Abstract: A system for detecting ultra-violet radiation has a cold cathode discharge tube which produces a pulse each time it avalanches. A logic arrangement steers these pulses successively to separate timers in that order. In response to each pulse, each timer sends its own output line HIGH for a preset period, the same for all the timers. An AND gate receives all the timer outputs and produces an alarm signal when all these are HIGH at the same time.

Abstract: A fire detecting arrangement has a longitudinal fire detector having conductors separated by a substance whose resistance decreases with temperature and whose charge acceptance capability increases with temperature. The detector is supplied with a rectangular waveform swinging between +5 and -5 volts through resistors, one of which is high compared with the other. High temperature will therefore cause a greater volt drop across the detector during positive waveform portions than during negative waveform portion, the potential division effect of the unequal resistors being enhanced by the increased charging current. Contamination or damage merely decreases the resistance of the detector and the lack of charging current means that the inequality of the voltage drops during positive and negative portions of the drive waveform is not so marked.