Thermocouple and RTD difference between the two devices and applications

Many people often ask the difference between the thermocouple and RTD, and the application of these two devices. So this is you need to know: thermocouple made of two different metals, two kinds of metal together. “ Thermal contact & throughout; Is under way, & other; Cold junction & throughout; In the controller. In theory, at each junction produce EMF ( Electromotive force) , namely the millivolt current, its associated with the temperature of every place. In order to measure a single temperature, one of the knot, Usually cold junction) In a known reference temperature, and the other a knot ( Hot junction) In the process to be detected. By combining the artificial cold junction compensation ( Thermal devices, such as thermal resistance or diode) , the controller from the thermocouple signal minus the cold end temperature, cold to eliminate the error, thus the real temperature of the hot end. This is called the cold junction compensation.

unlike thermocouple, RTD ( Resistance temperature detector) Usually consists of winding on the ceramic or glass core platinum, nickel or copper wire, or you can through the plating membrane element and the element sealed in a ceramic or glass capsule. As a result of the RTD work resistance changes, thus lead ( From the RTD to controller) With a resistance will increase to the signal error. If the wire is long enough, the error may be large enough and must be corrected.

industrial RTD applications use 3 line. Two wire connection on both sides of the resistor. This measures the temperature of the resistor and the error of the lead. One of the two wire with another wire. When measuring the two wire on controller, they only give the two wire resistance. Then from the two wire resistor minus the measurement values, to eliminate lead resistance. Now the controller only read the temperature of the resistor.

application differences:

based on the thermocouple type ( Used in the manufacture of different metals) Thermocouple has wide temperature range: - From 328 to 4800 degrees Fahrenheit. Thermocouple have fast response time, low initial cost and durability, suitable for harsh industrial applications. RTD temperature range for - From 328 to 1202 degrees Fahrenheit. Due to the low temperature range, RTD more accurate than thermocouple, the output is more stable over time, easier to calibration.