What is the difference between and a resistance temperature detector (RTD)  and a thermocouple?  Both RTDs and thermocouples are sensors used to measure heat in scales such as Fahrenheit and Kelvin. Such devices are used in a broad range of applications and settings, often presenting people with the dilemma of choosing to use either RTDs or thermocouples. Each kind of temperature sensor has its own advantages and disadvantages that make it suitable for certain conditions and circumstances.

Resistance Thermometer Detectors

The electrical resistance of metals rises as heat increases and the metals become hotter, while their electrical resistance falls as heat decreases and the metals become colder. RTDs are temperature sensors that use the changes in the electrical resistance of metals to measure the changes in the local temperature. For the readings to be interpretable, the metals used in RTDs must have electrical resistances known to people and recorded for convenient reference. As a result, copper, nickel, and platinum are all popular metals used in the construction of RTDs.


Thermocouples are temperature sensors that use two different metals in the sensor to produce a voltage that can be read to determine the local temperature. Different combinations of metals can be used in building the thermocouples to provide different calibrations with different temperature ranges and sensor characteristics.