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Technical reference

Specifications

Technical Specifications for PR2/4 and PR2/6

Measurement

Volumetric soil moisture content,

θ

V

(m

3

.m

-3

or %vol.).

Range

Accuracy specified from 0 to 0.4 m

3

.m

-3

,

Full range is from 0.0 to 1.0 m

3

.m

-3

after soil specific
calibration

±

0.04 m

3

.m

-3

, 0 to 40°C

Accuracy

with generalised soil
calibration in 'normal' soils

±

0.06 m

3

.m

-3

, 0 to 40°C

Salinity errors

Included in above figures (50 to 400 mS.m

-1

)

Vertically: ~95% sensitivity within ±50mm of upper ring
of each pair.

Soil sampling
volume

Horizontally: ~95% sensitivity within a cylinder of radius
100mm.
0 to 40°C for full accuracy specification,

Environment

–20 to 60°C full operating range.
IP67 rated

Stabilisation

Full accuracy achieved within 1s from power-up.
Minimum: 5.5V DC with 2m cable, 7.0V with 100m.*
Maximum: 15V DC

Power
requirement

PR2/4 consumption: < 80 mA
PR2/6 consumption: < 120 mA
4 (PR2/4) or 6 (PR2/6) analogue voltage outputs:

Outputs

~0 to 1.0V DC corresponding to 0 - 0.6 m

3

-3

m

(mineral

calibration)

Cable

8-core screened. Maximum length: 100m

Construction
material

25.4mm polycarbonate tube with pairs of stainless steel
rings
PR2/4 length: 750mm

Weight: 0.6kg

Size / weight

PR2/6 length: 1350mm

Weight: 0.95kg

*using cables supplied by

Δ

T

26

z

Technical reference

Profile Probe User Manual

3.0a

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Summary of Contents for PR2

Page 1: ...User Manual for the Profile Probe type PR2 PR2 UM 3 0 Delta T Devices Ltd ...

Page 2: ...t pending CE conformity The Profile Probe type PR2 conforms to EC regulations regarding electromagnetic emissions and susceptibility when used according to the instructions contained within this user manual and is CE marked by Delta T Devices Ltd Design changes Delta T Devices Ltd reserves the right to change the designs and specifications of its products at any time without prior notice User Manu...

Page 3: ...ert the Profile Probe 11 Portable monitoring 12 Record readings with a data logger 13 Calibration 17 Conversion to soil moisture 19 Reading accuracy 22 Troubleshooting 24 Problems 24 Technical reference 26 Specifications 26 Performance 27 Definitions 29 References 31 Technical Support 32 Soil specific calibration 34 Laboratory calibration non clay soils 35 Laboratory calibration for clay soils 37 ...

Page 4: ...urrounding soil The output from each sensor is a simple analogue dc voltage These outputs are easily converted into soil moisture using the supplied general soil calibrations or the probe can be calibrated for specific soils Advantages The Profile Probe is dual purpose each probe can be used both for portable readings from many access tubes and for installation within one access tube for long term...

Page 5: ...PR2 6 and PR2 4 in soil Electromagnetic fields extend into the soil and detect soil moisture Sensor 1 Pair of sensor rings 1 metre Profile Probe User Manual 3 0a Introduction z 5 ...

Page 6: ...s Short or long fibreglass tubes suitable for PR2 4 or PR2 6 including cap bung and collar ATS1 or ATL1 Augering equipment See Augering Manual Insertion equipment See Augering Manual Extraction equipment See Augering Manual Meter Moisture meter plus accessories HH2 Data logger 6 channel data logger optimised for PR2 DL6 or or DL2e General purpose multi channel logger adaptable for many logging nee...

Page 7: ...with other equipment Lay as much of the cable as possible along the surface of the soil when taking a reading in order to Routine maintenance into an e ould be returned for routine re calibration every 5 years Periodically examine the o rings and centring springs They should be kept clean and if they show any signs of damage replace them Pay attention particularly to the lowest centring spring whe...

Page 8: ...t to follow these guidelines Failure to observe these precautions can damage the probe and may invalidate the warranty Clean the probe in use if necessary by wiping with damp plain paper towels Use only clean water to damp the paper Do not use chemicals or cleaning agents of any sort in the water Never use any chemical solvents or cleaners on the probe or near to it Avoid strong chemical vapours e...

