Delta-T Devices WET150 User Manual
  1. Manuals
  2. Brands
  3. Delta-T Devices Manuals
  4. Accessories
  5. WET150
  6. User manual

Delta-T Devices WET150 User Manual

Hide thumbs Also See for WET150:
Table of Contents

Advertisement

Quick Links

Download this manual
User Manual for the
WET150 Sensor
WET150
type
W ET 1 50 - U M- 1 . 1
Delta-T Devices Ltd

Advertisement

Table of Contents
loading
Need help?

Need help?

Do you have a question about the WET150 and is the answer not in the manual?

Questions and answers

Related Manuals for Delta-T Devices WET150

Summary of Contents for Delta-T Devices WET150

  • Page 1 User Manual for the WET150 Sensor WET150 type W ET 1 50 - U M- 1 . 1 Delta-T Devices Ltd...

  • Page 2: Notices

    Design changes Delta-T Devices Ltd reserves the right to change the design and specification of its products at any time without prior notice. Patents...

  • Page 3: Table Of Contents

    Use with a WET150 Meter Take a Reading Options WET150 Meter Buttons Temperature Pore Water EC (ECp) Use WET150 Meter to Change Address Network Cabling Maximum cable length and network size Connecting to loggers or controllers Wiring Other loggers and systems wiring:...
  • Page 4 Power supply Power supply and communication Warm-up time Multiple WET150s in a network Other data loggers Installation in the Ground Surface installation and spot measurements Installing at depth SDI-12 commands Address Query Address Assign Identify Table of default / pre-configured measurements36 Specifications Edge Effects Trouble Shooting...

  • Page 5: Introduction

    Introduction SDI-12 Industry-standard digital Cables interface, compliant to version 1.3 To meter Connector Extension cables Fully waterproof M12 connector - To GP2 and other loggers Installation Threads enable extension rods to be screwed on for easy insertion in augured holes – minimising soil disturbance Detectors Soil moisture content...

  • Page 6: Description

    Description The WET150 Sensor is a multi-parameter sensor for use in soils, substrates and other growing media. It measures the dielectric properties of the soil and calculates: • ater Content • lectrical Conductivity • emperature The sensor converts the measured dielectric properties into...

  • Page 7: How The Wet150 Sensor Works

    How the WET150 Sensor works Measurement Principle When you insert the WET150 Sensor into soil and take a reading..it generates a 100 MHz signal..which is applied to the pins and produces a small electromagnetic field within the soil.

  • Page 8: Parts And Accessories

    Parts and Accessories WET150 sensor WET150 Kit WET150 + WET150 Meter 5m cable with 200 mm flying leads. Connects WET150 to GP2 SMSC/lw-05 directly, or via SDI-12 network of EXT/5W-xx cables 1 m, 5 m,10 m and 25 m EXT/5W-01...

  • Page 9: Care And Safety

    • Do not pull the WET150 out of the soil by its cable. • If you feel strong resistance when inserting the WET150 into soil, it is likely you have encountered a stone. Stop pushing and re-insert at a new location.

  • Page 10: Use With A Wet150 Meter

    Use it to take readings or change the address. Settings for soil type, conductivity units and temperature units can also be changed. Take a Reading Gently insert WET150 pins into soil or substrate. 2. Press READ to take and display water content, temperature and pore water conductivity.

  • Page 11: Temperature

    Temperature he thermistor in the WET150 is internal to the white body, so it can be slow to equilibrate with the soil temperature. This can affect the EC measurement accuracy as the conductivity of typical plant nutrients changes by ~2% / °C. If for use as a portable sensor, use it in well- equilibrated environments where the air temperature doesn’t differ...

  • Page 12: Use Wet150 Meter To Change Address

    Each sensor must have a different address on an SDI-12 network or it will not work. You can use this key stroke sequence on a WET150 Meter to change the SDI-12 address of any attached SDI-12 sensor*, including WET150 or PR2s*.

