A differential double-coil inductive transducer for measuring electrical conductivity

Abstract

A differential system of two double-coil inductive transducers for the contactless measurement of the electrical conductivity of conducting materials has been presented. The differential system can be employed in applications that require smaller measurement uncertainty than that provided by the single-transducer system. A mathematical model of the differential system is based on the model of a single double-coil inductive transducer; in this case, a so-called processing function is defined as a ratio of voltages at the measurement coil terminals with and without the test sample. The relative differential voltage of the differential system is derived as a difference of processing functions of two single transducers and depends on a relative difference between conductivities of the test and reference samples. The conductivity of the test sample is obtained either using precalculated graphs or by numerically processing the equation of the differential voltage. In order to verify the obtained theoretical results, experimental investigations have been carried out using a computer-controlled measurement system with the differential system of the transducers. The conductivity measurements have been carried out using samples made of aluminum rods. During the measurements, the temperature of the reference sample was equal to room temperature (20 degrees C), whereas the temperature of the test sample was changed in the range of 0-20 degrees C to obtain the conductivity variation. The obtained experimental results confirmed the accuracy of the theoretical model of the differential transducer.