Users´s Manual

Version: 01/06/12

PL-300

14.34.01 (PL-300): Instrument for field measurement of

• Air permeability • Soil moisture tension • Soil volumetric moisture content

P.O. Box 4, 6987 ZG GiesbeekNijverheidsstraat 30, 6987 EM Giesbeek,The NetherlandsT +31 313 880200F +31 313 880299E info@eijkelkamp.comI http://www.eijkelkamp.com

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Contents

1 Introduction 1.1 Definition of the PL value 1.2 PL value and soil moisture content

2 Measuring principle of air permeability meter PL-300 2.1 Air permeability PL 2.2 Air permeability measuring chambers 2.2.1 Air permeability measurement with sampling ring 2.2.2 Air permeability measurement with surface-attached measur-

ing chamber 2.2.3 Air permeability measurement with lance probe 2.2.3.1 Measuring principle 2.2.3.2 Parameters of air permeability meter PL-300 for con-

nection of the lance probe 2.3 Function control of air permeability (PL) measurement 2.4 Water content 2.5 Tension

3 The micro-computer in the air permeability meter PL-300 3.1 Function and key allocation 3.2 Data transfer

4 Power supply

5 Applications

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1. Introduction 1.1 Definition of the PL value The PL value is the air permeability of a pore system when flown through by the fluid “Air”. By analogy with the hydraulic conductivity kf, the PL value is defined as the factor of proportionality between the rate of air flow in the pore system and the pressure gradient over the flow distance. The measuring system consists of a measuring chamber which creates a definite flow form in the examined sample volume, and a measuring instrument for metering the flow rate and the pressure gradient. With these quantities, the PL value for a homogeneous flow is calculated according to DARCY’s equation:

l

hPLvL

∆⋅= (1)

vL rate of air flow l height of measuring chamber

∆h pressure difference over the chamber height l in cm water column

For practical reasons, in this definition of the PL value the measuring pressure is stated as hydraulic pressure head and measured in cm water column. The air conductivity kl in the mapping instructions “Bodenkundliche Kartieranleitung“ (AG Boden, Hannover 1996) requires the measuring pressure to be entered as pneu-matic pressure head. This unit is not used here. Therefore, kl and the PL value defined here differ by the ratio of the densities of air (under standard conditions) and water. PL kl= ⋅ 820 (2) Irrespective of the fluid used, the permeability of a pore system is also described by the ”intrinsic permeability” koo. In the experiment with the fluid “Air” therefore applies DARCY’s equation:

(3)

vL rate of air flow

ηL dynamic viscosity of air l height of measuring chamber

ρW density of water g gravitational acceleration

∆h pressure difference over the chamber height l in cm water column

l

hgkv W

L

OOL

∆⋅⋅⋅⋅=

ρ

η

1

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Between the PL value and kOO applies the equation:

In addition to the flow gradient, the definition of air permeability according to Equation (1) includes only the rate of air flow in the flow experiment. Comparing the saturated hydraulic conductivity kf and the air permeability PL of a pore system, there remains only the ratio of the dynamic viscosities of the fluids “Water” and “Air”.

k PL PLf

L

W

= ⋅ = ⋅η

η

1

56 (at 760 Torr, 20°C) (5)

The kf value can thus be calculated from the PL value of an aerated pore system; this kf value applies to that same pore system if is fully flown through by water.

1.2 PL value and soil water content

For air permeability measurement in the field, the soil normally has a certain moisture content. That water blocks part of the soil pores which then do not contribute to the air perme-ability. Air permeability is always a function of the soil water content. For characterization of the soil water content therefore a tensiometer (recording of water tension) and a TDR probe (recording of volumetric water content) can be operated with the air permeability meter PL-300. Saturated air permeability is recorded in dry soil only if the pore system is com-pletely filled with the fluid “Air”.

gPLk

W

LOO

⋅⋅=

ρ

η(4)

5

6

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2. Measuring principle of air permeability meter PL-300 2.1 Air permeability PL For air permeability determination according to Equation (1), a volume flow (Flow) is controlled by a pump in the measuring instrument, and this flow passes through a cali-brated measuring throat and at the same time through the connected measuring chamber (Fig. 2). The volume flow and the size of the measuring chamber define the flow velocity in the measuring chamber. The volume flow is determined from the pressure drop over the measuring throat (Throat pressure). The pressure sensor has a measuring range of 30 cm water col-umn. The volume flow can be passed through the measuring chamber either to suck (Air in) or to press (Air out). The measuring pressure in the attached measuring chamber (Chamber pressure) is carried through the probe lines (P+, P-) to a pressure sensor with a final value of 3 cm water column. Low chamber pressure provides for laminar flow, and in moist soils it prevents a marked change of the moisture content in the examined soil volume. If these measuring ranges are exceeded, “Overflow” will appear on the display of the measuring instrument. To ensure the stable display of measurements, pressure of about 5% below the given measuring range should be avoided. A suitable volume flow is set with the pump control “Flow”. Depending on the permeability of the soil under review, the selector switch is used to set throat D1 for high permeability or D2 for low permeability.

Measuring range with D1: PL ca. 30....1.6 cm/s

Measuring range with D2: PL ca. 1.5....0.03 cm/s

The computer of the air permeability meter PL-300 calculates from the applied meas-uring pressure the pressure gradient for a homogeneous flow according to Equation (1). The geometry of the measuring chamber is defined by “Chamber height” and “Chamber area”. Fictitious values for “Chamber height” and “Chamber area” are assigned to meas-uring chambers with inhomogeneous flow forms (surface chamber, lance probe). Note: The measuring throat in the PL-300 was calibrated at 20°C air temperature and 760 Torr standard pressure. At identical air temperature in the measuring throat and in the measuring chamber therefore the recorded PL value always goes for 20°C air temperature, irrespective of the given test temperature.

2.2 Air permeability measuring chambers

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Depending on the proposed use, the air permeability meter can be operated with different measuring chambers:

Sampling ring adapter

A separate sampling ring is taken out of the soil and connected through the sam-pling ring adapter which carries the air flow through the sampling ring. The pressure difference between chamber and external air is passed on through a pressure line to the sensor in the air permeability meter. This pressure difference then gives the gradi-ent of a homogeneous flow over the height of the sampling ring.

Sampling ring measuring chamber

When using the sampling ring measuring chamber, the measuring chamber re-mains in the soil. The remaining pressure at the base of the sampling ring in the soil is recorded using a supplemental pressure line. The pressure difference between the pressure lines (P+ and P-) then gives the gra-dient of the homogeneous flow over the soil volume in the chamber. In real soils, this measuring chamber normally cannot be fitted without ground failure leading to distortion of the measuring results. Therefore the sampling ring measuring chamber can be used with suitable substrates (e.g., structureless sands) for calibrating measuring chambers with inhomogeneous flow patterns.

Surface-attached measuring chamber

When using the surface-attached measuring chamber, the pore system will remain completely undisturbed. This chamber is put onto the soil surface, defining a source area for the air flow. The surface around that source area gets gel-sealed, causing air to flow from this source area through the underground and to the open soil surface. The surface-attached measuring chamber produces an inhomogeneous flow in the soil, which is also calculated with DARCY’s equation. The relation between the pressure in the measuring chamber, the volume flow through the soil, and the air permeability (PL value) can be calculated by solving the respective boundary value problem. For the surface-attached measuring chamber used in the PL measuring instrument, the sampling ring measuring chamber was used for experimental determination of this relation in structureless sands.

Lance probe

The lance probe is used for measuring in the underground. In a borehole with defined diameter, a source area is delimited with a packer. The volume flow is then carried into that source area. A pressure line records the pressure at the source area. The calibration data “Chamber height” and “Chamber area” are determined, assum-ing a radial-symmetric flow (see 3.3).

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2.2.1 Air permeability measurement with sampling ring

Soil samples in the sampling ring can be connected to the measuring instrument through a suitable adapter. The adapter gets sealed by tightening the screws. Calibration data include the height and cross-sectional area of the connected sampling ring.

