Flame rectification sensor employing pulsed excitation

In flame sensing apparatus of the type including a signal generator for impressing an alternating electrical signal between reference and injector electrodes adapted to cause electric current to flow through flame in a flame region, whereby the signal is rectified when a flame is present, the rectified signal being conditioned by a filter including a capacitor having a bleed resistor thereacross, the voltage on the capacitor being used to control amplifier apparatus whose output is indicative of presence or absence of a flame, improved means for detecting failure of critical components, including the capacitor, bleed resistor and amplifier device, in the filter and amplifier apparatus, comprising:

• signal generator means for supplying to the injector electrode a pulse of alternating voltage;
• and
• logic means connected to receive the amplifier apparatus output, and operable to indicate failure of an electrical component in the filter or amplifier apparatus if the amplifier apparatus output indicates presence of a flame at any time except during the time a pulse of alternating voltage is being supplied by said signal generator means.

In flame detection apparatus of the type including a generator for supplying an alternating voltage signal to first and second electrodes adapted to produce substantially unidirectional electric current flow therebetween through an ionization region associated with a flame, and a detector for producing a flame indicating output in response to presence of substantially unidirectional electric current flow between the first and second electrodes, the improvement which comprises:

• a generator adapted to produce an alternating voltage in packets having a predetermined envelope, the packets being produced at a predetermined repetition rate;
• a filter for receiving the voltage between the first and second electrodes, said filter being formed of electrical components which, if functioning properly, produce a biased voltage signal corresponding to the envelope of the alternating voltage produced by said generator;
• an amplifier responsive to the biased voltage signal produced by said filter to produce an output uniquely corresponding to the envelope of the alternating voltage produced by said generator only if the biased voltage signal corresponds to the envelope of the alternating voltage.