| 摘要 |
A circuit for reducing or eliminating the sensitivity of alarm circuitry to false alarms caused by noise occurring synchronously with a 60 Hz line voltage. The 60 Hz line signal is applied to a variable-threshold circuit which produces a 60 Hz clock signal. The clock signal produced by the variable-threshold circuit may be selected to occur at different points during a cycle of the 60 Hz line signal. In response to successive alarm signals, the clock signal produced by the variable-threshold circuit occurs with different phasing relationships to the 60 Hz line signal. Before an alarm indication is made, an alarm signal must be provided by the smoke sensor in response to a plurality of successive samples. If, the alarm signal is a false alarm signal produced by the pickup of noise pulses which are synchronous with the 60 Hz line signal, subsequent samples taken at different points during a cycle of the line frequency sample the output from the smoke detection circuitry during periods when the alarm circuitry does not pick up such synchronous noise pulses; and the false signal is rejected.
|
