Insert the Profile Probe
Contents
1. m gt m V a 3 where a and 4 are the calibration coefficients above For a generalised mineral soil this becomes And for an organic soil 3 Op 0 023 0 72V 8 72V 30 44V 53 71V 46 32V 15 78V M M Slope and offset conversion Combining the Soil calibration and linear Profile Probe response equations 9 x 0 37 4 43V a m m up to 0 3 m m a Using the values of a and a for generalised mineral and organic soils From probe V to w ae m m Mineral soil 3 3 m m Organic soil To convert data readings from volts multiply by the slope and add the offset This gives readings in m m Linearisation table conversion The following table of values is used for the DL2e logger sensor codes P2M P20 P2C P2D 20 Operation Profile Probe User Manual 3 0a mineral organic soil moisture i d soil soil a m vol Volt Volt 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 are mV and Engineering units are Y vol Conversion Offset From probe mV to Factor 0 O ovol mV vol volume Mineral soil 18 96 146 volume Organic soil 17 38 124 Profile Probe User Manual2. 33 Soil specific calibration This note provides details of 3 techniques for generating soil specific calibrations 1 Laboratory calibration for substrates and non clay soils 2 Laboratory calibration for clay soils 3 Field calibration We use the term substrate to refer to any artificial growing medium Underlying principle Dielectric property of soil compared to moisture content Soil moisture content 0 is a proportional to the refractive index 5 00 of the soil Ve as measured by the ThetaProbe and Profile Probe see Calibration section The goal of calibration is to generate two coefficients do a1 0 00 0 10 0 20 030 040 which can be used in a linear arei equation to convert probe readings into soil moisture Je a a x0 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 Ve at the same frequency 100MHz However both their calibrations are influenced by their slight sensitivity to conductivity and they differ in how this sensitivity changes with water content The ThetaProbe and methods 1 or 2 below can be used effectively for creating soil specific Profile Probe calibrations at low water contents and or low conductivities At high conductivity and high water content it is far better to generate Profile Probe calibrations using the field cal
3. units is restricted to 0 01 m m 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 supply significant power to other sensors or accessories we recommend powering the data logger and sensors from an external power supply The DL2e has two warm up relay controlled outputs Each relay can typically power up to 12 PR2 4 or 8 PR2 6 Profile Probes Note For best economy the Profile Probe should be powered up using a 1 second warm up time Profile Probe User Manual 3 0a Operation 15 Other data loggers The connections and power requirements will usually be the same as for the DL2e If you simply want to log the sensor voltages directly they can be treated as differential voltage sources of range 0 1 1 V DC and the data logger should be configured accordingly Warning we recommend connecting Profile Probes as differential voltage sensors because 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
4. Check that the 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 e The Probe or the connecting cable Then try to narrow down the area further e Mechanical problems faults or damage e Electrical or electronic problems or faults Calibration check We recommend that you check the calibration of your PR2 at least once a year by taking an air reading and a water reading as follows Air reading Keep the PR2 in its protection tube and hold it away from any other objects Take a reading using an HH2 meter or other meter or logger The reading should be 75 20mV 24 Troubleshooting Profile Probe User Manual 3 0a Water reading Insert the PR2 fully into an access tube and immerse the tube into a large body of water at 20 to 25 C The water container should be sufficiently large so that the PR2 is gt 100mm from any edge Take a reading using an HH2 meter or other meter or logger Although this reading is outside the PR2 s specified accuracy range the reading should lie between 1040 and 1100mV Centring springs Check that the centring springs are all fitted clean and undamaged Immediately 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
5. 8 your soil cracks when it dries again measurement errors are likely to be higher than calibration errors The procedure for carrying out a soil specific calibration is detailed in Appendix A 18 Operation Profile Probe User Manual 3 0a Profile Probe response All Profile Probes have the same dielectric performance Profile Probe output 5 PR2 readings fitted curve 0 0 0 2 0 4 0 6 PR2 output Volts This relationship can be fitted very precisely up to 0 5 m m by the following polynomial Ve 1 125 5 53V 67 17V 234427 413 56V 356 68V 4 121 53V 2 and can be approximated by the following linear relationship 3 Je 037 4 43V up to 0 3 m m 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 content Three data conversion methods can be used polynomial conversion linear conversion slope and offset linearisation table conversion Profile Probe User Manual 3 0a Operation 19 Polynomial conversion Combining the Soil calibration and Profile Probe response steps the conversion equation becomes B 1 125 5 53V 67 17V 234 42V 413 56V 356 68V 121 53V
