SM300 user manual
Contents
1. Mineral Read a Read d a Volts nn Read eae SM150 User Manual 1 Operation 12 HH2 Meter This assumes you have version 2 6 or later for both the PC software HH2Read and the HH2 firmware see foot of page Connect the SM150 to the HH2 meter Press Esc to turn the meter on and if necessary press again until the HH2 displays the start up screen Set the meter to read from an SM150 ties Press and scroll down to the Device option Press Set again and scroll down to select SM150 Press Set to confirm this choice Make sure the HH2 is correctly configured for your soil type At the start up screen press Set and scroll down to the Soil Type option Press Set again and scroll down to the appropriate soil type use Mineral for sand silt or clay soils or Organic for peaty soils Press Set to confirm this choice Choose the units you want for displaying readings At the start up screen press Set and scroll down to the Display option Press Set again and scroll down to select units Press Set to confirm this choice Press to take a reading Press to save or Esc to discard the reading Remove the SM150 from the soil and move to a new location If you have saved data connect your HH2 to a PC and run HH2Read to retrieve the readings For an upgrade contact Delta T See also HH2 User Manual and HH2 User Manual Addendum to V4 SM150 Support SM150 User Manual 1 Operation 13 Logg2. calibration for non clay soils 36 Laboratory calibration for clay soils 39 Technical Support 42 Index 44 SM150 User Manual 1 Introduction 4 Introduction Description The SM150 measures soil moisture content lts sealed plastic body is attached to two sensing rods which insert directly into the soil for taking readings A waterproof plug connects to a choice of signal cables Both extension cables and extension tubes can be used The soil moisture output signal is a differential analogue DC voltage This is converted to soil moisture by a data logger or meter using the supplied general soil calibrations lt can also be calibrated for specific soils Features Soil moisture accurate to 3 Low salinity sensitivity Excellent stability Minimal soil disturbance Easy installation at depth in augured holes Waterproof connector to IP68 E Rugged weather proof and can be buried i Good electrical immunity Choice of cabling system options Cable connector cylindrical profile and extension tube design simplifies removal for servicing Dedicated HH150 meter kit for simple readings HH2 meter GP1 DL6 or DL2e loggers compatible See also Specifications on page 26 SM150 User Manual 1 0 Introduction 5 Dimensions Cable connector sealed to IP68 M12 5 pin male Thread inch BSP for connecting to Extension Tube s SM150 User Manual 1 Introduction 6 Parts list Your shipment may
3. 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 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 returned 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 re
4. property of soil compared to moisture content 6 00 5 00 4 00 3 00 2 00 0 20 0 30 moisture content m m The goal of calibration is to generate two coefficients ao a1 which can be used in a linear equation to convert probe readings into soil moisture Je a a xO SM150 User Manual 1 Appendix 1 35 Laboratory calibration for 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 Process SM150 and meter Soil corer if doing a calibration for a cohesive soil rather than sand or a substrate Heat resistant beaker gt 0 5 litre Weighing balance accurate to lt 19 Temperature controlled oven for mineral soils or substrates 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 0 5 litre 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 occup
5. reduces as the temperature increases This produces a negative temperature response particularly in soils or substrates with high water content Water that is bound to the surface of soil particles has a much lower refractive index than free water The percentage of bound water decreases with temperature and this produces a positive temperature response particularly in clay soils at lower water contents The last two effects partially offset each other but in soil conditions where one or the other effect dominates the SM150 will appear to have a significant temperature response This illustration is based on the model in reference 7 see page 34 Illustrating temperature dependence of SM150 readings in a clay soil 6 0 4 6 0 3 0 2 0 1 sence bound water a m U G cD 0 c e cod td a2 e O N ab om Q lt 20 30 Soil temperature C Note ice has a quite different refractive index from water so SM150 soil moisture readings cannot be interpreted reliably when inserted into soil below 0 SM150 User Manual 1 Technical Reference 28 Sampling Volume The SM150 is most sensitive to signals very close to the two rods but a small proportion of the signal reaches up to 50mm from the rods SM150 field of sensitivity surrounding the rods Distance parallel to plane of rods fromacentre line between the rods mm Minimum soil sample
