Resistance thermometers — also called resistance temperature detectors (RTDs) — are sophisticated temperature sensors that function based on the principle that a material’s electrical resistance changes as temperature does.
Resistance temperature detectors contain a resistor that changes resistance value as its temperature shifts. They are suitable for the measurement of temperatures between -200 °C and approximately 600 °C. (At temperatures above 660 °C, it becomes difficult to prevent platinum from becoming contaminated by impurities from the metal sheath of the thermometer.)
Many RTD elements consist of a length of fine wire wrapped around a ceramic or glass core; the wire is constructed of a pure material, such as platinum, nickel, or copper.
The relationship between a thermometer’s resistance and its surrounding temperature is easily predictable, as these instruments are built for optimal accuracy, repeatability, and stability. These versatile thermometers are typically used in laboratory and industrial processes but are valuable in other applications as well, such as the food, beverage, and dairy industries.
Temperature Detectors: Standards & Benefits
To fully grasp how resistance temperature detectors function, it’s crucial to have an understanding of their key characteristics, which include temperature coefficient of resistance, nominal resistance at 0 °C and tolerance class. The temperature coefficient of resistance determines the relationship between the resistance and the temperature:
- The most common industry standard is the platinum 3850 ppm/K, which means the resistance of the sensor will increase 0.385 ohms per 1 ° increase in temperature.
- The nominal resistance of the sensor, meanwhile, is the resistance the sensor will have at 0 °C.
- The most common value is the platinum 100 ohms (pt100).
- Finally, the tolerance class determines the accuracy of the sensor, usually specified at 0 °C. Various organizations have set different industry standards for accuracy; ASTM and the European DIN standards are some of the most well-known
Resistance temperature detectors offer many unique benefits. In addition to providing a high level of accuracy, repeatability, and stability, they also offer low drift, a wide operating range, robust signals, and easy calibration. RTDs are particularly well-suited to precision applications.
Using Resistance Temperature Detectors in the Food & Beverage Industry
Resistance temperature detectors are commonly used in the food, beverage, and dairy industries.
Most foods and beverages are processed for packaging or storage, and that requires the use of precise temperature measurement to ensure quality control and safety. And since this sector is highly regulated, products must be able to adhere to strict health, sanitation, and safety guidelines during production, transportation, and storage.
Food manufacturing equipment, ovens, cooking plates, and fermentation chambers, as well as refrigerators, deep freezers, freezers, and coolers all require precise temperature instrumentation. Bakery, milk, confectionery, and pastry packaging processes also make frequent use of RTDs.
To meet the needs of these diverse applications, there are a variety of sensor sizes and clamp, gasket, bevel-seat, and adaptor fittings available. Quick-response resistance temperature detectors are also offered, and transmitters can be built into assemblies as needed. Penetration-style resistance temperature detectors and thermocouples are commonly utilized for fresh and frozen meat, fish, poultry, dough, and other food products.
Endress+Hauser is proud to manufacture industry-leading high-temperature thermometers suitable for a wide range of applications and industries. To learn more about our selection or RTDs or discuss how we can help with your particular needs, contact the team today.