| 摘要 |
The intruder detector has two sets of sensor wires (12,14). Each set of sensor wires comprises a field wire (16) energised by a respective oscillator (18,20) and a ground wire (22) and is arranged to protect or cover a portion of a protected zone. Each set of wires (12,14) is arranged to have a different capacitance and thus each associated oscillator (18,20) will have a different centre, i.e. steady state frequency. A digital frequency comparator (24) compares variation in the two sets of sensor wires and sounds an alarm, via a processor (26) when there is a change in the capacitance of one set only.
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