What is the function of the cad cell in an oil burner?

• A. Detect light
• B. Detect heat
• C. Detect pressure
• D. Detect sound

Answer: (A)

The cad cell is a flame sensor that detects light. It’s a photoelectric device (a cadmium sulfide cell) that responds to the light produced by the burner’s flame. When ignition occurs and the flame is present, the light reaching the cad cell generates a signal the control uses to confirm flame safety. If the flame goes out or fails to ignite, the light level drops, the signal decreases, and the burner is shut off to prevent unburned fuel from accumulating. It isn’t measuring heat, pressure, or sound, so those senses aren’t what the cad cell provides.