verzoegerungsschaltungsanordnung operated with alternating current

摘要

1,243,436. Time delay switching circuits. WAGNER ELECTRIC CORP. 4 July, 1969 [5 July, 1968], No. 33737/69. Heading H3T. [Also in Division G1] An A.C. timer circuit, for example for supplying water to a wash-basin so long as the hands are present and for a period after their removal, comprises a first switch which when operated by an input signal of predetermined minimum duration operates a second switch, the latter remaining operated for a variable predetermined time after the cessation of the signal. When the hands are present a capacitive detector 18 so reduces the negative pulses from oscillator 22 to a switching circuit 26, 28 that they are insufficient to overcome a positive bias which is a capacitor 34. This bias is developed by current flowing through resistor 36 and the emitter-collection junction of 26 during the positive half-cycles of the supply and is limited in magnitude by Zener breakdown at the base of transistor 28. Accordingly the bias voltage causes the circuit to switch on, shorting the pulse input fed via 58, 60 to a further switch 52, 54, which becomes non- conducting, allowing positive half-cycles of the supply to operate a relay 63 controlling the water supply. The capacitor 40 is charged negtively by the pulses so that if the hands are momentarily removed restoration of switch 26, 28 does not stop the flow of water. If the hands are removed for a sufficient time the oscillator input rises in voltage and makes switch 26, 28 turn off. Capacitor 50 maintains switch 52, 54 off until it has discharged sufficiently to allow the pulses at its input to switch in or, whereupon the relay current is by-passed from the relay coil and the water flow is interrupted.