In what situation will a thermocouple NOT produce a warning signal?

A thermocouple operates on the principle of detecting temperature differences between its two junctions—the hot junction and the cold junction. The generated voltage signal, which can indicate temperature variations, arises from the temperature gradient between these two points.

When both junctions heat at the same rate, there is effectively no temperature difference for the thermocouple to detect. Since the output voltage from the thermocouple is proportional to the temperature differential, if both junctions are at the same temperature, the voltage signal will drop to zero, meaning no warning signal will be produced. This unique situation is crucial because it highlights how thermocouples rely on differential temperatures to function correctly.

In contrast, if the thermocouple is fully submerged in water, it may produce a signal reflective of the water's temperature. When the system is powered off, while it will not provide any readings, it may still have a physical temperature difference if there are residual conditions. Exposure to cold temperatures can still produce a voltage signal as long as there is a temperature differential with respect to the reference junction. Hence, only in the scenario where both junctions experience identical temperatures does the thermocouple fail to generate a signal.