What Is a Resistance Thermometer?
Resistance thermometers, also called resistance temperature detectors (RTDs), are temperature sensors made of materials with known resistance-dependent temperature changes. Because they are made from platinum almost without exception, they are often referred to as platinum resistance thermometers. In many industrial applications below 600 ° C, they are slowly replacing thermocouples.
- High precision
- Low drift
- Wide application range
- Suitable for high precision applications
- RTDs are rarely used in industrial applications in environments over 660 ° C. At very low temperatures, such as below -270 ° C (or 3K), the resistance of the resistor is zero and therefore impractical.
- Compared to thermistors, platinum RTDs are less sensitive and have a slower response time. [1]
- Common RTD sensing elements made of platinum, copper or nickel have a repeatable resistance-temperature relationship (R vs T) and operating temperature range. The relationship between R and T is defined as the amount of change in resistance of the sensor with each degree of temperature change. The relative change in resistance (temperature coefficient of resistance) varies little within the useful range of the sensor.
- In order to characterize the R and T relationship of any RTD in the temperature range representing the intended use range, it must be calibrated at temperatures outside 0 ° C and 100 ° C. Although RTDs are considered linear in actual use, they must be proven to be accurate for actual use temperatures. The two commonly used calibration methods are the fixed-point method and the comparison method.