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.