Eddy current material testing systems - method and equipment for eliminating effects of interference signals

摘要

In a material testing system, the physical quantity which causes the interference is modulated. The composite signal containing the non-modulated test signal and the modulated interference signal, is subjected to a phase shift and applied to a phase discriminator which delivers a D.C. voltage proportional to the test signal, and an A.C. voltage proportional to the test signal, and an A.C. voltage proportional to the interference signal. The A.C. signal is rectified and the resulting D.C. voltage amplified and applied to the phase shifter, so that the interference signal is eliminated. Alternatively, the physical quantity which generates the test signal is modulated and the interference signal source is not. The two signals are then treated as above.