TEROS 21 Soil Water Potential Sensor

Do not settle for less

When it comes to measuring water potential (or soil suction), it's hard to find a sensor that meets your every need. You're either forced to deal with lowered accuracy or high-maintenance hassles (plus getting soaked on cost). That's why we invented TEROS 21.

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 using a process that we have spent years refining and perfecting, so the TEROS 21 water potential sensor can come to a fixed water potential. The result: a long-term monitoring solution you can finally trust.

A true full-range water potential sensor that's low maintenance and low cost

The TEROS 21 water potential sensor 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 water potential sensor, and you'll know if that water is available to plants and where it will move. Plus, unlike water content, matric potential isn't dependent on soil type, so you can compare moisture between different sites. Not only that, the TEROS 21 is surprisingly affordable, and the new Gen 2 version boasts an improved circuit, a more robust microprocessor, and an improved measurement range. It now measures all the way from near saturation to air dry (0 to ?100,000 kPa) making it the world's first true full range water potential sensor.

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, the TEROS 21 water potential sensor 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 labour.

Soil water measuring that's immeasurable in value

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

Feature summary

Easy to use
Improved accuracy comes from the six-point factory calibration
Tough, Long-lasting body
No recalibration
Low salt sensitivityAffordability
Excellent range sensitivity from 0 kPa all the way to air dry [-100,000 kPa])
Onboard temperature measurement
Plug and play capability
Use with the ZL6 for remote access to data on the cloud
SDI-12 compatible

Feature	Specification
Accuracy	Soil water potential: ±(10% of reading + 2 kPa) from -100 to -5 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.
Resolution	Soil water potential: 0.1 kPa Soil temperature: 0.1 °C
Range	Soil water potential: -5 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
Output	RS232 (TTL) with 3.6 volt levels or SDI-12 communication protocol
Operating environment	-40 to 60 °C
Dimensions	9.6 cm (l) x 3.5 cm (w) x 1.5 cm (d)
Data logger compatibility	METER: ZL6 & ProCheck Other: Any data acquisition system capable of 3.6-15V excitation and serial or SDI-12 communication
Cable length	5 m (standard) 75 m (maximum custom cable length)
Connector types	3.5-mm stereo plug connector or stripped and tinned wires
Warranty	One year, parts and labour

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