Self-monitoring ionisation fire detector - has combined alarm and circuit malfunction detector stage with operating voltage across base-emitter path of circuit transistor

摘要

An ionisation fire detector is built into a circuit that both generates a warning signal and indicates any error state. The comparison chamber (3) and reference chamber (4) are coupled over a voltage divider (15, 10) to the supply (1, 2). The separating wall is connected to the gate of an FET (5) that operates together with the source resistance (6) as an impedance converter. The alarm trigger consists of transistors (10, 11), coupled to the output of the impedance converter. A malfunction trigger stage is provided by two transistors (13, 14) and a switching stage (7).