| 摘要 |
PURPOSE:To prevent the contact resistance value inferiority of a contact, by gathering the metallic foreign matter in a reed switch to the vicinity of the contact point of the contact to measure the contact resistance of the contact. CONSTITUTION:A reed switch 2 is inserted in a drive coil 10 and a contact S is connected to terminals S1, S2 and, when an electric key TS is pushed down, a control circuit 16 starts a drive circuit 15. Next, the circuit 16 receives a continuous pulse from a pulse oscillator 19 to send out a driving current pulse P to the coil 10. A counter 12 counts the pulse P and sends a signal to the circuit 15 when the number of the pulses P reach a preset number (n) to allow a definite operating current to flow to the coil 10. Further, the send-out finish signal of the pulse P is sent to the circuit 16. The circuit 16 starts a comparing circuit 17 when detects the send-out finish signal of the pulse P. At this point of time, the metallic foreign matter adhered to a contact spring is gathered to the vicinity of the contact point of the contact S in the switch 2. The circuit 17 compares the voltage Vs between both terminals of a resistor R2 (prescribed resistor) with the voltage Vt between both terminals of the contact S and, when the voltage Vt exceeds the voltage Vs, the inferiority of the contact is judged to be displayed on a display device 18.
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