Moonachie, N.J.— The challenge for industrial Ethernet is often the same faced by traditional networking protocols—to deliver more open, plug-and-play solutions that can interface with users' enterprise-wide, intranet or Internet-enabled systems. Unfortunately, Ethernet faces many interoperability headaches similar to other protocols, such as a lack of standardization among drivers.

Acrison Inc., which manufactures dry solids feeding equipment, works with many network protocols when it sets up, configures, and tests its equipment for clients. Because of numerous, rapid weight changes handled by its feeders, the company uses a lot of algorithms in its homegrown "MD2" control system, which can update 300 parameters every 0.25 sec.

However, to meet growing customer demands for Ethernet products, Acrison is working with third-party suppliers to develop an Ethernet solution using TCP/IP and Modbus/TCP, an open protocol originally developed by Schneider Electric's Automation Business (North Andover, Mass.). John Laidlaw, Acrison's electrical engineering vp, says complete Ethernet implementation still needs a lot of work.

"Ethernet can be fine if you're working with standards like TCP/IP and Modbus. However, it's at the bottom of seven layers, and our problem is that you're limited in what you can do when you get to the top layers," says Mr. Laidlaw. "In general, our use of network protocols may not be what they were initially intended to support. Consequently, a protocol designed to handle 244 I/O points may not work right when we try to embed a data string. The product we want to communicate with still dictates the method.

"Our controls work with values that can quickly fluctuate from 1/1000^th to a billion in magnitude, and this highly dynamic range ideally requires floating-point values. Modbus is a 16-bit protocol, so its ability to easily handle ranges like this is limited. A lot of suppliers are in this position.

"Customers want updates very quickly, but reality limits how fast data can be refreshed. I think Ethernet will be a little easier for us to work with in the long run, but I don't think it will replace the previous protocols. The real carrot is high-speed Ethernet, though we don't know how all this will end up.""

For more information, visit www.modicon.com or www.controleng.com/freeinfo, or see this issue's "Many Benefits, No Magic Bus, in Networking Trenches" article, p. 122.