values are the results compared and analysed for the comparison.

16

Supporting information was reported, including pressure and flow rates of sample gas

supplied to the hygrometers, coolant temperatures, and other relevant background

information. All measurements were made at nominally (just above) atmospheric pressure

and at flow rates of approximately 0.5 l/min through each instrument.

The indicated value of dew point for the instrument was derived from the measured resistance

of the mirror PRT after stabilisation of the instrument at each condition measured. This

resistance value was converted to a nominal temperature indication by using the nominal

PRT resistance-temperature characteristic in IEC 60751 (1995-07) (corresponding to

EN 60751:2008), defined as follows:

For temperature above 0 °C:

Rt = R0(1 + At + Bt2) (1)

and for temperature below 0 °C:

Rt = R0[1 + At + Bt2 + C(t-100)t

3] (2)

where

t = temperature (ITS-90), °C,

Rt = resistance at temperature t,

R0 = nominal resistance of 100 Ω at 0 °C

A = 3.9083 × 10-3

°C-1

,

B = -5.775 ×10-7

°C-2

,

and

C = -4.183 × 10-12

°C-4

.

Note that this is a deliberately arbitrary nominal temperature value for the purpose of

comparison, with no absolute significance.

Reporting templates are shown in the appendices to this report

3.3 IMPARTIALITY

The impartiality (“blindness”) of the comparison was ensured by the pilot conserving the

confidentiality of the data throughout, and no communication of results between partners was

allowed during the comparison. This was true during instrument evaluation, during

participant measurements, and during interim decisions about the comparison where needed.

Any limited data shared during the comparison for the purpose of discussing concerns about

the instruments (See Section 4 below) was strictly in coded terms, not absolute values.

The use of a general function (IEC 60751) for conversion of resistance to temperature,

together with the tendency of these instruments to have (stable) calibration offsets, both also

contributed to the blindness of the measurements.

For a period overlapping this comparison, some participants also took part in the

corresponding RMO comparison EUROMET.T-K6. This involved INRIM, INTA, MIKES,

NPL, and VSL. However there is no reason to suggest this affected the blindness of CCT-K6.

17

Since NPL, as the pilot, measured at more than one time during the comparison, the first full

set of NPL results is used as the reported comparison data, while other NPL results are used

for instrument drift assessment.

3.4 COMPLIANCE WITH OTHER REQUIREMENTS

Other requirements of the CIPM Mutual Recognition Arrangement [25] are met in respect of

the following points.

The comparison participants have formally approved this report.

Consistency has been ensured between this CCT key comparison and the several

corresponding RMO and bilateral comparisons to date. Protocols or reports of corresponding

comparisons to date have been reviewed by CCT/WG7 for consistency with this one, even

though several of these comparisons, notably APMP.T-K6 and EUROMET.T-K6, were

initiated or completed before CCT-K6 itself. Certain of the comparisons have covered more

measurement points than CCT-K6. For these cases, it has been noted that linkages to CCT-

K6 are possible at values measured in common between comparisons, but not at other values.

4 PERFORMANCE OF THE TRANSFER STANDARDS

Stability of the transfer standards is critical to the uncertainty and validity of the comparison.

This was particularly a concern for two reasons: the long duration of the comparison, and the

several interventions made to diagnose and repair problems with the instruments.

The performance of the transfer standards during the comparison was monitored in three

ways:

On receipt of the instruments, every participant was required to execute comparison

measurements at a dew point of 20 °C as a first step, and to report the results immediately

to the pilot. From this, the pilot assessed the consistency of agreement between the two

transfer standards as an indication of safe transit, and confirmed to the participant to

proceed with full measurements.

Secondly, the between-instrument agreement at all measured values throughout the

comparison gives an indication of consistent performance of the instruments.

Thirdly, drift of the instruments over the whole period of the comparison was assessed

from pilot measurements at the beginning and end of the comparison, and at certain times

in between, especially at times of repair or other concern raised about the hygrometers. In

addition, extra measurements by INTA of Hyg2 before, during and after the comparison

gave further evidence of stability of this instrument.

The three types of checks are detailed further below in sub-sections 4.2 to 4.4.

18

4.1 PROBLEMS WITH THE TRANSFER STANDARDS

The transfer standards represented the state of the art when the comparison started, and were

selected for their history of stable and reliable operation. However, due to the age of the

instruments, they suffered a large number of minor failures. There was also a suspected

electrical measurement anomaly that was not an instrument failure. The repairs and other

interruptions considerably delayed the comparison at many stages. However, no significant

effect on the long-term characteristic of either instrument was observed (as detailed in Sub-

sections 4.2 to 4.4 below). At every intervention, the pilot briefed participants and secured

participant agreement to appropriate actions. The incidents are summarised in Table 4.1 to

put into context the results of checks of instrument stable performance throughout the

comparison.

Overall there were more than 12 distinct breakdowns or problems with the instruments. Only

a small number of these (queries over NMI and MIKES measurements, and head-heater

problem at NPL) have any potential implications for the comparison outcome. The checks

throughout the comparison assume extra significance because of the need to be able to

demonstrate that none of the incidents affected comparison results. Where relevant, the

events are marked as A to Q on the graphs in Section 4.

It was not obvious how any of these instrument problems could have been avoided at the

time. However the recent new generation of similar hygrometers is more reliable, and

subsequent comparisons have benefited from that.

19

Table 4.1 List of problems with the transfer standards, and interventions made

Date Event Problem Action Impact on comparison

results

Oct to

Dec

2003

A After measurements

completed, VSL

expressed some concern

about reproducibility of

Hyg1 in low range.

No action, but scrutiny of

subsequent results at all

participant labs

Direct concern only for

VSL data. Not observed

to affect other results

Jan to

May

2004

B MIKES results

(completed Jan-Mar and

analysed up to May)

appeared to show

discrepancy between AC

and DC resistance

measurements of

hygrometer PRT, of up

to 0.07 °C.

Extensive investigation on

identical model at NPL could

not replicate the effect. Lesser

effects (due to stray

capacitance, inductance, self-

heating) were measurable or

calculable – none significant at

this level.

MIKES accepted that

the anomaly could not

be reproduced, and

chose which results to

report. Participants were

involved in discussion,

but “blindness” of

results was preserved

throughout.

April

2004

C Hyg2 light source (part

of optical detection of

condensate formation

and feedback) failed

while at INRIM.

Hygrometer component

(measuring head) sent to INTA

for replacement of light source,

then returned to INRIM where

gain of photodiode circuit was

adjusted in situ. This element

of the instrument is part of the

control electronics, but does

not determine the instrument

reading.

Delay, but no impact on

instrument

characteristic.

May

2004

D Hyg2 refrigerator failed

at INRIM –

Complete replacement of

refrigeration system needed.

Repaired by manufacturer

(necessarily travelling via

INTA, as owner). Instrument

then checked at INTA (against

past calibration history, but

retaining “blindness” of

comparison). Instrument was

then re-checked at NPL.

Delay, but checks did

not show any departure

from previous

characteristic.

Late

2004

E Hyg2 failure of a

compressor valve within

refrigeration system

Returned to manufacturer for

further repair,


instrument

characteristic.

Late

2004

F Hyg1 film thickness control

reinstated on front panel of

instrument (from internal

position) for improved

usability. Instrument was then

re-checked by pilot, alongside

Hyg2.

No impact on instrument

characteristic

Sep

2005

G Mid-comparison measurements

as planned, by pilot (NPL)

No adverse findings

20

Date Event Problem Action Impact on comparison

results

May

2006

H Hyg2 photodiode failed

while at NMIJ.

Measuring head sent to

manufacturer agent in Japan for

repair. NMIJ made extra

measurements to confirm

satisfactory operation after

repair. The photodiode is part

of the control electronics but

does not determine the

instrument reading.


instrument

characteristic.

August-

Sep

2006

I Additional check at NPL to

confirm no change due to

photodiode replacement

Delay, but no adverse

findings

March

2007

J Hyg2 failed to operate at

NMC

Identified as failure of a power

supply smoothing capacitor. On

manufacturer’s advice,

remedied by removal of

capacitor.


instrument

characteristic.

March

2007

K Hyg2 “mirror check”

indicator flashing

False indication, solved by

switching to “standby” and

switching off, as needed


characteristic.

March-

April

2007

L Hyg1 power supply cut

out several times

Cause unsure. No action. No impact on instrument

characteristic.

May to

August

2007

M Instruments re-checked at NPL.


instrument

characteristic.

May to

August

2007

N Query over sensitivity of

instrument readings to

coolant temperature

Additional checks made by

NPL.


findings

Oct-Dec

2007

P Hyg1 display panel

meter failed at NIM

(display not used or

reported in comparison)

NIM completed measurements

by data-logging electronically

as planned. On return to NPL,

the loose connection to one pin

of the display was repaired by

the manufacturer.


characteristic.

Jan 08 Q While at NPL, Hyg2

head heater control

failed, leading to

excessive heating of

head.

Head heater control was

repaired in situ by the

manufacturer. This was the first

and only problem with risk of

affecting key comparison

results. Full set of repeat NPL

measurements carried out after

repair, to be sure no effect on

results.


findings.

21

4.2 CHECKS OF SAFE TRANSPORTATION

Results of initial between-instrument consistency checks at a nominal dew point of 20 °C are

shown in Figure 4.1. These served to inform the pilot as in indication of safe arrival at each

participant lab (in some cases after remedying instrument problems). The results at 20 °C

were sent to the pilot immediately for review. In every case results were judged sufficiently

consistent by inspection.

From Figure 4.1, retrospective analysis shows that:

Although scatter at 20 °C varies from participant to participant, no lab or labs have

significantly worse scatter or deviation than the typical.

Instrument events (A to Q) are shown relative to the progress of the comparison. By

inspection, no clear effects of breakdown or repair are visible at a dew point of 20 °C.

Further discussion is included in Section 8.

Figure 4.1 Between-instrument initial consistency checks at a nominal dew point of +20 °C, on

arrival at each participant laboratory. Standard uncertainty of individual measurements ranged

between 0.02 °C and 0.05 °C approximately. Data shown are differences (Hyg1 minus Hyg2). Event

markers A, B, C etc. refer to Table 4.1.

22

4.3 CONSISTENCY OF PERFORMANCE OF INSTRUMENTS THROUGHOUT THE

COMPARISON

The consistency of between-instrument differences at all measured values throughout the

comparison gives a measure of consistent performance of the instruments throughout the

comparison. Figure 4.2 shows the between-instrument differences summarised for all

participant sets of measurements at all five nominal dew-point values measured.

The difference data for NMIJ, VSL and NIM showed some untypical features. However, the

consistent pattern of results among a majority of participants at beginning, middle and end of

the comparison gives one form of assurance of the stability and consistency of the instrument

pair. No clear progressive drift or trend is evident. If the difference were changing suddenly

or progressively with time, this would imply a change in at least one instrument. This was not

observed.

Although the pilot reviewed difference values for the 20 °C point immediately, as a check of

safe arrival, difference values at lower ranges showed some greater disparities (not analysed

until later).

Figure 4.2 Graph showing consistency of the difference between the transfer standards as reported by

the participants, four measurements (usually), at all five nominal values. Each data point is the

difference between results of two hygrometers measuring simultaneously. NPL additional data (NPL

2, 3, 4, 5 and 6) were limited checks, rather than full sets of four measurements. Standard uncertainty

of individual measurements ranged between 0.02 °C and 0.08 °C approximately.

I

23

By inspection, data from NMIJ, VSL and NIM appear to have more scatter than others. NMIJ

and NIM data appear to show an unusual pattern between results in different parts of the

range. Other isolated cases of scatter in individual measurements can be seen.

4.4 STABILITY OF EACH HYGROMETER

4.4.1 Pilot measurements

Measurements were made by the pilot NPL to monitor the stability of both travelling

standards relative to the NPL standards. These checks were made as full sets of

measurements at planned stages at beginning, middle and end of the comparison, plus some

more limited checks at other stages. Figure 4.3 shows a graph of data for Hyg1 and figure 4.4

for Hyg2. The data are plotted as difference (pilot applied values minus instrument dew/frost-

point temperatures calculated from the resistance measurement results). Only the mean values

are shown. For measurements in 2003, 2005, 2008 and 2009 these were means of full sets of

reproduced measurements – in most cases sets of four. At other dates, measurements were

fewer (single results at each dew point). Event markers A to Q are also shown.

Figure 4.3 Graph showing overview of pilot stability checks on Hyg1 hygrometer (lines joining the

data to guide the eye).

24

Figure 4.4 Graph showing overview of pilot stability checks on Hyg2 transfer standard, (lines joining

the data to guide the eye).

4.4.2 INTA measurements of Hyg2

As owner of Hyg2, INTA performed measurements before and after the comparison, as well

as their own comparison measurements, plus another measurement set after one of the

instrument repairs. The results are shown in the graphs in Figure 4.5 and 4.6. Each data point

in these figures represents the result of a single calibration; hence the uncertainties as shown

by the error bars are somewhat larger than uncertainties elsewhere in this report which are for

aggregated multiple results.

25

Figure 4.5 INTA data for overall calibration characteristic for Hyg2, years 2000 to 2010.

Uncertainties shown are at coverage factor k=2.

Figure 4.6 Graph showing INTA measurements for Hyg2 relative to INTA standard generator(s),

with straight-line weighted fits to the data to indicate trend. Uncertainties shown are at coverage

factor k=2.

In general, the INTA data show much less scatter than the NPL data, but with larger

uncertainties. This is considered in the analysis of drift that follows.

26

4.4.3 Drift estimates and discussion

The data for each instrument were analysed to establish whether any significant secular drift

should be taken into account in the comparison results and uncertainties. There are two

possible cases: drift estimated to be not detectably significant, counted as “zero drift” with

some assigned uncertainty – or a significant rate of drift detected and estimated with some

uncertainty, and a correction for drift applied to results where relevant.

The pilot data for travelling standards, at several occasions spread through the whole

comparison, were analysed for drift by evaluating a best-fit curve for data at each dew-point

temperature. The fitting used an NPL-developed validated function in MSExcel,

XLGENLINE V1.1 [26], to provide a weighted best-fit straight line, together with

uncertainty in gradient taking into account both residuals and number of data. In each case a

check was made to confirm that a higher order fit did not appear better (smaller residuals).

The results are shown in Table 4.2, which gives the drift as gradient in degrees Celsius per

year, and as a total drift for the whole comparison, and the uncertainty in both of these taking

into account the measurement uncertainty together with the residuals from fitting. In addition,

the outcomes of INTA drift checks on Hyg2 are also shown. The uncertainties for INTA

values are larger than those or NPL, partly because of the larger uncertainty of the INTA

references used, and partly due to fewer INTA data.

Table 4.2 Estimates of hygrometer drift, per year, and for the total duration of the comparison, Hyg1

data from NPL, Hyg2 data from NPL with additional results from INTA.

Instrument Dew-point

temperature

(°C)

Gradient (°C

/yr)

Standard

uncertainty in

gradient (°C

/yr)

Total

estimated

drift (gradient

x time

interval) °C

Standard

uncertainty

in total drift

(°C)

Hyg1 -50 +0.001 0.002 +0.003 0.013

Hyg1 -30 -0.002 0.002 -0.009 0.013

Hyg1 -10 -0.005 0.002 -0.027 0.013

Hyg1 +1 -0.006 0.002 -0.034 0.012

Hyg1 +20 +0.006 0.002 +0.036 0.012

Hyg2 (NPL) -50 +0.000 0.002 +0.000 0.013

Hyg2 (NPL) -30 -0.003 0.002 -0.016 0.013

Hyg2 (NPL) -10 -0.002 0.002 -0.010 0.013

Hyg2 (NPL) +1 -0.008 0.002 -0.045 0.012

Hyg2 (NPL) +20 -0.002 0.002 -0.012 0.012

Hyg2 (INTA) -50 +0.001 0.007 +0.008 0.041

Hyg2 (INTA) -30 +0.002 0.006 +0.011 0.037

Hyg2 (INTA) -10 +0.001 0.003 +0.007 0.018

Hyg2 (INTA) +1 +0.001 0.004 +0.004 0.022

Hyg2 (INTA) +20 +0.000 0.004 -0.001 0.022

Drift can be approximated as zero where the best-fit gradient is not significantly different

from zero when considered along with its k=2 uncertainty. According to this criterion, drift

was found to be negligibly different from zero in the range below 0 °C. However, for Hyg1 at

1 °C and 20 °C, and for Hyg2 at 1 °C, the criterion was not met. In these cases it is necessary

27

to decide whether to treat this as a sign of significant drift, and whether to make an allowance

for this as a correction or additional uncertainty.

An overview of the drift data is shown in the graphs in figures 4.7, 4.8, and 4.9. These show

for Hyg1, Hyg2, and for the two together, estimated drift, and uncertainty in this, at all five

comparison values.

Figure 4.7 Estimated total drift of Hyg1 hygrometer during comparison based on pilot NPL

measurements. Error bars show standard uncertainty of drift estimates.

Figure 4.8 Estimated total drift of Hyg2 hygrometer during comparison based on pilot NPL

measurements (squares) and INTA measurements (triangles). Error bars show standard uncertainty of

drift estimates.

28

Figure 4.9 Summary graph of estimates of total drift of both hygrometers during comparison based

on pilot NPL measurements (Hyg1 diamonds, Hyg2 squares) and INTA measurements (Hyg2

triangles). Error bars show standard uncertainty of drift estimates.

Overall, the estimates of drift from the INTA measurements had larger uncertainties then

those from the NPL measurements. However, INTA generally obtained particularly

reproducible results (as can be seen from the low scatter in figures 4.5 and 4.6). In addition

the relatively smooth trend found by INTA across the range (Figure 4.8) is more believable

than the variations that would be suggested by the NPL results.

The drift estimates and their uncertainties are summarised in Table 4.3. Drift can be

considered negligible if the estimated amount of drift, relative to its uncertainty, is not

significantly different from zero. This is the case for Hyg1 at -50 °C and -30 °C, and for

Hyg2 at all values except +1 °C. In addition, all but one of these individual drift values are

small − approximately 0.01 °C or less (one is less than 0.02 °C).

The drift estimates needing special consideration are those for Hyg1 at and above -10 °C and

for Hyg2 at +1 °C. Each of these taken in isolation suggests possible drift of more than

0.02 °C – which, if true, could be considered significant relative to the participant

uncertainties. Impact on the KCRV, and on the agreement of individual results with this,

could be up to half the magnitude of total drift (up to of order 0.01 °C).

For Hyg2 at +1 °C, the two drift estimates are discrepant – INTA results suggesting a

minimal drift upwards of order +0.004 °C ±0.022 °C (standard uncertainty) over the whole

comparison, while the NPL estimated downwards drift is -0.045 °C ±0.012 °C (standard

uncertainty). Their k=2 uncertainties would overlap, however. In spite of having larger

uncertainty, the INTA estimate of drift is credible, because of the small scatter, and because

across the range any physically feasible drift is unlikely to take the overall form implied by

the NPL +1 °C result.

29

For Hyg1, at 1 °C the NPL estimate of total drift is -0.034 °C and at 20 °C the estimate is

+0.036 °C. These both differ from zero by more than 2 standard uncertainties, and would

both be considered significant levels of drift. However drift of this type seems implausible,

because it does not fit known, physically feasible explanations – it would be surprising to

have little drift below 0 °C tending towards downward drift at 1 °C and upward drift at 20 °C.

In addition, the doubt about the NPL estimate of drift for Hyg2 at 1 °C may also cast doubt

on the estimate for Hyg1 at the same value.

In considering drift, the main component capable of drifting is the instrument PRT. For this,

there are a small number of physically feasible mechanisms of drift. One would be drift in R0

(resistance at 0 °C) which would result in drift in one direction, for all measured values.