6. following connections Cable Function Notes Colour Red Power V 5 15V DC PR2 4 80mA PR2 6 120 mA Black Power OV Green Signal COM Yellow Vout 1 Grey Vout 2 Brown Vout 3 White Vout 4 Blue Vout 5 Pink Vout 6 Notes Power OV is cable screen Common signal output Top sensor 100 mm depth For PR2 4 Vout 5 and 6 are not connected 1 These connections are not the same as the PR7 2 The cable screen serves as the power return and is given black insulation 3 Do not connect the Power OV and Signal common at the logger This will create reading errors 14 Operation Profile Probe User Manual 3 0a L9 i Link the green wire to the minus terminal on every channel used by the PR o ae wee gt _ gt ON ON P9FON ON 9 29 This diagram shows the connections for Profile Probe sensor 1 connected to channel 1 of a DL2e in differential mode and powered through the logger s internal power supply Further details can be found in your Ls2Win installation The DL2 Program Editor contains on line help and an application note on each sensor type Four DL2e sensor codes are supplied for the PR2 P2M provides a conversion from mVolts to soil water content in m m suitable for general mineral soils P20 converts to m m for general organic soils P2C converts to vol for general mineral soils P2D converts to vol for general organic soils Note All DL2e data in m m
7. 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 to hammer the access tube into the soil will often result in gaps forming around the tube at the top and compaction of the soil lower down the tube Refer to the Augering Manual for advice on augering holes of the correct size Profile Probe User Manual 3 0a Troubleshooting 25 Technical reference Specifications Technical Specifications for PR2 4 and PR2 6 Volumetric soil moisture content 6v m m or vol Accuracy specified from 0 to 0 4 m m Range i 3 3 Full range is from 0 0 to 1 0 m m 3 3 P after soil specific ee 3 3 with generalised soil 0 06 m m 0 to 40 C calibration in normal soils Salinity errors Included in above figures 50 to 400 mS m Vertically 95 sensitivity within 50mm of upper ring Soil sampling of each pair volume Horizontally 95 sensitivity within a cylinder of radius 100mm O 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 Power Maximum 15V DC requirement PR2 4 consumption lt 80 mA PR2 6 consumption lt 120 mA 4 PR2 4 or 6 PR2 6 analogue voltage out
8. 00 400 mS m moderately saline 400 800 mS m_ strongly saline 800 1600 mS m extremely saline gt 1600 mS m_ 30 Technical reference Profile Probe User Manual 3 0a References 1 Gaskin G J and J D Miller 1996 Measurement of soil water content using a simplified impedance measuring technique J Agr Engng Res 63 153 160 j Topp G C J L Davis and A P Annan 1980 Electromagnetic determination of soil water content Water Resour Res 16 3 574 582 3 Whalley W R 1993 Considerations on the use of time domain reflectometry TDR for measuring soil moisture content Journal of Soil Sci 44 1 9 4 White I J H Knight S J Zegelin and Topp G C 1994 Comments on Considerations on the use of time domain reflectometry TDR for measuring soil water content by W R Whalley Journal of Soil 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 I Or D and J M Wraith 1999 Temperature effects on soil bulk dielectric permittivity measured by time domain reflectrometry A physical model Water Resour Res 35 371 383 8 Whalley W R R
9. 1 0 Volts Works reliably even in saline soils 4 Introduction Profile Probe User Manual 3 0a PR2 6 and PR2 4 in soil C 1 metre Electromagnetic fields extend into the soil and detect soil moisture Profile Probe User Manual 3 0a Introduction 5 Parts list Your consignment may have the following parts Sales Code Profile Probe we PR2 4 PR2 4 with 4 sensors as j 5 shown or PR2 6 with 6 sensors Both supplied in PR2 6 protective tube with spare o rings and centring springs Access tube spacer SPA1 Corrects PR2 depths when access tubes are mounted flush with soil surface AT CR1 Cleans access tubes PR CB2 Carrying bag for PR2 Access tubes 4 La Short or long fibreglass tubes suitable for PR2 4 or PR2 6 including cap bung and collar Le See Augering Manual a See Augering Manual fa See Augering Manual Moisture meter plus accessories DL6 6 channel data logger ol optimised for PR2 or DL2e General purpose multi channel logger adaptable for many logging needs PRC d HH2 1 5m to HH2 PRC M12 05 5m to DL6 PRC w 05 5m to DL2e or other loggers EXT M12 05 5m 10m and 25m extension 3 cables PRC M12 05 and FAUNIA EXT M12 10 are identical EXT M12 25 6 Introduction Profile Probe User Manual 3 0a Care and safety instructions Keep your PR2 in its protection tube and fit the connector cap when the probe is not in use The Profile Probe should be stored in a dry envir
