Which device is primarily affected by the ohmmeter reading in a cad cell test?

The photocell is a device that detects the presence of light, and in the context of a cad cell test, it plays a crucial role in the operation of a heating system, especially in oil burners. The cad cell, or cadmium sulfide cell, is a type of photocell that changes its resistance based on the amount of light it receives. When testing this device with an ohmmeter, you measure its resistance, which is indicative of whether it is functioning correctly.

If the photocell is exposed to adequate light, its resistance will be low, indicating that it is operational and can allow current to pass through, thus helping in the ignition process of the burner. Conversely, if the resistance is high, it suggests that the photocell is not receiving enough light or is defective, which can prevent the burner from operating properly. This direct relationship between resistance and the photocell's ability to respond to light makes it primarily affected by the ohmmeter reading during a cad cell test.

Other devices like thermocouples, relays, and transformers do not operate based on light detection and thus are not directly linked to the ohmmeter readings in this specific test scenario. While each has its own function within HVAC systems, they do not