Selecting an automation network

re you trying to make sense of all the different industrial automation networks on the market today? Whether you're a novice industrial network user or someone who simply needs to brush up on the technology, Automation Network Selection will help you better understand and select the "right" network for a given application. Author Dick Caro walks you through the various industrial networks (e.g., sensor, fieldbus, control, safety buses, and so on) and then gives you a perspective on the typical applications for industrial automation network technology. The emphasis is on the intended application for each network, rather than on the network protocol that is more typically discussed in most textbooks.

All process industries in general and water/wastewater in particular will be migrating to some form of fieldbus systems over the next half-decade. Caro’s book tells you why. The various fieldbus products are described and key features of fieldbus vs. current common buses and networks are identified and compared. The book is recommended for all technical persons from technicians to plant managers—anyone who may benefit by gaining a decision-making understanding of networking in the process industries.

An appropriate subtitle for this book could well be: All You Wanted to Know About Fieldbus But Were Afraid to Ask. It is written at a technician level; in a text format. The trend to integrating Ethernet to device levels is well covered, as are special needs of process networks such as intrinsic safety and powering devices from the network.

Author Dick Caro merits special mention. His process control engineering career parallels major advances in process control technology along with the emergence of digital methods for data handling & networking. He served on the ISA SP-50 and the IEC SC65/WG6 Fieldbus committees for over a decade; about half as the Chair. Leaders of these committees suffered through exasperating company and international pressures.

Why are there so many different industrial automation networks? Why can’t there be just one network? We hear these questions very often. Indeed, it could have been, but… Well that would be a long story too.

Here is the short version. In 1985, a bunch of us recognized the need for standardizing network communications for process control and we tried to prepare a standard in advance of the competition under ISA’s SP50 standards committee. We called our effort fieldbus since it was meant for field instruments. Almost immediately, we were joined by suppliers of programmable logic controllers (PLCs) who believed that they needed to standardize upon their remote I/O networks and we could share the same technology. We completed the physical layer protocol (wiring/cabling and signaling) in 1989 and the data link layer protocol in 1993. However, by then there were already numerous competitive commercial networks. The standards work was eventually completed in 1999 with the adoption of many of these commercial network architectures into the international fieldbus standard IEC 61158, which contains eight different protocols.

Market forces could not wait for a standard, and the standard could not incorporate all market forces into a single protocol. Not only that, but a standard cannot immediately, if ever, displace already implemented commercial products. Five of the network technologies included in IEC Fieldbus standard represent commercial products other than the two prepared by the Fieldbus Foundation based on the parts of IEC 61158 that were developed as the ISA S50.02 Fieldbus standard. One protocol has never been implemented.

I chaired both ISA SP50 and the IEC SC65C/WG6 Fieldbus committees for the end of their efforts. They were very turbulent times. Cullen Langford, a user from DuPont, chaired these committees during most of the time that they were creating the fieldbus protocol, while I was a contributing member of the user layer subcommittee. Being surrounded by some of the brightest people in the universe was a rare privilege and the experience of a lifetime. I didn’t enjoy many of the political moves being made by major manufacturers, but it did provide a challenge to my management style.

While politics was raging in the ISA/IEC committees, discrete automation identified by the use of PLCs was also developing rapidly. For a while, it appeared that one of the standards bodies, NEMA (National Electrical Manufacturer’s Association), was going to use the highspeed version (H2) of ISA’s fieldbus. However, NEMA concluded that H2 standards were too expensive and too complex for use in discrete manufacturing. As a result, most of the data communications buses developed by PLC manufacturers were incompatible with each other and did not conform to a standard set of specifications. Most of the manufacturers countered criticism about the “closed” nature of these protocols by forming “open” groups 1-2 to make the long-term evolution for each of these bus technologies independent from the originating manufacturer. These open bus associations contributed five of the additional protocols to the IEC eight-part fieldbus standard.