10. 20 PR2 output vol 40 20 0 20 40 60 80 Temperature C This relationship is dependent on soil composition particularly clay content and the soil moisture level see ref 7 Electromagnetic Compatibility EMC Europe The Profile Probe has been assessed for compatibility under the European Union EMC Directive 89 336 EEC and conforms to the appropriate standards provided the probe body and moisture measuring rings are completely inserted into the access tube within 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 lf 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 Probes installed near to each other will not malfunction due to interference North America This device complies with Part 18 of the FCC Rules Operation is subject to the following two conditions 1 this device may not cause harmful interference and 2 this device must accept any interference received including interference that may cause undesired operation 28 Technical reference Profile Probe User Manual 3 0a Definitions Volumetric Soil Moisture Content is defined as B Vy where V is the volume of water contained in 0 7 the s
11. 3 0a Operation 21 Reading accuracy The Profile Probe is accurate and reliable However this doesn t guarantee that the readings you take with a PR2 are an accurate measure of the soil moisture There are three particular sources of error that you need to consider when measuring soil moisture with the Profile Probe Installation problems Soil type and Sampling errors Salinity Installation problems An ideal installation would avoid creating either air gaps or soil compaction around the access tube and then the soil would not shrink or swell as it dried out or rewetted It s possible to get remarkably close to this ideal in some deeply cultivated soils and close to impossible in some stony soils or hard clay We obviously can t quantify your potential installation errors but experience suggests that a loose gappy access tube installation could lead to errors of 10 0 1 m m 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 worst in heavy clay Soils If your soil cracks badly in dry conditions the readings from your Profile Probe may be more indicative of crack size than soil moisture content The linear relationship in equation 1 is less applicable
12. E Cope C J Nicholl and A P Whitmore 2004 In field calibration of a dielectric soil moisture meter designed for use in an access tube Soil Use and Management 20 203 206 Profile Probe User Manual 3 0a Technical reference 31 Technical Support Terms and Conditions of Sale Our Conditions of Sale ref COND 1 07 set out Delta T s legal obligations on these matters The following paragraphs summarise Delta T s position but reference should always be made to the exact terms of our Conditions of Sale which will prevail over the following explanation Delta T warrants that the goods will be free from defects arising out of the materials used or poor workmanship for a period of twelve months from the date of delivery Delta T shall be under no liability in respect of any defect arising from fair wear and tear and the warranty does not cover damage through misuse or inexpert servicing or other circumstances beyond their control If the buyer experiences problems with the goods they shall notify Delta T or Delta T s local distributor as soon as they become aware of such problem Delta T may rectify the problem by replacing faulty parts free of charge or by repairing the goods free of charge at Delta T s premises in the UK during the warranty period lf 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
13. Specifications 26 Index 43
14. User Manual for the Profile Probe type PR2 PR2 UM 3 0 Delta T Devices Ltd Notices Copyright All rights reserved Under the copyright laws this manual may not be copied in whole or in part without the written consent of Delta T Devices Ltd Under the law copying includes translation into another language Copyright 2004 Delta T Devices Ltd Patent pending The Profile Probe has been developed by Delta T Devices and uses novel measurement techniques patent 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 Manual Version PR2 UM 3 0 Jan 2008 Delta T Devices Ltd Tel 44 1638 742922 130 Low Road Fax 44 1638 743155 Burwell E mail sales delta t co uk CAMBRIDGE CB25 OEJ Web www delta t co uk UK Contents Introduction Description Parts list Care and safety instructions Routine maintenance PR2 Cleaning and Chemical Avoidance Instructions How the Profile Probe works Operation Preparation for reading Insert the Profile Probe Portable monitoring Record readings with a data logger Calibration Conversion to soil moisture Reading accuracy Trou
