METER TEROS 11 User manual
TEROS 11/12
i
TABLE OF CONTENTS
1. Introduction..............................................................................................1
2. Operation ...................................................................................................2
2.1 Installation ................................................................................................2
2.2 Connecting................................................................................................. 6
2.2.1 Connect to METER Logger.................................................................6
2.2.2 Connect to Non-METER Logger.........................................................7
2.3 Communication .........................................................................................8
3. System....................................................................................................... 10
3.1 Specifications.......................................................................................... 10
3.2 Components ............................................................................................ 13
3.3 Theory...................................................................................................... 15
3.3.1 Volumetric Water Content .............................................................. 15
3.3.2 Temperature ................................................................................... 15
3.3.3 Electrical Conductivity (TEROS 12 Only) ......................................... 15
3.3.4 Converting Bulk EC to Pore EC (TEROS 12 Only).............................. 15
3.3.5 Pore Water Versus Saturation Extract EC (TEROS 12 Only) ............. 16
4. Service....................................................................................................... 18
4.1 Calibrations ............................................................................................. 18
4.1.1 Mineral Soils................................................................................... 18
4.1.2 Soilless Media ................................................................................ 18
4.1.3 Apparent Dielectric Permittivity..................................................... 19
18225-02
2.15.2019
ii
4.2 Cleaning................................................................................................... 19
4.3 Troubleshooting....................................................................................... 19
4.4 Customer Support.................................................................................... 20
4.5 Terms and Conditions .............................................................................. 21
References .................................................................................................... 22
Index ................................................................................................................. 23
iv
1
TEROS 11/12
1. INTRODUCTION
Thank you for choosing the TEROS11 Soil Moisture and Temperature sensor and the
TEROS12 Soil Moisture, Temperature, and Electrical Conductivity (EC) sensor from
METERGroup.
The TEROS11/12 sensors are designed to be installed in mineral soils, many types of
growingmedia, and other porous materials. This manual guides the customer through
thesensor features and describes how to use the sensor successfully.
TEROS 11/12 sensors are accurate tools for monitoring volumetric water content (VWC),
temperature in soil and soilless substrates, and EC (TEROS 12 only). The TEROS11/12
determines VWC using capacitance/frequency-domain technology. The sensor uses a
70-MHz frequency, which minimizes textural and salinity effects, making the
TEROS11/12 accurate in most mineral soils. The TEROS 11/12 uses a thermistor in the
center needle to measure temperature and EC (TEROS 12 only) using a stainless-steel
electrode array.
Prior to use, verify the TEROS11/12 sensor arrived in good condition. METER
recommends testing the sensors with the data logging device and software before going
to the field.
2
OPERATION
2. OPERATION
Please read all instructions before operating the TEROS11/12 to ensure it performs to its full
potential.
SAFETY PRECAUTIONS
METER sensors are built to the highest standards. Misuse, improper protection, or improper
installation may damage the sensor and possibly void the manufacturer’s warranty. Before
integrating the TEROS11/12 into a system, follow the recommended installation instructions
and have the proper protections in place to safeguard sensors from damage. If installing
sensors in a lightning-prone area with a grounded data logger, see the application note
Lightning surge and grounding practices.
2.1 INSTALLATION
Follow the steps listed in Table1 to set up the TEROS11/12 and start collecting data. For more
detailed installation information, consult the TEROS Sensors Best Practices Installation Guide.
Installation
Tools Needed
Auger or Shovel
Secure Mounting Location for Data Logger and Cable
Borehole Installation Tool (Optional)
jack
cradle
carriage
shaft
actuator
lever
flashlight
TEROS
sensor
Preparation
Determine Best Installation Method
There are several methods for installing soil moisture sensors. These methods
are described in Table2.
Conduct System Check
Plug the sensor into the data logger (Section2.2) to make sure the sensor is
operating as expected.
Verify all sensors read within expected ranges. To validate both sensor function
and logger functionality, take a sensor measurement in air and water. The
TEROS11/12 will read ~0.70 m3/m3 in water and a slightly negative value in air.
