Delta-T Devices ML3 ThetaProbe soil moisture sensor, GP2, GP1, DL6, DL2e data logger, HH2 meter User manual
Below you will find brief information for soil moisture sensor ML3 ThetaProbe, data logger GP2, data logger GP1, data logger DL6, data logger DL2e, meter HH2. The ML3 ThetaProbe is a versatile soil moisture sensor that can be used to measure soil moisture content and temperature at various depths. The sensor is waterproof and can be buried in the soil. It is compatible with a variety of data loggers and meters, including the GP1, GP2, DL6, DL2e, and HH2. The sensor can be calibrated for specific soil types and is accurate to within ±1% vol. The ML3 ThetaProbe is a valuable tool for researchers and farmers who need to monitor soil moisture levels. This document provides guidance on installing, calibrating, and operating the ML3 ThetaProbe sensor.
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User Manual for the
ML3 ThetaProbe
Soil Moisture Sensor
ML3-UM-1.0
Delta-T Devices Ltd
Notices
Patents
The ML3 ThetaProbe has been jointly developed by The Macaulay
Land Use Research Institute and Delta-T Devices Ltd. and uses novel measurements. They are subject to the following patents:
UK:
US:
GB2300485B
5804976
Copyright
All parts of the ML3 ThetaProbe design and documentation are the exclusive right of Delta-T Devices and covered under copyright law.
© 2013 Delta-T Devices Ltd
EMC Compliance
Design changes
Delta-T Devices Ltd reserves the right to change the designs and specifications of its products at any time without prior notice.
User Manual Version:
ML3-UM-1.0 April 2013
Delta-T Devices Ltd
130 Low Road,
Burwell
Cambridge CB25 0EJ
UK
Tel
Fax
:
:
+44 1638 742922
+44 1638 743155 email : [email protected]
web : www.delta-t.co.uk
Contents
Introduction
Description
Features
Dimensions
Parts list
Care and Safety
How the ML3 works
Operation
Cable Connections
Installation
Logger connections and configuration
GP2
GP1
DL6
DL2e
Other data loggers
HH2 Meter
Calibration
Soil calibration
Sensor calibration
Soil moisture reading
Troubleshooting
Technical Reference
Specifications
Volumetric water content
ML3 User Manual 1.0
24
26
26
26
Introduction
3
13
14
15
16
17
18
18
21
22
10
10
11
12
12
7
8
9
5
5
5
6
Temperature
Definitions
References
Technical Support
Appendix 1
Soil-specific Calibration
Laboratory calibration for non-clay soils
Laboratory calibration for clay soils
Appendix 2:
The ML3 Temperature Sensor
ML3 Temperature Measurement
Effect of Temperature on Water Permittivity
Index
Resistance to Temperature Lookup Table
26
30
32
33
35
35
36
39
42
42
43
44
45
46
ML3 User Manual 1.0 Introduction
4
Introduction
Description
The ML3 measures soil moisture content and temperature
Its sealed plastic body is attached to four sensing rods which insert directly into the soil for taking readings.
A waterproof plug connects to a choice of signal cables.
Both extension cables and extension tubes can be used.
The soil moisture output signal is a differential analogue DC voltage. This is converted to soil moisture by a data logger or meter using the supplied general soil calibrations.
It can also be calibrated for specific soils.
Features
Soil moisture accurate to ± 1%
Soil temperature to ± 0.5°C over 0-40°C
Low salinity sensitivity
Excellent stability
Minimal soil disturbance
Easy installation at depth in augered holes
Waterproof connector to IP68
Rugged, weatherproof and can be buried.
Good electrical immunity
Choice of cabling system options
Cable connector, cylindrical profile and extension tube design simplifies removal for servicing.
See also Specifications on page 26
1
A data logger is required for temperature measurements
ML3 User Manual 1.0 Introduction
5
Dimensions
Signal cable connector
IP68, M12, 5 pin
Extension tube connector
¾ inch BSP thread
ML3 User Manual 1.0
39.8 mm
Introduction
6
Parts list
Your shipment may include the following:
Part Sales Code
ML3
Description
ML3 sensor with Quick Start Guide
SMSC/d-
HH2
0.9m cable connects to
HH2 meter via 25-way D-connector
SMSC/sw-
05
5m cable with
100 mm flying leads for GP2, GP1 or DL6 logger
SMSC/lw-05
5m cable with
200mm flying leads for DL2e logger
EXT/5W-05
EXT/5W-10
EXT/5W-25
5, 10 and 25m extension cables. IP68 M12 connectors
ML/EX50
ML/EX100
50 and 100cm Extension
Tube
SM-AUG-
100
45mm spiral auger
1.2m long
ML3 User Manual 1.0 Introduction
7
ML3-Kit
ML3 sensor, HH2 meter, cable SMSC/d-HH2,
Insertion kit ML-INK1,
4 spare steel pins, spare battery, carry case
HHCC3, HH2 manual,
ML3 Quick Start
Care and Safety
The rods of the ML3 are sharp in order to ease insertion. Care must be taken and handling precautions followed.
To prevent personal injury and damage to the probe always store and transport the ML3 in this protective tube
CAUTION
SHARP PINS
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 ML3 out of the soil by its cable.
If you feel strong resistance when inserting the ML3 into soil, it is likely you have encountered a stone. Stop pushing and re-insert at a new location.
Avoid touching the rods or exposing them to other sources of static damage, particularly when powered up.
Keep the ML3 in its protective tube when not in use.
þ
ML3 User Manual 1.0 Introduction
8
How the ML3 works
When power is applied to the ML3...
...it creates a 100MHz waveform (similar to FM radio).
The waveform is applied to an array of stainless steel rods which transmit an electromagnetic field into the soil.
The water content of the soil surrounding the rods...
ε
...dominates its
permittivity
.
