TEROS 31 and TEROS 32 tensiometers


  • Low cost, easy to install, METER Group tensiometers
  • Read with a handheld meter or connect to a data logger
  • SDI-12 output for digital devices such as LoRaWAN and NB-IoT
  • Outputs soil water potential and soil temperature
  • Ideal for field, lab or soil column installations


The TEROS 31/32 are ideal soil water potential measuring devices for Australian and New Zealand scientists and engineers. The tensiometers are manufactured by METER Group (formally UMS and Decagon Devices) and are considered the most accurate, reliable and rugged tensiometers available. Consequently, the tensiometers are used across a wide range of applications in Australia and New Zealand, from soil columns experiments in Queensland and Auckland, to agricultural monitoring in Western Australia and the South Island and mining, landfill and other engineering projects.


TEROS 31 and TEROS 32 compared

The TEROS 31 and TEROS 32 are both tensiometers with SDI-12 digital output. The main difference between the models is their size.

The TEROS 31 diameter is 0.5 cm and lengths range between 2 and 20 cm. The TEROS 31 is a miniature tensiometer typically used for laboratory applications, soil columns, pots, or other applications with a small soil or substrate volume.

The TEROS 32 diameter is 2.5 cm and lengths range between 40 and 120 cm. The TEROS 32 is a traditional style tensiometer and is wider and longer than the TEROS 31 mini tensiometer. The TEROS 32 is typically used in field applications for hydrology, engineering, agriculture, irrigation management and more. The TEROS 32 can also be used for soil columns or other laboratory applications.



why measure water potential or tension with a tensiometer?

Water potential, by definition, is a measure of the difference in potential energy between the water in a sample and the water in a reference pool of pure, free water. The tensiometer is an actualization of this definition.

The tensiometer tube contains a pool of (theoretically) pure, free water. This reservoir is connected (through a permeable membrane) to a soil sample. Thanks to the second law of thermodynamics, water moves from the reservoir to the soil until its energy is equal on both sides of the membrane. That creates a vacuum in the tube. The tensiometer uses a negative pressure gauge (a vacuometer) to measure the strength of that vacuum and describes water potential in terms of pressure.

Tensiometers are probably the oldest type of water potential instrument (the initial concept dates at least to Livingston in 1908), but they can still be quite useful. In fact, in the wet range, a high-quality tensiometer used skillfully, can have excellent accuracy.



TEROS 31 (T5, T5x)

The TEROS 31 is the next generation of the T5 and T5x tensiometers. METER Group (formally UMS) released the TEROS 31 is 2021. It has all the same features as the T5 and T5x tensiometers except it is now far easier to integrate with the ZL6 data logger, data acquisition systems, or handheld devices. The TEROS 31 has SDI-12 output which can be easily supported by a range of data loggers.

The TEROS 31 sensor is designed for soil columns, plant pots, laboratory lysimeters, and point measurements. With an active surface of only 0.5 cm² and a diameter of 5 mm, the ceramic tip has all advantages of small dimensions: little soil disturbance, selective pick-up and fast response. The very thin and high flexible cable transfers minimal force to the sensor unit and tensiometer shaft. So TEROS 31 can be installed in nearly every position and no stiff cable will interrupt the measurement or loosen the sensor in the soil.

The TEROS 31 (T5) tensiometer has been cited in over 2000 peer-reviewed publications because, as noted by Yan et al 2022, “due to the fast responding speed of the [TEROS 31] Tensiometer, it is beneficial for studying dynamic soil suction or capillary pressure”.


TEROS 31 and T5/T5x tensiometers compared

The main difference between the TEROS 31 and the older models of the T5 and T5x is the electronics. The TEROS 31 has digital, SDI-12 output whereas the T5 and T5x had analog output. This means the TEROS 31 is easier to integrate with data loggers and portable devices such as the ZL6 and ProCheck.

The TEROS 31 has the same measurement range as the T5 and T5x. The TEROS 31 measurement range is –85 to +50 kPa and up to –150 kPa during boiling retardation.

The shaft diameter of the TEROS 31 is 5 mm.

The TEROS 31 also has the same options for shaft lengths as the T5 and T5x in the following options: 2, 5, 7, 10, 15, or 20 cm.


TEROS 31 applications

The mini TEROS 31 tensiometer is an ideal sensor for a large range of applications. It is mostly deployed in a laboratory or indoor setting, rather than the field, for testing numerous soil and engineering hypotheses. For example, some applications include:

- Soil water retention curves in sand soil column experiments

- Agricultural irrigation of salt-laden soils

- The role of soil compaction and salinity in the context of shallow groundwater

- Cover crops and their effects on soil hydraulic properties


further information



TEROS 32 sensors measure the soil water potential and soil temperature. TEROS-32 applications include measuring soil water availability, controlling irrigation, and measuring soil-water storage.

The TEROS 32 is the ideal tensiometer for field monitoring. It has been designed for irrigation management, agriculture, horticulture, as well as hydrology and engineering applications.