3
TEROS 11/12
Table 1 Installation (continued)
Installation
There are several methods for installing soil moisture sensors (Table2). Keys to a
good installation and collecting good soil moisture data are described below.
Create Hole
Avoid interferring objects.
• Installations near large metal objects can affect the sensor function and
distort readings.
• Large objects like roots or rocks could potentially bend the needles.
Auger or trench a hole to the desired sensor installation depth and direction
according to the installation method desired.
Insert Sensor
Determine sensor orientation. The TEROS 11/12 sensor may be positioned in
any direction. However, with the body in a vertical position (as shown below),
there is less restriction to water ow. A vertical position will also integrate
more soil depth into the soil moisture measurement. Installing the sensor with
the body in a horizontal position will provide measurements at a more discreet
depth. See Measurement volume of METER volumetric water content sensors
for more information on sensor measurement volume.
Sensor body vertical and needles horizontal
Any metal located between the sensor and the ferrite core can interfere with
VWC measurements and should be avoided.
ATTENTION! Minimize air gaps around the sensor. Air gaps around the sensor needles will
result in low readings of soil moisture.
1. Load the TEROS11/12 using the Borehole Installation Tool (BIT).
NOTE: The BIT provides a significant amount of mechanical advantage.See
2. Lower the tool into the hole or trench with the back of the tool supported
by the far wall.
3. Pull the tool lever to activate the jack and insert the sensor into the sidewall.
WARNING: When installing sensors in rocky soils,use care to avoide bending sensor needles.
4
OPERATION
Table 1 Installation (continued)
Installation
(continued)
Return soil to the hole, packing the soil back to its native bulk density.
Do not hit the ferrite core as this could potentially pull the sensor out of the soil.
Connecting
Connect to Data Logger
Plug the sensor into a data logger.
Use the data logger to make sure the sensor is reading properly.
Verify that these readings are within expected ranges.
For more specific instructions on connecting to data loggers, refer to
Section2.2.
Secure and Protect Cables
NOTE: Improperly protected cables can lead to severed cables or disconnected sensors.
Cabling issues can be caused by many factors such as rodent damage, driving over sensor
cables, tripping over cables, not leaving enough cable slack during installation, or poor
sensor wiring connections.
Install cables in conduit or plastic cladding when near the ground to avoid
rodent damage.
Gather and secure cables between the TEROS 11/12 and the data logger to the
mounting mast in one or more places.
Port1Port2Port3Port4 Port 5Port 6
TEST
OK
ERROR
(-)
(-)(-) (-)
(-)(+)(-)(+)(+)
(+)(+)(+)
Securing excess cable
Table2 contains brief descriptions for typical installation methods. Each has its own
advantages and disadvantages. For more information about which installation method is
best for specific applications, please see the TEROS11/12 Installation Guide or contact
Customer Support.
5
TEROS 11/12
Installation methods
Borehole
This method uses the Borehole
Installation Tool (Table1) that
allows a prole of soil moisture
sensors to be installed at
different depths within a single
augered borehole. A 10-cm (4-in)
borehole is augered vertically at
the measurement location. The
Borehole Installation Tool is then
used to install the sensors in the
sidewall of the borehole.
NOTE: The borehole method
Advantage
Minimizes soil
disturbance at
measurement
site.
Disadvantage
Requires a
specialized
installation
tool that can
be rented from
METER.
Trench
The trench installation method
is best for shallow installations
(less than 40 cm). This requires
digging a trench with a shovel,
excavator, or other tool. The
trench needs to be dug to the
depth of the deepest installed
sensor. For deep installations,
this may require a large trench.
The sensor is installed carefully
by hand into the undisturbed soil
of the trench sidewall. The trench
is carefully backlled to preserve
the bulk density of the soil.
Advantage
Does not
require
specialized
equipment.
Disadvantage
Large soil
disturbance at
measurement
site.
Potentially
large
excavation
effort.
NOTE: Carefully backfill to avoid dislodging the installed sensor by accidentally snagging the ferrite core.