Another would be change in PRT sensitivity, which would be reflected in a trend (slope) of

data points in Figures 4.7 to 4.9. A third possibility would be loss of thermal contact of the

PRT with the measurement head, which would result in a change likely to be more significant

at the lowest values measured. The discrepant drift data do not clearly fit any of these

patterns. Checks were also made to be sure the anomaly was not an inversion of results

(“error” versus “correction”).

One further consideration is whether the pilot reference (NPL generator) could have

performed anomalously in the range, from -10 °C upwards. However the overall comparison

results in Section 5 do not suggest this: NPL results generally show good agreement with the

KCRV.

Overall, what evidence there is for significant drift from -10 °C upwards is too conflicting to

allow a clear conclusion – one that would support the application of a correction for drift, and

allow a value of such a correction to be confidently proposed. The potentially anomalous drift

estimates cannot be rejected, because no cause is identified. Nor can any of the anomalies be

treated as a single “rogue” value: each is the combination of multiple results. Therefore,

instead, an additional uncertainty to allow for the doubt about drift has been added to the

instrument-related uncertainty.

It should be noted that the impact of any drift (and its uncertainty) in either instrument is

partly mitigated by the derivation of the reported comparison results from the average of both

instrument readings. According to this, the combined effect of the estimated drift is shown in

Table 4.3 below.

30

Table 4.3 Table comparing outcomes of using estimates of drift, and uncertainty in this, based on

either NPL data for Hyg2 or INTA data for that instrument. Estimated drift and its standard

uncertainty, shown for Hyg1 and Hyg2 individually, and combined effect. Uncertainty values marked

(*) are used in the subsequent analysis.

In summary, for the range of the comparison below -10 °C there is little evidence for

significant drift. At and above -10 °C the evidence of drift is inconclusive. For the values

where there is more doubt, a larger estimated uncertainty is assigned to allow for this,

conservatively, by directly adding a component to the uncertainty – so that when a coverage

factor of 2 is applied, the entire bounds of the apparent discrepancies will be included in the

interval. In the rest of the analysis that follows, the values from Table 4.3 marked with

asterisks (*) are used as standard uncertainties due to instrument drift. Those for -50 °C

and -30 °C are based on the pilot (NPL) data, which appear reliable; at other values the larger

uncertainty estimate of the two (NPL or INTA) is used.

Instrument drift does not contribute uncertainty to the individual laboratory results, but needs

to be taken into account in the assignment of KCRV and in the calculations of equivalence.

Dew

point

Total proposed

standard uncertainty

in (zero) correction

°Cdue to drift, enlarged

for discrepancy

Estimated

driftu

Estimated

driftu

Estimated

mean driftu

°C °C °C °C °C °C °C °C

-50 0.003 0.013 0.000 0.013 0.0014 0.0093 0 0.010*

-30 -0.009 0.013 -0.016 0.013 -0.0126 0.0093 0 0.016*

-10 -0.027 0.013 -0.010 0.013 -0.0182 0.0093 0 0.019*

1 -0.034 0.012 -0.045 0.012 -0.0395 0.0088 0 0.028*

20 0.036 0.012 -0.012 0.012 0.0116 0.0088 0 0.015

-50 0.008 0.041 0.0058 0.0213 0 0.024

-30 0.011 0.037 0.0009 0.0197 0 0.020

-10 0.007 0.018 -0.0098 0.0113 0 0.016

1 0.004 0.022 -0.0152 0.0128 0 0.020

20 -0.001 0.022 0.0172 0.0128 0 0.022*

NPL

NPL

Lab

(NPL estimates and

standard uncertainty)

Combined estimates (drift

of mean of Hyg1 and

Hyg2, and combined

standard uncertainty of

mean)

Proposed

correction

for drift

Lab

NPL

Hyg2

(NPL and INTA estimates,

and standard uncertainty)

As above As above INTA

Hyg1

31

5 PARTICIPANT RESULTS

Participant data are reported for measurements using the instrument pair simultaneously, for

four measurements separately reproduced at each of the five dew-point values. The full data

sets are reported in the Appendices of this report.

NPL and INTA both made extra measurements, due to providing several checks and drift

estimates for the hygrometers. However just one set of measurements was considered for the

comparison: for NPL the first complete set of measurements was used, and for INTA the

main scheduled comparison measurements at March to April 2005 were used.

For each participant, at each nominal dew point, the data were aggregated by taking a mean

of pooled results for both instruments to provide a single result for comparison and

calculation of KCRV. (The calculated mean of simultaneous readings of two instruments is

the mid-point between the two instrument mean readings, and the combined uncertainty is the

uncertainty in the value of that mid-point.) Following the same notation as used for

EUROMET.T-K6 [2] already reported, the result Rlab i at each dew point can be given as

4

1

Hyg2Hyg1

4

1

Hyg21Hyg )(8

1)(

2

1

4

1

ii

ilab RRRRR , (3)

where (RHyg1 and RHyg2) are the results of the two transfer standards, and where

dInddrefn ttR Hyg , (4)

with tdref the laboratory reference value for the applied dew/frost-point temperature and tdInd

the dew/frost-point temperature indicated (calculated) from the PRT resistance .

The uncertainty of the results are those reported by the participants taking into account both

Type B estimates as routinely reported, plus type A estimates of components such as short-

term variation (standard deviation) in repeated readings during the comparison

measurements.

All participants have independent dew-point scale realisations, including independent

traceability of supporting temperature measurements to national realisations of the

International Temperature Scale (ITS-90). The uncertainties can therefore be expected to be

uncorrelated between participants. Where within-laboratory correlations are known,

participants have taken these into account in the values reported.

Below, results for each participant at all dew points are plotted for Hyg1 in Figure 5.1, and

for Hyg2 in Figure 5.2. Mean results Rlab for the two instruments are shown for all

participants at all measured values in Figure 5.3.

Each set of results was initially reviewed by the pilot on receipt, to check for anomalies in

case of misreporting or other causes. In only one case, results as received appeared unusual,

and that participant was notified of a possible anomaly at certain measured values (but not the

magnitude or sign of the apparent discrepancy – as specified in Guideline CIPM MRA – D-

05) [27]. After making additional checks, the participant did not propose any change to

reported results.

32

In some cases participants observed supercooled water on hygrometer mirrors at the

nominal -10 °C point, and applied conversions to obtain equivalent frost point, using

formulae for saturation vapour pressure curve of water. This is not expected to affect the

validity of those results.

Figure 5.1 Mean reported values of applied condition minus measured value for Hyg1, shown in

participant time sequence. Connecting lines between data are shown to guide the eye.

Figure 5.2 Mean reported values of applied condition minus measured value for Hyg2, shown in

participant time sequence. Connecting lines between data are shown to guide the eye.

33

Figure 5.3 Results of entire comparison shown as reported values for mean (mid-point) of Hyg1 and

Hyg2 results combined (Rlab), grouped by dew-point value (data points staggered in x-direction for

visibility). Error bars show participant reported standard uncertainties (k=1). As shown here,

uncertainty allowance for instrument drift is not included.

34

6 BILATERAL EQUIVALENCE

Bilateral equivalences at each dew point were calculated from differences Dij between

participants i and j, where

Dij = jlabilab RR , (5)

The bilateral degree of equivalence (DoE) is determined as

(Dij, Uij) = (Dij, ku(Dij)) , (6)

where the coverage factor k=2 provides a coverage probability of 95 % for sufficiently large

effective number of degrees of freedom of u(Dij). [28].

In this case, u(Dij) is given by

u2(Dij) = u

2(Rlab i) + u

2(Rlab j) + u

2drift, (7)

where u2

drift is the uncertainty in the comparison due to drift of both hygrometers at a given

dew point value, with drift having been assigned an expectation value of value of zero as in

Section 4. For simplicity here, u2

drift, is assigned a single generalised value at each dew point,

irrespective of whether participants measured in immediate succession or separated in time.

The DoE was calculated for each pair of participants at each nominal measurement point. The

results are summarised in tables 6.1 to 6.5. In a small number of cases, where participants

assigned a coverage factor k greater than 2, due to a low effective number of degrees of

freedom of an uncertainty estimate, the larger coverage factor is used to obtain the 95 %

coverage interval for equivalences.

35

Table 6.1 Degree of equivalence between the participants of CCT-K6 at the frost-point temperature -50 °C. DoE is expressed as (Dij, Uij) in degrees Celsius. Instrument drift

uncertainty is included in the uncertainty shown.



-50 °C NPL NMIJ VSL MIKES INTA INRIM NIST NMC NIM VNIIFTRI

NPL 0.037 0.123 0.167 0.136 -0.023 0.048 0.026 0.039 0.014 0.042 0.142 0.036 0.059 0.070 0.074 0.121 0.025 0.038

NMIJ -0.037 0.123 0.131 0.180 -0.060 0.128 -0.011 0.125 -0.022 0.126 0.105 0.124 0.023 0.138 0.038 0.169 -0.012 0.124

VSL -0.167 0.136 -0.131 0.180 -0.191 0.140 -0.142 0.137 -0.153 0.138 -0.025 0.136 -0.108 0.149 -0.093 0.178 -0.142 0.137

MIKES 0.023 0.048 0.060 0.128 0.191 0.140 0.049 0.051 0.038 0.053 0.165 0.049 0.083 0.077 0.098 0.125 0.048 0.050

INTA -0.026 0.039 0.011 0.125 0.142 0.137 -0.049 0.051 -0.011 0.046 0.117 0.040 0.034 0.072 0.049 0.122 -0.001 0.042

INRIM -0.014 0.042 0.022 0.126 0.153 0.138 -0.038 0.053 0.011 0.046 0.128 0.043 0.045 0.074 0.060 0.123 0.011 0.045

NIST -0.142 0.036 -0.105 0.124 0.025 0.136 -0.165 0.049 -0.117 0.040 -0.128 0.043 -0.083 0.071 -0.068 0.121 -0.117 0.039

NMC -0.059 0.070 -0.023 0.138 0.108 0.149 -0.083 0.077 -0.034 0.072 -0.045 0.074 0.083 0.071 0.015 0.135 -0.035 0.072

NIM -0.074 0.121 -0.038 0.169 0.093 0.178 -0.098 0.125 -0.049 0.122 -0.060 0.123 0.068 0.121 -0.015 0.135 -0.049 0.122

VNIIFTRI -0.025 0.038 0.012 0.124 0.142 0.137 -0.048 0.050 0.001 0.042 -0.011 0.045 0.117 0.039 0.035 0.072 0.049 0.122

-30 °C NPL 0 NMIJ VSL MIKES INTA INRIM NIST NMC NIM VNIIFTRI

NPL 0.083 0.080 0.019 0.119 0.018 0.072 0.037 0.069 0.007 0.069 0.106 0.067 0.062 0.083 0.089 0.109 0.047 0.068

NMIJ -0.083 0.080 -0.064 0.115 -0.065 0.066 -0.046 0.062 -0.076 0.062 0.023 0.060 -0.022 0.078 0.006 0.105 -0.037 0.061

VSL -0.019 0.119 0.064 0.115 -0.001 0.110 0.018 0.108 -0.012 0.108 0.087 0.107 0.043 0.118 0.070 0.137 0.028 0.107

MIKES -0.018 0.072 0.065 0.066 0.001 0.110 0.019 0.052 -0.011 0.052 0.088 0.050 0.044 0.070 0.071 0.099 0.029 0.050

INTA -0.037 0.069 0.046 0.062 -0.018 0.108 -0.019 0.052 -0.030 0.048 0.069 0.045 0.025 0.067 0.052 0.097 0.010 0.046

INRIM -0.007 0.069 0.076 0.062 0.012 0.108 0.011 0.052 0.030 0.048 0.099 0.045 0.055 0.066 0.082 0.097 0.040 0.045

NIST -0.106 0.067 -0.023 0.060 -0.087 0.107 -0.088 0.050 -0.069 0.045 -0.099 0.045 -0.044 0.065 -0.017 0.096 -0.059 0.043

NMC -0.062 0.083 0.022 0.078 -0.043 0.118 -0.044 0.070 -0.025 0.067 -0.055 0.066 0.044 0.065 0.027 0.108 -0.015 0.065

NIM -0.089 0.109 -0.006 0.105 -0.070 0.137 -0.071 0.099 -0.052 0.097 -0.082 0.097 0.017 0.096 -0.027 0.108 -0.042 0.096

VNIIFTRI -0.047 0.068 0.037 0.061 -0.028 0.107 -0.029 0.050 -0.010 0.046 -0.040 0.045 0.059 0.043 0.015 0.065 0.042 0.096

36



Table 6.4 Degree of equivalence between the participants of CCT-K6 at the dew-point temperature +1 °C. DoE is expressed as (Dij, Uij) in degrees Celsius. Instrument drift


-10 °C NPL NMIJ VSL MIKES INTA INRIM NIST NMC NIM VNIIFTRI

NPL 0.023 0.070 -0.061 0.057 -0.024 0.056 -0.006 0.054 -0.031 0.055 0.046 0.054 0.036 0.066 0.099 0.104 0.039 0.052

NMIJ -0.023 0.070 -0.084 0.068 -0.046 0.067 -0.028 0.066 -0.054 0.066 0.024 0.065 0.013 0.076 0.076 0.111 0.016 0.064

VSL 0.061 0.057 0.084 0.068 0.038 0.054 0.056 0.052 0.030 0.053 0.107 0.052 0.097 0.064 0.160 0.103 0.100 0.050

MIKES 0.024 0.056 0.046 0.067 -0.038 0.054 0.018 0.051 -0.008 0.052 0.070 0.050 0.059 0.063 0.122 0.103 0.062 0.049

INTA 0.006 0.054 0.028 0.066 -0.056 0.052 -0.018 0.051 -0.026 0.050 0.052 0.048 0.041 0.062 0.104 0.102 0.045 0.047

INRIM 0.031 0.055 0.054 0.066 -0.030 0.053 0.008 0.052 0.026 0.050 0.077 0.049 0.067 0.062 0.130 0.102 0.070 0.048

NIST -0.046 0.054 -0.024 0.065 -0.107 0.052 -0.070 0.050 -0.052 0.048 -0.077 0.049 -0.011 0.061 0.053 0.102 -0.007 0.046

NMC -0.036 0.066 -0.013 0.076 -0.097 0.064 -0.059 0.063 -0.041 0.062 -0.067 0.062 0.011 0.061 0.063 0.109 0.003 0.060

NIM -0.099 0.104 -0.076 0.111 -0.160 0.103 -0.122 0.103 -0.104 0.102 -0.130 0.102 -0.053 0.102 -0.063 0.109 -0.060 0.101

VNIIFTRI -0.039 0.052 -0.016 0.064 -0.100 0.050 -0.062 0.049 -0.045 0.047 -0.070 0.048 0.007 0.046 -0.003 0.060 0.060 0.101

+1 °C NPL NMIJ VSL MIKES INTA INRIM NIST NMC NIM VNIIFTRI

NPL 0.043 0.082 0.101 0.132 0.028 0.076 0.023 0.074 0.034 0.073 0.056 0.074 0.074 0.094 0.116 0.097 0.071 0.073

NMIJ -0.043 0.082 0.058 0.131 -0.015 0.074 -0.020 0.072 -0.009 0.071 0.013 0.072 0.031 0.092 0.073 0.095 0.028 0.071

VSL -0.101 0.132 -0.058 0.131 -0.073 0.127 -0.078 0.126 -0.067 0.126 -0.045 0.126 -0.027 0.139 0.015 0.141 -0.030 0.126

MIKES -0.028 0.076 0.015 0.074 0.073 0.127 -0.005 0.064 0.006 0.063 0.028 0.065 0.046 0.086 0.088 0.090 0.043 0.063

INTA -0.023 0.074 0.020 0.072 0.078 0.126 0.005 0.064 0.012 0.061 0.033 0.062 0.051 0.085 0.093 0.088 0.048 0.061

INRIM -0.034 0.073 0.009 0.071 0.067 0.126 -0.006 0.063 -0.012 0.061 0.022 0.061 0.039 0.084 0.082 0.087 0.037 0.060

NIST -0.056 0.074 -0.013 0.072 0.045 0.126 -0.028 0.065 -0.033 0.062 -0.022 0.061 0.018 0.085 0.060 0.088 0.015 0.062

NMC -0.074 0.094 -0.031 0.092 0.027 0.139 -0.046 0.086 -0.051 0.085 -0.039 0.084 -0.018 0.085 0.042 0.105 -0.003 0.084

NIM -0.116 0.097 -0.073 0.095 -0.015 0.141 -0.088 0.090 -0.093 0.088 -0.082 0.087 -0.060 0.088 -0.042 0.105 -0.045 0.088

VNIIFTRI -0.071 0.073 -0.028 0.071 0.030 0.126 -0.043 0.063 -0.048 0.061 -0.037 0.060 -0.015 0.062 0.003 0.084 0.045 0.088

37

Table 6.5 Degree of equivalence between the participants of CCT-K6 at the dew-point temperature +20 °C. DoE is expressed as (Dij, Uij) in degrees Celsius. Instrument drift


+20 °C NPL NMIJ VSL MIKES INTA INRIM NIST NMC NIM VNIIFTRI

NPL -0.014 0.065 -0.009 0.061 -0.008 0.056 -0.029 0.052 -0.028 0.052 -0.008 0.055 0.014 0.084 0.083 0.077 -0.010 0.051

NMIJ 0.014 0.065 0.005 0.071 0.006 0.067 -0.015 0.064 -0.014 0.064 0.006 0.066 0.028 0.092 0.097 0.085 0.004 0.063

VSL 0.009 0.061 -0.005 0.071 0.002 0.062 -0.020 0.059 -0.019 0.059 0.001 0.061 0.023 0.089 0.092 0.082 -0.001 0.058

MIKES 0.008 0.056 -0.006 0.067 -0.002 0.062 -0.022 0.054 -0.021 0.054 0.000 0.057 0.021 0.086 0.090 0.078 -0.003 0.053

INTA 0.029 0.052 0.015 0.064 0.020 0.059 0.022 0.054 0.001 0.050 0.021 0.053 0.043 0.083 0.112 0.076 0.019 0.049

INRIM 0.028 0.052 0.014 0.064 0.019 0.059 0.021 0.054 -0.001 0.050 0.020 0.053 0.042 0.083 0.111 0.075 0.018 0.049

NIST 0.008 0.055 -0.006 0.066 -0.001 0.061 0.000 0.057 -0.021 0.053 -0.020 0.053 0.022 0.085 0.091 0.077 -0.002 0.052

NMC -0.014 0.084 -0.028 0.092 -0.023 0.089 -0.021 0.086 -0.043 0.083 -0.042 0.083 -0.022 0.085 0.069 0.100 -0.024 0.083

NIM -0.083 0.077 -0.097 0.085 -0.092 0.082 -0.090 0.078 -0.112 0.076 -0.111 0.075 -0.091 0.077 -0.069 0.100 -0.093 0.075

VNIIFTRI 0.010 0.051 -0.004 0.063 0.001 0.058 0.003 0.053 -0.019 0.049 -0.018 0.049 0.002 0.052 0.024 0.083 0.093 0.075

44

7 KEY COMPARISON REFERENCE VALUES (KCRV)

7.1 CALCULATION OF KCRV

In comparisons of dew/frost-point temperature scales, comparison reference values have no

absolute significance outside the comparison. However the availability of a comparison

reference value is essential to the use of comparison results for review of CMC claims.

In this comparison and other corresponding RMO comparisons, a reference value is

calculated for each nominal value of dew point, treating them as separate data populations

for this purpose.

