| 摘要 |
In a radio frequency detector, a high pass filter is provided to attenuate any undesired low frequencies present in signals applied to the filter. The filter output serves as an input to an AND gate. A low pass filter directs power line voltage to a one-shot multivibrator which is biased to respond to the positive-going zero crossing of the power supply to produce an output of limited duration which is applied to the gate as an enabling input. The output of the gate is joined to a second one-shot multivibrator which responds to a pulse generated when the gate is fully enabled causing energization of an alarm actuator. An additional pulse detector optionally is interposed between the gate and the second one-shot to eliminate any random pulses which may occur at the gate output at a frequency below r.f. level, and an additional filter optionally is included between the high pass filter and the AND gate to eliminate the effects on the circuitry arrangement of high frequencies above a predetermined level.
|
