Which mechanical element is often used with filled thermal systems for measuring?

The use of Bourdon tubes in filled thermal systems is well-established in instrumentation for measuring pressure. A Bourdon tube operates on the principle of mechanical deformation; as pressure is applied to the tube, it tends to straighten out, which can be translated into a dial reading via a pointer. This makes them highly effective for measuring pressures in various applications, especially in scenarios involving filled thermal systems where changes in pressure need to be monitored accurately.

In filled thermal systems, the liquid or gas within the system expands or contracts with temperature changes, often impacting the fluid pressure. The Bourdon tube responds to these alterations in pressure, allowing for accurate temperature measurement indirectly, which is essential in many industrial processes.

Other options like thermistors, pneumatic tubes, and relay switches have specific roles: thermistors are primarily used for temperature measurement through electrical resistance changes, pneumatic tubes are used to transport materials or signals, and relay switches are employed for controlling electrical circuits. These do not fit the context of measuring pressure in filled thermal systems as closely as Bourdon tubes do.