6. 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 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 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
7. 150 readings from milliVolts into soil moisture units by using either Polynomial conversion on page 22 or Linearisation table conversion on page 23 Note Output signals in the range 0 to 1 0 volts from the SM150 corresponding to 0 to 60 water content in mineral soils see Linearisation table conversion on page 23 Note The SM150 has been optimised for warm up of 0 5 to 1 second duration It is recommended that the sensor is not powered continuously SM150 User Manual 1 Operation 17 Calibration The SM150 is provided with general calibrations for mineral and organic soils which can be used to convert the output from the sensor directly into soil moisture when used with Delta T loggers and moisture meters This section explains how these calibrations work how to adapt them for other soils and how to provide calibrations for other data loggers The SM150 measures volumetric soil moisture 6 by detecting the dielectric properties of the damp soil the permittivity or more conveniently the refractive index which is closely equivalent to Ve The SM150 response is best understood in these stages 1 Soil calibration 2 Sensor calibration 0 ve V ve Soil calibrations M150 dielectric performance mE 60 4 6 0 40 VE A 20 4 Q 00 4 i 0 0 o 20 40 s0 30 0 00 0 20 0 40 0 60 0 80 1 00 1 20 8 vol SM150 output V 3 Soil mois
8. 6 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 l 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 l 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 and J M Wraith 1999 Temperature effects on soil bulk dielectric permittivity measured by time domain reflectometry A physical model Water Resour Res 35 371 383 SM150 User Manual 1 References 34 Appendix 1 Soil specific Calibration This note provides details of 2 techniques for generating soil specific calibrations Laboratory calibration for substrates and non clay soils Laboratory calibration for clay soils We use the term substrate to refer to any artificial growing medium Underlying principle Soil moisture content 8 is proportional to the refractive index of the soil ve as measured by the SM150 see Calibration section Dielectric
9. 87 0 859 16 0 195 0 140 72 1 039 0 910 20 0 248 0 180 76 1 087 0 962 24 0 308 0 226 80 1 130 1 010 28 0 373 0 279 84 1 170 1 056 32 0 440 0 336 88 1 206 1 099 36 0 507 0 397 92 1 238 1 138 40 0 573 0 458 96 1 267 1 174 44 0 636 0 520 100 1 294 1 207 48 0 699 0 580 104 2 090 2 090 SM150 User Manual 1 Operation 23 Troubleshooting Always try to identify which part of the measurement system is the source of the difficulty For the SM150 this may fall into one of the following areas The measurement device What equipment is being used to read the probe output An HH150 or HH2 Moisture Meter A data logger such as the GP1 DL6 or DL2e Check Versions Check you have the correct versions HH2 Meter Firmware version 2 6 or later and PC software HH2Read version 2 6 or later are recommended GP1 amp DL6 Loggers DeltaLINK version 2 6 or later is required DL2e Logger Ls2Win 1 0 SR8 or later is required 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 Check that you are using an appropriate soil calibration and the correct conversion method see Calibration section The SM150 itself Try to isolate the problem into one of the following areas The SM150 or the connecting cable Then try to narrow down the area further Mechanical problems faults or damage Electrical or electronic problems or faults SM150 User Man