Page 9: ...m into the soil The field passes easily through the access tube walls but less easily through any air gaps The water content of the soil surrounding the rings dominates its permittivity ε A measure of a material s response to polarisation in an electromagnetic field Water has a permittivity 81 compared to soil 4 and air 1 The permittivity of the soil has a strong influence on the applied field Vou...

Page 10: ...ubes is described in the Augering Manual Equipment You may require the following equipment for a site visit PR2 in protective tube Access tube spacer Spare collars caps centring springs If setting up logging Data logger DL6 or DL2e and cable For portable reading HH2 meter and cable Roll of paper towels Cleaning rod 10 z Operation Profile Probe User Manual 3 0a ...

Page 11: ...ed to fit the access tube spacer SPA1 Slide the spacer over the tip of the probe and push all the way up past the top o ring Insert the Profile Probe Take care as the first centring spring is pushed into the tube not to pinch the spring unevenly against the side of the tube A slight twisting motion as the spring goes in will help protect it Align the probe The probe should be aligned consistently ...

Page 12: ... option See Calibration section for advice on setting Soil Type and Soil Set Up For other options refer to the HH2 User Manual Taking readings Insert the Profile Probe into an access tube Press Read to take a reading it takes about 3 seconds Press the arrow keys to view readings from other depths You can choose different units from the Display option PR2 Store 22 7 vol v100mm Press Store to save o...

Page 13: ...cket DeltaLINK Connect the Profile Probe The PR2 can be connected directly to the DL6 with the supplied cable Extension cables can be added as required up to 100m Configure the DL6 Using Pocket DeltaLINK or DL6 Control Panel Click on Connect to Logger and for the Programs window then in the Sensors tab set Channel 1 either to PR2 4 or PR2 6 Set the Recording Interval in the Main tab there are many...

Page 14: ...y connector When used with a DL2e this should be connected using the PRC w 05 cable which provides the following connections Cable Function Notes Colour Power V Red 5 15V DC PR2 4 80mA PR2 6 120 mA Power 0V is cable screen Power 0V Black Signal COM Common signal output Green Top sensor 100 mm depth Yellow Vout 1 Grey Vout 2 Brown Vout 3 White Vout 4 Blue Vout 5 For PR2 4 Vout 5 and 6 are not conne...

Page 15: ... m 3 m 3 resolution The P2C and P2D codes using vol show much better resolution and are preferred Power supply Profile Probes types PR2 require 5 5 to 15 Vdc power Power can be applied continuously or via a warm up relay for greater economy of power consumption You can power Profile Probes directly using DL2e internal batteries However if several probes are to be used or if the data logger has to ...

Page 16: ...they are powered sensors Although you can measure Profile Probes single ended this will introduce an additional measurement error that depends mainly on the length of your cable It may also have undesirable side effects on the apparent reading from other sensors attached to the data logger You can either convert the data to soil moisture units after logging or program your data logger to convert t...

Page 17: ...oil vol ε damp soil Slope a1 Soil offset a0 This method of detection is very sensitive and accurate but of course soils can be enormously different one from another The soil offset and the slope of the line in the graph above both depend slightly on soil type varying with density clay content organic matter etc This can be usefully summed up in a simple equation describing the relationship between...

Page 18: ...alised calibrations you can expect typical errors of 0 06 m 3 m 3 including installation and sampling errors If instead you use a soil specific calibration you can expect typical errors of 0 05 m 3 m 3 As a guideline we suggest that you only need to do a soil specific calibration if one of the following applies 4 Your soil is heavy clay highly organic or in some respect extreme 4 You are working t...

Page 19: ...lowing linear relationship V 43 4 37 0 ε up to 0 3 m 3 m 3 3 Conversion to soil moisture Profile Probes can either be used to give instantaneous readings of soil moisture using a hand held meter or they can be connected to a data logger to record moisture data over time In either case you will probably want to configure the meter or data logger to convert the Profile Probe output to soil moisture ...

Page 20: ...2 8 72 0 023 0 V V V V V V org θ m m Slope and offset conversion Combining the Soil calibration and linear Profile Probe response equations 1 0 43 4 37 0 a a V V θ 3 3 3 3 m up to 0 3 m m m Using the values of a and a 0 1 for generalised mineral and organic soils From probe V to Slope Offset m3 m 3 V m 3 m 3 3 m m 3 0 528 0 146 Mineral soil 3 m m 3 0 575 0 121 Organic soil To convert data readings...

