Stanko Milun

Measurement of soil thermal properties by spherical probe

The thermal resistivity of the soil surrounding a power cable is a very important factor in evaluating the load-carrying capability of underground cable. This paper presents a method for measurements of soil thermal properties with a spherical probe along the cable installation routes. On the basis of two-port network analysis, equations for the temperature response of the hollow spherical probe are obtained. The paper offers a mathematical model for calculation of the soil thermal parameters, including the related standard deviations, using the least square method. The propagation time of thermal flux is calculated, and it is shown that the transient stage of the spherical probe can be used for measurements in infinite as well as limited samples of soil. Thermal self-capacity and contact thermal resistance between probe and surroundings are taken into the calculations. The realization of the probe with electrical heater and temperature detector, as well as additional measuring devices, is described.

Ring-core flux-gate magnetometer with microprocessor

Abstract In this paper the realisation of a flux-gate magnetometer based on a microprocessor is presented. This magnetometer operates as a closed-loop feedback system which is controlled by the microprocessor. The main part of the magnetometer is a sensor consisting of ferromagnetic core, drive coil and sense coil. Because of many advantages, the ring-core sensor, instead of an open core, is used. The external magnetic field is measured by means of filtering the second harmonic amplitude of the sense coil induced voltage. The amplitude of the second harmonic is filtered by the band-pass so that the analog output signal is accessible. After the A/D conversion of this signal, additional digital filtering using Discrete Fourier Transform (DFT) is applied and an output signal in digital form is obtained.