Fieldbus

Has anyone done comparison of the performance of Foundation Fieldbus and Profibus systems? or know where can I search such a document? We need to network about 50 field instruments on a fieldbus to a PLC and therefore need to choose either of the above interfaces. Can anyone help? Thanks.

You will find a Fieldbus Portal (Comparison)
under http://www.dachs.net/fb_comp.htm

and a Fieldbus Classification under
http://www.dachs.net/fb_class.pdf

For 50 field instruments in a PROFIBUS network you have to use 2 segments, coupled by a repeater. (only 32 devices are allowed for one segment)

Best regards,
Armin Steinhoff
http://www.steinhoff-automation.com/

I have not had experience with Fieldbus have used Profibus before and have several systems running a profibus here at my current job. Profibus is widely used and many integrators consider it above others because of its reliability. One can even become easily certified in Profibus from their training program. They might be a little more expensive, but you will probably find that Profibus is easier to support in the long run, then Fieldbus will be.

Hope it helps.

Few PLCs will accept a Foundation Fieldbus H1 segment but many will accept Profibus segments so you probably do not have any choice here.

In any case, segment performance is related to length and loading. If you haven't done this before, consider having a control systems integrator supply the segment calculations and design drawings. In reviewing these you will learn much.

Hari,

If all you want to do is connect field instruments to a PLC for data acquisition, then either Profibus-PA or Foundation Fieldbus H1
will provide about the same performance. They use the same physical layer specification and run at the same speed.

First you need to determine which interfaces are offered by your chosen PLC supplier. For example, if you choose Siemens PLCs, you
will need to use Profibus since there is no support for Foundation Fieldbus. If you use Rockwell's Allen Bradley PLCs, you should
use Foundation Fieldbus since they fully support it. Profibus interfaces are available, but you become the system integrator.

The real reason to choose Foundation Fieldbus is to perform both signal conditioning and feedback loop control in the field devices,
rather than in the PLC. Doing control in the field devices reduces the performance requirement for scanning data.

Dick Caro
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CMC Associates
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +.978.764.4728
Fax: +1.978.246.1270
E-mail: [email protected] <mailto:[email protected]>
Web: http://www.CMC.us
Buy my books: Automation Network Selection
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Hi,
When it are fieldinstruments (such as flowmeters etc.), then you need Profibus PA with a DP/PA-Link and 2 couplers or something like that. The programming can be made with SIMATIC PDM and this package can be used under the SIMATIC Manager when you use S7 equipment above it.

Those Profibus PA instruments are to recognize with the power and data over one cable (with two wires, a Profibus PA cable). When you want to know how to do that then you might find a ebook on the link www4.ad.siemens.de and might search on Profibus+PA and for the wiring you can search on a ebook with the ID Nr. 1971286 "SIMATIC NET PROFIBUS Networks". In this ebook al the wiring and so on are discussed.

Please consider that the Profibus DP cable is NOT the same as Profibus PA cable !!

Best regards,
Lowiek

Well, I would like to put a software twist on that to put it in a different perspective.

First, there are some PLCs or PLC-like systems (it's hard to tell the difference between a DCS and a PLC these days) that offer FoundationT Fieldbus (plus plenty of DCS) so you do have a choice.

Many PLCs have an INTERFACE card for Profibus. However, please look beyond the interface card if you really want to benefit from network technology. Some of the Profibus solutions I have seen on some of the PLCs that are not
native Profibus do not have the SOFTWARE to support Profibus very well. These third party cards only handle the cyclic Profibus-DPv0 type of data. I.e. they may only support basic input/output. You need to work with many
tools to map this basic input/output data from one bus into the PLC memory registers. The PLC's software tool doesn't support the acyclic parameterization of the instruments introduced by Profibus-DPv1 used by e.g.
Profibus-PA so you need to have a second master connected to all your DP networks, i.e. a PC with interface card and software that supports EDDL or FDT/DTM. This may not be so neat using non-native Profibus PLCs. It is better if the instruments are supported by the same tool as you use to
configure the PLC itself.

The big deal with Fieldbus-H1/Profibus-PA is asset management, so you do want to have a PERMANENT connection of the EDDL/DTM tool to all DP networks (PA instruments coupled to DP networks). If you just connect the tool ad-hoc, you cannot continuously monitor conditions and manage your instruments as easily. Then, if all DP networks are joined together you better have a good solution for redundancy. However, I'm not so impressed with the redundancy solutions I have seen for DP (especially to mix DP devices from different suppliers), and for systems that don't have native support for Profibus there may be no DP redundancy at all. Please check to see what is offered. Anyway, my advice is that to benefit fully from Profibus you need support for EDDL or DTM in the software. And if more than a dozen devices depend on the backbone network it should be redundant.

Fieldbus HSE includes a true redundancy scheme far superior to any other open solution in the market. This makes a reliable solution for tying together all the instruments on the different H1 networks.

I.e. although fewer PLCs have Fieldbus interfaces, I would like to make the broad generalization that these few systems do a better job of supporting Fieldbus than what the other Profibus card systems do of supporting Profibus. If you look at the number of systems that have a full-fledged support of Fieldbus with DD in their software vs. those for Profibus supporting EDDL/DTM in their software I think you will find that Fieldbus provides more choices.

But, at the end of the day, you have to pick a bus supported by the PLC you already have.

Jonas Berge
SMAR
===========
[email protected]
www.smar.com
Learn fieldbus at your own pace: www.isa.org/fieldbuses

Why is Profibus easier to support?

FoundationT Fieldbus includes network and system management functionality such as automatic address assignment which saves you a lot of trouble, particularly for PA/H1 type instruments of which there are so many.

Jonas Berge
SMAR
===========
[email protected]
www.smar.com
Learn fieldbus at your own pace: www.isa.org/fieldbuses

There are many forms of Profibus and there are two forms of FoundationT Fieldbus. Since you want to connect field instruments you need to look at Profibus PA and FoundationT Fieldbus H1.

PA and H1 use the same physical media so the raw speed is the same. However, H1 provides modern communication relations ship such as scheduled publisher-subscriber which provide higher performance than the poll-response
used by PA. There are other differences as well.

Look beyond interface cards when you want to integrate instruments to your PLC.

The book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" discusses features and benefits of Fieldbus and Profibus in great detail. Based on this you can see which one fits you better:
http://www.isa.org/fieldbuses

If you can't buy the book now, you can download chapter 1 (overview) for free in softcopy form. It's free, but you must register an account. If your email does not support this hyperlink feature correctly, please copy the entire link and paste it into your Internet browser. Mind the line wrap, make sure to get the complete path all the way to the 4585:
http://www.isa.org/Template.cfm?Sec...=/Ecommerce/ProductDisplay.cfm&ProductID=4585

Jonas Berge
SMAR
===========
[email protected]
www.smar.com
Learn fieldbus at your own pace: www.isa.org/fieldbuses