Siemens or Allen Bradley ?

[Paul B]

In america i think it's better for service and support from Siemens to use their web service instead of trying to reach someone on the phone.

Not so! The Siemens hotline in Johnson City, TN is first class. I call all the time and always receive expert advice in no time at all. I'll call, open a case, they verify my phone number and I get a call back within less than an hour. No waiting on the phone at all. The support is first class, better than GE or AB and I call each about as often. I have spoken to several different support engineers, some multiple times on different problems over the last ten years. I have nothing but good things to say about the Siemens Hotline.

 

[Peter Nachtwey]

Hi, will soon be evaluating our current manufacturer against Siemens and Allen Bradley, interested to hear peoples opinions before we get the sales\tech guys in to see us.

All our comms is ethernet. Important to us is Modbus TCP so they must be able to support this pretty much out of the box.

Rockwell has the superior Ethernet implementation but it isn't Modbus/TCP. If you want to know why Modbus/TCP is lame compared to Ethernet/IP you can ask.

Our current software is IEC compliant so again this is a must as most of our DFB's are developed and set in stone.

What is a DFB?

Siemens S7 supports Modbus TCP. But each CPU that uses this protocol require a special license.

Now that I have done some Siemens Ethernet programming I know I can easily implement Modbus/TCP in STL and LAD. The problem is that it is inefficient. The customer I wrote my Siemens Ethernet driver for decided on Profibus instead. Modbus/TCP has no concept of aligning data on 32 bit boundaries.

There is another problem with TCP. If there is a failure the TCP stack will retry with old data. UDP can retry with new data.

Surely OPC is the way to go

OPC is server software an has nothing to do with the communications between the server and the slave I/O devices. The slave I/O devices speak Ethernet/IP, Modbus/TCP, FINs etc.

 

[Brodin]

Too bad that's not true in my geographical location, there is definitely something lacking from the local sales people.

Granted it has been about 7 years since I was up there, but Electro-Matic in Farmington Hills was very responsive for all of our Siemens stuff.

 

[Fiddeflygare]

I'm not sure if it matters in your situation but have you considered Beckhoff? They have much cheaper licenses and parts compared to Siemens exept in a few cases where you need to run many servos. And the Twincat programming tool and CX control units in my opinion is very versatile. Just a hint for you to check. I know it shouldn't be a problem to intergrate Modbus Comm in their systems either.

 

[Jeff23spl]

]Rockwell has the superior Ethernet implementation but it isn't Modbus/TCP. If you want to know why Modbus/TCP is lame compared to Ethernet/IP you can ask.

I want to know, because one major difference i experienced between ethernet/ip and profinet is that profinet only poll the specified client when ip fill the network with many empty packet trying to reach everyone....I know it doesn't hurt but some computer freak bother about it....
I didn't get bad feedback about traffic where i did a modbus tcp projet..


What is a DFB?


Now that I have done some Siemens Ethernet programming I know I can easily implement Modbus/TCP in STL and LAD. The problem is that it is inefficient. The customer I wrote my Siemens Ethernet driver for decided on Profibus instead. Modbus/TCP has no concept of aligning data on 32 bit boundaries.

When doing it, i convert my data to 16 bits data block and it works fine. But i more usually use modbus RTU

There is another problem with TCP. If there is a failure the TCP stack will retry with old data. UDP can retry with new data.
Maybe, i didn't have problem with it but my application wasn't critical with a few second comm failure...?

 

[nickephx]

I see that the topic has strayed a little, but I thought I would put in my two cents...

I just posted an article with some practical comparisons of Siemens and Allen-Bradley use of modular functions. I focused on RSLogix5000 and Simatic Manager (S7-300/400), but I would say the principles also apply to the new Step 7 Basic (S7-1200).

Check it out here: Siemens vs Allen-Bradley: Function Blocks

Hope it is helpful for those of you looking to compare features of Allen Bradley and Siemens.

Nick
DMC, Inc.
Expert Engineering & Software Services
www.dmcinfo.com

 

[MuotioJ]

I see that the topic has strayed a little, but I thought I would put in my two cents...

I just posted an article with some practical comparisons of Siemens and Allen-Bradley use of modular functions. I focused on RSLogix5000 and Simatic Manager (S7-300/400), but I would say the principles also apply to the new Step 7 Basic (S7-1200).

Check it out here: Siemens vs Allen-Bradley: Function Blocks

Hope it is helpful for those of you looking to compare features of Allen Bradley and Siemens.

Nick
DMC, Inc.
Expert Engineering & Software Services
www.dmcinfo.com

"Disadvantage: Potentially large and complex rungs of ladder that include both the function block instance call in addition to related input parameter logic."