For each nominal dew point value, a key comparison reference value (KCRV) [28] was

calculated as the weighted mean, y, of results xi

𝑦 =𝑥1 𝑢2(𝑥1)⁄ + … +𝑥𝑁 𝑢2(𝑥𝑁)⁄

1 𝑢2(𝑥1)⁄ + … +1 𝑢2(𝑥𝑁)⁄, (8)

this method of calculation having been agreed by CCT Working Group 6. For comparison,

values of arithmetic mean and median were also calculated. The uncertainty in weighted

mean due to dispersion was calculated from [28]

1

𝑢2(𝑦)=

1

𝑢2(𝑥1)+ … +

1

𝑢2(𝑥𝑁). (9)

After collection of participant results, but before circulation of Draft A, results of NIST

at -50 °C and -30 °C were identified as outliers. NIST confirmed that they recognised an

inconsistency with expected results at these values (relative to additional data for another

NIST generator). A multimeter used for comparison measurements was identified as a

possible cause of the inconsistency. However it was not possible to make further

measurement checks, because of a lengthy breakdown of the NIST generator refrigeration

system, and eventual updating of the LFPG facility.

Calculations of weighted mean were made both with and without the outlying results.

Values of arithmetic mean and median were also calculated. These are summarised in

Table 7.1. At +20 °C and -50 °C the median is somewhat lower than the general trend,

which suggests consideration of whether a skew or outlier is present in the data. As well as

the uncertainty in weighted mean due to dispersion, an additional uncertainty in KCRV was

included for the drift of the hygrometers (expectation value zero, with standard uncertainty

as given in Section 4.4). The uncertainties are summarised in Table 7.2.

45

Table 7.1 Values of weighted mean, arithmetic mean and median at each nominal dew point,

estimated from all results, and also after exclusion of outlying results at -50 °C and -30 °C (in italics)

Dew-point

value

°C

Weighted

mean

°C

Arithmetic

mean

°C

Median

°C

-50 +0.028 +0.017 -0.003

-50 +0.055 +0.027 -0.003

-30 +0.072 +0.077 +0.071

-30 +0.090 +0.084 +0.080

-10 +0.096 +0.092 +0.085

1 +0.111 +0.102 +0.098

20 +0.147 +0.134 +0.106

Table 7.2 Standard uncertainties due to variance of weighted mean, combined effect of

hygrometer drift, and their quadrature sum, for each dew point, estimated from all

results, and also after exclusion of outlying results at -50 °C and -30 °C (in italics)

Dew-

point

value

°C

Standard

uncertainty of

weighted mean

°C

Standard uncertainty

due to combined

hygrometer drift

°C

Quadrature

sum

°C

-50 0.005 0.010 0.011

-50 0.006 0.010 0.012

-30 0.005 0.016 0.017

-30 0.006 0.016 0.017

-10 0.004 0.019 0.019

+1 0.004 0.028 0.028

+20 0.004 0.022 0.022

7.2 CHI-SQUARED TEST

A chi-squared test [28] was carried out on the results with and without the identified NIST

outliers, as a measure of the consistency of the data and uncertainties. Based on the

participant reported uncertainties alone, the test fails. Repeating the test with correct

inclusion of uncertainty allowance for instrument drift, the test succeeds for results above -

10 °C, but initially fails for the full set of participant results at -10 °C, -30 °C and -50 °C.

Discrepant results can be identified using the criterion [28]:

)()(2 22

KCRVilabKCRVilab RuRuRR (10)

Inspection of the data and the test for discrepancy show that several participant results

deviate from the KCRV by between 2 and 3 standard uncertainties, u(Rlab i). Only 1

participant (NIST) had any result with greater deviation relative to uncertainty – by more

46

than 4 standard uncertainties at -50 °C. Removal of the NIST results from the KCRV and

chi-squared test at -50 °C and -30 °C allows the remaining results to pass the test at those

points. At -10 °C the chi-squared test fails, but is passed if the VSL result is removed.

The results that cause the chi-squared test to fail at -30 °C and -10 °C are not dramatic

outliers. The decision whether to exclude marginally-outlying data is also a matter of

considering the impact on the KCRV. Inclusion of the NIST outliers at -50 °C and -30 °C

influences the KCRV significantly at those points – reducing it by 0.027 °C and 0.018 °C

respectively. In contrast, exclusion of the VSL -10 °C result would affect the KCRV at that

value by only 0.004 °C, which can be considered not a significant influence. Accordingly,

the NIST results -50 °C and -30 °C have been excluded from the calculation of KCRV, but

the VSL result at -10 °C has been included.

Overall, the chi-squared test is only narrowly passed, suggesting that the uncertainties are

probably not generally overestimated.

7.3 COMPARISON RESULTS PRESENTED IN TERMS OF KCRV

The results of all laboratories relative to the KCRV are shown in Table 7.3 below, and in

figures 7.1 to 7.5, with uncertainties as shown in Table 7.4. The error bars in the graphs

show a combination of the participant reported error with the uncertainty allowance due to

hygrometer drift, at coverage probability of 95 %, using a coverage factor k=2 in most cases

except where participants assigned a higher coverage factor.

Table 7.3 Participant result, Rlab, minus KCRV (weighted mean), in degrees Celsius.

-50 °C -30 °C -10 °C +1 °C +20 °C

NPL +0.014 +0.034 +0.007 +0.045 -0.014

NMIJ -0.023 -0.050 -0.015 +0.002 +0.000

VSL -0.153 +0.015 +0.069 -0.056 -0.005

MIKES +0.037 +0.016 +0.031 +0.017 -0.006

INTA -0.012 -0.003 +0.013 +0.022 +0.016

INRIM 0.000 +0.027 +0.039 +0.010 +0.015

NIST -0.128 -0.072 -0.039 -0.011 -0.006

NMC -0.046 -0.028 -0.028 -0.029 -0.028

NIM -0.060 -0.055 -0.091 -0.071 -0.097

VNIIFTRI -0.011 -0.013 -0.031 -0.026 -0.003

47

Table 7.4 Uncertainty in difference between participant result and KCRV, at 95 % coverage

probability, in degrees Celsius.

-50 °C -30 °C -10 °C +1 °C +20 °C

NPL 0.028 0.064 0.050 0.071 0.049

NMIJ 0.100 0.057 0.062 0.070 0.062

VSL 0.134 0.105 0.047 0.125 0.057

MIKES 0.043 0.046 0.046 0.061 0.051

INTA 0.034 0.041 0.044 0.059 0.048

INRIM 0.037 0.040 0.045 0.058 0.047

NIST 0.030 0.038 0.043 0.060 0.050

NMC 0.067 0.062 0.058 0.083 0.082

NIM 0.119 0.094 0.099 0.086 0.073

VNIIFTRI 0.032 0.038 0.041 0.058 0.046

Figure 7.1 Difference between participant results and KCRV, at the nominal frost-point temperature -50 °C.

Error bars show the expanded uncertainties at coverage probability of 95 %. Estimated uncertainty due to

instrument drift is included. “NPL Final” values are shown but not included in evaluation of KCRV.




48




Figure 7.4 Difference between participant results and KCRV, at the nominal dew-point temperature +1 °C.



Figure 7.5 Difference between participant results and KCRV, at the nominal dew-point temperature +20 °C.



49

8 DISCUSSION

The comparison results mainly demonstrate consistency with the key comparison reference

value, within the estimated uncertainties. A small proportion (8 %) of results are not within

two standard uncertainties of the KCRV. Only one participant (NIST) had any result

deviating by more than three standard uncertainties.

It was understood, from the outset of the comparison, that the reproducibility of the

available state-of-the-art travelling standard hygrometers would be barely sufficient to

provide a stringent test of equivalence of standards at the level of uncertainty claimed by the

participants. However, the travelling standards were at least expected to be reliable, given

their history, and so the failures of components were unexpected. Fortunately, there is no

evidence that the instrument values were affected by any of the breakdowns or repairs.

Future dew-point key comparisons can benefit (or already have done) from a new

generation of transfer standard hygrometers that have been improved in several respects.

The long duration of more than six years for participant measurements was far from ideal.

It raises two concerns: potential drift of the travelling standards; and the question of linkage

to regional comparisons that are separated in time by several years.

The drift of the travelling standard hygrometers has been considered in detail in Section 4.

They appear to have been sufficiently stable, but some of the evidence in the drift

assessment is conflicting. Because of that ambiguity, the uncertainty allowed for instrument

drift is slightly conservative in this analysis. Less conservative treatment of drift was also

considered, but would not significantly change the broad outcome of which participant

results were consistent with the KCRV within the uncertainties. In general, the results of

participants with the smaller uncertainties were the most affected by the inclusion and the

extent of drift-related uncertainty.

In evaluating the magnitude and significance of travelling standard drift, and the impact on

KCRV and bilateral equivalences, various other measures have been considered, not

detailed fully here. These included: the character of the within-laboratory deviations; the

pilot initial and final values as a simple measure of drift; the impact of potential drift on

agreement of those measuring early and late in the comparison; and others. None of these

considerations contradicted the chosen approaches to the analysis of the comparison.

Between-instrument consistency (as discussed in Section 4.3) was also reviewed in case it

might provide further insight about drift. While the degree of consistency appears worse for

some of the participants whose agreement with the KCRV is weaker, there was no obvious

further conclusion to be drawn from this.

Two participants, MIKES and NIST, reported doubts about the electrical measurements they

had made during the comparison, using multimeters. For VSL, some results had

unexpectedly high scatter which also could possibly have arisen from electrical

measurement problems – although the cause was not identified.

Linkages between key comparisons are generally of interest and the KCRV is relevant to

these. However, in this field of measurement, the value of the KCRV is only a comparison

parameter, with no absolute significance in the SI (unlike, for example, a fixed-point

temperature in thermometry). To enable valid linkage it is important that RMO and CC

50

comparisons have consistent protocols. For dew-point key comparisons, this consistency is

generally being ensured through review by the CCT Working Group on Key Comparisons.

The consideration of linkages between this key comparison and those of regional metrology

organisations is a matter for further discussion, with the primary responsibility being with

the coordinators of other comparisons requiring links to this one.

9. CONCLUSION

This comparison was lengthy and challenging, because of the numerous difficulties

encountered with the travelling standard hygrometers. However, careful study of the results

does not reveal any shift in hygrometer performance attributable to instrument failures or

repairs. It is therefore believed that the instrument problems did not compromise the results

of the comparison.

Instrument stability over the long period of the comparison was assessed, and drift was

concluded to be low, although with some inconsistency in the evidence at and above -10 °C.

The assessment of drift at these values was not conclusive enough to merit correction for

drift, but an additional uncertainty allowance was made, because of the associated doubt.

With the provisos above, a key comparison reference value was evaluated, together with

bilateral equivalences between pairs of participants, and between participants and the

KCRV. Mainly good agreement was demonstrated between participants.

The comparison was effective despite instrument difficulties. However, comparison

uncertainties would potentially have been reduced if more reliable travelling instruments

had been available at that time, if comparison measurements had been more quickly

completed, and if evidence about drift had been unambiguous.

10. ACKNOWLEDGEMENTS

In addition to the listed authors, Leena Uusipaikka is acknowledged for contributions to the

measurements at MIKES.

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[18] Stevens M and Bell S A, “The NPL Standard Humidity Generator - An analysis of

uncertainty by validation of individual component performance” Measurement Science

and Technology 3 (1992) pp 943-952

[19] Stevens Mark, “The new NPL low frost-point Generator” in Proceedings of

TEMPMEKO '99, 7th International Symposium on Temperature and Thermal

Measurements in Industry and Science, (Delft, 1999), pp191-196 [20] The Russian national standard of gases humidity and traceability system of humidity

measurements. Book of Abstracts. Vol A, Joint International Symposium on Temperature,

Humidity, Moisture in Industry and Science 31 May- 4 June 2010.Portoroz. Slovenia, p 182

http://c.g.wanfangdata.com.cn/periodical/hkjcjs/2006-z1.aspx

52

[21] de Groot M J, Papers and Abstracts from the Third International Symposium on

Humidity and Moisture, National Physical Laboratory, UK, 1998, pp 53-61

[22] Nielsen J and de Groot M J, “Revision and uncertainty evaluation of a primary dew

point generator”, Metrologia 41, n.3 pp 167-172 (2004)

[23] Bosma R and Peruzzi A, “Development of a dew-point generator for gases other than

air and nitrogen and pressures up to 6 MPa”, Int.J.Thermophys. September 2012 33

Issue 8-9, pp 1511-1519

[24] Bosma R, Mutter D and Peruzzi A, “Validation of a dew-point generator for pressures

up to 6 MPa using nitrogen and air”, Metrologia 49 (2012), 597-606

[25] CIPM, MRA. "Mutual recognition of national measurement standards and of calibration and

measurement certificates issued by national metrology institutes." Comité International des

Poids et Measures (1999).

[26] Smith, Ian, Software for determining polynomial calibration functions

by generalised least squares: user manual NPL REPORT MS 11, December 2010

(Teddington, UK: National Physical Laboratory)

[27] Measurement comparisons in the CIPM MRA, CIPM MRA-D-05, Version 1.4 June

2013, www.bipm.org/utils/common/CIPM_MRA/CIPM_MRA-D-05.pdf (accessed

4 October 2013)

[28] Cox M, “The evaluation of key comparison data”, Metrologia 39 (2002) 589-595

53

APPENDIX 1: TECHNICAL PROTOCOL

The following pages show the technical protocol for CCT-K6, together with its Appendix 5

listing conditions to be reported as background information. The names of participating

institutes and the measurement sequence shown are those at the time the comparison started.

In addition (not shown here) the protocol included appendices giving: participant contact

details; reporting template to document safe receipt of instruments and checklist of

associated items; IEC 60751 (EN 60751) formula for nominal resistance-temperature

relationship (see Section 3.2); and MS Excel reporting templates for comparison results and

uncertainty.

54

International Committee for Weights and Measures (CIPM)

Consultative Committee for Thermometry (CCT)

CCT-K6 Key Comparison of Humidity Standards

Dew/Frost-Point Temperature –50 °C to +20 °C

Technical protocol

55

1. INTRODUCTION

1.1 Under the Mutual Recognition Arrangement (MRA)3 the metrological equivalence

of national measurement standards will be determined by a set of key comparisons

chosen and organized by the Consultative Committees of the CIPM working closely

with the Regional Metrology Organizations (RMOs).

1.2 At its 20th meeting in April 2000, the Consultative Committee for Thermometry,

CCT, considered a Key Comparison on humidity as imperative for the related

laboratories. It was decided that the Working Group on Humidity Measurements

(WG 6) be called upon to draft a key comparison protocol.

1.3 To date, the Working Group consists of 13 members, the National Institute of

Standards and Technology, USA (NIST, Chair), the National Physical Laboratory,

UK (NPL), the National Metrology Institute of Japan (NMIJ-AIST), the Korea

Research Institute of Standards and Science, Republic of Korea (KRISS), the

Standards, Productivity and Innovation Board, Singapore (SPRING Singapore), the

National Research Centre for Certified Reference Materials, China (NRCCRM) the

Consiglio Nazionale delle Ricerche - Istituto di Metrologia "G. Colonnetti", Italy

(IMGC), the Bureau National de Métrologie - Cetiat, France (BNM-Cetiat), the D.I.

Mendeleyev Institute of Metrology, Russia (VNIIM), Nederlands Meetinstituut –

Van Swinden Laboratorium, the Netherlands (NMi-VSL), the Physikalisch-

Technische Bundesanstalt, Germany (PTB), the Measurement Standards Laboratory,

New Zealand (MSL) and the Ulusal Metroloji Enstitüsü, Turkey (UME).

1.4 This technical protocol has been drawn up by the working group described above,

and in consultation with the nominated participants listed in Section 2.

1.5 The procedures outlined in this document cover the technical procedure to be

followed during measurement of the transfer standards. The procedure, which

follows the guidelines established by the BIPM4, is based on current best practice in

the use of dew/frost-point hygrometers and takes account of the experience gained

from the regional comparisons and that of the working group over the years.

1.6 This comparison is aimed at establishing the degree of equivalence between

realisations of local scales of dew/frost-point temperature of humid gas, in the

range -50 °C to +20 °C, among the participating national measurement institutes.

3 MRA, Mutual Recognition Arrangement, BIPM, 1999.

4 T.J. Quinn, "Guidelines for key comparisons carried out by Consultative Committees," Appendix F to the

MRA, BIPM, Paris.

56

2. ORGANIZATION

2.1 Participants

2.1.1 A list of participants representing RMOs of SIM, APMP, EUROMET and

COOMET has been approved by the CCT. Details of mailing and electronic

addresses are given in Appendix 1. The nominated institutes5* are:

Centre for Metrology and Accreditation (MIKES) Finland

DI Mendeleyev Institute of Metrology (VNIIM) Russia

Instituto Nacional de Técnica Aeroespacial (CEM/INTA) Spain

Istituto di Metrologia “G. Colonnetti” (IMGC) Italy

National Institute for Standards and Technology (NIST) USA

National Metrology Centre (SPRING) Singapore

National Metrology Institute of Japan (NMIJ) Japan

National Physical Laboratory (NPL) UK

National Research Centre For Certified Reference Materials (NRCCRM) China

Nederlands Meetinsituut (NMi)

Netherlands

2.1.2 NPL is the Pilot of the key comparison, taking main responsibility for running the

key comparison.

2.1.3 NMIJ is assigned as Assistant Pilot in verifying the data analysis for the draft A.

The assistant will also perform additional measurements as required.

2.1.4 By their declared intention to participate in this key comparison, the laboratories

accept the general instructions and the technical protocol written down in this

document and commit themselves to follow strictly the procedures of this protocol as

well as the version of the "Guidelines for Key Comparisons" in effect at the time of

the initiation of the Key Comparison.

2.1.5 Once the protocol and list of participants have been approved, no change to the

protocol or list of participants may be made without prior agreement of all

participants.

2.1.6 All participants must be able to submit an uncertainty budget of their humidity

standard generators.

2.2 Method of comparison

2.2.1 The key comparison is a comparison of the realisations of the scale of dew-point

temperature at the participating national institutes.

2.2.2 The comparison will be made by calibration of a pair of travelling transfer standards.

Each transfer standard will independently measure dew/frost-point temperature of a

* At the time of planning the comparison, several participant institutes were known by previous names: INRIM

was IMGC, NIM was NRC-CRM, NMC was SPRING, and VSL was NMi.

57

sample of moist gas (air or nitrogen) produced by a participant's standard generator

using the same measuring process.

2.2.3 Simultaneous measurements using a pair of standards gives information about the

within-laboratory consistency of the measurements, the reproducibility of the

instrument performance, and continuous feedback about the successful transport of

the instruments without any major shift in performance.

2.2.4 The comparison will take the form of a closed circulation in two consecutive loops.

There is one pair of hygrometers, which are at all times measured simultaneously.

Measurements will start in the pilot laboratory. The assistant will perform the

measurements next. The other participants in Loop 1 will then make comparison

measurements at the dew/frost-point temperatures required. After loop 1, the

travelling standards will return to the Pilot for checks mid-way through the

comparison, and optionally to the Assistant Pilot to repeat these checks. The

comparison will then proceed through loop 2, and the last participant will then return

the transfer standards to the pilot to carry out final measurements to monitor drift.

The assistant will also carry out repeat measurements following those of the pilot.

The sequence would therefore be*: NPL NMIJ MIKES NMi IMGC

INTA NPL ( NMIJ optional) NIST SPRING NRCCRM VNIIM

NPL NMIJ. Allowing between 6 and 8 weeks per set of measurements (and

additional time for shipping), this set of measurements will take up to 32 months.

2.2.5 The proposed circulation scheme for travelling standards for CCT dew-point key

comparison is illustrated below*.

* At the time of planning the comparison, several participant institutes were known by previous names: INRIM

was IMGC, NIM was NRC-CRM, NMC was SPRING, and VSL was NMi

58

2.2.6 All results are to be communicated directly to the pilot within six weeks of the

completion of the measurements by a laboratory.

