Which of the following instruments requires careful filtration of compressed air?

The correct choice pertains to pneumatic instrumentation, which relies on compressed air as a medium for signal transmission. This type of instrumentation often operates with precise and sensitive mechanical components that can be adversely affected by contaminants present in the compressed air, such as dust, moisture, or oil.

Filtration is essential because any particles or droplets in the air can interfere with the instrument's performance, leading to inaccurate measurements or potential failure of the system. By ensuring that the compressed air is thoroughly filtered, the reliability and accuracy of pneumatic instruments can be maintained, providing consistent performance in critical applications.

While other instruments may have their own requirements for function and performance, they do not share the same direct dependence on clean and filtered compressed air as pneumatic instrumentation does. For instance, temperature transmitters and electrical control relays generally do not utilize pneumatic signals and therefore are less susceptible to issues arising from contaminated air supply.