Instrument parameters

“Chamber height“ ⇒⇒⇒⇒ Height of ring cylinder chamber

“Chamber area“ ⇒⇒⇒⇒ Area of ring cylinder chamber

Height Area UGT chamber 250 ccm: 6.1 cm 40.7 cm² Eijkelkamp chamber 250 ccm: 5.0 cm 50.0 cm² Readjustment of instrument parameters:

From display menu ⇒⇒⇒⇒ ESC ⇒⇒⇒⇒ Input ⇒⇒⇒⇒ ETR 2.2.2 Air permeability measurement with surface-attached measuring

7 Air in

5 P -

Chamber height

Chamber area

Screw

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chamber

The surface-attached measuring chamber should be used for field measurement of undisturbed soil. For this, the soil surface only should be plane, with more than 40 cm diameter. First, the ring screen is put with its small aperture onto the centre of this surface. Then the measuring chamber is placed into the centre of the aperture. Be careful not to press the chamber into the soil, as this would disturb the pore system. Then the surface between the ring screen and the measuring chamber gets sealed with a viscous gel layer (commercial wallpaper glue, viscous). For optimal sealing of the soil surface, during measurement the PL-300 evacuates the air from the measuring chamber (Air in). The air flows from the surface outside the ring through the test soil below the sealing and then to the surface area within the measuring chamber.

Instrument parameters (fictitious)

“Chamber height“ ⇒⇒⇒⇒ 3.0 cm (for diameter = 14.5 cm)

“Chamber area“ ⇒⇒⇒⇒ 40.7 cm² Readjustment of instrument parameters:

From display menu ESC ⇒⇒⇒⇒ Input ⇒⇒⇒⇒ ETR 2.2.3 Air permeability measurement with lance probe

2.2.3.1 Measuring principle

7 Air in

5 P -

Ring screen

Gel

Chamber

Diameter = 14.5 cm

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The principle of the lance probe is based on the effect of a point source in a medium with homogeneous air permeability. The following expression for that radial-symmetric flow is obtained from DARCY’s equation and the continuity equation:

PLQ

R p p=

⋅ − ∞4

1

1 1π ( ) (6)

Q flow rate from infiltration source (cm³/s)

R1 radius of the spherical source (cm) p1 pressure at the source (cm water column !)

p∞ pressure at long distance from source In the practical version of the lance probe, for a spherical area with radius R1 the free infiltration area is set at the base of a borehole. This infiltration area is delimited by the packer of the lance probe. The packer-sealed space is fed, through the source aperture of the lance probe, with the volume flow of the PL-300. The resulting excess pressure in that source space is recorded through a pressure line. The relation between the spherical chamber radius R1 and the effective cylinder area of the borehole with radius rz and height hz was determined experimentally by cali-brating the probe according to Equation (6) in a fine sand of known air permeability.

2.2.3.2 Parameters of air permeability meter PL-300 for connection of the lance probe

By way of calibration, an effective radius R1 for a radial-symmetric flow according to Equation (6) was allocated to the lance probe. The data logger in the PL-300 has been programmed for a measuring chamber with homogeneous flow. It asks for the input of chamber height and chamber area.

Flow from ideal point source

R1, p1

Flow from lance probe

Borehole

Packer

Source

Probe aperture

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The following relations apply:

Radial-symmetric flow: Homogeneous flow:

PLQ

R p p=

⋅⋅

− ∞4

1

1 1π ( ) PL

Q

F

l

p p= ⋅

−( )1 2

(7)

Therefore, a fictitious chamber height l* has been defined for connection of the lance probe, which is determined by equating the relations (7):

lF

R* =

⋅4 1π (8)

The fictitious chamber height l* of a homogeneous flow is derived from the area of the standard chamber F = 40.7 cm² and the determined effective radius R1 = 0.88 cm. Parameters for the measuring chamber when connecting the lance probe: (fictitious) chamber height l* = 3.6 cm (fictitious) chamber area F = 40.7 cm²

2.2.3.3 Installation of the lance probe

At the place of measurement, the lance probe needs a cylindrical borehole that has a diameter of 24 mm and is 12 cm high. This measuring hole can be cut with the attached borer at the base of a larger bore-hole. It is advisable to cut the measuring hole with a cover tube that remains in the borehole during measurement. For this, the borer gets a stop which limits the depth below the cover tube. The lance probe gets inserted into the measuring hole, with its face standing on the base of the borehole. For repeated measurement in one borehole, the shape of the borehole can be fixed by inserting a dummy. The lance probe in the borehole gets sealed with a packer to be loaded by means of a pressure ball with a pressure of ca. 0.8......1 bar. The packer sealing can be seen from the chamber pressure build-up on the switched on measuring instrument.

