GB1108884A - Proximity detector circuitry for elevator closures - Google Patents

Abstract

1,108,884. Proximity detectors. OTIS ELEVATOR CO. July 5, 1965, No. 28354 /65. Heading G1N. A proximity detector, used for example to control the doors of a lift according to the presence of passengers in the doorway, comprises: two pairs of antennae UA1, UA2, and UB1, UB2, the capacitance to earth of each pair constituting two arms of a respective capacitive bridge circuit, the unbalance of each bridge being amplified by a respective three-transistor amplifier AMA, AMB, and an output from one or both amplifiers causing a common switching circuit, FF, to prevent door closure. A transistorized square wave generator OSC, energizes the bridges via conductor BO, the energizing circuit being completed by the capacity to earth of the antennae. The measuring diagonals of the bridges, each of which includes in its other pair of arms capacitors C and zero setting capacitors C1 and C2, are transformer coupled, TRBA, TRBB, to the amplifier input transistors TA1, TB1, the secondaries being shorted out by switches KSA, KSB for zero setting of the bridges. The amplifier outputs are fed to voltage rectifying and doubling circuits VDA, VDB; and the switching circuit FF, to which the resultant D. C. signals are fed, consists of a transistor monostable multi-vibrator.