GB1509705A - Monitoring gas fuel burners - Google Patents

Abstract

1509705 Burner controls PACTROL CONTROLS Ltd 22 May 1975 [22 May 1974] 22852/74 Heading F4T A circuit for monitoring the presence of a flame of a gas burner and for controlling a fuel line of the burner in dependence upon the presence of the flame comprises a probe 16 connectible to an A.C. source and locatable in a combustion area of the flame, so that an A.C. signal is applied to the probe to be rectified by ionization when the flame is present, means being coupled to the probe and triggerable by the A.C. signal to convert the rectified signal into a pulsed signal, and switch means switchable by the pulsed signal from a first to a second switched state for opening a valve in the fuel line to the burner. An A.C. signal is applied from input 12 to flame probe 16 by way of a capacitor 18 and resistor 20, and when a flame is present the signal is rectified and during the negative half-cycle the signal is smoothed by a resistor 22 and a capacitor 24, whilst a transistor TR3 is driven by resistors 20, 42, and capacitor 40, by an A.C. signal applied across inputs 12, 14, thus removing the rectified signal applied to the base of transistor TR1 and applying a pulsed D.C. signal to transistor TR1. This smoothed signal is applied to the base of transistor TR1 via resistors 28, 30, and thence to line 26 via a Darlington circuit TR2, the collectors of transistors TR1, TR2, being connected to terminal 12 via resistor 32, and diode 34, and to line 26 via a capacitor 36 and either a solenoid 38 of a relay (not shown) to control the fuel valve or a parallel diode 44. The circuit of Fig. 1 may be modified to include an additional capacitor 45, Fig. 2. A timing circuit (50) Fig. 3 (not shown), can be used with the flame sensing circuit of Figs. 1 or 2.