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Modbus: Does it deserve more respect?
It seems lately I keep encountering Modbus references which have driven me to spend more time researching some of its fine points. For example:
1. The Profibus folks don't consider it a real fieldbus architecture, but more of a messaging system and one that may be a little too open allowing various vendors to create peculiar variations that aren't always compatible.
2. In a podcast (available next week) Randy Underwood from EPCO and the Honeywell User Group steering committee, bemoans the fact that most DCS providers don't like to support it and would much prefer to work with platforms like Foundation Fieldbus.
3. I was talking to Bill Tatum from Foundation Fieldbus, and he considers it primitive compared to FF, in that it lacks sophisticated diagnostic capabilities and functions like data mapping, assigning registers, etc. have to be done manually much of the time.
3. Moore Industries likes it for transmitting HART data and the like (Watch for an article in the Process Instrumentation & Sensors Monthly coming out Thursday. Subscribe if you don't see it.) because it is flexible, reliable, and inexpensive.
Modbus apparently exists in a lot of plants and showed up in our last Product Research on Networking at just under the 50% mark. That's pretty impressive. Still, if you want pieces of process instrumentation with Modbus connectivity, you'll have to hunt. There really isn't much out there. Most of the time you will need to use an interface to convert your 4-20 mA into a Modbus signal. There's no provision for power to an instrument via Modbus.
For one of those "legacy" technologies, it shows up everywhere you look if you're paying attention. Of course if you were launching a new project and considering various networking / wiring topology options, Modbus probably wouldn't be the top on your list. Current fieldbus architectures offer lots of advantages. However like many old technologies, it has formidable capabilities. Watch for more on it in the September Process & Advanced Control newsletter.
Modbus: Does it deserve more respect?
August 14, 2007
It seems lately I keep encountering Modbus references which have driven me to spend more time researching some of its fine points. For example:1. The Profibus folks don't consider it a real fieldbus architecture, but more of a messaging system and one that may be a little too open allowing various vendors to create peculiar variations that aren't always compatible.
2. In a podcast (available next week) Randy Underwood from EPCO and the Honeywell User Group steering committee, bemoans the fact that most DCS providers don't like to support it and would much prefer to work with platforms like Foundation Fieldbus.
3. I was talking to Bill Tatum from Foundation Fieldbus, and he considers it primitive compared to FF, in that it lacks sophisticated diagnostic capabilities and functions like data mapping, assigning registers, etc. have to be done manually much of the time.
3. Moore Industries likes it for transmitting HART data and the like (Watch for an article in the Process Instrumentation & Sensors Monthly coming out Thursday. Subscribe if you don't see it.) because it is flexible, reliable, and inexpensive.
Modbus apparently exists in a lot of plants and showed up in our last Product Research on Networking at just under the 50% mark. That's pretty impressive. Still, if you want pieces of process instrumentation with Modbus connectivity, you'll have to hunt. There really isn't much out there. Most of the time you will need to use an interface to convert your 4-20 mA into a Modbus signal. There's no provision for power to an instrument via Modbus.
For one of those "legacy" technologies, it shows up everywhere you look if you're paying attention. Of course if you were launching a new project and considering various networking / wiring topology options, Modbus probably wouldn't be the top on your list. Current fieldbus architectures offer lots of advantages. However like many old technologies, it has formidable capabilities. Watch for more on it in the September Process & Advanced Control newsletter.
Posted by Peter Welander on August 14, 2007 | Comments (0)
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