You should correct it then, look at screens I posted. As you see you can even access stat variables symbolically if needed.

Siemens is very flexible system. There usually is more than one way of doing things. Its advantage that you can do it either way.

This is code inside fb200:

      A     #in1
      =     #out1
      =     #stat1

PS. Ofcourse siemens as every system has its disadvantages.

 

[mmp]

Hi MuotioJ. You bring up a good point! I think that all that Nick was trying to say is that if you want to call a function block from ladder, you do at some point in time have to actually have the function block in a rung, which can be large and ugly if it has a lot of IO. However you bring up a great point about an elegant way to put the inputs and outputs on different rungs so that all of the logic for each function block IO does not have to be on one large, ugly rung.

Let me know if I misunderstand.

 

[Jason A Jensen]

Both systems are similar is form and functionality.

Support

Siemens is the preferred UK solution. I cannot speak to their support in the UK but I can speak to it in the US. Siemens, if you can contact the correct people, will work with you to make the product successful. I have even seen Siemens spec their product for a solution, seen it not work, and Siemens retro upgraded everything to make it work at no cost to the customer. They stand behind their solutions. This is something I have never seen from Rockwell. They will, however, dictate what successful means. You may not agree on their idea of success. Their technical knowledge and their ability to supply you with a stable product is less than practical. WinCC Flexible has dozens of "features" that will really cause you headaches. (SAY AWAY FROM FACEPLATES!!)

Rockwell has excellent technical support, but the specs are ultimately designed by you. So if you know what you are doing you will have a lot of luck with Rockwell. If not, you will not be able to rely upon Rockwell for a solution. I have seen Rockwell bend over backwards to setup test system and help with code and design. Siemens has offered similar solutions but have failed to deliver, from my point of view, to the point Rockwell has. Their software does have issues, but their PLC programmer (RSLogix) is rock hard stable. I have rarely seen it crash or have issues. (I was not using RSLogix 5000 in the version 12 era.)

PLCs

Siemens

Siemens offers a very good product at a very competitive price. The Siemens platform, however, is very unlike that of Modicon. The scan is different (as with everything.. only APACS DCS scans like modicon) but, moreover, the programming design methodology that Siemens promotes is very different then that of Modicon. One thing you have to understand in the Siemens PLC is there ARE NO SUCH THING AS NAMED TAGS. Sure, the programmer may make it look like you have a tag that is named, but in reality this is merely a dog and pony show. If you are unsure, go online with a Siemens S7-300/400 PLC without the project file. If they used FB and FC blocks.. LET THE FUN BEGIN! This lack of tags by named causes interoperability issues between the PLCs. For example, if you send one block from a s7-300 to another s7-300 for data use, and later you go online with the first plc and make a change to the DB the second PLC will not handle the change. In fact it may even be looking at the wrong memory locations now. This problem exists in their safety PLCs as well. Their HMI is effected by this too. For example, consider the following datablock:

Motor1 (DB1)
--------------
Start (Bool) (Input)
Stop (Bool) (Input)
Interlock (Bool) (Input)
Forward (Bool) (Input)
SpeedFeedback (Real) (Input)
Speed (Real) (Input)
Running (Bool) (Output)
AtSpeed (Bool) (Output)

No you want to add another element to the block called: Runtime. You want to do this for maint reasons. Since the data element is a stat element in the FB it must be placed in the middle of the FB. You are left with:

Motor1 (DB1)
--------------
Start (Bool) (Input)
Stop (Bool) (Input)
Interlock (Bool) (Input)
Forward (Bool) (Input)
SpeedFeedback (Real) (Input)
Speed (Real) (Input)
Runtime (Integer) (Stat)
Running (Bool) (Output)
AtSpeed (Bool) (Output)

The datapoints in red have now CHANGED MEMORY locations. Every PLC and HMI that address this location will have to be recompiled and downloaded again.

Rockwell

Rockwell has the equivalent of FB and FC blocks all combined into what they call and Add-On Instruction (AOI). This allows you to encapsulate code into a common unit so that you can create multiple instances without much additional work. (No copy and past.. change on change them all) Their PLC also support REAL named based tags. When you go online you will see TAG NAMES and the AOI come back as well. All you loose is comments. If you use Alias tags for you IO you will get those as well. However, unlike Siemens, YOU CANNOT CHANGE AN ADD ON INSTRUCTION WHILE RUNNING. This includes the code AND the structure. This can be prohibitive if your process never shuts down.