10. EMC directive 2004 108 EC based on the following test standards EN61326 1 2006 Electrical requirement for measurement control and laboratory use EMC requirements Group 1 Class A equipment emissions section only EN61326 1 2006 Electrical requirement for measurement control and laboratory use EMC requirements Basic Immunity immunity section only FCC compliance USA This device conforms to Part 18 of FCC rules Industrial Scientific amp Medical Equipment Note with reference to FCC Part 18 115 Elimination and investigation of harmful interference a The operator of the ISM equipment that causes harmful interference to radio services shall promptly take appropriate measures to correct the problem SM150 User Manual 1 Technical Reference 31 Definitions Volumetric Soil Moisture Content is defined as where V is the volume of water contained in the sample 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 where M is the mass of water in the sample 6 qaq_ and M is the total mass of the dry sample G M g g S To convert from v
11. User Manual for the SM150 Soil Moisture Sensor SM150 UM 1 AT Delta T Devices Ltd Notices Copyright All parts of the SM150 design and documentation are the exclusive right of Delta T Devices and covered under copyright law Copyright 2011 Delta T Devices Ltd Patents The SM150 is protected under international law by the following patents USA Patent US7944220 Europe Patent EP1836483 Australia Patent AU2005315407 China Patent Application CN101080631 EMC Compliance See page 31 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 SM150 UM 1 Nov 2011 Delta T Devices Ltd Tel 44 1638 742922 130 Low Road Burwell Fax 44 1638 743155 Cambridge CB250EJ email sales delta t co uk UK web www delta t co uk Contents Introduction Description Features Dimensions Parts list Care and Safety How the SM150 works Operation Cable Connections Installation HH150 Meter HH2 Meter Logger connections and configuration GP1 Logger DL6 Logger DL2e Logger Other data loggers Calibration Soil calibration sensor calibration Soil moisture reading Troubleshooting Technical Reference Specifications Definitions SM150 User Manual 1 0 o Ol 18 19 21 22 24 26 26 32 Introduction 3 References 34 Appendix 1 35 Soil specific Calibration 35 Laboratory
12. V is the SM150 output in Volts SM150 User Manual 1 Operation 21 0 000 0 075 0 150 0 225 Linearisation table for use over the full range of SM150 readings VE V Ve V Ve V Ve V VE 1 000 0 300 3 576 0 600 5 101 0 900 6 778 1 200 8 924 1 942 0 375 3 964 0 675 5 503 0 975 7 232 1 275 9 743 2 620 0 450 4 337 0 750 5 917 1 050 7 720 1 350 10 808 3 144 0 525 4 713 0 825 6 342 1 125 8 270 1 425 12 242 Soil moisture reading Polynomial conversion Combining the Soil calibrations and Sensor calibration steps the conversion equation becomes 1 0 14 4396V 31 2587V2 49 0575V 36 5575V 10 7117V ay Qy where a and a are the calibration coefficients For a generalised mineral soil this becomes O mineral 0 0714 1 7190V 3 7213V2 5 8402V3 4 3521V4 1 2752V And for a generalised organic soll O organic 0 0390 1 8753V 4 0596V 6 3711V3 4 7477V4 1 3911V SM150 User Manual 1 Operation 22 Linearisation table conversion The conversion from SM150 reading Volts to soil moisture 0 m m or vol can be accomplished by a look up table The following table lists the values used for the DL2e data logger Soil Mineral Organic Soil Mineral Organic moisture soil soil moisture soil soil vol Volts Volts vol Volts Volts 4 2 090 2 090 52 0 758 0 638 O 0 046 0 022 56 0 818 0 695 4 0 076 0 046 60 0 876 0 750 8 0 110 0 074 64 0 933 0 805 12 0 149 0 105 68 0 9
13. calibration 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 Technical Support Tel 44 1638 742922 Delta T Devices Ltd 130 Low Road Fax 44 1638 743155 Burwell E mail tech support delta t co uk Cambridge CB25 0EJ sales delta t co uk England UK Web www delta t co uk Index Air reading 25 C Cable Connections 10 Calibration 18 check 25 generalised 22 sensor 21 22 soil 19 22 Soil 35 soil specific 35 Care and safety 8 Care and Safety 8 Certification emc 31 Conductivity response 27 Connections 10 14 Conversions linearisation table 20 21 polynomial 20 21 Copyright 2 D Data logger 17 23 24 25 DL2e 16 23 24 DL6 15 24 GP1 14 15 24 other 17 Definitions 32 Description 5 Dielectric performance 21 refractive index 18 19 35 Dimensions 6 DL6 15 EMC 31 Exte