15. aProbe into the sample and record its output in Volts Vw 0 672V Dry the sample thoroughly With mineral soils this is usually achieved by keeping it in the oven at 105 C for several hours or days the time required depends on the sample size and porosity For organic soils and composts it s usual to air dry the sample to avoid burning off any volatile factions Weigh the dry sample in the beaker W 627 29 Re insert the ThetaProbe into the dry sample and record this reading Vo 0 110V For the ML2 Je 1 07 6 4V 6 4V 4 7V In the dry soil V Vo 0 110 Volts and substituting this value into the above equation gives 61 102 Since amp 0 this is the value needed for ap ao 1 70 The water content of the wet soil 6 can be calculated from the weight of water lost during Profile Probe User Manual 3 0a Appendix A drying W Wo and its volume Ls 6 W W L 743 3 627 2 463 5 0 25 Oy 0 25 Calculate a In the wet soil V Vy 0 672 Volts and substituting gives Je 3 91 Finally a Je Je 0 3 91 1 70 0 25 0 8 80 a 8 80 Laboratory calibration for clay soils This technique is adapted to avoid the near impossibility of inserting the ThetaProbe into a completely dry clay soil It requires taking measurements at 2 significantly different but still damp moisture levels Equipment you will need ThetaProbe and meter Soil corer Heat resi
16. ample Vs and V is the total volume of the soil sample The preferred units for this ratio are m m though vol is frequently used Soil Moisture Content varies from approx 0 02 m m for sandy soils at the permanent wilting point through approx 0 4 m m for clay soils at their field capacity up to values as high as 0 85 m m in saturated peat soils Gravimetric Soil Moisture Content is defined as M P where M is the mass of water in 0 g7 g g the sample and M is the total mass of the dry sample To convert from volumetric to gravimetric water content use the equation where is the density of water 1 0 0 H G V p and p is the bulk density of the S sample ans S Organic and Mineral definitions The generalised calibrations have been optimised to cover a wide range of soil types based on the following definitions optimised bulk use for use for around density bulk Soil type organic i ee organic _ range densities contents 3 3 content g cm g cm Profile Probe User Manual 3 0a Technical reference 29 Salinity The preferred SI units for ionic conductivity are mS m where S is Siemens the unit of electric conductance ohm The following conversions apply 1mS m 0 01 dS m 0 01 mS cm 0 01 mmho cm 10 uS cm Soil salinity is also partitioned into the following descriptive categories non saline 0 200 mS m slightly saline 2
17. 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 the output automatically before logging the data using the information supplied in the Conversion to Soil Moisture section 16 Operation Profile Probe User Manual 3 0a Calibration The Profile Probe detects soil moisture by responding to the permittivity e of the damp soil see illustration on page 8 or more accurately to the refractive index of the damp soil which is equivalent to Ve As a result the performance of the Profile Probe is best understood if it is split into these two stages Soil calibration soil moisture 0 determines Ve Profile Probe response Ve determines PR2 output Volts Soil calibration Soil calibration Ve damp soil wo Soil offset ao 0 10 20 30 40 50 Water content of soil Yvol 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 ve and the soil water content 6 which contains two parameters a and a that reflect the influence of the soil Ve a a x0 1 The accuracy of
18. ata logger as they have been designed to work together DL6 connection and configuration You will need access either to a PC with DL6 Control Panel software installed or to a Pocket PC with Pocket DeltaLINK E 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 STATUS Soil Moisture Logger E Configure the DL6 Using Pocket DeltaLINK or DL6 Control Panel Click on Connect to Logger and Er 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 other options refer to the DL6 user manual for details When finished click on to install the program in the logger Profile Probe User Manual 3 0a Operation 13 To check the connections select the Sensors tab and click on L to see the PR2 readings E Start logging When ready click on a to select the Logger window and Start to start logging E Collect the data later when you want to collect the data connect to the DL6 and click on to select the Dataset window from which you can retrieve and display all stored readings See the DL6 User Manual for configuration options DL2e connection and configuration The Profile Probe is fitted with a screened 8 way connector When used with a DL2e this should be connected using the PRC w 05 cable which provides the
