TC temperature measurement

Two of the most common sensor technologies in temperature measurement devices are resistance temperature detectors (RTDs) and thermocouples (TCs). The technology behind them is different, and each has its own benefits that drive the choice. In a thermocouple sensor, two different metals are joined together at one end. At this junction, changes in the temperature induce a voltage / electromotive force that is measured. TCs are not measuring an absolute temperature, but the temperature difference between the measuring point (T₁) and a reference point (T_ref).

• Wide temperature range from -270°C (454°F) to +1820°C (3308°F)
• Fast response time, suitable for dynamic temperature measurements
• High vibration resistance
• Lower cost compared to RTDs
• Rugged and durable, especially useful in harsh environments

Thermocouple types
The Seebeck effect, which is made use of for TCs, states that a voltage is generated when two dissimilar metals are joined together. The voltage generated can then be measured and converted into temperature readings, using a calibration curve or table. There are different types of thermocouples, based on different wire pairs and measuring ranges. Each type of TC has a unique relationship between the voltage generated and the temperature. The type can be identified by an assigned letter, e.g. TC type K, type J or type T.

Endress+Hauser has developed a unique sensor called iTHERM ProfileSens for high temperatures, pressures and aggressive media, consisting of a robust double metal sheathed MI cable and temperature profiling with up to four TCs in one cable.