Delta-T Devices WET150 User manual

User Manual for the
WET150 Sensor
type WET150
Delta-T Devices Ltd
WET150-UM-1.1

2⚫Notices
Notices
UKCA conformity
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 emissions and susceptibility when used
according to the instructions contained within this user manual,
and is CE marked by Delta-T Devices Ltd
FCC Emissions
CFR47 Pt 15 B [Unintentional Radiator emission limits as per
Pt 15.109]
Note: This equipment has been tested and found to comply with
the limits for a Class A digital device, pursuant to part 15 of the
FCC Rules. These limits are designed to provide reasonable
protection against harmful interference when the equipment is
operated in a commercial environment. This equipment
generates, uses, and can radiate radio frequency energy and, if
not installed and used in accordance with the instruction manual,
may cause harmful interference to radio communications.
Operation of this equipment in a residential area is likely to
cause harmful interference in which case the user will be
required to correct the interference at their own expense.
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
The WET150 is protected under international law by the
following:-
USA: Patent US7944220
Europe: Patent EP1836483
Australia: Patent AU2005315407
China: Patent CN101080631
Copyright © 2021 Delta-T Devices Ltd

Contents ⚫3
Contents
Notices 2
Contents 3
Introduction 5
Description 6
How the WET150 Sensor works 7
Parts and Accessories 8
Care and Safety 9
Use with a WET150 Meter 10
Take a Reading 10
Options 10
WET150 Meter Buttons 10
Temperature 11
Pore Water EC (ECp) 11
Use WET150 Meter to Change Address 12
Network Cabling 13
Maximum cable length and network size 14
Connecting to loggers or controllers 15
Wiring 15
Other loggers and systems wiring: 15
GP2 wiring using internal power 16
GP2 wiring using external power 17
Give Each WET150 a Unique Address 18
Install DeltaLINK 18
1 Open DeltaLink Transparent Mode 19
2 Find out WET150’s current address 19
3 Change the address 20
Create GP2 Program 21
1: Add a WET150 SDI-12 Measurement 21
2: Sensor type Settings 23
3: Set Recording Intervals 25
4: Next Steps 25

4⚫
Power supply 26
Power supply and communication 26
Warm-up time 27
Multiple WET150s in a network 27
Other data loggers 29
Installation in the Ground 30
Surface installation and spot measurements 30
Installing at depth 31
SDI-12 commands 32
Address Query 33
Address Assign 34
Identify 35
Table of default / pre-configured measurements36
Specifications 40
Edge Effects 41
Trouble Shooting 42
Error Codes 42
How it works 43
Sensing soils and substrates 43
Permittivity and soil composition 43
Converting permittivity to water content 44
Generic soil calibrations 46
Soil-specific calibrations 48
Technical Reference 49
Dielectric properties 49
Measuring Soil Moisture 50
Pore water conductivity 51
References 55
Definitions 56
Technical Support 61
Appendix 63
Soil-specific Calibration 63
Laboratory calibration for non-clay soils 64
Laboratory calibration for clay soils 67
Index 70

Introduction ⚫5
Introduction
Cables
To meter
Extension cables
To GP2 and other
loggers
Connector
Fully waterproof
M12 connector -
Installation
Threads enable extension
rods to be screwed on for
easy insertion in augured
holes –minimising soil
disturbance
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 the soil
temperature when
installed, less well for
portable
measurements

6⚫Introduction
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:
•Water Content
•Electrical Conductivity
•Temperature
The sensor converts the measured dielectric properties into
Water Content over the full range, 0 to 100%, being most
accurate, ±3%, over 5 to 100% water content and over 0 to 500
mS/m soil bulk conductivity. Generalised calibrations are
provided for most common soil types.
The WET150 Sensor also measures the bulk electrical
conductivity of soil (ECb) over 0 to 2000 mS/m, being most
accurate, ±(10 mS/m + 6%), from 0 to 1200 mS/m.
It also calculates Pore Water Conductivity, the electrical
conductivity of the water within the pores of the soil (ECp).
Temperature is measured by a miniature sensor built into the
body of the sensor.
The WET150 Sensor works with the WET150 Meter and the
GP2 logger controller.
It can also be used with other SDI-12 loggers, and with SDI-12
fertigation and irrigation control systems.
Advantages of the WET150 Sensor
•Fast, accurate, adaptable and easy to use
•Rapid measurements (~1 second) of all 3 parameters
•In-situ Pore Water Conductivity measurements
•Easy insertion into growing media and soil
•Works with many different soils and growing media
•Stable, accurate readings from
5 to 100% water content
0 to 1200 mS.m-1
-20 to +50°C
•Lightweight ergonomic design
•Versatile SDI-12 digital output
•Systems integrator friendly
•Wide choice of settings, outputs and units
•Low power for long battery life
•2-year warranty extends to 5 years if registered on
delivery

Introduction ⚫7
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.
The water content, electrical conductivity, and
composition of the soil surrounding the pins...

