GROUND THERMAL CONDUCTIVITY
Instrumentation for geognostic investigation
The measurement method is based on the so called unstable sensor technique, that uses a probe (also called thermal needle), which mounts a heating wire and a temperature sensor. The probe is introduced in the ground. From its response when subject to a heating cycle for a few minutes, it is possible to calculate the thermal resistivity (or its opposite, the heat transmission).
The principle of the measurement is based on a peculiar characteristic of a rectilinear heat course (the heating wire of the probe): after a short transitional period, the increase of the temperature depends only on the heating power and heat transmission of the medium. Once the first is known, the second can be calculated. The main applications of the technique consists in the testing of high voltage cables and heating ducts.