What is the main difference between an RTD and a thermocouple?
Resistance temperature equipment changes its resistance when heating and cooling, so by applying current to it, it can measure the temperature very accurately, without being affected by the circuit and the rest of the measurement equipment. RTD is more accurate than thermocouple. However, the temperature of the RTD is limited to between 500 and 932 degrees Fahrenheit. Generally speaking, RTDs are more expensive than thermocouples, but the actual instruments, wiring and installation are usually less, so it can make up for some cost differences.
A thermocouple is a device with a dissimilar metal junction that actually generates a thermal current that can be calibrated and measured. The accuracy of the thermocouple will be affected by the connection of the copper lead to the device, so this cold junction must be compensated. Thermocouples can be made from a combination of several different metals, so temperatures range from -453 to 4,000 degrees Fahrenheit. This thermocouple can obviously be used in applications where RTD cannot be achieved, but the accuracy is not high. Its price is lower, but the instrument, wiring and installation costs are higher.