19. bleshooting Problems Technical reference Specifications Performance Definitions References Technical Support Soil specific calibration Laboratory calibration non clay soils Laboratory calibration for clay soils Field calibration Index NN DP B amp B 10 10 11 12 13 17 19 22 24 24 26 26 27 31 32 34 35 37 40 43 Introduction Description The Profile Probe measures soil moisture content at different depths within the soil profile It consists of a sealed polycarbonate rod 25mm diameter with electronic sensors seen as pairs of stainless steel rings arranged at fixed intervals along its length When taking a reading the probe is inserted into an access tube The access tubes are specially constructed thin wall tubes which maximise the penetration of the electromagnetic field into the surrounding 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 monitoring Fully sealed and robust High accuracy 4 Easy installation with minimal soil disturbance Large sampling volume 1 0 litres at each profile depth Simple analogue output O to
20. ibration technique 3 34 Soil specific calibration Profile Probe User Manual 3 0a Appendix A Laboratory calibration non clay soils This is the easiest technique but it s not suitable for soils that shrink or become very hard when dry Equipment you will need ThetaProbe and meter Soil corer if doing a calibration for a cohesive soil rather than sand or a substrate Heat resistant beaker gt 500ml Weighing balance accurate to lt 1g Temperature controlled oven for mineral soils or substrates Process Notes and example Collect a damp sample of the soil or substrate This sample needs to be unchanged from its in situ density to be gt 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 composts often require measurement of the in situ density and then need to be carefully reconstituted at that density within the beaker Measure the volume occupied by the sample L 463 5ml Weigh the sample including the beaker W 743 3g Profile Probe User Manual 3 0a Soil specific calibration 35 Appendix A Calculate ao Calculate 6 36 Soil specific calibration Insert Thet
21. 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 to supply products free of charge or repair any goods where the products or goods in question have been discontinued or have become obsolete although Delta T will endeavour to remedy the buyer s problem Delta T shall not be liable to the buyer for any consequential loss damage or compensation whatsoever whether caused by the negligence of the Delta T their employees or distributors or otherwise which arise from the supply of the goods and or services or their use or resale by the buyer Delta T shall not be liable to the buyer by reason of any delay or failure to perform their obligations in relation to the goods and or services if the delay or failure was due to any cause beyond the Delta T s reasonable control 32 Technical Support Profile Probe User Manual 3 0a Service Repairs and Spares Users in countries that have a Delta T distributor or technical representative should contact them in the first instance Spare parts for our own instruments can be supplied and can normally be despatched within a few working days of receiving an order Spare parts and accessories for products not manufactured by Delta T may have to be obtained from our supplier and a certain amount of additional delay is inevitable No goods or equipment should be retur
22. ituting in the ML2 equation VJe 1 07 6 4V 6 4V 4 7V provides two dielectric values Ve and Vem at two known water contents 6 and 6 Substituting Vy 0 672 gives Je 3 91 a a 0 for 8 743 3 627 2 463 5 0 25 Substituting Vm 0 416 gives Jep 290 d a 6 For 0 693 2 627 2 463 5 0 14 Then a Je Je 0 8 73 d 8 73 and ay J a TAE ao 1 72 Profile Probe User Manual 3 0a Soil specific calibration 39 Field calibration Field calibration is the surest method of calibration We strongly recommend it for Profile Probe installations featuring high water content usually high clay content and high conductivity as it is the only technique likely to give good results However it is typically far more time consuming and requires access to considerably more equipment than laboratory calibration General principle Install access tubes and take Profile Probe measurements as voltages over a period of time when the soil moisture content is changing Over the same period measure the water content at appropriate depths and spacing around the access tubes either by gravimetric sampling or using a Neutron Probe or using ThetaProbes These comparison readings can then be used to construct a calibration for the Profile Probe For best results this approach requires comparison readings over a significant range of soil moisture contents If the changes in water content
