Lift off compensation of eddy current crack detection system by controlling damping resistance of oscillator

摘要

An eddy current crack detection system has an inductive probe coil forming part of an oscillatory circuit. The coil voltage is fed to a measuring device a change in amplitude of the coil voltage being used as an indication of a crack. In order to compensate for lift-off in the amplitude of the coil voltage, a control signal is generated related to the magnitude of lift-off, and controls the value of a variable damping resistor in the oscillatory circuit.