...determines its dielectric properties.
➔
The WET150 sensor detects these dielectric
properties from their influence on the
electromagnetic field and calculates ...
… Soil Moisture and Pore Water Conductivity.
It also records Temperature and uses that to
improve the accuracy of the other measurements
… and sends the results, on demand, to either an
WET150 meter, GP2 logger-controller
or other SDI-12 enabled device

8⚫Introduction
Parts and Accessories
WET150 sensor
WET150 Kit
WET150 + WET150 Meter
SMSC/lw-05
5m cable with 200 mm
flying leads.
Connects WET150 to GP2
directly, or via SDI-12
network of EXT/5W-xx
cables
EXT/5W-01
EXT/5W-05
EXT/5W-10
EXT/5W-25]
1 m, 5 m,10 m and 25 m
extension cables with 5-
way M12 connectors.
Connects WET150 to an
SDI-12 sensor network
GP2-NTP
3-way network T- Piece for
connection WET150 and
EXT/5W-xx cables
ML/EX50
ML/EX100
Extension tubes,
50 and 100 cm
SM-AUG-100
Spiral Auger 1.2 m

Introduction ⚫9
Care and Safety
The pins of the WET150 are sharp
in order to ease insertion. Care
must be taken and handling
precautions followed.
•Avoid touching the pins or exposing
them to other sources of static charge, particularly when powered
up.
Keep the WET150 in its protective package when not in use.
•Take care when attaching cables to ensure that the connectors are
clean, undamaged, and properly aligned before pushing the parts
together.
•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.
•WET150 is unsuitable for use in hard soils unless holes are pre-
formed. Rough handling may cause irreparable damage to the pins

10 ⚫Use with a WET150 Meter
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
1. Gently insert WET150 pins into soil or
substrate.
2. Press READ to take and display water
content, temperature and pore water
conductivity.
Options
Water content can be displayed as volumetric water
content (%) using the Mineral, Peat mix, Coir, Min. wool and Perlite
calibrations or the meter can display the RAW (unconverted) permittivity
reading (ε’) which has no units.
Temperature can be displayed in °C or °F.
EC is displayed as the pore water conductivity, ECp, in mS.m-1, or the soil
bulk conductivity, ECb, when the RAW display option is selected.
Address can be ato z, Ato Zor 0to 9( 0 is not advised on a network)
WET150 Meter Buttons
READ –takes and displays a reading.
SET shows the settings menu. You can scroll up or down
through these options: Soil type, Units and Address and
Contrast... Press SET to select the highlighted menu and show
the current setting in that menu. Again, scroll up or down and
press SET to confirm the choice and return to the start-up
screen. Alternatively, press READ to save the setting, exit the
menu and take a reading.
and scroll through the current options.
Auto-off - after 1 minute saves the current selection and
switches off.
See also WET150 Kit Quick Start Guide

Use with a WET150 Meter ⚫11
Temperature
The 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
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 measured bulk electrical conductivity (ECb) in the same
sample volume at the same frequency (100MHz). The Hilhorst equation
ceases to be a good approximation when there is too little water present, so
the meter displays “too dry” instead (typically at <12.5%, as in mineral soil)
ECp can be displayed in mS/m, mS/cm or μS/cm.

