Thermocouple and thermal resistance(RTD) arecontact temperature measurement, although its role is the same, are measuring the temperature of the object, but their principles and characteristics are not the same.
First of all,thermocouple temperature measurement is the most widely used temperature devices,it’s main feature is a wide temperature range, performance, relatively stable, while simple structure, good dynamic response,remote 4-20mA signal, easy to automaticand centralized control.The principleof thermocouple temperature measurementis based on the thermoelectric effect. Two different conductors or semiconductors connected into a closed loop, when the two contacts at different temperatures, the circuit will produce thermoelectric power, thisphenomenon known as the thermoelectric effect, also known as the Seebeck effect.
Thermocouples generated in closed loops are composed of two potentials: thermoelectric potential and contact potential.Temperature difference potential is the potentialgenerated by the same conductor at both ends of thedifferent temperature , different conductors with different electron density, so thepotentialthey produceis not the same. The contact potential, as the name implies, refers to two different conductors in contact, and because of their different electron density so that a certain degree of electron diffusion, when they reach a certain balance, then forma potential, the size of contact potential depends on thematerial of two different conductorsand the temperature at their point of contact.
At present, the international application of thermocouple has a standard specification, it is divided into eight different divisions, namely B, R, S, K, N, E, J and T. The minimum temperature measurement can be measured below minus 270 ℃, up to 1800 ℃. B, R, S belong to platinum series of thermocouple, platinum is precious metals, so they are called precious metalthermocouple and the remaining few are known as the cheap metal thermoelectricity. There are twothermocouple structures, common type and armored type.Ordinary thermocouple generallycombined withthe hot electrode, insulation tube, protective casing and junction boxes and other components. The armored thermocouple is assembling the thermocouple wire, insulation materials and metal protection sleeve, and after drawing from a solid combination of processing.
But the electrical signalof the thermocoupleneeds a special wire to transmit, this wireis calledthe compensation wire.Different thermocouples require different compensation wire, its main role is to connect with the thermocouple, so that the reference end of the thermocouple away from the power, so that the reference junction temperature stability.
(Some types of temperature instruments: Thermocouple, RTD)
Secondly, thethermal resistance,Although the thermal resistance is wide used in the industrial application, but because of its temperature rangelimitits application, the working principle of thermal resistanceis based on the resistance valueof conductor or semiconductor changes with the temperature change.Italso hasthe advantagesof high sensitivity, stability, interchangeability andbetteraccuracy,and can alsoremote transmit the electrical signal, Butit needs the power excitation, can not make the instantaneous measurement of temperature changes.In industrial, thermal resistance commonly use Pt100, Pt10, Cu50, Cu100. Platinum thermal resistance of the temperature range is generally minus 200-800℃, copper heat resistance is minus 40 to 140℃. and thermocouple the same type of distinction, but the thermal resistancedoes not needthe compensatewire, and cheaper than the thermocouple.
Finally, above information is just a simple introduction of the temperature instruments: thermocouple and RTD, and for selecting them,you must think of other parameters to choose the suitable instruments for your working environment.
Post time: 21-09-21