2.2.7 Each laboratory has estimated a time for measurement and transportation. If for

some reason, the measurement facility is not ready or customs clearance takes too

much time in a country, the participating laboratory must contact the pilot laboratory

immediately. Exclusion of a participant's results from the report may occur if the

results are not available in time to prepare the draft report.

2.2.8 In case of serious difficulty with customs, or other delays which might over-run the

time period of the ATA Carnet or temporary import licence, the pilot may request

the instruments be returned to NPL, or the sequence of participation be changed to

the most practical arrangement.

2.3 Handling of artefacts

2.3.1 The artefacts should be examined immediately upon receipt at the laboratory. All

participants are expected to follow all instructions in the operator's manual provided

by the instrument manufacturers for proper unpacking, subsequent packing and

shipping to the next participant. During packing and unpacking, all participants

should check the contents with the packing list including the operator's manual.

2.3.2 The transfer standards should only be handled by authorized persons and stored in

such a way as to prevent damage.

NPL

NMIJ

Pilot

Assistant Pilot

Participants

IMGC

MIKES NIST

NMi

NRCCRM

SPRING

VNIIM INTA

Loop 1 Loop 2

59

2.3.3 During operation of the transfer standards, if there is any unusual occurrence, e.g.,

loss of heating or cooling control, the pilot laboratory should be notified

immediately before proceeding.

2.4 Transport of artefacts

2.4.1 The transportation process begins when the artefact leaves the sending laboratory

and does not end until it reaches the destination laboratory. All participants should

follow the following general guidelines:

(1) Plan the shipment well in advance. The recipient should be aware of any

customs issues in their country that would delay the testing schedule. The shipping

laboratory must be aware of any national regulations covering the travelling standard

to be exported;

(2) Mark the shipping container "FRAGILE SCIENTIFIC INSTRUMENTS" “TO

BE OPENED ONLY BY LABORATORY STAFF” and with arrows showing

"THIS WAY UP"; attach tip and shock indicators if such devices are available;

(3) Determine the best way to ship the travelling standard to the next participant;

(4) Obtain the recipient's exact shipping address. If possible, have it shipped

directly to the laboratory;

(5) Coordinate the shipping schedule with the recipient. The sending laboratory

should provide the recipient with the carrier, the exact travel mode, and the

estimated time of arrival;

(6) Instruct the recipient to confirm receipt and condition upon arrival to the sender

and the pilot. A form for reporting on the receipt of the travelling standards is shown

in Appendix 2.

2.4.2 Each transfer standard is supplied with its shipping container, which is sufficiently

robust to ensure safe transportation.

2.4.3 The artefacts will be accompanied by a suitable customs ATA Carnet or temporary

import bond (TIB) (as deemed most appropriate by the pilot laboratory) and

documentation uniquely identifying the item. Care should be taken with the timing

of the ATA Carnet, which only lasts for one year.

2.5. Shipping Costs

2.5.1 Each laboratory is responsible for the cost of shipping to the next participant

including any customs charges and insurance. The insurance should be sufficient to

cover the costs of the travelling standards and any damages that could occur.

60

2.6. Timetable

Activity Start Month Provisional date

Submission of a revised technical protocol to

Participants for unanimous approval

Re-submitted Feb

2003

Submission of revised protocol to CCT/WG7 for

approval

Mar 2003

Travelling standards characterized by the pilot 2002-early 2003

Pilot’s fist set of key comparison measurements

according to the protocol

Month 1-2 May-Jun 2003

Travelling standards sent to assistant pilot and

successive participants for measurements

Month 3-12 July 2003

Travelling standards re-measured by pilot(s) at

mid-point

Month 13-14 May-Jun 2004

Completion of measurements Month 28 approx Mid 2005

Draft A ready Month 32 approx Late 2005

Deadline for comments on draft A Month 35 approx Early 2006

Draft B ready and submitted to CCT Month 40 approx Mid 2006

3. DESCRIPTION OF THE TRANSFER STANDARDS

3.1. Artefacts

3.1.1 Two travelling standards selected for the key comparison are state-of-the-art,

commercially available chilled-mirror type of dew-point hygrometers. They have

proven to be robust with known performance characteristics such as repeatability

and transportability.

3.1.2 Details of travelling standards:

Travelling Standard #1 Travelling Standard #2

(Figure 1) (Figure 2)

Model: Michell S4000 MBW DP 3DSH III K-1806

Serial Number: 114155 / 91527 92-0319

Size

(in Packing case): 60 cm x 65 cm x 105 cm 60 cm x 55 cm x 60 cm

Weight (in Packing case): 55 kg 55 kg

Manufacturer: Michell Instruments, UK MBW Elektronik AG,

Switzerland

Owner: NPL, UK CEM-INTA, Spain

Electrical supply: 240 V 50 Hz 240 V 50 Hz

Electrical connection:2 × UK 3-pin plugs 1 × European 2-pin plug

Power: 1500 W total 500 W

(100 W plus 1400W approx)

Approximate value £25 000 £15 000

for insurance and

customs declaration

61

Figure 1. Travelling standard 1, Michell S4000

Figure 2. Travelling standard 2, MBW

62

4. MEASUREMENT INSTRUCTIONS

4.1 Measurement process

4.1.1 All participants should refer to the operating manuals for instructions and

precautions for using the travelling standards. Participants may perform any initial

checks of the operation of the hygrometers that would be performed for a normal

calibration. In the case of an unexpected instrument failure at a participant institute,

the pilot institute should be informed in order to revise the time schedule, if

necessary, as early as possible.

4.1.2 Sample gas generated by a participant's standard generator, is introduced into the

inlet of a travelling standard hygrometer through a stainless steel tube terminating

with a 6 mm Swagelok fitting for the Michell and ¼ inch Swagelok fitting for the

MBW. The instruments should be connected in parallel. For dew points near ambient

temperature (e.g. +20 °C) normal precautions (heating of pipework) should be used

to protect against condensation in sample lines.

4.1.3 A total of five dew-point temperatures humidity levels are used for the comparison

at nominal values of +20 °C and +1 °C and frost-point temperatures at nominal

values of –10 °C, -30 °C and –50 °C. The value of +1 °C nominally represents 0 °C,

while avoiding any complication due to phase change between water and ice.

4.1.4 At –10 °C, the applied condition should be generated with respect to ice in the

saturator of a single-pressure generator. Where a two-pressure generator is used, the

phase in the saturator at elevated pressure will be according to local procedure, to

result in a water vapour pressure corresponding to saturation over ice at –10 °C at

the pressure of the travelling standards. Participants should report the applied

condition in terms of frost-point temperature. The phase of condensate apparent on

the mirrors of the travelling standards should also be reported. At -30 °C and –50 °C,

all data will be assumed to be with respect to ice unless otherwise reported.

4.1.5 Measurements should be made in rising order of dew/frost point.

4.1.6 The condensate should be cleared and re-formed for each value or repetition of

dew/frost point.

4.1.7 The values of dew/frost point applied to the travelling standards should be within

±0.5 °C of the five agreed nominal values for the comparison, and ideally closer than

this. Deviations greater than this may increase the uncertainty in the comparison, for

a particular result.

4.1.8 The conditions for operation of the travelling standard Michell S4000:

(1) Set the Michell S4000 to “Standby” and “Manual”.

(2) Clean the mirror surface using cotton tips with distilled or de-ionised water. This

may be preceded by initial cleaning with alcohol if necessary

(3) Set the coolant temperature to 30 °C above the generated frost point, for

63

measuring frost-point temperatures of –50 °C and –30 °C. The cooling must be

switched off for all other points.

(4) Set the indicated flow rate of sample gas at approximately 0.5 litres per minute.

(5) Monitor the cooling as detailed in 4.2.3 below

(6) After the cooling has stabilised for 20 minutes press the “Initiate” button to

initiate an optical balance cycle. Set the “Optical Balance Control” to the centre

position. When the balance cycle is complete switch from “Standby” to “Operate”.

(7) A cable is connected between the 100 °C cut-out socket of the measurement head

and the temperature measurement socket of the monitor. This is to allow monitoring

of the operating temperature of the back of the Peltier element. When connected in

this way, the hygrometer display and the analogue output both indicate the Peltier

temperature (not the dew/frost-point). The analogue output is nominally 10 mV per

degree Celsius, with 0 volts equal to 0 °C.

(8) The dew/frost-point indication of the hygrometer is measured directly from the

hygrometer PRT resistance, using the supplied cable (See below, 4.2 Data

collection).

4.1.9 The conditions for operation of the travelling standard MBW K1806:

IMPORTANT:

Due to the nature of the mechanical configuration of the head and endoscope, the

head should only be opened once the following instructions have been read and fully

understood. Failure to observe these may result in severe damage to the transfer

standard. The unit is provided with a blank outer cover for transport.

(1) Ensure the service jack is inserted and set the MBW to Standby, with the

automatic mirror check set to “Off”.

(2) Set the mode switch to “Cooler Temp” and set the temperature to 30°C. Wait for

the mirror temperature indication to reach at least 25 °C.

(3) In order to gain access to the mirror for cleaning, carefully follow the instructions

below:

-Starting from the closed position “at 6 o’clock”, turn the bayonet socket release of

the endoscope 90 ° anti-clockwise until the notch on the endoscope guide tube and

the rotatable arm are aligned.

- Gently withdraw the endoscope. (Special care must be observed to ensure no

bending moment is applied to the endoscope at any time).

- Turn the outer blue alloy head cover anti-clockwise using the knurled surface (not

the endoscope guide tube).

- Remove the grey head cover along the guide pin.

- The mirror is now ready for cleaning.

(4) Clean the mirror surface using cotton buds with distilled or de-ionised water.

This may be preceded by initial cleaning with alcohol if necessary.

(5) In order to replace the measurement head cover, carefully follow the instructions

below:

- Replace the grey head cover, aligning the hole with the guide pin.

- Replace the outer blue alloy head cover by turning it clockwise until the endoscope

guide tube is at the “12 o’clock” position. This should only be finger-tight. Correct

alignment can be checked by observing the light emitted from the head, ensuring that

the full circular cross-section of the tube (reduced by the internal o-ring) is visible.

- Slowly insert the endoscope until a slight resistance is felt as the tip touches the o-

ring.

64

If the endoscope cannot be inserted smoothly, remove and slightly adjust the

position of the outer head cover. Once the endoscope passes the o-ring, align the

notch on the endoscope with that of the guide tube, at the 6 o’clock position. Once

the endoscope has been fully inserted, starting from the open position “at 3 o’clock”

with the two notches aligned, turn the bayonet socket release of the endoscope 90 °

clockwise.

IMPORTANT:

Never turn the head with the endoscope inserted. Special care must be observed to

ensure no bending moment is applied to the endoscope at any time.

(6) Do not adjust the light intensity potentiometer. If the mirror check fails consult

the pilot before proceeding.

(7) Control the flow rate of sample gas at approximately 30 litres per hour.

(8) Ensure the cooler mode switch is set to “Cooler Temp” and set the temperature to

30 °C higher than a nominal frost-point temperature to be measured. This is a setting

(nominal value) and the actual value achieved will not be exactly the set value.

(Note: For the measurement points below 0 °C, ensure that the hygrometer has been

adequately purged by the sample gas to a dew-point temperature below the nominal

cooler temperature setting, before setting the cooler temperature.)

(9) Monitor the cooling as detailed in 4.2.3 below.

(10) After the cooling has stabilised for 20 minutes, ensure the service jack is

inserted and activate the “Mirror Check”. When this is complete, take the MBW off

“Standby”.

(11) During the mirror check, when the mirror is heated, the pointer should lie just to

the left of the boundary between the red and green backgrounds.

(12) Once the mirror check has finalised (the illumination of the meter is

extinguished), the service jack is replaced by the measurement cable provided and

the potentiometer attached to the cable adjusted until the indication of the

hygrometer display is nominally “+60 °C”. This cable provides direct electrical

access to the PRT in the mirror.

IMPORTANT:

Once the measurement cable is connected to the hygrometer, the Manual “Mirror

Check” function must not be activated and the automatic function must remain in the

“Off” position.

(13) Hygrometer head heater is to remain off during all measurements.

4.1.10 Each measurement should be conducted with the instruments measuring in parallel

and nominally simultaneously. Each dew/frost-point temperature should be

separately repeated (reproduced) four times, to reduce the effect of any

irreproducibility of the travelling standards.

4.1.11 Participants should avoid lengthy additional measurements, except those necessary

to give confidence in the results of this comparison.

4.1.12 The transfer standards used in this comparison must not be modified, adjusted, or

used for any purpose other than described in this document, nor given to any party

other than the participants in the comparison.

4.1.13 The Pilot will make an assessment of any drift in the travelling standards during the

comparison, based on measurements at the Pilot laboratory at the beginning, middle

and end of the comparison period, and in case of doubt using optional extra

65

measurements at the Assistant pilot laboratory. If significant drift is found, then this

will be taken into account in the final overall analysis of the comparison.

4.1.14 If unacceptable performance or failure of a travelling standard is detected, the Pilot

will propose a course of action, subject to agreement of the participants.

4.2. Data collection

4.2.1 In the travelling standards, a 100-ohm platinum resistance thermometer (PRT) is

embedded beneath the surface of the chilled-mirror to measure the dew/frost-point

temperature. The current input to the PRT should be nominally 1 mA. The resistance

of the PRT should be measured using a calibrated multi-meter or a resistance bridge,

and then converted to a corresponding nominal dew/frost-point temperature using

the reference function of IEC 60751 as shown in Appendix 3. This reference

function should be used to convert resistance to (arbitrary nominal) temperature.

4.2.2 At each measured value, the mean and standard deviation of multiple readings of the

resistance of the PRT should be monitored. Participants may apply their own criteria

of stability for acceptance of measurements. When hygrometer is in equilibrium with

the gas sample, the standard deviation of a set of 10 resistance readings, taken over a

period of 10 to 20 minutes, is likely to be no more than 0.010 ohms or 0.025 °C

approximately.

4.2.3 As a supporting measurement, the coolant/Peltier temperature in the travelling

standards should be monitored. The mean and standard deviation a set of 10

readings, taken over the same period as the frost point measurements should be

reported. For the Michell, an analogue voltage signal from the USER I/O is

monitored while the 100 °C cut-out socket of the measurement head is connected to

the temperature measurement socket of the monitor. The output is nominally 10 mV

per °C, with 0 V corresponding to 0 °C. This temperature will not be the same as the

set temperature but is an indication of the temperature of the heat exchanger behind

the Peltier cooler. For the MBW the analogue voltage output from the Cooler Temp

plug is monitored (cables supplied). In this case also, the output is 10 mV per °C,

with 0 V=0 °C.

4.2.4 Values reported for dew/frost-point temperatures produced by a participant's

standard generator should be the value applied to the instruments, after any

allowances for pressure and temperature differences between the point of realisation

(laboratory standard generator) and the point of use (travelling standards).

4.2.5 The data reported for the pair of instruments should be for simultaneous or near-

simultaneous measurement of the same applied condition.

5. REPORTING OF MEASUREMENT RESULTS

5.1 Participants must report their measurement results of four repeated experiments,

within six weeks of completing their measurements.

66

5.2 The pilot should accumulate data continually and should analyse the results for

possible anomalies in the travelling standard. If problems arise, the pilot should

consult with the participant that submitted the data as soon as possible, and certainly

before the distribution of Draft A of the Report of the comparison.

5.3 The parameter to be compared between laboratories in CCT-K6 is the mean

difference found between the laboratory standard generator and the travelling

standards. Note that the values of dew-point temperature reported for the travelling

standards are “arbitrary” values calculated from the measured resistance output. The

travelling standards are used simply as comparators.

5.4 Participants should report results to the pilot in terms of dew/frost-point temperature.

The main measurement results comprise:

values of dew/frost-point applied to the travelling standards, and associated

standard uncertainty

values measured using both travelling standards simultaneously (and their

associated standard uncertainties derived from standard deviation of the set

of readings)

values of difference between applied dew/frost point and measured dew/frost

point.

A provisional template for reporting results is shown in Appendix 4, and can be

made available to participants in electronic form as an Excel spreadsheet. Use of this

format, including calculations of means and differences, allows participants to see

clearly the values and uncertainties of the parameters they are submitting for

comparison.

5.5 From the data measured by each participant, results will be analysed in terms of

differences between applied and measured dew points. In each case, the difference

will be taken between the applied (realised) value and the mean (mid-point) between

the two hygrometer values.

5.6 In addition, the difference between the two hygrometer readings on all occasions

will be analysed and will serve as a check of consistency.

5.7 The participants should report the conditions of realisation and measurement, as

background information to support the main results. These conditions should

include, where relevant, pressure and temperature in saturator, pressure difference

between saturator and travelling standards, measurement traceability, frequency of

AC (or DC) resistance measurement, travelling standard coolant measurements, and

other items. A provisional checklist for reporting conditions of measurement is

shown in Appendix 5.

5.8 Participants should provide a general description of the operation of their dew/frost-

point apparatus.

5.9 Participants should also provide an example plot of equilibrium condition (resistance

versus time) at a nominal frost-point temperature of -30 °C, over a suggested period

of at least one hour.

67

5.10 Any information obtained relating to the use of any results obtained by a participant

during the course of the comparison shall be sent only to the pilot laboratory and as

quickly as possible. The pilot laboratory will be responsible for coordinating how the

information should be disseminated to other participants. No communication

whatsoever regarding any details of the comparison other than the general conditions

described in this protocol shall occur between any of the participants or any party

external to the comparison without the written consent of the pilot laboratory. The

pilot laboratory will in turn seek permission of all the participants. This is to ensure

that no bias from whatever accidental means can occur. These constraints on

communication apply until the circulation of Draft A of the report of the

comparisons.

5.11 If a participant significantly delays reporting of results to the Pilot, then a deadline

will be agreed among the participants. If that deadline is not met, then inclusion of

those results in the comparison report will not be guaranteed.

6. UNCERTAINTY OF MEASUREMENT

6.1 The uncertainty of the key comparison results will be derived from some or all of:

o the quoted uncertainty of the dew/frost-point realisation (applied dew/frost point)

including any uncertainties due to pressure drop or other influences acting

between the point of realisation and the point of use (travelling standards).

o the estimated uncertainty relating to the short-term stability of the travelling

standards at the time of measurement

o the estimated uncertainty due to any drift of a travelling standard over the period

of the comparison (estimated by the pilot)

o the estimated uncertainty in mean values due to dispersion of repeated results

(reflecting the combined reproducibility of generator and travelling standards)

o the estimated uncertainty due to the resolution of the travelling standards (if

found to be significant)

o the estimated uncertainty due to non-linearity of the travelling standard in any

case where measurements are significantly away from the agreed nominal value

o the estimated covariance between applied (generator) and measured (travelling

standard) values of dew/frost-point (if found to be significant)

and

o any other components of uncertainty that are thought to be significant

6.2 Participants are required to submit detailed analyses of uncertainty for their dew-

point standards. Uncertainty analyses should be according to the approach given in

the ISO Guide to the Expression of Uncertainty of Measurement. A list of the all

significant components of the uncertainty budget should be evaluated, and should

support the quoted uncertainties. Evaluations should be given at a level of one

standard uncertainty. Type B estimates of uncertainty may be regarded as having

infinite degrees of freedom, or an alternative estimate of the number of degrees of

freedom may be made following the methods in the ISO Guide. A provisional

template for documentation of uncertainties is shown in Appendix 6, and can be

made available to participants in electronic form as an Excel spreadsheet. Individual

institutes may add to the template any additional uncertainties they consider relevant.

