Patent GB-1276672-A (GB)
Title: Flame detector
Inventor: SELLORS JOHN JR
IPC: F23N5/20
Filed: 1969-06-02
Abstract: 1276672 Burner control devices PYRONICS Inc 2 June 1969 [3 June 1968] 27712/69 Heading F4T In a flame detector for detecting whether a flame is emitted from an electrically conductive burner member B, at least one electrically conductive flame rod FR1, FR2, FR3 is positioned so as to be within a respective flame emitted from the burner member B, circuit means including an electronic switching element (e.g. a diode 50) is connected in a series path with the respective burner member B and a respective flame rod across an A.C. voltage source V, whereby when a flame is emitted from the burner member a flame rectified current flows through the series circuit and an energizable load L such as a gas safety shut-off valve, alarm or timer indicates if the flame is present. As shown in Fig. 1, there may be a plurality of flame rods FR1, FR2, FR3 such that each is positioned so as to be within a flame emitted from a respective one of a plurality of burner members B1, B2, B3 and burner circuits 1, 2 and 3 connect the flame rods FR1, FR2, FR3 respectively to a power supply and detector circuit PS/DC shown in greater detail in Fig. 2. When power is supplied to the circuit, a relay CR1 becomes energized through normally closed contacts CR2-1. This causes contacts CR1-1 to become closed to provide a holding circuit. An A.C. voltage of approximately 25 volts is applied between the burner body B and flame rod electrodes 10. So long as a flame is emitted from each of the burners B1, B2, B3 a relay coil CR2-C is energized to close contacts CR2-2 and energize load L. As shown in the circuit diagram in Fig. 2 identical flame detector circuits DC-1 and DC-2 each incorporate a two-stage detector circuit including PNP transistors 30 and 32 having their emitters connected together and to the common line CL. A filter capacitor 34 and a resistor 36 are connected in series with resistors 38 and 40 to burner circuit 1 and thence to flame rod FR1. A neon lamp 42 is connected to the junction of resistors 38 and 40 and thence to a tapping X on the transformer T. The diodes 50 of each detector circuit DC-1, DC-2 are connected together at Y to define an AND circuit. The common output circuit includes a gating device, such as a PNP transistor 60 which, when a flame is emitted from the burner B1, is forwardly biased and energizes the relay CR2 to control the load L as described above. Should flame failure occur at burner B1 the transistor 30 in detector circuit DC-1 and the transistor 60 will each become forwardly biased causing the relay CR2 to become de-energized and neon lamp 46 in the first detector circuit will be illuminated. If a second burner has a subsequent flame failure, the voltage available will be insufficient to light the neon lamp in the second detector circuit. Neon lamp 46 in each detector circuit serves as a voltage protective means to prevent damage to the components in the associated detector circuit. In an alternative embodiment (Fig. 3, not shown) a line delay circuit (TD) is provided together with logic circuitry coupled to the detector circuits DC-1, DC-2 and flame relay coil (CR4-C).