Delta-T Devices WET150 User manual

WET150 kit
Rapid measurement of Water content, EC and Temperature
QuickStartGuide version1.1

© 2021, Delta-T Devices Ltd ` Page 2
The WET150 Kit
WET150 Sensor
Rapid and accurate
measurement of water
content, pore water EC
(ECp) and temperature
WET150 Meter
Display readings,
configure units and
soil calibrations, set
SDI-12 address
Batteries
Two standard alkaline
AA cells
Kit case
The WET150 kit is
supplied in a small
protective case with
WET150, Meter and a
couple of spare
batteries

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The WET150
Connector
Fully waterproof
M12 connector
Detectors
Soil moisture content
and EC are detected by
sensitive circuits
operating at 100MHz
Sensing field
Extends ~100mm into
the soil, but field is
strongest close to the
rods - install carefully
to avoid air gaps
SDI-12
Industry-standard digital
interface, compliant to
version 1.3
Outputs
Sophisticated correction
algorithms ensure
accurate readings across
the full range of water
content, EC and
temperatures
Temperature
Thermistor is located
within the base –
equilibrates to soil
temperature when
installed, less well for
portable
measurements

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Taking readings
1. Gently push the WET150 rods into the soil or
substrate.
2. Press READ to take and display a reading.
The meter displays all 3 parameters (water content,
temperature and pore water EC) using its current
configuration.
Water Content
Water content is calculated from the sensor
measurements by applying a soil calibration which
can be configured using the SET button (see next
section).
Water content is displayed in %vol.
If the soil type is set to RAW, the meter will instead display the underlying
readings of permittivity (ε’), temperature and bulk conductivity (ECb):
Temperature
Note: the temperature sensor in the WET150 is internal to the white body, so it
takes over a minute to equilibrate. This can potentially affect the EC
measurement accuracy as the conductivity of typical plant nutrients changes by
~2% per °C. We recommend the WET150 is used as a portable sensor only in
well-equilibrated environments where the air temperature doesn’t differ
significantly from the soil/substrate temperature.
Temperature can be displayed in °C or °F.
Pore Water EC (ECp)
The EC (Electrical Conductivity) of the water in the soil pores is calculated by
applying the Hilhorst equation. This is a very useful approximation that works
exceptionally well with the WET150 because the sensor measures permittivity
and ECb in the same sample volume at the same frequency (100MHz).
However...the Hilhorst equation ceases to be a good approximation when there
is too little water present, so the meter will display “too dry” instead.
ECp can be displayed in mS/m, mS/cm or μS/cm.
°
ε′°

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Configuration
Press SET to configure the meter or sensor. Scroll up or down to the option that
you want to configure, and press [SET] again. There are 4 menu options:
Soil type
Select the calibration that will be used when calculating water content. The
options are:
•Mineral
•Peat mix
•Coir
•Mineral wool
•Perlite
•RAW
Once you have scrolled to the appropriate setting, press SET to select.
If RAW is chosen, the meter will display the base readings: Permittivity (ε’), Bulk
EC (ECb) and Temperature.
Units
EC can be configured to display as:
•mS/m
•mS/cm
•μS/cm
Temperature can display as:
•°C
•°F
Address
Each SDI-12 sensor has an “address”, a 1-character code that it uses to
recognise when to respond to commands sent over a network of sensors.
The WET150 Meter interrogates the connected sensor and automatically uses
that address when taking readings. It can also be used to set sensor addresses
prior to their installation in a network. The following 62 addresses are available:
•a to z
•0 to 9
•A to Z
Contrast
LCD contrast can be adjusted up or down using the scroll buttons.

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Troubleshooting SDI-12 sensor networks
Checking sensors
SDI-12 sensor networks can include up to 62 sensors of different types and
manufacture, and a single malfunctioning sensor may prevent the whole network
from working. The WET150 Meter can conveniently help locate faults.
The WET150 Meter can only take and display readings from WET150 sensors,
however it can display the address of most attached SDI-12 sensor with a
compatible power requirement*. Displaying the address checks that the attached
sensor powers up correctly and responds to an SDI-12 command. This can
prove a useful diagnostic aid when troubleshooting networks of SDI-12 sensors:
◼Divide the network up into groups of 5 to 10 sensors and attempt to take
readings from each group using your data logger / wireless module.
◼When a group is identified which does not respond, separate the individual
sensors and connect each in turn to the WET150 Meter.
◼For each sensor, press [SET], scroll down to Address and press [SET] again
to display the current SDI-12 address.
◼Remove, repair or replace any sensor that fails to correctly display its
address, then reconnect all sensors to the network.
*The WET150 Meter supplies 6 Volts to attached sensors. Most SDI-12 sensors
will work fine with this, but please check the sensor specifications.

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Specifications
Volumetric Water Content
Accuracy
± 3% (with a calibration matching the soil / substrate)
Range
Accurate range: 5 to 100%vol, ECb0 to 500mS.m-1
Full range: 0 to 100%vol
ECb(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 buried to accurately measure soil temperature)
Accuracy
± 1°C
Range
Accurate range: -20 to +50°C
Full range: -20 to +60°C
WET150
Interface
SDI-12 v1.3
Sealing
IP68
Sample volume
55 x 70 mm diameter
Dimensions
143 x 40 mm diameter
Weight
77g
Warranty
5 years
Meter
Power requirement
2x AA alkaline batteries
Battery life
~2,400 readings
Dimensions
130 x 66 x 25 mm
Weight
160g
Warranty
2 years

© 2019, Delta-T Devices Ltd Page 8
Changing the batteries
You will need a small cross-head screwdriver to access the batteries.
◼Unscrew the 2 screws holding the battery cover in place, taking care
not to lose the fitted o-rings.
◼Remove and replace the 2 AA batteries, making sure to retain the
correct polarity.
◼Replace the 2 screws.
Note: All configuration settings will be retained.
Care and maintenance
◼Do not touch the WET150 rods or expose them to other sources of static damage,
particularly when powered up.
◼Ensure that the connector is clean, undamaged and properly aligned before
pushing the parts together. Screw together firmly for a water-tight seal.
◼If inserting the sensor into soil and you feel strong resistance, it is likely you have
encountered a stone. Stop pushing and re-insert at a new location.
◼Do not pull the sensor out of soil by its cable.
◼Protect the meter from heavy rain or submersion.
Delta-T Devices Ltd
130 Low Road, Burwell, Cambridge CB25 0EJ, UK
Tel: [phone]
[email protected] www.delta-t.co.uk
WET150 Quick Start Guide version 1.1