Proximity switch for series load connection - comprises sensing coil fitted in oscillator circuit whose amplitude triggers controlled rectifier

摘要

A proximity switch operates in a series with an electric motor or a counter when a metallic object is present within the magnetic field of a sensing coil. An inhibiting circuit prevents circuit operation during initial excitation. A proximity switch (15) is connected in series with an alternating current supply to a load circuit. The rectified supply is switched by a controlled rectifier (31) in the proximity switch circuit. A metallic object passing within the magnetic field of the high frequency oscillator coil (51) causes amplitude of oscillation to decrease to block the controlled rectifier triggering transistor (41). A timing circuit (60) connected to the transistor (41) base delays operation of the switch during initial excitation. A light emitting diode (81) indicates when the controlled rectifier is conducting.