| 摘要 |
1285476 Signalling over power lines FRANKLIN ELECTRIC CO Inc 2 Sept 1969 [3 Sept 1968] 43442/69 Heading H4R A transmitter for signalling over power lines comprises a potential breakdown device and a storage device connected in series across the power lines. As the potential across the breakdown device rises during an A.C. supply cycle breakdown occurs allowing the storage device to charge, reducing the potential across the breakdown device to below the extinction potential, and producing a narrow pulse which is transmitted over the lines to a suitable detector. A number of suitable transmitters and receivers are described. Transmitter.-Fig. 2 comprises a circuit using a neon 26 in series with a capacitor 27 connected across power lines via a bimetallic switch 28, actuated, e.g., by the temperature rise in an electric motor winding. The neon may be replaced by a spark gap or a TRIAC which may be biased by a D.C. source or triggered by connecting a neon between the gate and the connection between the TRIAC and the capacitor (Fig. 6, not shown). Alternatively a S.C.R., e.g. 52, Fig. 5, may be used which is triggered when the voltage across a TRIAC 66 reaches the firing potential. Since the S.C.R. will only conduct with one polarity of supply a pair of S.C.R.'s 62, 62a are used back-to-back to provide pulses on both half-cycles. Diodes 67 and 67a are provided across the S.C.R.'s to allow the capacitors to discharge during the inoperative half-cycles. If the diodes are omitted, Fig. 4 (not shown), the pulses will be generated only during the first half-cycle in which the transmitter is connected to the line and not in any subsequent half-cycle unless the capacitor is discharged, e.g. by a discharge resistor manually connected into circuit (57 and 57a). The pulses may be selectively generated, by operation of switches 64 or 64a to provide selective signalling. The receiver, Fig. 12, may comprise a filter circuit 177 which discriminates against mains supply frequency and passes the higher frequency pulses to an integrator 179. When the integrator voltage exceeds the threshold of Zener diode 184, S.C.R. 187 fires to operate a relay 188 which opens a contactor coil circuit at 189 and lights a neon indicator 197. When the alarm signal has ceased the S.C.R. can be extinguished by operation of push-button 193. A "press to test" circuit is included comprising an elementary form of transmitter including the neon 202 connectable across the power line by switch 201. Modifications of the control switching are described with respect to Figs. 13 and 14 (not shown), the Fig. 14 embodiment employing an indicator plunger type fuse connected across the line terminals by the operation of the control relay.
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