23. ly In the example shown ao 1 537 and a 8 656 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 for a 7 194 Profile Probe User Manual 3 0a Index A Access tube 4 6 7 9 10 11 12 20 22 26 28 31 40 41 bung 6 cap 6 7 11 12 Accuracy 22 26 Air gaps 9 22 C Calibration 12 17 18 20 26 31 34 35 37 40 41 42 soil specific 18 34 Cleaning and Chemical Avoidance Instructions 8 Connections 14 15 16 Conversion factor 21 Conversions 16 18 19 21 linearisation table 18 19 21 polynomial 19 slope and offset 17 18 19 20 21 D Data logger 6 11 13 14 15 16 19 20 40 DL2e 6 14 15 16 20 21 DL6 6 13 14 Definitions 29 Dielectric performance 19 31 34 39 E Field sensitivity 27 Profile Probe User Manual 3 0a Installation 4 10 15 18 22 Moisture content 4 9 19 22 26 31 34 40 41 P Power supply 9 14 15 16 26 R Range 26 References 31 S Salinity 22 23 26 27 30 Sampling volume 4 12 26 41 Soil clay 17 18 22 28 29 34 35 37 40 42 composition 28 dry 22 35 mineral 15 18 20 21 26 36 39 organic 15 17 18 20 21 29 36 type 12 22
24. ned to Delta T without first obtaining the return authorisation from Delta T or our distributor On receipt of the goods at Delta T you will be given a reference number Always refer to this reference number in any subsequent correspondence The goods will be inspected and you will be informed of the likely cost and delay We normally expect to complete repairs within 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 available on Delta T products and systems Your initial enquiry will be acknowledged immediately with a reference number Make sure to quote the reference number subsequently so that we can easily trace any earlier correspondence In your enquiry always quote instrument serial numbers software version numbers and the approximate date and source of purchase where these are relevant Contact details Tech Support Team Delta T Devices Ltd 130 Low Road Burwell Cambridge CB25 OEJ U K email tech support delta t co uk email repairs delta t co uk web www delta t co uk Tel 44 0 1638 742922 Fax 44 0 1638 743155 Profile Probe User Manual 3 0a Technical Support
25. onment definitely non condensing and protected from sharp blows Earth yourself on the metal connector before touching the detector rings to avoid any possibility of damage by electrostatic discharge Don t lay the PR2 in a puddle because water may creep under the rings if you suspect this has happened warm gently lt 50 C for 24 hours Lay as much of the cable as possible along the surface of the soil when taking a reading in order to minimise any electrical interference with other equipment Routine maintenance 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 when inserting the PR2 into an access tube a gentle twisting action helps The Profile Probe should be periodically recalibrated You should run a simple annual check on the calibration see the Troubleshooting section and contact your local Delta T representative if there is a problem Otherwise the PR2 should be returned for routine re calibration every 5 years Profile Probe User Manual 3 0a Introduction 7 PR2 Cleaning and Chemical Avoidance Instructions The PR2 shaft is made of polycarbonate plastic which is an exceptionally strong material and it can withstand bending forces far in excess of anything likely to be encountered in practice However polycarbonate can develop stress cracking when exposed to cer
26. 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 ao Equipment you will need Installed Profile Probe access tubes and Profile Probe with either meter or data logger 7 Either installed ThetaProbes 150mm from the access tubes at the appropriate depth Or Neutron Probe access tubes installed 300mm from the Profile Probe tubes Or gravimetric sampling equipment see previous methods Or a portable ThetaProbe attached to a suitable length extension rod and a suitable auger for sampling at depth The gravimetric and portable ThetaProbe methods both require essentially destructive measurements which limit their re use at the same site so they may require a number of similar sites But see below for fixed intercept calibration 40 Soil specific calibration Profile Probe User Manual 3 0a Appendix A Process Notes and exampe i Take Profile Probe readings as voltages over a period of time as the soil moisture content changes Ideally this would include 3 or more distinct soil moisture levels covering a change gt 0 1m m At the same time take several independent soil moisture readings spaced around the Profile Probe access tube These co
27. puts Outputs 0 to 1 0V DC corresponding to 0 0 6 m m mineral calibration 8 core screened Maximum length 100m Construction 25 4mm polycarbonate tube with pairs of stainless steel material rings l l PR2 4 length 750mm Weight 0 6kg ENE PR2 6 length 1350mm Weight 0 95kg using cables supplied by AT 26 Technical reference Profile Probe User Manual 3 0a Performance Field sensitivity The signal is applied to the upper ring of each pair so the electromagnetic field is stronger around the upper ring Although this field extends a considerable distance into the soil 100mm it is strongest close to the rings and so the soil close to the rings contributes most to the output Normalised sensitivity versus sample radius Yj s 06 amp AS gt yA pee f Qe 0 4 4 gt Damp Soil fe RY YY 0 2 A 0 20 40 60 80 100 120 140 160 Radius of sample cylinder mm Salinity The Profile Probe output has been tested as follows PR2 conductivity response PR2 output vol s PR2 in wet soil ideal response in wet soil PR2 in damp soil ideal response in damp soil 0 100 200 300 400 500 600 Pore Water Conductivity mS m 1 Profile Probe User Manual 3 0a Technical reference 27 Temperature The Profile Probe has a very low intrinsic sensitivity to changes in temperature as in this example PR2 output versus temperature 50 40 30
