GB1083806A - Improvements in or relating to devices for checking the operation of gas or oil furnaces - Google Patents

Abstract

1,083,806. Photo-electric furnace control. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. July 14, 1965 [July 17, 1964], No. 29845/65. Heading G1A. In circuits for detecting the failure of a furnace flame a detector responsive to ultraviolet light and of the threshold ignition voltage type receives chopped radiation from the flame, the resulting modulation of the unsmoothed alternating voltage . supplying the detector provides a signal for operating indicating means. In the arrangement shown in Fig. 2 during the periods of illumination of the detector 1 provided by the chopper the voltage across resistor 8 turns on transistor 10 so reducing the voltage across capacitor 11 to below the Zener diode 11 threshold and maintaining transistor 13 turned off. During the non-illuminated periods of the detector the voltage on capacitor 11 rises above the threshold level to turn on transistor 13. An alternating output voltage is derived from transistor 13 which is rectified and smoothed by components 17 to 22 to provide a direct voltage to operate transistors 22 and 23 and their associated relays, contacts of which in the make position actuate indicator 32 showing flame present. Failure of the flame or any component results in the transistors 22 and 23 not being operated and the break contact of relay 25 actuates indicator 33 for failure. In the arrangement shown in Fig. 5 the periods of illumination provide a voltage at resistor 8 to periodically operate transistor 22 and relay 24 so indicating correct furnace functioning. Transistor 23 and relay 25 are only operated in the detector 1 short circuits since the transistor 42 is turned off by switch 46 during the period of illumination. In a further embodiment Fig. 1 (not shown) the detector is in one arm of a bridge circuit which becomes unbalanced to operate a flame failure indicator of the detector is no longer illuminated.