Control Net vs Profibus

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Thread Starter

Chris Corne

Hello,

We are in the process of choosing our PLC platform for upgrading our melt shop and casting processes. We have narrowed the choices down to the A/B Control Logix or the S7 400 series products.
There are reasons that we like and dislike going to either option, specifically support, availability of spares and training, ease of programming, etc. The question I would like to ask is about the network for each. The availability of Profibus components and manufacturers is quite extensive. We are also familiar with profibus, as we are using it now.
A/B brought a fellow in here to demo Control Net, and of course he believed it to be far superior with it's consumer/producer model. But we don't see much support at all for this network from other manufacturers. It's touted
as being an "open" protocol, but I guess being "open" and being supported are different beasts altogether. Any information would be appreciated, I'm even open to discussion of the Control Logix vs. S7 altogether.

Thank you for any consideration,

Chris Corne
Melt Shop Electrical
Nucor Steel Arkansas
(870) 762-2100 ext 239
 
Just a thought,
If you are already familiar with AB and want to have the best of both worlds try looking at Profibus and AB via a SST Profibus Card in either the SLC5 rack or in the PLC5. The AB people don't like this because they do not have a Profibus card of their own. You can now use anyone's remote I/O you want with very fast speed.

www.mysst.com

Good Hunting


Brian Rode
 
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If I recall correctly, AB (in Europe ?) developed a Profibus card but it was dropped by them and transferred to SST. I've encountered the SST Profibus scanner in several applications and it is an excellent product.

My own take on Profibus DP V DeviceNet having worked on development of slaves for both over some years is that they're pretty much equivalent in capability, though Profibus DP is simpler to apply and has somewhat better throughput when dealing with mid-level devices (max scan payload for I/O data being 234 bytes each way, with DeviceNet using 8 unless fragmentation is used which chews bandwidth). I would personally use Profibus if it were my plant and I had full control over the PLC to be used, but wouldn't lose
sleep if I had to use DeviceNet.

ControlNet seems to me to be losing ground - when I looked at it the chipset was very expensive and I don't think third party support is tremendous
compared to Profibus/DeviceNet. I'm expecting Ethernet/IP to largely replace ControlNet per se.

Tim Linnell (Eurotherm Controls)
 
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John Paley--Graphic Pkg Corp

Hi,

I'm not sure whose network is the best, but I wouldn't use the siemens s7 just to get profibus.(sst has an a-b compatible profibus card). We just purchased a european machine with the s7-400 processor. It has been programmed in statement language with no hope of converting to ladder without a big price tag (they'll have to re-write the code--europeans just like to write code in statement text and they don't care whether the customer can read it, or not--siemens says that it will translate to ladder but lines of statement code that are needed to convert are not needed to execute and therefore, often left out of the program.) I just attended a siemens s7 school after the machine delivered and if I knew before what I know now, the damn machine WOULD HAVE BEEN WRITTEN IN LADDER!! From what I've seen of statement code, it's just too damn hard to troubleshoot. (The software engineer who wrote the code came to our plant and had a hell of a hard time figuring out what to change where to get the thing commissioned--he wrote it--that's hard to follow in my book)

I know i'm a ladder junkie from the old school--and I learned on and most always use allen bradley, but this s7 stuff just seems like a nightmare. I think it's not only different--but it's harder--with the potential to be near impossible!
 
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Andrew Piereder

Actually, Rockwell is somewhat conflicted about it. Rockwell phased out its own Profibus scanner probably for political reasons, figuring that a
third party product provided them with both a fig leaf and a way to crack open the European market. For obvious reasons, AB people aren't crazy about promoting Profibus I/O compatibility with there ubiquituous SLCs in the home market.

Andy Piereder
Pinnacle IDC

 
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Bob Peterson

If you want to see conflicted ask them about their Interbus interface. At one time they flat out denied to me that it even existed. Then they told me is was only available in Europe. When I pointed out that several places in the US already had them, they told me that these end users had
some kind of special permission from AB to use the Interbus interface in the US.

This was a few years ago so perhaps they have had a change of heart by now, but they have always been very protective of their I/O sales.
Allowing you to easily connect up to all kinds of other I/O just is not in their best interests because their I/O is more costly and generally less flexible then some others.

