ELECTRIC IGNITION SYSTEM USING A PTC IGNITER AS A SENSING MEANS

1293202 Controlling burners; igniting burners ROBERTSHAW CONTROLS CO 19 March 1970 [20 March 1969] 13288/70 Headings F4F and F4T An electric ignition and control system for a fuel burner comprises an electric igniter 10 with a positive temperature coefficient of resistance in series with a relay 12, ballast resistor 14 and switch 16, and an electrically operated fuel valve 20, switch 22, and relay contacts 24 in parallel with the igniter 10. When switch 16 is open, contacts 24 are open, but when switches 16 and 22 are closed then relay 12 is energized and contacts 24 closed, current flowing through and heating igniter 10 thereby increasing its resistance and thus the voltage applied across the valve 20. Only after the igniter has reached a sufficient temperature to ignite the fuel is the voltage applied to the valve sufficient to turn it on. The relay 12 may also be current-sensitive. In a modification (Fig. 2, not shown) a hot-wire ballast relay (30) serves as a current-sensing means, and a P.T.C. thermistor is (32) used as a flame sensor since when connected in series with the igniter it will reduce the voltage drop across the igniter to a value insufficient to maintain the valve open unless the igniter is heated by a burner flame.