How do you check the flame sensor current when a separate flame sensor is used?

To check the flame sensor current when a separate flame sensor is used, it is essential to measure the actual current flowing through the sensor to ensure it is functioning correctly. Installing a DC millivolt meter in series with the flame sensor wire allows for an accurate measurement of the voltage generated by the flame sensor, which is directly related to the current flowing through it. This method provides insight into the performance of the flame sensing system by quantifying the millivolt output that corresponds to the presence or absence of a flame.

This approach is critical because flame sensors typically produce a small voltage output in the range of millivolts when they detect a flame. By placing the millivolt meter in series, the technician can effectively measure the output under real operating conditions, confirming the sensor's functionality and allowing for troubleshooting if the readings fall outside the expected range.

Using a standard voltmeter across the sensor does not give the technician an accurate current measurement, as it only provides information about the voltage, not the current that is critical for evaluating the sensor's performance. Similarly, a clamp meter capturing the sensor wire would provide current measurement as well, but it might not be suitable due to the low millivolt ranges typical of flame sensors, possibly leading to inaccurate readings