operating manual air pycnometer · by default, ambient air is used as measuring gas (air...

Operating Manual

Air Pycnometer Version: 05/02/19

with external gas supply line

Umwelt-Geräte-Technik GmbH

Eberswalder Str. 58 | D-15374 Müncheberg

phone: +49 (0) 33 43 2 - 89 575 | fax: +49 (0) 33 43 2 - 89 573

e-Mail: [email protected] | www.ugt-online.de

Umwelt-Geräte-Technik GmbH | Eberswalder Str. 58 | D-15374 Müncheberg | phone: +49 (0) 33 43 2 - 89 575 | www.ugt-online.de of 19

Content

1. Introduction ...................................................................................................................................... 3

1.1. Safety Instruction....................................................................................................................... 4

1.2. Scope of supply .......................................................................................................................... 5

2. General Information ......................................................................................................................... 6

2.1. What is an Air Pycnometer used for?.......................................................................................... 6

2.2. How Does an Air Pycnometer Work? .......................................................................................... 7

3. Set Up and Technical Parameters ..................................................................................................... 9

3.1. Set Up ........................................................................................................................................ 9

3.2. Technical Parameters ............................................................................................................... 11

4. Measurement Procedure ................................................................................................................ 12

4.1. Initial Operation ...................................................................................................................... 12

4.2. Selection of the measurement method .................................................................................... 12

4.3. Calibration ............................................................................................................................... 12

4.4. Measuring Process ................................................................................................................... 14

5. Handling of the Digital Manometer ................................................................................................ 17

6. Evaluation........................................................................................................................................ 18

6.1. Using the Excel-file “Evaluation Air Pycnometer” ..................................................................... 18

6.2. Errors and Advices for effective Measurements ........................................................................ 19

http://www.ugt-online.de/


1. Introduction

Thank you for choosing the air pycnometer. This manual can help you understand the pycnometer features. We designed this air pycnometer as an innovative measuring device for the determination of the air-filled pore volume, the solid volume, and the solid density of a substrate sample in the laboratory. As an option, a different gas can be used with an external gas supply line. There are several ways to contact UGT if you ever need assistance with your product, have any questions, or feedback. Email: [email protected] or [email protected]

Phone:

+ 49 (0) 33432 – 89 575

Fax:

+ 49 (0) 33432 – 89 573

If contacting us by email or fax, please include as part of your message your instrument serial number, your name,

address, phone, and a description of your problem or question.

Please read these instructions before operating your air pycnometer to ensure that it performs to its full potential.



1.1. Safety Instruction

If a defect is found in our product, please notify us immediately by fax or e-mail.

CAUTION While placing the lid on top and tightening the tension screw there is a risk of crushing or bruising your fingers

Hazard of crushing

CAUTION Gas hoses must be securely fastened, and the hose connections must be checked for leaks before use. Gases may only be released into apparatus if it has been ensured that no unacceptable pressure can build up in the apparatus. Use a pressure reducer (2.5 -2.8 bar).

Gas under pressure

CAUTION No flammable gases may be used.

flammable gas



1.2. Scope of supply

Figure 1 scope of supply

air pycnometer 1 clamp with tensioning screw 1 lid of measurement chamber with valve 1 sealing ring 1 power cord 1 supply hose external gas 1 glass blocks for reducing the chamber volume

3

manual 1 manual manometer Leo1 1

air pyknometer

clamp with tensioning screw

lid of measurement chamber with valve

sealing ring glass blocks

power cord supply hose external gas



2. General Information

2.1. What is an Air Pycnometer used for?

The air pycnometer is an innovative measuring device for the determination of the air filled pore volume, the solid volume, and the solid density of a substrate sample in the laboratory.

The pore volume is a relevant parameter for soil specification. It provides important information for many questions of water balance studies, cultivation of land or land reclamation. Air- and water conductivity as well as water- and nutrient retention are directly related to the pore volume.

The air pycnometer is suitable for undisturbed soil samples as well as for bulk solids like sand, gravel or plant granulate. It provides faster and easier measurements compared to glass pycnometers. A high content of fine particles may reduce the applicability of the gas pycnometer.

