What does the term 'thermowell' refer to?

The term 'thermowell' refers to a protective sleeve installed into a process stream. A thermowell serves as a barrier that protects the temperature sensor, such as a thermocouple or resistance temperature detector (RTD), from direct contact with the process media. This is crucial for several reasons, including protecting the sensor from harsh conditions like high pressure, corrosive liquids, or extreme temperatures that might damage the sensor or affect its performance. The design of a thermowell allows for easy removal and replacement of the temperature sensor without needing to drain the process line, ensuring that process integrity is maintained while allowing for maintenance of the measurement device.

In contrast, the other options describe different concepts: a temperature measurement device is the sensor itself rather than the protective sleeve, an electrical circuit for temperature measurement represents the system that reads and processes the signal from the sensor, and a bimetallic sensor refers to a type of temperature sensor that operates on the principle of differing expansion rates of two metals, which is not inherently related to the protective function of a thermowell.