Inductive Proximity Switches
Inductive type proximity switches incorporate a damped L-C oscillator driven coil generates a high frequency magnetic field that surrounds the active surface of the device (Fig. 1)
Introduction of metal (ferrous or non-ferrous) into the field causes damping of the L-C oscillator. The resulting change in operating current of the oscillator is sensed to provide an output.
Capacitive Proximity Switches
Capacitive type proximity switches incorporate a damped R-C oscillator. When a material ie. wood, plastic, water, glass, ferrous or non-ferrous metal, is placed within operating range of the switch, the resulting change in capacitance causes the oscillator to begin operating. The operating of the oscillator is sensed to provide an output (Fig. 2)
Magnetic-Inductive Proximity Switches
Magnetic inductive switches incorporate a damped L-C oscillator. Introduction of a permanent magnet into the proximity of the switch causes undamping of the oscillator with the resulting change in operating current being sensed to provide an output.