Due to the large measurement chamber with a volume of 2120 cm³ it is possible to investigate samples of large volume.



2.2. How Does an Air Pycnometer Work?

The measurement method is based on the fact that only the solid’s volume displaces gas while pore or cavity volumes are filled with gas. The air pycnometer consists of two connected chambers, a measurement chamber and an additional volume chamber. The additional volume chamber is filled with compressed air and connected via a shut-off valve to the measurement chamber that contains the sample. Opening the shut-off valve leads to pressure equalization between both chambers.

Fig. 1 Schematic illustration of the measuring principle

Based on the ideal gas law the solid volume of the sample can be determined from the measured change in pressure. For isothermal conditions the ideal gas law reduces to the BOYLE-MARIOTTE law.

From the isothermal base equation

𝑝 ∙ 𝑉 = 𝑐𝑜𝑛𝑠𝑡 (1)

follows:

𝑝𝐴 ∙ 𝑉𝑍 = 𝑝𝐸 ∙ (𝑉𝐾 − 𝑉𝐹 + 𝑉𝑍 ) (2)

With VF for all incompressible substances in the measurement chamber:

𝑉𝐹 = 𝑉𝑆𝑆 − 𝑉𝑆𝑊 + 𝑉𝑊 (3)



VZ … Additional volume

VK … Volume of the measurement chamber

Vss … Volume of the granular structure of the sample (soil solid)

Vsw … Volume of the pore water (soil water)

VW … Volume of the wall of the sample cylinder(wall)

The volumes VK and VZ are determined by calibration.

By transposing equation (2) one derives:

𝑉𝐹 = 𝑉𝐾 −(𝑝𝐴 − 𝑝𝐸)

𝑝𝐸 ∙ 𝑉𝑍 (4)

For a dry sample without test cylinder VF equates the volume of the granular structure (Vss)

The evaluation of the air filled pore volume VL follows from:

𝑉𝐿 = 𝑉𝑆 − 𝑉𝐹 (5)

VL … volume of air filled pores = Volume of soil air

Vs … Volume of the whole sample

Inserting (3) into (4) and rearranging to the relevant components on the left side of the equation results in:

𝑉𝑆𝑆 + 𝑉𝑆𝑊 = (𝑉𝐾 −(𝑝𝐴 − 𝑝𝐸)

𝑝𝐸 ∙ 𝑉𝑍) − 𝑉𝑊 (6)

After inserting (6) in (5) one gets the air filled pore volume:

𝑉𝐿 = 𝑉𝑆 − (𝑉𝐾 −(𝑝𝐴 − 𝑝𝐸)

𝑝𝐸 ∙ 𝑉𝑍 − 𝑉𝑊) (7)



3. Set Up and Technical Parameters

3.1. Set Up

figure 3 Air pycnometer Front view

figure 4 Air pycnometer Back view

[1] Body with compressor and pressure vessel as additional

volume [2] measurement chamber

[3] lid

[4] clamp with tensioning screw

[5] measure valve:

„Filling“, „Measuring“,

„Venting“

[6] digital manometer

[8] switch for compressor

[9] supply valve:

„External“, „Closed“, „Compressor“

[12] flushing valve

[7] lock valve

[10] power cord

[11] Supply hose external gas with coupling plug



By default, ambient air is used as measuring gas (air pycnometry). Optionally, another sample gas can be used via a separate supply line (gas pycnometry). The measuring chamber is firmly connected to the base body and is closed with a lid which is pressed on by a bracket. A lancing cylinder is not necessary to carry out the measurement.



