GB1377408A - Flasher switch - Google Patents

Abstract

1377408 Lamp failure indicator TRIDON Ltd 5 Sept 1972 [10 Sept 1971] 41159/72 Heading G4N A lamp flasher circuit giving lamp failure indication by a change in flashing rate comprises a relay 15 having contacts 25, 26 and two opposing coils 16, 17 one of which is connected in series with a capacitor 20, and means 19 for detecting the magnitude of the current flowing through contacts 25, 26 when closed, to connect an impedance 21 in series with one of the windings when the current passes a threshold value, to change the flashing rate. On closing switch 28, opposing currents flow initially through windings 16, 17 of relay 15, so that contacts 25, 26 are not closed. As capacitor 20 charges, the current in winding 17 falls and the, now larger, current in winding 16 closes contacts 25, 26 to energize lamps 14, and short out the relay windings. The currents in the two windings now decay until the relay releases and the cycle recommences. With both lamps lit, reed relay 19 operates shorting out resistor 21, but if one fails, resistor 21 remains in circuit, reducing the decay time of the current through winding 17, and thus increasing the flashing rate. In a modification, the resistor 21 may be replaced by an additional winding on core 15. In another modification, Fig. 2 (not shown), the reed relay is replaced by a transistor circuit.