Connecting tube for packer: black mark Evacuation of packer: through drain cock

Note: The packer must be loaded with excess pressure only in the borehole or in the cover tube.

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Connection of lance probe to PL-300

6 Air out

4 P +

Pressure ball for packer

Source aperture

Probe aperture

Packer

Borehole wall

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Instrument parameters

“Chamber height“ ⇒⇒⇒⇒ 3.6 cm

“Chamber area“ ⇒⇒⇒⇒ 40.7 cm² Readjustment of instrument parameters:

From display menu ⇒⇒⇒⇒ ESC ⇒⇒⇒⇒ Input ⇒⇒⇒⇒ ETR

2.3 Function control of air permeability (PL) measurement (calibration throat)

The displayed value of air permeability is determined by the instrument parameters of the connected measuring chamber and the volume flow and chamber pressure values recorded in the measuring instrument. The overall function of the air permeability meter can be checked by connecting a spe-cific calibration throat. Control is effected with the parameters "Chamber height" = 3.0 cm "Chamber area" = 40.7 cm² For the measuring ranges "Throat 1" und "Throat 2", “Flow” is used for setting the pressure over the measuring throat (“Throat pressure”) as prescribed in the test proto-col. The displayed air permeability shall not vary by more than 10% from the target value. In the case of larger variations, the device must be checked by the manufacturers.

2.4 Moisture (Water content) A TDR probe (UGT 111710) at the “Moisture” jack can be operated with the PL-300. The combination of air permeability measurement and moisture measurement is always required for field measurement, as the soil water makes part of the pore volume inaccessible for air permeability measurement. The TDR probe has an antenna that is 11 cm long. For recording a representative soil moisture content, it must be placed at the PL measuring depth.

2.5 Tension At jack “Tension”, an electronic tensiometer (UGT 151300) can be connected to the PL-300. Its measuring depth in the soil is 3 cm.

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3. The micro-computer in the air permeability meter PL-300 3.1 Function und key allocation After the measuring instrument has been switched on, the display shows "UGT PL-300 Data logger". Only in that basic position the instrument is ready for data transfer with a PC (readout of stored data). After any key has been pressed, the instrument will switch to the data log-ging mode for measurement: First, the current geometric parameters “Chamber height” and “Chamber area” are displayed and offered for correction. (Chamber height, Chamber area) For acknowledgement of the displayed value, press ETR.

Press ESC to change a value: The Instrument now expects a number with five digits or less, then press ETR. If you close with ESC instead, the value stored before will be preserved. In both cases the current value appears for acknowledgement with ETR.

After the geometric data have been acknowledged, there appears the stan-dard display for chamber pressure and throat pressure (Chamb. , Throat). To set relevant values, use control “Flow“. "Overflow" signals that the measuring range of a pressure sensor has been exceeded. In such case, re-duce the volume flow. "ERROR" indicates an arithmetic problem which may be due to insufficient chamber pressure or geometric garbage for chamber height or chamber area. If in such status the logging of measurements gets activated, PL will be as-signed the value of 55.555 cm/s. The following values can be displayed by pressing the control keys: F1: Moisture Soil moisture (TDR) F2: Tension Water tension F3: battery Battery tension F4: Throat nr. Throat No. and PL value F5: Chamber Chamber pressure F6: Throat Throat pressure These are the allocations for other functions. ETR: Standard display ESC: Geometric parameters Store: Activation of moisture measurement and data storage As some time is needed (e.g., for measurement) for response to pressing a key, the instrument acknowledges a key press with (:) in the last digit posi-tion. Key “Store” initiates the storage of measurements F1 to F6.