68

6.3 The pilot laboratory will collect draft uncertainty budgets as background information

to the uncertainties quoted by participants for the comparison measurements. The

pilot will review the uncertainty budgets for consistency among participants.

6.4 The uncertainty budget stated by the participating laboratory should be referenced to

an internal report and/or a published article.

7. DETERMINATION OF THE KEY COMPARISON REFERENCE VALUE

7.1 The outputs of the key comparison are expected to be:

Results of individual participants for comparison of the hygrometers against their

dew point reference in terms of mean values for each hygrometer at each measured

value, estimated standard uncertainty of each mean result and of comparison process

if necessary.

Estimates of bilateral equivalence between every pair of participants at each

measured dew point

A key comparison reference value (KCRV) for each nominal value of dew/frost

point in the comparison. The KCRV might be calculated as the arithmetic mean of

all valid results, or a weighted mean.

Estimates of equivalence of each participant to the KCRV. This might be expressed

in terms of the Degree of Equivalence (DOE) given as a difference and its

uncertainty (∆ ±U), in °C.

7.2 Values of the above will be reached by an appropriate method proposed by the Pilot,

subject to confirmation by the Assistant Pilot and agreement of all participants and

confirmation by CCT Working Groups 6 (Humidity) and 7 (Key Comparisons).

7.3 In the field of dew-point standards, the KCRV does not have any absolute

significance with respect to an SI unit. It is calculated only for purposes such as the

presentation and inter-relation of key comparison data for the MRA.

7.4 The Pilot will make an assessment of any drift in the travelling standards during the

comparison. The assessment will be based on initial measurements by the Pilot and

Assistant Pilot, together with measurements when the instruments return to the pilot

mid-way through the comparison (repeated by the Assistant Pilot if necessary), and

final measurement by both Pilot and Assistant Pilot. If significant drift of one or both

travelling standards is observed, then this will be taken into account in the final

overall analysis of the comparison. This may be by assigning a time-dependent value

to the KCRV, or by other suitable method so that estimates of equivalence can be

meaningfully calculated between results taken at different times.

7.5 If a travelling standard fails or performs poorly during the comparison, the Pilot and

Assistant Pilot will propose a course of action, subject to agreement of the

participants. If the results of one of the travelling standards (from some or all

participants) are deemed un-usable, and if measurements cannot be re-attempted, the

69

KCRV and estimates of equivalence may be based on the results of satisfactory

measurements using only one travelling standard.

70

APPENDIX 5. PROVISIONAL CHECKLIST FOR REPORTING OF

CONDITIONS OF MEASUREMENT

The following is guidance for reporting of the background information to the key

comparison measurements. This information is likely to be of secondary importance, but

will become relevant if there should be any need to resolve anomalies which might appear

in the results. Reporting of the main results is outlined in Appendix 4.

The report should include the following information:

A full description of the humidity generator used in the comparison and the

traceability of the realisation to the SI, including

o The gas used (air or nitrogen)

o The connection between the hygrometer and the standard - tubing material

and dimensions

o Description of cleaning the mirror

o Value of flow rate set for each hygrometer

o Frequency of AC (or DC) resistance measurement of hygrometer PRTs, and

current used.

o Description of any problems with the hygrometers, or with the participant’s

generator system.

For each separate repetition of each measurement point:

o Applied reference value(s) (generated dew-point temperature determined by

the generator, after any correction for pressure drop to the point of use)

o Standard deviation of the applied value(s)

o Standard uncertainty of the applied value(s)

o Values indicated by the travelling standard hygrometers

o Standard deviation of the hygrometer indicated values

o Difference between the applied (generator) value and the measured

(hygrometer) values

o Combined standard uncertainty of the difference

o Date when the measurements were carried out

o Hygrometer coolant temperature settings

o Measured temperatures of MBW coolant and Michell Peltier

o Temperature and pressure in saturator of generator

o Pressure difference between the hygrometer and the generator, and value of

correction(s) applied to compensate for this, if any.

o Environmental conditions (temperature, humidity, pressure)

o Number of recorded values

o Stabilisation time

o Time interval taken to record the values

o “Raw data” in units of resistance for the PRT measurements, and in units of

voltage for the analogue outputs

71

APPENDIX 2: RESULTS REPORTED BY THE PARTICIPANTS

The participant reported results are shown on the following pages in the form of extracts

pasted from the MS Excel reporting template for the comparisons. In general, each result is a

standard uncertainty reported at sufficiently high number of effective degrees of freedom that

a coverage factor k=2 can be used to give a coverage probability of 95 %. In cases where a

lower number of effective degrees of freedom necessitated a larger coverage factor, to give a

95 % coverage probability, participants were asked to calculate and report that, and where

relevant details are given in Appendix 3.

72

NPL

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: -50 °C Lab name NPL

Results

Hygrometer 1(Michell) Hygrometer 2 (MBW)

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -50.16478 80.26079 -50.11455 -0.05023 -50.16478 80.1708 -50.341085 0.176305

Meas 2 -50.160017 80.26184 -50.11191 -0.048107 -50.160017 80.17319 -50.335115 0.175098

Meas 3 -50.16478 80.25266 -50.13502 -0.02976 -50.16478 80.16229 -50.3625 0.19772

Meas 4 -50.37259 80.1762 -50.32754 -0.04505 -50.37259 80.08754 -50.55071 0.17812

Uncertainties (in °C) Hygrometer 1 Hygrometer 2

Meas 1 Meas 2 Meas 3 Meas 4 Meas 1 etc.

Standard uncertainty of applied condition 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015

Std uncert due to short-term stability (from standard deviation) of measurements of travelling standard (type A) 0.009 0.009 0.018 0.018 0.023 0.011 0.011 0.011

Std uncert due to long-term drift of travelling standard [if needed]

Std uncert due to resolution of travelling standard [if needed]

Std uncert due to non-linearity of travelling standard [if needed]

Covariance between applied and measured values of dew/frost-point [if needed]

Combined standard uncertainty (8 values) 0.017 0.017 0.023 0.023 0.027 0.019 0.019 0.019

Aggregation of results

Hyg 1 Hyg 2

Mean of 4 dew-point differences (for 2 instruments) -0.04329 0.181811

Type A standard uncertainty due to reproducibility of difference results 0.009 0.011

two values (each derived from standard deviation of 4 values on same instrument)

Uncertainty of mean dew point difference for each instrument (2 values) 0.014 0.015

I column

Difference between 2 means (each the mean of 4 results) -0.2251 (consistency indicator - all labs should hope to get the same value for this)

Average (mid-point) of 2 means (each the mean of 4 results) ** # 0.069262 (aggregated result - parameter to be compared between institutes)

Uncertainty in average ** # 0.010 (uncertainty in the parameter being compared)


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -29.854992 88.2796 -29.853102 -0.00189 -29.854992 88.19335 -30.071659 0.216667

Meas 2 -29.67928 88.32125 -29.747505 0.068225 -29.67928 88.23359 -29.969635 0.290355

Meas 3 -29.91683 88.25534 -29.914606 -0.002224 -29.91683 88.17278 -30.123804 0.206974

Meas 4 -29.845501 88.2749502 -29.86489 0.019389 -29.845501 88.20569 -30.040387 0.194886











Hyg 1 Hyg 2

Mean of 4 dew-point differences (for 2 instruments) 0.020875 0.227221




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73


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -9.7817855 96.15944 -9.812339 0.0305535 -9.7817855 95.59664 -10.0178 0.2360145

Meas 2 -9.7452112 96.18957 -9.73547 -0.0097412 -9.7452112 95.62716 -9.947 0.2017888

Meas 3 -9.6436027 95.76809 -9.62459 -0.0190127 -9.6436027 95.67374 -9.84021 0.1966073

Meas 4 -9.8018231 95.69577 -9.79003 -0.0117931 -9.8018231 95.60114 -10.0074 0.2055769











Hyg 1 Hyg 2





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REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 1 °C Lab name NPL

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 0.860989 100.33017 0.844899 0.01608968 0.860989 100.24616 0.630002 0.23098633

Meas 2 0.863954 100.32975 0.844899 0.01905536 0.863954 100.23194 0.5946978 0.26925653

Meas 3 0.827529 100.30271 0.77462 0.05290925 0.827529 100.20634 0.527727 0.29940736

Meas 4 1.26788017 100.47733 1.221544 0.04494065 1.26788017 100.37381 0.956587 0.31546763











Hyg 1 Hyg 2





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74

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 20 °C Lab name NPL

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 19.644452 10765218 19.63628 0.008172 19.644452 107.54303 19.355476 0.288976

Meas 2 20.157491 107.85785 20.165633 -0.008142 20.157491 107.75373 19.897725 0.259766

Meas 3 19.698272 107.68064 19.709525 -0.011253 19.698272 107.57563 19.439278 0.258994

Meas 4 19.788426 107.71226 19.790905 -0.002479 19.788426 107.60687 19.519764 0.268662











Hyg 1 Hyg 2





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75

NMIJ

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: -50 °C Lab name NMIJ

Results

Hygrometer 1(Michell) Hygrometer 2 (MBW) Number of data

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C Hyg 1 Hyg 2

Meas 1 -49.964 80.400 -49.765 -0.199 -49.953 80.225 -50.205 0.252 73 73

Meas 2 -49.961 80.401 -49.761 -0.200 -49.950 80.220 -50.218 0.268 42 42

Meas 3 -49.969 80.400 -49.763 -0.206 -49.958 80.210 -50.242 0.285 52 52

Meas 4 -49.960 80.399 -49.768 -0.192 -49.949 80.223 -50.209 0.260 21 21











Hyg 1 Hyg 2

Mean of 4 dew-point differences (for 2 instruments) -0.200 0.266 (average weighted proportional to number of data)




Effective degree of freedom of uncertainty of mean dew point difference 6.641 6.972

I column


Average (mid-point) of 2 means (each the mean of 4 results) ** 0.033 (aggregated result - parameter to be compared between institutes)

Uncertainty in average ** 0.049 (uncertainty in the parameter being compared)

Effective degree of freedom of uncertainty in average ** 5.974

Uncertainty in difference between 2 means 0.030

Effective degree of freedom of uncertainty in difference between 2 means 7.059


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -


Meas 1 -30.010 88.284 -29.841 -0.169 -30.009 88.121 -30.255 0.246 20 20

Meas 2 -30.007 88.284 -29.843 -0.165 -30.006 88.122 -30.252 0.246 14 14

Meas 3 -30.004 88.283 -29.844 -0.160 -30.002 88.124 -30.246 0.244 22 24

Meas 4 -30.005 88.284 -29.842 -0.163 -30.004 88.124 -30.248 0.245 46 46











Hyg 1 Hyg 2






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76


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -


Meas 1 -10.001 96.133 -9.880 -0.121 -10.000 95.981 -10.268 0.267 38 38

Meas 2 -9.998 96.126 -9.898 -0.100 -9.998 95.981 -10.267 0.270 12 12

Meas 3 -9.997 96.125 -9.901 -0.095 -9.996 95.983 -10.263 0.266 25 25

Meas 4 -9.996 96.126 -9.899 -0.098 -9.996 95.983 -10.263 0.267 40 40

-0.103 0.268

0.012 0.001











Hyg 1 Hyg 2






I column




REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 1 °C Lab name NMIJ

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 0.993 100.412 1.054 -0.061 0.993 100.278 0.710 0.283

Meas 2 1.000 100.414 1.059 -0.059 1.000 100.283 0.725 0.274

Meas 3 1.013 100.417 1.068 -0.055 1.013 100.286 0.731 0.282

Meas 4 1.010 100.412 1.056 -0.045 1.010 100.283 0.723 0.287









Uncertainty of resistance measurement 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018



Hyg 1 Hyg 2





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77

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 20 °C Lab name NMIJ

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 19.987 107.795 20.004 -0.017 19.987 107.670 19.682 0.304

Meas 2 20.002 107.800 20.016 -0.014 20.002 107.675 19.695 0.307

Meas 3 20.002 107.799 20.013 -0.012 20.002 107.676 19.698 0.304

Meas 4 20.007 107.800 20.016 -0.009 20.007 107.676 19.697 0.310









Uncertainty of resistance measurement 0.018 0.018 0.018 0.018 0.018 0.018 0.018 0.018



Hyg 1 Hyg 2





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78

VSL

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: -50 °C Lab name NMi-VSL

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -50.00 80.3768 -49.82 -0.18 -50.00 80.3295 -49.94 -0.06

Meas 2 -50.01 80.3530 -49.88 -0.13 -50.01 80.3312 -49.94 -0.08

Meas 3 -50.02 80.3464 -49.90 -0.12 -50.02 80.3333 -49.93 -0.08

Meas 4 -50.02 80.3887 -49.79 -0.22 -50.02 80.3573 -49.87 -0.14

Uncertainties (in °C) Hygrometer 1(Michell) Hygrometer 2 (MBW)

Meas 1 Meas 2 Meas 3 Meas 4 Meas 1 Meas 2 Meas 3 Meas 4









Hyg 1 Hyg 2

Mean of 4 dew-point differences (for 2 instruments) -0.143 -0.054



Uncertainty of mean dew point difference for each instrument (2 values) 95% 0.136 0.163

I column


Average (mid-point) of 2 means (each the mean of 4 results) ** -0.098 (aggregated result - parameter to be compared between institutes)

Uncertainty in average ** 95% 0.133 (uncertainty in the parameter being compared)


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -30.03 88.1814 -30.10 0.07 -30.03 88.1375 -30.21 0.18

Meas 3 -30.02 88.1727 -30.12 0.10 -30.02 88.1227 -30.25 0.23

Meas 4 -30.03 88.2331 -29.97 -0.06 -30.03 88.1404 -30.21 0.18

Meas 5 -30.03 88.2326 -29.97 -0.06 -30.03 88.1363 -30.22 0.19











Hyg 1 Hyg 2





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79


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -10.00 96.0748 -10.03 0.02 -10.00 95.9667 -10.30 0.30

Meas 2 -10.01 96.0546 -10.08 0.07 -10.01 95.9687 -10.30 0.29

Meas 3 -10.00 96.0731 -10.03 0.03 -10.00 95.9749 -10.28 0.28

Meas 4 -10.00 96.0664 -10.05 0.05 -10.00 95.9748 -10.28 0.28











Hyg 1 Hyg 2





I column




REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 1 °C Lab name NMi-VSL

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 0.994 100.395 1.011 -0.016 0.994 100.317 0.810 0.184

Meas 2 1.002 100.377 0.965 0.037 1.002 100.296 0.758 0.244

Meas 3 1.000 100.391 1.001 -0.001 1.000 100.370 0.946 0.054

Meas 4 0.999 100.391 1.001 -0.002 0.999 100.381 0.974 0.025

Meas 5 1.001 100.391 1.000 0.001 1.001 100.381 0.975 0.026


Meas 1 Meas 2 Meas 3 Meas 4 Meas 5 Meas 1 Meas 2 Meas 3 Meas 4 Meas 5

Standard uncertainty of applied condition 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028

Std uncert due to short-term stability (from standard deviation) of measurements of travelling standard (type A) 0.009 0.003 0.003 0.002 0.002 0.006 0.003 0.003 0.003 0.003





Combined standard uncertainty (8 values) 0.030 0.028 0.028 0.028 0.028 0.029 0.028 0.028 0.028 0.028


Hyg 1 Hyg 2





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80

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 20 °C Lab name NMi-VSL

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 19.88 107.7385 19.86 0.02 19.88 107.6449 19.62 0.26

Meas 2 19.95 107.7606 19.92 0.03 19.95 107.6719 19.69 0.26

Meas 3 19.94 107.7571 19.91 0.03 19.94 107.6741 19.69 0.25

Meas 4 19.96 107.7722 19.95 0.02 19.96 107.6774 19.70 0.26











Hyg 1 Hyg 2





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81

MIKES

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: -50 °C Lab name MIKES

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -49.58 80.495 -49.54 -0.04 -49.58 80.413 -49.75 0.17

Meas 2 -50.13 80.252 -50.16 0.02 -50.13 80.183 -50.33 0.20

Meas 3 -50.10 80.268 -50.12 0.02 -50.10 80.192 -50.31 0.21

Meas 4 -50.08 80.294 -50.05 -0.03 -50.08 80.210 -50.26 0.19






(Std uncert due to resolution of travelling standard [if needed]) Uncertainty of resistance measurement 0.052 0.052 0.052 0.052 0.023 0.023 0.023 0.023


Covariance between applied and measured values of dew/frost-point [if needed] 9.70E-07 5.70E-07 -6.30E-07 1.10E-06 4.70E-07 2.70E-07 4.80E-07 -7.30E-07



Hyg 1 Hyg 2





I column



Standard uncertainty in average ** 0.019 (uncertainty in the parameter being compared)


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -30.10 88.170 -30.13 0.03 -30.10 88.093 -30.33 0.23

Meas 2 -29.92 88.267 -29.89 -0.02 -29.91 88.176 -30.12 0.21

Meas 3 -29.97 88.240 -29.96 -0.01 -29.97 88.156 -30.17 0.20

Meas 4 -29.92 88.251 -29.93 0.01 -29.92 88.175 -30.12 0.20








Covariance between applied and measured values of dew/frost-point [if needed] -1.86E-07 4.40E-07 -3.90E-07 1.40E-07 -3.03E-06 1.40E-07 1.50E-07 2.50E-07



Hyg 1 Hyg 2





I column




82


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -10.10 96.053 -10.08 -0.02 -10.10 95.950 -10.34 0.25

Meas 2 -9.84 96.155 -9.82 -0.01 -9.84 96.050 -10.09 0.26

Meas 3 -10.02 96.082 -10.01 -0.01 -10.02 95.978 -10.28 0.26

Meas 4 -10.04 96.055 -10.08 0.04 -10.04 95.970 -10.30 0.26








Covariance between applied and measured values of dew/frost-point [if needed] 1.87E-06 1.50E-05 6.90E-07 2.40E-08 -3.00E-08 1.80E-05 -1.20E-06 9.10E-06



Hyg 1 Hyg 2





I column




REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 1 °C Lab name MIKES

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 1.01 100.383 0.98 0.03 0.99 100.284 0.73 0.26

Meas 2 1.01 100.395 1.01 0.00 1.00 100.290 0.74 0.26

Meas 3 0.99 100.390 1.00 -0.01 0.99 100.291 0.75 0.25

Meas 4 0.96 100.375 0.96 0.00 0.96 100.282 0.72 0.24








Covariance between applied and measured values of dew/frost-point [if needed] 1.92E-06 -4.43E-07 4.80E-07 -6.30E-09 -3.15E-06 -8.40E-07 5.17E-07 -9.62E-07



Hyg 1 Hyg 2





I column




83

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 20 °C Lab name MIKES

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 19.99 107.779 19.96 0.03 20.00 107.691 19.74 0.26

Meas 2 19.99 107.786 19.98 0.01 20.00 107.695 19.75 0.25

Meas 3 19.93 107.767 19.93 0.00 19.94 107.669 19.68 0.26

Meas 4 19.76 107.692 19.74 0.02 19.78 107.593 19.48 0.29








Covariance between applied and measured values of dew/frost-point [if needed] -1.30E-06 -1.40E-06 2.00E-07 -9.70E-07 -3.00E-08 5.20E-07 1.70E-08 5.20E-07



Hyg 1 Hyg 2





I column




84

INTA

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON CCT/K6 Nominal value: -50 °C Lab name INTA

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -50.009 80.3303 -49.939 -0.069 -50.009 80.2421 -50.162 0.153

Meas 2 -50.009 80.3264 -49.949 -0.060 -50.009 80.2423 -50.161 0.152

Meas 3 -50.009 80.3287 -49.943 -0.066 -50.009 80.2419 -50.162 0.153

Meas 4 -50.009 80.3278 -49.946 -0.063 -50.009 80.2420 -50.162 0.153








Covariance between applied and measured values of dew/frost-point temperature [if needed]

