| 摘要 |
<p>The alarm detection circuit includes a number of two-way switches (A,B,C,D) each of which has a terminal (0) which may be connected to one of two other terminals (R,T). In their rest state the switches are in the position connecting to O and T, and they are connected in series using these terminals. The series line is connected atone end to earth, and at the other end to a processing unit (10). The two terminals (R,T) of each switch are in fact connected together so that when a switch changes, the circuit is interrupted only for the time taken for the mobile switch contact to move. The temporary break in the circuit may be detected by the processing unit (10), but immediately after the incident the unit is reset and able to detect any subsequent interruption. The switches may be arranged to detect unauthorised entry to a building.</p> |
