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Related Manuals for Delta-T WET150
Summary of Contents for Delta-T WET150
- Page 1 Version 2.0 User Manual for the WET150 sensor Doc No.: WET150-UM-01-2...
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Page 2: Notices
The WET150 Sensor conforms to UK regulations regarding electromagnetic emissions and susceptibility when used according to the instructions contained within this user manual, and is UKCA marked by Delta-T Devices Ltd CE conformity The WET150 Sensor conforms to EC regulations regarding electromagnetic... -
Page 3: Table Of Contents
Parts and Accessories Use with a WET150 Meter Take a Reading Options WET150 Meter Buttons Using the WET150 Meter to Change Address Connecting to Loggers & Controllers Wiring Non-Delta-T loggers and systems wiring: GP2 wiring (1): Using internal power GP2 wiring (2): Using external power... - Page 4 Dielectric properties Measuring Soil Moisture Pore water conductivity References Definitions Technical Support Soil-specific Calibration Laboratory calibration for non-clay soils Laboratory calibration for clay soils Soil-specific Parameter Derivation Appendix 2 Soil-specific Parameters Index 4 ⚫ Contents Copyright © 2022 Delta-T Devices Ltd...
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Page 5: Getting Started
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 6: Introduction
Introduction SDI-12 Industry-standard digital Cables interface, compliant to version 1.3 To Meter Extension cables Connector To GP2 and other Fully waterproof loggers M12 connector Installation Threads enable extension rods to be screwed on for easy insertion in augured holes – minimising soil disturbance Detectors Soil moisture content... -
Page 7: 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 Water Content over... -
Page 8: Parts And Accessories
1 m, 5 m,10 m and 25 m EXT/5W-01 extension cables with 5-way EXT/5W-05 M12 connectors. Connects EXT/5W-10 WET150 to an SDI-12 sensor EXT/5W-25 network 4-pin network T- Piece for networking of SDI12 sensors GP2-STP1 and EXT/5W-xx cables. Not to be used for logger communication networks. -
Page 9: Use With A Wet150 Meter
Use with a WET150 Meter The WET150 Meter Kit enables portable monitoring of water content, electrical conductivity and temperature. It can also be used to change the address of an SDI12 sensor. Settings for soil type, conductivity units and temperature units can be customised. -
Page 10: Using The Wet150 Meter To Change Address
The address must be set BEFORE attaching to the network. 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. Only attach one sensor at a time to a WET150 Meter. -
Page 11: Connecting To Loggers & Controllers
Connecting to Loggers & 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. -
Page 12: Gp2 Wiring (1): Using Internal Power
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 13: Gp2 Wiring (2): Using External Power
GP2 wiring (2): Using external power The WET150 is a highly energy efficient sensor. Depending upon the measurement frequency and the number of WET150 sensors in the network, the internal GP2 logger/controller batteries are capable of providing power for many tens of thousands of sensor readings over periods longer than a year. -
Page 14: Assigning Addresses Using A Gp2
0 to 9, a to z or A to Z. Use either a WET150 Meter connected directly to a WET150 sensor - see page 5, or use a GP2 and PC running DeltaLINK as described below. -
Page 15: 1: Open Deltalink Transparent Mode
Once the SDI-12 Transparent Mode Terminal is open, the GP2 behaves like a transparent serial link between SDI-12 sensors and the PC. 2: Find out WET150’s current address Send a command to tell the sensor to reply with its address. -
Page 16: 3: Change The Address
You type 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. Any sensors which share the same address on the network will be unable to communicate. -
Page 17: 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. With DeltaLINK 3.9 or later running on your PC and connected to a GP2 select Program. - Page 18 1 hour recording period. Select the Address to that of the WET150 sensor, as described on page14. 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.
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Page 19: 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 20 Address: Enter the WET150 address so the GP2 will know which sensor to contact. You must do this. Use DeltaLINK, SDI-12, Transparent mode (or a WET150 Meter) to give it a unique address before putting it on the SDI-12 network with other sensors, or else the network will crash.
