Which component is a closed tube designed to protect temperature instruments from process conditions and allows maintenance without draining the process fluid?

• A. Intrinsically Safe
• B. O2 Sensor
• C. Thermowell
• D. Split Range Control

Answer: (C)

A thermowell is a closed tube placed into a process so temperature sensing devices stay protected while the process remains in operation. The temperature sensor (like an RTD or thermocouple) sits inside the tube, while the process fluid only contacts the outer wall. This shields the sensor from high pressures, flow-induced wear, corrosion, and other harsh conditions. Because the sensor is housed inside the tube, maintenance becomes much easier: you can withdraw or replace the sensor without draining the process fluid or shutting down the line, and you can replace the thermowell itself if needed. This arrangement is common in industrial settings where continuous operation is essential and sensors must be protected yet easily accessible.

Other options aren’t about a protective component for sensors. Intrinsically Safe describes electrical safety limits in hazardous areas, not a physical tube. An oxygen sensor is a measuring device for oxygen levels, not a protective conduit. Split range control is a control strategy, not a hardware element for protecting temperature instruments.