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TEROS 31 Lab Tensiometer

Updated:2025-03-13

Brand: METER
Model: TEROS 31
Description: If you need spot measurements of water potential in soil columns, soil cores, or sampling rings, there aren’t a lot of options. Until now. With the TEROS 31, we put our 25 years of expertise to work i
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Product Details

TEROS 31 Lab Tensiometer Description：

User's Manual

Lab tensiometer with heroic strength and speed

TEROS 31 is the only tensiometer in the world small enough and precise enough to perform excellent water potential spot measurements in even the tightest spaces. And now it’s even more robust than ever. We've incorporated a more ruggedized, highly precise pressure transducer, giving you higher data resolution in an almost unbreakable form. And the TEROS 31 tensiometer has a superheroic response time of only 5 seconds for a pressure change of 0 to –85 kPa. It reacts much faster to changing soil conditions because of its small water volume, enabling you to measure even the most minute changes in water potential—something lower-quality tensiometers cannot do. It measures matric potential within the gravitational range where most water movement occurs and into the capillary range, helping you understand whether water will move and where it will go.

Tensiometer measurement range—extended

Most tensiometers have a measuring range of at least 100 to –85 kPa. But the TEROS 31 increases the matric potential measuring range to nearly –150 kPa. How is this possible? Normally, when a tensiometer reaches –85 kPa, the water boils, forming an air bubble. The air bubble expands and contracts with changes in pressure, making the tensiometer unable to measure suction. But the TEROS 31 retards the boiling point, extending the measurement range well beyond normal limits.

Small tensiometer—huge benefits

For more than a quarter century, METER has been the leading expert in the development of tensiometers with over 10,000 sold. Nobody in the world makes an instrument this small, this simple, or this precise. Trust the TEROS 31 lab tensiometer for fast, accurate spot measurements in all your tightest spaces.

Double your data power

The TEROS 31 combines METER world-renowned precision technology with the power of ZENTRA Cloud, giving you easier, faster water potential data in near-real time. And compatibility with the ZL6 data logger means precision is now plug-and-play, making setup a breeze. The TEROS 31 minor footprint allows major advantages over larger tensiometers, such as very little soil disturbance and incredibly fast response time. And, because of its small size, it’s one of the only tensiometers in the world that can extend its measuring range.

Setup in seconds

Now you can spend far less time on complex setup. Just insert the TEROS 31 stereo plug into the ZL6 data logger, and start seeing numbers. ZENTRA Cloud makes it possible to see near-real-time data wherever you are. TEROS 31 can be installed in any position and orientation with a miniature auger (not included) to ensure as little soil disturbance as possible. For spot measurements, just auger a 5-mm hole and insert the tensiometer. It’s that simple. To save you even more time and effort, bubbles are detectable through the transparent shaft, making it easy to see when it’s time to refill.

Feature：

Laboratory tensiometer

Easy data visualization in real time: plug and play with ZL6 logger and ZENTRA Cloud

Small and fast

Little soil disturbance

Extended range

Install tensiometer in any position or orientation

Bubbles easily detectable through the transparent shaft

Output signals are balanced

Accurate zero-tension reading

TEROS 31 Lab Tensiometer Specification：

Measurement Specifications	Water Potential	Range: –85 to +50 kPa (up to –150 kPa during boiling retardation)
		Resolution: ±0.0012 kPa
		Accuracy: ±0.15 kPa
	Temperature	Range: –30 to +60 °C
		Resolution: ±0.01 °C
		Accuracy: ±0.50 °C
		NOTE: If the sensor unit is not buried, measured temperature may diverge from soil temperature.
Communication Specifications	Output	DDI serial SDI-12 communication protocol TensioLINK^TMcommunication protocol Modbus^TMRTU communication protocol
Communication Specifications	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	Dimensions	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
	Materials	Ceramic:Al₂O₃， bubble point 500 kPa Shaft: PMMA Sensor Unit: PMMA and TPE
	Operating Temperature Range	Minimum: 0.00 °C Maximum: 50.00 °C
	Cable Length	1.5 m
	Cable Diameter	3.0 mm (0.12 in)
	Connector Types	4-pin stereo plug connector
	Stereo Plug Connector Diameter	3.5 mm
	Conductor Gauge	31 AWG drain wire
Electrical and Timing Characteristics	Supply Voltage (VCC to GND)	Minimum: 3.6 VDC Typical: 12.0 VDC Maximum: 28.0 VDC
	Digital Input Voltage (Logic High)	Minimum: 1.6 V Typical: 3.3 V Maximum: 5.0 V
	Digital Input Voltage (Logic Low)	Minimum: -0.3 V Typical: 0.0 V Maximum: 0.9 V
	Digital Output Voltage (Logic High)	Typical: 3.6 V
	Power Line Slew Rate	Minimum: 1.0 V/ms
	Current Drain (During Measurement)	Minimum: 18.0 mA Typical: 25.0 mA Maximum: 30.0 mA
	Current Drain (While Asleep)	Minimum: 0.03 mA Typical: 0.05 mA Maximum: 0.90 mA
	Power Up Time (DDI Serial)	Minimum: 125 ms Typical: 130 ms Maximum: 150 ms
	Power Up Time (SDI-12)	Minimum: 125 ms Typical: 130 ms aximum: 150 ms
	Power Up Time (SDI-12, DDI Serial Disabled)	Minimum: 125 ms Typical: 130 ms Maximum: 150 ms
	Measurement Duration	Minimum: 60 ms Typical: 65 ms Maximum: 70 ms
Other	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.
Other	Compliance	Manufactured under ISO 9001:2015 EM ISO/IEC 17050:2010 (CE Mark)