14. er connections and configuration GP1 Logger 4 SM150s can connect to a GP1 but results recorded via channels 3 amp 4 are less accurate Requirements GP1 logger with v1 47 firmware or later PC running DeltaLINK version 2 6 or later SM150 with SMSC sw 05 cable Channel 1 and 2 wiring SM150 wire Colour GP1 terminal Power OV brown CH1 2 GND Power V white CH1 2 PWR Signal HI blue CH1 2 Signal LO black CH1 2 Cable shield green CH1 2 GND Not used grey Not connected Channel 3 and 4 wiring SM150 wire Colour GP1 terminal Power OV brown CH1 2 GND or WET GND Power V white CH1 2 PWR or WET PWR Signal HI blue Temp3 4 IN Signal LO black Temp3 4 GND Cable shield green Temp3 4 GND or WET GND Not used grey Not connected In the DeltaLINK sensor menu configure each sensor type SM150 Note channels 1 amp 2 are wired differently to 3 amp 4 Note also that the relative positions of the terminals change on the left and right sides of the GP1 See also GP1 Quick Start Guide and the DeltaLINK on line Help SM150 User Manual 1 Operation 14 DL6 Logger 6 SM150s can be connected to a DL6 Each is wired as a differential powered sensor DL6 These details illustrate connection to channel 6 SM300 wiring Colour DL6 terminal Power OV brown OV Power V white V Signal HI blue IN Signal LO black IN Cable shield green EEE Not used grey Not connected In DeltaLINK configure c
15. g Reweigh Win 693 2g Re measure with the SM150 Vm 0 180 V Dry the sample thoroughly With clay 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 2g SM150 User Manual 1 Appendix 1 40 Calculations For the wet soll For the moist soil Calculate a Calculate ao Result Substituting in the SM150 equation Ve 1 0 14 4396V 31 2587V2 49 0575V 36 5575V4 10 7117V provides two dielectric values Vew and Vem at two Known water contents 6w and On Substituting Vw 0 349 gives J w 3 83 ao 4 0 __ 743 3 627 2 463 5 Substituting Vm 0 180 gives V m 2 84 ao t a 0 __ 693 2 627 2 for Ow 0 25 for Om e 0 14 Then a VEW V m 9 0 Ow 0m a 9 00 and do 4 Ew a 0y 1 58 Ao 1 58 a 9 00 Ao 1 58 In this example this soil is now calibrated You can now use these two numbers in place of the standard mineral or organic calibration factors to convert SM150 readings into volumetric water content using Ve a a x0 See also page Underlying principle on page 35 SM150 User Manual 1 41 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
16. hannel 6 as type SM150 See also the DL6 Quick Start Guide and the DeltaLINK online Help You need the PC logger software DeltaLINK version 2 6 or later obtainable online at www delta t co uk or from the Software and manuals CD Issue 5 SM150 User Manual 1 Operation 15 DL2e Logger Up to 60 SM150s can be connected to a DL2e Each moisture sensor is connected as a differential powered sensor These details illustrate connection to channel 58 using a LAC1 input card configured in 15 channel mode and warm up channel 63 SM150 wiring Colour DL2e terminal Power OV brown CH62 or 61 Power V white CH63 NO Signal HI blue CH58 Signal LO black CH58 Cable shield green CH61 or 62 Not used grey Not connected Note If using channel 58 ensure the LAC1 card ribbon is attached to the connecior block opposite terminal groups 46 60 See page 3 of DL2e Quick Start Guide Configure the chosen DL2e logger channels by selecting the appropriate S1M and S10 sensor types for mineral and organic soils listed in the Ls2Win sensor library See also the DL2e User Manual and the Ls2Win online help You need a PC running Ls2Win version 1 0 SR8 or later A free upgrade can be obtained from www delta t co uk or from the Software and manuals CD Issue 5 SM150 User Manual 1 Operation 16 Other data loggers The SM150 soil moisture output should be connected as a differential powered sensor Configure the logger to convert the SM
17. ied by the sample L 463 5ml Weigh the sample including the beaker Wy 743 3g SM150 User Manual 1 Appendix 1 36 Insert SM150 into the sample and record its output in Volts V 0 350 V 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 e pi d we I ae Pe I i a 3 E nye i a rad 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 Mo 627 2g reading Re insert the SM150 into the dry sample and record this Vo 0 051 V Calculate ao For the SM150 In the dry soil V Vo 0 051 Volts Substitute this into the equation Ve 1 0 14 4396V 31 2587V2 49 0575V 36 5575V4 10 7117V gives Ve 1 66 Since o 0 this is the value needed for ao Ao 1 66 Calculate 6 The water content of the wet soil 8 can be calculated from the weight of water lost during drying Ww Wo and its SM150 User Manual 1 Appendix 1 37 volume Ls 0 W W L 743 3 627 2 463 5 0 25 6 0 25 Calculate a In the wet soil V Ww 0 350 Volts and substituting gives JE 3 79 Finally a Je e Vio 0 3 79 1 66 0 25 0 8 51 a 8 51 Result Ao 1 66 ad 8 51 In this example this soil is now calibrated You can now use these t
