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User Manual
EnviroPro Soil Moisture Sensor
Version 4.7
August 2014
Copyright 2014 EnviroPro Dielectrics
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Table of Contents
1
The EnviroPro Sensor .......................................................................... 4
2
Specifications ........................................................................................ 6
3
Ordering Details: ................................................................................... 8
4
Warranty ............................................................................................... 9
5
Wiring Details ...................................................................................... 10
5.1
Sensor Wiring ............................................................................. 10
5.2
Power Supply .............................................................................. 10
6
Sensor Setup and Configuration ........................................................ 11
7
Standard SDI-12 Commands ............................................................. 12
7.1
Initialisation and power up .......................................................... 13
7.1.1.1
Initialisation ..................................................................... 13
7.1.1.2
SDI-12 Operation ............................................................ 13
7.2
SDI-12 Info Command ................................................................ 14
7.3
SDI-12 Measurement.................................................................. 15
7.3.1
7.4
8
Limitations of M Command ................................................. 16
To Change a Probe Address ...................................................... 17
Installation ........................................................................................... 18
8.1
Soil Slurry.................................................................................... 18
8.2
Bentonite Slurry .......................................................................... 18
8.3
Installation ................................................................................... 19
8.4
Cable Considerations ................................................................. 19
8.4.1
At the Probe end ................................................................. 20
8.4.2
At the logger/telemetry end................................................. 20
8.5
Probe Removal ........................................................................... 21
8.5.1
Probe Removal Tool ........................................................... 21
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8.5.2
8.6
9
Removal with Vice Grips ..................................................... 23
Slurry and Probe Installation....................................................... 24
8.6.1
Large format (50mm) probes .............................................. 24
8.6.2
EnviroPro and Slurry........................................................... 26
Connection to Data Loggers / Telemetry Systems ............................. 27
10
Sensor Calibration .......................................................................... 28
10.1
Simple Calibration ....................................................................... 28
10.2
Bucket Calibration ....................................................................... 29
11
Regulatory Compliance Declaration ............................................... 30
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1 The EnviroPro Sensor
This manual is written for the Series “D” EnviroPro family of soil moisture
probes. Manuals for earlier versions of the product are available on request
from EnviroPro Dielectrics Pty Ltd. The “D” version probes are recognizable
by their green colour (earlier versions utilized a white outer tube).
The EnviroPro sensor monitors changes in the dielectric properties of the
soil to provide users with continuous monitoring of soil moisture, soil salinity
and soil temperature.
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Simple capacitance or dielectric sensors, which determine soil moisture
levels using a frequency change, suffer from errors caused by the salinity
of the water in the soil. By measuring the salinity of the soil, the EnviroPro
soil probe can compensate for the salt induced changes and provide a
more accurate soil moisture measurement. Measurement of soil salinity
provides users with additional information to help them improve the
application of nutrients and to deal with irrigation induced salt build up.
The electronic components on the probe are fully encapsulated in epoxy –
nothing can move, and all circuits are protected against moisture and
chemicals, which makes it reliable, consistent and very stable.
The EnviroPro is completely maintenance free with a long lifespan. The
probe does not need to be removed and opened up for annual
maintenance like competing sensors. To provide certainty to users,
EnviroPro Dielectrics provides the probes with a 5 year, return to base
warranty.
The EnviroPro is available in a number of standard segment lengths: 40cm,
80cm, 120cm and 160cm. Sensors are located at 10cm along the probe
body. A 40cm probe this carries 4 sensors and a 160cm probe 16. Two
variants of the probe are available:
• The EnviroPro – which returns soil moisture and soil temperature
from each sensor element
• The EnviroPro EC – which returns soil moisture, soil temperature
and soil conductivity from each sensor element.
Upon payment of the difference in price between the standard and EC
version, the former may be upgraded to return EC at any time. This
requires use of the EnviroPro Probe Updater unit. When an upgrade is
ordered (quoting the serial number), your distributor will be sent a probe
specific unlock code, which is entered into the Probe Updater unit.
The EnviroPro probe connects to any SDI-12 compatible data logger. If
more than one probe is to be connected to the same logger, the probes
need to be programmed to occupy different addresses: e.g. the first as
Address 0 and the second as Address 1. The address can be changed at
any time using the standard SDI-12 commands (Refer Section 6).
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2 Specifications
The following table shows the specifications of the EnviroPro sensor.
