Smart Home Technology: Five Introductions of Fieldbus Technology and Features of Four Fieldbuses

From the definition of terms, fieldbus is an open, fully digital, bi-directional, multi-station communication system used between on-site electrical appliances, field instruments, and field devices and control room host systems. Fieldbus standards specify how a certain number of field devices in a control system exchange data. The data transmission media can be wires and cables, optical cables, telephone lines, radios, and the like.

In layman's terms, fieldbus is the bus technology used in the field. The connection mode of the traditional control system is a parallel connection mode. A programmable logic controller (PLC) controls each electrical component. Each component has an I/O port, and two lines are required between the two components. Connect as a control and/or power source. When the number of electrical components controlled by the PLC reaches dozens or even hundreds, the wiring of the entire system becomes very complicated, easy to make mistakes, and construction and maintenance are very inconvenient. For this reason, people consider how to combine so many wires together and connect all devices with one wire, all data and signals are circulated on this wire, and the control and communication between devices can be arbitrarily set. So this line is naturally called the bus, just like the bus concept inside the computer.

Because the control objects are at the industrial and mining site, unlike the computer is usually used indoors, so this bus is called the field bus, referred to as the field bus.

Field bus features

Fieldbus technology is actually a method of using serial data transmission and connection instead of the traditional parallel signal transmission and connection method. It in turn realizes the data transmission between the control layer and fieldbus device layer, while ensuring the real-time transmission The reliability and openness of information are achieved in the circumstances. The general field bus has the following characteristics.

1) Simple wiring

This is a common feature of most fieldbuses. The greatest revolution of fieldbus is the revolution of wiring. Minimized wiring and maximized network topology make the wiring and maintenance costs of the system greatly reduced. Due to the serial mode, most field buses use twisted pairs and there are bus types that directly load power on the two signal lines. In this way, the obvious feeling of using fieldbus type devices and systems is simple and intuitive.

2) Openness

A bus must be open. This refers to two aspects: on the one hand, it can be connected with different control systems, that is, the openness of applications; on the other hand, it is the opening of communication protocols, that is, the openness of development. Only with openness can the field bus not only have the low cost of the traditional bus, but also be suitable for the networked and systematic requirements of advanced control.

3) Real-time

The real-time requirement of the bus is to adapt to the characteristics of on-site control and on-site acquisition. The general field bus requires higher transmission rate and transmission efficiency under the condition of ensuring data reliability and integrity. The faster the transmission speed of the bus is, the better, and the faster the speed, the shorter the response time of the system, but the transmission speed cannot be solved simply by increasing the transmission rate, and the efficiency of transmission is also very important. Transmission efficiency is mainly the proportion of valid user data in the transmission frame and the proportion of successful transmission frames in all transmission frames.

4) Reliability

The general bus has certain anti-interference ability, at the same time, when the system breaks down, have certain diagnostic ability, in order to protect the network to the maximum extent, find and replace the faulty node faster at the same time. The size of the bus fault diagnosis capability is determined by the physical media used for transmission and the software protocol used for transmission, so different buses have different diagnostic capabilities and processing capabilities.

Fieldbus application field

There are many types of fieldbuses. According to the complete statistics, there are currently more than 40 fieldbuses in the world. There are two reasons for the simultaneous development of multiple fieldbuses. On the one hand, the rapid development of industrial technology has enabled the rapid development of fieldbus technology in various technological contexts, and it has rapidly gained popularity, but the level and degree of popularization are due to different technologies. The development focuses are different and different; on the other hand, the field of industrial control is “highly decentralized and difficult to monopolize”. This is different from the popularization of home appliance technologies. The areas covered by industrial control are often multidisciplinary and multi-technology. It is possible that the bus technology that can be promoted in one area can be moved to another new area.

The level of control system

The control system has different levels. The text on the left represents the logical level of the system. From the top to the bottom are the coordination level, plant level, plant level, field level, and operator and sensor levels. Fieldbus involves the lowest two levels. The words on the right represent the physical device hierarchy of the system. From top to bottom, the main computer, programmable logic controller, small controller, sensors, and operators (such as sensor switches, position switches, solenoid valves, contactors, etc.) are used.

Various field bus application areas

Corresponding to different system levels, fieldbus has a different range of applications. From the bottom up, the ordinate indicates that the equipment is simple to complex, that is, from a simple sensor, a complex sensor, a small PLC or an industrial control machine to a workstation, a medium PLC, a large PLC, and a distributed control system (DCS) monitoring machine. And so on, data traffic from small to large, equipment functions from simple to complex. The abscissa represents the mode of communication data transmission, from left to right, followed by binary bit transmission, 8-bit and 8-bit or more word transmission, 128-bit or more out-of-frame transmission, and larger data volume transmission file transfer.

ASI, Sensorloop. Se-shirts, such as Lex, are suitable for low-level control systems organized by various digital sensors and manipulators. DeviceNet, PROFIBUS-DP and WorldFIP are suitable for various devices for word transmission. As for PROFIBUS-PA, Fieldbus Foundation and many more. The instrument suitable for frame transmission visualizes the graveyard. So the bus for us is in the area of ​​the Sensor and Equipment.

In developed countries, field bus technology has emerged from the 1980s and has been gradually extended to the present, and has been widely used in industrial control. It is said that in 2002, 40% of the automation projects in Europe used fieldbus control systems, reaching 65% to 70% by 2005. In China, field buses are first used in production lines invested by foreign companies in China. For example, almost all foreign automobile manufacturers have production lines that use field buses. The field bus is also widely used in production lines such as beer canning, tobacco processing, mechanical assembly, and product packaging.

Some municipal projects also started using fieldbus. In China, the introduction of fieldbus in the mid-to-late 1990s has so far been widely accepted in terms of technology concept. The number of users and usage areas has rapidly increased and expanded. Many automation projects use fieldbus control as one of the options. Localized fieldbus products have emerged and are rapidly being industrialized.

At present, the application of fieldbus technology is mainly concentrated in various industries such as metallurgy, electric power, water treatment, dairy beverages, tobacco, cement, petrochemical, mining, and original equipment manufacturers (OEM) users, as well as unmanned road monitoring. , building automation, smart home and other new technologies.

Fieldbus national standards and corporate standards

Due to the fact that the international standards of fieldbus could not be established, various field buses, device buses and sensor buses take this opportunity, surging, and they are established one after another. There is no need for publicity, promotion and application, and some large field buses. The organization is trying hard to expand its own territory in an attempt to create a fait accompli and make itself an international standard.

Fieldbus national standards, such as PROFIBUS in Germany, FIP in France, ERA in the UK, FINT in Norway, etc., PNET in Denmark, DeviceNet and ASI in China.

Fieldbus enterprise standards, such as LonWorks from Echelon, HART from CAN. Rosemount from InterBus. Rober Bosch from Phenix Contact, Dupline from Carlo Garazzi, P-NET from Process Date, and F-MUX from Peter Hans, According to incomplete statistics, there are about 40 kinds.

At present, it seems that the fieldbus standards will not be unified and multi-standard coexistence will continue. Because different standards represent different manufacturers' interests in a certain sense, the competition between market and interests among vendors will reflect the breadth and depth of the promotion, application, and adoption of standards. Therefore, there is actually competition between the agreements. Those agreements with relatively backward technology and few or weak supporters are gradually phased out. Agreements with advanced technology, support for multiple vendors, and high openness are more easily accepted and have more room for survival and development.

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