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Doubts about its reliability have proved to be much exaggerated or even false. Future products, including field devices, will greatly expand on the vast bandwidth made available by high-speed Ethernet.

Traditionally, "the experts" would eschew the thought of putting Ethernet in the same sentence as process control. They regarded Ethernet as so nondeterministic that it couldn't transfer any critical information.

As a result, proprietary and standard network protocols were created to provide highly deterministic data transfer. Meanwhile, Ethernet, with all its faults, continued its march on the office data networks, conquering token bus, token ring, AppleTalk, ARCnet, DECnet, asynchronous transfer mode, and all other local-area networks (LANs) to the desktop.

Ethernet has proved to be highly reliable, very fast, low cost, and essentially risk free for office applications. Thus, use of Ethernet for networked PCs, e-mail, and Internet access in the workplace has surged. Is this happening in industrial automation as well?

Critical data not lost
Ethernet has begun to appear as a standard product on industrial automation LANs—not as a strategic interface but more as a convenient means to connect to office LANs. These interfaces began on programmable logic controllers (PLCs), replacing slower EIA-485 or -232 interfaces. Suppliers of remote I/O modules and multiplexers have added Ethernet interfaces to enable the integration of their devices into PC-based control systems replacing conventional PLCs.

Now Ethernet is available on practically all I/O modules made by PLC companies and third-party I/O suppliers. Vendors of automation products are leading this stampede, and users are responding by purchasing these systems. Behavior has been excellent and problems few. The predicted loss of critical data has not occurred. Users are pleased.

Enabling this success has been the dramatic decline in the cost of Ethernet adapters for the PC and many changes in the products and standards supporting Ethernet. The selling price for a PC add-in board has dropped. Many PC suppliers include an Ethernet interface on the basic PC motherboard at no additional cost.

The IEEE 802.3 standards for Ethernet have provided speed increases, from the original 10 megabits per second (Mbps) to Fast Ethernet at 100 Mbps and now to gigabit (1,000 Mbps) data rates. Wiring for Ethernet has progressed from costly 4-shield, difficult-to-install 10Base-5 thick coaxial cable to less costly 10Base-2 Thinnet coaxial cable to inexpensive 10Base-T category 5 unshielded twisted-pair wiring.

For plant use, shielded twisted-pair and even 10Base-FX fiber optic cables are available. These provide the noise immunity and isolation needed for the worst industrial environments.

Determinism issue solved
Finally, data communications suppliers have responded to the need to segment large, flat Ethernet networks, which are suffering from delays resulting from collisions, with active switching hubs. In fact, Ethernet switch prices have also dropped from prohibitive levels to the point of being inexpensive, in just a few years.

It is the Ethernet switching technology and its low cost that enable recovery from the classic Ethernet problem of nondeterminism caused by the protocol's stochastic recovery from collisions. Determinism is defined as the ability to deliver a message between any two points in the network with an acceptable (to the concerned application) and predictable worst-case delay.

Switched Ethernet solves the determinism issue by enabling network configurations with only one Ethernet device per segment using 10Base-T wiring between each device and the switching hub. Synchronization is an issue not resolved by Ethernet protocols. Few other network technologies have resolved it either.

In development or already announced are Ethernet versions of Foundation fieldbus, Profibus, DeviceNet, ControlNet, and LonWorks. Each of these encapsulates its native messages within an Ethernet frame and delivers them across an Ethernet or even Internet link. All of these implementations use Internet protocol and can coexist on the same network. Interoperability, however, is a concern that must wait for future networking technology developments.

Don't expect it this year
How far will Ethernet eventually reach into the industrial automation market? All indications are present that Ethernet could reach all the way down to the sensor and actuator, but don't expect it this year. The low-cost and low-power technology needed to enable this degree of Ethernet penetration has not yet appeared.

However, silicon chips that were invented to support the networks developed to run Ethernet through simple telephone wiring will probably make Ethernet more affordable for automation products. These chips will provide full Ethernet support at 1–2 Mbps on unshielded twisted-pair cable and will be inexpensive because they will be mass produced for networking home appliances and home computers.

The Foundation fieldbus high-speed Ethernet (HSE) project produced a final specification in 1999 and will result in product this year. This technology will provide Foundation fieldbus with its much-needed bridge to link slower H1 segments into a single two-level network.

HSE, based on the suite of Internet protocols, should open process control fieldbus networks to the plant backbone network. HSE is an important step in opening factory automation networks, but it does not itself open sensors and actuators to broad Internet access. It provides the protocol for moving all of the Foundation fieldbus functionality to a field device using Ethernet.

Why should Ethernet reach down to the field device? Network technologies such as DeviceNet, LonWorks, Profibus-DP, and WorldFIP have the capability (bandwidth) to address increased field device functionality. Suppliers, however, have completely ignored this capability.

Users are generally unaware
One reason users ignore new features with potentially valuable benefits is the enormous cost they would incur to implement and then support the technology on multiple architectures.

Also, few suppliers have felt pressure from end users to supply such solutions. Users are generally unaware of these potential benefits, nor have they felt any competitive pressures. They are simply not providing their sensor or actuator products with the intelligence or communications bandwidth necessary to support advanced diagnostic or application features.

However, suppliers of systems on chip (SOC) technology with built-in Ethernet support and low power consumption are now making these products available at ever-decreasing prices. SOC vendors sell their products to the major device suppliers as a means to easily "Web enable" their products. This gives the most basic sensors and actuators an Internet-addressable presence.

Finally, IEEE 1451 technology is now out in the market and offers to bring Ethernet all the way down to the field sensor or actuator. While this technology can work with any network protocol, it has already shown it can work with Ethernet.

IEEE 1451 makes the field device appear to be an automation object with methods and attributes. Ethernet serves only as the conduit to tunnel between the field object and the host controller.

Intelligence is rapidly moving to field devices in applications beyond process control where it is already pervasive. The addition of high-bandwidth networks makes it possible to communicate with field intelligence. New functionality in smart sensors and actuators will enable better control and lower cost production.