(A measure of a material’s response to polarisation in an electromagnetic field. Water has a permittivity ≈ 81, compared to soil ≈ 4 and air ≈ 1)
The permittivity of the soil has a strong influence on the applied field…
V
out
…which is detected by the ML3, resulting in a stable voltage output that…
Soil Moisture
22 %
...acts as a simple, sensitive measure of
soil moisture content
.
ML3 User Manual 1.0 Introduction
9
Operation
Cable Connections
HH2 cable
0.9m
5m
10m
25m
Extension cables
Logger cables
5m with
100 or 200 mm bare leads brown white blue black grey green
Power 0V
Power V+
Soil Moisture Signal HI
Soil Moisture Signal LO
Temperature +
Cable shield
Take care when attaching cables to ensure that the connectors are clean, undamaged and properly aligned
before
pushing the parts together.
Screw together firmly to ensure the connection is water-tight.
Extension cables can be joined up to a recommended maximum of
100m – see Specifications on page 26
ML3 User Manual 1.0 Operation
10
Installation
Surface installation and spot measurements
Clear away any stones. Pre-form holes in very hard soils before insertion.
Push the ML3 into the soil until the rods are fully inserted. Ensure good soil contact.
If you feel strong resistance when inserting the ML3, you have probably hit a stone.
Stop, and re-insert at a new location.
Note: The ML3 is not suitable for soil surface temperature measurements. For soil temperature near the surface dig a trench and install horizontally as shown below. Cover both ML3 and the first 30cm of cable with at least 5cm of soil.
Installing at depth
Make a 45mm diameter hole, preferably at about 10° to the vertical using the
SM-AUG-100 auger.
Connect an extension tube e.g. ML/EX50
Push the ML3 into the soil until rods are fully inserted. Ensure good soil contact.
Alternatively
Dig a trench, and install horizontally.
ML3 User Manual 1.0 Operation
11
Logger connections and configuration
GP2
6 ML3s can connect to each GP2 wired as a differential, powered sensors.
12 ML3s can be connected if you do not use the temperature sensor. For this you will also need a 5 gland expansion lid GP2-G5-LID.
These details illustrate connection to Channels 1 and 2:
ML3 wiring Colour GP2 terminal
Power 0V and Thermistor LO brown
CH1 (PGND)
Power V+ white
CH1 (PWR)
Soil Moisture Signal HI blue
CH1 (+)
Soil Moisture Signal LO
Thermistor HI black grey
CH1 (-)
CH2(+) and CH2(-)
Cable shield green
CH1 (PGND)
For configuration details see the
DeltaLINK 3
Info Panel, Help or the GP2 User Manual.
Download the latest version of the DeltaLINK logger software from www.delta-t.co.uk
or from our Software and Manuals DVD
2
The GP2 logger needs the PC logger software DeltaLINK 3. This can be obtained from www.delta-t.co.uk
or the Software and Manuals DVD.
ML3 User Manual 1.0 Operation
12
GP1
Two ML3s can connect to each GP1.
Each ML3 is wired as a differential, powered sensor.
These details illustrate connection to
Channels 1 and 3:
ML3 wiring
Power 0V and
Thermistor LO
Power V+
Colour GP1 terminal
brown
CH1 (GND) or Temp (GND)
white
CH1 (PWR)
Soil Moisture
Signal HI
Soil Moisture
Signal LO blue black
CH1 (+)
CH1 (-)
Temperature + grey
Cable shield green
Temp3 (IN)
CH1 (GND)
Using the DeltaLINK
logger software, configure channel 1 or 2 as sensor type
ML3
and channel 3 or 4 as an
ML3 Temperature
sensor.
See also GP1 Quick Start Guide and the DeltaLINK on-line Help.
3
The GP1 logger needs
the PC logger software DeltaLINK version 3 or later. A free upgrade can be obtained from www.delta-t.co.uk
or from the
Software and Manuals
DVD.
ML3 User Manual 1.0 Operation
13
DL6
6 ML3s can be connected to a DL6.
Each ML3 is wired as a differential, powered sensor.
A DL6 logger can only read one ML3 temperature sensor.
These details illustrate connection to channels 6 & 7:
ML3 wiring
Power 0V
Power V+
Colour DL6 terminal
brown
0V
white
V+
Soil Moisture
Signal HI
Soil Moisture
Signal LO blue black
Temperature + grey
Cable shield green
IN+
IN-
RES IN+
In DeltaLINK
configure channel 6 as type
ML3
and channel 7 as a type
ML3 Temperature
sensor.
See also the DL6 Quick Start Guide and the DeltaLINK online Help.
4
The DL6 logger needs the PC logger software DeltaLINK version 3 or later.
A free upgrade can be obtained from www.delta-t.co.uk
or from the
Software and
Manuals DVD.
ML3 User Manual 1.0 Operation
14
DL2e
Up to 60 ML3s can be connected to a DL2e logger (if not using the temperature sensor channel).
Up to 30 ML3s can be connected if also reading the temperature sensor.
Each ML3 is connected as a differential, powered sensor.
These details illustrate connection to Channels 57 and 58 using a
LAC1 input card configured in 15-channel mode, and warm-up channel
63:
ML3 wiring
Power 0V
Power V+
Soil Moisture
Signal HI
Soil Moisture
Signal LO blue black
Temperature + grey
Cable shield
Colour DL2e terminal
brown
CH62- or 61-
white
CH63 NO
green
CH58+
CH58-
CH57+ and CH57-
CH61- or 62-
Configure the chosen DL2e logger channels by selecting the appropriate
S3M and S3O
sensor types for mineral and organic soils and
S3T
for the temperature sensor type listed in the Ls2Win
library.
See the DL2e User Manual and the Ls2Win online help
5
You need a PC running Ls2Win version 1.0 SR10 or later.
A free upgrade can be obtained from www.delta-t.co.uk
or from the Software and Manuals DVD.
