When the burner is off, what is the condition of the cad cell in the dark combustion chamber?

In a dark combustion chamber, when the burner is off, the cadmium cell, also known as a cad cell, is designed to detect the presence of a flame. In the absence of light, the cad cell does not conduct electricity; therefore, it creates a condition of high resistance. This high resistance indicates to the burner control system that there is no flame, which allows the system to prevent any unwanted fuel flow and ensures safety.

The key functionality of the cad cell relies on its ability to sense light levels: when a flame is present, the cad cell conducts electricity due to the light emitted. However, when the burner is off and the combustion chamber is dark, the cad cell does not allow electricity to flow.

Understanding this mechanism is critical for operating gas-fired combustion systems safely and effectively, as it prevents potentially dangerous conditions from arising when there is no flame present.