Electronic alarm circuit using wheatstone bridge - has timing circuit suppressing short lived alarm signals and responding only to longer duration alarm before activating relay

摘要

The detector includes an automatic system providing brief pulses on the terminals of a wheatstone bridge circuit. The pulses appear across by detecting resistors, and their absence initiates a fault alarm. The circuit also includes a relay with several switch contacts, and a capacitor for timing the interruption of the signal. Verification of the signal is carried out by timing the duration of the alarm signal. If the interruption is short the circuit is returned to its normal position so that the alarm signal is only initiated if the alarm signal persists for a certain length of time. Typically, the time delay is of the order of 2 to 3 minutes.