ML3 User Manual 1.0 Operation
15
Other data loggers
The ML3 should be connected as a differential, powered sensor.
Configure the logger to convert the ML3 readings from milliVolts into soil moisture units by using either :-
Output signals in the range 0 to 1.0 volts from the ML3 correspond to a range of ~0 to 60% water content in mineral soils – see
Note: The ML3 has been optimised for warm-up of 0.5 to 1 second duration.
It is recommended that the sensor is not powered continuously.
The temperature sensor output should be read as a resistance and the logger configured with a look-up table to covert the measured resistance to temperature.
and
Resistance to Temperature Lookup Table on page 45.
ML3 User Manual 1.0 Operation
16
HH2 Meter
You need version 2.7 or later for both the PC software
HH2Read and the HH2 firmware (see foot of page).
Connect the ML3 to the HH2 meter.
Press
Esc
to turn the meter on, and if necessary press again until the HH2 displays the start-up screen.
Set the meter to read from an ML3:
►
Press
Set
and scroll down to the
Device
option.
►
Press Set again and scroll down to select
ML3.
►
Press Set to confirm this choice.
Device:
ML3
Make sure the HH2 is correctly configured for your soil type:
►
At the start-up screen, press Set and scroll down to the
Soil Type
option.
►
Press Set again and scroll down to the appropriate soil type (use
Mineral
for sand, silt or clay soils or
Organic
for peaty soils)
►
Press Set to confirm this choice.
Soil Type:
Mineral
Choose the units you want for displaying readings.
►
At the start-up screen, press Set and scroll down to the
Display
option.
►
Press Set again and scroll down to select units.
►
Press Set to confirm this choice.
Press
Read
to take a reading.
Press
Store
to save or Esc to discard the reading.
ML3 Store?
20.3 %vol
Remove the ML3 from the soil and move to a new location...
If you have saved data, connect your HH2 to a PC and run
HH2Read to retrieve the readings.
See also: Support for the ML3 Soil Moisture Sensor with an HH2 and HH2 User Manual and HH2 User Manual Addendum to V4 - ML3.
Note: the HH2 does not display or store ML3 temperature readings.
Note: For an upgrade contact Delta-T.
ML3 User Manual 1.0 Operation
17
Calibration
The ML3 is provided with general calibrations for
mineral
and
organic
soils which can be used to convert the output from the sensor directly into soil moisture when used with Delta-T loggers and the HH2 moisture meter. This section explains how these calibrations work, how to adapt them for other soils and how to provide calibrations for other data loggers.
The ML3 measures volumetric soil moisture
θ
, by detecting the dielectric properties of the damp soil – the permittivity, ε, or more conveniently the refractive index, which is closely equivalent to
√ε . The ML3 response is best understood in these stages:
ML3 User Manual 1.0 Operation
18
Soil calibration
Damp soil is essentially a mixture of soil particles, air and water, and together these components determine its dielectric properties, including the refractive index √ε. The refractive index of the mixture is approximated simply by adding the contributions from the individual components [ref 4.].
For a particular soil, the contribution from the soil particles can be assumed to be constant, so the refractive index measured by the
ML3 is only affected by changes to the water content, θ. This relationship simplifies to:
ε
=
a
0
+
a
1
⋅
θ where the coefficients
a
0
and dielectric properties of soils.
a
1
conveniently parameterise the
Soil calibrations
8.0
6.0
4.0
Slope (a
1
)
2.0
Offset (a
0
)
0.0
0.0
0.2
0.4
Soil moisture (m
3
.m-
3
)
0.6
0.8
Note that:
a
0
=
ε
dry
_
soil
is usually between 1.3 to 2.3
a
1 corresponds approximately to
ε
water
− 1
and usually takes a value about 8.0. Real soil values for
a
0
and
a
1
can vary significantly from these guidelines when they are affected by other factors – in particular, bound water in clay may result in higher values of
a
1
.
ML3 User Manual 1.0 Operation
19
General soil calibrations
Most soils can be characterised simply by choosing one of the two general calibrations we supply, one for mineral soils (predominantly sand, silt and clay) and one for organic soils (with a high organic matter content).
Mineral soils
Organic soils
a
0
1.6
1.3
a
1
8.4
7.7
General soil calibrations
8.0
6.0
Mineral
Organic
4.0
2.0
0.0
0.0
0.2
0.4
Soil Moisture
(m
3
.m
-3
)
0.6
0.8
These values have been used to generate the polynomial conversions and linearisation tables in the Soil moisture reading section.
Soil-specific calibration
Instead of adopting these general calibrations, you may wish to determine specific calibration values of
a
0
and
a
procedure is fairly straightforward if you can get access to standard laboratory equipment and is described in detail in Appendix 1 on
1
for your soil. This
Soil specific calibration can significantly improve the accuracy of individual readings - but make less of an improvement to readings where installation and sampling errors are high.
