The Differences Between RDT and Thermocouple Sensors

Whether applied in aircraft or employed for industrial applications, temperature management systems and the components that comprise them are integral for many regulatory functions. Often found in the form of a resistance temperature detector (RTD) or thermocouple (TC), both temperature sensor types are broadly versatile, but come with their own set of advantages and disadvantages when implemented within various applications. To get a better understanding on how thermocouples and resistance temperature sensors work based on industry demand, we will go over their common functions and differences that set them apart.

Fluctuating in resistance when exposed to increasing or decreasing temperatures, resistance temperature detectors are known for their common presence within industrial settings. Commonly manufactured as a length of wire that is wrapped in a ceramic or glass core, RTDs are capable of higher temperature accuracy and reliability, but are best suited for lower temperature settings. As the wiring of RTDs are fragile, often made from a single pure metal such as nickel or copper, they function best at 600 degrees Celsius or below. For improved durability, stability, and accuracy, platinum can also be substituted as a reinforced option due to its support against strain and resistance against vibrations.

Unlike an RTD, a thermocouple can be made from a myriad of metals capable of deciphering up to 1,370 degrees Celsius or more depending on the materials being used to construct each sensor. Having the ability to be calibrated to suit a broad temperature spectrum, thermocouples are frequently constructed out of Nickel-Chromium and Nickel-Alumel alloys, costing up to two times less than a standard RTD. Easy to manufacture and lower in cost when compared to RTDs, the easy modification and assembly of thermocouples allows the potential for each component to compete with its resistance temperature competitors.

Though RTDs have an advantage against thermocouples for their high accuracy, low drift, and precision of temperature reading when applied, they can rarely be used to decipher readings above 600 degrees Celsius. As the wiring making up an RTD is prone to contamination by the core encasing its thermometer when exceeding 600 degrees Celsius, if it is tarnished, it will no longer be useful. When additional range is needed to support an excessive amount of heat, thermocouples are often the best alternative for stress-induced operations. Otherwise, while thermocouples are proficient at sustaining their role in many functions while being exposed to tremendous fluctuations in temperature, they are not as accurate as compared to RTDs. Capable of being used anywhere from gas turbines to diesel engines, homes, offices, thermostats, and more, the wrong implementation of a thermocouple will potentially provide inaccurate readings, rendering the component unusable for such an application.