Fieldbus

Fieldbus is an industrial data bus that has developed rapidly in recent years.

It mainly solves the digital communication between field devices such as intelligent instrumentation, controllers and actuators in the industrial field and the information transmission between these field control devices and advanced control systems.

Due to the outstanding advantages of fieldbus, such as simple, reliable, economical and practical, it has been highly valued by many standards bodies and computer manufacturers.

Introduction

Fieldbus (Fieldbus) was developed internationally in the late 1980s and early 1990s for field intelligent device interconnection communication networks in the fields of process automation, manufacturing automation, and building automation.

It serves as the basis for the plant’s digital communications network and communicates the links between the production process site and control equipment and its level of higher control management.

It is not only a grassroots network, but also an open, new fully distributed control system.

This integrated technology with intelligent sensing, control, computer, digital communication and other technologies has attracted worldwide attention and become a hot spot in the development of automation technology, and will lead to profound changes in the structure and equipment of automation systems.

Many powerful and influential companies in the world have developed fieldbus technologies and products to varying degrees.

The working environment of the fieldbus device is at the bottom of the process device.

As a factory equipment-level basic communication network, it requires the characteristics of simple protocol, strong fault tolerance, good security and low cost.

It has certain time determinism and high real-time requirements. It also has stable network load, most of which are characterized by short frame transmission and frequent information exchange.

Due to the above characteristics, the field bus system has the characteristics of different upper layer high speed data communication networks from network structure to communication technology.

The fieldbus system is generally referred to as the fifth generation control system, also known as FCS, the fieldbus control system.

People generally refer to the PCS, the pneumatic signal control system before the 1950s, as the first generation.

The electric analog signal control system such as 4~20mA is called the second generation.

The digital computer centralized control system is called the third generation.

The distributed distributed control system DCS since the mid-1970s is called the fourth generation.

Fieldbus control system FCS as a new generation control system.

On the one hand, it broke through the limitations of the DCS system using a communication-dedicated network, and adopted a solution based on openness and standardization to overcome the defects caused by the closed system.

On the other hand, the distributed system structure that combines the concentration and dispersion of DCS has become a new fully distributed structure, and the control function has been completely decentralized to the scene.

It can be said that openness, dispersion and digital communication are the most prominent features of the fieldbus system.

History

In 1984, Intel Corporation of the United States proposed a computer distributed control system – bit bus (BITBUS).

It mainly separates the low-speed process-oriented input and output channels from the high-speed computer multi-bus (MULTIBUS), forming the original concept of the field bus.

In the mid-1980s, Rosemount Corporation of the United States developed an addressable remote sensor (HART) communication protocol.

A frequency signal is superimposed on the analog quantity of 4-20 mA, and the digital signal transmission is realized by the twisted pair.

The HART protocol is already a prototype of the fieldbus.

In 1985, it was initiated by big companies such as Honeywell and Bailey, and World FIP was established to develop the FIP agreement.

In 1987, a special committee interoperability agreement (ISP) was established with several well-known companies such as Siemens, Rosemount, and Yokogawa, and the PROFIBUS protocol was established.

Later, the American Instrument and Control Society also developed the fieldbus standard IEC/ISA SP50.

Over time, the world has gradually formed two competing fieldbus groups.

One is the ISP group headed by Siemens, Rosemount, and Yokogawa; the other is the WorldFIP group led by companies such as Honeywell and Bailey.

In 1994, the two major groups announced their merger and integration into the Fieldbus Foundation (FF).

For the technical development of the fieldbus and the development of standards, the Fund Committee has reached the following consensus:

  • Co-developed to comply with the IEC/ISA SP50 protocol standards;
  • A schedule for the development phase of the fieldbus technology is agreed.

Characteristics

The open system of the system refers to the disclosure of the communication protocol, and the devices of different manufacturers can be interconnected and exchange information.

Fieldbus developers are committed to building a unified open system for the underlying network of the plant.

Openness here refers to the consistency and openness of relevant standards, emphasizing consensus and compliance with standards.

An open system that can be connected to any other device or system that adheres to the same standards.

A bus-based fieldbus network system must be open, and the open system gives the user the right to integrate the system.

Users can make products from different suppliers into random systems according to their own needs and objects.

Interoperability and interusability

Interoperability here refers to the realization of information transmission and communication between interconnected devices and systems, and can implement point-to-point, point-to-multipoint digital communication.

Interusability means that devices of similar performance from different manufacturers can be interchanged for interusability.

Intelligent and functional autonomy

It distributes sensing measurement, compensation calculation, engineering quantity processing and control functions into field devices.

The basic functions of automatic control can be completed only by field devices, and the operating status of the device can be diagnosed at any time.

Highly dispersed system structure

Since the field device itself can complete the basic functions of automatic control, the field bus has formed a new architecture of a fully distributed control system.

It fundamentally changed the system of distributed control system combining the concentration and dispersion of existing DCS, which simplified the system structure and improved reliability.

Adaptability to the on-site environment

Working at the front end of the field equipment, as the field bus at the bottom of the factory network, is designed for working in the field environment.

It can support twisted pair, coaxial cable, optical cable, RF, infrared, power line, etc., with strong anti-interference ability.

It can realize power transmission and communication by two-wire system, and can meet intrinsic safety explosion-proof requirements.

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