Mains Failure Alarm

by A Treps This circuit was originally developed to detect and signal interruptions of the mains supply to artificial respiration systems. The signalling is done in two ways: a buzzer is sound- ed, and a small lamp is quenched. The supply current to the monitored equipment induces a variable flux in a small trans- former that serves to keep the relays actuated, so that La, lights and Bz is off when the mains voltage is available. When a mains failure occurs, apparatus X no longer draws current, so that both Re, and Reg are de- actuated, resulting in the lamp being turned off, and the battery-operated buzzer being activated. Transformer Tr2 is a modified 3 VA mains type which func- tions as a current transducer: the original primary winding functions in this application as the secondary, while the original secondary winding is replaced by about 7 turns of 20SWG (0 1 mm) enamelled copper wire. Every precaution should be taken to ensure that LI 12V1100 mA 4 SUPPLEMENT the new winding...