diapositivas del seminario humedad 201

8/12/2019 Diapositivas Del Seminario Humedad 201

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Page 1/ 2011 / McDuffee / Humidity Seminar/Vaisala / #humidity

WelcomeHumidity 201

what you need to know about humidity

#HUMIDITY201


What business are you in?

Pha

rmaceutic

al...

Instrum

entatio.

..

Engine

ering

&...

Industrial

Man

...

Governm

ent o

r...

HVA

COther

0% 0% 0% 0%0%0%0%

1. Pharmaceutical/Biotechnology/MedDevices

2. Instrumentation & Controls

3. Engineering & Architecture

4. Industrial Manufacturing

5. Government or Education

6. HVAC

7. Other


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What is your job role?

Facilitie

s

Quality

Process

Executiv

eMana..

.

Other

0% 0% 0%0%0%

A. Facilities

B. Quality

C. Process

D. Executive Management

E. Other


How far did you travel to get here?


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Do you already use one or more?(choose up to 5)

Vais

alahum

idity

inst.

..

Vais

ala(oth

er)in

str...

Vais

alaVerite

qlog

ger

Vais

alaVerite

qmo

nit...

Vais

alaVerite

qvalid

a...

0 0 000

1. Vaisala humidity instrument

2. Vaisala (other) instrument

3. Vaisala Veriteq logger

4. Vaisala Veriteq monitoringsystem

5. Vaisala Veriteqvalidation/mapping system

Humidity 201what you need to know about humidity


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Why do we measure humidity?

Human comfort

Animal comfort

Energy efficiency


Critical Environments

Quality Control

Product Quality


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Controlled Environments

FDA

ISO

GxP


Industrial ProcessProcess Control


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Why do you measure humidity?(choose up to 3)

Productqualit...

Laws

&regulat

...

Hum

an/Anim

alc..

.

Energyefficie

...

Process

contro...

Research

Other

0% 0% 0% 0%0%0%0%

A. Product quality

B. Laws & regulations

C. Human/Animal comfort

D. Energy efficiency

E. Process control

F. Research

G. Other

The first step towards a proper measurement is to understand the parameter you will measure.

Theory, terms & definitions


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Water Vapor Theory - H2O

- Exists in the three phases

- Which phase depends on the amount of thermal energy that is present


American Meteorological Society GlossaryHu-mid-i-ty

Humidity

1. Generally, some measure ofthe water vapor content of air.


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Daltons Law

The total pressure of a gas is equal to the sumof the different gases partial pressures

Pt = P1 + P2 + Pn

air around us

Pt = PN2 + PO2 + Pw + Pmisc.

English chemist,meteorologist, physicist

(1766 1844)


Practical Example of Daltons LawNitrogen..................... 77%

Oxygen ..................... 21%

Water vapor ............. 1%

Other gasses ........... 1%

1000 mbar= 770mbar+ 210mbar+ 10mbar+ 10mbar

In Denver

Pt = 840 mbar _____N2 + ____O2 + ____Pw + _____Other

Pt = Pw + Pdry

647 177 8 8

840 x 77% 840 x 21% 840 x 1% 840 x 1%


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Partial Pressure of Water Vapor (psi,mbar,hPa,inhg)

The key parameter that affects all other humidi ty

parameters

Pw

Note: The only two properties that can affect a change in Pw

adding or removing water vapor changes in system pressure


Saturation Vapor Pressure (psi,mbar,hPa,in Hg)

Saturation Curve

On the saturation cu rve

evaporation and condensationare in equilibrium and occur atthe same rate

Pw = Pws

dewpoint = temperature

wet bulb = dry bulb

RH = 100%

Note: The only property thataffects Pws is temperature

Pws

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90 100

Temperature (C)

Pw(mbar)


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Pws Saturation Vapor Pressure

Pws - maximum vapor pressure or amount of water vapor that canexist at a given temperature. Expressed in units of pressure.

480Pws = 480 mbar

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90 100

Temperature (C)

Pw(mbar)


Relative Humidity (%)

Relative humidity is the ratio of water vapor partial pressure present

in a gas (Pw) to the saturation vapor pressure of water at that

temperature [Pws(t)]

RH


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Relativefill=1/1100%Relative

fill

=

1/520%Relativefill=1/10

10%

Bucket Analogy

Pws = bucket size or max amount of water

Pw = amount of water in the bucket


%RH = 100 x

%RH = 100 x =

Note: Relative humidity is strongly proportional to temperature and its measurement isvery sensitive to temperature differences.

