Temperature compensation device for security system - utilises bridge compensating elements controlled by motors from coincidence detector circuits

摘要

A bridge (1) contains an element (2) whose impedance is monitored and compared with a compensating element (3) in similar ambient conditions. The bridge output (7) is applied to a self maintaining circuit (8,9) and an alarm (10). The output consists of a phase shift w.r.t. the bridge supply (6) frequency and is applied to coincidence circuits (14) connected to delays (13) which receive a sync. frequency (15A) derived from the bridge supply. The coincidence is detected to operate relays (17) in switching circuits (18) to operate motors (19) to control the bridge elements (4,5) to re-establish balance.