A good thermocouple should read approximately how many millivolts on a D.C. meter?

A good thermocouple typically generates a voltage signal that is directly proportional to the temperature difference between its two junctions. For most thermocouples, especially common types like type K or type J, the output voltage is often in the range of 30 millivolts at standard temperatures.

When measuring a well-functioning thermocouple with a DC meter, a reading around 30 millivolts indicates that it is operating within the expected parameters, suggesting that the thermocouple is properly detecting temperature changes. This value allows technicians to effectively monitor and verify the operational status of the heating system they are servicing.

Understanding the specific voltage output of thermocouples is crucial for HVAC technicians, as it assists in diagnosing whether a thermocouple is functioning correctly or if it requires replacement. Therefore, the value of approximately 30 millivolts represents a standard benchmark for assessing thermocouple performance in gas heat systems.