This is akin to the situation that existed when the SLC first came out and they did not come out with remote I/O for the SLCs to reduce the impact on 1771 sales. Eventually they did come out with RIO for the SLC I/O, but they strung it out over a long period of time, and made it difficult to
use to encourage you to use the 1771/PLC5 platform for RIO systems.

Finally they were forced by market conditions to allow full use of RIO with SLC I/O systems. But they fought it all the way.

Personally, I do not blame them at all. Their job is to maximize profits (among other things) and thats what they did. It certainly has not hurt
them any (at least in the medium term).



 
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Hi All,

I'm with you John !. We made a choice many years ago to stick with AB PLC's the *new 5/25* (having learned on PLC 2's) against the competing S5 range of PLC's. Most of the reasons were people just were not comfortable with the STL programming style and the poor quality manuals. The translation's into English seemed to be done on the back of a postage stamps. We still have
some S5's but nobody goes near them much. I have always felt that they were probably really powerful PLC's and always perhaps ahead of AB in what they were capable of but the trade off was not worth it.

It's a strange process you go though because we have drive controllers from Siemens, AB, and Toshiba, both AC and DC, yet we wouldn't go past Siemens if we had the choice on brand alone they kill the AB stuff. The ability to mix and max different Fieldbus's has come along way since the old days. The best solution if your a AB person is get the SST profibus module for your AB
plc/slc and have the best of both worlds.

Neil F.
 
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Michael Griffin

I also don't have any opinion to express on Control Net or Profibus, but I can offer some suggestions which may help with Mr. Paley's S7 program. If the program you have is like the typical S5 statement list monstrosities I have had the misfortune to have to work with, there are ways of fixing up parts of it.

The usual reason why a rung (or "network") won't convert to ladder is that it is actually several independent rungs. If you split up the independent parts into several rungs, most of the new rungs may convert to
ladder. If you do a copy and paste on a rung, you can get several copies of it. You would then erase different parts of each copy to get several new simpler rungs in ladder.
Certain parts of the program won't convert without completely replacing them, but you should be able to get the majority into ladder just by splitting things up as mentioned above. The remaining difficult part is probably best left alone.
There are certain things which you cannot do in ladder with an S7-300/400, but most of these are things you wouldn't really want to do
anyway. One of the exceptions may be using the block move SFC (SFC20 if I recall). It takes about a half a page or so of very obscure statement list just to set up the pointers before you can call it. I would simply encapsulated all that into an FC so that nobody has to look at it if they don't want to.

I am just completing a project using an S7-300 which is similar to (but simpler than) a machine which we used an S7-200 in previously. I have noticed that it is taking considerably more effort to use the S7-300 in this project than it did to perform equivalent features with an S7-200. The S7-300 documentation (your S7-400 will be similar) is very poor and unorganised. I have also found there seems to be a lot more steps required to accomplish an equivalent task.

I don't think that I would say that Europeans like statement list though. I work with several electricians of European origin (Polish and German), and they don't seem to like it any better than anyone else does.
What I have noticed is that statement list and Siemens S5 and S7-300/400 PLCs seem to appeal to people who like to fiddle with things, or who like complex intricate things for their own sake. It can be an interesting toy to play with if you ever lose sight of the fact that you
have a job to accomplish.

You mentioned that the original programmer had difficulty reading his own program. That does not surprise me. Nicholas Wirth once said something to the effect that programming languages exist to make it easy for
people to read the program, not for computers to execute them. Statement list is a poor programming language by that criteria.

There are some good features in the S7-300/400, but unfortunately Siemens seems to have kept most of the bad ones from the S5 as well. Most of the features of the S7-300/400 PLC can be used in ladder mode though. You should be able to specify this in future projects. A few features *have* to be used in statement list, but you should be able to require that most or all of these be encapsulated in small FCs.


