Abstract: A fail-safe, self-checking flame monitoring circuit is provided without the use of a mechanical shutter in which a photodetector provides a signal corresponding to flame intensity (including flicker), an amplifier amplifies the signal, the amplification is controlled by a negative feedback circuit in relation to the peak amplitude of the signal (including flicker) such that all frequencies down to DC are amplified equally, and all amplified signals are passed, without threshold, downstream for further processing.

Abstract: Apparatus for monitoring flames is provided with means for sampling both the value of a flame and the period of time during which a flame remains above a given intensity level during start-up. Flame-off delay means is also provided in combination with means for delaying a flame-on indication, means for segregating the respective operations thereof, and means for maintaining the durations of the flame-on and flame-off delays in fixed proportional relationship.

Abstract: A fail-safe system for monitoring a condition and activating controls in response either to the non-existence of that condition or the failure of any component in the system, in which a preliminary fail-safe oscillation train derived from sensing the condition is converted into a steady state indication of that condition, and a secondary fail-safe oscillation train is generated in a fail-safe way from said steady state indication for further transmission downstream for control purposes. In the context of flame monitoring, means associated with the preliminary oscillation train are provided for discriminating between separate flames and for time delay purposes.

Abstract: A burner control system has a field device and control logic for providing a control signal to change the state of the field device. A comparator that compares signals from field and the control logic comprises translation circuitry that is arranged to produce an output pulse train signal in response to a corresponding input pulse train signal, and power supply circuitry that has two logic inputs. The power supply circuitry supplies power to the translation circuitry only in response to a proper comparison between a field signal applied to one logic input and the control signal applied to the other logic input.

Abstract: A burner control system in which signals indicating the condition at various locations within the system are applied to a control circuit in the form of pulse trains, causing a continuous alternation of state of solid state switching elements therein. The system actuates a switch to open a fuel valve only when the level of the control circuit output signal is alternating, indicating that the said switching elements are operative. A comparison circuit compares the control circuit output signal with a signal denoting the condition of the fuel valve, to ensure proper operation of the fuel valve switch.