| 摘要 |
A telemetry system for use with AC power lines, comprising a pulse transmitter connected to the lines for generating pulses on the power lines only in a selected portion of each full cycle of the power line voltage waveshape. The system further comprises a pulse receiver including first means for counting pulses in the selected portion and second means for counting pulses in another portion of each full cycle. The two counts are compared (one is subtracted from the other) over a plurality of full cycles to produce a net pulse count. Since the noise signals appear throughout the cycles and, over a sufficient number of full cycles, are present in substantially equal numbers in both portions, the subtraction of the two counts essentially eliminates the noise pulses. Any remaining pulses are those produced by the transmitter and may be processed as needed, and false tripping due to noise signals is avoided.
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