Control unit for detecting a flame in operation using flame monitors suitable for burners and flame monitoring system

A system for detecting a flame in operation comprising:

• at least two flame monitors, each flame monitor comprising:
• a sensor configured to detect radiation emitted by a flame in a combustion region;
• and
• an evaluation circuit operatively coupled to the sensor, the evaluation circuit being configured to analyze a signal generated by the sensor to determine whether the detected radiation corresponds to a burning flame;
• and
• a control unit operatively coupled to the at least two flame monitors, the control unit comprising:
• a logic circuit configured to receive output signals from the evaluation circuits of the at least two flame monitors, wherein at least one flame monitor of the at least two flame monitors is provided on either end of an extension of the flame of a flame field and the at least two flame monitors are connected in such a way as to form the logic circuit that processes the output signals of the at least two flame monitors via closing contacts in an OR operation or via closing contacts in an AND operation, wherein processing of the output signals of the at least two flame monitors is performed depending on which of at least two operating states of flame detection is assigned to the output signals of the flame monitors, wherein in combination with the OR operation the AND operation is arranged in a subordinate position;
• switching logic configured to selectively switch between the at least two different operating states of flame detection;
• an intelligent subsystem operatively coupled to the switching logic, the intelligent subsystem being configured to implement a logic function plan for controlling one single flame monitoring input of a burner control unit, and to increase the detection options by means of OR operation of said flame monitors a switch back from the AND operation to the OR operation is provided by the switching logic;
• and
• an output configured to generate a control signal for a fuel supply system, wherein the control signal indicates whether a flame is detected, and wherein, if the output signals from the at least two flame monitors indicate absence of a flame under the selected operating state, the control signal comprises a fuel supply switch-off signal.