3.2. Technical Parameters

Measurement Chamber:

Height 12 cm

Ø 15 cm

Volume ≈ 2120 cm³

Pressure vessel (additional volume):

Volume ≈ 1000 cm³

Digital Manometer:

Pressure Range -1 bis 3 bar

Resolution 1 mbar

Overpressure 10 bar

Accuracy RT (room temperature) < 0,1 %FS

Total Error Band (0…50°C) < 0,2 %FS

Storage- / Operating Temperature -20…70 °C / 0…50 °C

Compensated Temperature Range 0…50 °C

Supply 3 V Battery, CR 2430

Battery Life •1000 hours continuously in Mano-mode

•150 hours continuously in Peak-mode

Pressure Connection G1/4”

Protection CEI529 IP65



4. Measurement Procedure

4.1. Initial Operation

During start-up, the power supply unit [10] is connected to the power source via the power cable. If an external measuring gas is used, the supply hose is connected to the gas source and then inserted into the coupling socket [11] using the coupling plug. The coupling is self-closing. The ring seal is inserted into the notch provided. Before the first measurement, the instrument must be calibrated as described in section 4.3.

4.2. Selection of the measurement method

The supply valve [9] is used to set the air pycnometer to one of two possible measuring methods before measurement. If the valve is in the "External" position, an external gas connected via the coupling socket can be used as measuring gas ("gas pycnometry"). In the "compressor" position, the compressed air generated in the compressor is used ("air pycnometry"). The setting "Closed" closes the valve and is recommended for the storage of the pycnometer.

4.3. Calibration

The calibration is carried out according to DIN 66137-2:2004-12. The calibration of the volumes of the additional volume chamber and the measurement chamber are carried out stepwise using a solid calibration probe of known volume (Vkal). The volume Vkal should be determined or known as exactly as possible.

The operating steps of the calibration correspond to the ones of the measurement. For a detailed description of the operating procedure see section 4.4.

The pressure in the measuring chamber and the additional volume chamber is equalized with respect to the atmosphere (see Figure 1) by opening both valves (for the measure valve [5] this means position "VENTING"). If external gas is used, the measurement chamber and the additional volume chamber must then be flushed and filled with external gas. These initial conditions are to

Note The scope of supply includes three glass blocks. The blocks can be used to artificially reduce the volume of the measurement chamber when working with small soil samples. This procedure provides more stable results due to a smaller influence of measurement errors.

Attention!

Use a pressure reducer for external gases. The maximum set pressure must not exceed 2.8 bar.



be realized again before each partial step of the calibration, i.e. after opening the measuring chamber.

In the first calibration step, the measuring pressure pA,1 is set in the additional volume chamber. The expansion takes place in the empty measuring chamber (equilibrium pressure pE,1). The second step is carried out analogous to step one with the calibration probe located in the measurement chamber. The initial pressure pA,2 before expansion and the equilibrium pressure pE,2 are again measured after expanding.

The following equations apply for the measuring chamber volume VK and the the additional volume VZ:

𝑉𝐾 =(𝑝𝐸,2 ∙ (𝑝𝐴,1 − 𝑝𝐸,1))

(𝑝𝐴,1 ∙ 𝑝𝐸,2 − 𝑝𝐴,2 ∙ 𝑝𝐸,1) ∙ 𝑉𝑘𝑎𝑙 (8)

𝑉𝑧 =(𝑝𝐸,1)

(𝑝𝐴,1 − 𝑝𝐸,1) ∙ 𝑉𝑘 (9)

The change of the measuring gas, the change of the gas purity and the working with a measuring pressure which has changed compared to the previous calibration require a new calibration of the instrument.

For an exact calibration at least 10 measurements should be taken redundant and analysed statistically (see Excel-file „Evaluation Air Pycnometer”).



4.4. Measuring Process

As with calibration, at least 10 redundant measurements should be taken and statistically evaluated when determining sample volumes. Before each measurement series, check the position of the supply valve [9] intended for the measurement method (see 4.2).

At the beginning of the measurement, the measuring valve [5] is set to " venting ", the lock valve [7] is completely open and the lid of the measuring chamber is removed, so that the complete system is under the currently prevailing atmospheric pressure. The digital manometer [6] is switched on by pressing "Enter". The displayed pressure must be noted as the current air pressure.