Parameter
Sensor Depths
Sensor Position on Probe
Body
Range /
Specification
Accuracy/
10cm Increments
-
Qualifier
Top sensor centred
5cm below top of
probe body
Dimensions
Diameter
Length
32mm
40cm – 47cm
80cm – 87cm
120cm – 127cm
160cm – 167cm
Interface
SDI-12
-
+6 to +15 V DC
The probe is
protected against
reverse polarity
and incorrect
connection
Sleep
0.4 mA
(per 40cm
segment)
During Measurement
60 mA
For 0.6 sec
During Data Transfer
18 mA
For 0.4 sec
0-50%
+/- 2 %
Power Supply
Power Consumption
Soil Moisture
(Volumetric Soil Moisture
Content)
(in standard
calibration media)
o
Soil Temperature
-10 to +60
Celsius
Soil Salinity
0 to 6 dS/m
o
+ / - 1 Celsius
Relative value
only. Requires
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calibration on site
to local soil
Operating Range
Cable Length
Cable termination
-10 to 100
Celsius
o
-
5m
-
Bare wire
Connectors
available on
request for
volume quantities
Note:
Soil Moisture Accuracy
In common with all other capacitance probes, the EnviroPro responds to
changes in the dielectric properties of the soil. The relationship between
dielectric properties and volumetric moisture content is well understood and
widely documented. However it varies from probe design to probe design
and from one soil type to another.
The EnviroPro is calibrated at the time of manufacture, to a standardized
soil media (fine sand) and it is the accuracy of the sensors in this media
which is shown in the table in the preceding section. Secondary calibrations
are then used to adjust the probe output for specific soils. Further details
are given in the section on probe calibration (Section 10).
Electrical Conductivity Accuracy
The EnviroPro responds to changes in the soil’s bulk conductivity which is
influenced by soil type, moisture content, soil temperature and the total salt
load of the soil. Bulk conductivity values should be compared between two
periods where the soil moisture content is the same.
The relationship between bulk conductivity and true pore water conductivity
is site specific. To convert the indicated EC to pore water conductivity, the
values obtained from the probe should be compared with those obtained
from soil samples or from a suction sampler.
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3 Ordering Details:
When ordering or identifying probes, please specify the model and version
as per the table below:
EP100DL-04
EP100DL-08
EP100DL-12
EP100DL-16
40cm 4 sensor probe for SM and ST
80cm 8 sensor probe for SM and ST
120cm 12 sensor probe for SM and ST
160cm 16 sensor probe for SM and ST
EP100D-04
EP100D-08
EP100D-12
EP100D-16
40cm 4 sensor probe for SM ST and EC
80cm 8 sensor probe for SM ST and EC
120cm 12 sensor probe for SM ST and EC
160cm 16 sensor probe for SM ST and EC
The Upgrader Unit is a distributor only tool and is required in order to
enable EC on a standard probe. Your distributor can perform the upgrade
for you. Part numbers for the upgrades are shown below:
EP-UPG-04
EP-UPG-08
EP-UPG-12
EP-UPG-16
Upgrade 40cm probe to enable EC
Upgrade 80cm probe to enable EC
Upgrade 120cm probe to enable EC
Upgrade 160cm probe to enable EC
EP-UPDATER EnviroPro Upgrader Unit (required to upgrade
Standard probes to enable the EC measurement,
only available to distributors)
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4 Warranty
The EnviroPro probes are covered by a five (5) year warranty.
Warranty is available on a return to base basis only. Probe owners must
pay for return shipment of faulty products either to EnviroPro Dielectrics or
their local distributor. If the probe is assessed by EnviroPro Dielectrics and
found to be a warranty failure, it will be replaced free of charge. EnviroPro
Dielectrics will pay the return shipment to the owner.
The warranty does not cover mechanical damage, damage inflicted during
probe installation or removal or damage caused by animals.
Prior to installing the product, please ensure that you read, understand and
accept the Warranty Statement. If you do not accept the conditions of the
Warranty Statement, please return the probe to the probe supplier for a
refund.
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5 Wiring Details
5.1 Sensor Wiring
The EnviroPro probes are normally shipped fitted with a 5m cable, the
colour code for which is shown in the table below:
Function
Power Supply (+6
to +15V)
Ground
SDI 12 Data
3 Core Cable
4 Core Cable
Brown
Red
Green/Yellow
Black
Blue
Blue
NOTE: The probes are protected against any combinations of incorrect
connections up to 30V AC or DC.