The TEROS 32 advances tensiometer technology by including digital, SDI-12 output. The tensiometer can be easily integrated into IoT devices such as LoRa WAN, NB-IoT, WiFi, modems and more. The TEROS 32 can also connect to the METER Group ZL6 data logger or any other device which supports the SDI-12 protocol.

The portable, handheld device, ZSC, can also be used for spot measurements of soil water potential or tension.


tensiometer tension

The tensiometer is, indisputably, the most accurate way to directly measure water potential in the wet range. But measuring with a tensiometer is complicated. Most tensiometers require sophisticated wiring and complex data logger programming skills to even get them up and running, not to mention the constant maintenance, checking, and refilling. Now there's a new way. Introducing the TEROS 32.

TEROS 32 is a simple, plug-and-play tensiometer that combines METER's legendary German precision engineering with the power of ZENTRA Cloud, giving you easier, faster, more accurate water potential data in near-real time. Just install it and plug it in. It's that easy. With ZENTRA Cloud software, you can review data as it happens from the comfort of your office, ensuring every tensiometer is working as expected. No more worrying if your tensiometer has cavitated. Combine the TEROS 32 with the TEROS 12, and you'll know the best time to go out and refill. Plus, you can use both sensors to generate in situ moisture release curves.


more robust, if that's even possible

Twenty-five years of tensiometer experience and fanatical attention to detail have made METER tensiometers practically bulletproof, but the TEROS 32 is more robust than ever before. Technological advancements have made it possible to incorporate a more ruggedized, highly precise pressure transducer, giving you higher data resolution in an almost unbreakable form, and making the TEROS 32 more affordable than its predecessors. Plus, the ceramic and shaft are engineered to be virtually indestructible when it comes to harsh weather (10-year warranty on the ceramic), which means the TEROS 32 is a tensiometer you can rely on year after year in every season.


spend more time on what matters

We think you should spend less time fussing with complex installations, and more time on your research. That's why unlike most tensiometers, the TEROS 32 is now plug and play. Just insert the stereo plug into the ZL6 data logger, and start seeing numbers. The TEROS 32 connects to the ZENTRA Cloud system, where all data are connected and delivered through the cloud. Pull up your data instantly wherever you are, and you'll know exactly when it's time to refill, before trekking out to the field.


faster field visits

To save you even more time and effort, we've outfitted the TEROS 32 with an external refilling tube. No more pulling the tensiometer out of the ground. When it's time to refill, the TEROS 32 can be filled externally without ever having to remove it, saving you hours of tedious maintenance. On top of all that, the tensiometer is highly responsive. It reacts much faster to changing soil conditions than lower-quality tensiometers, enabling you to measure even the most minute changes in soil water potential. Plus, it measures both positive and negative pore pressure.


accuracy has never been this easy

At METER, we know tensiometers. We've sold over 20,000 across the span of a quarter century, so we're confident that if you need a precise, easy-to-use, reliable field tensiometer with outstanding year-round performance, you can rely on the TEROS 32. More usable, robust, and precise than other tensiometers, it provides superior quality data in near-real time and remains one of the most reliable instruments in the world for year-round outdoor monitoring.


connect to the ZL6 or your own data logger

The TEROS-12 is a highly versatile sensor and is compatible with a range of data loggers. Connect the TEROS-12 to the ZL6 data loggers for hassle free monitoring. Data can be accessed from the ZL6 directly or remotely via the internet with the ZENTRA Cloud platform.

Alternatively, Edaphic Scientific can connect the TEROS-12 to the ES-SYS monitoring system with a range of other sensors including sap flow, dendrometers, canopy temperature and weather sensors.

Or, the TEROS-12 comes with SDI-12 digital output so that you can connect it to your own, existing data logging system.


whole system monitoring solutions

Edaphic Scientific is a one-stop shop for a whole system monitoring solution. We provide plant and soil monitoring systems for researchers and growers including wireless, LoRaWAN and modem options.

Our systems not only support dendrometers, but related sensors such as sap flow, soil moisture, weather parameters, and more.

At Edaphic Scientific we want to work with you from the start of your project through to its completion. We can provide:

  • Assistance with project and experimental design
  • Procurement of all monitoring equipment, including sensors, data loggers and data management software. Edaphic Scientific is a one-stop shop where we can source and find any necessary equipment for your project from our preferred suppliers or third party suppliers
  • Installation and training
  • On-going assistance with data interpretation and equipment maintenance
  • Data correction and analysis, including statistical analysis with the R-package
  • Report and publication preparation including tables, figures, graphs, and manuscript writing


advanced data collection and management solutions

Edaphic Scientific recognises the need for flexible and adaptable sensor and data logging solutions for experimental or environmental monitoring projects.

Data can be downloaded directly in the field from data loggers. A direct connection between the data loggers and your computer, via a USB cable, can be used for manual downloading of data.

Alternatively, data can be downloaded over the internet on your iPhone, iPad or desktop computer with the Eagle.io cloud-based, data management software solutions. Through this remote based downloading capabilities, you can download, view and manage your data, and system, anywhere in the world and at anytime.


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