As traditional manufacturing enterprises accelerate their transformation towards intelligent manufacturing, the Industrial Internet is rapidly emerging worldwide. A crucial component of the Industrial Internet's technological architecture is the collection of massive amounts of data through various communication methods connecting different devices, systems, and products. This article will introduce two communication methods for low-level industrial devices: fieldbus and industrial Ethernet.
Understanding Fieldbus
A review of the history of fieldbus development reveals that fieldbuses emerged roughly in the late 1980s and early 1990s. During this period, with the increasing scale of production, factories needed to interconnect their equipment (primarily for remote I/O data transmission and data exchange between different devices within the production line). The goal was to achieve multi-point information control by comprehensively understanding the operating parameters and information of multiple points. However, computer systems at this time suffered from system silos; each manufacturer's products were self-contained, and devices from different manufacturers could not interconnect. Achieving a network system for wider information sharing faced many difficulties due to the technological limitations of the time.
In the course of practical development, many well-known fieldbus technologies have emerged, such as Foundation Fieldbus (FF), HAPT Fieldbus, CAN Fieldbus, LONWORKS Fieldbus, DeviceNet Fieldbus, INTERBUS Fieldbus, PROFIBUS Fieldbus, WorldFIP Fieldbus, and CC-Link Fieldbus. These fieldbuses each have their own characteristics and have formed specific application ranges. However, there are simply too many types of fieldbuses, and the communication protocols they use are completely different. Therefore, a unified fieldbus standard has not yet been achieved, ultimately resulting in the IEC 61158 fieldbus standard, which covers multiple fieldbuses. There is a wealth of information on this topic online, so it will not be elaborated upon here.
I've searched for various definitions of fieldbus, but neither the definitions on Baidu Baike nor those provided by the International Electrotechnical Commission (IEC) remain easy to understand for beginners. It wasn't until recently, when I came across a simplified explanation of fieldbus, that things became clear. I'd like to share it with you: Fieldbus is a real-time control communication network that interconnects the lowest-level field controllers and intelligent field instruments in automation. It follows all or part of the communication protocols of the ISO/OSI Open Systems Interconnection reference model.
Beginners can understand fieldbus from two aspects: First, according to the hierarchical structure of factory automation information networks (factory management level, workshop monitoring level, field device level), fieldbus is located at the bottom layer of production control and network structure, and is the communication network between the bottom-level devices in the factory. The advantage of applying fieldbus technology at the factory bottom layer is that it can realize transparent communication for vertical integration of factory information, that is, data access from the management level to the bottom layer of automation.
Typical workshop automation architecture (Image source: Internet)
Second, fieldbus is based on the ISO/OSI seven-layer model, but can have fewer than seven layers. It should be noted that in practical applications, the ISO model is only a reference. Different types of fieldbus protocol stacks differ significantly, and the ISO/OSI seven-layer model is usually simplified to achieve lower communication latency, faster speed, and better facilitate the real-time characteristics of the fieldbus.
ISO/OSI Open Systems Interconnection Reference Model (Image source: Internet)
Note: The Open Systems Interconnection (OSI) reference model is a framework jointly developed by the International Organization for Standardization (ISO) and the International Telegraph and Telephone Consultative Committee (CCITT). It provides a functional structure framework for open interconnected information systems. From lowest to highest, it consists of: Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer, and Application Layer.
Entering the world of industrial Ethernet
Given that fieldbus standards are still based on compromises of multiple fieldbus standards, and multiple standards are, in a sense, no standard at all, people began to seek new solutions for industrial communication. This is when Ethernet technology came into view. Due to its simplicity, openness, and low cost, Ethernet technology has a very high market share in office and business applications. Some manufacturers (such as Schneider Electric, which proposed a solution based on Ethernet + TCP/IP) proposed introducing Ethernet technology into the underlying layers of factory equipment, thus giving rise to Industrial Ethernet.
However, Ethernet, the most common communication protocol standard in computer local area networks, was initially designed for office automation applications and did not consider the needs of industrial environments, such as high and low temperatures and dust protection. Therefore, Ethernet cannot be directly used in industrial settings. Think Tank Encyclopedia defines Industrial Ethernet as the application of Ethernet components and technologies in automated control and process control within industrial environments. Industrial Ethernet uses the TCP/IP protocol and is compatible with the IEEE 802.3 standard, but it incorporates its own unique protocols at the application layer. From a definitional perspective, Industrial Ethernet is also a type of fieldbus, just like the various protocols of fieldbuses.
Just as Ethernet is suitable for information management and processing systems, Industrial Ethernet is also widely used in information integration fields such as factory management and workshop monitoring. The biggest advantages of Industrial Ethernet are: it can meet the requirements of various levels of the control system, enabling the unification of an enterprise's information and control networks; Ethernet is easy to integrate, fast, has a wide range of development technologies, broad hardware upgrade capabilities, low cost, and is easily supported by numerous manufacturers.
Industrial Ethernet architecture diagram (Image source: Internet)
However, Ethernet is a random network with uncertain communication characteristics, which led to industrial Ethernet being labeled as "unsuitable for high-speed real-time data communication." Therefore, major companies worldwide have turned to researching the deterministic and real-time communication issues based on Ethernet, achieving some success. Currently, some of the more influential real-time industrial Ethernet technologies include: Siemens' PROFINET, Beckhoff's EtherCAT, B&R's Powerlink, Yokogawa's VNET/IP, Toshiba's TCnet, Schneider Electric's Modbus-IDA, and Zhejiang University Control System's EPA, among others.
In general, industrial network communication has evolved from fieldbus to Industrial Ethernet, and then to real-time Industrial Ethernet. According to the latest survey data from Swedish networking expert HMS, in 2016, the number of secure fieldbus nodes accounted for 48% of the entire market, a significant decrease from 58% in 2015, while the market share of Industrial Ethernet rose from 38% to 46%. Industry analysts say that the development of strategies such as the Industrial Internet and Industry 4.0 has driven more and more industrial equipment to achieve interconnectivity; however, the industrial network communication market remains fragmented.
