GB1037234A - Flame detector - Google Patents

Abstract

1,037,234. Transistor pulse circuits. COMBUSTION ENGINEERING Inc. Oct. 30, 1963 [Nov. 2, 1962 (2)], No. 42813/63. Heading H3T. [Also in Division G1] In a flame detector, random pulses produced by avalanche processes in a glow discharge detector tubes due to radiation from the flame, are transmitted to a receiver circuit which includes e.g. a relay which actuates an indicator to show whether or not the flame is alight. The lightly loaded transmitter circuit includes the discharge tubes UV (Fig. 8) arranged to produce pulses superimposed randomly as voltage spikes on the A.C. supply waveform from 10. The duration of the pulses is increased by means of R 1 and C 1 . The pulses are separated from the supply by means of capacitors C 2 and C 4 and the negative pulses shorted to earth through diode D 2 . The positive pulses trigger on an S.C.R. the signals from which are stored in a tank circuit K L , C 5 . The diode D 1 produces halfwave rectification for the receiver supply. On extinction of the flame, the pulses from the U.V. tubes stop and the relay is caused to actuate an alarm or indicator. A circuit to check whether or not the S.C.R. and other components are operating correctly, involves a bridge rectifier 26, tuned to a band of frequencies about the random signal frequency, having a relay 28 which can operate an alarm 34 if a fault is detected, and which can be connected either across the relay R L or across the secondary of a transformer (Fig. 9, not shown), the primary of which is connected in the output of the receiver. Various modifications of the receiver circuit are described. In one (Fig. 4, not shown), negative pulses from the transmitter switch on the transistor Q 1 and capacitor C 6 is charged to a desired value, and increases the time constant of the gate pulse to the S.C.R. The rate of firing of the S.C.R. is again dependent on the rate of pulses from the tubes UV. The capacitor C 7 helps the S.C.R. to recover after each pulse. The circuit has a full-wave rectified supply at a low voltage, an alternative highvoltage circuit being provided in a circuit which includes a Zener diode and a resistor to limit the voltage across the transistor (Fig. 5, not shown). In a high-voltage circuit which may be supplied by a half-wave supply (Fig. 6, not shown), the capacitor C 6 may be omitted since a shorter gating time is required for a higher voltage S.C.R. A transistor Q 2 (Fig. 7, not shown) may be used to receive the pulses from the transmitter and forms part of an emitter follower circuit. The emitter-collector current is limited by resistor R 6 . C 8 acts to store some of the energy of Q 1 to maintain Q 3 turned on between signal pulses to Q 2 . Transistor amplifier stages are provided with relay R L as the load for transistor Q 4 .