Irrometer 200SS-5, Model 200SS Watermark Soil Moisture Sensor with 5' Wire. This 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.
 
Includes: Model 200SS Watermark Sensor with 5 ft Wire
 
Specifications:
Proven stable calibration
Range of measurement from 0 to 239 cb (kPa)
Fully solid-state
Will not dissolve in soil
Not affected by freezing temperatures
Internally compensated for commonly found salinity levels
Inexpensive, easy to install and use
Compatible with AC or DC reading devices (specialized circuit required)
No maintenance required