6
OPERATION
2.2 CONNECTING
The TEROS11/12 works seamlessly with METER data loggers. The TEROS11/12 can
also be used with other data loggers, such as those from Campbell Scientific, Inc. For
extensive directions on how to integrate the sensors into third-party loggers, refer to the
TEROS11/12 Integrator Guide.
TEROS11/12 sensors require an excitation voltage in the range of 4 to 15VDC and operate
at a 4VDC level for data communication. TEROS11/12 can be integrated using DDI serial or
SDI-12 protocol. See the TEROS11/12 Integrator Guide for details on interfacing with data
acquisition systems.
TEROS11/12 sensors come with a 3.5-mm stereo plug connector (Figure 1) to facilitate easy
connection with METER data loggers. TEROS 11/12 sensors may be ordered with stripped
and tinned wires to facilitate connecting to some third-party loggers (Section2.2.2).
Ground
Data output
Power
Figure 1 Stereo plug connector
The TEROS11/12 sensor comes standard with a 5-m cable. It may be purchased with custom
cable lengths for an additional fee (on a per-meter basis). METER has successfully tested
digital communication on cable lengths up to 1,000 m (3,200 ft). This option eliminates the
need for splicing the cable (a possible failure point). However, the maximum recommended
length is75 m.
2.2.1 CONNECT TO METER LOGGER
The TEROS11/12 sensor works most efficiently with METER ZENTRA, EM60, and
Em50 series data loggers. Check the METER download webpage for the most recent data
logger firmware. Logger configuration may be done using either ZENTRA Utility (desktop and
mobile application) or ZENTRA Cloud (web-based application for cell-enabled ZENTRA data
loggers).
1. Plug the stereo plug connector into one of the sensor ports on the logger.
2. Use the appropriate software application to congure the chosen logger port for the
TEROS11 or TEROS12.
METER data loggers wil automatically recognize TEROS 11/12 sensors.
3. Set the measurement interval.
METER data loggers measure the TEROS11/12 once every minute and return the average
of the 1-min data across the chosen measurement interval.
7
TEROS 11/12
TEROS11/12 data can be downloaded from METER data loggers using either ZENTRA
Utility or ZENTRA Cloud. Refer to the logger user manual for more information about these
programs.
2.2.2 CONNECT TO
The TEROS11/12 can be purchased for use with non-METER (third-party) data loggers. Refer
to the third-party logger manual for details on logger communications, power, and ground
ports. The TEROS11/12 Integrator Guide also provides detailed instructions on connecting
sensors to non-METER loggers.
TEROS11/12 sensors can be ordered with stripped and tinned (pigtail) connecting wires for
use with screw terminals. Refer to the third-party logger manual for wiring details.
Connect the TEROS11/12 wires to the data logger illustrated in Figure 2 and Figure 3, with
the power supply wire (brown) connected to the excitation, the digital out wire (orange) to a
digital input, and the bare ground wire to ground.
Ground (bare)
Data output (orange)
Power (brown)
Figure 2 Pigtail wiring
Excitation Digital
in
Data Logger
Ground
Data output
(orange)
Ground
(bare)
Power
(brown)
Figure 3 Wiring diagram
NOTE:
Scientific, Inc.data loggers, power the sensors from a switched 12-V port or a 12-V port if using a multiplexer.
If the TEROS11/12 cable has a standard stereo plug connector and needs to be connected to
a non-METER data logger, please use one of the following two options.
8
OPERATION
Option 1
1. Clip off the stereo plug connector on the sensor cable.
2. Strip and tin the wires.
3. Wire it directly into the data logger.
This option has the advantage of creating a direct connection and minimizes the chance of
the sensor becoming unplugged. However, it then cannot be easily used in the future with a
METER readout unit or data logger.
Option 2
Obtain an adapter cable from METER.
The adapter cable has a connector for the stereo plug connector on one end and three
wires (or pigtail adapter) for connection to a data logger on the other end. The stripped and
tinned adapter cable wires have the same termination as seen in Figure 3; the brown wire is
excitation, the orange is output, and the bare wire is ground.
