| 摘要 |
<p>The burglar alarm has a conductor which is fastened to the surface of a sheet of plate glass forming a window. The conductor forms part of the circuit attached to a relay so that if the glass is broken, the circuit is also broken and the relay operates an alarm. In order to prevent the alarm being disabled by the conductor being short circuited, a known resistance may be provided by the length of conductor. The relay then responds either to an increase in current due to short circuiting, or an interruption in current due to breakage. Alternatively, one or more conductors adhering to the surface of the glass may be used to provide a known capacitance or inductance to which the supply circuit is sensitive. A time delay may then be incorporated to prevent accidental operation of the alarm.</p> |