  • Page 13: Network Cabling

    M12 connectors on cables and the WET150 are waterproof to an IP rating of IP68, but must be screwed together tightly to form this waterproof seal. Failure to sufficiently tighten the thumb-screw / collar may allow water ingress into the cable or sensor, leading to premature failure which is not covered by warranty.

  • Page 14: Maximum Cable Length And Network Size

    The theoretical maximum number of sensors on any SDI-12 network is 62, as defined by valid address ranges 0-9, A-Z, a-z. Tests so far have shown that at least 35 WET150 sensors can be connected to one GP2 logger/controller. The test was performed using a star configuration with each WET150 connected using 2m cables.

  • Page 15: Connecting To Loggers Or Controllers

    Connecting to loggers or controllers The WET150 is fully compliant with the SDI-12 communication protocol standard (version 1.3). Because of this the WET150 can be used with any third-party logging or metering device which is also SDI-12 compliant as well as with Delta-T Devices GP2 logger controllers and the WET150 Meter.

  • Page 16: Gp2 Wiring Using Internal Power

    This is a shielded 5-way, 5-metre-long cable with bare wires on one end and a 5-way M12 connector on the other. Use this to connect one WET150 directly to a GP2, or with the addition of other 5-way M12 extension cables and T-pieces, connect multiple sensors in a network.

  • Page 17: Gp2 Wiring Using External Power

    If the WET150 is used in conjunction with other more power-hungry SDI-12 sensors, it may be desirable to use a larger external power supply for the SDI-12 network.

  • Page 18: Give Each Wet150 A Unique Address

    Delta-T website at: www.delta-t.co.uk/software/deltalink DeltaLINK version 3.9 or later is required for use with the WET150. If your existing install of DeltaLINK is older than this version, please install the latest version to gain access to WET150 libraries. DeltaLINK is available for Microsoft Windows only.

  • Page 19: Open Deltalink Transparent Mode

    We usually expect the address of a new sensor is to be zero, but it might not be. If you already have another sensor with the same address on the same network the command will not work. Give Each WET150 a Unique Address ⚫ 19...

  • Page 20: Change The Address

    Send a command to change its address You type aAb! Reply The WET150 is now at address b. It could be anything from a to z, A to Z, or 0 to 9. Avoid address 0 as it tends to be the default used in new sensors and putting more than one sensor on the network with the same address will crash the network.

  • Page 21: Create Gp2 Program

    Create GP2 Program 1: Add a WET150 SDI-12 Measurement Change Illustration: showing steps in the creation of a WET150 soil moisture sensor measurement type in a GP2 program. 1. With DeltaLINK 3.9 or later running on your PC and connected to a GP2 select Program.
  • Page 22 1 hour recording period. 5. Select the Address to that of the WET150 sensor, as described on page18. You should now see the following: Illustration: showing three sensor measurement types added to take readings from a single WET150, for soil moisture, pore water conductivity and temperature.

  • Page 23: 2: Sensor Type Settings

    This explains the Measurement and Parameter settings supplied in the WET150 sensor types in the DeltaLINK sensor library. Sensor type: This is the name of the default WET150 Sensor type as loaded from in the GP2 sensor library. Change the Measurement name to anything useful e.g Theta (100mm) or Treatment A.
  • Page 24 SDI-12 network with other sensors, or else the network will crash. See also Give Each WET150 a Unique Address on page 18. Mode: The default WET150 sensor type uses the SDI-12 Sequential data measurement and reporting method.