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90 100

Temperature (C)

Pw(mbar)

Relative humidity

Pw=200Pws=480

200480

42%

PwPws (t)

(t=80)


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0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90 100

Temperature (C)

Pw(mbar)

Ta = 90 C Pws = mbar

Pw = mbar

RH = 100 x / = %RH

Temperature and Relative Humidity

Ta = 60 C Pws = 200 mbar

Pw = 70 mbar

RH = 100 x 70/200 = 35 %RH 700 10

70

70

%RH = 100 x Pw / Pws (t)

700


0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90 100

Temperature (C)

Pw(mbar)


Pw = mbar

RH = 100 x / = %RH



Pw = 70 mbar

RH = 100 x 70/200 = 35 %RH70 100

70

70

%RH = 100 x Pw / Pws (t)

70


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Rule of Thumb #1

Rule of Thumb #1*

-As temperature increases, air becomes drier (RH decreases)

-As temperature decreases, air becomes wetter (RH increases)

drier and wetter are relative terms; applies to a closed system where pressure and water vaporcontent do not change


What about pressure and RelativeHumidity?

If double total pressure;

then 2(Pt) = 2(Pw + Pdry) = 2Pw + 2Pdry

so Pw changes proportionately to overall pressure changes

Recall Daltons Law of Partial Pressures Pt = Pw + Pdry

remember that Pws remains unchanged because T is unchanged


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0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90 100

Temperature (C)

Pw(mbar)


Pw = 200 mbar

RH = 100 x 200/500 = 40 %RH

Pressure and Relative Humidity


Pw = mbar

RH = 100 x / = %RH

500

80

400

500400

Pt = 1000 mbar

We double the total pressure

so Pt = 2000 mbar

What happens to Pw? Pws?


Pressure and Relative Humidity Rule of Thumb #2

Rule of Thumb #2*

-As pressure decreases, air becomes drier (RH goes down)

-As pressure increases, air becomes wetter (RH goes up)

* drier and wetter are relative terms; applies to a closed system where temperature and water vapor content do notchange


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Relative Humidity Application Example

Static discharge or product quality in a cleanroom

Product storage

Critical processing systems (capsules, powders)


Td Dewpoint (C,F)

The temperature to which a given portion of air must be cooled at constant

pressure and constant water vapor content in order for saturation to occur

Td

The temperature at which a moist gas is saturated with respect to a plane

surface of pure liquid water


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Glass temperature above the dewpoint no condensation

Td = -10C

Beer temperature = 2C


Glass temperature below the dewpoint condensation appears

Td = 10C

Beer temperature = 2C


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Dewpoint changes with water vapor

changes with pressure

1

log

A

P

m

TT

w

n

d

Note: Dewpoint is not a temperature dependent parameter


Dewpoint & PressureRule of Thumb

Rule of Thumb

-As pressure increases, dewpoint temperature rises, air becomesmore moist (RH increases)

-As pressure decreases, dewpoint temperature goes lower, airbecomes drier (RH decreases)

drier and wetter are relative terms; applies to a closed system where water vapor content doesnot change


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Td/f Frostpoint (C,F)

Td/fThe temperature to which a given portion of air must be cooled at constant pressure and

constant water vapor content in order for saturation to occur

The temperature at which a moist gas is saturated with respect to a plane surface of

pure ice

Note: Td/f is a Vaisala term which means dewpoint above 32F and frost point 32F and below


Dewpoint versus Frostpoint

Frostpoint Dewpoint

-0.10 C -0.11 C

-5.00 C -5.64 C

-10.00 C -11.23 C

-20.00 C -22.25 C

-30.00 C -33.09 C

-40.00 C -43.74 C

-50.00 C -54.24 C

-60.00 C -64.59 C

-70.00 C -74.88 C

-80.00 C -85.29 C

-90.00 C -96.37 C

AIR evaporation

ICEcondensation


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Td/f Frostpoint

Td orTd/fTd/f gives you dewpoint at 0 degrees (C) and above and frost point below 0 degrees (C)

Td gives you dewpoint across the entire range of temperatures and assumes

supercooled water below 0 degrees (C)


Application Example - compressed air orsensitive manufacturing environments

compressor picture courtesy of Atlas Copco


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x Mixing Ratio or Humidity Ratio(g/kg, gr/lb)

xthe ratio of the mass of water vapor per unit mass of dry air towhich it is associated

Note: mixing ratio is an absolute measure, not affected bytemperature or pressure


Application Example drying process

Mixing ratio can be used as a measure to help determine drying timewhere moisture content of a product is important like paper drying ordog biscuit drying.


