RTD temperature measurement

What are RTDs?

Resistance temperature detector types
An RTD sensor is typically a length of wire made from a pure metal such as platinum, nickel, or copper. It is available either as a thin film sensor, where the wire is placed in a ceramic body, or as a wire wound in a helix construction around a glass or ceramic bobbin. The most commonly used RTDs are platinum Pt100 sensors (industry standard). The 100 in Pt100 represents the nominal resistance of 100 ohms at 0°C (32°F).

The Pt100 sensor is also known as a PTC, which stands for "positive temperature coefficient", meaning that the resistance increases as the temperature rises. A Pt100 RTD is suitable for the measurement of temperatures between -200°C (300°F) and +850°C (1562°F), depending on the sensor and the design. It is important to note that RTD sensors do not follow an ideal linear temperature-resistance curve and, unfortunately, the RTD becomes less linear as the temperature rises. The use of temperature transmitters can compensate these non-linearities. Endress+Hauser developed innovative, patented sensor technologies such as the iTHERM StrongSens with highest vibration resistance, the fast-responding sensor iTHERM QuickSens and the iTHERM TrustSens with self-calibration function. Endress+Hauser RTD instruments meet the IEC 60751 accuracy class A as standard.

The right sensor element for your application
Several factors influence the choice between TC and RTD thermometers, all of which depend on the specific application requirements.

• Accuracy: RTDs are generally more accurate than TCs, especially in lower temperature ranges

• Temperature range: TCs are suitable for higher temperature measurements, while RTDs are usually used for lower temperature measurements

• Response time: TCs are normally faster responding than RTD thermometers

• Durability: TCs can withstand harsher environments (pressure, vibration, corrosive environment etc.) than RTDs

• Cost: In general, TCs are less expensive than RTD temperature sensors

• Reliability: TCs are more susceptible to electromagnetic interference than RTDs

• Material choice: Compared to RTD temperature sensors, TCs only offer a limited number of options for the specific temperature ranges