Home   |   INFO CENTER   |   NEWS   |  

Two-wire system and its advantages

Home  >  INFO CENTER  >  NEWS  > 

Two-wire system and its advantages

Two-wire system and its advantages

2023-02-24

"Wire system" is a term often encountered in the automation industry, referring to the number of emergency pull-wire switches used for instrument power supply and standard signal transmission. The title of multi-wire system came into being after the birth of two-wire transmitter. So, what is the two-tier system? What are its advantages?

news-Kaidi Sensors-Two-wire system and its advantages-img

The two-wire system is relative to the four-wire system (two power supply lines and two communication lines). It combines the power supply line and the signal line. The two lines are both power lines and signal lines to realize communication and power supply It is generally used for 4~20mA signal transmission.

The advantage of the two-wire system is that the wiring is simple, and it is only applicable to the primary sensors with small power, such as pressure change, differential pressure change, temperature change, capacitive level gauge, level switch, electromagnetic flowmeter, vortex flowmeter, etc. As the two-wire system saves construction and cable costs, and brings great convenience to on-site construction and later maintenance, it is widely used in sensor, industrial control and other fields.

Moreover, compared with three-wire system and four-wire system, two-wire system also has the following advantages:

news-Kaidi Sensors-img

1. It is not easy to be affected by parasitic thermocouples and resistance voltage drop and temperature drift along the pull wire switch, and can be used with very cheap and thinner wire; It can save a lot of cable and installation costs.

2. When the output resistance of the current source is large enough, the voltage in the wire loop induced by the magnetic field coupling will not have a significant impact, because the current caused by the interference source is very small, and generally the interference can be reduced by using twisted pair; The two-wire system and three-wire system must use shielded wire, and the shielding layer of the shielded wire must be properly grounded.

3. Capacitive interference will cause errors related to the receiver resistance. For the 4~20mA two-wire loop, the receiver resistance is usually 250 Ω (sampling Uout=1~5V), which is too small to produce significant errors. Therefore, the allowable wire length is longer and farther than the voltage telemetry system.

news-Two-wire system and its advantages-Kaidi Sensors-img

4. Each single readout device or recording device can be switched between different channels with different wire lengths, without causing differences in accuracy due to different wire lengths, so as to realize decentralized acquisition. The advantages of decentralized acquisition are: decentralized acquisition and centralized control.

5. Using 4mA for zero level makes it very convenient to judge open circuit and short circuit or sensor damage (0mA state).

6. It is very easy to add one or two lightning and surge protection devices at the two-wire output port, which is conducive to safe lightning protection and explosion protection.

The above is the relevant introduction of "two-wire system and its advantages". If you want to know more about level measuring instruments, please consult us!

Chat Online 编辑模式下无法使用
Leave Your Message inputting...