5.2 Power Supply
The EnviroPro sensors can operate from a power supply in the range of +6
to +15Volts.
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6 Sensor Setup and Configuration
The sensors should be configured and tested prior to installation in the soil.
This may be done with one of 3 methods:
From the telemetry or logging device to which the probe will be
connected (using transparent mode)
Using an SDI-12 Verifier or USB to SDI-12 converter such as the
Tekbox TBS03 (which provides a complete terminal program, SDI
Commander, for sending and receiving SDI-12 commands)
Using an SDI-12 Sniffer. The Sniffer” can be connected across the
SD-12 data line between the SDI-12 logging device and the probe.
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7 Standard SDI-12 Commands
The EnviroPro sensors are compatible with the basic requirements of the
SDI-12 interface specification (SDI-12 Specification Version 1.2, October
1996).
The commands can be sent to the sensor using a PC and terminal software
– an SDI-12 verifier is not required. The sensor will respond to the following
SDI-12 commands:
Name
Command
Response
Break
Continuous spacing for
at least 12 milliseconds
Sensor / Interface unit
wakes from Sleep mode
Acknowledge Active
a!
a<CR><LF>
Send Identification
aI!
allccccccccmmmmmmv
vvxxx...xx<CR><LF>
Change Address
aAb!
b<CR><LF> (Note 1)
Address Query
?!
a<CR><LF> (Note 2)
Start Measurement
aM!
atttn<CR><LF>
Send Data
aD0!
a<values><CR><LF>
.
a<values><CR><LF>
.
a<values><CR><LF>
.
a<values><CR><LF>
aD9!
a<values><CR><LF>
aM1!
atttn<CR><LF>
.
.atttn<CR><LF>
.
. atttn<CR><LF>
.
. atttn<CR><LF>
Additional
Measurements
.
aM9!
atttn<CR><LF>
Start Verification
aV!
atttn<CR><LF>
Start Concurrent
aC!
atttnn<CR><LF>
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Measurement
Additional Concurrent
Measurements
aC1!
atttnn<CR><LF>
.
atttnn<CR><LF>
.
atttnn<CR><LF>
.
atttnn<CR><LF>
aC9!
Continuous
Measurements
aR0! ... aR9!
a<values><CR><LF>
(same as the D
commands)
In the above table:
a
Sensor address (0 to 9, a to z, A to Z)
As a minimum, you should confirm that the sensor responds to an “I”
command and preferably also perform a Concurrent (C) Measurement with
the probe inserted into a suitable test medium. A test medium may be
made up by placing a wetted sponge into a zip lock bag. The bag may be
wrapped around the probe body and secured with a rubber band. It may
then be slid up and down the probe body and measurements taken at each
sensor position.
7.1 Initialisation and power up
7.1.1.1 Initialisation
Under the SDI-12 protocol, the sensor interface normally remains
permanently powered. The sensors connected to the interface go in to idle
mode between reads and draw minimal current between measurements.
After receipt of a Break Command, all sensors on the bus wake and listen
for a command addressed to them.
Note however that to save power, some logging devices / telemetry units
support a Power Save mode, which shuts off sensor power between reads.
The EnviroPro is compatible with Power Save mode.
7.1.1.2
Sleep
SDI-12 Operation
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When the Interface is not executing any commands, it reverts to
Sleep mode to minimize power consumption
although the SDi_12 Bus Power line remains active at all times, the
Interface shuts down power to the probes during sleep.
Command Mode
the SDI-12 logger wakes the Interface box by issuing a Break
command
• the data line rests in the mark state (typically 0 volts)
• a break is signalled by setting the data line in the space state (3.5
to 5.5V) for at least 12 mSec
upon receipt of the Break, the Interface will execute any SDI-12
commands issued from the logging device or computer
in response to a Measure Command, the probe responds with the
number of values it will return and the time after which they will be
ready. The logging device / telemetry unit then queries the sensor
again to collect the measurement values.
7.2 SDI-12 Info Command
Use the “I” command to query the sensor and return the sensor information
– model, serial number etc.
Example: From a telemetry unit which supports Transparent SDI-12
commands:
Command
0I!
Response
012EP100DL041120529185012
29185012 Serial No
205
Version
04011
Model
EP100DL
Vendor
12
SDI-12 version
0
SDI-12 Address
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7.3 SDI-12 Measurement
To make an SDI-12 Measurement you should always use the C
(Concurrent Measure) commands rather than the Measure (M) commands.