28. r HH2 using the supplied PRC d HH2 cable Press Esc to turn the meter on and if necessary press again until it displays Make sure the meter is set to read from a PR2 Press Set Jand scroll down to the Device option Press Set again and scroll down to Press Set to confirm this choice If you intend to store readings you may find it useful to define each reading by setting a plot label and sample number accessed by pressing Set and scrolling to the Data option See Calibration section for advice on setting Soi Type and Soil Set Up For other options refer to the HH2 User Manual E 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 ee se can choose different units from the Disp lay option Press to save or Esc to discard the reading If you want to maximise the sampling volume take 2 further readings with the probe rotated through 120 each time Remove the PR2 replace the access tube cap and move on toa new site E Viewing stored readings Ts If you have saved data connect the HH2 to your z PC and run HH2Read to retrieve the readings HHiBead 12 Operation Profile Probe User Manual 3 0a Record readings with a data logger The Profile Probe has been designed to make its use with data loggers straightforward It is particularly simple to use with the DL6 d
29. stant beaker gt 500ml Weighing balance accurate to lt 1g Temperature controlled oven Process Notes and example 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 gt 500ml to have the correct dimensions to fit the beaker and to be generally uniform in water content This is most easily done with soil corer Measure the volume occupied by the sample L 463 5ml Profile Probe User Manual 3 0a Soil specific calibration 37 Appendix A Weigh the wet sample including the beaker Wy 743 3g Insert ThetaProbe into the wet sample and record its output in Volts Vw 0 672V Dry the sample 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 Win 693 2g Re measure with the ThetaProbe Vin 0 416V 38 Soil specific calibration Profile Probe User Manual 3 0a Appendix A Calculations For the wet soil For the moist soil Calculate a Calculate do Dry the sample thoroughly With mineral soils this is usually achieved by keeping it in the oven at 105 C for several hours or days the time required depends on the sample size and porosity Weigh the dry sample in the beaker Wo 627 29 Subst
30. t the probe is correctly centred within an access rod j tube They must be fitted and working properly for g UUN the probe to take accurate readings Each centring spring coiled spring sits on top of an o ring see illustration o ring E Fit spacer if required If your access tube has been installed flush with the soil surface you will need 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 E 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 E Align the probe The probe should be aligned consistently each time it is inserted using the alignment marks on the access tube and the label on probe handle If you want to maximise the sampling at each location we suggest that you take the average of three readings at each location with the tube rotated through 120 each time the three small screw heads can be used for this purpose Ensure that the Profile Probe is pushed all the way down over the top o ring The PR2 is then fully sealed in its access tube and ready either for immediate reading or for attaching to a logger for extended monitoring Profile Probe User Manual 3 0a Operation 11 Portable monitoring E Set up the HH2 meter Connect the Profile Probe to you
31. tain chemicals Such stress cracking greatly weakens the polycarbonate and may lead to brittle fracture of the shaft even at very low stresses It is important 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 especially during probe storage Do not immerse the probe in water If this happens allow the probe to dry in warm air for at least 24 hours Make sure the probe is thoroughly dry before storing it in the protection tube 8 Introduction Profile Probe User Manual 3 0a How the Profile Probe works Before you rush out and hammer your access tubes into the soil it will help to understand a little about how the Profile Probe works T P When power is applied to the Profile Probe it creates a 100MHz signal similar to FM radio The signal is applied to pairs of stainless steel rings which transmit an electromagnetic field extending about 100mm into the soil The field passes easily through the access tube walls but less easily through any air gaps 9 amp The water content of the soil surrounding the rings dominates its permi
