Compensation of the material temperature influence on specific electrical conductivity during eddy current structurescopy

Abstract

The importance of eddy current measurements of specific electrical conductivity (SEC) of materials in non-destructive testing for solving problems of structuroscopy is discussed. In particular, their significant role is shown for estimation of the degree of changes in the mechanical characteristics of structural materials due to degradation processes in their structure. The influence of the temperature of metallic structural materials on the results of eddy current measuring of SEC has been studied. An analytical expression for the output signal of the SEC measuring channel of an electrical eddy current conductivity meter for real temperature of material is obtained. It depends on the value of the material SEC at a nominal temperature value (usually 20 C), temperature coefficient of electrical resistance of the material and the deviation of the material real temperature from the nominal value. It is shown that in order to tune out this effect and bring the measurement results to the nominal temperature, it is necessary to use eddy current meters with an additional channel for measuring the material temperature in the testing zone. The output signal of this channel is used to correct the SEC measurement results. This is carried out by multiplying the output signal of the SEC measurement channel and some auxiliary signal. This auxiliary signal is generated from the output signal of the temperature measurement channel by it scaling and summation with the signal of the direct current voltage reference source. A functional diagram of the eddy current SEC meter with temperature correction is proposed. A detailed description of it operation is given. In the absence of preliminary information about the grade of material and the value of its temperature coefficient of electrical resistance, is proposed to suppress the influence of temperature by test changes in the temperature of the material in the testing zone. At the same time, it is necessary to adjust the gain of the scale converter. This is done until the readings of the eddy current SEC meter do not depend on the material temperature in the testing zone.