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ppmv ppmw parts per million (volume/weight)

ppmv- volume of water vapor per total volume of dry gas

ppmw- mass of water vapor per total mass of dry gas

Note: ppm is an absolute measure, not affected by temperature or pressureMw is molecular mass of water ; Md is molecular mass of dry air


ppmv and ppmw

Td/f PPMw PPMv

-40.00 14 23

-35.00 24 39

-30.00 42 67

-25.00 69 111

-20.00 113 181

-15.00 181 290-10.00 284 456

-5.00 439 706

Mw/Md = .621980


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Application Example glove box

ppm is sometimes used in dry environments where very preciseabsolute measurement is required such as in a glove box or clean room


a Absolute Humidity (g/m3, gr/ft3, lbs/MMcf)

a- the mass of water vaporper unit volume of moist air

- the density of the water vapor


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Application Example Precision Mass

Labs where precise measurements of mass are recorded and thebuoyancy caused by the air must be considered


Tw Wet bulb temperature (C,F)

Tw

the temperature indicated by a thermometer sheathed in a

wet cloth as air is passed over it


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Application Example evaporative cooler or swamp cooler

By comparing the wet bulb temperature to the dry bulbtemperature we can determine cooling capacity of anevaporative cooler.


h Enthalpy (kj/kg; btu/lb)

h Measure of the total energy in a

moist gas

heat content

sum of the latent heat + sensibleheat


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Application Example - HVAC

Enthalpy is a useful measurement for determining HVACequipment size and efficiency


Psychrometric Terms

relative humidity RH [%RH]

partial pressure of water vapor Pw [mbar; in.Hg]

saturation pressure Pws [mbar; in.Hg]

dewpoint/frost point Td/f [C; F]

absolute humidity a [g/m3; gr/ft3]

mixing ratio/humidity ratio x [g/kg; gr/lb]

wet bulb temperature Tw [C; F]

ppmv

ppmw

enthalpy h [kJ/kg; Btu/lb]


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Summary

1. Daltons Law of Partial Pressures Pw2. Saturation Vapor Pressure Pws only changes with

temperature

3. Other terms pressure and temperature effects

4. Rule of Thumb #1 temperature and RH

5. Rule of Thumb #2 pressure and RH

6. Dewpoint only pressure and water vapor content affect it

7. Absolute parameters versus relative parameters


End of Section 1

Humidity Theory, Terms & Defini tions


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Humidity SensorTechnology


Brief History of the Hygrometer1450 - Nicolas Cryfts determines humidity by using a scale

1480 Leonardo DaVinci reproduced the concept andrecorded it in the Codex Atlanticus


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Brief History of the Hygrometer

1625 Santorrio Santorre invented the first strain typehygrometer

1783 Horace Benedict de Saussere invented the hairhygrometer


Brief History of the Hygrometer1657 Grand Duke Ferdinand deMedici invented the first condensationhygrometer

1801 John Dalton re-invented thecondensation hygrometer anddeveloped Law of PartialPressures


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Brief History of the Hygrometer

1853 August Bravais invented the whirling psychrometer

1973 Vaisala patented the HUMICAP thin film polymercapacitive sensor


MechanicalExploit the expansion and contraction of organic materials with changesin humidity; changes are amplified through the use of levers that move aneedle or pointer.

horse hair, human hair, catgut, goldbeaters skin, textile, or plastic

hair element


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Mechanical

hair element

+ inexpensive

+ no power needed

- 2090% best range

- Uncertainty from +/-5% up to +/-15%

- calibrated with a wet rag to 100%;no dry end calibration

- considerable hysteresis

- responds to changes in humidityvery slowly


Psychrometer (wet bulb-dry bulb)Two matched thermometers over which air is drawn. One thermometerhas the bulb covered by a wet cloth or wick. This is the wet-bulb.

