What is the normal CAD cell resistance with flame present?

The correct answer indicates that the normal CAD (Cadmium) cell resistance with a flame present is typically less than 1,600 Ohms. This is due to the fact that the CAD cell is designed to detect the presence of a flame by changing its resistance based on the light emitted from the flame. When a flame is detected, the resistance drops significantly, typically below the threshold of 1,600 Ohms, allowing the control system to operate the burner effectively and maintain proper functioning.

In practice, a CAD cell is part of a safety mechanism that ensures that the heating system only operates when a flame is present. If the resistance were greater than or equal to 1,600 Ohms, it would likely indicate that there is insufficient flame detection, which could result in the burner shutting down as a safety precaution. Therefore, understanding the normal resistance range for a CAD cell helps in diagnosing issues related to flame detection and ensuring safety in heating systems.