32. to heavy clay soils at low soil moisture levels lt 0 1 mm See ref 7 Soil moisture content may vary significantly even within a small volume of soil When you rotate the Profile Probe within its access tube the reading changes you observe reflect real soil moisture variability 22 Operation Profile Probe User Manual 3 0a Salinity Changes in soil salinity cause a change in reading which will appear as a change in soil moisture Typical effects on Profile Probe readings are an apparent change of lt 0 005 m m soil moisture for a change of 100 mS m soil Salinity In most situations this sensitivity is of little significance because a change of 100 mS m 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 23 Troubleshooting Problems When getting problems from a probe or sensor always try to identify which part of the measurement system is the source of the difficulty For the Profile Probe this may fall into one of the following areas The measurement device What equipment is being used to read the probe output e A Delta T HH2 Moisture Meter e A Delta T DL6 logger e A Delta T DL2e logger Consult the user manuals or the on line help for these devices and their related software Try alternative types of equipment if you have them available
33. ttivity 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 AVATAVAY The permittivity of the soil has a strong ALLS vy influence on the applied field Vout resulting in a stable voltage output that actS as a simple sensitive measure of soil moisture content Profile Probe User Manual 3 0a Introduction 9 Operation Preparation for reading Install access tubes The Profile Probe must be used within an access tube The process of augering holes and installing access tubes is described in the Augering Manual Equipment You may require the following equipment for a site visit PR2 in protective tube 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 Operation Profile Probe User Manual 3 0a Insert the Profile Probe E Remove the tube cap and check for damp If the access tube has been left empty for several weeks check for condensation by threading paper towel into the slot in the cleaning rod and pushing this to the bottom of the tube If there is any water present you will need to dry the tube thoroughly E Check the centring springs centring spring Remove the PR2 from its protective tube 8 8 77 The Profile Probe is fitted with centring springs so Yee Y tha
34. uld be taken either with ThetaProbes or a Neutron Probe or by gravimetric sampling The number of samples required 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 V aA ve Convert the Profile Probe measurements 0 462 2 31 into Ve using its calibration equation 2 0 577 2 178 Variable Intercept calibration of Profile Probes Graph these Ve readings against the soil moisture measurements This illustration and the following procedures are taken from Excel but the principles can also be applied within other graphing or spreadsheet programs 0 00 0 10 0 20 0 30 0 40 Moisture content m m Profile Probe User Manual 3 0a Soil specific calibration 41 Variable Intercept calibration of Profile Probes Moisture content m m 0 00 0 10 0 20 0 30 0 40 Fixed Intercept calibration of Profile Probes 5071 ly 7 794x 1 800 Moisture content m m 42 0 00 0 10 0 20 0 30 0 40 Variable Intercept Fit a linear trendline to the data and in the Options tab choose to display the equation You may need to adjust the number format for the equation to 3 decimal places The calibration coefficients can then be read off direct
35. your Profile Probe readings can be improved if you choose appropriate values for a and a This is usually very simple Profile Probe User Manual 3 0a Operation 17 Generalised calibrations Most soils can be characterised simply by choosing one of the two generalised calibrations we supply one for mineral soils predominantly sand silt or clay and one for organic soils with a very high organic matter content Hm a These values have been used to generate the slope and offset conversions and linearisation tables in the Conversion to soil moisture section Soil specific calibration If it is important to work to higher accuracy you may choose to carry out a soil specific calibration but please bear this in mind For normal agricultural soils if you use one of the generalised calibrations you can expect typical errors of 0 06 m m including installation and sampling errors If instead you use a Soil specific calibration you can expect typical errors of 0 05 mm 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 to high levels of accuracy or you need a controlled error figure rather than a typical error figure and the following do not apply 8 Your soil is very stony insertion errors are likely to outweigh the calibration errors
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