NOTE: Secure the stereo plug connector to the pigtail adapter connections using adhesive-line heat shrink to ensure
the sensor does not become disconnected during use.
2.3 COMMUNICATION
The TEROS11/12 sensor communicates using two different methods:
• DDI serial string
• SDI-12 communication protocol
To obtain detailed instructions, refer the TEROS11/12 Integrator Guide.
The SDI-12 protocol requires that all sensors have a unique address. TEROS 11/12 sensor
factory default is an SDI-12 address of 0. To add more than one SDI-12 sensor to a bus, the
sensor address must be changed as described below:
1. Using a ProCheck connected to the sensor, press the Menu button to bring up the
CONFIG menu.
NOTE: If the ProCheck does not have this option,please upgrade its firmware to the latest version from the
METER Legacy Handheld Devices webpage.
2. Scroll down to SDI-12 Address. Press Enter.
3. Press the UP or DOWN arrows until the desired address is highlighted.
Address options include 0...9, A…Z, and a…z.
4. Press Enter.
9
TEROS 11/12
Detailed information can also be found in the application note Setting SDI-12 addresses on
METER digital sensors using Campbell Scientific data loggers and LoggerNet.
When using the sensor as part of an SDI-12 bus, excite the sensors continuously to avoid
issues with initial sensor startup interfering with the SDI-12 communications.
SYSTEM
3. SYSTEM
This section reviews the components and functionality of the TEROS11/12 sensor.
3.1 SPECIFICATIONS
MEASUREMENT SPECIFICATIONS
Volumetric Water Content (VWC)
Range
Mineral soil calibration 0.00–0.70 m3/m3
Soilless media
calibration
0.0–1.0 m3/m3
Apparent dielectric
permittivity (εa)
1 (air) to 80 (water)
NOTE: The VWC range is dependent on the media the sensor is calibrated to. A custom calibration will
accommodate the necessary ranges for most substrates.
Resolution 0.001 m3/m3
Accuracy
Generic
calibration
±0.03 m3/m3 typical in mineral soils that have solution
EC <8 dS/m
Medium specific
calibration
±0.01–0.02 m3/m3 in any porous medium
Apparent dielectric
permittivity (εa)
1–40 (soil range) , ±1 εa(unitless)
40–80, 15% of measurement
Dielectric Measurement Frequency
70 MHz
Temperature
TEROS 11
Range −40 to +60 °C
Resolution 0.1 °C
Accuracy ±1 °C from −40 to 0 °C
±0.5 °C from 0 to +60 °C
NOTE: Temperature measurement, for applicable sensors, may not be accurate if sensor is not fully immersed in the
medium of interest, due to longer equilibration time.
11
TEROS 11/12
TEROS 12
Range −40 to +60 °C
Resolution 0.1 °C
Accuracy ±0.5 °C from −40 to 0 °C
±0.3 °C from 0 to +60 °C
Bulk Electrical Conductivity (EC) (TEROS 12 Only)
Range 0–20 dS/m (bulk)
Resolution 0.001 dS/m
Accuracy ±(5% + 0.01 dS/m) from 0–10 dS/m
±8% from 10–20 dS/m
COMMUNICATION SPECIFICATIONS
Output
DDI serial or SDI-12 communications protocol
Data Logger Compatibility
METER ZL6, EM60, and Em50 data loggers or any data acquisition system capable of
4.0- to 15-VDC power and serial or SDI-12 communication
PHYSICAL SPECIFICATIONS
Dimensions
Length 9.4 cm (3.70 in)
Width 2.4 cm (0.95 in)
Height 7.5 cm (2.95 in)
Needle Length
5.5 cm (2.17 in)
Cable Length
5 m (standard)
75 m (maximum custom cable length)
NOTE: Contact Customer Support if a nonstandard cable length is needed.
