Accurate temperature measurement is critical across industries, and thermocouples remain the most widely used sensors for this purpose. Their accuracy depends not just on their inherent design, but on how they are selected, manufactured, installed, and maintained. Thermocouples come in two tolerance classes—Standard Limits of Error and Special Limits of Error—with the latter offering tighter accuracy for applications where precision is essential. ASTM E230 is the governing standard in the United States, and examples show how even small differences in tolerance can translate into several degrees of accuracy at high operating temperatures.
Different thermocouple types (K, J, T, E, N, S, R, B, and C) serve different needs. Base metal types like K, J, T, and E are common for general applications, while noble and exotic metal types such as S, R, B, and C are used for very high-temperature or specialized environments. Each has its own strengths, weaknesses, and atmospheric requirements, making proper selection a critical first step toward reliable measurement.
Beyond selection, accuracy is shaped by immersion depth, response time, cold junction compensation, and protection against interference or “noise.” Errors can also arise from poor manufacturing, material degradation, oxidation, or contamination. Best practices include using quality materials, ensuring correct installation, shielding against electrical interference, and performing regular calibration. Importantly, calibration does not “fix” a sensor but reveals its error, allowing process instruments to adjust accordingly.
In short, precision temperature measurement is achievable with the right thermocouple, properly specified tolerances, careful installation, and ongoing calibration. By following these principles, companies can ensure repeatability, stability, and credibility in their processes—turning what may seem like a simple sensor into a critical component of process accuracy and reliability.
Duro-Sense Corporation
Address: 869 Sandhill Avenue Carson, California 90746
Phone: (310) 533-6877
Fax: (310) 533-0330
E-mail: sales@duro-sense.com
