GB801276A - Improvements in circuit arrangements for detecting or indicating the opening of an electric switch - Google Patents

Abstract

801,276. Protective arrangements. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 30, 1956 [Feb. 3, 1955], No. 3236/55. Class 38 (5). In an arrangement for indicating the opening of a switch connected in series with other switches, a branch including an electric discharge device in series relationship with the switch is connected in shunt to one portion of a potential divider, the circuit characteristics being such that a discharge in the device initiated with the switch closed is maintained while the switch remains closed and is interrupted when the switch is opened. The switches may comprise the contacts C1 ... C4 of overload relays, the contacts being connected in series with the coil CB of a circuit-breaker across a D.C. supply. Neon diodes D1 ... D4 in series with resistors P1 ... P4 are connected between the contacts and the junction T between resistors R1, R2 forming the potentiometer. When all the contacts C1 ... C4 are closed, the momentary depression of a push-button switch S short-circuits the resistor R2 and full voltage is applied to the diodes D1 ... D4 causing them to strike, the glow of the diodes indicating normal operating conditions. Should, for example, contacts C3 open, then the polarity of the voltage across diode D3 and any following diodes, i.e. D4, is reversed momentarily, the diodes D3, D4 extinguish and remain extinguished, even though the contacts C3 may reclose, as the voltage across the diodes is not sufficient for striking to occur until the switch S is pressed. Reference is made to the use of the arrangement in detecting the faulty operation of a series contactor system.