ML3 User Manual 1.0 Operation
20
Sensor calibration
Each ML3 is individually adjusted to provide consistent dielectric performance:
ML3 dielectric performance
8.0
6.0
4.0
2.0
0.0
0.000
0.200
0.400
0.600
ML3 output (Volts)
0.800
1.000
1.200
This response can be approximated either by a polynomial (below)
or by a linearisation table (see page 23):
Polynomial
(for use over the full range of ML3 readings)
√𝜖 = 1.0 + 6.175𝑉 + 6.303𝑉
2
− 73.578𝑉
3
+ 183.44𝑉
4
− 184.78𝑉
5
+ 68.017𝑉
6
where
V
is the ML3 output in Volts
ML3 User Manual 1.0 Operation
21
Soil moisture reading
Polynomial conversion
Combining the Soil calibrations and Sensor calibration steps, the conversion equation becomes: 𝜃 =
[
1.0 + 6.175𝑉 + 6.303𝑉
2
− 73.578𝑉
3
+ 183.44𝑉
4 𝑎
1
− 184.78𝑉
5
+ 68.017𝑉
6 ] − 𝑎
0 where
a
0
and
a
1
are the calibration coefficients. 𝜽 𝒎𝒊𝒏𝒆𝒓𝒂𝒍
For a generalised mineral soil this becomes:
= −0.071 + 0.735𝑉 + 0.75𝑉
2
− 8.759𝑉
3
+ 21.838𝑉
4
− 21.998𝑉
5
+ 8.097𝑉
6
And for a generalised organic soil: 𝜽 𝒐𝒓𝒈𝒂𝒏𝒊𝒄
= −0.039 + 0.802𝑉 + 0.819𝑉
2
− 9.556𝑉
3
+ 23.823𝑉
4
− 23.997𝑉
5
+ 8.833𝑉
6
ML3 User Manual 1.0 Operation
22
Linearisation table
F or use over the full range of ML3 readings
V
√ε
V
√ε
V
√ε
V
√ε
V
√ε
0.000 1.000 0.240 2.305 0.480 3.139 0.720 4.269 0.960 6.001
0.060 1.381 0.300 2.521 0.540 3.385 0.780 4.601 1.020 6.890
0.120 1.741 0.360 2.719 0.600 3.659 0.840 4.966 1.080 8.282
0.180 2.050 0.420 2.920 0.660 3.955 0.900 5.406 1.140 10.531
Linearisation table conversion
The conversion from ML3 reading (Volts) to soil moisture or %vol) can be accomplished by a look-up table.
θ
(m
3
.m
-3
Soil moisture
%vol
28
32
36
40
44
48
-4
0
4
8
12
16
20
24
The following table lists the values used for the DL2e data logger:
Mineral
soil
Volts
-2.090
0.096
0.156
0.232
0.326
0.427
0.514
0.591
0.659
0.724
0.783
0.838
0.886
0.924
Organic
soil
Volts
Soil moisture
%vol
-2.090
52
0.048
56
0.097
60
0.153
64
0.220
68
0.304
72
0.396
76
0.482
80
0.557
84
0.620
88
0.683
92
0.740
96
0.795
100
0.844
104
Mineral soil
Volts
0.956
0.982
1.004
1.023
1.040
1.054
1.068
1.080
1.091
1.101
1.110
1.119
1.127
2.090
Organic soil
Volts
0.887
0.922
0.951
0.976
0.997
1.016
1.032
1.046
1.059
1.071
1.082
1.092
1.101
2.090
ML3 User Manual 1.0 Operation
23
Troubleshooting
Always try to identify which part of the measurement system is the source of the difficulty. For the ML3 this may fall into one of the following areas:
The measurement device
What equipment is being used to read the probe output?
A Delta-T HH2 Moisture Meter.
Note: the HH2 does not measure ML3 temperature.
A Delta-T data logger such as the GP1, GP2, DL6 or DL2e
Check Versions
Check you have the correct versions:
HH2 Meter: Firmware version 2.7 and PC software HH2read version 2.7 or later are recommended.
GP1, GP2 & DL6 Loggers: DeltaLINK version 3.0 or later is required.
DL2e Logger: Ls2Win 1.0 SR10 is required
Consult the user manuals or the on-line help for these devices and their related software.
Try alternative types of equipment if you have them available.
Check that you are using an appropriate soil calibration and the correct conversion method – see
Calibration section.
The ML3 itself
Try to isolate the problem into one of the following areas
The ML3 or the connecting cable
Then try to narrow down the area further
Mechanical problems faults, or damage
Electrical or electronic problems or faults
ML3 User Manual 1.0 Troubleshooting
24
Functional check
The following two simple checks can be used to establish whether your ML3 is functioning within expected bounds:
Air reading
Hold the ML3 away from other objects and take a reading using an
HH2 meter, or voltmeter or logger.
The reading should be 0 ±4mV when used with a 5m cable.
Warning : Do not touch the pins
Mid range reading – dip rod tips in water
If you wish to take a quick reading to check the sensor is working you can dip the sensor into water.
With the pins half-immersed in tap water an
HH2 should read over 1000 mV or, if set to read
%vol and with soil type set to Organic, it should read in the range 80 to 100%vol.
ML3 User Manual 1.0 Troubleshooting
25
Technical Reference
Specifications
Volumetric water content
Accuracy
±1% vol over 0 to 50% vol and 0-40°C using soil specific calibrations
Measurement range 0 to 100% vol with reduced accuracy
≤3.5%vol over 50 to 500 mS.m
-1
and 0-50% vol
Output Signal
Output compatible with
0-1V differential ≈ 0 to 60% vol nominal
GP1, GP2, DL6, DL2e, HH2
Temperature
Sensor accuracy
Output
Output compatible with
Cabling error contribution
(to temperature readings)
Maximum cable length
Power requirement
Operating range
Environment
Sample volume
Dimensions/weight
ML3 must be fully buried to accurately measure soil temperature
±0.5°C over 0-40°C
not including logger or cabling error
Resistance
: 5.8kΩ to 28kΩ
GP1, GP2, DL6
Negligible for GP1, GP2 & DL6 (any cable length)
Negligible for DL2e (with 5m cable)
100m (GP1, GP2 & DL6 data loggers)
100m (DL2e: water content measurement)
25m (DL2e: temperature measurement)
5-14VDC, 18mA for 0.5 to 1s
-20 to +60°C
IP68
>95% influence within 40mm dia. cylinder 60mm long (approx. 75 cm
3
) around central rod.
170.5 mm x 39.8 mm dia./138 gm (without cable)
6 In water (no soil present) the reading may not be 100% vol. It depends on a0 and a1 but can still be
used as a quick check that the unit is working. See page 25.