Connector Types
3.5-mm stereo plug connector or stripped and tinnedwires
12
SYSTEM
ELECTRICAL AND TIMING CHARACTERISTICS
Supply Voltage (VCC to GND)
Minimum 4.0 VDC
Typical NA
Maximum 15.0 VDC
Digital Input Voltage (logic high)
Minimum 2.8 V
Typical 3.6 V
Maximum 3.9 V
Digital Input Voltage (logic low)
Minimum –0.3 V
Typical 0.0 V
Maximum 0.8 V
Digital Output Voltage (logic high)
Minimum NA
Typical 3.6 V
Maximum NA
Power Line Slew Rate
Minimum 1.0 V/ms
Typical NA
Maximum NA
Current Drain (during 25-ms measurement)
Minimum 3.0 mA
Typical 3.6 mA
Maximum 16.0 mA
Current Drain (while asleep)
Minimum NA
Typical 0.03 mA
Maximum NA
13
TEROS 11/12
Operating Temperature Range
Minimum –40 °C
Typical NA
Maximum +60 °C
NOTE: Sensors may be used at higher temperatures under certain conditions; contact Customer Support
for assistance.
Power-Up Time (DDI serial)
Minimum 80 ms
Typical NA
Maximum 100 ms
Power-Up Time (SDI-12)
Minimum NA
Typical 245 ms
Maximum NA
Measurement Duration
Minimum 25 ms
Typical NA
Maximum 50 ms
COMPLIANCE
Manufactured under ISO 9001:2015
EM ISO/IEC 17050:2010 (CE Mark)
2014/30/EU and 2011/65/EU
EN61326-1:2013 and EN55022/CISPR 22
3.2 COMPONENTS
The TEROS11/12 sensor measures soil moisture, temperature, and EC (TEROS 12 only) of
soil using stainless steel needles (Figure 4). TEROS11/12 sensors measure soil moisture
between Needle1 and Needle2. TEROS 12 measures EC between Needle 2 and Needle 3.
Temperature is measured with an embedded thermistor. These sensors have a low power
requirement, which makes them ideal for permanent burial in the soil and continuous
reading with a data logger or periodic reading with a handheld reader.
14
SYSTEM
Ferrite
core
TEROS 12
thermistor in Needle 2
TEROS 11
thermistor located on
PCB near Needle 1
Needle 3
Needle 2
Needle 1
VWC
EC
Figure 4
A ferrite core positioned on the TEROS11/12 sensor cable 7.6 cm (3 in) away from the sensor
head is utilized to isolate the sensor from any interferences in the system. This mitigates any
potential noise from the system on the measured sensor data. It is important to not attach
anything to the section of cable between the sensor head and the ferrite core as this may
influence the measurements.
The TEROS11/12 VWC measurement sensitivity is contained within a 1,010-mL volume
roughly depicted in Figure 5. Please see the application note Measurement volume of METER
volumetric water content sensors for testing protocol and more thorough analysis.
3 cm
3 cm
3 cm
1 cm
1 cm
7.5 cm
9.3 cm
3 cm
Figure 5
NOTE:
15
TEROS 11/12
3.3 THEORY
The following sections explain the theory of VWC, temperature, and EC (TEROS 12 only)
measured by TEROS11/12.
3.3.1 VOLUMETRIC WATER CONTENT
TEROS11/12 sensors use an electromagnetic field to measure the dielectric permittivity
of the surrounding medium. The sensor supplies a 70-MHz oscillating wave to the sensor
needles, which charge according to the dielectric of the material. The charge time is
proportional to substrate dielectric and substrate VWC. The TEROS11/12 microprocessor
measures the charge time and outputs a raw value based on the substrate dielectric
permittivity. The raw value is then converted to VWC by a calibration equation specific to the
substrate (Section 4.1).
3.3.2 TEMPERATURE
The TEROS 11 uses a small thermistor mounted on the PCB near the lower needle. The
TEROS 11 temperature measurement is optimized to be accurate when the TEROS 11 is
fully buried in soil or substrate. The TEROS12 uses a thermistor in the center needle to take
temperature readings and responds faster to temperature changes and is better suited for
needle-only insertion into greenhouse and nursery substrates. The TEROS11/12 sensors
output temperature is in degrees Celsius unless otherwise stated in the data logger program,
such as in preferences in the ZENTRA software.