Only use M if your logging device does not support C.
When a measure command is issued, the probe will make a measurement
of all available parameters and retain them in its memory for 12 seconds. If
a subsequent read is issued within this time, the values will be returned
from memory rather than making a new measurement. If a command is
received after 12 seconds, a fresh measurement will be made.
C!
C1!
C2!
C3!
C4!
C5!
Returns salinity compensated soil moisture
Note: the “0” is omitted rather than sending 0C0!
Returns soil salinity
Returns soil temperature (degrees Celsius)
Returns un-compensated soil moisture
Returns raw salinity
Note: the manufacturer reserves the right to
alter this command in future versions
Returns soil temperature (degrees Fahrenheit)
The results are returned using the D<n>! command:
Under the SDI-12 protocol, after receiving a C or M commands, the
sensor must return the number of values which will be sent. When a
D command is issued, the SDI-12 logger checks to see if all of the
required values were received. If not, it continues to execute D
commands (incrementing the suffix each time) until all values are
received.
In response to an M command, the EnviroPro returns 4 values with
each D command
• A 40cm probe will thus return all of its values with D0
• an 80cm probe will require D0 and D1
• a 120cm probe will require D0, D1, D2 (See notes below on
limitation on number of readings)
• a 160cm probe will require D0, D1, D2 (See notes below on
limitation on number of readings)
the C (Concurrent Measure) command allows more values to be
returned using a single D command hence reducing the time taken
to return results which in turn reduces total power consumption.
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M Command with D0 to Dn:
Example from a telemetry unit which supports Transparent SDI-12
commands, for a sensor on Address 0, using the Measure (M) command:
Command
0M!
Response
00018
8 measurements in 1 sec
Command
Response
Command
Response
0D0!
0+23.45+23.30+25.49+25.3
0D1!
0+0.001+0.023+0.032+0.042
C Command with D0:
Example from a telemetry unit which supports Transparent SDI-12
commands, for a sensor on Address 0, using the Concurrent Measure (C)
command:
Command
0C!
Response
000108
8 measurements in 1 sec
Command
0D0!
Response
0+008.67+000.85+000.77+000.75+001.43+000.55+000.17+000.00
7.3.1 Limitations of M Command
The M Command has a number of limitations:
The M command only has one character value with which to return
the number of readings being given.
• the response to an M is <address><nnn sec><x readings>
• the response to a C is <address><nnn sec.<xx readings>
Hence only 9 measurements can be returned from a sensor. This
means that on a 120 or 160cm probe, you will not be able to retrieve
all of the sensor values
• The 120cm will return the 10, 20, 30, 40, 50, 60, 80, 100 and
120cm values
• The 160cm probe will return the 10, 20, 40, 60, 80, 100, 120, 140
and 160cm values
In response to an M command, the D command will only return 4
values at a time, increasing the time taken to get values from the
longer probes.
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7.4 To Change a Probe Address
The address of a probe may be changed with the a / A command.
Example: From a telemetry unit which supports Transparent SDI-12
commands, change probe address from “0” to “s”:
Command
0As
Response
s
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8 Installation
Installation should only be completed once the probes have been tested
and the probe address set.
The probe is installed into an over-sized hole and must be set into a slurry
mix. See section 8.6 for a discussion on the impact of slurry on narrow
versus large format probes.
Installation augers are available through EnviroPro
Dielectrics or your local Distributor.
EP-AUGER
Installation auger 36mm
EP-INST-EXT10
Extension bar 1m
EP-INST-EXT05
Extension bar 0.5m
Note: the EP-AUGER kit comprises a 36m gouge
auger, T-Handle, 1.0m extension bar and auger
cleaning tool. Additional extension bars may be
required for probes longer than 80cm.
The slurry may be made up of soil removed from the site or using a
bentonite-sand mix.
8.1 Soil Slurry
In most cases, the slurry may be made up using soil removed from the
hole.
Preparation:
Pass the soil through a sieve to remove any rocks and organic
material
Mix the sieved soil with water to form a creamy paste.
8.2 Bentonite Slurry
The bentonite slurry can be used is the soil on site is unsuitable.