wet bulb

dry bulb

water

cloth


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Psychrometer (wet-dry bulb)

+ simple & fundamental measurement

+ low price ($35 to $80 for sling)

+ can have good stability

+ tolerates condensation withoutdamage

- High uncertainty (+/- 2% to 5%)

- requires some skill to use & maintain

- results usually must be calculated

- requires large air sample

- sample will be humidified (altered) bywater that is evaporating

- accuracy affected bycontaminated/dirty wick

1

23

4

HYGROMETER

1 2

3

4

5

6

7

8

ENCLOSUREHYGROMETRICTABLES

fan motor heat introduc ed

turbulancethick wickcontaminated wickwick qualityporous(ceramic) sleevenon-sealed thermometersnon-identical thermometerspoor resolution instrumentslow acc uracy instruments

poor water q uality

water temperature changes affect depressionwater container material non-plastictwo-wire system ca uses errorstables, accurac y of reading

5

678


Condensation Hygrometer

Chilled Mirror

l ightdetector

chilled mirror

NO D EW DEW

lightdetector

chilled mirror


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+ precise measurement (+/-.1C)

+ wide measurement range (-100..+100C)

+ very good long term performance

+ fundamental measurement

- expensive

- usually requires some skill/training to operate

- mirror cannot tell ice or dew

- contamination on mirror causes errors

- requires frequent maintenance

- complex in construction


Electrical Sensors

Resistive

Capacitive thin film polymer

Capacitive aluminum oxide


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Resistive Humidity Sensors

Measures the electrical impedance or resistance of a hygroscopicmedium such as conductive polymer, salt, or a treated substrate.

The resistance changes inversely w ith

humidity.


Resistive Humidity Sensors

+ small and cheap

+ mass production possible

+ Interchangeable/fieldreplaceable

- limited range (typically 15...95 %RH)

- high temperature dependency

- poor stability

- sensitive to contamination, condensation

- reading altered by all substances thataffect resistance; salts, hydrogen,oxidizing agents, other chemicals


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Capacitive - Aluminum Oxide (Al2O3)

capacitor which consists of aluminum and gold electrodes and analuminum oxide insulator

responds to the partial pressure of water vapor and converted toabsolute units (for Td or ppm)


Capacitive - Aluminum Oxide (Al2O3)

+ small

+ suitable for in-line site use

+ wide measuring rangemeasures dew point downto -75...-100 C

- condensation orcontamination on sensorcauses significantcalibration shift

- slow response time

- long stabilization time

- need frequent calibration

- significant drift

- considerable hysteresis


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Measures the capacitance of an electrode where a polymer acts asthe dielectric portion of the capacitor

The properties of the polymer/dielectric change proportionately withthe change in relative humidity which results in a change of themeasured capacitance

glass substrate

upper electrode

lowerelectrode thin-film polymer



glass substrate

upper electrode

lowerelectrode thin-film polymer

+ wide measurement range0...100 %RH

+ wide temperature range (up to200C)

+ excellent stability

+ fast response

+ full recovery from condensation

+ highly resistant to contaminants

+ small

+ low cost+ require very little maintenance

- can be limited by distance fromelectronics to sensor

- loss of relative accuracy at lowend (


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Other technologies

Saturated Lithium Chloride

uses hygroscopic salt as a sensing medium, with voltage applied across the salt and measurescurrent; usually displays dewpoint

Spectroscopic measures the light at a specific bandwidth where water vapor absorbs the light, based on the

principle of infrared absorbance.

Color change material such as cobalt chloride will change color based on the amount of water vapor in the air

as it reacts with the chemical

Acoustic transmission of sound in air can indicate humidity

Adiabatic Expansion cooling of air on expansion produces a cloud or fog if the dewpoint temperature is reached


Which technology gives you the mostaccurate dew point measure?

Resisti

ve

Aluminu

mOxid

e

Chilled

mirror

Noneoft

hese

...

0% 0%0%0%

A. Resistive

B.Aluminum Oxide

C.Chilled mirror

D.None of these isvery accurate


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Thin film polymer sensor is highlyresistant to contamination.

True False

0%0%

A. True

B. False


Wet bulb temperature is measureddirectly with a ____________.

