METER TEROS 12 Advanced Soil Moisture Sensor with Electrical Conductivity Added


Soil moisture sensing—reinvented

In the field, soil moisture accuracy can make or break a study. But accuracy is about more than just the sensor. It’s about eliminating anything that confounds the data. That’s why we’ve completely reinvented not just our sensor, but the entire soil moisture sensor experience. Introducing the new TEROS 12.

Pushes past traditional boundaries

For 20 years, our experts have worked on achieving the highest possible accuracy spec. Now we’ve turned our attention to something nobody else is thinking about—the accuracy of the entire system. The new TEROS 12 sensor is more than just a sensor. It’s a complete soil moisture system that treats the whole accuracy problem, rather than just one part of it, by eliminating common problems that cause uncertainty in the data—things like sensor-to-sensor variability, air gaps, or preferential flow. No other soil moisture system on the market addresses these issues.

Sensor to sensor variability—solved

Accuracy is only as good as a sensor’s consistency. And if you’re calibrating every sensor individually, errors can occur, especially when you’re installing hundreds of sensors. The TEROS 12 uses a completely new calibration procedure that maximizes accuracy and minimizes sensor-to-sensor variability, while keeping the TEROS 12 cost reasonable. So you can be confident that every sensor you install is going to read exactly like the next one.

Sensor performance—maximized

Accurately characterizing soil moisture variability demands a large volume of influence. The TEROS 12 delivers the best volume of influence to sensor size on the market. We’ve optimized the circuitry in this 9.4-cm sensor to deliver an incredible one-liter volume of influence (versus the 200 mL typical for most sensors). Most soil sensors that measure this much volume are 20 cm or longer, causing installation headaches. Not only that, we’ve positioned a temperature sensor perfectly inside the middle needle so the needles are robust, yet extremely sensitive to soil temperature change. These high-quality stainless steel needles slip easily into even hardened soils, and a durable epoxy fill means the sensor lasts up to 10 years in the field.

Installation error—eliminated

Everything comes down to installation, in terms of accuracy. If installation is poor, it doesn’t matter how good the calibration is, your data will be bad. The new TEROS Borehole Installation Tool mistake-proofs installation. The tool and sensor were designed as a unit to fit down a 4-inch diameter hand-augered hole. This delivers consistent, flawless installation into any soil type (even hard clay) while minimizing site disturbance. Sensors are installed straight in and perpendicular with uniform pressure then gently released to prevent air gaps.

TEROS offers an excellent way to measure the soil profile. Major advantages: install into undisturbed soil instead of a slurry, at depths you choose, without creating the preferential flow issues that plague traditional profile sensors. The TEROS Borehole Installation Tool can install sensors at borehole depths up to 1.8 meters.

Seamless data collection—mastered

Easy and reliable data collection is part of the TEROS 12 experience. Combine the TEROS 12 with the new ZL6, where all data are connected and delivered through the cloud. So all you have to do is sit back and let the data flow.

Why not have it all?

Traditional soil moisture sensors miss the forest for the trees. The new TEROS 12 goes beyond merely optimizing the reading to optimize the accuracy of the whole data set. It combines consistent, flawless installation, minimal sensor-to-sensor variability, and a large volume of influence to deliver performance, accuracy, and reliability at a price you can afford.

With the release of the TEROS 12, it is now our unanimous recommendation for every application.

Volumetric water content (VWC)

Mineral soil calibration: 0.00–0.70 m3/m3
Soilless media calibration: 0.0–1.0 m3/m3
Apparent dielectric permittivity (εa): 1 (air) to 80 (water)

NOTE: The VWC range is dependent on the media the sensor is calibrated to. A custom calibration will accommodate the necessary ranges for most substrates.

0.001 m3/m3
Generic calibration: ±0.03 m3/m3 (±3.00% VWC) typical in mineral soils that have solution EC <8 dS/m
Medium specific calibration: ±0.01–0.02 m3/m3 (±1–2% VWC) in any porous medium
Apparent dielectric permittivity (εa): 1–40 (soil range) , ±1 εa (unitless) 40–80, 15% of measurement

Dielectric measurement frequency

70 MHz


Range: −40 to 60 °C
Resolution: 0.1 °C
Accuracy: ±0.5 °C from −40 to 0 °C
±0.3 °C from 0 to +60 °C

Bulk electrical conductivity (ECb)

Range: 0 to 20 dS/m (bulk)
Resolution: 0.001 dS/m
Accuracy: +/- (5% +0.01 dS/m) from 0 to 10 dS/m
+/- 8% from 10 to 20 dS/m


DDI serial or SDI-12 communications protocol

Data logger compatibility

METER ZL6, EM60, and Em50 data loggers or any data acquisition system capable of 4.0- to 15-VDC power and serial or SDI-12 communication


Length: 9.4 cm (3.70 in)
Width: 2.4 cm (0.95 in)
Height: 7.5 cm (2.95 in)

Needle length

5.5 cm (2.17 in)

Cable length

5 m (standard)
75 m (maximum custom cable length)

NOTE: Contact Customer Support if a nonstandard cable length is needed.

Connector types

3.5-mm stereo plug connector or stripped and tinned wires

Supply voltage (VCC) to GND

Minimum: 4.0 VDC
Typical: NA
Maximum: 15.0 VDC

Digital input voltage (logic high)

Minimum: 2.8 V
Typical: 3.6 V
Maximum: 3.9 V

Digital input voltage (logic low)

Minimum: –0.3 V
Typical: 0.0 V
Maximum: 0.8 V

Digital output voltage (logic high)

Minimum NA
Typical 3.6 V
Maximum NA

Power line slew rate

Minimum: 1.0 V/ms
Typical: NA
Maximum: NA

Current drain (during 25-ms measurement)

Minimum: 3.0 mA
Typical: 3.6 mA
Maximum: 16.0 mA

Current drain (while asleep)

Minimum: NA
Typical: 0.03 mA
Maximum: NA

Operating temperature range

Minimum: –40 °C
Typical: NA
Maximum: +60 °C

NOTE: Sensors may be used at higher temperatures under certain conditions; Contact Customer Support for assistance.

Power up time (DDI serial)

Minimum: 80 ms
Typical: NA
Maximum: 100 ms

Power up time (SDI-12)

Minimum: NA
Typical: 245 ms
Maximum: NA

Measurement duration

Minimum: 25 ms
Typical: NA
Maximum: 50 ms


Manufactured under ISO 9001:2015
EM ISO/IEC 17050:2010 (CE Mark)
2014/30/EU and 2011/65/EU
EN61326-1:2013 and EN55022/CISPR 22

Teros 12 Manual


Teros 12 Quick Start Guide