8 Note: The DL6 has only one temperature channel. The DL6 error contribution to ML3 temperature measurement is negligible compared to the accuracy of the ML3 temperature sensor itself. The two only become comparable below -15C.
9 DL2e logger users can apply a correction in the Ls2Win logging software (for cable lengths >5m)
ML3 User Manual 1.0 Technical Reference
26
Conductivity response
This chart shows how salinity affects the output of the soil moisture sensor at various soil moisture levels.
ML3 Conductivity response at different water contents
1.0
0.8
0.6
0.4
1.4
1.2
0.2
0.0
0 100 200 300
Conductivity EC p
400
(mS.m
-1 )
500
Water content
100%
55%
45%
35%
25%
17%
7%
600
0 nonsaline
200 slightly saline
400 moderately saline
600
0 2 4 6
1000 strongly saline
1200 1400 1600
16 extremely saline mS.m
-1 dS.m
-1
8 10 12
Classification of salinity
14
ML3 User Manual 1.0 Technical Reference
27
Temperature response of soil moisture readings
The effect of temperature on the ML3 soil moisture readings in any particular soil will depend on a combination of effects:
The ML3 soil moisture electronics has very low temperature sensitivity, and makes a negligible contribution to the overall sensitivity.
The refractive index of water (√ε, see Calibration section) reduces as the temperature increases. This produces a negative temperature response particularly in soils or substrates with high water content.
Water that is bound to the surface of soil particles has a much lower refractive index than free water. The percentage of bound water decreases with temperature and this produces a positive temperature response particularly in clay soils at lower water contents.
The last two effects partially offset each other, but in soil conditions where one or the other effect dominates, the ML3 will appear to have a significant temperature response. This illustration is based on the model in
Illustrating the temperature dependence of ML3 readings in clay soil
Note: ice has a quite different refractive index from water, so ML3 soil moisture readings cannot be interpreted reliably when inserted into soil below 0°C.
ML3 User Manual 1.0 Technical Reference
28
Electromagnetic Compatibility (EMC)
General information
ML3 is a Class A product, intended for operation in non-residential environments.
Only use cables and accessories authorised by Delta-T (sensor cables from other sources for example may adversely affect product performance and affect quality of results).
If possible route cables along the soil surface or bury them – this also reduces possible trip hazard and animal damage.
Do not modify the product or its supplied accessories.
See also ML3 EMC Guidance on the Software and Manuals DVD
Issue 3.
Regulatory information
Europe
This device conforms to the essential requirements of the EMC directive 2004/108/EC, based on the following test standards:
EN61326-1:2006 Electrical requirement for measurement, control and laboratory use. EMC requirements: Group 1, Class A equipment – (emissions section only).
EN61326-1:2006 Electrical requirement for measurement, control and laboratory use. EMC requirements: Basic Immunity (immunity section only).
FCC compliance (USA)
This device conforms to Part 18 of FCC rules – Industrial, Scientific
& Medical Equipment.
Note: with reference to FCC Part 18.115 Elimination and investigation of harmful interference.
(a) The operator of the ISM equipment that causes harmful interference to radio services shall promptly take appropriate measures to correct the problem.
ML3 User Manual 1.0 Technical Reference
29
Definitions
Volumetric Soil Moisture Content
is defined as
θ
V
=
V
V
W
S where V w
is the volume of water contained in the sample and
Vs is the total volume of the soil sample.
The preferred units for this ratio are
m
frequently used.
3
.m
-3
, though %vol is
Soil Moisture Content varies from approx. 0.02 m soils at the permanent wilting point, through approx. 0.4 m clay soils at their field capacity, up to values as high as 0.85 m in saturated peat soils.
3
.m
-3
for sandy
3
.m
-3
for
3
.m
-3
Gravimetric Soil Moisture Content
is defined as
θ
G
=
M
M
W
S g.g
-
1
where M
W
is the mass of water in the sample, and
M
S
is the total mass of the
dry sample.
θ
To convert from volumetric to gravimetric water content, use the equation
G
=
θ
V
×
ρ
ρ
W
S where
ρ
W
is the density of water (= 1g.cm
-3
), and
ρ
S
is the bulk density of the sample (
M
V
S
S
).
ML3 User Manual 1.0 Technical Reference
30
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 around organic content: use for organic contents: bulk density range:
(g.cm
-3
)
use for bulk densities:
(g.cm
-3
)
Mineral ~ 1 %C* < 7 %C 1.25 - 1.5 > 1.0
Organic ~ 40 %C > 7 %C 0.2 - 0.7 < 1.0
* Note: %C denotes “percentage Carbon” and is a measure of organic content
Salinity
The preferred SI units for ionic conductivity are
mS.m
-1
Siemens, the unit of electric conductance = ohm
-1
).
(where S is
The following conversions apply:
1 mS.m
-1
= 0.01 dS.m
-1
= 0.01 mS.cm
-1
= 10 µS.cm
-1
Soil salinity can be classified using the following descriptive categories:
0 nonsaline
200 slightly saline
400 moderately saline
600 1000 strongly saline
1200 1400 1600 extremely saline mS.m
-1
0 2 4 6 8 10 12 14 16 dS.m
-1
Classification of salinity
See also http://www.land.vic.gov.au/DPI/Vro/vrosite.nsf/pages/water_spotting_soil_salting_class_ranges#s1
ML3 User Manual 1.0 Technical Reference
31
References
1. Gaskin, G.J. and J.D. Miller, 1996
Measurement of soil water content using a simplified impedance measuring technique.
J. Agr. Engng Res 63, 153-160
2. Topp, G.C., J. L. Davis and A. P Annan 1980
Electromagnetic determination of soil water content .
Water Resour. Res 16(3) 574-582
3.
Whalley, W.R. 1993
4.
5.
6.
7.
Considerations on the use of time-domain reflectometry
(TDR) for measuring soil moisture content.
