TM111

The working principle of Resistance Temperature Detector (RTD) is temperature measurement based on the property that the resistance of metallic conductors varies with temperature. Core principle: when temperature changes, the lattice‑vibration amplitude of metallic conductors such as platinum and copper alters, creating different degrees of obstruction to electron movement and resulting in corresponding resistance changes. Taking the Pt100 platinum RTD as an example, its nominal resistance is 100 Ω at 0 °C; resistance increases by approximately 0.385 Ω per 1 °C temperature rise, exhibiting highly‑linear behaviour within a certain temperature range. In practical measurement, a constant‑current source or bridge circuit converts resistance variations into electrical signals. Three‑wire / four‑wire wiring eliminates lead‑wire errors. Finally, resistance values are converted into temperature values according to international standard reference tables. Thermocouples feature simple construction and high robustness. Thermocouple sensors measure temperature based on the Seebeck effect. Two dissimilar conductors are connected to form a closed loop. A tiny voltage difference is generated in the loop when temperatures differ at the two junctions. This voltage difference is known as thermoelectric voltage or thermoelectromotive force. Its magnitude depends on the materials of the two conductors and the temperature difference between the “measuring junction” (the joint of the two conductors) and the “cold junction” (open‑circuit ends of the conductors). Therefore, thermocouples are generally used for differential‑temperature measurement. The absolute temperature at the measuring junction can be obtained if the cold‑junction temperature is known, or measured separately for compensation. Standards IEC 60584 and ASTM E230/ANSI MC96.1 list common thermocouple conductor material combinations and their corresponding thermoelectric‑voltage‑temperature characteristics.

High-end Application

The explosion‑proof thermometer iTHERM ModuLine TM111 is widely suitable for industrial applications and hazardous areas. It allows easy installation of RTD or thermocouple sensors. When combined with modular transmitters supporting all common communication protocols and Bluetooth® technology, it delivers enhanced measurement accuracy and reliability. The sensor technologies (iTHERM StrongSens and QuickSens) provide vibration resistance, fast response and hazardous‑area approvals.