METER TEROS 21 Soil Water Potential Sensor

Do not settle for less

When it comes to measuring water potential (or soil suction), it’s difficult to find a device that will meet your every need. You’re either forced to deal with lowered accuracy or high-maintenance hassles (not to mention getting soaked on cost). You wouldn’t think taking such a simple reading would be so challenging.

Highly accurate. Yet low maintenance and low cost.

The TEROS 21 is incredibly easy to use. It requires no maintenance, and it’s accurate enough for most applications. In fact, the TEROS 21 provides an even more accurate soil moisture picture than measuring water content alone. A water content sensor only shows the percentage of water in the soil, but add a TEROS 21, and you’ll know if that water is available to plants and where it will move. Plus, unlike water content, matric potential isn’t dependant on soil type, so you can compare moisture between different sites. Not only that, the TEROS 21 is surprisingly affordable, especially when you consider it measures across a wide range, including dry values.

Broad soil applications. Dependable accuracy.

To say TEROS 21 is more accurate than competitor sensors doesn’t do it justice. That’s because unlike competitor models, we calibrate each and every sensor for you. To do this, we use a chamber system that allows the TEROS 21 matric potential sensor to come to a fixed water potential. We put sensors in silica flour, and by controlling the water potential, we’re able to set calibration points from -10 kPa to -80 kPa. The result: a long-term monitoring solution you can finally trust.

The only worry-free soil water potential sensor

Ease of use isn’t something you normally associate with water potential measurement devices. Until now. That’s because TEROS 21 is plug and play in a number of ways.  First, once it’s in the ground, the durable epoxy coating ensures long-lasting usage. Second, no maintenance is involved. That means no refilling. And no worrying about frozen conditions. Lastly, TEROS 21 is also easy to integrate into systems (SDI-12 compatible) so it can be used with third-party loggers. All this adds up to saving you time and a lot of unnecessary labor.

Coverage—Get the maximum for the minimum

This is where you may expect to see a high price point for all of the extra value we engineered into TEROS 21. Instead, we offer them at a low cost so you don’t have to spend more money to get the measurement coverage you need. Not only do more sensors for the money make more sense, but because they use less energy and include a temperature sensor, you’ll also be getting more value for your money. And it’s all backed by 15 years of research.

Soil water measuring that’s immeasurable in value

Accurate. Easy to use. Affordable. TEROS 21 outperforms in every aspect because we specifically designed it to save you time, hassle and money.


Soil water potential: ±(10% + 2 kPa) from -9 to -100 kPa;
Soil temperature: ± 1 °C

NOTE: The TEROS 21 is not well calibrated beyond -100 kPa. Therefore, we do not specify an accuracy beyond this range. For more information on using the TEROS 21 beyond this range, see user manual.


Soil water potential: 0.1 kPa
Soil temperature: 0.1 °C


Soil water potential: -9 to -100,000 kPa
Soil temperature: -40 to 60 °C*

*Sensors can be used at higher temperatures under some conditions

Measurement speed

150 ms (milliseconds)

Equilibration time

10 min to 1 hr depending on soil water potential

Sensor type

Frequency domain with calibrated ceramic discs, thermistor


RS232 (TTL) with 3.6 volt levels or SDI-12 communication protocol

Operating environment

-40 to 60 °C


3.6 – 15 VDC, 0.03 mA quiescent, 10 mA max during 150 ms measurement


Sensors come standard with 5 m cable. Custom cable lengths available. Maximum cable length of 75 m.

Cable connectors type

3.5 mm "stereo" plug or stripped and tinned lead wires (3)

Sensor dimensions

9.6 cm (l) x 3.5 cm (w) x 1.5 cm (d)

Data logger compatibility

METER data loggers (ZL6, EM50/60 series), ProCheck (rev 1.53+), Campbell Scientific, any SDI-12-capable data logger

Teros 21 Manual


Teros 21 Quick Start Guide


Teros 21 Integrator Guide