Overview
Resistance thermometers (RTDs) and thermocouples are common temperature sensors. Each has advantages and disadvantages when measuring temperature. The following explains their differences in detail.
Definition
Resistance thermometer (RTD): An RTD measures temperature by using the property that a material's electrical resistance changes with temperature. It typically consists of a sensing element, insulation, and lead wires.
Thermocouple: A thermocouple measures temperature by the voltage generated at the junction of two different metal conductors. It is composed of two different metal conductors, insulation, and a connection head or terminal box.
Working Principle
RTD working principle: The RTD principle is based on the change of a material's electrical resistance with temperature. When the temperature of the measured object changes, the resistance of the RTD changes accordingly. Measuring that resistance change yields the temperature of the object.
Thermocouple working principle: The thermocouple principle is based on the thermoelectric voltage generated at the junction of two different metals. When the junctions of the two metals are at different temperatures, a small electromotive force is generated at the junction. Measuring that voltage allows determination of the temperature.
Comparison
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Measurement range
RTDs are generally suitable for measurement in the range of about -40°C to +150°C, which is relatively narrow. Thermocouples are suitable for a wider temperature range, typically from about -200°C to +250°C.
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Accuracy and resolution
The article states that RTDs, due to their simple structure, have relatively lower accuracy and resolution, typically around ±0.5°C, while thermocouples, due to their more complex structure, have relatively higher accuracy and resolution, potentially around ±0.1°C.
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Response time
RTDs are described as having relatively fast response times, typically within a few seconds for the temperature change to be reflected in resistance. Thermocouples are described as having relatively slower response times, requiring tens of seconds for the temperature change to be reflected in the measured voltage difference.
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Stability
RTDs are described as relatively stable and less susceptible to environmental influences. Thermocouples are described as less stable and more susceptible to environmental effects such as oxidation and corrosion.
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Ease of use
RTDs are described as simpler to use and do not require additional adjustment equipment for measurement. Thermocouples typically need to be used with display instruments or recorders, making their use relatively more involved.
Application Scenarios
RTDs are suitable for scenarios that require higher-precision temperature measurement, such as industrial production and laboratory testing.
