What do hot-wire and thermocouple movements primarily measure?

Hot-wire and thermocouple movements are primarily used to measure temperature, which is related to thermal energy in a system. Specifically, a hot-wire anemometer utilizes a thin wire heated by an electrical current, and as the airflow changes, it cools the wire down, causing a change in the amount of current that needs to be supplied to maintain that temperature. Thus, the primary measurement is the current flowing through the wire as it responds to environmental conditions.

In the case of a thermocouple, it generates a voltage that is proportional to the temperature difference between its two junctions. While the voltage can be measured, the fundamental concept here is that it is ultimately used to infer temperature changes directly.

Current becomes the relevant measurement in both cases due to the relationship between the electrical properties of the systems and the thermal effects of the environments they are measuring. Hence, the answer is grounded in the necessity to measure the current to deduce temperature readings, which is vital in various sensing applications in a Navy context.