G2 Gas Fitter Practice Exam

In a closed-circuit test, what should the reading of a thermocouple flame sensor be?

1. 0-5 mV

2. 10-20 mV

3. 20-30 mV

4. 30-40 mV

The correct answer is: 10-20 mV

In a closed-circuit test, the reading of a thermocouple flame sensor is typically expected to fall within the range of 10-20 mV. This range indicates that the sensor is functioning properly and is able to detect the heat from the flame effectively. Thermocouples operate on the principle that a voltage is generated at the junction of two different metals, which is influenced by temperature. In the presence of a flame, the thermocouple generates a voltage that is proportional to the flame's temperature. A reading within the specified range shows that the sensor is adequately responding to the heat, ensuring that the safety mechanisms reliant on this sensor can operate correctly. If the reading is out of this range, it might indicate a malfunction of the thermocouple, which could lead to safety risks in a gas system by failing to detect the presence of flame.