Proximity switch.

摘要

Disclosed is a proximity switch which includes an oscillation circuit (1) whose oscillation output is variable depending on the inductance of a coil so that an object in proximity may be detected from the decline in the oscillation output. Further, the oscillation gain of this oscillation circuit (1) is variable according to an input from an external source. Thus, for the purpose of increasing the recovery speed of the oscillation which has dropped as a result of detecting an approaching object, comparison circuits (24,25) are provided so that upon reduction in the oscillation output of the oscillation circuit (1) a certain signal is applied to the oscillation circuit (1) to increase its oscillation gain. As a result, even when an object in proximity is detected and the oscillation level is maintained at a certain low level so that the oscillation may be resumed quickly when the object has moved away from the proximity switch. By virtue of the increased response speed of the proximity switch, not only its detection capability is improved but also it is usable in an environment where a strong AC magnetic field is present.