Proximity switch for sensing metallic object, with constant total resistance in processing circuit - includes sensing impedance controlled in dependence on measured current and providing output signal from its voltage drop

摘要

The switch is based on an oscillatory circuit (1) comprising a capacitance (3) and the inductance of an electromagnet coil (2) with its resistance (9). Current is supplied form a constant-voltage source (8) via conductors having appreciable resistance (7). The processing circuit (6) consists of a sensing impedance (10) such as a controllable transistor (12) addressed with a measuring signal from the current in an additional internal resistance (11). The aggregate resistance of the device including the source, conductors and oscillatory circuit remains constant. ADVANTAGE - Response time and sensitivity of the switch are improved with energy input independent of the actual position and movement of a metallic object.