| 摘要 |
A central alarm system has a central unit, at least one terminal station and transmission lines which connect the central unit to each terminal station. The system is operated in normal, monitoring and control modes in repeated succession. The occurrence of an abnormal or undesirable condition in one terminal station is identified during monitoring mode and a specific desired alarm device is selected during control mode. If three transmission lines are provided, one line is used to transmit the monitoring signal in order to verify the occurrence of an abnormal condition, and the other line is used to transmit the control signal in order to select the desired alarm device. If, however, only one pair of transmission lines is provided, one line is used as a data line for time-sequential transmission of all signals. <IMAGE>
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