Journal of Soil Sci. 44, 1-9
White, I., J.H. Knight, S.J. Zegelin, and Topp, G.C. 1994
Comments on ‘Considerations on the use of time-domain reflectometry (TDR) for measuring soil water content’ by W R
Whalley
Journal of Soil Sci. 45, 503-508
Roth, C.H., M.A. Malicki, and R. Plagge, 1992
Empirical evaluation of the relationship between soil dielectric constant and volumetric water content as the basis for calibrating soil moisture measurements.
Journal of Soil Sci. 43, 1-13
Knight, J.H. 1992
Sensitivity of Time Domain Reflectometry measurements to lateral variations in soil water content.
Water Resour. Res., 28, 2345-2352
Or, D. and J.M. Wraith 1999
Temperature effects on soil bulk dielectric permittivity measured by time domain reflectrometry: A physical model.
Water Resour Res., 35, 371-383
ML3 User Manual 1.0 References
32
Technical Support
Terms and Conditions of Sale
Our Conditions of Sale (ref: COND: 1/07) set out Delta-T's legal obligations on these matters. The following paragraphs summarise Delta T's position but reference should always be made to the exact terms of our Conditions of Sale, which will prevail over the following explanation.
Delta-T warrants that the goods will be free from defects arising out of the materials used or poor workmanship for a period of twelve months from the date of delivery.
Delta-T shall be under no liability in respect of any defect arising from fair wear and tear, and the warranty does not cover damage through misuse or inexpert servicing, or other circumstances beyond their control.
If the buyer experiences problems with the goods they shall notify Delta-T
(or Delta-T’s local distributor) as soon as they become aware of such problem.
Delta-T may rectify the problem by replacing faulty parts free of charge, or by repairing the goods free of charge at Delta-T's premises in the UK during the warranty period.
If Delta-T requires that goods under warranty be returned to them from overseas for repair, Delta-T shall not be liable for the cost of carriage or for customs clearance in respect of such goods. However, Delta-T requires that such returns are discussed with them in advance and may at their discretion waive these charges.
Delta-T shall not be liable to supply products free of charge or repair any goods where the products or goods in question have been discontinued or have become obsolete, although Delta-T will endeavour to remedy the buyer’s problem.
Delta-T shall not be liable to the buyer for any consequential loss, damage or compensation whatsoever (whether caused by the negligence of the
Delta-T, their employees or distributors or otherwise) which arise from the supply of the goods and/or services, or their use or resale by the buyer.
Delta-T shall not be liable to the buyer by reason of any delay or failure to perform their obligations in relation to the goods and/or services if the delay or failure was due to any cause beyond the Delta-T’s reasonable control.
ML3 User Manual 1.0 Technical Support
33
Service, Repairs and Spares
Users in countries that have a Delta-T distributor or technical representative should contact them in the first instance.
Spare parts for our own instruments can be supplied and can normally be despatched within a few working days of receiving an order.
Spare parts and accessories for products not manufactured by Delta-T may have to be obtained from our supplier, and a certain amount of additional delay is inevitable.
No goods or equipment should be returned to Delta-T without first obtaining the return authorisation from 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.
The goods will be inspected and you will be informed of the likely cost and delay.
We normally expect to complete repairs within one or two weeks of receiving the equipment. However, if the equipment has to be forwarded to our original supplier for specialist repairs or recalibration, additional delays of a few weeks may be expected. For contact details see below.
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.
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
Delta-T Devices Ltd
130 Low Road
Burwell
Cambridge CB25 0EJ
England (UK)
Tel : +44 1638 742922
Fax : +44 1638 743155
E-mail : [email protected] [email protected]
Web : www.delta-t.co.uk
ML3 User Manual 1.0 Technical Support
34
Appendix 1
Soil-specific Calibration
This note provides details of 2 techniques for generating soil-specific calibrations:
Laboratory calibration for substrates * and non-clay soils
Laboratory calibration for clay soils
* We use the term substrate to refer to any artificial growing medium.
Underlying principle
Soil moisture content (θ) is proportional to the refractive index of the soil
(√ε) as measured by the ML3 (see Calibration section).
The goal of calibration is to generate two coefficients (a
0
, a
1
) which can be used in a linear equation to convert probe readings into soil moisture:
ε
=
a
0
+
a
1
×
θ
ML3 User Manual 1.0 Appendix 1
35
Laboratory calibration for non-clay soils
Process
This is the easiest technique, but it’s not suitable for soils that shrink or become very hard when dry.
Equipment you will need:
ML3 and meter
Soil corer (if doing a calibration for a cohesive soil rather than sand or a substrate)
Heat-resistant beaker (≥ 0.5 litre)
Weighing balance (accurate to < 1g)
Temperature controlled oven (for mineral soils or substrates)
Notes and example
Collect a damp sample of the soil or substrate.
This sample needs to be unchanged from its in-situ density, to be ≥ 0.4 litre, to have the correct dimensions to fit the beaker, and to be generally uniform in water content.
For cohesive soils this is most easily done with a soil-corer.
Sandy soils can be poured into the beaker, but you should take the subsequent measurements immediately, as the water will quickly begin to drain to the bottom of the beaker.
Compressible soils and composts often require measurement of the in-situ density and then need to be carefully reconstituted at that density within the beaker.
Measure the volume occupied by the sample.
L s
= 463.5ml
Weigh the sample, including the beaker.
W w
= 743.3g
ML3 User Manual 1.0 Appendix 1
36
Insert ML3 into the sample and record its output in Volts.
V w
= 0.572V
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).
For organic soils and composts it’s usual to air-dry the sample to avoid burning off any volatile factions.
Weigh the dry sample in the beaker.
W
0
= 627.2g
Re-insert the ML3 into the dry sample and record this reading.