At 17:15 05/09/01 -0400, John Paley wrote:
<clip>
>We just
>purchased a european machine with the s7-400 processor. It has been
>programmed in statement language with no hope of converting to ladder
>without a big price tag (they'll have to re-write the code--europeans
>just like to write code in statement text and they don't care whether the
>customer can read it, or not--siemens says that it will translate to
>ladder but lines of statement code that are needed to convert are not
>needed to execute and therefore, often left out of the program.) I just
>attended a siemens s7 school after the machine delivered and if I knew
>before what I know now, the damn machine WOULD HAVE BEEN WRITTEN IN
>LADDER!! From what I've seen of statement code, it's just too damn hard
>to troubleshoot. (The software engineer who wrote the code came to our
>plant and had a hell of a hard time figuring out what to change where to
>get the thing commissioned--he wrote it--that's hard to follow in my
>book)
>
>I know i'm a ladder junkie from the old school--and I learned on and most
>always use allen bradley, but this s7 stuff just seems like a nightmare.
>I think it's not only different--but it's harder--with the potential to be
>near impossible!
<clip>

**********************
Michael Griffin
London, Ont. Canada
**********************

 
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Andrew Piereder

I had that happen as recently as a year ago with an AB distributor. In fairness, this could be an easy mistake to make since these "foreign"
backplane modules are not included in the Encompass program and are not shown at AB Automation Fairs.

Andy P.
 
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John Paley--Graphic Pkg Corp

Thanks for the conversion tips. I'll get into the code and see what I can do.

j paley
 
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Shahid Waqas Chaudhry

Sorry, this is definately off topic but I am learning to program AB (I am a siemens programmer).

Can you make a Function (or Function Block) in Allen Bradley (I believe they call it files) so that you can pass formal parameter to it (like the IN, OUT, IN_OUT parameters in the S7)? Also, can we recall a same function (or function block) multiple time (with different parameters)?

Personally, I think just plain ladder spoils the taste of programming. We should have a choice to select between available languages which we can
choose according to our requirement. The emphasis should not be using Ladder, STL or FBD (or Graph or SCL) but documentation. A well documented
software is a no problem to anyone.

Shahid
 
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Ralph Mackiewicz

Their motivation comes from the fact that PLC manufacturers are lucky to break even selling processors. The vast majority of their product
profits comes from the I/O. If everybody bought AB processors and Opto22 I/O (or whatever) AB would not be around very long.

Regards,

Ralph Mackiewicz
SISCO, Inc.


 
C
John,

Thanks for your reply, I appreciate your reply along with the others who have helped in our decision. Just one of the many things that makes this list great!!

Our decision to go with S7 would not be based solely on profibus. We have an all Siemens platform here now, and do not have issues with code written in STL. I will submit that no one here, though prefers to troubleshoot the process while getting through STL code. Some like Ladder
representation, others (myself) prefer CSF (FBD now in S7). The S5 platform though would not let us take advantage of the PLC's power without using STL for some functions. What I have seen with the S7 interface is that a majority of the program instruction set can be represented in Ladder or FBD, and what cannot should be "packaged" into a Function call.

On the A/B control logix platform, the guys here who looked at it were very impressed with it's "eye-appeal". They believe that the interface has a slicker look to it. The program seems to be as easy to use as a MS Office
product. Configuration of analog inputs also seemed to be better that what others have to offer. And most believe that our phantom "next-hire" tech will be able to learn the A/B system quicker than they would be able to pick up Siemens.

Unfortunately, the decision is not mine..my job is to give the boss the options. The last thing he is waiting to here has nothing to do with what we've all talked about up to now....it's about price!! The two companies
should have their bids in by the end of next week, then it should get interesting!

Chris Corne
Melt Shop Electrical
Nucor Steel Arkansas
(870) 762-2100 ext 239


 
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rameshbparmar

Hello Chris,

We are expanding our plant activity & we are going for control system. We come across AB-Control Logix , Delta-V, &CS-1000. As you aware of Control Logix i Want to Know that What Type of System is This?(Control LOgix)Is it PLC or Higher end PLC. Also I want to know that is SCAN time is configurable in Control Logix. In addition how much I/O can we configure in one controller.

Please mail me the details.

Waiting for your reply.

Thanking You.

Yours Faithfully,

Ramesh B. Parmar
[email protected]
 
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