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INTEGRATOR GUIDE
TEROS 21 SOIL WATER POTENTIAL SENSOR
SENSOR DESCRIPTION
The TEROS 21 Soil Water Potential Sensor measures a wide range of soil water potentials without user
maintenance. This dielectric water potential sensor can be packed into a hole, plugged into a data logger, and
left to log water potential data. While the TEROS 21 sensor does not have the accuracy of tensiometers, its
extended range makes this sensor ideal for measuring the water potential in natural systems or other drier
systems where cavitation of tensiometers is a concern. The added temperature measurements can be used to
determine approximate soil water potential in frozen soils.
APPLICATIONS
• Deficit irrigation monitoring and control
• Water potential monitoring in the vadose zone
• Crop stress
• Waste water drainage studies
• Plant water availability
• SDI-12 implementation
ADVANTAGES
• Three-wire sensor interface: power, ground, and data
• Digital sensor communicates multiple measurements over a
serial interface
• Robust thermistor for accurate temperature measurements
• Low-input voltage requirements
• Low-power design supports battery-operated data loggers
• Robust epoxy encapsulation resists corrosive environments
• Supports SDI-12 or DDI serial communications protocols
• Modern design optimized for low-cost sensing
• Does not require a skilled operator
• Can measure drier systems where tensiometer cavitation
is a concern
• Needs no user maintenance
PURPOSE OF THIS GUIDE
METER provides the information in this integrator guide to help TEROS 21 Soil Water Potential Sensor
customers establish communication between these sensors and their data acquisition equipment or field
data loggers. Customers using data loggers that support SDI-12 sensor communications should consult the
data logger user manual. METER sensors are fully integrated into the METER system of plug-and-play sensors,
cellular-enabled data loggers, and data analysis software.
COMPATIBLE FIRMWARE VERSIONS
This guide is compatible with firmware versions 3.89 or newer.
METER Group, Inc. USA
2365 NE Hopkins Court, Pullman, WA 99163
T
+1.509.332.2756
F
+1.509.332.5158
E
info@metergroup.com
W
metergroup.com
Figure 1 TEROS 21 sensor
18204-00
11.10.2017
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Summary of Contents for METER TEROS 21
- Page 1 This dielectric water potential sensor can be packed into a hole, plugged into a data logger, and left to log water potential data. While the TEROS 21 sensor does not have the accuracy of tensiometers, its extended range makes this sensor ideal for measuring the water potential in natural systems or other drier systems where cavitation of tensiometers is a concern.
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Page 2: Measurement Specifications
SPECIFICATIONS MEASUREMENT SPECIFICATIONS Water Temperature Operating Temperature Range: −9 to −100,000 kPa −40 to 60 °C (0% to 100% RH) (1.96 to 6.01 pF) No water potential measurement < 0 °C Resolution: 0.1 kPa NOTE: Sensors may be used at higher temperatures under certain conditions;... -
Page 3: Safety Precautions
Figure 3 Connection types SAFETY PRECAUTIONS METER sensors are built to the highest standards, but misuse, improper protection, or improper installation may damage the sensor and possibly void the warranty. Before integrating sensors into a sensor network, follow the recommended installation instructions and implement safeguards to protect the sensor from damaging interference. -
Page 4: Sensor Communications
TEROS 21 and the data acquisition device to the mounting mast in one or more places. Install cables in conduit or plastic cladding when near the ground to avoid rodent damage. Tie excess cable to the data logger mast to ensure cable weight does not cause sensor to unplug. - Page 5 COMMON SDI-12 COMMANDS This section includes tables of common SDI-12 commands that are often used in an SDI-12 system and the corresponding responses from METER sensors. IDENTIFICATION COMMAND (aI!) The Identification command can be used to obtain a variety of detailed information about the connected 1, where the command is in bold and sensor.
- Page 6 The Change Address command is used to change the sensor address to a new address. All other commands support the wildcard character as the target sensor address except for this command. All METER sensors have a default address of 0 (zero) out of the factory. Supported addresses are alphanumeric (i.e., a–z, A–Z, and 0–9).
- Page 7 NOTES: This command does not adhere to the SDI-12 concurrent command requirements. See METER SDI-12 Implementation for more information. The measurement and corresponding data commands are intended to be used back to back. After a measurement command is processed by the sensor, a service request a <CR><LF>...
- Page 8 This protocol is subject to change as METER improves and expands the line of digital sensors and data loggers. NOTE: Out of the factory, all METER sensors start with SDI-12 address 0 and print out the startup string when power cycled. TEROS 21 will omit the DDI serial startup string when the SDI-12 address is nonzero.
- Page 9 DDI SERIAL TIMING Table 8 lists the DDI serial communication configuration. Table 8 DDI serial communication configuration Baud Rate 1200 Start Bits Data Bits 8 (LSB first) Parity Bits 0 (none) Stop Bits Logic Standard (active high) At power up, the sensor will pull the data line high within 100 ms to indicate that the sensor is taking a reading (Figure 6).
- Page 10 char LegacyChecksum(char * Response) int length, sum = 0, i, crc; // Finding the length of the response string length = strlen(Response); // Adding characters in the response together for( i = 0; i < length; i++ ){ sum += Response[i]; // Converting checksum to a printable character crc = sum % + 32;...
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Page 11: Customer Support
Name Email address Address Instrument serial number Phone number Description of problem NOTE: For TEROS 21 sensors purchased through a distributor, please contact the distributor directly for assistance. REVISION HISTORY The following table lists document revisions. Revision Date Compatible Firmware Description 11.10.2017...
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