  • Page 25: 3: Set Recording Intervals

    For instance, if sandy it may drain quickly, in which case the fastest recording rate possible is about once every 5 seconds for one WET150 on a GP2. (62 sensors may take 50-55 seconds in the standard, sequential mode). In a heavy clay you may wish to start recording once per hour and wait and see how quickly the soil responds to wetting and drying events.
  • Page 26 Power supply Power supply and communication The WET150 operates from a 6 to 20 Volt DC power supply. Power can be applied continuously, or for greater battery economy just as needed when taking measurements. The power, ground and SDI-12 data pins all have protection against accidental reverse voltage or mis-wiring of the connections up to 24 Volts.
  • Page 27 WET150s in the network. Only one WET150 is fully active at a time. All the others are either in SDI-12 network activity mode when the data line is active, or idle mode when it is not.
  • Page 28 The time taken for SDI-12 commands to be sent by the logger and for measurement results to be reported back by the WET150 forms a large part of the overall measurement time. This is due to the communication speed required by the SDI-12 specification.
  • Page 29 Conversion to Soil Moisture section. Alternatively, by using one of the available SDI-12 commands, a WET150 can be instructed to output data in soil moisture units, for a range of soils. See WET150 SDI-12 Programmers Guide.pdf.
  • Page 30 Clear away any stones. Pre-form holes in very hard soils before insertion. ◼ Push the WET150 into the soil, fully inserting the pins to ensure good soil contact. If you feel strong resistance when inserting the WET150, you have probably hit a stone. Stop, and re-insert at a new location.
  • Page 31 ◼ Auger a 45mm diameter hole. ~10° to vertical is recommended. ◼ Fit an extension tube to the WET150 – remember to pass the cable through the extension tube and fit the connector first. ◼ Push the WET150 into the soil, fully inserting the pins to ensure good soil contact.
  • Page 32 The following examples explain what you need to type in the command entry box and how to interpret responses in the terminal window. Full details of these and all SDI-12 commands used by the WET150 are given in the WET150 SDI-12 Programmer’s Guide available as a PDF at www.delta-t.co.uk...
  • Page 33 GP2 logger/controller. If more than one sensor is connected when the address query command is issued, all sensors will respond at the same time causing network corruption. With just one WET150 connected to the GP2, type into the DeltaLINK transparent mode terminal window: Type in Press the <ENTER>...
  • Page 34 WET150, the Address Assign command can be sent specifically for that addressed sensor to change its address. At this stage it is best if just one WET150 connected to the GP2, particularly if you are configuring brand new sensors which may all be configured respond on the same address.
  • Page 35 This command can also be used to identify if a specific SDI-12 address is already in use within the network. In this example WET150 at address d will be queried. Using the DeltaLINK transparent mode terminal window.
  • Page 36 Table of default / pre-configured measurements The WET150 can use any of these measurement sets (shown in detail on the next page) as sequential or concurrent measurements, either with or without CRC error checking. In summary, these measurement commands are:...
  • Page 37 The factory defaults for the ten pre-configured measurement sets (shown only using the M command for clarity) are: Response Command Units Notes parameters Ɛ (permittivity) (none) (pore water Compensated to 25°C linearly at 2%/°C, soil mS.m parameter= 4.1 °C Water content %vol Using Mineral soil-type calibration (pore water...
  • Page 38 Multi-parameter measurement sets M and M1 to M8 in the table above can be customised to better suit your application, particularly for use with third- party (non-Delta-T Devices) loggers and controllers. For information on how to make these measurement customisations see the WET150 SDI-12 Programmer’s Guide.
  • Page 39 Lower limit soil Generic soil-type moisture content for calibration calculation Mineral 12.67 %vol Organic 17.72 %vol PeatMix 21.22 %vol Coir 20.30 %vol MinWool 21.43 %vol Perlite 24.57 %vol For further SDI-12 commands see the WET150 SDI-12 Programmer’s Guide. SDI-12 commands ⚫ 39...
