Question 206Steam Plants - 1st Asst/Chief

The correct answer is D) sense light from the burner flame. The photoelectric cell installed as part of the combustion safety controls of an automatically fired boiler is designed to sense the presence of the burner flame. If the flame is extinguished or fails to ignite, the photoelectric cell will detect the lack of light and signal the control circuit to shut down the boiler to prevent a hazardous condition. The other answer choices are incorrect because A) closing the control circuit on flame failure is the opposite of the photoelectric cell's function, B) opening the circuit on an intense flame is not the normal operation, and C) the photoelectric cell does not directly control the modulating pressure circuit.