| 摘要 |
1277402 Flame detecting device UNITED GAS INDUSTRIES Ltd 21 Aug 1969 [27 Aug 1968] 40958/68 Heading F4T A flame detector 5 which makes use of rectifying action of a flame, comprises electrodes 11, 12 across which is supplied, via a d-c blocking capacitor 14, an alternating voltage so that when a flame is present at the burner 13 the rectifying action thereof causes a charge to build up on the capacitor 15, thus applying a potential difference between the base and emitter of PNP transistor 19 and rendering it conductive. A NPN transistor 21 has its base connected to the emitter of transistor 19 so that when transistor 19 is conductive 21 is non-conductive which in turn renders the emitter of transistor or 24 positive with respect to earth and thus diode 26 conductive and provides the "flame present" or "OR" line with an output. If a flame is absent the emitter 24 is negative with the result that diode 27 is rendered conductive and an output provided in the "flame absent" or "AND" line. A plurality of such detectors are used for a set of burners having a common fuel supply, in which case all the "OR" lines are connected to a common thyristor 32 which operates a relay 33 which is energized when any flame is present, while the AND lines are connected to a common thyristor 36 which operates a relay 37 which is not energized if any flame is absent. The relays 33, 37 are incorporated in a controller 6 which opens the fuel supply prior to ignition only if both relays are not energized, i.e. flames are absent from each burner, the valves being maintained open after ignition only if both relays 33 and 37 are energized i.e. fumes are present at every burner. |
