GB1294698A - Circuit for monitoring faults in a signal lamp circuit - Google Patents

Abstract

1294698 Lamp failure alarms HASLER AG 14 Nov 1969 [25 Nov 1968 7 May 1969] 55996/69 Heading G4N In a circuit for monitoring faults in a signal lamp control circuit having a transistor 5, controlled by a signal voltage E, a pulse transmitter 20 is arranged to deliver test pulses to transistor 5 and to a fault indicator circuit 22-26 which provides an indication if a voltage which does not correspond to the switched state of transistor 5, determined by the test pulse, occurs at the junction of transistor 5 and lamp 1. As shown, a signal at E may be passed by gates 3, 4 to turn on transistor 5 and operate lamp 1. Each test pulse A inhibits gate 3 so as to turn off transistor 5 and hence provide a pulse at the collector which is fed to a fault indicating circuit 23 . . . 26 which lights lamp 26 if lamp 1 is faulty or if transistor 5 fails to turn off. Pulses B are used in conjunction with a fault indicating circuit 33 ... 36 to light lamp 36 if an open-circuit fault should occur in gate 4 or transistor 5. AND gates 7, 8; 17, 18 couple a further lamp 11 (controlled by transistor 15) to the fault indicators. Lamp 39 indicates a fault of either type in circuits 2 and 12. The mark/space ratio of pulses A may be sufficiently small as to have no effect on the brightness of lamps 1, 11 or may be varied to provide a brightness control.