A Ground Temperature Profile Sensor Based on NTC Thick Film Segmented Thermistors: Main Properties and Applications

A new ground temperature profile sensor comprising of a row of thermistors enables a large number of equidistantly arranged measuring points. The row of thermistors was formed using a group of negative temperature coefficient thick film segmented thermistors connected in series. After that calibration of the DC thermistor resistance R was performed at room temperature and the sensor was placed in a hole drilled on the lawn. DC resistances R of the row of thermistors were measured versus depth z as a parameter and converted to actual temperature T(z) in the ground using the Steinhart-Hart equation. The temperature profile of the ground depending on deepness z and time t as a function T(t, z) was measured on different days during one year in the early morning and in the afternoon. The temperature at the ground surface was compared with the temperature of the deepest sensor point in the ground. Thermal diffusivity D of the ground was determined using measured data T(t, z) in the periods of steady ground temperatures. The new ground temperature profile sensor was realized to investigate the correlation between air and ground temperature, observation of ground temperature profile changes and heat exchange (heat transfer, diffusion, gradient, and heat flow direction) through the ground top layer and finally humidity estimation versus deepness.