V
0
= 0.089V
Calculate a
0
For the ML3,
In the dry soil V = V
0
= 0.089 Volts
Substitute this into the equation
√𝜖 = 1.0 + 6.175𝑉 + 6.303𝑉
− 184.78𝑉
5
2
− 73.578𝑉
+ 68.017𝑉
6
3
+ 183.44𝑉
4 gives
ε
0
= 1 .
56
Since
θ
0
= 0, this is the value needed for a
0
a
0
= 1.56
Calculate
θ
w
The water content of the wet soil,
θ the weight of water lost during drying, (W volume, L
s
:
w
, can be calculated from
w
– W
0
) and its
ML3 User Manual 1.0 Appendix 1
37
Calculate a
1
Result
θ
w
=
(
W w
−
W
0
)
L s
=
(
743 .
3 − 627 .
2
)
463 .
5 = 0 .
25
θ
w
= 0.25
In the wet soil V = V
w
= 0.572 Volts and substituting gives
ε
w
= 3 .
53
Finally
a
1
=
(
ε
w
−
ε
0
)
(
θ
w
−
θ
0
) (
3 .
53 − 1 .
56
) (
0 .
25 − 0
)
= 7 .
87
a
1
= 7.87
a
0
= 1.56
a
1
= 7.87
In this example this soil is now calibrated.
You can now use these two numbers in place of the standard mineral or organic calibration factors to convert ML3 readings into volumetric water content θ using:
ε =
a
0
+
a
1
× θ
ML3 User Manual 1.0 Appendix 1
38
Laboratory calibration for clay soils
Process
This technique is adapted to avoid the near-impossibility of inserting the ML3 into completely dry clay soil. It requires taking measurements at 2 significantly different, but still damp, moisture levels.
Equipment you will need:
ML3 and meter
Soil corer
Heat-resistant beaker (≥ 500ml)
Weighing balance (accurate to < 1g)
Temperature controlled oven
Notes and example
Collect a wet sample of the clay soil: 25 to 30% water content would be ideal.
This sample needs to be unchanged from its in-situ density, to be ≥ 400ml, to have the correct dimensions to fit the beaker, and to be generally uniform in water content.
This is most easily done with soil-corer.
Measure the volume occupied by the sample
.
L s
= 463.5ml
Weigh the wet sample, including the beaker
.
W w
= 743.3g
ML3 User Manual 1.0 Appendix 1
39
Insert ML3 into the wet sample and record its output in Volts.
V w
= 0.572V
Dry the sample until still moist, ~15% water content. Gentle warming can be used to accelerate the process, but take care not to over-dry in places, and allow time for the water content to equilibrate throughout the sample before taking a reading.
Reweigh.
W m
= 693.2g
Re-measure with the ML3.
V m
= 0.348V
Dry the sample thoroughly.
With clay 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).
Weigh the dry sample in the beaker
.
W
0
= 627.2g
ML3 User Manual 1.0 Appendix 1
40
Calculations
Substituting in the ML3 equation
√𝜖 = 1.0 + 6.175𝑉 + 6.303𝑉
− 184.78𝑉
2
5
− 73.578𝑉
3
+ 68.017𝑉
6
+ 183.44𝑉
4
For the wet soil provides two dielectric values, √ε at two known water contents, θ
w w
and √ε
and θ
m m
,
Substituting Vw = 0.572 gives
√𝜖 = 3.53 = a
0
+ 𝑎
1 𝜃 for
θ
w
=
(
743 .
3 − 627 .
2
)
463 .
5 = 0 .
25
For the moist soil
Calculate a
Substituting Vm = 0.348 gives
√𝜖 = 2.68 = a
0
+ 𝑎
1 𝜃 𝑚
For
θ
m
=
(
693 .
2 − 627 .
2
)
463 .
5
1
Then
a
1
=
(
ε
w
−
ε
m
)
(
θ
w
−
θ
m
)
=
=
0 .
14
7 .
86
a
1
= 7.86
ε
w
−
(
a
1
⋅
θ
w
)
= 1 .
56
Calculate a
0
and
a
0
=
a
0
= 1.56
Result a
1
= 7.86
a
0
= 1.56
In this example this soil is now calibrated.
You can now use these two numbers in place of the standard mineral or organic calibration factors to convert ML3 readings into volumetric water content θ using:
ε
=
a
0
+
a
1
×
θ
See also page Underlying principle on page 35
ML3 User Manual 1.0
41
Appendix 2:
The ML3 Temperature Sensor
Soil moisture content is used with the measurement of soil temperature in several major application areas including the following:
Global warming and climate studies
Soils contain more than four times as much carbon as the CO2 in the atmosphere, and each year they release about ten times as much carbon through soil respiration as the combined release through burning fossil fuels. Soil respiration rates are particularly sensitive to changes in both temperature and the moisture content of the soil.
Soils also have a significant interaction with climate as they store and release heat – soil temperature provides a measure of the energy partitioning, which in turn is strongly influenced by the effect of soil moisture on thermal conductivity.
Civil engineering
Most civil engineering projects depend critically on the mechanical properties of soils. Those properties are effected by many different parameters, but moisture content and temperature are the two variables that are most likely to change over time, so may be measured together in order to assess their impact.
Soil contamination and hydrogeology
Soil moisture is the main determinant for the movement of contaminants and solutes through soils, but temperature also has a significant influence so they are often measured together.
Agriculture
Temperature may be measured alongside soil water content for studies of evapotranspiration, soil water balance and irrigation. Soil strength and seedling emergence depend on soil moisture and temperature, and both need to be taken into account when deciding when to sow.
ML3 User Manual 1.0 Appendix 2:
42
ML3 Temperature Measurement
The ML3 Temperature sensor uses a thermistor with a 10K resistance at 25 ˚C. However:
A. This sensor has a different response curve from the more widely used 10K3A1B type. The response curve is given in the
Resistance to Temperature Lookup Table on page 45.