Wetthum

b

Psychr

omete

r

Chilled

mirror

Swamp

cooler

0% 0%0%0%

A. Wet thumb

B. Psychrometer

C.Chilled mirror

D.Swamp cooler


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Summary

1. Sensor Technologies

Mechanical/Organic

Psychrometers

Chilled mirror

Electronic


Was the Sensor Technology SectionBeneficial?

Veryb

eneficial

Som

ewhatb

eneficial

Neutral

Mini

mallyb

eneficia

l

Not

atall b

eneficia

l

0% 0% 0%0%0%

A. Very beneficial

B. Somewhat beneficial

C. Neutral

D. Minimally beneficial

E. Not at all beneficial


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End of Section 3

Humidity Sensor Technology

Best Practices in HumidityMeasurement

First, you must understand the parameter that you want to measure


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7 General Points

1. Choose the correct instrument

2. Follow the manufacturers instructions

3. Ensure a proper calibration

4. Keep records

5. Spot-check performance

6. Be knowledgeable about the parameter

7. Be aware of potential external factors


What is your biggest challenge inmeasuring humidity?

Cantg

et repe

...

Toohigh

uncer...

Toofrequently

...

Cantt

rustsp

...

Educatin

gtech..

.

Other

0% 0% 0%0%0%0%

A. Cant get repeatability

B. Too high uncertainty

C. Too frequently out oftolerance

D. Cant trust specifications

E. Educating technicians

F. Other


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Be aware of what the sensor is measuring and how the

environment could affect it.


Good Measurement can be- affected by temperature differences?

- affected by pressure differences?

- affected by changes in water vapor content?

Note: Be aware of the possibility of condensation in a sample line

Flow

NO

YES

YES




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Measures wet bulb and dry bulb temperatures

Good measurement depends uponAccuracy of the thermometers

Consistency in operation

Contamination of water/sock

Accuracy of the conversion

Volume of the air sample

Psychrometer



Measures water vapor partial pressure

Good measurement depends upon Keeping the sensor dry

Regular calibration

Accurate pressure measurement

Clean air sample

Generous stabilization time (up to 24 hours)

Aluminum Oxide



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Measures relative humidity

Good measurement depends upon temperature temperature temperature

Polymer capacitor



How do you decide what instrument topurchase? (choose top 3 in order)

Refe

rral fromac

olle..

.

Web

research

Glob

alSpec,Th

omas...

Vendor w

ebsites

Vendor sale

sperson

0% 0% 0%0%0%

A. Referral from a colleague

B. Web research

C. GlobalSpec, ThomasNet,etc.

D. Vendor websites

E. Vendor salesperson


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2. Follow the Manufacturers Instructions

Read the Manual

Use the Technical Support

Use the Application Engineers

Use the Sales Engineers



Must be mounted in area where air or gas isrepresentative of the process or environment

Air should flow around or past the sensorgood air flow is an advantage; it ensures that the probe

and ambient air are at the same temperature & ensuresthat the measurement is representative of the space

Avoid anomalous sources of heat or cold; i.e.sunlight

Proper installation


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horizontal is preferred; bend in the cable

allow for temperature and pressure fittings

use insulation and sample line heating

ensure representative sample of air with flow preferredto be sealed

to be insulated

Probe installation




Is the calibration within the recommended interval?

Is it traceable?

Is there a valid certificate available?

Does the calibration comply with your requirements?


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4. Keep records

Record of calibration

Record of adjustments

Record of repairs

Out of tolerance results

Record of any damage to the instrument



Check at intervals between calibrations

Check before and after any event that may stressthe instrument

Transportation

Packaging or shipping

Check against one or, even better, two other

instruments


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Tdppm RHha x Tw

Know what parameter you are measuring and be aware ofthe potential effects of the environment around the point ofmeasure.

sensor type

gas effect

CO2, pure hydrogen, other high concentrations of gas

temperature & pressure effect

is output parameter measured or calculated


0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90 100

Temperature (C)

Pw(mbar) Saturation Curve

PwPws (t)

%RH = 100 x

Note: at 20C a temperature difference of just 1C may add 3% error to the RH measurement


Polymer & organic sensors measure RH

temperature temperature - temperature - temperature


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Adequate time varies depending on the difference inconditions and the sensor technology

Temperature

Vapor pressure

Sensor type


Al low adequate time for equil ibrat ion


Is it measured directly or calculated?

