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Delta-T Devices Ltd SM300 User Manual

Soil moisture sensor
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User Manual for the
SM300
Soil Moisture Sensor
Delta-T Devices Ltd
SM300-UM-1.2

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Summary of Contents for Delta-T Devices Ltd SM300

  • Page 1 User Manual for the SM300 Soil Moisture Sensor Delta-T Devices Ltd SM300-UM-1.2...
  • Page 2 Notices Copyright All parts of the SM300 design and documentation are the exclusive right of Delta-T Devices and covered under copyright law. Copyright © 2014 Delta-T Devices Ltd. Patents The SM300 is protected under international law by the following patents:-...

  • Page 3: Table Of Contents

    Contents Introduction Description Features Dimensions Parts list Care and Safety How the SM300 works Operation Cable Connections Installation Logger connections and configuration GP1 Logger GP2 Logger Controller DL6 Logger DL2e Logger Other data loggers Logging Advice Logger Grounding HH2 Meter...
  • Page 4 Technical Support Appendix 1 Soil-specific Calibration Laboratory calibration for non-clay soils Laboratory calibration for clay soils Appendix 2: The SM300 Temperature Sensor SM300 Temperature Measurement Effect of Temperature on Water Permittivity Resistance to Temperature Lookup Table Index SM300 User Manual 1.2...

  • Page 5: Introduction

    Introduction Description The SM300 measures soil moisture content and temperature. Its 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.

  • Page 6: Dimensions

    Dimensions Cable connector sealed to IP68 M12, 5 pin, male Thread ¾inch BSP for connecting to Extension Tube(s) 22mm 40 mm SM300 User Manual 1.2 Introduction ...

  • Page 7: Parts List

    5m cable with SMSC/lw-05 200mm flying leads for DL2e logger EXT/5W-05 5, 10 and 25m EXT/5W-10 extension cables. EXT/5W-25 IP68 M12 connectors ML/EX50 50 and 100cm ML/EX100 Extension Tube SM-AUG-100 45mm spiral auger 1.2m long SM300 User Manual 1.2 Introduction ...

  • Page 8: Care And Safety

     Do not pull the SM300 out of the soil by its cable. If you feel strong resistance when inserting the SM300 into soil, it is  likely you have encountered a stone. Stop pushing and re-insert at a new location.

  • Page 9: How The Sm300 Works

    ≈ 4 and air ≈ 1) The permittivity of the soil has a strong influence on the applied field… …which is detected by the SM300, resulting in a stable voltage output that… soil moisture ...acts as a simple, sensitive measure of Soil Moisture content.

  • Page 10: Operation

    Screw together firmly to ensure the connection is water-tight.  Extension cables can be joined up to a recommended maximum of  100m – see Specifications on page 29 SM300 User Manual 1.2 Operation ...

  • Page 11: Installation

    Note: The SM300 is not suitable for soil surface temperature measurements. For soil temperature near the surface dig a trench and install horizontally as shown below. Cover both SM300 and the first 30cm of cable with at least 5cm of soil.

  • Page 12: Logger Connections And Configuration

    See also GP1 Quick Start Guide and the DeltaLINK on-line Help. You need the PC logger software DeltaLINK version 2.4 or later. A free upgrade can or from the Software and Manuals DVD. be obtained from www.delta-t.co.uk SM300 User Manual 1.2 Operation ...

  • Page 13: Gp2 Logger Controller

    Info Panel and Help or the GP2 User Manual. You need the PC logger software DeltaLINK version 3.0 or later. A free upgrade can be obtained from www.delta-t.co.uk or from the Software and Manuals DVD. SM300 User Manual 1.2 Operation ...

  • Page 14: Dl6 Logger

    DL6 Logger 6 SM300s can be connected to a DL6. Each soil moisture sensor is wired as a differential, powered sensor. A DL6 logger can only read one SM300 temperature sensor.* These details illustrate connection to channels 6 & 7:...

  • Page 15: Dl2E Logger

    See the DL2e User Manual and the Ls2Win online help You need a PC running Ls2Win version 1.0 SR6 or later. A free upgrade can be obtained from www.delta-t.co.uk or from the Software and manuals DVD. SM300 User Manual 1.2 Operation ...

  • Page 16: Other Data Loggers

    Polynomial conversion on page 25 or Linearisation table conversion on page 26 Note: Output signals in the range 0 to 1.0 volts from the SM300, corresponding to ~0 to 60% water content in mineral soils – see Linearisation table conversion on page 26.

