What is the closed circuit output of a thermocouple?

What is the closed circuit output of a thermocouple?

• A. 30 mv
• B. 15 mv
• C. 60 mv
• D. 0 mv

Answer: (A)

A thermocouple generates a small DC voltage whenever its hot junction is hot relative to its cold junction. In many gas appliance pilot systems, that voltage is what powers and holds the valve open in a closed circuit. Under normal operating flame conditions, the nominal closed-circuit output is in the tens of millivolts, with about 30 millivolts being a common and practical value. This level is enough to energize the valve while the pilot is lit. If the flame goes out, the voltage drops toward zero. Values like 15 mV or 60 mV aren’t typical nominal outputs for this circuit, and 0 mV would indicate no flame or a fault.

A thermocouple generates a small DC voltage whenever its hot junction is hot relative to its cold junction. In many gas appliance pilot systems, that voltage is what powers and holds the valve open in a closed circuit. Under normal operating flame conditions, the nominal closed-circuit output is in the tens of millivolts, with about 30 millivolts being a common and practical value. This level is enough to energize the valve while the pilot is lit. If the flame goes out, the voltage drops toward zero. Values like 15 mV or 60 mV aren’t typical nominal outputs for this circuit, and 0 mV would indicate no flame or a fault.