Does the calculation require pressure input?

Is the calculation dependent on temperature?

Dewpoint or Frostpoint? (for example)

Pressure dewpoint or atmospheric dewpoint?

Mixing ratio or ppm calculation require actual pressure input (forexample)


How is the parameter determined?


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Do not introduce external factors that will affectthe measurement

direct sunlight

body heat and humidity

non-representative sources of heat

stagnant and/or non representative air samples

temperature leakage




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Anomalous Sources of Heat or Cold



if the temperature of the process is considerably higherthan that of the environment, the whole probe andpreferably a part of the cable must be in the process

80C70%RH 22C

78

[adds 3.2% error]

Temperature Leakage



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28C22C

Temperature leakage Less critical, but enough difference where you want the

whole portion of the metal probe inside the process and thecable sealed.



180C 85%RH

Temperature leakage

Very large differencesrequire heavy insulation


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Anomalous Sources of Heat or Cold




70Fambient

temp

Temperature From room to high temperature high humidity chamber

104F60% RH

Testing chamber

You must PRE-HEAT the probe!!

Td = 87F


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80F @ 35%RH

Water Vapor Pressure

120F

Testing chamber

Td = -76F

ppmv=11

What is Td?

What is ppmv?

50F

12,000 ppmv



Water Vapor Pressure

ensure a tight seal

be aware of the cable feed through (is itvapor tight)

positive pressure can help prevent ingress


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Summary Good Measurement Practice

7 Points


2. Follow the manufacturers instructions


4. Keep records





Was the Good Measurement Practice

section beneficial?

Veryb

eneficia

...

Som

ewhatb

enef.

..

Neutral

Mini

mallyb

ene..

.

Not

atall b

en...

0% 0% 0%0%0%

A. Very beneficial


C. Neutral




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End of Section 5

Best Practices in HumidityMeasurement

Calibration of the Hygrometer

In fact, all humidity instruments drift to some extent.


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Why do we calibrate?

Economical Impact

Health, Safety & Environment

Scientific Research Results

Distributed Manufacturing


Premise for Humidity Calibration

A humidity sensor cannot be protected hermetically: its

active parts are always exposed to the dirt and chemicals

in the ambient air. This may cause the sensor to drift

under some circumstances.

The electronics of a measurement instrument may be

affected by time, temperature changes and mechanical or

electrical shocks.


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Definitions

Calibration = comparing the output of a measurementinstrument against a reference instrument and reporting theresult

Adjustment = changing the output to correspond to theoutput of a reference instrument

Specification = the performance criteria for aninstrument

Normal service procedure (also called calibration): first calibration + adjustment

then calibration


Quality Measurement Standards(QMS)

States the minimum requirements and guidance forthe maintenance of measurement equipment

ISO/TS 16949:2002

GLP (good laboratory practice)

ISO 10012

ISO/IEC 17025ANSI/NCSL Z540


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Traceability


Traceability

a traceable measurement is one which can be related to

appropriate measurement standards, generally national or

international, through an unbroken chain of comparisons

further

humidity parameters may be considered as traceable if they

are derived from actual realized measurements at the national

level along with recognized numerical conversions


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RH Traceabil ity Chain VaisalaBoston Lab


Metre Convention May 20, 1875

May 20th

National Metrology Day


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International System of Units (SI Units)

Administered by the BIPM in Paris or International Bureau of

Weights & Measures

Bureau International des Poides et Measures


Seven basic units of measure

1. Length (meter)

2. Mass (kilogram)

3. Time (second)

4. Current (ampere)

5. Temperature (kelvin)

6. Amount of a substance (mole)

7. Light intensity (candela)

IPK International Prototype Kilogram


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RH Traceabil ity Chain Vaisala

Boston Lab

Compared to average reading oftwo hygrometers

Calibrated every 3 months

Primary standard goes to NIST once ayear for traceable calibration

Calibrated against MBW


Traceabili ty, by itself, ensures a goodand proper measurement?