Combination of these standard uncertainties in quadrature (8 values) 0.042 0.037 0.041 0.041 0.033 0.033 0.033 0.033


Hyg 1 Hyg 2





I column





Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -30.005 88.2263 -29.9883 -0.017 -30.005 88.1422 -30.201 0.196

Meas 2 -30.005 88.2330 -29.9712 -0.033 -30.005 88.1408 -30.205 0.200

Meas 3 -30.005 88.2291 -29.9810 -0.024 -30.005 88.1403 -30.206 0.201

Meas 4 -30.004 88.2291 -29.9811 -0.023 -30.004 88.1418 -30.202 0.198











Hyg 1 Hyg 2





I column




85


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -9.991 96.1009 -9.962 -0.030 -9.991 95.9926 -10.238 0.247

Meas 2 -9.990 96.1007 -9.962 -0.028 -9.990 95.9926 -10.238 0.248

Meas 3 -9.988 96.0986 -9.967 -0.021 -9.988 95.9930 -10.237 0.249

Meas 4 -9.991 96.0952 -9.976 -0.014 -9.991 95.9914 -10.241 0.251











Hyg 1 Hyg 2





I column




REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON CCT/K6 Nominal value: 1 °C Lab name INTA

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 0.988 100.3851 0.985 0.002 0.988 100.2807 0.718 0.269

Meas 2 0.984 100.3859 0.988 -0.004 0.984 100.2809 0.719 0.265

Meas 3 0.982 100.3839 0.982 0.000 0.982 100.2791 0.714 0.268

Meas 4 0.982 100.3849 0.985 -0.003 0.982 100.2795 0.715 0.267











Hyg 1 Hyg 2





I column




86

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON CCT/K6 Nominal value: 20 °C Lab name INTA

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 20.003 107.7856 19.980 0.024 20.003 107.6776 19.702 0.302

Meas 2 20.004 107.7860 19.981 0.023 20.004 107.6782 19.703 0.300

Meas 3 20.001 107.7859 19.980 0.021 20.001 107.6780 19.703 0.299

Meas 4 20.002 107.7860 19.981 0.022 20.002 107.6785 19.704 0.298











Hyg 1 Hyg 2





I column




87

INRIM

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: -50 °C Lab name INRiM

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference (applied

dp - meas dp) in °C

Meas 1 -50.149 80.2743 -50.081 -0.07 -50.149 80.1760 -50.328 0.18

Meas 2 -50.149 80.2811 -50.063 -0.09 -50.149 80.1796 -50.319 0.17

Meas 3 -50.142 80.2798 -50.067 -0.08 -50.142 80.1759 -50.328 0.19

Meas 4 -50.141 80.2734 -50.083 -0.06 -50.141 80.1732 -50.335 0.19






Std uncert due to resolution of travelling standard [if needed] 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003





Hyg 1 Hyg 2





I column





Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference (applied


Meas 1 -30.353 88.0880 -30.339 -0.01 -30.353 87.9931 -30.579 0.23

Meas 2 -30.345 88.0877 -30.340 -0.01 -30.345 87.9938 -30.578 0.23

Meas 3 -30.354 88.0800 -30.359 0.01 -30.354 87.9834 -30.604 0.25

Meas 4 -30.179 88.1527 -30.175 0.00 -30.179 88.0550 -30.423 0.24











Hyg 1 Hyg 2





I column




88


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference (applied


Meas 1 -9.908 96.1306 -9.886 -0.02 -9.908 96.0171 -10.176 0.27

Meas 2 -10.161 96.0202 -10.168 0.01 -10.161 95.9090 -10.451 0.29

Meas 3 -10.101 96.0503 -10.091 -0.01 -10.101 95.9416 -10.368 0.27

Meas 4 -10.016 96.0800 -10.015 0.00 -10.016 95.9697 -10.296 0.28











Hyg 1 Hyg 2





I column




REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 1 °C Lab name INRiM

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference (applied


Meas 1 1.015 100.4050 1.036 -0.02 1.015 100.2932 0.750 0.26

Meas 2 1.014 100.4021 1.029 -0.02 1.014 100.2930 0.750 0.26

Meas 3 1.014 100.4060 1.039 -0.03 1.014 100.2931 0.750 0.26

Meas 4 1.012 100.4046 1.035 -0.02 1.012 100.2905 0.743 0.27











Hyg 1 Hyg 2





I column




89

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 20 °C Lab name INRiM

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference (applied


Meas 1 19.963 107.7754 19.953 0.01 19.963 107.6563 19.647 0.32

Meas 2 19.963 107.7745 19.951 0.01 19.963 107.6555 19.645 0.32

Meas 3 19.967 107.7805 19.967 0.00 19.967 107.6585 19.653 0.31

Meas 4 19.968 107.7804 19.966 0.00 19.968 107.6582 19.652 0.32











Hyg 1 Hyg 2





I column




90

NIST

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: -50.000 °C Lab name NIST

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -50.005 80.374 -49.830 -0.174 -50.005 80.271 -50.089 0.084

Meas 2 -50.005 80.398 -49.769 -0.236 -50.005 80.280 -50.067 0.062

Meas 3 -50.002 80.396 -49.775 -0.228 -50.002 80.277 -50.073 0.071

Meas 4 -50.002 80.399 -49.767 -0.235 -50.002 80.276 -50.076 0.074



Standard uncertainty of applied condition Type B uncertainty documented in paper 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007

Standard deviation of the calculated dew / frost-point temperature (Deg. C) 0.032 0.051 0.045 0.041 0.007 0.005 0.009 0.006

Number of observations. 57 197 323 71 56 68 180 197






Combined standard uncertainty (8 values)


Hyg 1 Hyg 2





The value reported here is the standard uncertainty obtained by combining the type A value in the boxes

immediately above with the uncertainty of the humidity generator.

I column





Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -30.005 88.250 -29.927 -0.078 -30.005 88.160 -30.157 0.152

Meas 2 -30.007 88.264 -29.892 -0.115 -30.007 88.160 -30.157 0.150

Meas 3 -30.002 88.272 -29.873 -0.129 -30.002 88.164 -30.147 0.144

Meas 4 -30.004 88.270 -29.879 -0.125 -30.004 88.164 -30.147 0.144



Standard uncertainty of applied condition Type B uncertainty documented in paper 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007










Hyg 1 Hyg 2







I column




91


Results

Notes: The condensate for all of the -10C points is dew. The applied dew point of -11.2 Deg. C corresponds to a frost point temperature of nominally -10.0 Deg. C.

A correction of +.005C is applied to the temperatures reported as Output in Deg. C.


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -11.219 95.641 -11.130 -0.089 -11.219 95.529 -11.416 0.198

Meas 2 -11.206 95.646 -11.117 -0.089 -11.206 95.533 -11.406 0.200

Meas 3 -11.241 95.627 -11.165 -0.076 -11.241 95.519 -11.440 0.199

Meas 4 -11.199 95.646 -11.116 -0.082 -11.199 95.535 -11.399 0.200













Hyg 1 Hyg 2







I column




REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 1.000 °C Lab name NIST

Results

Note: A correction of +.005C is applied to the temperatures reported as Output in Deg. C.


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 0.981 100.400 1.029 -0.048 0.981 100.285 0.734 0.246

Meas 2 0.981 100.398 1.025 -0.044 0.981 100.289 0.743 0.238

Meas 3 0.983 100.401 1.031 -0.047 0.983 100.287 0.739 0.244

Meas 4 0.984 100.397 1.020 -0.036 0.984 100.285 0.735 0.249













Hyg 1 Hyg 2







I column




92

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 20.000 °C Lab name NIST

Results

Note: A correction of +.005C is applied to the temperatures reported as Output in Deg. C.


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 20.058 107.814 20.059 -0.001 20.058 107.704 19.775 0.283

Meas 2 20.069 107.815 20.060 0.008 20.069 107.712 19.795 0.273

Meas 3 20.068 107.816 20.064 0.004 20.068 107.716 19.804 0.264

Meas 4 20.069 107.815 20.060 0.009 20.069 107.708 19.784 0.285













Hyg 1 Hyg 2







I column




93

NMC

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON

Nominal

value: -50 °C Lab nameNMC/SPRING

Results


Applied

frost point

(°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied fp -

meas fp)

in °C

Applied

frost point

(°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied fp -

meas fp) in

°C

Meas 2 -49.980 80.353 -49.881 -0.099 -49.987 80.278 -50.071 0.084

Meas 3 -49.986 80.328 -49.945 -0.040 -49.986 80.328 -50.055 0.069

Meas 4 -49.986 80.327 -49.947 -0.039 -49.986 80.277 -50.074 0.088

Meas 5 -49.980 80.348 -49.896 -0.084 -49.981 80.274 -50.081 0.100

Note: Meas 1 was not a full simultaneous dataset

Uncertainties (in °C)


Standard uncertainty of applied condition except type A 0.035 0.035 0.034 0.034 0.035 0.035 0.034 0.034

0.0018 0.0016 0.0017 0.0014 0.0018 0.0016 0.0017 0.0014

0.0241 0.0201 0.0311 0.0359 0.0159 0.0148 0.0127 0.0119

0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005

Std uncert due to resolution of traveling standard (resolution is 1 mK) 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003 0.0003

Std uncert due to long-term drift of traveling standard [Not observed]

Std uncert due to non-linearity of traveling standard [not involved]

Covariance between applied and measured values of dew/frost-point [not applicable]

Difference between ABC/MMC (insignificant)

Drift due to longer waiting time (insignificant)


Average of combined standard uncertainty Auc 0.0446 0.0372


Hyg 1 Hyg 2

Mean of 4 dew-point differences for Michell/MBW -0.066 0.085



0.054 0.039

Difference between 2 means (each the mean of 4 results) Hyg2-hyg1 0.151 (consistency indicator - all labs should hope to get the same value for this)



Standard uncertainty of applied condition type A (when there are more than one records, max

value is taken)

Std uncert due to short-term stability (from standard deviation) of measurements of traveling

standard (type A) (when there are more than one records, the average of the standard deviations of

records is taken)

Std uncert due to the resistance measurement uncertainty of traveling standard (the uncertainty of

the two bridges is 1 mK 95% k=2)

Uncertainty of mean dew point difference for each instrument (2 values) (Auc combined with the

reproducibility

Hygrometer1 Hygrometer 2

94


Nominal

value: -30 °C Lab name NMC/SPRING

Results


Applied

frost

point (°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied fp

- meas fp)

in °C

Applied

frost point

(°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied fp

- meas fp)

in °C

Meas 1 -29.974 88.245 -29.940 -0.034 -29.974 88.162 -30.151 0.177

Meas 2 -29.984 88.250 -29.929 -0.054 -29.984 88.170 -30.131 0.148

Meas 3 -29.978 88.247 -29.935 -0.042 -29.978 88.163 -30.150 0.172

Meas 4 -29.977 88.248 -29.934 -0.043 -29.977 88.162 -30.151 0.174




0.0016 0.0011 0.0010 0.0010 0.0016 0.0011 0.0010 0.0010

0.0275 0.0265 0.0223 0.0593 0.0090 0.0082 0.0108 0.0063

0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005










Hyg 1 Hyg 2

Mean of 5 dew-point differences -0.043 0.168



0.044 0.030




Standard uncertainty of applied condition type A (when there are more than one

records, max value is taken)

Std uncert due to short-term stability (from standard deviation) of measurements of

traveling standard (type A) (when there are more than one records, the average of the

standard deviations of records is taken)

Std uncert due to the resistance measurement uncertainty of traveling standard (the

uncertainty of the two bridges is 1 mK 95% k=2)

Uncertainty of mean dew point difference for each instrument (2 values) (Auc combined

with the reproducibility

95


Nominal

value: -10 °C Lab name NMC/SPRING

Results Generator Model 4500


Applied

frost

point (°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied fp

- meas fp)

in °C

Applied

frost point

(°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied fp

- meas fp)

in °C

Meas 1 -11.197 95.646 -11.122 -0.075 -11.211 95.547 -11.374 0.163

Meas 2 -11.197 95.644 -11.127 -0.070 -11.197 95.541 -11.389 0.193

Meas 3 -11.205 95.635 -11.150 -0.054 -11.205 95.534 -11.407 0.202

Meas 4 -11.196 95.636 -11.148 -0.048 -11.196 95.542 -11.388 0.192




0.0020 0.0020 0.0010 0.0016 0.0020 0.0020 0.0010 0.0016

0.0032 0.0029 0.0034 0.0027 0.0109 0.0013 0.0009 0.0014

0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005










Hyg 1 Hyg 2




0.024 0.027

Results Generator Model 2500


Applied

dew

point (°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied

dp - meas

dp) in °C

Applied

dew point

(°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied

dp - meas

dp) in °C

Meas 1 -11.235 95.622 -11.184 -0.050 -11.235 95.522 -11.439 0.204

Meas 2 -11.228 95.628 -11.169 -0.059 -11.228 95.531 -11.415 0.187

Meas 3 -11.238 95.618 -11.193 -0.045 -11.238 95.523 -11.435 0.198

Meas 4 -11.242 95.617 -11.196 -0.045 -11.242 95.521 -11.440 0.199




0.0052 0.0065 0.0040 0.0058 0.0052 0.0065 0.0040 0.0058

0.0073 0.0099 0.0100 0.0080 0.0072 0.0038 0.0045 0.0042

0.0003 0.0003 0.0003 0.0003

Std uncert due to resolution of travelling standard (resolution is 1 mK) 0.0003 0.0003 0.0003 0.0003 0.003 0.0003 0.0003 0.0003

Std uncert due to long-term drift of travelling standard [Not observed]

Std uncert due to non-linearity of travelling standard [not involved]







Hyg 1 Hyg 2






Hyg 1 Hyg 2

Average of 2 generators -0.056 0.192

0.031 0.032




Uncertainty of mean dew point difference for each instrument (2 values) (average of the

uncertainties of the two generators)




Std uncert due to the resistance measurement uncertainty of travelling standard (the













96


Nominal

value: 1 °C Lab nameNMC/SPRING

Results


Applied

dew

point (°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied

dp - meas

dp) in °C

Applied

dew point

(°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied

dp - meas

dp) in °C

Meas 1 0.987 100.406 1.040 -0.053 0.987 100.304 0.778 0.208

Meas 2 1.008 100.410 1.048 -0.040 1.008 100.309 0.790 0.219

Meas 3 0.996 100.407 1.041 -0.045 0.996 100.307 0.786 0.210

Meas 4 0.991 100.405 1.038 -0.046 0.991 100.307 0.786 0.205




0.0044 0.0041 0.0038 0.0056 0.0044 0.0041 0.0038 0.0056

0.0096 0.0178 0.0084 0.0085 0.0043 0.0180 0.0034 0.0053

0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005










Hyg 1 Hyg 2




0.042 0.042













97


Nominal

value: 20 °C Lab nameNMC/SPRING

Results


Applied

dew

point (°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied

dp - meas

dp) in °C

Applied

dew point

(°C)

Resistance

output

(ohms)

Output

in °C

Difference

(applied

dp - meas

dp) in °C

Meas 1 19.983 107.791 19.995 -0.011 19.983 107.689 19.731 0.252

Meas 2 19.989 107.792 19.996 -0.007 19.989 107.691 19.735 0.253

Meas 3 19.988 107.794 20.001 -0.013 19.988 107.689 19.731 0.257

Meas 4 19.987 107.798 20.010 -0.023 19.987 107.695 19.746 0.242




0.0038 0.0042 0.0043 0.0049 0.0038 0.0042 0.0043 0.0049

0.0060 0.0081 0.0052 0.0054 0.0199 0.0219 0.0244 0.0204

0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005 0.0005










Hyg 1 Hyg 2




0.047 0.051













98

NIM

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: -50 °C Lab name NIM China

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C) Output (mV)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -49.76 80.492 -49.53 -0.23 -49.76 -499.70 -49.97 0.21

Meas 2 -50.51 80.187 -50.30 -0.21 -50.51 -507.02 -50.70 0.19

Meas 3 -50.51 80.190 -50.29 -0.22 -50.51 -507.40 -50.74 0.23

Meas 4 -50.57 80.184 -50.31 -0.26 -50.57 -508.34 -50.83 0.26











Hyg 1 Hyg 2





I column

Difference between 2 means (each the mean of 4 results) 0.450 (consistency indicator - all labs should hope to get the same value for this)




Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Output

(mV)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -30.17 88.228 -29.98 -0.19 -30.17 -304.31 -30.43 0.26

Meas 2 -30.14 88.225 -29.99 -0.15 -30.14 -304.02 -30.40 0.26

Meas 3 -30.07 88.264 -29.89 -0.18 -30.07 -303.24 -30.32 0.25

Meas 4 -30.16 88.243 -29.94 -0.22 -30.16 -304.18 -30.42 0.26











Hyg 1 Hyg 2





I column




99


Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Output

(mV)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -10.14 96.099 -9.97 -0.17 -10.14 -103.71 -10.37 0.23

Meas 2 -10.15 96.121 -9.91 -0.24 -10.15 -103.19 -10.32 0.17

Meas 3 -10.15 96.116 -9.93 -0.22 -10.15 -103.54 -10.35 0.2

Meas 4 -10.25 96.058 -10.07 -0.18 -10.25 -104.77 -10.48 0.23











Hyg 1 Hyg 2





I column




REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 1 °C Lab name NIM China

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Output

(mV)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 1.04 100.442 1.13 -0.09 1.04 8.33 0.83 0.21

Meas 2 0.94 100.430 1.10 -0.16 0.94 7.10 0.71 0.23

Meas 3 0.96 100.441 1.13 -0.17 0.96 7.51 0.75 0.21

Meas 4 1.14 100.491 1.26 -0.12 1.14 9.30 0.93 0.21











Hyg 1 Hyg 2





I column




100

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 20 °C Lab name NIM China

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Output

(mV)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 19.83 107.761 19.92 -0.09 19.83 196.31 19.63 0.2

Meas 2 19.84 107.780 19.97 -0.13 19.84 196.40 19.64 0.2

Meas 3 19.83 107.750 19.90 -0.07 19.83 196.25 19.63 0.2

Meas 4 19.89 107.783 19.97 -0.08 19.89 197.20 19.72 0.17











Hyg 1 Hyg 2





I column




101

VNIIFTRI ESB

REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: -50 °C Lab name VNIIFTRI ES

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 -50.23863 80.230185 -50.19161 -0.0471 -50.23017 80.173120 -50.33529 0.1051

Meas 2 -49.81143 80.398098 -49.76879 -0.0426 -49.80320 80.351449 -49.88626 0.0831

Meas 3 -49.89061 80.366741 -49.84776 -0.0429 -49.88891 80.271832 -50.08675 0.1978

Meas 4 -50.00567 80.314387 -49.97959 -0.0261 -50.00485 80.253659 -50.13250 0.1279











Hyg 1 Hyg 2





I column





Nominal

value: -30 °C Lab name VNIIFTRI ES

Results


Applied

dew point

(°C)

Resistanc

e output

(ohms)

Output in

°C

Difference

(applied

dp - meas

dp) in °C

Applied

dew point

(°C)

Resistanc

e output

(ohms)

Output in

°C

Difference

(applied

dp - meas

dp) in °C

Meas 1 -29.60836 88.390700 -29.57142 -0.0369 -29.60719 88.315073 -29.76317 0.1560

Meas 2 -29.74895 88.325140 -29.73764 -0.0113 -29.74665 88.260019 -29.90274 0.1561

Meas 3 -30.34831 88.096864 -30.31635 -0.0320 -30.34592 88.002911 -30.55450 0.2086