  • Page 40 Soil conductivity (ECb)) Accuracy ±(10 mS/m + 6%) from 0 to 1200 mS/m Operating range 0 to 2000 mS/m Temperature (WET150 must be fully buried to accurately measure soil temperature) Accuracy ± 1°C Accurate range: -20 to+ 50°C Range Full range: -20 to +60°C...
  • Page 41 Keep the sensor pins away from the edge of plant plots if possible, to avoid the edge effect shown in the graph below. WET150 Error close to wall of plant pot. live pin nearest to pot wall Gap between WET150 body and wall of pot (mm) Specifications ⚫ 41...
  • Page 42 See Note about Pore EC (EC ) calculations: on page 39 for more information. All other error codes indicate a possible sensor fault condition. Please contact Delta-T devices support for assistance. See also: Technical Support on page 62 42 ⚫ Trouble Shooting...
  • Page 43 The processor in the WET150 then calculates the dielectric properties of the soil or substrate from these impedance measurements to give: Real permittivity Ɛ′...
  • Page 44 Water 80.4 When these and other materials are combined together to form a soil or substrate, the WET150 detects the overall mixed bulk permittivity which is formed from their individual permittivity contributions, depending upon their relative quantity in the mix Converting permittivity to water content The relationship between soil permittivity (Ɛ′) and its equivalent...
  • Page 45 where the coefficients �� and �� conveniently parameterise the dielectric properties of the soil. Soil calibrations Slope (a Offset (a Soil moisture (m Note that: �� = √ Ɛ′ is usually between 1.3 and 2.3 ������_�������� �� corresponds approximately to √Ɛ′ −...
  • Page 46 Mineral Organic Soil Moisture (m In DeltaLINK, the soil type for a WET150 logging program can be selected from a drop-down in the properties panel on the right of the program editor window, under the calculation section. This auto-populates the ��...
  • Page 47 The WET150 is also able to directly compute and output soil water content for the generic soil types (on page 46). The pre-...
  • Page 48 Note: . As the properties panel is context sensitive, the ‘Theta’ measurement must first be selected in the overview panel on the left of the program editor window. The WET150 is also able to directly compute and output soil soil- water content using custom ��...
  • Page 49 Technical Reference Dielectric properties When an electric field passes through a material (such as soil) some of the energy in the field is transmitted (unchanged), some is reflected, some is stored and finally some is absorbed and converted into heat. The extent to which each of these occurs within a particular material is determined by its dielectric...
  • Page 50 Measuring Soil Moisture Whalley (1993), White, Knight, Zeggelin and Topp 1994) have shown that there is a simple linear relationship between the   complex refractive index (which is equivalent to  ), and  volumetric water content, , of the form: ...
  • Page 51   relationship between , and explains how this is used within the WET150 Sensor to derive readings of pore water conductivity. Bulk Soil Conductivity v. Pore Water Conductivity Consider the water that can be extracted from the pores of the soil matrix.
  • Page 52 WET150 Sensor  The complex permittivity of the pore water, , is equal to that of pure water. The real part of the complex permittivity of the pore  water = 80.3 at 20°C, with a temperature coefficient of about -...
  • Page 53  where is a geometry factor which is determined by the distance between the electrodes and their areas in contact with the soil. Note that contact problems of the electrodes with the  soil will be reflected in The equivalent circuit for such a lossy capacitor is a loss-free capacitor, , with a conductor, , in parallel.
  • Page 54   (S.m (S.m   Fig. 1 Examples of the relationship between , showing the  offset for two different soils.    The relationship between the bulk soil parameters   the corresponding pore water parameters is different when the water present is bound to the soil matrix rather than free water.
  • Page 55 References • Topp, G. C., J. L. Davis, A. P Annan (1980). Electromagnetic determination of soil water content. Water Resour. Res 16(3) 574-582 • Whalley, W R (1993). Considerations on the use of time-domain reflectometry (TDR) for measuring soil moisture content.