B. The Thermistor circuit shares the Power 0V wire. If the thermistor is measured when the ML3 is powered, the measured resistance measurement may need to be corrected for 18 mA ML3 supply current.
GP2, GP1 and DL6 loggers
The ‘ML3 Temperature’ sensor type in DeltaLINK 3 performs the supply current correction.
DL2e Logger
The linearization table for the ‘S3T’ sensor code (‘ML3
Temperature’) provides supply current correction for the
SMSC/lw-05 5m logger cable ONLY.
Extension cables and other cable lengths
Create your own custom sensor type(s) and linearization tables as described in Ls2Win Help topic, How to… ‘Add or modify a sensor type in the sensor library’.
Enter corrected resistance values (R) for each linearization table point:
R = R5 + (0.059 x Lex) kΩ (See footnote
or R = R5 + (0.9 x Rc – 0.297) kΩ where
R5 = value supplied in the table for the ‘ML3 Temp, 5m’ sensor type.
Lex = length of extension cable, excluding the 5m of SMSC/lw-05 cable.
Rc = total cable resistance, including resistance of
SMSC/lw-05
cable, if fitted.
10
Note: This equation only applies to Delta-T ML3 cables
ML3 User Manual 1.0 Appendix 2:
43
Other loggers
If your logger can be programmed so that the soil moisture and temperature readings can be taken sequentially (i.e. the sensor is not powered during the temperature reading), then the temperature
can be obtained directly from the response curve on page 45.
Otherwise, correct the resistance reading before applying the response curve.
You need to know the resistance of the Power 0V wire in the ML3 cable (Rc) and establish whether your logger uses voltage or current excitation for resistance measurement.
Voltage Excited
You need to know the excitation voltage (Vref), reference resistance (Rref).
The correct resistance is given by the equation:
R = a0 + a1 * Rmeas
Where: a0 = – Ic.Rc.Rref / Vref a1 = 1 – Ic.Rc / Vref
Ic = 18 mA (ML3 sensor supply current)
For Delta-T EXT/5W-xx series cables:
Rc = 0.066 Ω.m
-1
For the SMSC/lw-05 5m logger cable
Rc = 0.33 Ω
Current Excited
You need to know the excitation current (Iex).
The corrected resistance is given by the equation (using terms defined above):
R = Rmeas – Ic.Rc/Iex
Effect of Temperature on Water Permittivity
See
Temperature response of soil moisture readings on page 28
ML3 User Manual 1.0 Appendix 2:
44
Resistance to Temperature Lookup Table
Temperature Resistance degrees C Kohms
-25 90.538
11
14
17
20
23
26
-1
2
5
8
-7
-4
-22
-19
-16
-13
-10
29
32
35
38
41
44
47
50
77.683
66.854
57.713
49.968
43.379
37.759
32.957
28.844
25.299
22.244
19.608
17.321
15.334
13.606
12.098
10.780
9.623
8.611
7.720
6.935
6.241
5.627
5.080
4.595
4.162
ML3 Resistance to Temperature
Conversion Chart
100
90
80
70
60
50
40
30
20
10
Resistance
(kOhms)
53 3.775
56 3.430
0
-40 -20 0 20 40 60 80
59
62
65
3.121
2.843
2.593
Temperature (degrees C)
Note: This table has been optimised for use as a look-up table.
To minimise linear interpolation errors the data points fall either side of the manufacturers’ specified sensor response curve. This helps optimise the overall accuracy of readings.
ML3 User Manual 1.0 Appendix 2:
45
Index
A
Agriculture, 42
Air reading, 25
Auger, 7
C
Cable Connections, 10
Cable length correction, 43
Calibration check, 25 generalised, 22 sensor, 21, 22 soil, 19, 22
Soil, 35 soil-specific, 35
Care and safety, 8
Care and Safety, 8
Certification emc, 29
Civil engineering, 42
climate, 42
Conductivity response, 27
Connections, 12
contamination, 42
Conversions linearisation table, 20, 21 polynomial, 20, 21
Copyright, 2
D
Data logger, 16, 23, 24, 25
DL2e, 23, 24
DL6, 24
GP1, 14, 24
ML3 User Manual 1.0
other, 16
Definitions, 30
Description, 5
Dielectric performance, 21 refractive index, 18, 19, 35
Dimensions, 6
DL6, 14
EMC, 29
Extension cables, 10
E
FCC compliance, 29
Features, 5
F
Global warming, 42
GP1, 13, 14, 24
GP2, 12
G
H
HH2, 7, 17, 18, 24, 25
hydrogeology, 42
Installation buried, 11 insertion rod, 11 surface, 11
I
Index
46
L
Linearisation table, 23 volts to %vol, 16, 23
M
Meter, 24
Moisture content, 5, 9, 32, 35
O
Organic and Mineral
, 31
P
Parts, 7
Permittivity, 9, 18, 32
Polynomial conversion, 22
R
References, 32
Regulatory information, 29
Rods, 8, 9, 11
S
Sales code, 7
Salinity, 31
Servicing, 34
SMSC/lw-05, 43
Soil clay, 19, 20, 30, 35, 36, 39 mineral, 18, 20, 22, 36, 37, 40 organic, 18, 20, 22, 31, 37 stony, 11 soil calibrations, 20
Specifications, 2, 26
T
Technical support, 33, 34
Temperature cable length correction, 16, 43
Temperature response of soil moisture readings, 28
Temperature sensor cable length correction, 44
Temperature Sensor Lookup Table, 45
Troubleshooting, 24
V
Volumetric Soil Moisture
, 30
W
Warning
Care and Safety, 8
Warning, 25
ML3 User Manual 1.0 Index
47

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Key features
- Measures soil moisture content and temperature
- Waterproof and can be buried
- Compatible with various data loggers and meters
- Can be calibrated for specific soil types
- Accurate to within ±1% vol
- Easy installation at depth in augered holes