Meas 4 -29.95452 88.227280 -29.98575 0.0312 -29.95270 88.183068 -30.09783 0.1451




Std uncert due to short-term stability (from standard deviation) of measurements of travelling standard (type A)0.0082 0.0063 0.0062 0.0042 0.0090 0.0125 0.0107 0.0134







Hyg 1 Hyg 2





I column




102


Nominal

value: -10 °C Lab name VNIIFTRI ES

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp)

in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in

°C

Meas 1 -11.10640 95.673620 -11.05152 -0.0549 -11.10443 95.567779 -11.32142 0.2170

Meas 2 -11.30619 95.593573 -11.25565 -0.0505 -11.27519 95.498638 -11.49773 0.2225

Meas 3 -11.24888 95.624613 -11.17649 -0.0724 -11.24655 95.532276 -11.41195 0.1654

Meas 4 -11.28372 95.612975 -11.20617 -0.0776 -11.28173 95.516799 -11.45142 0.1697











Hyg 1 Hyg 2





I column




REPORTING TEMPLATE FOR DEW-POINT KEY COMPARISON Nominal value: 1 °C Lab name VNIIFTRI ES

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp) in °C

Meas 1 1.06886 100.423079 1.08269 -0.0138 1.08514 100.335072 0.85744 0.2277

Meas 2 0.96621 100.401048 1.02630 -0.0601 1.00193 100.309507 0.79201 0.2099

Meas 3 1.08839 100.446285 1.14208 -0.0537 1.08968 100.341697 0.87440 0.2153

Meas 4 1.21559 100.507623 1.29908 -0.0835 1.21885 100.383155 0.98050 0.2384











Hyg 1 Hyg 2





I column




103


Nominal

value: 20 °C Lab name VNIIFTRI ES

Results


Applied dew

point (°C)

Resistance

output

(ohms)

Output in

°C

Difference

(applied dp -

meas dp)

in °C

Applied dew

point (°C)

Resistance

output (ohms)

Output in

°C

Difference

(applied dp -

meas dp) in

°C

Meas 1 19.86280 107.735573 19.85091 0.0119 19.88897 107.6534408 19.63953 0.2502

Meas 2 19.90056 107.737380 19.85488 0.0457 19.90921 107.6484400 19.62600 0.2832

Meas 3 20.31663 107.910350 20.30005 0.0166 20.31795 107.8150393 20.05475 0.2632

Meas 4 20.04904 107.815613 20.05622 -0.0072 20.05249 107.7046259 19.77059 0.2819











Hyg 1 Hyg 2





I column




104

APPENDIX 3: UNCERTAINTY ANALYSES OF PARTICIPANTS

Uncertainty budgets of each participant are shown on the following pages. These were

reported either in the MS Excel template provided for comparison reporting or as tabulated

information giving a suitable level of detail to cover the main sources of uncertainty. Where

the template was used, included here are selected pages detailing uncertainty calculations at

+20 °C and -50 °C, the extremes of the comparison. The protocol required participants to

report the effective number of degrees of freedom of the uncertainty estimates. In cases

where this was sufficiently large, a coverage factor of 2 is used to obtain an interval for

confidence probability of 95 %. In the few cases where a larger coverage factor was needed,

the detail is included in this Appendix.

105

NPL

The uncertainty routinely reported for calibrations is based on the combined standard

uncertainty of the standard applied condition, together with an allowance for the resolution

and short-term stability of the instrument being calibrated. The result is reported with an

expanded uncertainty at a coverage factor k=2 giving a coverage probability of approximately

95 %.

106

NMIJ

Uncertainty analysis of dew-point standardNominal

value: -50 °C Lab name: NMIJ

CCT Key Comparison in humidity (dew-point temperature) CCT-K6

- each participant submits one spreadsheet summary per nominal dew point measured in the comparison (5 sheets in total)

Quantity Components Standard Degrees of freedom Sensitivity Uncertainty Unit of u (Qi)

(symbol) uncertainty components evaluated coefficient contribution and/or

by a type A method * comment

Qi u (Qi) n i u i in °C

Primary dew-point generator Saturation temperature

Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.00236567 infinite 1 0.002 °C

Long-term stability (sensor and indicator) 0.00866179 2.001422222 1 0.009 °C

Self-heating and residual heat fluxes (sensor) 0.00500076 2.001216794 1 0.005 °C

Resolution and accuracy or linearity (indicator unit) 0.00289749 146126.5652 1 0.003 °C

Saturator:

Temperature homogeneity 0.0057735 2 1 0.006 °C

Temperature stability 0.003 8 1 0.003 °C

Saturation pressure

Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 1.59058426 infinite 8.0068E-05 0.000 Pa

Long-term stability (sensor and indicator) 20.9808492 infinite 8.0068E-05 0.002 Pa

Resolution and accuracy or linearity (indicator unit) 0.57735027 infinite 8.0068E-05 0.000 Pa

Pressure differences in the saturator cell 37.9248709 2 8.0068E-05 0.003 Pa

Stability of the pressure 0.55555556 8 8.0068E-05 0.000 Pa

Effect of the tubing between the saturator and the pressure gauge 1.17710124 18.12897416 8.0068E-05 0.000 Pa

Gas pressure at the generator outlet:

Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 1.59058426 infinite 8.0068E-05 0.000 Pa

Long-term stability (sensor and indicator) 20.9808492 infinite 8.0068E-05 0.002 Pa

Resolution (indicator unit) 0.57735027 infinite 8.0068E-05 0.000 Pa

Stability of the pressure 0 0.000 This uncertainty is included in the uncertainty due to stability of saturation pressure because gas pressure at the generator outlet is almost same as saturation pressure in our two-temperature generator.

Effect of the tubing between the saturator and the pressure gauge 0.81139293 6.30353879 8.0068E-05 0.000 Pa

Flow measurement:

Flow meter

Stability of the flow 0.01154701 8 0.05 0.001 L/min

Reproducibility 0.02886751 8 0.05 0.001 L/min

Saturation efficiency

Saturation efficiency 0.00103957 6.128943835 8.097518522 0.008 Non-dimentional. Relative uncertainty of efficiency

Correlation between pressure and temperature measurement (if relevant)

Correlation between pressure and temperature measurement if relevant 0 0.000 Not relevant

Uncertainty due to formulae/calculations

Saturation vapour pressure formula(e) 1.509E-05 2.142975853 8.097518522 0.000 Non-dimentional. Relative uncertainty of vapour pressure due to uncertainty of formula(e)

Water vapour enhancement formula(e) 1.2535E-06 8 8.097518522 0.000 Non-dimentional. Relative uncertainty of vapour pressure due to uncertainty of formula(e)

Other uncertainties

vapor pressure change in tubing, mainly due to water adsorption and desorption0.02236068 4.411764707 2.057404355 0.046 Pa

resistance of PRT in the travelling standard 0.00601458 264630.4746 2.5 0.015 ohm

Combined standard uncertainty 0.051

Effective degrees of freedom 6.61045735

Expanded uncertainty 0.102

107


value: 20 °C Lab name: NMIJ



Quantity Components Standard Degrees of freedom Sensitivity Uncertainty

(symbol) uncertainty components evaluated coefficient contribution

by a type A method *



Thermometer:

t1-1 Calibration uncertainty (sensor and indicator unit) 0.0070 0.98467 0.007

t1-2 Long-term stability (sensor and indicator) 0.0028 0.98467 0.003

t1-3 Self-heating and residual heat fluxes (sensor) 0.0013 0.98467 0.001

t1-4 Resolution and accuracy or linearity (indicator unit) 0.0045 0.98467 0.004

Saturator:

t1-5 Temperature homogeneity 0.0020 99 0.98467 0.002

t1-6 Temperature stability 0.0010 99 0.98467 0.001

Saturation pressure

Pressure gauge:

p1-1 Calibration uncertainty (sensor and indicator unit) 10.4 0.000140856 0.001

p1-2 Long-term stability (sensor and indicator) 76.9 0.000140856 0.011

p1-3 Resolution and accuracy or linearity (indicator unit) 32.2 0.000140856 0.005

p1-4 Pressure differences in the saturator cell

p1-5 Stability of the pressure 4.0 29 0.000140856 0.001

p1-6 Effect of the tubing between the saturator and the pressure gauge 0.0 0.000140856 0.000


Pressure gauge:

p2-1 Calibration uncertainty (sensor and indicator unit) 5.0 0.000159349 0.001

p2-2 Long-term stability (sensor and indicator) 22.9 0.000159349 0.004

p2-3 Resolution (indicator unit) 6.8 0.000159349 0.001

p2-4 Stability of the pressure 1.6 29 0.000159349 0.000

Effect of the tubing between the saturator and the pressure gauge

p2-5

Effect of the tubing between the pressure gauge and the measuring

instrument 29.0 0.000159349 0.005

Flow measurement:

Flow meter

Stability of the flow

Reproducibility




Correlation between pressure and temperature measurement if relevant


Saturation vapour pressure formula(e)

Water vapour enhancement formula(e)

Relative Uncertainty due to formulae/calculations

e Saturation vapour pressure formula(e), e(t1),e(td) 0.000071 16.142 0.001

f Water vapour enhancement formula(e), f(p1,t1), f(p2,td) 0.000312 16.142 0.005

Other uncertainties


Effective degrees of freedom 508000


108

VSL


value: -50 °C Lab name: NMi-VSL







Primary dew-point generator Infinite if not specified

Saturation temperature

Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.005 1 0.005

Long-term stability (sensor and indicator) 0.010 1 0.010

Self-heating and residual heat fluxes (sensor) 0.005 1 0.005

Resolution and accuracy or linearity (indicator unit) 0.00003 1 0.000

Saturator:

Temperature homogeneity 0.004 1 0.004

Temperature stability 0.005 9 1 0.005

Saturation pressure

Pressure gauge:

Calibration uncertainty (sensor and indicator unit)

Long-term stability (sensor and indicator)

Resolution and accuracy or linearity (indicator unit)

Pressure differences in the saturator cell

Stability of the pressure



Pressure gauge:



Resolution (indicator unit)



Flow measurement:

Flow meter


Reproducibility


Saturation efficiency 0.008 1 0.008






Other uncertainties

Contaminations 0.001 1 0.001

Pressuredrop over generator /Pa 43 0.00015 0.00645

Pressuredrop over dewpointmeters /Pa 130 0.00015 0.0195



Expanded uncertainty (95.45 %) 2.03 0.053

109


value: 20 °C Lab name: NMi-VSL







Primary dew-point generator Infinite if not specified


Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.007 1 0.007



Resolution and accuracy or linearity (indicator unit) 0.00025 1 0.000

Saturator:



Saturation pressure

Pressure gauge:








Pressure gauge:






Flow measurement:

Flow meter


Reproducibility








Other uncertainties

Contaminations 0.001 1 0.001

Pressuredrop over generator /Pa 43 0.00015 0.00645

Pressuredrop over dewpointmeters /Pa 130 0.00015 0.0195



Expanded uncertainty (95.45 %) 2.86931517 0.084

110

MIKES


value: -50 °C Lab name: MIKES








Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.006 50 1 0.006



Resolution and accuracy or linearity (indicator unit) 1.00E-06 125.8 0.0001

Saturator:


Temperature stability 1.43E-06 9 125.8 0.0002

Saturation pressure

Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 2 50 7.94E-05 0.0002

Long-term stability (sensor and indicator) 2.3 7.94E-05 0.0002

Resolution and accuracy or linearity (indicator unit) 1 7.94E-05 0.0001

Pressure differences in the saturator cell (eli Pes) 14.13 7.94E-05 0.0011

Stability of the pressure 2.89 7.94E-05 0.0002

Effect of the tubing between the saturator and the pressure gauge 12 7.94E-05 0.0010


Pressure gauge:


Long-term stability (sensor and indicator) 2.3 7.94E-05 0.0002

Resolution (indicator unit) 1 7.94E-05 0.0001

Stability of the pressure 2.89 7.94E-05 0.0002

Effect of the tubing between the dew-point cell and the pressure gauge 10.68 7.94E-05 0.0008

Flow measurement:

Flow meter


Reproducibility








Other uncertainties




Effective degrees of freedom including type B components 44

111


value: 20 °C Lab name: MIKES








Thermometer:




Resolution and accuracy or linearity (indicator unit) 0.000 128.5 0.0001

Saturator:


Temperature stability 2.59E-06 9 128.5 0.0003

Saturation pressure

Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 2 50 0.0002 0.0003

Long-term stability (sensor and indicator) 2.3 0.0002 0.0004

Resolution and accuracy or linearity (indicator unit) 1 0.0002 0.0002

Pressure differences in the saturator cell, Pes 15.48 0.0002 0.0024

Stability of the pressure 2.89 0.0002 0.0004

Effect of the tubing between the saturator and the pressure gauge 12 0.0002 0.0018


Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 2 50 0.0002 0.0003

Long-term stability (sensor and indicator) 2.3 0.0002 0.0004

Resolution (indicator unit) 1 0.0002 0.0002

Stability of the pressure 2.89 0.0002 0.0004

Effect of the tubing between the dew-point cell and the pressure gauge 48.35 0.0002 0.0074

Flow measurement:

Flow meter


Reproducibility






Saturation vapour pressure formula(e) 0.004


Other uncertainties




Effective degrees of freedom including type B components 44

112

INTA


value: -50 Lab name INTA



Saturator temperature (ºC) -42.04

Saturator pressure (Pa) 264402

Chamber pressure (Pa) 101310




Qi u(Qi) n i u i in °C


Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.002 50 0.932 0.0019

Long-term stability (sensor and indicator) 0.005 50 0.932 0.0047

Self-heating and residual heat fluxes (sensor) 0.001 50 0.932 0.0009

Resolution and accuracy or linearity (indicator unit) 0.001 50 0.932 0.0009

Saturator:

Temperature homogeneity 0.012 50 0.932 0.0108

Temperature stability 0.003 30 0.932 0.0028

Saturation pressure

Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 6 50 -3.020E-05 -0.0002

Long-term stability (sensor and indicator) 112.4 50 -3.020E-05 -0.0034

Resolution and accuracy or linearity (indicator unit) 1 50 -3.020E-05 0.0000

Pressure differences in the saturator cell 20 50 -3.020E-05 -0.0006

Stability of the pressure 60 30 -3.020E-05 -0.0018

Effect of the tubing between the saturator and the pressure gauge 10 50 -3.020E-05 -0.0003


Pressure gauge:


Long-term stability (sensor and indicator) 90.8 50 7.948E-05 0.0072

Resolution (indicator unit) 0.6 50 7.948E-05 0.0000

Stability of the pressure 20 30 7.948E-05 0.0016

Effect of the tubing between the saturator and the pressure gauge 6 50 7.948E-05 0.0005

Flow measurement:

Flow meter


Reproducibility






Saturation vapour pressure formula(es) 0.0022 50 7.99 0.0176

Water vapour enhancement formula(fs) 0.001 50 8.10 0.0065

Saturation vapour pressure formula(ed) 0.0026 50 -8.10 -0.0211

Water vapour enhancement formula(fd) 0.0003 50 -8.10 -0.0026

Other uncertainties

Pressure drop in sampling line 5.77 50 7.948E-05 0.0005

0.0000

0.0000



Expanded uncertainty 2.01 0.064

113


value: 20 Lab name INTA



Saturator temperature (ºC) 30.01

Saturator pressure (Pa) 184503

Chamber pressure (Pa) 101322


(symbol) coefficient

Qi


Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.002 50 0.927 0.0019

Long-term stability (sensor and indicator) 0.005 50 0.927 0.0046

Self-heating and residual heat fluxes (sensor) 0.001 50 0.927 0.0009

Resolution and accuracy or linearity (indicator unit) 0.001 50 0.927 0.0009

Saturator:

Temperature homogeneity 0.012 50 0.927 0.0107

Temperature stability 0.003 30 0.927 0.0028

Saturation pressure

Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 6 50 -8.703E-05 -0.0005

Long-term stability (sensor and indicator) 112.4 50 -8.703E-05 -0.0098

Resolution and accuracy or linearity (indicator unit) 1 50 -8.703E-05 -0.0001

Pressure differences in the saturator cell 100 50 -8.703E-05 -0.0087

Stability of the pressure 60 30 -8.703E-05 -0.0052

Effect of the tubing between the saturator and the pressure gauge 10 50 -8.703E-05 -0.0009


Pressure gauge:






Flow measurement:

Flow meter


Reproducibility






Saturation vapour pressure formula(es) 5.000E-05 50 16.057 0.0008

Water vapour enhancement formula(fs) 1.122E-04 50 16.138 0.0018

Saturation vapour pressure formula(ed) 5.000E-05 50 -16.138 -0.0008

Water vapour enhancement formula(fd) 6.858E-05 50 -16.138 -0.0011

Other uncertainties

Pressure drop in sampling line 5.77 50 1.587E-04 0.0009

0.0000

0.0000



Expanded uncertainty 2.01 0.048

114

INRIM


value: -50 Lab name: INRIM








Thermometer:


Long-term stability (sensor and indicator) 0.006 50 1 0.006

Self-heating and residual heat fluxes (sensor) 0.005 50 1 0.005

Resolution and accuracy or linearity (indicator unit) 0.003 50 1 0.003

Saturator:

Temperature homogeneity 0.020 50 1 0.020


Saturation pressure

Pressure gauge:


Long-term stability (sensor and indicator) 50 50 7.5E-05 0.004

Resolution and accuracy or linearity (indicator unit) 0.2 50 7.5E-05 0.000

Pressure differences in the saturator cell 10 20 7.5E-05 0.001




Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 3.3 50 7.5E-05 0.000





Flow measurement:

Flow meter

Stability of the flow 0 10 3.0E-03 0.000

Resolution 0.05 50 3.0E-03 0.000


Saturation efficiency 0.005 50 1 0.005






Other uncertainties

Desorption Effect 0.004 50 1 0.004

Saturator thermometer interpolation curve 0.006 50 1 0.006




Additional uncertainty in applied condition at point of use

Pressure drop between point of realisation and measuring instrument 7 20 7.5E-05 0.001

Other

* for type B method the number of degrees of freedom will be considered as being larger than 50.

(Degrees of freedom of 50 for a component of type B corresponds 10 % in relative uncertainty of the uncertainty estimate u Qi; see Annex G of the ISO Guide)

Combined uncertainty 0.025



115


value: 20 °C Lab name: INRiM








Thermometer:


Long-term stability (sensor and indicator) 0.012 50 1 0.012

Self-heating and residual heat fluxes (sensor) 0.005 50 1 0.005

Resolution and accuracy or linearity (indicator unit) 0.003 50 1 0.003

Saturator:

Temperature homogeneity 0.005 50 1 0.005


Saturation pressure

Pressure gauge:


Long-term stability (sensor and indicator) 50 50 1.5E-04 0.007

Resolution and accuracy or linearity (indicator unit) 0.2 50 1.5E-04 0.000

Pressure differences in the saturator cell 35 20 1.5E-04 0.005




Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 3.3 50 1.5E-04 0.000



Stability of the pressure 3.1 20 1.5E-04 0.000


Flow measurement:

Flow meter

Stability of the flow 0 10 0.006 0.000

Resolution 0.05 50 0.006 0.000


Saturation efficiency 0.005 50 1 0.005






Other uncertainties

Desorption Effect 0 50 1 0.000

Saturator thermometer interpolation curve 0.004 50 1 0.004




Additional uncertainty in applied condition at point of use

Pressure drop between point of realisation and measuring instrument 40 50 1.5E-04 0.006

Other

* for type B method the number of degrees of freedom will be considered as being larger than 50.

