The difference between two-wire system (two-wire system), three-wire system, and four-wire system

    The terms of two-wire system (two-wire system), three-wire system, and four-wire system generally refer to the wiring method of thermal resistance or sensor, and it is said that several wires are connected. The several-wire connection method of the thermal resistance and the sensor is different, but the most widely used is the three-wire connection. Below we will introduce the difference between the three-wire connection of the thermal resistance and the sensor.

    Let us first talk about the three connection methods of thermal resistance:

    Two-wire system: The method of connecting a wire at each end of the thermal resistance to lead out the resistance signal is called the two-wire system. This lead method is very simple, but there must be lead resistance r in the connecting wire. The size of r is related to the material and length of the wire Therefore, this lead method is only suitable for occasions with low measurement accuracy.

    Three-wire system: The method of connecting one lead at one end of the root of the thermal resistance and connecting two leads at the other end is called three-wire system. This method is usually used in conjunction with a bridge, which can better eliminate the influence of lead resistance. It is industrial The most commonly used in process control.

    Four-wire system: The method of connecting two wires at each end of the thermal resistance is called a four-wire system, in which two leads provide a constant current I for the thermal resistance, convert R into a voltage signal U, and then pass the other two leads Lead U to the secondary meter. This type of lead wire can completely eliminate the influence of lead wire resistance and is mainly used for high-precision temperature detection.

    Let's talk about the three connection methods of the sensor:

    Two-wire system: The sensor has only two wires, one is connected to the power supply, and the other is the signal wire connected to the other pole of the power supply after passing through the instrument. Wiring is the simplest.

    Three-wire system: The sensor has three wires, which are the positive pole of the power supply, the negative pole of the power supply, and the signal output. The three-wire connection is the most commonly used.

    Four-wire system: The sensor has four wires, two of which are power wires and two are signal wires.

    It is important to note that the power lead of the sensor is divided into positive and negative poles, and the signal line is divided into NPN and PNP. It cannot be connected incorrectly. The wrong connection may cause damage to the sensor.

    (huiputech)