TEROS 31 Tech Specs
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Technical Specifications

Measurement Specifications
Water potential
Range: –85 to +50 kPa (up to –150 kPa during boiling retardation)
Resolution: ±0.0012 kPa
Accuracy: ±0.1500 kPa
Range: -30 – 60 °C
Resolution: ±0 °C
Accuracy: ±1 °C
NOTE: If the sensor unit is not buried, measured temperature may diverge from soil temperature.
Communication Specifications
DDI serial
SDI-12 communication protocol
TensioLINKTM communication protocol
ModbusTM RTU communication protocol
Data Logger Compatibility
METER ZL6 and EM60 data loggers or any data acquisition system capable of 3.6- to 28.0-VDC excitation and SDI-12, Modbus RTU, or TensioLINK communication.
Physical Specifications
Width: 23.5 mm (0.93 in)
Height: 49.0 mm (1.93 in)
Depth: 17.5 mm (0.69 in)
Tensiometer shaft diameter
5 mm (0.19 in)
Tensiometer shaft length
2, 5, 7, 10, 15, or 20 cm
Ceramic: Al2O3, bubble point 500 kPa
Shaft: PMMA
Sensor unit: PMMA and TPE
Operating Temperature Range
Minimum: 0 °C
Maximum: 50 °C
Cable Length
1.5 m
Cable Diameter
0.165 ± 0.004 (4.20 ± .10 mm) with minimum jacket of 0.030 (0.76 mm)
Connector Types
3.5-mm 4-pin stereo plug connector
Stereo Plug Connector Diameter
3.5000 mm
Conductor Gauge
22 AWG/24 AWG drain wire
Electrical and Timing Characteristics
Supply Voltage (VCC to GND)
Minimum: 3.6000 VDC
Typical: 12.0000 VDC
Maximum: 28.0000 VDC
Digital Input Voltage (logic high)
Minimum: 1.6000 V
Typical: 3.3000 V
Maximum: 5.0000 V
Digital Input Voltage (logic low)
Minimum: -0.3000 V
Typical: 0.0000 V
Maximum: 0.9000 V
Digital Output Voltage (logic high)
Typical: 3.6000 V
Power Line Slew Rate
Minimum: 1.0000 V/ms
Current Drain (during measurement)
Minimum: 18.0000 mA
Typical: 25.0000 mA
Maximum: 30.0000 mA
Current Drain (while asleep)
Minimum: 0.0300 mA
Typical: 0.0500 mA
Maximum: 0.9000 mA
Power Up Time (SDI-12)
Minimum: 125 ms
Typical: 130 ms
Maximum: 150 ms
Power Up Time (DDI Serial)
Minimum: 125.0000 ms
Typical: 130.0000 ms
Maximum: 150 ms
Power Up Time (SDI-12, DDI Serial disabled)
Minimum: 125 ms
Typical: 130 ms
Maximum: 150 ms
Measurement Duration
Minimum: 60.0000 ms
Typical: 65 ms
Maximum: 70.0000 ms
BARO Module
When using the METER tensiometers TEROS 31 and TEROS 32 in combination with a non-METER data logger, a highly accurate barometric compensation is needed to get the most precise soil water potential measurement. The BARO Module can be used as a stand-alone sensor for measuring atmospheric pressure at a measuring site. It is also available with different connectors, so the BARO Module can be connected directly in between a tensiometer and a data logger. BARO Module can also act as a digital/analog converter to connect a tensiometer with serial output to a data logger with analog input channels. The logger obtains a barometric compensated analog matric potential signal. The BARO Module can be used for varied logger communications: SDI-12, Modbus, tensioLINK, analog voltage signal.
Manufactured under ISO 9001:2015
EM ISO/IEC 17050:2010 (CE Mark)