Abstract: A method and an instrument for testing materials using the eddy current principle, at different frequencies depending on the output quantity of a coil system, compensation values are generated being typical of interfering factors. These compensation values are subsequently superposed on the output values in order to remove the influence of the interfering factors on the measuring. In this manner with a favorable setting of the working point of an amplifier charged with the output values, an overmodulation is avoided and the dynamic range of the amplifier optimally utilized. Therefore good measuring results can be obtained even if the percentage of the interfering signals as compared to the signal controlling the detecting of defects, is relatively high.

Abstract: An electrodynamic instrument transformer head (10) for the non-destructive testing of materials by means of ultrasonics has a pole shoe (20) provided with exciting and receiving coils (14, 16), said pole shoe comprising a slotted end section (24) to prevent a formation of eddy currents. The end section (24) thereby is continuing into a basic body (22) preferably being made of a different material.