  • Page 17: Logger Grounding

    M12 connector of an SM300 soil moisture sensor. In addition, if used in an electrically noisy environment - such as a farm or greenhouse - then the presence of a ground loop can permit AC signals to inject noise and so disrupt readings.
  • Page 18 Figure 2 This diagrams shows that if the logger is not well grounded then a potential ground loop can exist between the sensor and the power supply and/or mains power, and also the risk of galvanic corrosion to buried M12 connectors on the SM300 and cable. SM300 User Manual 1.2 Operation ...
  • Page 19 Fully grounded system Figure 3 This diagram shows the logger, power supply and sensor all grounded. This minimises the possibility of galvanic corrosion of the SM300 connector. It also minimises the possibility of nearby AC-powered machinery injecting noise into the readings.

  • Page 20: Hh2 Meter

    HH2Read to retrieve the readings. See also: Support for the SM300 Soil Moisture Sensor with an HH2 and HH2 User Manual and HH2 User Manual Addendum to V4 - SM300. Note: the HH2 does not display or store SM300 temperature readings.

  • Page 21: Calibration

    , by detecting the dielectric properties of the damp soil – the permittivity, ε, or more conveniently the refractive index, which is closely equivalent to √ε. The SM300 response is best understood in these stages: SM300 User Manual 1.2 Operation ...

  • Page 22: Soil Calibration

    [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 SM300 is only affected by changes to the water content, θ. This relationship simplifies to: ε...
  • Page 23 Appendix 1 on page 38. 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. SM300 User Manual 1.2 Operation ...

  • Page 24: Sensor Calibration

    Sensor calibration Each SM300 is individually adjusted to provide consistent dielectric performance: SM300 dielectric performance SM300 output (Volts) This response can be approximated either by a polynomial (below) or by a linearisation table (see next page): √ �� = 1.0 + 14.868�� − 33.56��...

  • Page 25: Soil Moisture Reading

    Linearisation table (for use over the full range of SM300 readings) √ε √ε √ε √ε √ε 0.000 1.000 0.300 3.556 0.600 4.956 0.900 6.471 1.200 7.961 0.075 1.963 0.375 3.913 0.675 5.327 0.975 6.841 1.275 8.411 0.150 2.641 0.450 4.254 0.750...
  • Page 26 Linearisation table conversion θ The conversion from SM300 reading (Volts) to soil moisture or %vol) can be accomplished by a look-up table. The following table lists the values used for the DL2e data logger: Mineral Organic Mineral Organic Soil Soil...

  • Page 27: Troubleshooting

    Troubleshooting Always try to identify which part of the measurement system is the source of the difficulty. For the SM300 this may fall into one of the following areas: The measurement device What equipment is being used to read the probe output? A Delta-T HH2 Moisture Meter.
  • Page 28 SM300 is functioning within expected bounds: Air reading Hold the SM300 away from other objects and take a reading using an HH2 meter, or voltmeter or logger. The reading should be 0 ±4mV when used with a 5m cable.

  • Page 29: Technical Reference

    See page 24. 6 See Appendix 2 on page 42. 7 Note: The DL6 has only one temperature channel. The DL6 error contribution to SM300 temperature measurement is negligible compared to the accuracy of the SM300 temperature sensor itself. The two only become comparable below -15C.
  • Page 30 Conductivity response This chart shows how salinity affects the output of the soil moisture sensor at various soil moisture levels. SM300 conductivity response at different water contents 100% (water) ~60% ~45% ~38% ~30% ~20% Conductivity EC (mS.m non- slightly moderately...
  • Page 31 The last two effects partially offset each other, but in soil conditions where one or the other effect dominates, the SM300 will appear to have a significant temperature response. This illustration is based on the model in reference 7, see page 36.
  • Page 32 SM300s may interact if they are placed too close together – they should be separated by at least 100mm. If the SM300 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.
  • Page 33 Electromagnetic Compatibility (EMC) General information SM300 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).

  • Page 34: Definitions

    To convert from volumetric to gravimetric water content, use the equation ρ where is the density of water (= 1g.cm ρ θ θ × ρ ρ is the bulk density of the sample ( SM300 User Manual 1.2 Technical Reference ...
  • Page 35 = 10 µS.cm Soil salinity can be classified using the following descriptive categories: non- slightly moderately strongly extremely saline saline saline saline saline 1000 1200 1400 1600 mS.m dS.m Classification of salinity See also http://www.land.vic.gov.au/DPI/Vro/vrosite.nsf/pages/water_spotting_soil_salting_class_ranges#s1 SM300 User Manual 1.2 Technical Reference ...

