Thermocouples produce a measurable voltage as the surrounding temperature increases or decreases, where thermistors change their resistance to electrical current as the temperature changes. Also, thermocouples and thermistors are used in different applications, depending upon the precision needed and the temperature ranges involved.
Thermocouples exploit the fact that when two dissimilar metals are joined together and in the presence of changing temperatures, a difference in the electrical potential, or voltage, between the two metals changes. This is known as the Seebeck Effect, named after its discoverer, Thomas Seebeck. Thermocouples are used in high-heat applications, typically where they are the only viable option. However, when compared to thermistors, thermocouples are not as precise or accurate and often need recalibration before and after each use.
Thermistors, on the other hand, are restricted to lower-temperature applications but have much better accuracy and reliably track changes far more precisely than the average thermocouple. Because they are small, lightweight and very accurate, thermistors are more often used in conjunction with microprocessors and data recording units. Thanks to their smaller sizes, thermistors are often arranged with redundant counterparts for data integrity. Since they produce such large, proportional changes in resistance for a given change in temperature, thermistors provide a much more accurate representation of the actual changes in temperature.