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Page 21: 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 22: Networking
Networking One WET150 can be read with a WET150 Meter. Multiple WET150s need a GP2 or other SDI-12 controller. Delta-T extension cables are terminated in M12 thumb-screw connectors. Other cable types can be used, but this system has several advantages. Cables can be joined together to extend runs, or can be connected via a T-piece to branch the network and to connect to sensors. -
Page 23: Maximum Cable Length And Network Size
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. -
Page 24: Warm-Up Time
One WET150 is instructed to take a measurement and then return its results before moving onto other 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 25 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.
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Page 26: Installation In The Ground
Installation in the Ground A video showing how to install the WET150 in the ground can be found at: https://youtu.be/ZRMUkiy-f3g or via the QR code. Surface installation and spot measurements Spot measurements Consistent technique is critical for repeatable results when taking spot measurements. -
Page 27: Installing At Depth
◼ 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 28: Sdi-12 Commands
This section gives a brief introduction to SDI-12 commands. The following command sequences are reviewed: 1. Address Query – find out the existing address of the single WET150 connected to the GP2 2. Address Assign – change the sensor’s existing address to a new address 3. -
Page 29: Address Query
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 30: Address Assign
At this stage it is best if just one WET150 is connected to the GP2, particularly if you are configuring brand new sensors which may all be configured to respond on the same address. -
Page 31: Identify
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. Press the <ENTER> key or click on the... -
Page 32: Take A Measurement
When an M! or C! command is sent, the WET150 will take a measurement, but it will not report it until asked to with a D0! command. See the SDI-12 Programmer’s Guide for more information. -
Page 33: Table Of Pre-Configured Measurements
Table of pre-configured measurements The factory defaults for the ten pre-configured measurement sets are as follows (shown only using the M command for clarity, and using a sensor address of “a”): Command Response Units Notes parameters Ɛ (permittivity) (none) (bulk EC) mS.m °C Water content... -
Page 34: Customising Measurement Sets
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. Before modifying certain of the soil-specific parameters, the “soil type” (Mineral, Organic, etc.) for the measurement set must be set to “custom”. - Page 35 If the WET150 is configured to calculate and output ECp, for example using pre- configured measurements M1 to M5, but the water content is too low to calculate a valid ECp, the WET150 will output error code -8020 (meaning “too dry”) in the place of ECp value.
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Page 36: Specifications
± (6% of reading + 10 mS.m Accurate range: 0 to 1200mS.m Operating range Full range: 0 to 2000mS.m Temperature (WET150 must be fully buried to accurately measure soil temperature) Accuracy ± 0.5 °C ± 0.7 °C Accurate range: 0 to +40 °C Full range: -20 to +60 °C... -
Page 37: Pore Water Ec (Ecp) Accuracy
Notes: [1] The WET150 has been carefully optimised to provide accurate readings in soils and substrates - readings taken in water or air may not meet the full specification. [2] The ECp contour map is based on measurements from 30 sensors at 20°C in NPL* traceable media. -
Page 38: Configuration
– for more information see the section “Technical Reference” (page 44). Please note that, when using the WET150 with a GP2 or WET150 Meter, the calculations of EC and water content are not done by the sensor but by the GP2/Meter handheld unit. -
Page 39: How It Works
Along with temperature (T, default units °C), these three measurements form the native WET150 outputs which can be logged directly or used in further calculations. It is possible to calculate the water content of any soil or substrate from its permittivity value, provided that certain composition properties of the soil or substrate are known. -
Page 40: Converting Permittivity To Water Content
WET150 is only affected by changes in water content. Also, by using the square- root of permittivity (called the refractive index), it is possible to further simplify the... - Page 41 relationship with water content as: √ Ɛ′ = �� + ( �� ∙ �� ) �� �� where the coefficients �� and �� conveniently parameterise the dielectric �� �� properties of the soil. Soil calibrations Slope (a Offset (a Soil moisture (m Note that: ��...
