Profi-bus or Ethernet

Shailesh10

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Join Date
Nov 2003
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Ranchi
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Hi :) friends & Experts & Gurus,

I am new to the PLC networking. Can U please give some points of differentiation or advatages/dis-advantages about when to use Profi-bus & when to use Industrial Ethernet connection.

If u can explain this in context of a configuration where many I/Os & remote I/os in field are there.Connecting to a Processor through bus. Again few HMIs and servers are located at upper level on a redundant bus. I also want this entire system to be connected to another plant having similar system having its own processor, I/Os and HMIs & Servers.

Please let me know what is preferable as a choice between Ethernet & Profi-bus at...

A. communication between I/Os & its processor
B. Communication between Server, HMI & processor
C. Communication between one plant to another and is it preferable at Server level or field level.

I hope i could be clear in my query..
Your expert opinions are awaited.
Thanking you...
:cool: Shailesh
 
Shailesh10,

Over the last few years, the practice at the various plants I worked at was to install both. This was because in the past the two were used for different purposes, and also Ethernet was often just not good enough for field bus jobs.
Ethernet is good for moving around large amounts of data that is not time critical, and Profibus was good at moving around many small, but time critical, chunks of data. Obviously, Profibus was best for machine control, and Ethernet for sending that word document to your boss.

This situation is changing. Ethernet is getting faster and more stable, and can now generally handle most field bus requirements. Profibus now also runs on Ethernet (called 'Profinet'), with converters to allow you to switch between blue and purple hoses.

In the future, I see Profibus slowly dieing off and being replaced by Ethernet, living on only as an Ethernet protocol. But that hasn't happened yet and there is still a long way to go. At the moment, the choice between them should probably be governed by what I/O you want to hang off them, and what PLC you want to use. It is no use choosing to install Ethernet if your PLC manufacturer hasn't yet released one with Ethernet capabilities, or if your main I/O devices won't communicate with it. It is also no good where you are modifing machinery with Profibus already installed.

Now to your questions:

Please let me know what is preferable as a choice between Ethernet & Profi-bus at...

A. communication between I/Os & its processor

Either, altough I would still go for Profibus because that is what I am familiar with and some of my favorite I/O still does not support Ethernet (but rumors have it that Ethernet modules ure under test).

B. Communication between Server, HMI & processor

Ethernet mostly. Server and HMI will generally be Ethernet, since these usually pass large amounts of non time critical data. HMI and Processor, Generally Ethernet as well, since I usually use either Siemens S7 or Modicon Quantum with Citect, and Ethernet is most convenient for this. Sometimes I connect an old Midicon onto Citect, and for that I generally use Modbus RS232 (nothing else available).

C. Communication between one plant to another and is it preferable at Server level or field level.

Server and Field are generally two different levels. Server, Ethernet is best. Field, you generally want some sort of peer to peer communication. Ethernet is better for this, but Profibus FMS could also be used (although I never used it). Actually, I am not sure if Profibus FMS is still a current standard.

Don't forget, Profibus is not the only field bus out there, although it is one of the best and most popular.

Hope this helps,

Doug
 

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