In this case, the following items are required for installation of the sensor
1kg of fine sand (e.g. Unimin AFS85 grade)
100g Bentonite (civil grade e.g. Unimin Active Gel 150)
1L water
Small bucket with lid
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Funnel
2 L plastic bottle with lid
Note: The volume of the mixture is about 1.4L, the weight is 2.1kg
Preparation
Mix the dry bentonite and sand together in a bucket
Pour the dry mix through the funnel into the 2 L plastic bottle
Pour in the water, close the lid and shake until thoroughly mixed
Continue to shake the mix at regular intervals until it is used.
8.3 Installation
After identifying a site for the sensor, drill a hole down to 10cm
greater than the probe length (e.g. 95cm for an 80cm probe)
Pre-wet the soil in the hole by pouring in enough water to fill it to
close to the surface. Wait until the water has drained in to the
surrounding soil before proceeding. If you do not pre-wet the hole,
the soil may draw the water from the slurry too quickly and you will
not be able to insert the probe. If this happens, you will have to
remove the probe, clear the slurry out with the installation auger and
repeat the process (Pre-wetting is usually not required with the
bentonite slurry
Pour approximately 7000 mL of the mixture into the hole (for an
80cm probe)
Push the sensor down into the hole: as the sensor moves down, it
will displace the slurry from the bottom
• The slurry mix will fill any air gaps around the sensor and provide a
consistent contact with the soil
• For the probe to measure the top 10cm of soil, the head of the
probe should sit 2.5cm below the surface
Remove any surplus slurry mix from above ground level
If probe does not push down to required depth on first attempt (15kg
maximum pressure allowed on top of probe), pull out the probe,
clean the hole with the auger and repeat the process.
8.4 Cable Considerations
If you are going to bury the EnviroPro cable – for example in turf or
broadacre crops – you need to be conscious of the risk of damage to the
probe if either the cable is snagged by machinery or stretched due to
compaction of the ground.
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The simplest way to avoid damage is to leave a goose neck at each end of
the cable. If the cable is pulled, the loop can tighten, preventing the cable
form being stressed at the junction with the probe body.
8.4.1 At the Probe end
As you install the probe, orient the probe body so that the cable entry point
is pointing in the opposite direction to your trench.
8.4.2 At the logger/telemetry end
Where the cable leaves the ground, you should consider placing it in a
protective sheath to prevent damage form vermin or machinery. The sheath
can be rigid conduit, flexible conduit or blind poly tube. Leave a goose neck
in the cable prior to routing the cable end to the telemetry unit or data
logger.
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Once you have made the goose neck, strap the cable to the post to which
the telemetry unit or data logger is attached using zip ties.
8.5 Probe Removal
The EnviroPro probes may be removed using a Probe Removal Tool. If one
is not available, Vice Grips and insertion foam may be used.
8.5.1 Probe Removal Tool
An EnviroPro Probe Removal Tool is available to order through EnviroPro
Dielectrics and your local Distributor.
Part Number
EP-REMOV
Removal Process:
Using a hand trowel or small spade, carefully remove the soil
around the head of the probe down to a depth of 15cm, being extra
careful not to damage the probe cable
Place the probe removal tool around the probe 10mm below the
cable
Tighten the wing nut firmly by hand
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Grip the two handles of the probe removal tool and rock it clockwise
and anticlockwise
After several attempts you should be able to gain 1 to 2mm of
movement
You should then be able to lift the probe vertically from the soil
Note:
If the soil is very dry, you may wish to pre-wet the soil 24 hours prior
to attempting the removal
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Ensure that you lift the probe vertically as any off vertical force may
damage the probe and such damage is not covered by the
manufacture warranty.
8.5.2 Removal with Vice Grips
If you do not have a Probe Removal Tool, you can use a pair of locking
pliers (Vice Grips). To avoid damaging the probe body you must first wrap
the unit a strip of insertion rubber.
Removal Process:
Using a hand trowel or small spade,
carefully remove the soil around the
head of the probe down to a depth of
15cm, being extra careful not to
damage the probe cable
Place the insertion rubber around the
probe just below the cable. It may be
easier if you fix it in place with
insulation tape
Lock the Vice Grips firmly on to the
insertion rubber
Grasp the Vice Grips firmly with two
hands and carefully rock clockwise
and anticlockwise
After several attempts you should be able to gain 1 to 2mm of
movement
You should then be able to lift the probe vertically from the soil
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8.6 Slurry and Probe Installation
8.6.1 Large format (50mm) probes
When the large format (50mm) capacitance probes were introduced to the
market, the manufacturers adopted a design wherein the sensors would be
hung on a central column (the “Probe column” or “Probe rod”), which was
dropped into a PVC tube (the “Access Tube”). The PVC tube would be
sealed at the bottom and have a cap fitted at the top.