  • Page 56 Definitions Volumetric Soil Moisture Content �� �� �� �� �� �� where is the volume of water contained in the sample is the total volume of the soil sample. The preferred units for this ratio are m , though %vol is frequently used.
  • Page 57 Organic and Mineral soil definitions: The general calibrations have been optimised to cover a wide range of soil types, based on the following definitions: Soil type optimised use for bulk use for around organic density bulk organic contents: range: densities: content: (g.cm (g.cm...
  • Page 58 Electrical Conductivity The Electrical Conductivity (EC) of a material is a measure of its ability to carry an electrical current. It is an “intrinsic” property of the material into which the electrodes are inserted, i.e. a property which is defined at a point and does not depend on how much material is present (q.v.
  • Page 59 Permittivity is commonly used as a means of measuring water content, because the real permittivity of water is ~80 at 20 MHz, 25°C, whereas the permittivity of most soil particles is typically in the range 3 to 8. Dielectric Best used as a descriptive term, e.g. “dielectric materials” usually refers to insulating materials with a high relative permittivity.
  • Page 60 Wilting Point The moisture content at which a particular crop is unable to extract any more water. Conventionally this is taken to correspond to a matric potential of –1500 kPa, but it’s really much more variable than that suggests. It’s a property of soil type and crop type, and can vary between about 0.04 m sandy soils to 0.22 m for clay soils.
  • Page 61 Extended Warranty All Delta-T Devices products have a two-year (24 month) warranty as standard, but the WET150, ML3, SM150T and SM300 soil moisture sensors benefit from a 5-year warranty (60 months from date of delivery). Simply register the product(s) with us via and we will add 3 more years to the standard warranty, extending it to the full 5 years duration.
  • Page 62 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 Fax: +44 1638 743155 130 Low Road E-mail: tech.support@delta-t.co.uk Burwell sales@delta-t.co.uk...
  • Page 63 Underlying principle Soil moisture content ( θ ) is proportional to the refractive index of the soil () as measured by the WET150 (see How it works on page 43) The goal of calibration is to generate two coefficients (a0, a1)
  • Page 64 Equipment you will need: • WET150 and WET150 Meter with the Soil type set to “RAW”. • Soil corer (if doing a calibration for a cohesive soil rather than sand or a substrate) •...
  • Page 65 Insert WET150 into the sample, press [Read] on ε’ the meter and record the permittivity reading ( ε ε √ = 9.06, I.e. = 3.01 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 66 WET150 readings into volumetric water content θ using:    See the WET150 SDI-12 Programmer’s Guide for details on how to configure the WET150 to output soil moisture readings directly using custom calibrations. See also Underlying principle on page 63.
  • Page 67 Laboratory calibration for clay soils This technique is adapted to avoid the difficulty of inserting the WET150 into completely dry clay soil. It requires taking measurements at 2 significantly different, but still damp, moisture levels. Equipment you will need: •...
  • Page 68 Reweigh. = 1573g 1573.0 Re-insert the WET150 into the moist sample and again record the permittivity reading. ε ε √ = 9.06, I.e.
  • Page 69 WET150 readings into volumetric water content θ using:    See the WET150 SDI-12 Programmer’s Guide for details on how to configure the WET150 to output soil moisture readings directly using custom calibrations. See also Underlying principle on page 63.
  • Page 70 Care and Safety, 9 GP2 logger CE conformity, 2 12V output for sensors, 26 Change Address GP2 Program using WET150 Meter, 12 Add WET150 sensor, 21 Concurrent Measurements, 27 GP2-NTP, 8 Conductivity Gravimetric Soil Moisture, 56 Electrical, 6, 51, 58...
  • Page 71 28 Maximum cable length, 14, 40 wiring, 15 Measurement name, 23 SDI12 commands, 32 change to show address in results, SDI12 WET150 Measurement Commands, 36 Measurement Principle, 7 Send data Command ML/EX50, 8 SDI12 command, 24 Mode, 24...
  • Page 72 Warranty, 61 Wilting Point, 60 Water content, 6, 7, 50, 51, 53, 54, Wiring, 15 55, 59 Wiring connection Water deficit, 60 external SDI12 power with GP2, WET150 Kit, 8 WET150 Meter, 10 72 ⚫ Index...

Table of Contents