Fieldbus selection

[xJAyx]

Hello Everyone,
This are a bit slow in this forum lately so I thouight I would start a discussion about network selection, a subject I have often thought about but never really got to the bottom of.
I have worked with a wide range of protocols over a wide range of hardware, but no protocol really stands out as the clear winner for any particular situation.
So what makes you choose one network over the other if the hardware platforms can support it. Where do certain protocols shine and where do they fall short?

 

[JLSeagull]

Network selection is a very big topic. Different network communications protocols apply to different applications. Some trade name and profit issues mix with the technical topics. I will throw out a few thoughts and step way back out of the way to avoid being hit with the splatter.

Are you dealing mostly with sensor busses like transmitter inuts, switch inputs; more complex serial data networks like Modbus; or really complex high speed Ethernet, etc. such as the HMI interface?

Are you dealing within hazardous classified electrical areas?

What measurement or control response speed is required?

Are you hung-up with the "deterministic" vs error crash and burn issues? Ethernet is not deterministic although potentially orders of magnitude faster than deterministic networks.

Are you familiar with the open systems lingo such as physical layer, data link later, application layer, user layer etc.?

Foundation Fieldbus (tm) is a network based upon IEC 61158-2 and ISA SP50 standards. HART is a digital communication protocol imbedded on a 4-20 mA signal. Profibus (tm) is another field sensor network. Device Net is another sensor network used with motor starters and descrete data. ASi (pronounced Aussi) is another discrete network.

Is peer-to peer communication between devices a requirement?

What kind of distances are involved? For example, copper Ethernet is limited to a football field, multi-mode fiber suits about two km and single-mode fiber may commumicate satisfactorily for 20 km or perhaps 20 miles. And then there is microwave, ...

 

[xJAyx]

There is no specific application to this post, just wanted to start some discussion on the actual fielbus protocols, for example canbus, profibus, profinet, modbus RTU, modbus TCP, foundation fieldbus etc.
I know what they are and have used a lot of them, but what really sets them apart when hardware is not a factor (by hardware not a factor I mean if every piece of hardware in a system could support any protcol)?
This being a non vendor specific forum I thought we could have some worthwhile conversation on a topic that most of us deal with these days.
Basically what are the best protocols for each answer to JLSeagull's questions and why?

 

[controlnovice]

Try some information here:
thread830-157589
thread830-112825
thread830-107161


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