When examining small soil samples, it is advisable to reduce the volume of the measuring chamber through the enclosed glass bodies in order to increase the accuracy of the measurement. This additional volume remains in the measuring chamber during the measuring process. In this case, the instrument must be calibrated with the glass bodies inserted.

figure 5 Closing the chamber

The sample container/sample (VF) is put in the measuring chamber [2], which is then sealed airtight by placing the lid [3] on it and tightening the clamping screw [4] by hand. The indicated air pressure should not change. Otherwise check that the measure valve is set to " Venting".

The samples used must be dry (Vsw not included in the evaluation). An external drying up to mass constancy is recommended. The dried sample must be weighed. It does not matter whether the weighing is carried out before or after the measurement. When fitting the lid, make sure that it is clean (after cleaning with water, allow it to dry completely) and that the sealing ring is in the notch provided for this purpose. The pike of the tensioning screw should rest in the cavity in the middle of the lid.

CAUTION!

Debris (e.g. sand grains) at the sealing ring may confine its functionality. To keep the air pycnometer work correctly always cover the sealing ring while the measurement chamber is open.



The following procedure is shown schematically in the following figure:

1. Initial State:

If an external measuring gas is used, the additional volume and the sample chamber must be flushed with the used gas after inserting the sample and closing the measuring chamber. To do this, open the flushing valve [12] and set the measuring valve [5] to "Filling" and flush the chambers sufficiently. Then close the flush valve and the lock valve.

For an air pynkometric measurement using the internal compressor, close the flushing and lock valve and set the measuring valve [5] to Filling.

2. Filling the additional volume:

If an external gas is used, the integrated pressure vessel (additional volume VZ) is filled with gas until the maximum pressure set via the external pressure regulator is reached.

With an air pyncometric measurement, the pressure vessel integrated in the device is filled with compressed air by switching on the compressor [8]. The controlled variable is a filling pressure of approx. 3 bar atmospheric pressure. When this pressure is reached, the compressor switches off automatically.

After reaching this pressure the measure valve [5] has to be switched to the “Measuring”-position immediately to separate the compressor or the external gas from the system and hence to avoid a loss of pressure. When the pressure in the additional volume is leveled out to a constant value (ca. 2 min.) the pressure has to be logged as initial pressure pA. The value can be taken over to the second line of the display as maximum value by pressing the “Select”-button and then the “Enter”-button.

open open close

flushing valve Lock valve Measuring valve

closed



3. Pressure Compensation:

Now the lock valve [7] has to be opened slowly. The external gas or compressed air flows from the additional volume into the measurement chamber.

A fast expansion would lead to a cooling of the gas and breach the test condition of an isothermal change of state (p*V=const.). The compensating pressure pE is read after the equilibrium has been set, i.e. at constant pressure.

Important for step 2 and 3: The criterion for constancy of pressure (maximum pressure variation per time step) has to be defined before the analysis.

4. Venting:

Before opening the measurement chamber after logging the equilibrium pressure it has to be vented. For venting the three-way valve [5] has to be switched to the “Venting”-position while the lock valve [7] is still open. The measurement chamber and the additional volume chamber are now under atmospheric pressure.

If the internal compressor is used, the air in the pipe from the compressor to the three-way valve [5] has not been depressurized since finishing step “2. Filling the additional volume”. The compressor is ready for further fillings. After finishing all measurements, the compressor has to be vented by switching the measuring valve from “Filling” to “Venting” several times.

After constancy of pressure open slowly

open



5. Handling of the Digital Manometer

The digital manometer is able to measure the pressure in different units and to show minimum and maximum values of a measuring period. It is operated with the two buttons “Select” and “Enter”

2 modes are available for the measurement:

Mano-Mode:

The pressure is measured and displayed twice per second. The upper value is the current pressure, the lower line displays the maximum (MAX) or minimum (MIN) pressure since the last “RESET”.

Peak-Mode:

The pressure is measured 5000 times and displayed twice per second. The upper value again is the current pressure, the lower line displays alternatively the maximum (MAX) or minimum (MIN) pressure.

The device comes with following functions:

Reset The reset-function sets the MAX or MIN value to the current value.

