What are the differences between four wire, three wire, and two wire thermal resistance systems?

Two wire system: The method of connecting a wire at each end of a thermal resistor to extract a resistance signal is called a two wire system: This lead method is simple, but due to the inevitable lead resistance of the connecting wire, the resistance of the entire circuit is the resistance value of the thermal resistor plus the resistance value of the two wire segments. The measurement error is large, and the size is related to the material and length of the wire. Therefore, this lead method is only suitable for situations with low measurement accuracy

Three wire system: The method of connecting a lead wire at one end of the root of a thermal resistor and two leads wire at the other end is called the three wire system. This method is usually used in conjunction with an electric bridge, where two wires are connected to the two bridge backs of the bridge and the other wire is connected to the power supply of the bridge, eliminating errors in lead resistance. It can effectively eliminate the influence of lead resistance and is a commonly used lead resistance in industrial process control.

Four wire system: The method of connecting two wires at each end of the root of a thermistor is called a four wire system, in which two leads provide a constant current I to the thermistor, convert R into a voltage signal U, and then lead U to the secondary instrument through the other two leads. It can be seen that this lead method can completely eliminate the influence of lead resistance and is mainly used for high-precision temperature detection. Usually used in laboratories.