12 ⚫Use with a WET150 Meter
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*.
Only attach one sensor at a time to a WET150 Meter.
*The WET150 Meter only takes readings from a WET150
sensor.
1. Press [SET]
Wakes the Meter and displays the first option in the settings
menu
2. Press [] twice
Scrolls down to the Address setting menu
3. Press [SET]
Selects that menu, and displays the current SDI-12 address
4. Press [] or [] as often as necessary
Scrolls to the desired target address
5. Press [SET]
Attempts to set that address
Success is indicated by the brief appearance of the ✓symbol,
after which it reverts to the Settings menu.
Failure is indicated by , after 3 seconds it reverts to the
Address setting menu.
See also WET150 Kit Quick Start Guide

Network Cabling ⚫13
Network Cabling
One WET150 can be read with a WET150 Meter.
Multiple WET150s need a GP2 or other SDI-12 controller.
These Delta-T extension cables are terminated in M12 thumb-screw
connectors, male at one end, female at the other. 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. An advantage of the M12 connector
system is that it is quick and easy to build and modify SDI-12 networks.
Later if a network fails due to a faulty sensor or damaged cable, it is easy to
isolate sections by temporarily disconnecting whole network branches or
individual sensors to trace the fault.
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.
M12 plugs with screw connectors are available for adding other sensors to
the SDI-12 network.
See also: SDI-12 for GP2 User Manual

14 ⚫Network Cabling
Before connecting on a network each WET150 sensor must be
individually set up with a unique address. So they must be
individually connected to either to a GP2 logger controller, or
WET150 Meter or other SDI-12 controller.
This is also a good opportunity to change individual sensor
parameters, e.g. for soil type
Maximum cable length and network size
The SDI-12 standard requires that a cabled sensor network with a logger
must be capable of supporting at least 10 sensors, each with 200 feet (61m)
of cable in a star configuration back to the logger. It also states that longer
cable lengths are possible if the network contains fewer sensors.
However, there is no defined maximum individual or total cable length as
this depends on many factors including the numbers of sensors, network
configuration, supply voltage, cable type, logger type and environmental
factors (such as whether the cable is buried) and proximity to electrical
noise sources like transmitters and power transformers.
While it is not possible to test every network configuration, tests have been
carried out on various configurations with different cable lengths and
numbers of WET150s. One such scenario was fifteen WET150 sensors
daisy-chained 5m apart using extension cables and T-piece connectors, all
on a single 245m backbone (so 320 m in total).
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.
If the SDI-12 network also contains devices other than the WET150, a
reduced maximum number of sensors or reduced overall cable length may
be needed due to their potentially higher network loading
NOTE

Connecting to loggers or controllers ⚫15
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.
Wiring
GP2 Logger Wiring: See pages 16 and 17
Other loggers and systems wiring:
** Optional. The green wire is connected to the cable screen. The SDI-12
specification does not require the green wire / cable screen connected.
If there is a lot of electrical noise in the environment, connecting the green
screen wire to ground in the logger or controller may help reduce data
corruption.
For other connection details to third-party loggers and controllers please
consult the SDI-12 sections of those products’ manuals.
For SDI-12 screw terminal cable
connector information see pages
12, 32 and 33 of the SDI-12 for
GP2 User Manual
See Power supply on page 26
Wire colour
Logger or
controller
SDI-12 function
M12 connector
pin
Brown
Not connected
1
White
+12V 0.5A
Network power
2
Blue
GND
Ground (for power and data)
3
Black
DATA
Data (send and receive)
4
Grey
Not connected
5
Green
Not connected **
(Cable screen) **
Shell / nut
4
4
51
3
2
GROUND
SDI-12 DATA
SDI-12 POWER
SCREEN (if present)
4
4
51
3
2
GROUND
SDI-12 DATA
SDI-12 POWER

16 ⚫Connecting to loggers or controllers
GP2 wiring using internal power
The GP2 logger controller incorporates a program-controlled power rail
specifically for SDI-12 applications. This 12V supply is generated from the
internal logger battery pack via a voltage step-up circuit and is current
limited in case of faults on the SDI-12 network.
SDI-12 sensors typically require a 3-wire connection: Power, Ground and
Data. This is the case with the WET150 but the cabling system includes
additional wires which are not normally used within an SDI-12 network.
To create an SDI-12 network based upon a GP2 logger controller, use cable
type “SMSC/lw-05” to bring the network connections out of the GP2 case.
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.
** Optional. The green wire is connected to the cable screen. The SDI-12
specification does not require the green wire / cable screen to be
connected. .
If there is a lot of electrical noise in the
environment, connecting the green screen wire to
the GND terminal (with the blue ground wire) in
the GP2 may help reduce data corruption. The
figure on the right illustrates the wire and terminal
connections with the optional green screen wire.
The brown and grey wires in cable type “SMSC/lw-05” are not normally
required for SDI-12 so should be insulated from shorting to any terminals
inside the GP2, or they may be trimmed off. The same applies to the
green screen wire if it is not used.
Power is automatically supplied when the WET150 sensor is selected in
the DeltaLINK program.
Wire colour
GP2 terminal
(SDI-12 block)
SDI-12 function
M12 connector
pin
Brown
Not connected
1
White
+12V 0.5A
Network power
2
Blue
GND
Ground
(for power and data)
3
Black
DATA
Data (send and receive)
4
Grey
Not connected
5
Green
Not connected **
(Cable screen) **
Shell / nut

