Difference 1: The principle of temperature measurement is different
Thermal resistance temperature measurement is based on the characteristic that the resistance value of a metal conductor increases with temperature. Its main features are high measurement accuracy and stable performance. Among them, the measurement accuracy of platinum thermal resistance is the highest. It is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.
The thermocouple welds two conductors or semiconductors A and B of different materials to form a closed loop. When there is a temperature difference between the two attachment points 1 and 2 of the conductors A and B, an electromotive force is generated between the two. Thus, a large current is formed in the loop. This phenomenon is called the thermoelectric effect.
Difference 2: The classification of thermocouple and thermal resistance is different.
The common thermal resistance materials are mostly single metal. The most widely used thermal resistance materials are platinum and copper. Platinum resistance has high precision, good stability, and certain nonlinearity. The higher the temperature, the smaller the resistance change rate. Copper resistance There is a linear relationship between the resistance value and the temperature in the temperature measurement range, the number of temperature lines is large, and it is easy to be oxidized if it exceeds 150. The index numbers of the thermal resistance are Cu50, Pt100, Pt1000, etc. The letter in the front refers to the material of the thermal resistance, and the number behind is the resistance value of the thermal resistance.
A thermocouple is composed of two different conductors (called thermocouple wires or thermoelectrodes) connected at both ends into a loop. The common K-type thermocouple is composed of nickel-chromium-nickel silicon. Standardized thermocouples China Since January 1, 1988, thermocouples and thermal resistances have all been produced in accordance with IEC international standards. Seven standardized thermocouples of S, B, E, K, R, J, and T are designated as China’s unified design. Thermocouple.
Difference 3: Different temperature range
Thermal resistance is a commonly used temperature sensor in the middle and low temperature areas. It is divided into platinum thermal resistance, copper thermal resistance, etc. The temperature measurement range is also different. In general, thermal resistance can measure the temperature from -200 to 600 ℃.
Compared with the thermal resistance, the temperature measurement range of the thermocouple is much larger. The B-type thermocouple with the largest temperature measurement range can even measure the temperature of 0-1800 ℃. The ordinary K-type thermocouple can also measure Temperature of -40-1200℃. But because the measurement of thermocouple in low temperature area is not very accurate. Therefore, it is more appropriate to use thermal resistance when measuring lower temperature.
Difference 4: Different connection methods
There are currently three main ways to connect thermal resistance: two-wire, three-wire, and four-wire. The accuracy of the two-wire system is relatively low, while the four-wire system is more used for accurate measurement in the laboratory. Most of our commonly used thermal resistances are three-wire systems. This is because the circuit for measuring thermal resistance is generally an unbalanced bridge. A three-wire system is used. One wire is connected to the power terminal of the bridge. The other two are connected to the heat. The bridge arm where the resistance is located and the bridge arm adjacent to it. This can eliminate the measurement error caused by the wire line resistance, and greatly improve the accuracy.
