Delta-T WET150 Soil Moisture Sensor User Guide

: June 6, 2024
: Delta-T

Table of Contents

The WET150
System parts (not to scale)
Care and maintenance
Installation
Connections
Connection to a GP2 data logger
- Using external power
GP2 configuration
SDI-12 commands
Specifications
References
Read User Manual Online (PDF format)
Download This Manual (PDF format)

Delta-T WET150 Soil Moisture Sensor User Guide

The WET150

System parts (not to scale)

System parts | WET150 sensor| Note: the WET150 and Meter are sold together as the WET150 kit with a dedicated Quick Start Guide
---|---|---
| WET150 Meter
| SMSC/lw-05m 5m cable with 200mm flying leads
| EXT/5w-01

EXT/5w-05 1, 5, 10 and 25m extension cables

EXT/5w-10

EXT/5w-25

| GP2-NTP T-connector
System parts | ML/EX50

ML/EX100 extension tubes

System parts | SM-AUG-100 45mm spiral auger

Care and maintenance

Do not touch the WET150 rods or expose them to other sources of static damage, particularly when powered up.
Ensure that connectors are clean, undamaged and properly aligned before pushing the parts together.
Screw together firmly for a water-tight seal.
Do not pull the sensor out of the soil by its cable.
If you feel strong resistance when inserting into soil, it is likely you have encountered a stone – stop pushing and re-insert at a new location.

Installation

Surface installation and spot measurements

Clear away any stones. Pre-form holes in very hard soils before insertion.
Push the WET150 into the soil, fully inserting the rods 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.

Note: With surface installation, air temperature and radiant heat on the sensor body can affect temperature readings. Partial or full burial of the WET150 will improve temperature accuracy, particularly where there is a large temperature difference between the air and the soil or substrate.

Installing at depth

Auger a 45mm diameter hole, ~10° to vertical is recommended.
Fit an extension tube to the WET150 – remember to fit the connector and pass the cable through the extension tube first.
Push the WET150 into the soil, fully inserting the rods to ensure good soil contact.

Alternatively

Dig a trench, and install horizontally into the wall of the trench.

Connections

Cables can be joined via extension cables and T-connectors. Maximum cable lengths depend on configuration details. As an example, 200m with 10 WET150s each connected via a 5m extension cable works reliably with the GP2 Data Logger.

Connection to a GP2 data logger

Using logger power

Wire color| GP2 terminal| | M12 plug pins| Using logger power
---|---|---|---|---
Black| | DATA| SDI-12 Data| 4
Blue| | GND| Sensor ground / power return| 3
White| | 12V| Sensor power| 2

Wiring diagram for connecting a WET150 (or SDI-12 network) to the SDI-12 channel in the GP2 using the SMSC/lw-05 cable and the logger’s internal +12V Power channel.

Note: the grey and brown wires are not connected and can be trimmed off.

Set DeltaLINK program’s Measurement, Power channel to +12V.

Power is only applied to the SDI-12 cable when required by a sensor.

Using external power

Wiring diagram for connecting a WET150 (or SDI-12 network) to the SDI-12 channel of a GP2 logger using an external permanent power supply or battery connection (which should be appropriately fused).
Using external power

Here the SDI-12 power is permanently on. If you only want the external power switched on when needed then feed the 12V (white) cable through one of the GP2 relays and select the relay, e.g. RLY1, for the DeltaLINK program’s Measurement, Power channel

See also SDI-12 for GP2 User Manual.

GP2 configuration

You need a PC running DeltaLINK version 3.9 or later and connected to the GP2.

For help on this see DeltaLINK Help “How to Connect to the logger”

Connect the WET150 directly to the GP2 with the supplied cable.
Start DeltaLINK:
Click on Program and select Change.
Right click on Channel 1 and select WET150 from the drop-down menu.
To change the default settings, double click on an Input channel to open Input Channel Properties, where you can change the Units, Soil type and Data storage settings.
Set the Recording Interval in the Program window. there are many other options – refer to the GP2 user manual for details.
When finished, click on Apply to install the program in the logger.
To check the connections, select the Sensors tab and click on Read now to see the WET150 readings.
When ready, select the Logger window and click on Start to start logging…
later to collect the data, connect to the GP2 and select the Dataset window from which you can retrieve and display all stored readings.

SDI-12 commands

The WET150 supports a full set of SDI-12 commands for configuring the sensor and its outputs and for taking readings. The full set can be found in the online WET150 User Manual (SDI-12 supplement), the following table lists just the 4 basic commands:

Command	Sensor response	Notes
?!	a	The connected sensor responds with its address (a in this

example). Cannot be used if more than one sensor is connected.
a A b!| b| Changes the address of sensor a from a to b
aM!| a tttn| Sensor a begins a measurement and responds with the time in seconds until the measurement will be ready (ttt) and the number of values to be returned (n).
aD 0!| a | Sensor a returns 3 default values:

Permittivity** (εʹ)
Pore water conductivity (ECp, mS.m-1) compensated to 25°C at 2%/°C.
Soil temperature (°C)

Permittivity is an electrical property of soils and substrates that is largely determined by water content and is measured by the WET150. See the online WET150 User Manual for details on how permittivity is used to calculate water content.

Specifications

Volumetric Water Content

Accuracy| ± 3% (with a calibration matching the soil / substrate)
Range| Accurate range: 5 to 100%vol , ECb 0 to 500mS.m-1 Full range: 0 to 100%vol
EC b (bulk conductivity)
Accuracy| ± ( 6% + 10mS.m -1 )

Range

| Accurate range: 0 to 1200mS.m -1

Full range: 0 to 2000mS.m-1

Temperature (WET150 must be fully buried to accurately measure soil temperature)
Accuracy| ± 1°C
Range| Accurate range: -20 to +50°C

Full range: -20 to +60°C

Please refer to the online WET150 User Manual for full specification and further details: