Classification of wiring methods for thermal resistors

There are three main ways to wire the leads of a thermal resistor

1. Two wire heating resistor: 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 r in connecting wires, the size of r is related to the material and length of the wire. Therefore, this lead method is only suitable for situations with low measurement accuracy

2. Three wire heating resistor: The method of connecting a lead at one end of the base of a thermal resistor and two leads at the other end is called the three wire system. This method is usually used in conjunction with an electric bridge to effectively eliminate the influence of lead resistance and is commonly used in industrial process control.

3. Four wire thermistor: The method of connecting two wires at each end of the root of the thermistor is called a four wire system, where 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.

1. The difference in wiring methods and detection principles: Two wire and three wire are measured using the bridge method, and the relationship between temperature value and analog output value is given after *. There is no bridge for the four wires, they are simply sent using a constant current source, measured with a voltmeter, and then the measured resistance value is given.

Why do different wiring methods occur
Due to the low resistance of thermal resistors, the resistance of connecting wires and contact resistance can have a significant impact on their temperature measurement accuracy. Therefore, introducing a three wire or four wire system is to eliminate these effects. The detection equipment (temperature control meter, PLC input, etc.) connected to the thermal resistance has four wiring terminals. I+,I-,V+,V-. Among them, the I+and I - terminals are used to provide a constant current to the thermistor, while the V+and V - terminals are used to monitor the voltage changes of the thermistor and sequentially detect temperature changes.

Four wires are led out from both ends of the thermistor and connected to four terminals.
3-wire means leading out 3-wire, which requires testing the I-V short circuit of the equipment side.
Two wires lead out two wires, which requires testing the device's I-V - and I+/V+short circuits.

3. The impact of different wiring methods on accuracy:
Two wires, current circuit and voltage measurement circuit combined into one, with poor accuracy. The error of the two-wire system mainly lies in the measurement error caused by the certain voltage drop generated by the current circuit in the cable
3 wires, the reference bit of the current circuit and the reference bit of the voltage measurement circuit are one line. The accuracy is slightly better.
4-wire, the circuit circuit and voltage measurement circuit are independently separated, with high accuracy, but require wires. In addition, Class A precision thermal resistors cannot be connected using a 2-wire system.