RTD vs. Thermocouple
Published on 07 24, 2024 in Category: GENERAL
For industrial process temperature measurement, two devices take center stage: Thermocouples and RTDs (Resistive Temperature Devices). While both serve the purpose of measuring temperature, their components and use in applications can differ significantly. KECO Engineered Controls is a primary source for RTDs, thermocouples, and the temperature transmitters that are used to send their temperature signals to monitoring and control systems.
Thermocouples: A Fusion of Metals
Picture a junction where two distinct metals converge, for example Chromel and Alumel in a type K thermocouple. This is the heart of a thermocouple. When subjected to temperature fluctuations, this junction generates a voltage, a phenomenon related to temperature changes. Thermocouples are used frequently because their construction is very versatile, offering various iterations: probes, thin films, and even infrared measurement.
The Operation of RTDs
Different from thermocouples, RTDs rely on electric voltage resistance that changes according to temperature variations. These devices often encase thin wires within protective stainless steel sheaths, ensuring longevity in rigorous industrial environments.
Contrasting Performance
When compared, key performance measures are used to define the difference in the applications where thermocouples and RTDs are used. Temperature range, cost, accuracy, sensitivity, linearity, and stability provide the basis for choosing a thermocouple or an RTD for an application.
Temperature Range
Thermocouples perform exceptionally well in high-temperature environments, with some reaching extraordinary limits from -200°C (-328 F) to 2320 C (4200 F). RTDs however operate best in lower temperature environments from -196 C (-321 F) to 600°C (1112 F).
Cost and Sensitivity
While thermocouples offer lower cost solutions with their wider range, RTDs excel in sensitivity and precision where the range is smaller. Despite their higher cost, RTDs deliver finer temperature resolutions,quicker response times, and better accuracy, vital requirements for certain applications.
Accuracy and Stability
RTDs are models of temperature accuracy and repeatability, possessing margins as narrow as 0.1°C. In contrast, while thermocouples can measure much higher temperatures and are less affected by high vibration they provide less accuracy and stability, succumbing to drift over time.
The Searching for the Right Fit
Choosing between the temperature sensing options demands careful consideration. Thermocouples, with their cost-effectiveness, are more favorable in high temperature and high vibration applications. On the other hand, RTDs offer better accuracy, repeatability and stability, but at a higher price. For increased protection RTDs and thermocouples are usually inserted into a strong metal thermowell to protect the sensors from the combination of pressure, temperature, and corrosive or erosive process fluids.
Making the Right Choice
As you search for the ideal temperature sensor, weigh the unique requirements of your application. Whether it's the precision of an RTD or the wide temperature range of a thermocouple, gather enough detail for an informed decision based on your specific needs.
For further guidance on selecting the best temperature measurement system for your operation, please reach out to KECO Engineered Controls. We offer RTDs, thermocouples, thermowells, and transmitters designed to meet your temperature measurement needs. Call today at 732.901.5900, email to sales@kecocontrols.com, or complete our contact form.