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The instrument offers text input of 16 digits at most for description of the measuring point: “Measuring text:.....“ The letter assignment over the keys applies after pressing “Alpha”. The “Shift” key (ac-knowledges with flashing cursor) each time applies to the next digit. After pressing “ETR” (Num), the keys go back to their basic assignment (figures and letters). The input ends with digit 16 or with “ETR”.

Then, but after 30 seconds of measurement at the earliest for the data F1 to F6 and their storage, the instrument returns to the basic position.

From the data logging mode the calibration data of the measuring throats too can be modified: CTRL 1: Throat 1 (measuring throat 1) CTRL 2: Throat 2 (measuring throat 2) As for the geometric data, input control is with ESC and ETR.

Never press more than two keys at the same time!

3.2 Data transfer By the provided UGTLog – Software you read out the data memory of the integrated data logger. At first you should connect the COM1 – socket to a serial – RS232 – interface socket (Sub D9) of your computer (laptop, notebook, pc workstation etc.) by the provided UGT – Data Cable.

Then start the UGTLog program by double click on the UGT icon on your desktop.

A click on the Project-Open-Button, as you can see in the right screen shot, opens the Project-Open-Window. Select the file PL***.upr for opening.

Now you can connect the data logger by a click on “Connect“ in the Logger roll up menu or on the Connect button as you can see in the screen shot.

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By a click on “Read“ in the Logger roll up menu or on the read out button the program starts to read out the logger data memory. Recorded data will be saved in the directory <instaldir>\DATA. For more information see the UGTLog description in the appendix

You close the connection to the device by a click on “Disconnect”.

The measured data will be saved as a pure ASCII file, with “Tab“ to separate the col-umns. The name of the data file has the following format: Project name + logger name + ’_’ +date +’_’+serial No. +’.TXT’

The first three lines contain the names of the measuring points, the units of measure-ment and an identification of the kind of data. This will be followed by the individual measured data. The first two columns always hold the date and time of day. The text file can be used directly into common spread-sheet programs (e.g., Excel). It has 14 columns with the following contents:

1 2 3 4 5 6 7

Date Time Chamber press.

Throat press. Moisture Tension battery

8 9 10 11 12 13 14

Chamber Height

Chamber Area

Throat 1 (ccm/s)

Throat 2 (ccm/s)

PL Throat nr. Comment

The throat No. in column 13 designates the value from columns 10 or 11 that is valid at the time.

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4. Power supply

The air permeability meter PL-300 has a rechargeable battery which, when fully charged, has an operating time of about six hours.

In the case of longer intervals between measurements the device should be switched off, as this switches the pump off as well.

Undue drop of the battery charge is displayed, with about 30 minutes operating time being left.

The data memory is backed up by a supplemental battery.

A battery charger is connected through the “Charger” jack.

5. Applications

Air permeability indicates the permeability of a soil pore system. It is correlated with a large number of soil physical quantities, such as bulk density, pore volume, grain size distribution, and hydraulic conductivity.

A proposal of BRUGGENWERT can be used to classify the PL value:

Class Intrinsic air permeability* cm². 10

-10

Air permeability (PL value) 10

-3 cm/s

Very slow < 3 < 1.6

Slow 3 – 15 1.6 – 8

Moderately slow 15 – 60 8 – 32

Moderate 60 – 170 32 – 91

Moderately fast 170 – 350 91 – 187

Fast 350 – 700 187 – 373

Very fast > 700 > 373

* BRUGGENWERT, M.G.M. e.a. ,1966, Algemene bodemkunde.

Handleiding kandidaatspraktikum Landbouwhogeschool, Wageningen

When using the correlation between air permeability (PL value) and hydraulic conduc-tivity (kf value) according to Equation (5) (see 1.1.), the following PL values can be assigned to the kf levels according to the Bodenkundliche Kartieranleitung:

Level kf value 10

-5 cm/s

PL value 10

-3 cm/s

kf 1 very low < 1.16 < 0.65

kf 2 low 1.16 – 11.6 0.65 – 6.5

kf 3 moderate 11.6 – 46.3 6.5 – 26

kf 4 high 46.3 – 116 26 – 65

kf 5 very high 116 – 347 65 – 190

kf 6 extremely high > 347 > 190

Bodenkundliche Kartieranleitung, AG Boden, Hannover 1996