| 摘要 |
In a security system, for status reporting from detectors (D1, D2, D3) set up in a protected local (P) to a monitoring centre (C), and monitoring the operational condition of communication lines (3) which are arranged to connect the detectors to the monitoring centre, an interrogation signal (F) is produced and transmitted from an interrogation unit (1) in the monitoring centre to an answering unit (2) connected to the interrogation unit and located in the detector. The answering unit replies by producing and sending back to the interration unit an answering signal (Sf) which is dependent on he interrogation signal. When alarm/sabotage status is indicated by the detector, the answering unit recognises this and sends an alarm/sabotage signal (sa/Ss) to the interrogation unit which is different from the answering signal (Sf) depending on the interrogation signal. In order to prevent or make unauthorised manipulation of the security system with a view to misleading the monitoring centre (C) extremely difficult, and to obtain a functionally-reliable arrangement in which both monitoring of the communication lines (3) and status reporting from the detectors (D1, D2, D3) is effected simultaneously with the aid of the same functional units by integrated communication, the interrogation signal (F) transmitted by the interrogation unit (1) is arranged to be transmitted continuously and also to be information-bearing with a stochastically varying content. The answering unit (2) is arranged to endow the answering signal with an information content which, in addition to the instantaneous information content of the interrogation signal, also depends on the actual status (a, s) of the detector, and to send back the answering signal continuously. |
