FTC-100 Fredlund Thermal Conductivity Sensor

  • Digital design
  • Transmission of data over 100 m without affecting signal quality
  • 1 to 1,000 kPa range
  • 5% accuracy
  • Accurate for all soil types
  • Measurements are unaffected by soil water salinity
  • Moisture barrier protects electronics from unfavorable moisture infiltrations
  • Special burial cable permits long-term installation in moist environments


The Fredlund Thermal Conductivity Sensor (FTC-100) is an unsaturated soil sensor for measuring soil suction and temperature in the field. The system consists of ceramic-tipped sensors, a suction sensor controller (data logger), and a power supply. Typically, 16 sensors are included with 10 m (30 ft.) of cable for each sensor. The data logger consists of a 16-channel multiplexer that can be connected to a laptop or PC.

The sensor tip has a miniature heating element and a temperature sensor embedded in the center. The heating curve of the sensor is obtained by sending a controlled current to the heating element. The temperature rise in the sensor after heating depends on the water content of the sensor, which is a function of the surrounding soil suction. Calibration curves developed in the laboratory are provided to obtain the suction corresponding to field measured change in temperature.


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