229 Water Matric Potential Sensor

Campbell Scientific

A soil water potential sensor using heat dissipation across a matrix

The 229-L Water Matric Potential Sensor measures soil water potential from 0.1 to 10 bars. The sensor consists of a heating element and thermocouple emplaced in epoxy in a hypodermic needle, which is encased in a porous ceramic matrix. To calculate soil water matric potential, a Current Excitation Module applies 50 mA to the 229's heating element, and the 229 thermocouple measures the temperature rise. The magnitude of the temperature rise varies according to the amount of water in the porous ceramic matrix, which changes as the surrounding soil wets and dries. Soil water matric potential is determined by applying a second-order polynomial equation to the temperature rise. Users must individually calibrate each of their 229 sensors in the soil type in which the sensors will reside.


  • Uses heat dissipation method for soil water matric potential measurement
  • Measurement time is 30 seconds
  • CE8 8-Channel or CE4 4-Channel 50 mA Constant Current Source used with heating element for heat source
  • Requires individual calibration



  • Measurement range: 0.1 to 10 bars
  • Measurement time: 30 seconds
  • Thermocouple type: copper/constantan
  • Length: 60 mm length of entire sensor
  • Weight: 10 g


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CE4 or CE8 required for use with 229

CE4 or CE8 required for use with 229