| 摘要 |
PURPOSE:To surely detect the generation of a defect under high reliability by passing the voltage or current detected between a pair of welding electrodes through a high frequency separation filter and passing further through the gate which passes only the several period parts after the initial several periods. CONSTITUTION:The voltage between steel plates 1, 1 is detected by a voltage detector 11. The detection voltage signal is passed through a high frequency separation filter 12 and only the high frequency component is separated and inputted to an AND gate. The voltage higher than the threshold value outputted from a comparator 13 is inputted to the AND gate, only the high frequency component to be detected by the motion of a switching signal removing circuit 30 is passed through the AND gate 21 and only in the case of a defect being caused the generation is surely detected. With this method, a defect can surely be detected.
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