18. include the following ee HH150 soil moisture sensor HH150 SM150 Kit HH150 includes 1m cable Connects to SM150 SMCS d HH2 1 5m cable Connects SM150 to HH2 SMSC sw 05 5m cable 100mm flying leads Connect to GP1 amp DL6 loggers SMSC Iw 05 5m cable 200mm flying leads Connect to DL2 data logger Logger extension cables EXT 5W 05 5m w EXT 5W 10 10m w EXT 5W 25 25m Extension tubes ML EX50 50cm ML EX100 100cm SM AUG 100 Spiral Auger 1 2m SM150 User Manual 1 0 Introduction 7 Care and Safety The rods of the SM150 are sharp in NF o prevent personal injury and damage to order to ease insertion Care must be the probe always store and transport the taken and handling precautions Sree nite protective lure followed CAUTION Avoid touching the rods or exposing them to other sources of static charge SHARP PINS particularly when powered up Keep the SM150 in its protective tube when not in use Take care when attaching cables to ensure that the connectors are clean undamaged and properly aligned before pushing the parts together Do not pull the SM150 out of the soil by its cable If you feel strong resistance when inserting the SM150 into soil it is likely you have encountered a stone Stop pushing and re insert at a new location Do not touch the pins particularly when the sensor is attached to a cable An electrostatic discharge from your body can typically cause a tempo
19. ns on page 26 Note for full accuracy do not use extension cables with the HH150 SM150 User Manual 1 Operation 10 Installation Surface installation and spot measurements Clear away any stones Pre form holes in very hard soils before insertion Push the SM150 into the soil until the rods are fully inserted Ensure good soil contact If you feel strong resistance when inserting the SM150 you have probably hit a stone Stop and re insert at a new location Installing at depth Make a 45mm diameter hole preferably at about 10 to the vertical using the SM AUG 100 auger Connect an extension tube e g ML EX50 Push the SM150 into the soil until rods are fully inserted Ensure good soil contact Alternatively Dig a trench and install horizontally SM150 User Manual 1 Operation 11 HH150 Meter Connect the SM150 to the HH150 meter With the meter OFF press the right off menu button This wakes and allows you to set the meter to display readings either as volumetric water content of Mineral or Organic soils or to show the sensor output in Volts Press off to save the current Setting and turn the meter off With the meter off press the left on read button to take a reading Repeat as required You may wish to write down the readings Turn on take and display reading qD Turn on show current setting Y Y iat a q Read lt j gt 7 OFF Organic
20. nsion cables 10 FCC compliance 31 Features 5 GP1 14 15 24 HH150 meter 12 HH2 25 HH2 Meter 13 Installation buried 11 insertion rod 11 surface 11 L Linearisation table 22 volts to vol 17 23 M Moisture content 5 9 34 35 O clay 19 20 32 35 36 39 mineral 18 20 22 36 37 40 Organic and Mineral 33 organic 18 20 22 33 37 stony 11 P soil calibrations 20 Specifications 2 26 Parts 7 Patent 2 T Permittivity 9 18 34 Polynomial conversion 22 Technical support 42 43 Temperature response of soil moisture R readings 28 Troubleshooting 24 References 34 Regulatory information 31 V Rods 8 9 11 Volumetric Soil Moisture 32 S W Salinity 33 Sampling Volume 29 Warning Do not touch the pins 25 Servicing 43 Water reading 25 Soil Technical Support Tel 44 1638 742922 Delta T Devices Ltd 130 Low Road Fax 44 1638 743155 Burwell E mail tech support delta t co uk Cambridge CB25 OEJ sales delta t co uk England UK Web www delta t co uk
21. olumetric to gravimetric water content use the equation 2 where p is the density of water 19 cm 0 0y x M Ps and p is the bulk density of the sample re s SM150 User Manual 1 Technical Reference 32 Organic and Mineral soil definitions The general calibrations have been optimised to cover a wide range of soil types based on the following definitions optimised use for bulk use for organic j density bulk contents range densities g cm g cm Note C denotes percentage Carbon and is a measure of organic content Salinity The preferred SI units for ionic conductivity are mS m where S is Siemens the unit of electric conductance Dimensionally it is equivalent to the inverse of resistance i e Ohm The following conversions apply 1mS m 0 01 dS m 0 01 mS cm 10 uS cm Soil salinity can be classified using the following descriptive categories non slightly moderately saline saline saline Classification of salinity See also http www land vic gov au DP Vro vrosite nsf pages water_ spotting soil salting class _ranges s1 SM150 User Manual 1 Technical Reference 33 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 2 Topp G C J L Davis and A P Annan 1980 Electromagnetic determination of soil water content Water Resour Res 1
