| 摘要 |
PURPOSE:To enable automatic apt adjustment of the sensitivity of a proximity switch by controlling the capacitance value of a variable capacitance circuit through operation of a control circuit in response to the proximity switch. CONSTITUTION:The sensitivity of each proximity switch 10... at the time of a power source rise is compared, from a maximal initial state, with a threshold value A in a detection circuit 26 and a decision circuit 46 to function as means for increasing the capacity of a variable capacitance circuit 52 via a control circuit 51, resulting in that all the sensitivities become equal to or lower than the threshold value A to a normal condition. During normal operation, not only each proximity switch 10... but also a reference proximity switch RSW for correcting the detection signal level makes its detection operation. The reference proximity switch RSW sends a control signal to a mechanical drive circuit 53 via the control circuit 51 when it is decided in the decision circuit 46 that a human finger touches on a sensor electrode 11 and the signal exceeds an on point threshold value B. Simultaneously, the detection signal of the reference proximity switch RSW is made stable within a specified range of level by the variable capacitance circuit 52. |
