| 摘要 |
1,161,743. Signalling over power circuits. W. H. WATTENBURG. 6 Oct., 1966 [24 Oct., 1965], No. 44629/66. Heading H4R. In a system for signalling over power circuits the transmitter comprises a power absorbing device which is connected so as to absorb power from the line at a frequency different from the power supply frequency and at an amplitude modulated by the power supply frequency. The transmitter may comprise, Fig. 2, a multivibrator 27 oscillating at 17 kc/s. to switch transistor 26 between its bottoming and cut-off conditions. The transistor 26 is connected in series with the parallel connected resistor 24 and capacitor 23 across the power supply line via a sensing device which is rendered conductive when signalling is to commence, e.g. on operation of a burglar alarm or fire detector. The signal produced on the line comprises a burst of 17 kc/s. during each positive half-cycle of the power supply waveform. The receiver for the signal comprises, Fig. 10, a 17 kc/s. filter 17 feeding a first detector and amplifier 47 which feeds, via a low-pass filter, an amplifier 56 tuned to the supply frequency. The resulting signal passes via a second detector 57 and an integrator to a current amplifier 62 which, on the arrival of a signal causes the S.C.R. 111 to fire to operate the appropriate alarm or indicator circuits. |