  • Page 36: References

    Water Resour. Res., 28, 2345-2352 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 SM300 User Manual 1.2 References ...

  • Page 37: Technical Support

    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. SM300 User Manual 1.2 Technical Support ...
  • Page 38 Contact details: Technical Support Tel: +44 1638 742922 Delta-T Devices Ltd Fax: +44 1638 743155 130 Low Road E-mail: tech.support@delta-t.co.uk Burwell sales@delta-t.co.uk Cambridge CB25 0EJ Web: www.delta-t.co.uk England (UK) SM300 User Manual 1.2 Technical Support ...

  • Page 39: Soil-Specific Calibration

    We use the term substrate to refer to any artificial growing medium. Underlying principle Soil moisture content (θ) is proportional to the refractive index of the soil (√ε) as measured by the SM300 (see Calibration section). The goal of calibration is to generate two coefficients (a ) which can be used in a linear equation to convert probe readings into soil moisture: ε...

  • Page 40: Laboratory Calibration For Non-Clay Soils

    Measure the volume occupied by the sample. = 463.5ml Weigh the sample, including the beaker. = 743.3g SM300 User Manual 1.2 Appendix 1 ...
  • Page 41 Insert SM300 into the sample and record its output in Volts. = 0.350V 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).
  • Page 42 = 1.68 = 8.44 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 SM300 readings into volumetric water content θ using: ε θ...

  • Page 43: Laboratory Calibration For Clay Soils

    Laboratory calibration for clay soils This technique is adapted to avoid the near-impossibility of inserting the SM300 into completely dry clay soil. It requires taking measurements at 2 significantly different, but still damp, moisture levels. Equipment you will need: ...
  • Page 44 Insert SM300 into the wet sample and record its output in Volts. = 0.349V 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.
  • Page 45 = 8.69 = 1.61 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 SM300 readings into volumetric water content θ using: ε θ...

  • Page 46: Appendix 2

    Appendix 2: The SM300 Temperature Sensor Soil moisture content is used with the measurement of soil temperature in several major application areas including the following: Global warming and climate studies Soils contain more than four times as much carbon as the CO2 in...

  • Page 47: Sm300 Temperature Measurement

    SM300 Temperature Measurement The SM300 Temperature sensor uses a thermistor with a 10K resistance at 25 ˚C. However: A. This sensor has a different response curve from the more widely used 10K3A1B type. The response curve is given in the Resistance to Temperature Lookup Table on page 50.
  • Page 48 R = R5 + (0.9 x Rc – 0.297) kΩ where R5 = value supplied in the table for the ‘SM300 Temp, 5m’ sensor type. Lex = length of extension cable, excluding the 5m of SMSC/lw-05 cable. Rc = total cable resistance, including resistance of SMSC/lw-05 cable, if fitted.

  • Page 49: Effect Of Temperature On Water Permittivity

    R = a0 + a1 * Rmeas Where: a0 = – Ic.Rc.Rref / Vref a1 = 1 – Ic.Rc / Vref Ic = 18 mA (SM300 sensor supply current) For Delta-T EXT/5W-xx series cables: Rc = 0.066 Ω.m For the SMSC/lw-05 5m logger cable Rc = 0.33 Ω...

  • Page 50: Resistance To Temperature Lookup Table

    Resistance to Temperature Lookup Table Temperature Resistance degrees C Kohms SM300 Resistance to Temperature 90.538 Conversion Chart 77.683 66.854 57.713 49.968 43.379 Resistance 37.759 (kOhms) 32.957 28.844 25.299 22.244 19.608 17.321 15.334 13.606 12.098 10.780 9.623 8.611 7.720 6.935 6.241 5.627...

  • Page 51: Index

    Conversions hydrogeology, 46 linearisation table, 23, 24 polynomial, 23, 24 Installation buried, 11 Data logger, 16, 26, 27, 28 insertion rod, 11 DL2e, 26, 27 surface, 11 DL6, 27 GP1, 14, 27 other, 16 SM300 User Manual 1.2 Index ...
  • Page 52 48 Temperature Sensor Lookup Table, 50 Troubleshooting, 27 References, 36 Regulatory information, 33 Rods, 8, 9, 11 Volumetric Soil Moisture, 34 Sales code, 7 Warning : Do not touch the pins, 28 Salinity, 35 SM300 User Manual 1.2 Index ...

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