Wiring method of thermal resistors

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This post was last edited by tiandiyi*an on 2018-1-3 at 14:09. Two-wire system: The method in which a wire is connected to each end of the thermal resistor in order to transmit the resistance signal is called the two-wire system. This wiring method is simple, but since there is inevitably a wiring resistance r, and the value of r depends on the material and length of the wires, this method is only suitable for applications where low measurement accuracy is sufficient. Three-wire system: The method in which one wire is connected to one end of the thermal resistor and two wires are connected to the other end is known as the three-wire system. This method is usually used in conjunction with bridges, and it helps to minimize the impact of wiring resistance; it is the most commonly used approach in industrial process control. 　　Four-wire system: The method in which two wires are connected to each end at the base of the thermal resistor is called the four-wire system. Two of these wires supply a constant current I to the thermal resistor, converting R into a voltage signal U; this signal U is then transmitted to the secondary instrument through the other two wires. It can be seen that this type of lead configuration completely eliminates the influence of lead resistance, and is mainly used for high-precision temperature detection. 　　The thermal resistor uses a three-wire connection method. A three-wire system is used to eliminate measurement errors caused by the resistance of the connection wires. This is because the circuit for measuring thermistors is generally an unbalanced bridge. As one of the bridge arm resistors in a bridge, the connecting wire of the thermoresistor (from the thermoresistor to the control room) also forms part of the bridge arm resistance. This portion of the resistance is unknown and changes with ambient temperature, resulting in measurement errors. A three-wire system is used, with one wire connected to the power supply terminal of the bridge, and the other two wires connected respectively to the bridge arm where the thermistor is located and to the adjacent bridge arm; this eliminates the measurement errors caused by the resistance of the wiring.