GB1412164A - Ionization-type fire sensor - Google Patents

Abstract

1412164 Ionization fire alarms CERBERUS AG 17 July 1973 [17 July 1972] 34093/73 Heading G4N An ionization fire sensor unit provides a warning signal at the approach to the alarm threshold, and before the alarm signal. The warning signal may indicate incipient fire, or a faulty detector, e.g. due to precipitation of dust. As shown, Fig. 1, an LED is connected in series with the FET monitoring the ionization chambers, and adjustable bias resistor 5 determines the warning level, at which the LED begins to glow. At the alarm level transistor 12 conducts and due to positive feed-back through resistor 5, abruptly draws an increased current, for signalling to the central station, and also "locks-on". Warning central station.-To repeat the warning signal to the central station the LED may co-operate with a photoresistor connected over a third line-wire Fig. 3 (not shown) or the LED current may be monitored by a third wire Fig. 4 (not shown). Alternatively the warning current may be monitored by a further transistor (22) to switchon a multivibrator (23, 24) sending an A.C. signal over the lines, Fig. 5 (not shown), or where an oscillating line termination is provided as in Specification 1,319,615, the warning transistor may switch a capacitor across the line to short-out the end-of-line signal, Fig. 6 (not shown).