Page 21: ...5 0 85 85 1 060 1 037 0 90 90 1 070 1 048 0 95 95 1 079 1 057 1 00 100 1 088 1 067 DL2e slope and offset conversion For DL2e data loggers you can create sensor codes using slope and offset if you cannot use the linearisation table codes above These will be accurate only for the restricted range up to 30 vol The sensor code Conversion Factor is the reciprocal of the Slope figures above Base units a...

Page 22: ...rrors but experience suggests that a loose gappy access tube installation could lead to errors of 10 0 1 m 3 m 3 so Take as much care as you can over the installation Remember to fit a collar to your access tube Soil type and sampling errors Again it s not really possible to quantify the potential errors associated with soil type but be aware of the following Almost all measurement problems are wo...

Page 23: ... 0 005 m 3 m 3 soil moisture for a change of 100 mS m 1 soil salinity In most situations this sensitivity is of little significance because a change of 100 mS m 1 is very unlikely but it may need to be considered particularly when irrigating with saline irrigation water See Salinity Performance in the Technical Reference section Profile Probe User Manual 3 0a Operation z 23 ...

Page 24: ... soil calibration being used is appropriate for your soil and that the correct conversion method is being used see Calibration section The probe itself Try to isolate the problem into one of the following areas The Probe or the connecting cable Then try to narrow down the area further Mechanical problems faults or damage Electrical or electronic problems or faults Calibration check We recommend th...

Page 25: ...replace any that do become damaged Installation problems Augering and access tube insertion Most PR2 errors are caused by inserting an access tube into the wrong size of augered hole If the hole is too large gaps around the tube will result in generally low readings and poor response to soil moisture changes unless the gaps fill with rainwater If the augered hole is too small the effort necessary ...

Page 26: ...sitivity within a cylinder of radius 100mm 0 to 40 C for full accuracy specification Environment 20 to 60 C full operating range IP67 rated Stabilisation Full accuracy achieved within 1s from power up Minimum 5 5V DC with 2m cable 7 0V with 100m Maximum 15V DC Power requirement PR2 4 consumption 80 mA PR2 6 consumption 120 mA 4 PR2 4 or 6 PR2 6 analogue voltage outputs Outputs 0 to 1 0V DC corresp...

Page 27: ...e output Normalised sensitivity versus sample radius 0 0 2 0 4 0 6 0 8 1 0 20 40 60 80 100 120 140 160 Radius of sample cylinder mm Output V out V max Damp Soil Salinity The Profile Probe output has been tested as follows PR2 conductivity response 0 0 10 0 20 0 30 0 40 0 50 0 60 0 0 100 200 300 400 500 600 Pore Water Conductivity mS m 1 PR2 output vol PR2 in wet soil ideal response in wet soil PR2...

Page 28: ...ithin the soil or other material being measured The cable connecting the Profile Probe to its associated instrumentation should be routed along the surface of the soil If the probe is not installed in this way some interference may be experienced on nearby radio equipment Under most conditions moving the equipment further from Profile Probe typically 1 2 metres will stop the interference Profile P...

Page 29: ...isture Content is defined as M where W is the mass of water in the sample and MS is the total mass of the dry sample θ G W S M M g g 1 To convert from volumetric to gravimetric water content use the equation θ θ ρ ρ G V W S where ρW is the density of water 1 and ρS is the bulk density of the sample M V S S Organic and Mineral definitions The generalised calibrations have been optimised to cover a ...

Page 30: ...ns apply 1 1 0 01 dS m 1 mS m 1 0 01 mS cm 0 01 mmho cm 1 10 µS cm 1 Soil salinity is also partitioned into the following descriptive categories non saline 0 200 mS m 1 slightly saline 200 400 mS m 1 moderately saline 400 800 mS m 1 strongly saline 800 1600 mS m 1 extremely saline 1600 mS m 1 30 z Technical reference Profile Probe User Manual 3 0a ...

Page 31: ...oil Sci 45 503 508 5 Roth C H M A Malicki and R Plagge 1992 Empirical evaluation of the relationship between soil dielectric constant and volumetric water content as the basis for calibrating soil moisture measurements Journal of Soil Sci 43 1 13 6 Knight J H 1992 Sensitivity of Time Domain Reflectometry measurements to lateral variations in soil water content Water Resour Res 28 2345 2352 7 Or D ...

Page 32: ...ta T s premises in the UK during the warranty period If Delta T requires that goods under warranty be returned to them from overseas for repair Delta T shall not be liable for the cost of carriage or for customs clearance in respect of such goods However Delta T requires that such returns are discussed with them in advance and may at their discretion waive these charges Delta T shall not be liable...

