Already facing several choices when choosing a fieldbus network, engineers now have another-Ethernet. Yes, that's the same Ethernet IT uses to connect PCs to the enterprise and ultimately the Internet. Well, it is almost the same.

In the face of all the other fieldbuses with vendor groups, big company support, technical committees, and compliance testing, why is anyone looking at Ethernet? Mike Justice, Synergetic (Downers Grove, Ill.) president, says that customers are asking for it. They think that Ethernet will be faster, easier, and cheaper. They can leverage current infrastructure and training. He warns that these reasons can be true, but not for all applications.

Dave Hietanen, GE Fanuc Automation (Charlottesville, Va.) communication products product manager, notes, 'The primary drivers for using Ethernet as a fieldbus are that it's a standard, it's readily available, it's easy to set up, and the parts are relatively inexpensive. Since Ethernet is the most popular and widely used networking technology, many people are knowledgeable about how to implement and maintain it.'

Dick Caro is vice president at ARC Advisory Group (Dedham, Mass.) and a long timeproponent of Ethernet as a fieldbus. 'Foxboro I/A Nodebus has used 10base5 Ethernet for years,' he says. 'The new I/A Fieldbus uses 10baseT. As for connectors, RJ-45 is OK in the control room or switchgear center-or even inside an equipment rack. In high vibration areas, General Motors has shown that it gives intermittent connection. Woodhead Connectivity has built an RJ-45 inside an IP67 sealed bulkhead connector. I think Hirschmann will propose a pin and socket connector similar to the one used for Profibus which provides both vibration and sealing.'

A major criticism of Ethernet for control is its supposed lack of determinism. The basic TCP version is based on probability theory, that is, the probability of collisions among packets of data on the wire can be calculated. Given certain loading considerations, a design can predict a 'good probability' of the packet reaching its destination in good shape.

Addressing this issue, Mr. Caro states, '10/100baseT full duplex switched Ethernet is deterministic. Use of an active switch eliminates all collisions and the statistical setback that makes collision domain Ethernet nondeterministic. Switches do not even cost much these days.'

One of the problems encountered when discussing Ethernet is lumping various terms together under a single name. Ethernet really describes a physical medium and data linking. (See sidebar 'Protocols unveiled.') The issue goes beyond Ethernet to Internet Protocols. The 'other' fieldbus organizations are proposing putting their protocols on IP and Ethernet so that well known and highly developed IT networking technology can be the industrial networking architecture.

Mr. Caro adds, 'TCP/IP is the plain vanilla protocol that is easiest for the fieldbus groups to use, but it has many known deficiencies since it was designed for the public highly routed Internet. UDP is a simpler protocol that is much harder to use, but provides ways to improve performance on private networks. Modbus TCP has been public for almost two years and is the best example of taking a private protocol and mapping it to TCP/IP. Foundation Fieldbus HSE (high- speed Ethernet) is the best example of mapping to UDP for efficiency.

It is Type 5 of the new IEC 61158 Fieldbus 'standard.' This is the basis of publisher/subscriber protocol.'

Protocols are perhaps the most confusing part of understanding Ethernet for I/O device communications. Companies' marketing strategies bring on part of the confusion. In a rush to point out benefits of its strategy, a company may lead potential protocol users and automation designers to believe that the entire architecture is in a state of chaos. Actually, some protocols are 'open,' while others are 'proprietary.' There is almost always a way to extract information from 'proprietary' systems to 'open' ones.

One important thing to remember is pointed out by Paul Ruland, PLC product manager for Automationdirect.com (Cumming, Ga.). 'One of the benefits of Ethernet,' he says, 'is that you can run many transport protocols over the same wire. There really isn't any reason to limit the use of a protocol.'

Martin Wojcik, National Instruments (Austin, Tex.) FieldPoint product manager, says, 'The Ethernet-based FieldPoint system can coexist with the TCP/IP system that is already present. We do recommend a dedicated Ethernet subnet in order to address the issues of reliability and determinism.'

National Instruments industrial hardware engineering manager, Garritt Foote, stresses, 'TCP/IP is often used in place of IP which includes TCP and UDP. UDP and other messaging methods may be more appropriate for a particular application. The real advantage of using IP is that network administrators already have knowledge and a range of tools available to set up, maintain, and diagnose Ethernet networks based on IP. For example, an I/O network based on IP may be connected to a corporate IP network simply by using an IP router or gateway allowing data access across networks while maintaining a level of isolation.'

Why would it be advantageous to use a protocol based upon UDP rather than the 'plain vanilla' TCP? Consider this comment from Sixnet (Clifton Park, N.Y.) president, Steve Schoenberg: 'Among reasons to maintain a proprietary protocol would be that Modbus uses number addressing while tag names allow easy communication with HMI software. The beauty is, you don't have to choose. Different protocols run over Ethernet at the same time. Ethernet gives people choices.'

Robert Oglesby, president of Host Engineering (Johnson City, Tenn.) developer of the WinPLC for Automationdirect.com, says its version of UDP, which is registered, allows a search of every piece of hardware on the network with the protocol in its firmware. Functions like autodetect and autodiscovery are enabled. Control software can use this to show the programmer all the hardware in the system, enhancing configuration accuracy. Further, in one scan of the controller an output packet is sent for all I/O points with request for input status as the reply. Thus one scan can take the place of the usual four scans increasing speed.

