2-wire/3-wire/4-wire introduction

What is the principle of two-wire/three-wire/four-wire system? What's the difference between two-wire/three-wire/four-wire? After the birth of the two-wire transmitter, there is a distinction between several wires. Two-wire system, three-wire system, and four-wire system actually refer to various transmitters whose output is analog DC current signal, the difference in working principle and structure, not only the wiring form of the transmitter. This is the result of the wide application of electronic amplifiers in instruments. The essence of amplification is an energy conversion process, which is inseparable from power supply. Therefore, the first appeared is the four-wire transmitter; that is, two wires are responsible for the supply of power, and the other two wires are responsible for outputting the converted and amplified signals (such as voltage, current, etc.). The emergence of DDZ-Ⅱ type electric unit combination instrument, the power supply is 220V.AC, and the four-wire transmitter with output signal of 0--10mA.DC has been widely used, and it can still be seen in some factories at present. In the 1970s, my country began to produce DDZ-Ⅲ type electric unit combination instrument, and adopted the International Electrotechnical Commission (IEC): analog signal standard for process control system. That is, the transmission signal of the instrument adopts 4-20mA.DC, and the contact signal adopts 1-5V.DC, that is, the signal system of current transmission and voltage reception is adopted. Using 4-20mA.DC signal, the field instrument can realize two-wire system. But limited by the conditions, the two-wire system was only used in pressure and differential pressure transmitters at that time, and the four-wire system was still used in temperature transmitters. Now the product range of domestic two-wire transmitters has also been greatly expanded, and there are more and more application fields. At the same time, the transmitters coming from abroad are mostly two-wire systems. Principle of two-wire system If the transmitter meets the above three conditions in design, two-wire system transmission can be realized. The so-called two-wire system means that the power supply and the load are connected in series, and there is a common point, while the signal connection and power supply between the field transmitter and the control room instrument only use two wires, which are both power lines and signal lines. The two-wire transmitter provides a static working current for the transmitter because the starting point current of the signal is 4mA.DC. At the same time, the electrical zero point of the instrument is 4mA.DC, which does not coincide with the mechanical zero point. power failure and disconnection. Moreover, the two-wire system is also convenient for the use of safety barriers, which is conducive to safe explosion-proof. The two-wire transmitter is shown in Figure 1. Its power supply is 24V.DC, the output signal is 4-20mA.DC, the load resistance is 250Ω, and the negative line potential of the 24V power supply is the lowest. It is the signal common line. The transmitter can also load the FSK keying signal of the HART protocol on the 4-20mA.DC signal. In order to reduce the volume and weight of the transmitter, improve the anti-interference performance, and reduce the wiring, some instrument factories change the power supply of the transmitter from 220V.AC to low-voltage DC power supply, such as the power supply from 24V The .DC power supply box is used, because the low-voltage power supply creates conditions for the sharing of the negative line, so there is a three-wire transmitter product. The three-wire transmitter is shown in Figure 3. The so-called three-wire system means that one line is used for the positive end of the power supply, one line is used for the positive end of the signal output, and the negative end of the power supply and the negative end of the signal share one line. Most of its power supply is 24V.DC, the output signal is 4-20mA.DC, the load resistance is 250Ω or 0-10mA.DC, and the load resistance is 0-1.5KΩ; some have mA and mV signals, but the load resistance or input The value of resistance varies depending on the form of the output circuit. Wiring diagram of three-wire transmitter The principle of four-wire system is based on the popularization and application of 4-20mA.DC (1-5V.DC) signal system. In order to facilitate connection in control system applications, the unification of signal system is required. For this reason It is required that some non-electric unit combination instruments, such as online analysis, mechanical quantity, electricity and other instruments, can adopt the output 4-20mA.DC signal system, but due to the complex conversion circuit and high power consumption, it is difficult to meet all the above-mentioned reasons. Three conditions, and can not achieve two-wire system, you can only use an external power supply method to make a four-wire transmitter with an output of 4-20mA.DC. The four-wire transmitter is shown in Figure 2. Most of its power supplies are 220V.AC, and some are 24V.DC. The output signal is 4-20mA.DC, the load resistance is 250Ω, or 0-10mA.DC, the load resistance is 0-1.5KΩ; some also have mA and mV signals, but the load resistance or input resistance, due to the different output circuit forms The numbers are different. Wiring diagram of four-wire transmitter The difference between two-wire, three-wire, and four-wire Wiring form. The selection should be based on the actual situation of the unit, such as the unification of signal system, explosion-proof requirements, requirements for receiving equipment, investment and other issues to comprehensively select.
There are many issues that affect customized level indicator, which has led to the need of getting specialists trained in certain areas so as to handle all issues that may arise as well as level gauge products that can solve customized level indicator problems.
Guangdong Kaidi Energy Technology Co., Ltd. will be familiar with the transformation from a generalist into a manufacturer, and will have the big-picture perspective necessary to stay focused on long-term goals.
We began investing in our workforce and negotiated deals with major suppliers and providers to lower the cost of equipment so the technicians could enhance the competitiveness of level gauge right away.
Through our distribution and marketing competencies, Guangdong Kaidi Energy Technology Co., Ltd. provides creative, customized, solutions for our customers. As a result, we achieve superior profit growth as the level gauge company of choice.
Turn to Guangdong Kaidi Energy Technology Co., Ltd. if you are looking for premier customized level indicator solution, affordable packages, and quality level gauge products! We produce wide series of high quality, first-class , and provide professional level gauge services at great prices.