What are the differences in the wiring of thermal resistors and the temperature measurement principle?

Thermocouple temperature measurement principle and materials Thermocouple temperature measurement is based on the characteristic that the resistance value of metal conductor increases with the increase of temperature to measure temperature.
Due to the above reasons, for dynamic instruments equipped with thermal resistors, when using the three-wire wiring method, there are regulations on the resistance value of the connecting wire. Generally, the resistance of each wire is 5Ω. If it is less than 5Ω, it must be supplemented with manganese copper resistors to ensure that the maximum additional error of the instrument does not exceed 0.5%. For display controllers using integrated operational amplifiers, their input impedance is very high, and the change in the resistance of the external wire is much smaller than the input impedance of the instrument, so the change in the resistance value of the wire can be ignored without affecting the measurement accuracy. Therefore, there is no requirement for the resistance value of the connecting wire, which can avoid the work of adjusting the external wire resistance.
Most thermal resistors are made of pure metal materials. Currently, platinum and copper are the most widely used. In addition, materials such as dian, nickel, manganese and rhodium have begun to be used to manufacture thermal resistors. The difference between two-wire, three-wire and four-wire thermal resistors From the temperature measurement principle of thermal resistors, it can be seen that the change of the measured temperature is directly measured by the change of the resistance value of the thermal resistor. Therefore, the change of the resistance of various wires drawn from the thermal resistor will affect the temperature measurement. In order to eliminate the influence of lead resistance, a three-wire system or a four-wire system is generally used. There are differences in the wiring of thermal resistors, which is mainly related to the application. Generally, 2 wires are used for close-range measurement; 3 wires are used for long-range measurement, mainly to overcome the influence of line resistance and interference. In addition, 4-wire thermal resistors are proposed for higher precision measurement. The main use is to apply a current to the thermal resistor, and then measure its voltage to improve the measurement accuracy and sensitivity. The detection equipment connected to the thermal resistor (temperature control meter, PLC input, etc.) has four wiring terminals. I+, I-, V+, V-. Among them, the i+ and i- terminals are used to provide a constant current to the thermal resistor, and the v+ and v- are used to monitor the voltage change of the thermal resistor and detect the temperature change in turn. 4 wires are 4 wires drawn from both ends of the thermal resistor and connected to 4 terminals. 3-wire leads to 3 wires, which requires the i- and v- of the detection device to be short-circuited. 2-wire leads to 2 wires, which requires the i-, v-, i+, and v+ of the detection device to be short-circuited. The temperature measurement principles of two-wire, three-wire, and four-wire thermal resistors are the same, but the wiring is different. To be precise, it is a question of whether the current loop and the voltage measurement loop are wired separately. 2-wire, the current loop and the voltage measurement loop are combined into 1, and the accuracy is poor. 3-wire, the reference position of the current loop and the reference position of the voltage measurement loop are one line. The accuracy is slightly better. 4-wire, the circuit loop and the voltage measurement loop are separated independently, with high accuracy, but it costs more wires.
Since the resistance value of the copper wire that connects the thermal resistor to the bridge will change with the change of ambient temperature, if the connecting wire is only connected to one bridge arm, when the ambient temperature changes, the change value of the connecting wire resistance will be superimposed on the change value of the resistance of the thermal resistor RT, resulting in additional errors. Therefore, the three-wire wiring method is widely used in industry, and wires 2 and 3 are connected to the two arms of the bridge respectively. When the resistance of the wires changes, they can offset each other partially to reduce the impact on the instrument display value. However, the error reduction is limited. For an unbalanced bridge, full compensation can only be obtained at the beginning of the instrument scale, and the above additional error is the largest at full scale. For an unbalanced bridge, the additional temperature error of the power lead must also be considered. When current flows through the wire 1 connecting the thermal resistor to the power supply, there will be a certain voltage drop. When the ambient temperature changes, the voltage of the upper and lower branches of the bridge will also change accordingly, which will bring a certain additional temperature error to the instrument.