HMIs

Siemens

WinCC SCADA is an exceptionally powerful platform that I am sure will meet any need you have. However, it is a bit pricey and the licensing scheme is bit complex.

WinCC Flexible (a completely different product sharing the same name for your confusion that cannot be upgraded to WinCC SCADA) has a HARD limit of 2048 tags that CANNOT be over come. It is also a buggy piece of software with many many MANY issues. But it is cheap and will work. AVOID copy and past on certain items use FLAT COPY and PASTE.

Rockwell

RSView is a very elegantly complicated system. If complexes itself by using DCOM just about everywhere. If you system starts having DCOm issues you will have a lot of fun fixing the issue. I recommend a reinstall. Even the tag export tool uses DCOM some some unknown reason. Its distributed application is even worst as its foundation is based on IIS for the central server. If you are not an expert on these technologies, be leery of a distributed application.

Rockwell does support more open technologies than ANY other vendor. Look for screen imports/exports via an open XML format.

Wonderware

Wonderware is a very cryptic HMI platform with most of its design based in the 90's. InTouch still uses DDE, which is actually a asset as DCOM can be a pain, and has not changed in many years. They did add smart symbols, but you need to learn how they work before you use them. I recommend avoiding them all together in large hmi projects.

However, Wonderware is a very stable platform. Its relatively static development has allowed for a lot of bug fixes to the point where it is less problematic. Its central deployment system (NAD) is simplicity itself. Just share the folder on the network and point the application to it. Changes are handled per your configuration.

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Just so everyone knows, I am not on one side or another. I walk on the fence. I take a very protagonistic view and am very critical of design and function. This is mostly to promote improvement. Both packages have their pluses and minuses. I chose to focus on their shortfalls in an attempt to let you know what you will be getting into one way or the other.

 

[nickephx]

MuotioJ,

Thanks for your comments! The "disadvantage" that I listed was meant only to temper the larger advantage that Siemens provides in giving you the option to directly interface with the function block instance. I realize that I never explicitly stated that larger advantage. Siemens definitely has the advantage in allowing you to directly interface with the function block like you can in FBD.

And you are correct, if you prefer to symbolically reference the function block input and output parameters in other rungs (like in AB), then you certainly have the flexibility to do so in Siemens - although I recommend taking advantage of the direct access option where possible for the sake of simplifying your code.

I have updated my article in an effort to clarify my original intent.

Siemens vs Allen-Bradley: Function Blocks

Sorry for any misunderstanding!

Best wishes,

Nick
DMC, Inc.
Expert Engineering & Software Services
www.dmcinfo.com

 

[Jason A Jensen]

I liked your article. You didn't seem 100% objective but, then, no one ever is.

I do agree that direct wiring to the inputs is an advantage in some cases. But...

Here is what I thought you left out:

AOI act like a mixture of FB and FC blocks. You example doesn't show but required inputs have a drop down to select the external tag. Your output would have been a perfect example of this.

Finally, when you go online with a Siemens PLC without a project file you get a real mess. Every FB is simply called FB## and every datapoint in that FB is called STAT##. Try figuring that ball of mess out when you need to and time is short. With Rockwell, all the AOI structure is retained in the PLC, the only comments are lost without the project file.

 

[ceilingwalker]

This is just my "2-cents". I'm new to AB, most of my experience is with Siemens controls. I remember starting out with Siemens controls and they are a alot easier to learn and instructions are easier to understand and apply, than say Logix500. I'll probably get booooo-ed that's just my opinion.

 

[Jeff23spl]

This is just my "2-cents". I'm new to AB, most of my experience is with Siemens controls. I remember starting out with Siemens controls and they are a alot easier to learn and instructions are easier to understand and apply, than say Logix500. I'll probably get booooo-ed that's just my opinion.

The one you know is always easier....Working with a new plateform can be frightening especialy when you lack of time and start from 0 but you need to ride out of that to be neutral in comparaison.

I prefer Siemens but i can't say RSlogix is more difficult to understand, both are way better and easier for ladder programming than everything else i have tried back then

 

[V0N_hydro]

Quantum to S7-300 or S7-400

If you were migrating from quantum to siemens, would the equivalent siemens PLC be the S7-300 or S7-400?

I am thinking the S7-300 is more like the M340 and the S7-400 is on par with the Quantum?

 

[OZEE]

You really ought to start a new thread for this instead of piggy-backing on an unrelated 2-year old thread.

We'd really need to know more about your application before anybody can make that kind of recommendation. Things like amount of distributed I/O, PID's, etc., will play a lot more into the decision than just the "physical architecture".

Honestly, unless you're into a really large system a -300 will most likely do everything you need and more.