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Page 42: Generic Soil Calibrations
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 43: Soil-Specific Calibrations
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 water content using custom ��... -
Page 44: Technical Reference
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 some is absorbed and converted into heat. The extent to which each of these occurs within a particular material is determined by its dielectric properties. -
Page 45: Measuring Soil Moisture
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 46: Pore Water Conductivity
The following discussion proposes a theoretical basis for the 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 47 The permittivity and conductivity of the bulk soil will be denoted by the subscript b. The complex permittivity of the bulk soil, , is proportional to both and a function of , g( ). For dry soil there is no water to facilitate ionic conduction, so ...
- Page 48 In terms of the measurable bulk quantities �� = �� ��(��) [13.] �� �� ��′ = ��′ + ��′ ��(��) [14.] �� �� =�� �� �� From Eq. [13] and [14] the ionic conductivity of the pore water can be written as: ��′...
- Page 49 . Ideally, a soil parameter would be chosen to give good accuracy across most moisture levels, and while it cannot be avoided, it would also minimise the transition from accurate readings to near-infinite output. In the WET150, the “too dry” threshold can then be adjusted to prevent the anomalous readings being reported.
- Page 50 Given the wide variety of soils and substrates in terms of their composition and properties, and the simplicity of the model, these two effects (viz. the overall accuracy and the size of the transition zone) are affected by different factors, and in reality it is often not possible to optimize for both.
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Page 51: References
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. Journal of Soil Sci. 44, 1-9 •... -
Page 52: Definitions
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 53 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 bulk around organic density densities: organic contents: range: (g.cm content: (g.cm...
- Page 54 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 55 component, , represents the total energy absorption or loss. Both values are frequency and temperature dependent. Permittivity is commonly used as a means of measuring water content, because the real permittivity of water is ~80 at 100 MHz, 20°C, whereas the permittivity of most soil particles is typically in the range 3 to 8.
- Page 56 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 for sandy soils to 0.22 m for clay...
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Page 57: Technical Support
No goods or equipment should be returned to Delta-T without first obtaining the agreement of 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. - Page 58 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.
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Page 59: Soil-Specific Calibration
This is the easiest technique, but it’s not suitable for soils that shrink or become very hard when dry. 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 60 Measure the volume occupied by the sample. = 960.0ml Weigh the sample, including the beaker. = 1573g Insert WET150 into the sample, press [Read] on the ε’ meter and record the permittivity reading ( ε ε = 9.06, I.e.
- Page 61 = ��. ���� Result = 1.60 = 7.82 This soil is now calibrated - you can now use these two numbers in place of the default calibrations to convert WET150 readings into volumetric water content θ using: ...
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Page 62: Laboratory Calibration For Clay Soils
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 63 Reweigh. = 1573g Re-insert the WET150 into the moist sample and again record the permittivity reading. ε ε = 9.06, I.e.
- Page 64 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 59.
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Page 65: Soil-Specific Parameter Derivation
) and conductivity ( ) of the free water on top of the soil using the WET150 Sensor, Push the sensor down into the soil (NB Ensure your cable is well connected to avoid water leakage!) and measure the bulk ... -
Page 66: Soil-Specific Parameters
7.58 -0.3 Table 1 - WET150 sensor soil-specific parameters for improved accuracy By default, the WET150 is shipped with generic parameters that match the generic parameters in Delta-T’s WET-2 sensor. For reference these are listed below: Soil Type Soil Parameter “Too dry”... -
Page 67: Index
Cabling GP2 logger SDI12 network cabling, 15 12V output for sensors, 28 Calibration GP2 Program generalised, 9, 49 Add WET150 sensor, 23 Soil, 64 GP2-NTP, 10 soil-specific, 64 Gravimetric Soil Moisture, 57 Care and safety, 7 Ground, 17 Care and Safety, 7... - Page 68 30 warm-up time, 29 wiring, 17 Warranty, 62 SDI12 commands, 33 Water content, 9, 49, 50, 52, 55, 60 SDI12 WET150 Measurement Commands, Water deficit, 61 WET150 Kit, 10 Send data Command WET150 Meter, 13 SDI12 command, 26...