GB1387372A - Flame detecting apparatus - Google Patents

Abstract

1387372 Flame detectors HITACHI Ltd 5 Jan 1973 [7 Jan 1972 5 April 1972 14 April 1972 28 April 1972] 789/73 Heading F4T A flame detector comprises a flame rod 3, Fig. 1, for location in a burner flame, an electr cally powered light emitting device 5 one side of which is connected to the flame rod, means for electrically connecting the other side of the device 5 to the burner 1 or to a further flame rod, a capacitor 15 connected across the device 5, and a photo-electric converter 7 to convert the radiation output of the device 5 into an electric signal to indicate the presence or absence of the flame. Capacitor 15 prevents incorrect activation of device 5 due to capacitance between ground and the lead to flame rod 3, and also prevents incorrect operation in the event of low insulation between the burner 1 and flame rod 3 in cases where the device is operable by D.C., the rectifying action of flame rod 3 and the flame 2 charging capacitor 15 until it reaches the starting voltage of device 5. In such latter cases, device 5 may give an intermittent output in the presence of a steady flame, a capacitor 16 then being provided in a control circuit to yield a continuous output. The light output of device 5 is detected by a photo-cell 7, formed with device 5 in a monolithic composite element, causing energization of a relay 9. On starting the burner a timer 13 closes a contact a supplying a spark igniter 10, 11 and a contact b supplying a fuel gas solenoid valve 14. If ignition does not occur before the timer times out ignition and fuel flow ceases. If ignition does occur, relay 9 closes contact c to continue energizing valve 14 after the timer opens contacts a, b. Relay 9 may also be used to operate an alarm device and a display device. If the device 5 is a discharge tube one electrode thereof may be grounded, to prevent the stray capacitance between ground and the device electrodes yielding small discharges in the absence of flame giving rise to incorrect operation, the A.C. power supply then being a transformer 17, Fig. 8. In such cases full wave rectification may be achieved using two flame rods connected to respective ends of the secondary of transformer 17, device 5 being connected to an intermediate top of said secondary. In cases where device 5 gives an intermittent output a series resistor 19 may be included to increase the periods of light output by increasing the discharge time of capacitor 15 through device 5.