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Is it practical to use Ethernet for all industrial networking?
March 09, 2012
Dear Control Engineering: I was reading the article and watching the video about replacing various networking protocols with Profinet. I understand the desire to have fewer protocols, but is this a practical solution?
The variety of networking protocols that we have available grew out of a desire to have the right tool for the right job. Engineers have always wanted to match the network to the needs of the application. Here are some basic considerations:
• How much information has to be communicated?
• Does the system need to carry power to individual devices?
• Must the devices operate in a hazardous environment?
• How fast does the communication need to be?
Ethernet can work in just about any situation, but there are exceptions. To use a crude analogy, let’s say you wanted to reduce the variety of cars and trucks on the road so you could simplify repairs, manufacturing, etc. If everybody drove the same vehicle, maintenance would be much easier to deal with. So you give everyone a full-size white utility van. Problem solved. If you need cargo, you’re covered. Ladders? Put on a roof rack. Big family? Add seats. Some modifications are possible, but everybody has the same platform. Maybe it only gets 10 mpg, but it’s standard. That’s sort of the way it is with Ethernet.
Like a big van, Ethernet is good at moving large amounts of data, it can be fast, and it can carry power to devices. If your van is full of cargo or people every time you drive it, it all makes sense. But, if you commute 20+ miles to work and it’s just you, it’s lots of vehicle to move one person. A small car would be much more efficient for commuting.
Historically the thought of moving Ethernet to the shop floor was pooh-poohed because it was overkill: far too much expensive overhead for low-data devices. But the picture has changed. There are fewer low-data devices, and Ethernet is not as expensive. Field devices that used to be very simple have become more sophisticated and gained diagnostic capabilities. The infrastructure to process Ethernet-based data is less expensive, so the two extremes are moving closer together. If that big van can get 50 mpg and costs $10,000, maybe you won’t mind driving it all the time.
The challenge will be converting users and equipment manufacturers. More field devices that used to communicate via an analog signal or a fieldbus protocol will need to be changed to Ethernet. Users can’t make the change until those devices are available. Manufacturers won’t make them until they see demand. It’s an evolutionary process, and it could take some time for it to become a groundswell. Nonetheless, such technological changes are happening faster these days than they have historically, so don’t be surprised if it becomes a reality faster than you expected.
Here’s an explanation of how to evaluate an application and select the right networking tool.
Here’s a discussion on this topic from three years ago. How much has the situation changed?
Peter Welander, pwelander(at)cfemedia.com