Profibus vrs Analog

Mark Buskell · Jun 22, 2005

I am currently quoting on a job. CompactLogix with 10 pumps and drives. The profibus card from SST is around $2500 and 2 analog inputs (IF8) and outputs (OF8C) are roughly the same price.

I will have some learning curve if I go with the SST card and none using straight I/O although I have used the SST Cards for profibus encoders in the past.

I checked on the pumps and drives and they both support DP so no couplers needed.

Other than wiring, can anyone think of a good reason to go with the profibus card vrs. traditional analog modules.

RussB · Jun 22, 2005

Diagnostics.

Werner · Jun 22, 2005

No errors on the signal. We had frequency inverters on analog signals from the plc. (0-10VDC). Even though the analog output of the plc is constant, the signal fluctuats a tiny bit. (5.1V instead of 5.0VDC for example). With profibus there are no such errors. If you start using profibus, make sure you get some information about maximum cable lengths en bitrates. 12Mbit/s is not possible over longer distances. Also for high bit rates (3Mbit/s-12Mbit/s) you need a minimum cable length of 1 meter. (Has something to with signal reflections on the bus).

TConnolly · Jun 22, 2005

I will have some learning curve....

So that next time you won't have to say that.

SimonGoldsworthy · Jun 23, 2005

Suggestion: Use analogue as the primary solution on all ten drives, but provide Profibus (as well) on one drive. If you get the time, you can "learn" the profibus system but at almost no risk to your project. OK you have to buy a Profibus card but you may be able "borrow" one from your supplier if he is keen to promote this type of solution.

RheinhardtP · Jun 23, 2005

Profibus

I think most new installation are moving to bussystems as a IO network with your discrete IO wired to a remote profibus node, alot of newly launched equipment cater for the profibus protocol, Ease of installation ,Ease Diagnostics, Faultfinding. No more messy wires in Control cabinets.

I love the idea, and where possible only use profibus with remote IO-->Profibus in the field and profibus on the drives.

Rheinhardt

Amr Hassan · Jun 23, 2005

Using profibus will allow you to collect more data just not the drive 4-20 ma and this is an advantage. If you decide to make a modification to your system , for example to see if the drive is tripped , using i/o u will have some complications while using profibus it will be easier

Ken Roach · Jun 23, 2005

If I may humbly suggest, you're going to get a much shallower learning curve, lower cost, and much better functionality using DeviceNet with CompactLogix than you will using Profibus with the same platform, just because the scanning and messaging are native to the controller instead of grafted on through a third party module.

If you can get those drives and pumps with DeviceNet, you're going to have a much easier time with this project.

Mark Buskell · Jun 23, 2005

Everyone has given me a lot to think about. I had just about made up my mind about Profibus till Ken's post about DH+. The meters are Endress+Hauser ProMass 83.

I see where it can save some wiring. On the drive, instead of having to wire a drive fault to a physical input, you could just read it over the profibus.

Ken, the processor is the CompactLogix L35E, not sure about DH+ that away.

Ken Roach · Jun 23, 2005

Confusion reigns

Maybe I'm not getting enough sleep.

You didn't say anything about flowmeters. I didn't say anything about DH+.

You might have to restate your system architecture before any experience or advice can be applied.

Mark Buskell · Jun 23, 2005

You are right Ken, I did misread your answer, did you ever read something and your brain saw it another way. (DeviceNet not DH+) I have found out a little more info on the meters since my first post. I have also did some research on the E&H profibus meters.

I also came across some articles about companies replacing their old meters and such with Profibus that was very educating.

Sleep now, reclaim brain cells.

Leadfoot · Jun 24, 2005

Using a network will simplify wiring. Watch the terminators. Only 1 needs to be on. You will most likely be able to change drive parameters from the master PLC. Profi bus need a continuous ground/shield connected on both ends and at every node to work right. With a networked sysetem you can connect at one point and monitor the TOTAL system. Yeah the up front cost is higher, but the long term benefits are worth the cost.

Then when the customer gets additional systems, the ability to network the plant is easier. BTW, you can network various mfgr's and networks on ONE system so I have been told.

BobB · Jun 24, 2005

you're going to get a much shallower learning curve, lower cost, and much better functionality using DeviceNet

A lot cheaper too and certainly does the job.

I use Device Net wherever I can quite frankly.

Profibus vrs Analog

Mark Buskell

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RussB

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Werner

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TConnolly

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SimonGoldsworthy

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RheinhardtP

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Amr Hassan

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Ken Roach

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Mark Buskell

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Ken Roach

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Mark Buskell

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Leadfoot

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BobB

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