JUDGMENT METHOD FOR MATERIAL QUALITY BY EDDY CURRENT TYPE DISPLACEMENT SENSOR

PURPOSE: To obtain a judgment method in which the reliability of the judgment of the material quality of a metal material is enhanced and in which a laser machining operation is automated easily. CONSTITUTION: The eddy current type displacement sensor is composed of an eddy current sensor 1 which is built in a bridge of a high frequency oscillator 3 which supplies a high frequency alternating current to the bridge, an amplifier 5 which amplifies the output of the bridge, a synchronous rectifying circuit 7 which full-wave-rectifies the output of the amplifier 5 and a smoothing circuit 5 which smoothes the output of the synchronous rectifying circuit 7. In the eddy current type sensor, a phase comparator 15 which detects the phase difference between the output voltage of the high frequency oscillator 3 and the output voltage of the bridge is installed. The material quality of a metal material is judged by the phase difference and by the average voltage of the smoothing circuit 9.