Should you replace thermocouples with resistance temperature detectors?

Resistance temperature detectors (RTDs) — sensors used to measure temperature by associating the resistance of the RTD element with temperature — are slowly replacing thermocouples in many industrial applications below 600 degrees C.

Why? RTDs have many advantages, including high accuracy, low drift and a wide operating range. Plus, they are suitable for precision applications. But there are also some disadvantages to using the technology — they are more expensive and less rugged than thermocouples, a current source is required, and vibration requires special construction. 

Weigh the pros and cons for your particular application. However, should you decide that RTDs are the technology for you, there are several options. 

Industrial platinum resistance thermometers: These are designed to withstand industrial environments. Sheath material is typically 316 stainless steel, with or without a thermowell. Higher temperature applications may require Inconel.

Standard platinum resistance thermometers (SPRT): These are generally used in laboratories and are very expensive because they use larger diameter reference grade platinum wire. They are usually supplied with a quartz or Inconel tube, depending on the temperature range.

Secondary standard platinum resistance thermometers: These are constructed like the SPRT, but the materials are more cost effective.

Wondering how RTDs can be applied to your application? Thermo-Kinetics, a Mississauga, Ont.-based company that specializes in solutions for process control and measurement challenges, manufactures RTD probes and assemblies, as well as averaging RTDs. Contact the company for element specifications and product details, and find out whether replacing thermocouples with resistance temperature detectors is the right choice for you. 

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