Zero The zero-function assigns the current pressure as zero value. Hence barometric pressure gradients can be compensated.

The factory setting of the zero value for the ranges -1…3 bar and -1…30 bar is absolute at 0 bar. To measure the reference pressure press „ZERO SET” at current atmospheric pressure.

Cont The device switches off automatically 15 minutes after the last key operation. Activating cont (Continuous) deactivates this automatic device switch-off.

Units All devices are calibrated in bar. The pressure can be displayed in the following units: bar, mbar/hPa, kPa, MPa, PSI, kp/cm2

Fig. 6 Display segments of the digital manometer Leo 1 and the manometer at the air pycnometer

Press the "Select" key several times to move through the menu. With "Enter" you can access the function and change or confirm it.



6. Evaluation

6.1. Using the Excel-file “Evaluation Air Pycnometer”

For a simple and fast evaluation of the calibration and the measurement, evaluation masks have

already been prefabricated in the enclosed Excel document, in which only the measured values have

to be entered. The result is the volume of the air-filled pore space, the volume of the solid, the solid

density and the bulk density.

In the "Measurement log" worksheet, the sample name, soil type, calibration volume (VKal), height

and diameter of the probe cylinder and the dry weight of the sample are entered in the "Metadata"

table. Alternatively, the externally determined volume of the sample can be entered instead of the

size of the cylinder. If a cylindrical sample without soil sample ring is used, its external dimensions

can be entered as "Inner diameter of soil sample ring [cm]" and "Height of soil sample ring [cm]".

"Chamber volume reduction [cm³]" should only be noted if an additional volume reduction body

was only used during the measurement. If no additional volume is added or if the same was already

present in the air pycnometer during calibration, the value must be set to zero.

In the "Calibration" section, the pressures pA,1, pE,1, pA,2 and pE,2 of the calibration are noted.

Furthermore, the measured ambient pressure for the calibration must be entered under

"Atmospheric pressure [bar]". The corresponding units must also be taken into account. The number

of measurements with and without volume must be identical. The relationship between pA,1 and

pE,1 and between pA,2 and pE,2 is automatically shown in the form of diagrams. These diagrams

make it possible to detect incorrect measured values.

In the "Measurement" section, the measured values for pA and pE of the actual measurement with the sample are then entered in the measuring chamber. Here, too, the display of the measured values in the diagram is used to check for possible error influences. The relationship between pA and pE should be as linear as possible. Measured values deviating from this linear correlation should not be considered in the further evaluation and should therefore be removed. The ambient pressure during the measurement is again noted under "Atmospheric pressure [bar]". A maximum of 20 measured values can be noted for both calibration and measurement.

The table “Results” displays the means and standard deviations of the solids volume, the solids density and the pore volume as well as the bulk density of the soil sample

Furthermore, the dry mass of the soil material is required, which is determined by drying at 105°C to constant weight. For the evaluation of the test it is assumed that the sample is used in a dry state (recommended). If soil samples are measured in a wet state, it is necessary to subtract the volume of water from the determined volume of soil material (not recommended).



6.2. Errors and Advices for effective Measurements

▪ If the sample contains enclosed pores, the gas pycnometric density value is smaller than the real density. In this case it is advisable to break up the sample to a fineness where all pores are destroyed

▪ Gases or vapors (e.g. water vapor) released during the measurement influence the equilibrium

pressure. This is indicated by a long response time at a continuously decreasing pressure. The effect is usually too low solid volume values.

▪ In order to ensure temperature constancy, measurements should be taken in a temperature-constant room.

▪ If you forgot to close the lock-off valve for step 2 "Filling the additional volume", the measuring chamber must first be vented again before the measurement is carried out.

▪ If a constant pressure does not appear within a short time at step 3 "Pressure compensation", the system is no longer airtight. Check the sealing ring for damage or dirt. Even a single grain of sand can cause such problems. Therefore, please make sure that the sealing ring is always covered as long as the measuring chamber is open.


operating manual air pycnometer · by default, ambient air is used as measuring gas (air...

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