| 摘要 |
<p>A secured room, such as a bank vault, has a range of alarm sensor modules coupled to a remote alarm control system within a protected area. The link between the sensors and the control unit is provided by two fibre optic bundles, that have the fibres freely mixed. When an alarm sensor is activated an oscillator circuit outputs a specific frequency and amplitude signal that is transmitted via an LED and one fibre optic link to a photo diode. A pair of comparators checks to determine the level relative to threshold values. If it is outside these values an alarm is triggered. Any disturbing light effect is felt by both fibre optic links and a second photo transistor is used to provide identification. A number of sensors may be coupled to the central facility.</p> |
