Patent attributes
First, it is confirmed that the contactor 1a is not damaged. Next, an initial preset signal PR is supplied at the state in which the contactor 1a is contacted to the master work MW. For this reason, CPU stores the reference value in EEPROM. If the timing signal is supplied at the state in which the contactor 1a is contacted to the non-defective object W, the CPU obtains the measurement value and corrects the measurement value by the reference value. When the difference between the reference value obtained during the measurement of the actual object W and the previous reference value stored in EEPROM is more than a predetermined value, it is judged that the contactor 1a is damaged, and warning signal is output. As this warning signal, the judgment signal Hi and the judgment signal Lo become from a low level to a high level.