As the sensors work by sending an electric field into the soil, any
discontinuities (such as air gaps) have a large impact on the sensor
performance. Installation techniques had to be developed which reduced
this risk.
To install the tubes in the ground, a slightly under-size hole would be
augered into the ground and a metal cutting edge would be fitted to the end
of the tube. The tube would then be hammered into the soil. As the tube
was driven down, the cutting edge would shave the hole to the correct
dimension, theoretically ensuring a tight fit of access tube to the soil. Two
different sized augers were designed: a sand auger, which could be
inserted inside the access tube allowing the hole to be augered “through
the tube” and a larger clay auger, which would not fit inside the tube. After
the hole was drilled and the access tube hammered in, the inside of the
tube would, be cleaned out and an expanding bottom stopper installed.
The direct install technique has a number of pitfalls:
Any gravel or organic matter in the hole can bind against the edge
of the access tube as it is driven in, creating air gaps
The method can be very slow in heavy soils (average rates of
drilling are 1m per hour in heavy soils)
If a stabilization tripod is not used or if the tripod is not perfectly
stable, the top of the hole elongates, creating air gaps around the
neck of the probe
Over time the expandable bottom stoppers degrade and water starts
to leak into the access tube (a large contributor to sensor failure)
In crops such as cotton, it is impractical to install large numbers of
probes in the time window available using this method.
To get around these problems, a “Slurry” installation technique was
developed. Rather than an under-size hole, an over-size hole would be
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drilled in the soil. The end of the access tube would be closed permanently
with a glued on stopper. A slurry mix would be poured into the hole and the
access tube pushed into the slurry.
Criticism of slurry installations tend to centre on the impact of the slurry on
the sensor performance. A quick look at the dimensions of the large format
probes explains why. The sensor design was initially based around the
dimensions of 50mm “DWV” PVC pipe, but later, custom pipe was extruded
in order to obtain tighter control over wall thickness and smoothness of the
pipe interior.
Tube
Dimensions
50 DWV
Nominal size
(mm)
50
Outside
Dimension (mm)
56
Auger Dimensions
Supplier
Sand Auger
C-Probe
Sentek
C-Probe
Sentek
C-Probe
Sentek
Clay Auger
Slurry Auger
Wall thickness
(mm)
2.2
Outside
Dimension
(mm)
53
47
56
53, 56
67
61
The diagram below shows a representation of a large format sensor
installed using a slurry technique.
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There are two important factors to note:
assuming a perfectly augered hole (which is rarely the case) there is
a minimum of 2.5m of slurry on either side of the access tube (if a
C-Probe slurry auger is used this can be up to 6mm)
the undisturbed soil (which after all is what we are trying to measure
is) is 5 to 6mm distant from the sensor ring.
Why are these numbers so important? Because the electric field which
radiates from the sensor decays in proportion to the distance from the
sensor ring: 90 % of the sensor’s measurement capacity comes from the
first 10mm out from the sensor ring. If 6mm of this is taken up by air, plastic
and slurry, then the proportion of the reading taken in the undisturbed soil
is indeed very small. This is why slurry installation of large format probes
has always been a bone of contention.
8.6.2 EnviroPro and Slurry
The EnviroPro is a “slim-line” probe, with an outer diameter of 32mm. The
installation auger is 36mm and there is no air gap between the sensor plate
and the probe tube. The probe tube is also only 1.5mm in thickness.
The net impact of all this is that not only is the slurry much thinner, but far
more of the electric field is in the undisturbed soil than is the case with a
large format probes.
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9 Connection to Data Loggers / Telemetry
Systems
The EnviroPro sensor may be used with any equipment which supports the
SDI-12 interface.
