| 摘要 |
<p>1529162 On-delay timer CUTLER-HAMMER WORLD TRADE Inc 20 April 1977 [10 June 1976] 16464/77 Heading H3T [Also in Division H2] A solid-state on-delay timer is supplied by AC on two lines 20,22 and via a rectifier D2, D 1 derives a DC supply which uses one AC line 20 as common and has another line 24. A timer is connected between common and D.C. and is controlled by a circuit connected to all three lines, itself controlled by a switch SW, the timer when operated controls conduction of a thyristor circuit Q7 connected in series with a pair of load terminals between the two A.C. lines to energize a load, if present. With switch SW open, current flows from L2 via R1, R5, R6, Q5 and C3 to L1, and charges R4. Meanwhile D.C. flows through R3 and Q3, acting as a Zener, to bias Q1, Q2 off. The peaks of the A.C. current turn these transistors on thereby discharging C5 and C6. When the transistors are off, these capacitors charge but with a time constant long enough for the voltage rise between discharges to be of no effect. When switch SW is closed, the A.C. current no longer passes through R4 in particular and the transistors Q1, Q2 are held off allowing C5, C6 to charge until a dual threshold device Q6 is operated to fire the triac Q7. The gate current of the triac partly flows through the LED which lights as an indication that firing has been initiated. Reopening SW causes discharge of the capacitors within one mains period, removing the trigger from Q7 which turns off at the next zero point. The resistances associated with the switch can be chosen to permit correct operation with "leaky" switches. The delay can be set by P1 or a remote potentiomenter RP.</p> |
