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The Watermark sensor (granular matrix sensor) is an indirect, calibrated method of measuring soil water. It is an electrical resistance type sensor, read by data logging equipment or a Soil Moisture Meter (pictured below, center) which converts the electrical resistance reading to a calibrated reading of Centibars (or kPa) of soil water tension.
In use since 1978, the patented WATERMARK sensor is a solid-state electrical resistance sensing device that is used to measure soil water tension. As the tension changes with water content the resistance changes as well. That resistance can be measured using the WATERMARK Sensor.
The sensor consists of a pair of highly corrosion resistant electrodes that are imbedded within a granular matrix. A current is applied to the WATERMARK to obtain a resistance value. The WATERMARK Meter or Monitor correlates the resistance to centibars (cb) or kilopascals (kPa) of soil water tension.
The WATERMARK is designed to be a permanent sensor, placed in the soil to be monitored and “read” as often as necessary with a portable or stationary device. Internally installed gypsum provides some buffering for the effect of salinity levels normally found in irrigated agricultural crops and landscapes.
- 0-200 Centibar range
- Stainless steel enclosure
- Fully solid state
- Will not dissolve in soil
- Not affected by freezing temperatures
- Internal compensation for commonly found salinity levels
- Easy to use
- No maintenance