Page 33: ...one or two weeks of receiving the equipment However if the equipment has to be forwarded to our original supplier for specialist repairs or recalibration additional delays of a few weeks may be expected For contact details see below Technical Support Users in countries that have a Delta T distributor or technical representative should contact them in the first instance Technical Support is availab...

Page 34: ...t probe readings into soil moisture θ ε 1 0 a a Using the ThetaProbe to calibrate the Profile Probe Soil calibrations using the ThetaProbe and Profile Probe are very similar because they measure the same fundamental dielectric property ε at the same frequency 100MHz However both their calibrations are influenced by their slight sensitivity to conductivity and they differ in how this sensitivity ch...

Page 35: ...be unchanged from its in situ density to be 500ml to have the correct dimensions to fit the beaker and to be generally uniform in water content For cohesive soils this is most easily done with a soil corer Sandy soils can be poured into the beaker but you should take the subsequent measurements immediately as the water will quickly begin to drain to the bottom of the beaker Compressible soils and ...

Page 36: ...o avoid burning off any volatile factions Weigh the dry sample in the beaker 627 2g W0 Re insert the ThetaProbe into the dry sample and record this reading 0 110V V0 Calculate a 3 2 7 4 4 6 4 6 07 1 V V V ε For the ML2 0 In the dry soil V V0 0 110 Volts and substituting this value into the above equation gives 70 1 0 ε 0 this is the value needed for a Since θ0 0 a 1 70 0 Calculate θ The water cont...

Page 37: ... 2 significantly different but still damp moisture levels Equipment you will need ThetaProbe and meter Soil corer Heat resistant beaker 500ml Weighing balance accurate to 1g Temperature controlled oven Notes and example Process Collect a wet sample of the clay soil 25 to 30 water content would be ideal This sample needs to be unchanged from its in situ density to be 500ml to have the correct dimen...

Page 38: ...ample until still moist 15 water content Gentle warming can be used to accelerate the process but take care not to over dry in places and allow time for the water content to equilibrate throughout the sample before taking a reading Reweigh 693 2g Wm Re measure with the ThetaProbe 0 416V Vm 38 z Soil specific calibration Profile Probe User Manual 3 0a ...

Page 39: ...lculations 3 2 7 4 4 6 4 6 07 1 V V V ε provides two dielectric values ε and ε w m at two known water contents θ and θ w m 0 672 gives Substituting V For the wet soil w w w a a θ ε 1 0 91 3 for 25 0 5 463 2 627 3 743 w θ For the moist soil Substituting Vm 0 416 gives m m a a θ ε 1 0 96 2 For 14 0 5 463 2 627 2 693 m θ 73 8 1 m w m w a θ θ ε ε Calculate a Then 1 a 8 73 1 72 1 1 0 w w a a θ ε Calcul...

Page 40: ...soil moisture contents If the changes in water content over the measurement period are small the calibration becomes very sensitive to any measurement errors The extreme case of this occurs when readings are only available at a single soil moisture content It is still possible to calibrate the Profile Probe in these cases by assuming a default value for the intercept coefficient a 0 Equipment you ...

Page 41: ...d depends on the uniformity of the soil and the size of the sampling volume If it is difficult to take readings over a range of moisture levels it is still possible to calibrate the Profile Probe using a single soil moisture comparison using the fixed intercept method below 150mm V ε 0 462 2 31 0 577 2 78 Convert the Profile Probe measurements into ε using its calibration equation 2 Graph these ε ...

Page 42: ...to 3 decimal places The calibration coefficients can then be read off directly In the example shown a0 1 537 and a 8 656 1 Fixed Intercept Fit a linear trendline as above but in the Options also choose Set intercept We suggest you use the following default intercept values Organic soil 1 4 Mineral soil 1 6 Heavy clay 1 8 In this example the intercept has been set to a 1 8 and the calculated value ...

Page 43: ...eferences 31 Connections 14 15 16 S S Conversion factor 21 Salinity 22 23 26 27 30 Conversions 16 18 19 21 Sampling linearisation table 18 19 21 volume 4 12 26 41 polynomial 19 Soil slope and offset 17 18 19 20 21 clay 17 18 22 28 29 34 35 37 40 42 composition 28 D D dry 22 35 Data logger 6 11 13 14 15 16 19 20 40 mineral 15 18 20 21 26 36 39 DL2e 6 14 15 16 20 21 organic 15 17 18 20 21 29 36 DL6 ...

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