Resistance Thermometer - Applications

Applications

Sensor assemblies can be categorized into two groups by how they are installed or interface with the process: immersion or surface mounted.

• Immersion sensors take the form of an SS tube and some type of process connection fitting. They are installed into the process with sufficient immersion length to ensure good contact with the process medium and reduce external influences. A variation of this style includes a separate thermowell that provides additional protection for the sensor. These styles are used to measure fluid or gas temperatures in pipes and tanks. Most sensors have the sensing element located at the tip of the stainless steel tube. An averaging style RTD however, can measure an average temperature of air in a large duct. This style of immersion RTD has the sensing element distributed along the entire probe length and provides an average temperature. Lengths range from 3 to 60 feet.

• Surface mounted sensors are used when immersion into a process fluid is not possible due to configuration of the piping or tank, or the fluid properties may not allow an immersion style sensor. Configurations range from tiny cylinders to large blocks which are mounted by clamps, adhesives, or bolted into place. Most require the addition of insulation to isolate them from cooling or heating effects of the ambient conditions to insure accuracy.

Other applications may require special water proofing or pressure seals. A heavy-duty underwater temperature sensor is designed for complete submersion under rivers, cooling ponds, or sewers. Steam autoclaves require a sensor that is sealed from intrusion by steam during the vacuum cycle process.

Immersion sensors generally have the best measurement accuracy because they are in direct contact with the process fluid. Surface mounted sensors are measuring the pipe surface as a close approximation of the internal process fluid.