(Degrees of freedom of 50 for a component of type B corresponds 10 % in relative uncertainty of the uncertainty estimate u Qi; see Annex G of the ISO Guide)




116

NIST

Uncertainty of dew/frost-point standard

Nominal

value: -10 °C Lab name: NIST/USA

CCT-K6


(symbol) uncertaintycomponents evaluatedcoefficient contribution



Primary dew-point generator


Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.001°C 0.8 0.001

Long-term stability (sensor and indicator) 0.001 °C 0.8 0.001

Self-heating and residual heat fluxes (sensor) 0.000 °C 0.8 0.000

Resolution and accuracy or linearity (indicator unit) 0.000 °C 0.8 0.000

Saturator:

Temperature homogeneity 0.001 °C 0.8 0.001

Temperature stability 0.001 °C 50 0.8 0.001

Saturation pressure

Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 39 Pa 0.00004 0.002

Long-term stability (sensor and indicator) 7 Pa 0.00004 0.000

Resolution and accuracy or linearity (indicator unit) 7 Pa 0.00004 0.000

Pressure differences in the saturator cell 7 Pa 0.00004 0.000

Stability of the pressure 9 Pa 50 0.00004 0.000

Effect of the tubing between the saturator and the pressure gauge0 Pa 0.00004 0.000


Pressure gauge:



Resolution (indicator unit) 1 Pa 0.00011 0.000



Flow measurement:

Flow meter


Reproducibility


Saturation efficiency 0.002 °C 0.002




Saturation vapour pressure formula(e) .06 Pa 0.044 0.002

Water vapour enhancement formula(e) 0.0005 11 0.007

Other uncertainties


Effective degrees of freedom


117

Uncertainty of dew/frost-point standard

Nominal

value: 20 °C Lab name: NIST/USA

CCT-K6


(symbol) uncertaintycomponents evaluatedcoefficient contribution



Primary dew-point generator


Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.001°C 1 0.001

Long-term stability (sensor and indicator) 0.001 °C 1 0.001

Self-heating and residual heat fluxes (sensor) 0.000 °C 1 0.000

Resolution and accuracy or linearity (indicator unit) 0.000 °C 1 0.000

Saturator:

Temperature homogeneity 0.001 °C 1 0.001

Temperature stability 0.000 °C 50 1 0.000

Saturation pressure

Pressure gauge:



Resolution and accuracy or linearity (indicator unit) 7 Pa 0.00016 0.001

Pressure differences in the saturator cell 7 Pa 0.00016 0.001


Effect of the tubing between the saturator and the pressure gauge0 Pa 0.000


Pressure gauge:



Resolution (indicator unit) 1 Pa 0.00016 0.000



Flow measurement:

Flow meter


Reproducibility


Saturation efficiency 0.002 °C 1 0.002




Saturation vapour pressure formula(e) .15 Pa 0.007 0.002

Water vapour enhancement formula(e) 0.0002 16 0.004

Other uncertainties


Effective degrees of freedom


118

NMC

Uncert

ain

ty o

f 4500 fro

st

poin

t genera

tor

Td

(°C

)

Ts

(°C

)

DTs

(°C

)

u(T

s)

(°C

)P

s(P

a)

DP

s

(Pa)

u(P

s)

(°C

)P

c (

Pa)

DP

c

(Pa)

u(P

c)

(°C

)

Es(T

s)

(Pa)

DE

s(T

s)

(form

ula

)

(Pa)

u(E

s(T

s))

(°C

)f(Ts,P

s)

D(fs)

u(fs)

(°C

)f(Td,P

c)

D(fd)

u(fd)

(°C

)

Es(T

d)

(Pa)

DE

s(T

d)

(form

ula

)

(Pa)

u(E

s(T

d))

(°C

)

Effe

ct

of

perm

eation

(°C

) u_c(T

d)

-50

-44.9

0.0

17

0.0

16

186848

103

-0.0

04

100663

14

0.0

01

7.3

0.0

20.0

19

1.0

100

0.0

006

0.0

05

1.0

055

0.0

003

-0.0

03

3.9

0.0

102

0.0

21

0.0

09

0.0

35

-50

-40.0

0.0

17

0.0

16

332120

103

-0.0

03

100663

14

0.0

01

12.8

0.0

30.0

17

1.0

172

0.0

010

0.0

08

1.0

055

0.0

003

-0.0

03

3.9

0.0

102

0.0

21

0.0

09

0.0

34

-50

-35.0

0.0

17

0.0

15

588123

103

-0.0

01

100663

14

0.0

01

22.3

0.0

40.0

15

1.0

293

0.0

017

0.0

13

1.0

055

0.0

003

-0.0

03

3.9

0.0

102

0.0

21

0.0

09

0.0

34

-50

-33.5

0.0

17

0.0

15

685339

103

-0.0

01

100663

14

0.0

01

26.3

0.0

50.0

14

1.0

337

0.0

020

0.0

15

1.0

055

0.0

003

-0.0

03

3.9

0.0

102

0.0

21

0.0

09

0.0

35

-30

-24.9

0.0

17

0.0

16

168232

103

-0.0

06

100663

14

0.0

01

63.9

0.0

90.0

13

1.0

074

0.0

004

0.0

04

1.0

045

0.0

002

-0.0

02

38.0

0.0

608

0.0

15

0.0

00

0.0

27

-30

-20.0

0.0

17

0.0

16

277307

103

-0.0

04

100663

14

0.0

01

103.2

0.1

10.0

10

1.0

117

0.0

006

0.0

06

1.0

045

0.0

002

-0.0

02

38.0

0.0

608

0.0

15

0.0

00

0.0

25

-30

-15.0

0.0

17

0.0

15

444712

103

-0.0

02

100663

14

0.0

01

165.3

0.1

40.0

08

1.0

181

0.0

009

0.0

09

1.0

045

0.0

002

-0.0

02

38.0

0.0

608

0.0

15

0.0

00

0.0

25

-30

-10.0

0.0

17

0.0

14

705334

103

-0.0

01

100663

14

0.0

01

259.9

0.1

60.0

06

1.0

277

0.0

014

0.0

13

1.0

045

0.0

002

-0.0

02

38.0

0.0

608

0.0

15

0.0

00

0.0

26

-10

-5.0

0.0

17

0.0

16

155822

103

-0.0

07

100663

14

0.0

02

401.7

0.1

40.0

04

1.0

060

0.0

003

0.0

03

1.0

040

0.0

002

-0.0

02

259.9

0.1

559

0.0

07

0.0

00

0.0

20

-10

0.0

0.0

17

0.0

14

239455

103

-0.0

05

100663

14

0.0

02

611.2

0.0

30.0

01

1.0

087

0.0

003

0.0

03

1.0

040

0.0

002

-0.0

02

259.9

0.1

559

0.0

07

0.0

00

0.0

17

Note

:1

23

45

67

89

Td

Fro

st

or

dew

poin

t

Ts

Satu

ration t

em

pera

ture

DTs U

ncert

ain

ty in s

atu

ration t

em

pera

ture

measure

ment

as in t

he u

ncert

ain

ty a

naly

sis

for

the s

atu

ration t

em

pera

ture

Ps

Satu

ration p

ressure

DP

sU

ncert

ain

ty in s

atu

ration p

ressure

measure

ment

as in t

he u

ncert

ain

ty a

naly

sis

for

the s

atu

ration p

ressure

Pc

Cham

ber

pre

ssure

DP

cU

ncert

ain

ty in c

ham

ber

pre

ssure

measure

ment

as in t

he u

ncert

ain

ty a

naly

sis

for

the c

ham

ber

pre

ssure

1,7

The w

ate

r satu

ration v

apor

pre

ssure

is c

alc

ula

ted b

ased o

n B

ob H

ard

y ITS

-90 form

ula

tion

2,8

Assum

e u

ncert

ain

ty o

n t

he w

ate

r satu

ration v

apor

pre

ssure

form

ula

tion is 0

.005%

for

t>=

0 a

nd (

0.0

1-0

.005*t

)% for

t<0

3,5

The e

nhancem

ent

facto

r is

calc

ula

ted b

ased o

n G

reenspan form

ula

tion

4,6

The u

ncert

ain

ty o

f th

e e

nhancem

ent

facto

r is

calc

ula

ted b

ased o

n J

ere

my L

ove

ll-S

mith's

fit t

o t

he o

rigin

al uncert

ain

ty o

f th

e G

reenspan form

ula

tion

9

The fitte

d v

alu

e o

f diff

ere

nces in s

atu

ration v

apor

pre

ssure

is c

onsid

ere

d a

s u

ncert

ain

ty a

nd c

om

bin

ed w

ith a

ll oth

er

uncert

ain

ty c

om

ponents

. N

o c

orr

ection is d

one.

Uncert

ain

ty o

f 2500 h

um

idity g

enera

tor

Td

(°C

)

Ts

(°C

)

DTs

(°C

)

u(T

s)

(°C

)P

s (

Pa)

DP

s

(Pa)

u(P

s)

(°C

)P

c (

Pa)

DP

c

(Pa)

u(P

c)

(°C

)

Es (

Ts)

(Pa)

DE

s (

Ts)

(form

ula

)

(Pa)

u(E

s(T

s))

(°C

)

Es(T

d)

(Pa)

DE

d

(form

ula

)

(Pa)

u(E

s(T

d))

(°C

)fs

(Ts,P

s)

D(fs)

u(fs)

(°C

)fd

(Td,P

c)

D(fd)

u(fd)

(°C

)E

s(T

s)

(Pa)

Des (

sat-

eff)

(Pa)

u(s

at-

eff)

(°C

)u_c(T

d)

-10

00.0

36

0.0

30

236835

145

-0.0

07

100663

14

0.0

02

611.2

10.0

30561

0.0

01

259.8

70.0

12994

0.0

07

1.0

0861

0.0

003

0.0

03

1.0

04

0.0

0018

-0.0

02

611.2

1291

0.8

7403446

0.0

16

0.0

35

12

0.0

36

0.0

36

107903

145

-0.0

19

100663

14

0.0

02

705.9

70.0

35299

0.0

01

657.0

80.0

32854

0.0

01

1.0

0408

0.0

001

0.0

02

1.0

0383

0.0

0011

-0.0

01

705.9

7325

1.0

0954175

0.0

20

0.0

45

115

0.0

36

0.0

32

262070

145

-0.0

08

100663

14

0.0

02

1705.7

0.0

85286

0.0

01

657.0

80.0

32854

0.0

01

1.0

0885

0.0

002

0.0

03

1.0

0383

0.0

0011

-0.0

01

1705.7

228

2.4

3918354

0.0

20

0.0

39

121

0.0

36

0.0

31

383280

145

-0.0

05

100663

14

0.0

02

2488.2

0.1

24408

0.0

01

657.0

80.0

32854

0.0

01

1.0

1228

0.0

003

0.0

04

1.0

0383

0.0

0011

-0.0

01

2488.1

697

3.5

5808263

0.0

20

0.0

37

20

21

0.0

36

0.0

36

106800

145

-0.0

22

100663

14

0.0

02

2488.2

0.1

24408

0.0

01

2339.3

0.1

16963

0.0

01

1.0

0417

7E

-05

0.0

01

1.0

0397

6.8

E-0

5-0

.001

2488.1

697

3.5

5808263

0.0

23

0.0

48

20

40

0.0

36

0.0

31

318676

145

-0.0

07

100663

14

0.0

02

7385.3

0.3

69265

0.0

01

2339.3

0.1

16963

0.0

01

1.0

103

0.0

003

0.0

05

1.0

0397

6.8

E-0

5-0

.001

7385.2

991

10.5

609777

0.0

23

0.0

40

Note

12

34

56

78

910

Ts

Satu

ration t

em

pera

ture

DTs U

ncert

ain

ty in s

atu

ration t

em

pera

ture

measure

ment

as in t

he u

ncert

ain

ty a

naly

sis

for

the s

atu

ration t

em

pera

ture

Ps

Satu

ration p

ressure

DP

sU

ncert

ain

ty in s

atu

ration p

ressure

measure

ment

as in t

he u

ncert

ain

ty a

naly

sis

for

the s

atu

ration p

ressure

Pc

Cham

ber

pre

ssure

DP

cU

ncert

ain

ty in c

ham

ber

pre

ssure

measure

ment

as in t

he u

ncert

ain

ty a

naly

sis

for

the c

ham

ber

pre

ssure

1,3

,9The w

ate

r satu

ration v

apor

pre

ssure

is c

alc

ula

ted b

ased o

n B

ob H

ard

y ITS

-90 form

ula

tion

2,4

Assum

e u

n u

ncert

ain

ty o

n t

he w

ate

r satu

ration v

apor

pre

ssure

form

ula

tion o

f 0.0

05%

for

t>=

0

5,7

The e

nhancem

ent

facto

r is

calc

ula

ted b

ased o

n G

reenspan form

ula

tion

6,8

The u

ncert

ain

ty o

f th

e e

nhancem

ent

facto

r is

calc

ula

ted b

ased o

n J

ere

my L

ove

ll-S

mith's

fit t

o t

he o

rigin

al uncert

ain

ty o

f th

e G

reenspan form

ula

tion

10

The s

atu

ration e

fficie

ncy is t

aken fro

m T

hunder

Scie

ntific

's e

stim

ation w

hic

h is 0

.143 %

of satu

ration p

ressure

The e

ffect

of perm

eation is v

erifie

d b

y g

enera

ting t

he s

am

e fro

st

poin

t at

diff

ere

nt

com

bin

ations o

f satu

ration t

em

pera

ture

and s

atu

ration p

ressure

. The o

bta

ined d

iffere

nces in fro

st

poin

t are

conve

rted t

o

equiv

ale

nt

diff

ere

nces in s

atu

ration v

apor

pre

ssure

. The d

iffere

nce in s

atu

ration v

apor

pre

ssure

is fitte

d a

gain

st

the s

atu

ration t

em

pera

ture

by a

lin

e a

nd e

xtr

apola

ted t

o s

atu

ration t

em

pera

ture

of -5

0°C

.

119

Uncertainty analysis for Michell at -50 point when minimum degree of freedom occurs

Sources of uncertainty [U](°C) kstd. uncertainty (u) u 2 degree of freedom u 4/DOF

1

Standard uncertainty of applied condition except

type A (average of 6 measures) 0.0345 1 0.0345 1.1902500E-03 100000000 1.4166951E-14

2

Standard uncertainty of applied condition type A

(average of 6 measures) (total 13 records and each

record has 20 rdgs) 0.0022 1 0.002233 4.9877778E-06 259 9.6053773E-14

3

Std uncert due to short-term stability (from

standard deviation) of measurements of traveling

standard (type A) (average of 6 measures) (total 13

records and each record has 120 rdgs) 0.0282 1 0.028193 7.9486607E-04 1559 4.0526752E-10

4

Std uncert due to the resistance measurement

uncertainty of traveling standard 0.0005 1 0.0005 2.5000000E-07 100000000 6.2500000E-22

5 Std uncert due to resolution of traveling standard 0.0003 1 0.0003 9.0000000E-08 100000000 8.1000000E-23

6 Reproducibility (6 measures) 0.0250 1 0.024982 6.2410913E-04 5 7.7902441E-08

sum u 2 0.00261455 sum u 4/DOF 7.83078186E-08

Combined Uncer. (Uc) 0.05113270 EDOF 87.29507964

k 2

120

NIM

-50

Quantity Estimate Standard

Uncertainty

Sensitivity

Coefficient

Contribution to

standard

uncertainty

ts -40.05 0.018 0.9/ 0.0162

ps 334256Pa 313Pa -0.00002 /Pa -0.0063

po 101405Pa 62Pa 0.00008/Pa 0.0050

es 13Pa 0.03Pa 0.63/Pa 0.0189

ed 4Pa 0.01Pa -2.06/Pa -0.0206

fs 1.017 0.001 8.0 0.0080

fd 1.006 0.0003 -8.1 -0.0024

td -50 0.0344

Permeation

& leaks 0.03 1/ 0.03

Saturator

efficiency 0.05 1/ 0.05

Combined uncertainty of generator 0.068

Sources of uncertainty uncertainty degree of

freedom

Standard Uncertainty of applied condition except type A 0.068 ∞

Standard Uncertainty of applied condition type A 0.019 11

Standard Uncertainty due to short-term stability of measurement of

traveling standard (type A) 0.012 11

Standard Uncertainty due to the resistance measurement of traveling

standard 0.005 ∞

Standard Uncertainty due to resolution of traveling standard 0.003 ∞

Combined uncertainty 0.072 EDOF

Expanded uncertainty(k=2) 0.15 1956

121

+20

Quantity Estimate Standard

Uncertainty

Sensitivity

Coefficient

Contribution to

standard

uncertainty

ts 30.02 0.018 0.9/ 0.0162

ps 184512 Pa 156Pa -0.00009/Pa -0.0140

po 101425Pa 62Pa 0.00016/Pa 0.0099

es 4247Pa 0.21Pa 0.01/Pa 0.0021

ed 2339Pa 0.12Pa -0.01/Pa -0.0012

fs 1.007 0.0002 16 0.0032

fd 1.004 0.0001 -16.1 -0.0016

td 20 0.0241

Permeation

& leaks 0.02 1/ 0.02

Saturator

efficiency 0.02 1/ 0.02

Combined uncertainty of generator 0.038

Sources of uncertainty degree of

freedom

Standard Uncertainty of applied condition except type A 0.038 ∞

Standard Uncertainty of applied condition type A 0.012 11

Standard Uncertainty due to short-term stability of measurement of

traveling standard (type A) 0.026 11

Standard Uncertainty due to the resistance measurement of traveling

standard 0.005 ∞

Standard Uncertainty due to resolution of traveling standard 0.003 ∞

Combined uncertainty 0.048 EDOF

Expanded uncertainty(k=2) 0.10 122

122

VNIIFTRI ESB


value: -50°C Lab name: VNIIFTRI ES



Meas 4 14.02.2009 00:24-00:34 (19)






Thermometer:

Calibration uncertainty (sensor and indicator unit) 0.005581 0.68149 0.0054


Self-heating and residual heat fluxes (sensor)


Saturator:

Temperature homogeneity 0.006 0.681490 0.0058

Temperature stability

Saturation pressure

Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 77.2868 2.67512E-05 0.0043







Pressure gauge:

Calibration uncertainty (sensor and indicator unit) 49.731775 3.92423E-05 0.0041





Flow measurement:

Flow meter


Reproducibility






Saturation vapour pressure formula(e) (saturation) 0.002 0.68149 0.0161

Water vapour enhancement formula(e) (saturation) 0.000187 3.864181 0.0015

Other uncertainties

Saturation vapour pressure formula(e) (at generator outlet) 0.002156 0.68149 0.0119

Water vapour enhancement formula(e) (at generator outlet) 0.0002 3.863028 0.0016

Std uncert due to short-term stability generaror (type A) 0.002097 9 1 0.0021


Effective degrees of freedom infinity

Expanded uncertainty (p=99.97) 0.0680

123


value: 20°C Lab name: VNIIFTRI ES



Meas 3 12.02.2009 21:23-21:30 (14)






Thermometer:



Self-heating and residual heat fluxes (sensor)


Saturator:

Temperature homogeneity 0.006 0.743459 0.0058

Temperature stability

Saturation pressure

Pressure gauge:








Pressure gauge:






Flow measurement:

Flow meter


Reproducibility






Saturation vapour pressure formula(e) (saturation) 0.000045 0.743458608 0.0007

Water vapour enhancement formula(e) (saturation) 0.00005 2391.902523 0.0008

Other uncertainties

Saturation vapour pressure formula(e) (at generator outlet) 0.000043 0.743458608 0.0005

Water vapour enhancement formula(e) (at generator outlet) 6.6667E-05 2391.902523 0.0011

Std uncert due to short-term stability generaror (type A) 0.000526 9 1 0.0005


Effective degrees of freedom infinity

Expanded uncertainty (p=99.97) 0.0448

npl report eng 57 final report to the cct on key ...npl report eng 57 final report to the cct on key...

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