EDDY CURRENT FLAW DETECTOR

摘要

PURPOSE:To always obtain almost constant detection sensitivity regardless of changes in the moving speed of an object to be inspected by controlling the time constant of feedback with a signal corresponding to the moving speed. CONSTITUTION:A balance time constant circuit 28 is composed of an integration circuit 35 and a gate circuit 34. To determine the balance time constant, a speed command is converted into a pulse with a voltage-frequency circuit 32 of a bias circuit 31. This pulse signal is introduced into a timing circuit 33 and the output thereof turns on or off a gate circuit 34 to control the time constant. According to changes in the frequency, the positive or negative duty varies in such a manner that the gate circuit 34 turns on only during the priod of the positive pulses. Controlling pulses enables linear control of the balance time constant in a wide range.