NOTE: Even though the sensor head is white,in direct sunlight, the temperature measurement may read high. Use
caution when installing the sensor with the sensor head in the sun.
3.3.3 ELECTRICAL
EC is the ability of a substance to conduct electricity and can be used to infer the amount
of ions that are present in solution. EC is measured by applying an alternating electrical
current to two electrodes and measuring the resistance between them. Bulk EC is
derived by multiplying the inverse of the resistance (conductance) by the cell constant
(the ratio of the distance between the electrodes to their area). TEROS12 sensor bulk
EC measurements are normalized to EC at 25 °C. The bulk EC measurement is factory
calibrated to be accurate over the range found in the vast majority of soil and growth
substrates.
EC measurements above 10 dS/m are sensitive to contamination of the electrodes by skin
oils, etc. Follow cleaning instructions in Section 4.2if measuring the EC of salty soils.
3.3.4 CONVERTING BULK EC TO
For many applications, it is advantageous to know the EC of the solution contained in the
soil pores (p), which is a good indicator of the solute concentration in the soil. Traditionally,
p is obtained by extracting pore water from the soil and measuring p directly, a time-
consuming and labor-intensive process. The TEROS12 sensor measures the EC of the bulk
16
SYSTEM
soil surrounding the sensors (b). A considerable amount of research has been conducted to
determine the relationship between b and p. Hilhorst (2000) took advantage of the linear
relationship between the soil bulk dielectric permittivity (b) and b to accurately convert b
to p if the b is known. The TEROS12 sensor measures b and b nearly simultaneously in the
same soil volume. Therefore, the TEROS12 is well suited to this method.
The pore water conductivity (p ) is determined from Equation 1 (see Hilhorst 2000 for derivation):
Equation 1
σp=
ε
p
σ
b
ε
b
−εσ
b
=
0
where
pis the pore water EC (dS/m),
pis the real portion of the dielectric permittivity of the soil pore water (unitless),
bis the bulk EC (dS/m) measured directly by the TEROS11/12,
bis the real portion of the dielectric permittivity of the bulk soil (unitless), and
b = 0 is the real portion of the dielectric permittivity of the soil when bulk ECis0 (unitless).
Dielectric permittivity of the soil pore water (p) is calculated from soil temperature using
Equation 2:
Equation 2
εp=80.3−0.37×Tsoil −20
( )
where Tsoil is the soil temperature (°C) measured by the TEROS12.
Finally, b = 0 is an offset term loosely representing the dielectric permittivity of the dry
soil. Hilhorst (2000) recommended that b = 0 = 4.1 be used as a generic offset. Hilhorst
(2000) offers a simple and easy method for determining b = 0 for individual soil types, which
improves the accuracy of the calculation of p in most cases.
METER testing indicates that the method for calculating p (Equation 1) results in
good accuracy (±20%) in moist soils and other growth media. In dry soils, where VWC
is less than 0.10 m3/m3, the denominator of Equation 1 becomes very small, leading
to large potential errors. METER recommends that p not be calculated in soils with
VWC<0.10 m3/m3using this method.
3.3.5 PORE WATER VERSUS
As noted in Section3.3.4, pore water EC can be calculated from bulk EC using the sensor-
measured dielectric permittivity of the medium. However, pore water EC is not the same as
saturation extract EC.
Pore water EC is the EC of the water in the pore space of the soil. This could be measured
directly if the soil was squeezed under high pressure to force water out of the soil matrix and
that water was collected and tested for EC.
Other manuals for TEROS 11
2
This manual suits for next models
1
Table of contents
Other METER Accessories manuals
METER
METER TEROS 10 User manual
METER
METER PHYTOS 31 User manual
METER
METER TEROS 12 User manual
METER
METER ATMOS 14 User manual
METER
METER TEROS 21 User manual
METER
METER TEROS 54 User manual
METER
METER TEROS 10 User manual
METER
METER ATMOS 14 User manual
METER
METER AROYA User manual
METER
METER TEROS 21 Assembly Instructions