22. ral soil calibrations Most soils can be characterised simply by choosing one of the two general calibrations we supply one for mineral soils predominantly sand silt and clay and one for organic soils with a high organic matter content Mineral Organic Soil refractive index Vz 0 0 0 2 0 4 0 6 0 8 Soil Moisture m m These values have been used to generate the polynomial conversions and linearisation tables in the Soil moisture reading section Soil specific calibration Instead of adopting these general calibrations you may wish to determine specific calibration values of and a for your soil This procedure is fairly straightforward if you can get access to standard laboratory equipment and is described in detail in Appendix 1 on page 35 Soil specific calibration can significantly improve the accuracy of individual readings but make less of an improvement to readings where installation and sampling errors are high SM150 User Manual 1 Operation 20 Sensor calibration Each SM150 is individually adjusted to provide consistent dielectric performance SM150 dielectric performance 0 40 0 60 0 80 SM150 output V This response can be approximated either by a polynomial below or by a linearisation table see next page Polynomial for use over the full range of SM300 readings Ve 1 0 14 4396V 31 2587V2 49 0575V2 36 5575V4 10 7117V where
23. rary 10mV offset in sensor readings for up to one hour At worse it may permanently damage the sensor SM150 User Manual 1 Introduction 8 How the SM150 works When power is applied to the SM750 The waveform is applied to a pair of stainless steel rods which transmit an electromagnetic field into the soil The water content of the soil surrounding the rods dominates its permittivity 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 V which is detected by the SM150 resulting in a stable out voltage output that acts as a simple sensitive measure of soil moisture content SM150 User Manual 1 0 Introduction 9 Operation Cable Connections HH150 includes 1m cable Connects to SM150 SMCS d HH2 1 5m cable Connects SM150 to HH2 Logger extension cables EXT 5W 05 5m ali EXT 5W 10 10m ae EXT 5W 25 25m For wiring colour codes see Logger connections and configuration on page 14 Take care when attaching cables to ensure that the conneciors are clean undamaged and properly aligned before pushing the parts together Screw together firmly to ensure the connection is water tight Extension cables can be joined up to a recommended maximum of 100m for GP1 DL6 or DL2e data loggers see Specificatio
24. size Full accuracy requires a soil volume of one litre but the additional error from taking a reading in a 0 5 litre sample is negligible SM150s may interact if they are placed too close together they should be separated by at least 100mm SM150 User Manual 1 Technical Reference 29 If the SM150 is inserted too close to the wall of a plant pot the sensing field can see outside the pot This behaviour is shown in the graph below SM150 Error close to wall of plant pot live pin nearest to pot wall a cr i v x e o i w Gap between SM150 body and wall of pot mm For best results keep a gap of at least 25mm 1 inch between the body of the sensor and the wall of the plant pot SM150 User Manual 1 Technical Reference 30 Electromagnetic Compatibility EMC General information SM150 is a Class A product intended for operation in non residential environments Only use cables and accessories authorised by Delta T sensor cables from other sources for example may adversely affect product performance and affect quality of results If possible route cables along the soil surface or bury them this also reduces possible trip hazard and animal damage Do not modify the product or its supplied accessories see also SM150 EMC Guidance on the Software and Manuals CD Issue 5 Regulatory information Europe This device conforms to the essential requirements of the