Connecting to loggers or controllers ⚫17
GP2 wiring 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.
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. The functioning of the GP2 logger/controller itself can
remain running on its own internal batteries independently of an external
power source for the SDI-12 network.
To use an external power supply for the SDI-12 network, do not connect
anything to the GP2’s “+12 0.5A” power terminal. Instead wire the SDI-12
network power (white wire on cable type “SMSC/lw-05”) to the external
power source +12Vdc terminal.
Wiring connection
diagram showing
external SDI-12 power
connections for the SDI-
12 network, along with
the optional green screen
wire
Ensure there is a fuse or other protection in-line with this external power
source in case short-circuit faults develop on the SDI-12 network.
The Ground or 0V terminal of the external power source should be wired into
the GND terminal on the GP2, along with the Ground wire of the SDI-12
network (blue wire on cable type “SMSC/lw-05”).
In the external power supply configuration shown above, power is
permanently applied to the SDI-12 network. This may not be the most
desirable or efficient way to run the network. An alternative would be to wire
one of the GP2 internal relays in series with the external power supply and
the SDI-12 network power wire.
The GP2 logger/controller program can then be configured to switch in the
power only when taking measurements for greater external power efficiency.
e.g In DeltaLINK program’s Measurement, Power channel select RLY1.

18 ⚫Give Each WET150 a Unique Address
Give Each WET150 a Unique Address
If two sensors have the same address an SDI-12 network will
not work. So, give each WET150 a unique address before
connecting it into a network of SDI-12 sensors.
The address of a new sensor is usually 0 (number zero).
It is best to change it.
It can be any one of the following 62 addresses: -
0 to 9, a to z or A to Z.
Use either a WET150 Meter connected directly to a WET150
sensor - see page 12, or use a GP2 and PC running DeltaLINK
as described below.
Install DeltaLINK
To operate the functions of the GP2 logger/controller, its
companion computer software “DeltaLINK” needs to be
downloaded and installed. This PC software is available from
the 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.
Once DeltaLINK is installed, connect the GP2 to your PC
computer using the USB to GP2 cable supplied with the GP2.
See also: the GP2 User Manual
SDI-12 for GP2 User Manual
WET150 SDI-12 Programmer’s Guide

Give Each WET150 a Unique Address ⚫19
1 Open DeltaLink Transparent Mode
You need a GP2 connected to a PC running DeltaLINK v 3.9 or
later.
With no other sensors on the network connect the sensor to
the GP2 SDI-12 terminal.
In DeltaLINK select Tools, SDI-12, Transparent mode to open
theSDI-12 Transparent Mode Terminal as shown below.
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.
You type
?!
Reply
a
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.
?!
1
2 3 4
Any logger on COM1
Example

20 ⚫Give Each WET150 a Unique Address
3 Change the address
Send a command to change its address
You type
aAb!
Reply
b
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.
Make a note of the address and the serial number.
Later when you have finished giving each sensor a unique
address, Close the Transparency Mode and Change the default
GP2 program to create a WET150 sensor type measurement
with the correct address, and repeat this for each sensor to go
on the network. See also Create GP2 Program on page 21.
You can change the default Measurement name to add useful
metadata –such as the address, e.g. Theta becomes Theta Z
and so see the address displayed in the results. But the ECp
calculation also uses the Permittivity and SoilTemp readings.
So, in the Calculation section of the ECp Measurement
parameters change the Permittivity name e.g. from Theta to
Theta Z and likewise for the Temperature name if you have
also changed that, e.g. from SoilTemp to SoilTemp Z.
If you change Measurement name you must also change the
Recording Rate entry to match.
Advanced
users
only