True

False

0%0%

A. True

B. False


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Accredited or Non-Accredited


3rd Party Accrediting Agencies


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Accredited Calibrations

QMS = ISO/IEC 17025 orin some cases ANSI/NCSLZ540

Competence andcompliance are ensured bythird party such as NVLAP or

A2LA

Agency assures that

Measurements carried out tothe highest standards oftechnical competence

Traceable to recognizednational or internationalstandards

Using accepted and agreedmethods

Realistic statements ofuncertainty



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Non-Accredited Calibrations

1. Operate according toother QMS guidelines

2. Competence is notcertified or audited andshould be audited byyou before entrustingyour calibration to anon-accredited lab


Do you need an accredited calibration?

Yes, if a regulating agency requires it

Yes, if your internal operating rules require it

Yes, if you will have a regular need to defend ordemonstrate proper procedures

No, if your internal guidelines do not specify

No, if you determine that calibration is not critical for

your operation


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The Calibration Process


Choose your approach...

1. In-house metrology lab Manage your own lab, training, standards, traceability,

documentation, etc.

2. Contract with outside commercial lab Send instruments to an independent lab for calibration,

adjustment, repair, etc.

3. Field Calibration

Calibrate instruments in the process or in-situ with a portablereference or transfer standard

Use in-house staff or contract for outside service


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1. Lab Calibration example of steps in a lab

1. Instrument equilibrates in the lab for 24 hours2. Conduct visual inspection

3. Calibrator uses saturated salts and 2 referencehygrometers

4. Place probe in each salt for 30 minutes Record as found data for 0%,11%, 33%, 75%

5. Make adjustments (2 point) adjustment is made if out of tolerance more than 50% of nominal

6. Record as left data

7. Print certificate and place calibration sticker


2. Field Calibrations 1 point or multi-

point

Choose 1 point

Measurement point does not change morethan +/- 20% RH

Conditions are not extreme in RH,temperature or other (i.e. gas composition)


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Field Calibrations 1 point or multi- point

Choose multi-point

RH or temperature varies across wide spectrum (i.e. 5 to 95% RHas in outdoor measurement conditions)

Extreme conditions (i.e. 90% + RH, 300F)


Field Calibrations choose transferstandard

Generator (multi point) Generator (multi point)

measurement only (one point)


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Field Calibration determine the interval

HUMICAP 180R sensor


Field Calibration follow your QMS

1. Confirm calibration and check operation of the standard Does the standard meet the specifications of the measurement

Standard should be at least 2x better uncertainty of the unit under calibration

2. Be aware of the conditions around the measurement point Breathing on the probe

Time for equilibration

Non-representative sources of heat or cold

3. Pre-heat and or Purge (if applicable)


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Field Calibration follow your QMS

4. Place probes together and allow equilibrium & takemeasurement

5. Repeat for multiple points

6. Make adjustments as necessary (one point or two point)

7. Record the results, place stickers, etc.


Note about Adjustment

One Point calibration usually in the ambient environment if an adjustment is necessary:

an OFFSET adjustment is made when RH < 65%

a GAIN adjustment is made when RH > 65%

Multiple Point calibration using two or more referencehumidities:

a salt calibrator or humidity generator is needed

if an adjustment is necessary:

first an OFFSET adjustment is made in the dry point

then a GAIN adjustment in the wet point


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OFFSET adjustment (for RH < 65%): the same correction is made for every point in the measurement

range

Example of an OFFSET adjustment at 20%RH



GAIN adjustment (for RH > 65%): the correction is in proportion to the measured value


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Point 1 = OFFSET; Point 2 = GAIN

the correction is in proportion to the measured value the same correction is made for every point in the measurement

range

Example of a 2 point adjustment at 11% and 75%RH

Good Calibration Practice

Reference: A Guide to the Measurement of Humidity, National Physical Laboratory


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Good Calibration Practice - general

1. Measure as close as possible to the U.U.C probe/sensor

2. Allow enough time for the instruments/probes to stabilize

temperature & water vapor

anywhere from 5 minutes to 30 minutes depending on the differences

use the graphing feature to see it visually

3. Read the measurement results simultaneously


Good Calibration Practice - general

4. Choose one point or multi point calibrations andadjustments carefully

5. Follow all manufacturers recommendations and procedures

6. Dont forget to calibrate the analog signal with a calibratedmulti-meter

if separate from the digital reading


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Good Calibration Practice Spot Checking

Use intermediate spot checking not the same as field calibration but similar

use procedures where full calibration is required if spot checking shows out oftolerance by a certain %


Good Calibration Practice & usingan outside commercial lab

Be familiar with your calibration lab procedures and

equipment

Is the lab going to adjust if out of tolerance? At what point?