25. ting 25 Technical Reference Specifications O to 100 vol but less accurate above 70 vol 5 vol over 100 to 1000 mS m and 0 60 vol Output signal 0 1 V differential 0 to 60 nominal Output compatible with HH150 HH2 GP1 DL6 DL2e Maximum cable length 1m HH150 meter 100m GP1 DL6 and DL2e data loggers 143 x 40 mm diameter 0 1 kg i In water no soil present the reading may not be 100 vol It depends on a0 and a1 but can still be used as a quick check that the unit is working See also page 25 4 With Delta T supplied cables SM150 User Manual 1 Technical Reference 26 Conductivity response This chart shows how salinity affects the output of the soil moisture sensor at various soil moisture levels SM150 conductivity response at different water contents 100 water 60 45 38 30 20 2 p gt Q gt O O LA i N 200 300 400 Conductivity EC mS m non slightly moderately saline saline saline Classification of salinity SM150 User Manual 1 Technical Reference 27 Temperature response of soil moisture readings The effect of temperature on the SM150 soil moisture readings in any particular soil will depend on a combination of effects The SM150 soil moisture electronics has very low temperature sensitivity and makes a negligible contribution to the overall sensitivity The refractive index of water Ve see Calibration section
26. ture reading V 6 M150 soil moisture reading 80 Organic 6056 Mineral 40 4 8 20 o t 0 0 0 2 0 4 0 6 0 8 10 SM150 output V SM150 User Manual 1 Operation 18 Soil calibration Damp soil is essentially a mixture of soil particles air and water and together these components determine its dielectric properties including the refractive index vs The refractive index of the mixture is approximated simply by adding the contributions from the individual components ref 4 For a particular soil the contribution from the soil particles can be assumed to be constant so the refractive index measured by the SM150 is only affected by changes to the water content 8 This relationship simplifies to V a a 0 where the coefficients a and a conveniently parameterise the dielectric properties of soils Soil calibrations 2 ro En fo lt I Slope a iS fo Pe Ww gt x a 5 v 2 40 pe Q Sa q o Sa Te A Offset ao ro 0 2 0 4 0 6 Soil moisture m m Note that Ay JEay soi S USUally between 1 3 to 2 3 a corresponds approximately to 1 and usually takes a value about 8 0 Real soil values for and a can vary significantly from these guidelines when they are affected by other factors in particular bound water in clay may result in higher values of aj SM150 User Manual 1 Operation 19 Gene
27. ual 1 Troubleshooting 24 Functional check Air reading Hold the SM150 in air and away from other objects and take a reading using an HH150 or HH2 meter or voltmeter or a logger with no more than 5m of cable Warning Do not touch the pins A typical electrostatic discharge from your body can create a temporary 10mV offset in sensor readings lasting an hour In air an SM150 gives an output of 0 4mV Note the HH150 reports under range if the reading is less than zero Water reading Immerse the pins in water and measure the output in volts In the UK the sensor will typically read about 1 5 volts in tap water because the salinity is typically 5 0mS m 1 The water reading you get will depend on the salinity of your local water Note HH150 meter indicates TOO WET above 1 5V or 85 vol SM150 fully immersed in water as read by HH150 and HH2 meters 100 00 Soil moisture TOO WET readings are not 90 00 correct when no 80 00 soil is present i e at 70 00 100 vol 60 00 SM150 tables and polynomial 40 00 constants are Volts imi ERN ee at 220 vol mineral mS m for soil 20 00 vol organic moisture values 10 00 below 70 vol 0 00 50 00 wn e gt w Q gt O 200 300 400 Conductivity EC mS m Graph showing the effect of salinity on SM150 sensor output when fully immersed in water with no soil present SM150 User Manual 1 Troubleshoo
28. wo numbers in place of the standard mineral or organic calibration factors to convert SM150 readings into volumetric water content 8 using Je a a x0 See also page Underlying principle on page 35 SM150 User Manual 1 Appendix 1 38 Laboratory calibration for clay soils This technique is adapted to avoid the near impossibility of inserting the SM150 into completely dry clay soil It requires taking measurements at 2 significantly different but still damp moisture levels Equipment you will need SM150 and meter Soil corer Heat resistant beaker gt 500ml Weighing balance accurate to lt 19 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 Weigh the wet sample including the beaker Wy 743 3g SM150 User Manual 1 Appendix 1 39 Insert SM150 into the wet sample and record its output in Volts Vw 0 349 V 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 readin
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