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RTDs Versus Thermocouples

RTDs vs. Thermocouples — Sensor Comparison at a Glance


An RTD is a sensor whose resistance changes as its temperature changes. The resistance increases as the temperature of the sensor increases. The resistance vs temperature relationship is well known and is repeatable over time.

An RTD is a passive device. It does not produce an output on its own. External electronic devices are used to measure the resistance of the sensor by passing a small electrical current through the sensor to generate a voltage.


A thermocouple is a device consisting of two different conductors (usually metal alloys) that produce a voltage proportional to a temperature difference between either ends of the pair of conductors. In contrast to most other methods of temperature measurement, thermocouples are self-powered and require no external form of excitation.

RTDs vs. Thermocouples: Sensor Comparison at a Glance

The following chart reveals the main differences between RTDs and thermocouples.

Feature RTD Thermocouple
Accuracy More Accurate Less Accurate
Temperature Range -200 to 600°C -200 - 2000°C
Initial Cost More Expensive Less Expensive
Sensitivity Many Available Lengths Point Sensing Only
Response Time 1 to 7 Seconds Less Than One Second
Robustness Good  Excellent
Reference Junction Not Required Required
Long Term Stability Excellent Good, (subject to drift)
Output Highly Linear Resistance .4 Ohm/ohm/°C Voltage, 10-40 Microvolts/°C Approximately Linear
EMF Resistance Less Susceptible More Susceptible