| 摘要 |
An electronic timing device opens an electrical circuit whenever the circuit, e.g., a lighting circuit, has been left closed accidentally. The device is wired in series with an existing wall switch 13 and the load 12 which it controls. Whenever the existing switch 13 is turned on, a load sensing circuit senses the flow of current and triggers a timing circuit. The timing circuit may be preset to some arbitrary time period. At the expiration of the time period, the timing circuit opens a switch circuit 1 to disconnect the load. The timer assembly is sufficiently compact that it fits within a modified switch plate having a slight recessed area surrounding the switch lever opening (Figs. 3 to 5). Optionally, when the timer times out, the switch 1 may be intermittently closed to give a flashing warning for a predetermined period before the switch 1 is finally opened continuously. An audible warning may alternatively be given. The device may be connected in parallel, rather than series, with the existing switch 13 to function as a turn-off delay. <IMAGE> |
