What happens to the voltage output of a thermocouple as temperature varies?

The voltage output of a thermocouple changes proportionally with temperature variations due to the Seebeck effect, which is the principle underlying the operation of thermocouples. When there is a difference in temperature between the two junctions of the thermocouple, it generates a voltage that is directly related to that temperature difference.

This relationship is often characterized by a specific conversion chart or equation based on the types of metals used in the thermocouple, which enables the precise calculation of temperature based on the measured voltage. As the temperature at one of the junctions increases or decreases, the voltage output similarly increases or decreases in a predictable manner, reflecting the change in temperature.

The other options do not accurately describe the behavior of a thermocouple. For instance, if the voltage were to remain constant, it would indicate no temperature change, contradicting the fundamental operational principle of a thermocouple. Similarly, a random fluctuation in voltage would suggest inconsistent temperature readings, which is not characteristic of thermocouple operation. Lastly, a decrease over time implies a drift or decay not inherent in the direct relationship between voltage output and temperature change that thermocouples maintain.