What is the traceability chain from NIST to your instrument?

Is the traceability chain documented?

In accordance with which QMS is the lab operating?

Does the service include documenting as found?

Are the lab technicians trained regularly?

Does the lab offer Accredited Services?

Is the lab able to calculate the uncertainty or just providing accuracy


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Common Sources of Error

1. Temperature fluctuations in the calibration environment

2. Temperature difference between reference and unit undercalibration

3. Temperature leakage into sensor environment

4. Not enough stabilization time

5. Accuracy of reference

6. Calibration methodology

Calibrating with Saturated Salts


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Saturated Salt Solutions

An aqueous salt solution generates a certain equilibrium relative

humidity in the air above it; different salts generate differentrelative humidity

equilibrium relative humidityin the air

saturated salt solution10...20 %

undissolved salt80...90 %




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Good choices for common salts (at 20C)LiCl (lithium chloride) 11.3 %RH

MgCl2 (magnesium chloride) 33.1 %RH

NaCl (sodium chloride) 75.5 %RH

K2SO4 (potassium sulphate) 97.6 %RH


Uncertainty of Saturated Salts

Reference: Vaisala HMK15 User Guide


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For NaCl at 25C;

1.4% + .1% = +/-1.5%


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Traceabili ty & Saturated Salts

ASTM E104-02 (2007), JIS Z 8806, DIN 50 008Standards

Batch Traceability

NaCl


Traceabili ty & Saturated Salts

For NIST traceability use areference hygrometer


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Summary

1. Approaches to calibration in-house lab, outside lab, field

2. Good Calibration Practices

3. Reference Equipment

4. Saturated Salts as a humidity reference


Was the Calibration section beneficial?

Veryb

eneficia

...

Som

ewhatb

enef.

..

Neutral

Mini

mallyb

ene..

.

Not

atall b

en...

0% 0% 0%0%0%

A. Very beneficial


C. Neutral




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End of Section 5

Calibration

Before we conclude

1. A few final evaluation slides

2. Raffle HM34F

3. Distribute Request Info & Comments sheet

Satisfaction Survey


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How well did the online registrationand confirmation process work?

A.Excellent

B.Veryg

ood

C.Ok

D.Fair

E.Poor

0% 0% 0%0%0%

A. Excellent

B. Very good

C. Ok

D. Fair

E. Poor



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Was the information on the web siterepresentative of the actual seminar?

A.Yes,veryc

omplet

e

B.Couldha

vebeen

...

C.Sufficien

t

D.Not

enough

E.Did

notu

sethew

e...

0% 0% 0%0%0%

A. Yes, very complete

B. Could have been more info

C. Sufficient

D. Not enough

E. Did not use the website



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How do you rate the instructorsknowledge of the subject?

A.Excellent

B.Veryg

ood

C.Ok

D.Fair

E.Poor

0% 0% 0%0%0%

A. Excellent

B. Very good

C. Ok

D. Fair

E. Poor



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How do you rate the instructorspresentation skills?

A.Excellent

B.Veryg

ood

C.Ok

D.Fair

E.Poor

0% 0% 0%0%0%

A. Excellent

B. Very good

C. Ok

D. Fair

E. Poor



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How do you rate the PowerPointslides and handout materials?

A.Excellent

B.Veryg

ood

C.Ok

D.Fair

E.Poor

0% 0% 0%0%0%

A. Excellent

B. Very good

C. Ok

D. Fair

E. Poor



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Would you recommend this seminarto a colleague?

A.Definitel

y

B.Mostlikely

C.Maybe

D.Probably

not

E.Not

atall

0% 0% 0%0%0%

A. Definitely

B. Most likely

C. Maybe

D. Probably not

E. Not at all



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What did you think about the pollingsystem as a feature of the seminar?

A.Great

feature B.Ok

C.Ok,buttoo

much

D.A

little

annoying

E.A

distractio

n,no...

0% 0% 0%0%0%

A. Great feature

B. Ok

C. Ok, but too much

D. A little annoying

E. A distraction, no value


Wrap up

Theory, terms & definitions

Psychrometrics

Best practices

Calibration


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End of Humidity 201 SeminarWhat you need to know about humidity

Thank you

diapositivas del seminario humedad 201

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