Recently, the Open DeviceNet Vendors Association (ODVA, Coral Springs, Fla., www.odva.org) announced a DeviceNet over Ethernet initiative. Control and Information Protocol (CIP), originally developed for ControlNet, is being adapted for use with DeviceNet and labeled 'EtherNet/IP.' A caveat is that the 'IP' in this case stands for 'industrial protocol.' The protocol allows peer-to-peer and I/O messaging on Ethernet TCP/IP with DeviceNet or ControlNet devices or eventually with devices embedded with CIP in their networking stack.

Andreas Somogyi, Rockwell Automation (Milwaukee, Wis.) Ethernet product manager, highlights an important part of this protocol-encapsulation. 'Encapsulation allows a data packet to be embedded within CIP and sent over Ethernet TCP/IP. With future development, this packet could be sent over other networks, as well. This would be a powerful communication device.'

ODVA is offering seminars providing in-depth technical information to help developers bring Ethernet I/O products to market.

Microprocessors are everywhere. They can be found in toasters, automobiles, and an ever-increasing number of factory devices. Tom Edwards, senior technical advisor at Opto 22 (Temecula, Calif.) suggests, 'When choosing Ethernet I/O for your application, investigate local processing options and how they can improve overall system performance, reliability, and ease of use. With greater processing power, web servers can be installed on I/O systems revolutionizing access to these systems. With a browser, you can load a page to configure I/O points, test points, configure event/reactions and SNMP traps, set up report-by-exception, etc.

'Local intelligence at the I/O level can relieve a central processor from tedious and time-consuming tasks like raw data conversion to engineering units. In addition, performance of a distributed Ethernet I/O system tends to be independent of overall system size because each I/O unit contains a processor.'

Horst Kohlbert, Siemens Energy & Automation (Alpharetta, Ga.) network product manager, addresses the crucial cabling issue. 'Standard Cat5 [category 5, unshielded twisted pair, 10baseT] is good for a large number of applications, but when it comes to really nasty environments with floating grounds and so on, look for industrial cables. It's the same story for connectors. RJ-45 is good for the majority of applications within a cabinet, but when we leave the cabinet, we usually use 9-pin D-shell connectors.

'What I think we will see next,' he continues, 'are field devices with embedded Ethernet chips. Embedded Internet will become more of a reality. Direct connectivity to the Internet really ignited things; it's the biggest benefit of the whole 'Ethernet everywhere' idea.' (Control Engineering, June 1999, cover story.)

Staffon Dahlstrom, vice president at HMS (Chicago, Ill. and Halmstad, Sweden), reports, 'We use the RJ-45 connector, but we also have 9-pin D-shell as an option. This connector is already standard for Profibus and ModbusPlus and widely accepted as an industrial connector.'

John McGilvreay, Hirschmann (Pine Brook, N.J.) automation network solutions group, says, 'The key to implementing Ethernet I/O architecture is switching technology. Within each control domain (comprising a controller, one or more Ethernet switches, and connected devices), controllers communicate with their attached devices through a switch that routes each TCP/IP packet through the appropriate port to the correct destination. For real-time applications, it's best for each device to have a dedicated full-duplex port. Depending upon the application, either wire or fiber can be used to connect the controller and devices.'

Another useful hardware device is an interface to connect serial communications to Ethernet. Mark Fondl, vice president of Lantronix (Irvine, Calif.), describes a device 'which can connect not only new devices but also any device that has a serial port. We are active in a number of fieldbus to Ethernet initiatives.'

Is using Ethernet on the factory floor a theory with a bunch of crazy evangelists loudly crying in the wilderness? Hardly. Several companies have offered Ethernet for I/O module communication for two to three years. All report growing acceptance and sales of Ethernet products.

Host Engineering's Mr. Oglesby responds, 'I haven't had a single customer complaint since we started shipping Ethernet I/O. Customer acceptance has been great.'

Opto 22 has offered Ethernet since the last quarter of 1998 and keeps adding refinements, like wireless access and SNMP for network management.

National Instruments has Ethernet communications to its FieldPoint I/O. Sixnet also offers Ethernet I/O modules. Schneider Electric (North Andover, Mass.) offers Ethernet connectivity to its Momentum I/O product.

Ethernet I/O connectivity continues to attract new products and players. Last year, Optimation (Huntsville, Ala.), a new company, announced Ethernet I/O modules. Automationdirect.com and Omron Electronics (Schaumburg, Ill.) have new product announcements in this article. GE Fanuc Automation announced at National Manufacturing Week that all of its automation devices will support Ethernet connectivity. Zoneworx (Temecula, Calif.) has introduced its first suite of products billed as the infrastructure enabling legacy devices access to Ethernet TCP/IP.

Steve Ewankowich, global account manager, applied materials for Schneider Electric, reports that ModbusTCP over Ethernet TCP/IP has achieved status as a standard in the semiconductor industry-SEMI E54.9-2000, Specification for Sensor/Actuator Network Communication for Modbus/TCP over TCP/IP).

Perhaps a glimpse of the future can be found in JetWeb by Jetter AG (Ludwigsburg, Germany, and Broadview Heights, O.). This product distributes control over Ethernet and promotes 'the network is the controller.' Certainly Ethernet can empower a vision of distributed control and universal information access for those who wish to bring it into reality.