What is Difference Between an RTD and Thermocouple?

Two important devices used to measure temperature are the thermocouple and RTD. Each of these devices operates as a temperature sensor. The key difference between a thermocouple and an RTD is the way they operate.

The former utilizes a thermoelectric effect to produce voltage resulting from temperature change. The latter utilizes electrical resistance as a measurement of temperature. At Nexthermal, we are your source for thermocouple and RTD temperature sensor devices which are ideal for various industrial applications.

Some of the key differences between an RTD and thermocouple include:


Generally, thermocouples are less expensive than RTDs by a factor of 2 to 3 when each device has the same style and temperature. The use of less expensive copper wire with RTDs makes their installation cheaper, but it does not provide sufficient savings to offset the higher price of the device itself.

Temperature Ranges

The vast majority of RTD temperature sensor devices are designed to operate at temperatures less than 400°C. On the other hand, thermocouples are designed for much higher temperatures, up to 2500°C.


RTD temperature sensor devices generally provide greater accuracy than thermocouples, specifically 0.1°C compared to 1°C for many thermocouples. There are some exceptions, however. Some thermocouple models can match the accuracy of RTDs. The various factors that can impact the accuracy of the sensor include repeatability, linearity, and stability.


Each of these types of sensors reacts quickly to temperature changes. However, thermocouples do so faster – in fact, three times faster than some RTDs. An exposed tip thermocouple is the fastest type of temperature sensor.


The readings on thermocouples tend to drift a light stability due to the chemical changes in the sensor, such as produced by oxidation. On the other hand, RTD probe readings are generally more stable and repeatable for a longer period. The linearity with little to no drift of RTDs give them more stability over the long run.


In the sensor range, the RTD has a temperature resistance relation that is almost lineal. On the other hand, a thermocouple produces an “S” type plot.

To learn about the RTD temperature sensor and thermocouple controller/sensor devices we offer at Nexthermal for various industrial applications, call us today at 269.964.0271 or reach us by email at sales@nexthermal.com.

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