By Ian Verhappen,
Networking technology has been around for at least as long as computers; however, it was not until the 1970s that the demand for permanent connection between distributed nodes became more important.
The emergence of the Xerox PARC Ethernet – a contraction of ether and net(work) – which 10 years later became the international standard native equipment in practically all computers, started the concept. In its initial applications, Ethernet was used for file and message transfer, as well as web page transmission.
The spread of information technology to all parts of industry by the 1990s led to the need for industry-wide connection. The World Wide Web – invented by CERN (the European Organization for Nuclear Research) in 1989 – was originally developed to enable different work teams scattered throughout the world to share information. The World Wide Web Consortium (W3C) was set up in 1994 to manage technical web developments.
As we know, the use of industrial protocols tends to follow the development of communications in the larger commercial environment. Since this is an industrial magazine, let’s take a look at the evolution of industrial communications between sensors and controllers.
Approximately every 20 years – which coincidentally is the life of a facility before it needs significant updates – control room technology evolves. Pneumatic pressure signals (3-15 psi) were the norm in the 1940s. This migrated to the 4-20 mA standard in the 1960s. Then, in the 1980s, smart processors combined with the digital processor-based control systems from the 1970s to make digital communications and, hence, bus networks possible. Of course, it took about 10 years for each of these technologies to gain traction and become the “plant standard,” but today digital networks are the norm for all installations. We are continuing this trend with the introduction of wireless systems during the first decade of this century.
Networks came in gradually – initially as serial links operating at baud per second speeds. Today, practically all protocols are also available as Ethernet-enabled versions, providing higher bandwidth over longer distances than was possible in the 1970s and 1980s.
The 1980s were a rich time for the development of industrial communications protocols, while the 1990s were known as the decade of the fieldbus wars. Below is a condensed chronology of the history of several of the major buses over the past 25 years.
• Modbus, a serial communications protocol published by Modicon in 1979, continues to be used to establish master-slave/client-server communication between intelligent devices. In 1996, Schneider Electric promoted the industrial Ethernet concept based on the addition of industrial tools and protocols, including Modbus, to existing standard Ethernet elements.
• The SERCOS (Serial Real-time Communication System) interface for digital communications, developed in November of 1985, has been used in machine engineering and has been implemented in more than 2.5 million real-time nodes.
• Robert Bosch introduced the CAN serial bus system at the Society of Automotive Engineers (SAE) Congress in Detroit in 1986. It was called the “Automotive Serial Controller Area Network” because CAN systems were originally developed for the automotive industry. Intel delivered the first CAN chip in 1987, and Phillips Semiconductors responded with a CAN chip of its own shortly after that. Motorola and NEC followed, and today, some 15 different semiconductor vendors build CAN chips. ISO published standard 11898 in November of 1993 to define CAN for general industry use, while the CAN in Automation (CiA) user group was founded in March of 1992.
• PROFIBUS (Process Fieldbus) for communication in the automation industries was launched in Germany in 1987 to a publicly sponsored alliance project with 21 companies and institutions participating. The original RS-485 Profibus DP (Decentralized Periphery) specification was targeted at the factory environment and was quickly followed by the Profibus PA (Process Automation) version to monitor measuring equipment via a process control system. Like many other networks, Profibus now includes support for Ethernet (Profinet) as well.
• Also in 1987, Phoenix Contact developed the Interbus standard for fieldbus technology, including an extensive line of fieldbus products that work with all of the major manufacturers of PLCs and other industrial automation controllers.
• The DeviceNet protocol, based on the CAN protocol, was introduced by Allen-Bradley in 1994 to serve the needs of the factory automation market and to connect its PLCs, controllers and distributed I/O products, including motor control centres.
• Also in 1994, two groups – ISP (Interoperable Systems Project) and WorldFIP (Factory Instrumentation Protocol) – merged to create the Fieldbus Foundation and to begin the development of fieldbus technology. ISP used an object-based client-server communication model at varying data rates as a function of distance. FIP included real-time capabilities using a publisher-subscriber model, thus necessitating a centralized control schema. The resulting Foundation Fieldbus combined features of both with client-server (pass token, report distribution) and publisher-subscriber capabilities in its object-based H1 specifications, which were published in April two years later. Then, in the spring of 2002, High Speed Ethernet (HSE) was released. Later that year, the Fieldbus Safety specification project was started; however, it wasn’t released until 2008. Like other protocols, this specification used the “black channel” approach, which removed the need to develop a new dedicated physical layer.
• The OPC Data Access Automation Specification, Version 2.0, OPC Foundation, was released in October of 1998 and provided a common interface that all protocols could use as a universal gateway. Developers no longer had to create a gateway to connect between every device on a system, but could now develop a single gateway between the protocol for their device and OPC, thus significantly reducing the complexity of multi-vendor installations.
• The CC-Link Partner Association (CLPA) started operations in November 2000 to promote CC-Link (Control and Communication Link) – an industrial network technology that allows devices from different manufacturers to communicate with each other – and manage the network specifications.
• The EtherCAT Technology Group was founded in November of 2003 by user companies who joined forces to support, promote and advance EtherCAT technology – the open, real-time Ethernet network originally developed by Beckhoff.
• The EDDL Cooperation Team was launched at Hannover Fair 2004 by the HART and Fieldbus Foundations, plus the OPC Foundation and Profibus user organization. The industry groups – along with more than 100 member suppliers of field devices and automation components that support Electronic Device Descriptions (EDDs) for their devices – saw EDDL technology as a key to decentralization and interoperability.
The first decade of this century saw the above fieldbuses evolve to provide support for safety buses, Ethernet versions and better integration with asset management systems. I believe this trend will continue in the near future.
What we know for certain is that all of these industrial protocols will continue to evolve, building off of their present IP versions to other media, such as wireless. At the same time, the protocols will expand their envelope of coverage to the manufacturing process, and become more tightly integrated with business systems, such as asset management and maintenance planning.
This column originally appeared in the September 2011 issue of Manufacturing AUTOMATION.