If the loggers / telemetry system in use supports the creation of standard
drivers for the sensors to which they are connected, use the table below to
configure the sensors:
Parameter
Soil Moisture
Soil Salinity
Sensor
Sensor type
Engineering Unit
SM xxxcm
SDI
Soil volume
percentage
Address
Measurement
Type
Measurement
Number
Index
0
Concurrent (C)
EC xxxcm
SDI
Conductivity
(DeciSiemens/m)
0
Soil
Temperature
ST xxcm
SDI
Temperature
(Celsius)
0
0
1
2
0 to 15
0 to 15
0 to 15
NOTE:
1. The default probe address is 0 but this can be changed to any
valid SDI-12 address (0 to 9, a to z, A to Z)
2. xxxcm = sensor depth in cm
3. the standard salinity units are S/m. The EnviroPro reports dS/m
where 1 S/m = 10 dS/m = 10mS/cm
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10 Sensor Calibration
The EnviroPro soil moisture sensors are pre-loaded with a calibration
based on the unit’s performance in a standardized calibration media. This
media is a fine sand. The values returned in other soils will differ in
accordance with the average particle size distribution in the soil which is in
turn dependent on the percentages of sand, loam and clay in the soil
(ignoring other factors such as organic matter and rock fraction which will
alter the net holding capacity).
The calibrations take the following form:
y = a * ln(x) - b
The Coefficients for a range of generic soils are as follows:
Soil Type
Sand
Loam
Clay
Default
a
8
10.6
13.4
12.9
b
7
9.5
13
13.6
10.1 Simple Calibration
A simple calibration can be completed by referencing the probe readings
against a known accurate point sensor such as a HydraProbe or Theta
Probe. This should be completed at 2 or 3 different moisture levels – the
wider apart the moisture is at each, the more representative will be the
calibration.
Process:
Install the probes and allow sufficient time for the probe readings to
equilibrate to those of the surrounding soil
Using a 15 or 20cm post-hole digger, begin digging a separate hole
about 1m away from the probe site
Starting from a depth of 10cm and then repeating at every change in
soil texture:
• stab the point sensor into the soil and take a measurement
• Repeat the measurement at 2 or 3 more positions around the hole
and then take the average of the readings (reject any outliers)
• Record the date and time of the reading
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Continue down through the soil profile
Return to the site and repeat the process in new sampling holes at 2
more points in the moisture range (i.e. close to field capacity, mid
range, close to refill point
Plot the Point Sensor readings in a spreadsheet against the
EnviroPro readings for the same time
Using the Solver function of the spreadsheet, calculate the
coefficients to relate the two. You can perform a line of best fit by
using the coefficients in the table above as a starting point.
10.2 Bucket Calibration
A more complete calibration can be obtained by taking samples of the soil
in 20 litre containers. Take the soil samples using a post hole digger,
ensuring you sample at 10cm and then at each change in the soil texture.
Procedure:
Oven dry the 20 litre soil samples
Using a calibrated water beaker, fill your containers with 10 litres of
water and mark the inside of the container at this level. Empty the
containers
Drill drain 4 holes in the bottom of the containers and fit them with
blanking grommets
Mount the EnviroPro probe in the centre of the bucket
Fill the containers to the 10 litre mark with soil – the bottom two
sensors should be in the soil. Gently compress the soil to compact it
to the original bulk density
Weigh the full containers to get dry bulk density and starting mass
Remove the blanking grommets from the bottom of the containers
Add 100ml of water to the container and allow it to equilibrate
through the soil
Record the Soil Moisture content indicated by the EnviroPro
Add another 100ml of water and repeat the measurement
Continue until water first emerges from the bottom of the container.
Record the EnviroPro reading – this will be a good estimate of Field
Capacity
Continue adding water until water pools on the surface – this will
give an indication of Saturation. Record the EnviroPro reading
Now plot the water contents and EnviroPro readings on a spreadsheet. Use the Solver function to determine the relationship
between the two. You can perform a line of best fit by using the
coefficients in the table above as a starting point.
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11 Regulatory Compliance Declaration
The EnviroPro Soil Moisture Probe has been tested for Electromagnetic
Compatibility (EMC) and Radio Frequency Interference (RFI).
Test Authority
Date of Testing
Test Standard
Manufacturer
Model Number
Type of Equipment
EMC Technologies Pty Ltd
176 Harrick Rd
KEILOR PARK VIC 3042
AUSTRALIA
th
4 May 2010
EN61326-1: 2006
(IEC61326-1: 2005 Ed 1)
Electrical requirements for
measurement, control and
laboratory use – EMC
requirements. Part 1 : General
Requirements
APCOS Pty Ltd
PO Box 380
MOUNT COMPASS SA 5210
AUSTRALIA
EP100D
EnviroPro dielectric soil probe
This is to certify that the EnviroPro dielectric soil moisture probe,
manufactured by EnviroPro Dielectrics Pty Ltd of South Australia,
meets or exceeds the standards for CE compliance as per the Council
Directives noted above.