| 摘要 |
A plurality of sensors at a transmitting station, responsive to different types of disturbances on premises to be kept under surveillance, generate respective bits of a basic binary word which is modulated onto a low-frequency carrier for communication to a receiving station. At the transmitter, an encoder successively converts the basic word into different bit combinations which are then reconverted at the receiver into the original word for evaluation in a shift register. Upon iterative reception of an abnormal code combination, a counter at the receiving station triggers an alarm distinctively indicating the nature of the disturbance on the basis of the improper bit or bits.
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