Comparison Of PLC's

Hello experts;
If i want to compare two companies PLC's features which points should be considered especially if i want to compare Siemens and Rockwell.

Regards

I would not be concerned with comparing but more so what are your needs and find the best PLC to fit your project also Siemens and RA both have several lines so it would be like comparing to car manufactures

If you're doing the comparison to choose the best PLC for your application, compare the features that are important to you.
If you're doing the comparison to choose the best PLC for your brother-in-law's application, compare the features that are important to him.
If you're doing the comparison to choose the best PLC for the entire world, abandon hope. You'll have better luck hunting unicorns.

Steve Bailey said:

If you're doing the comparison to choose the best PLC for your application, compare the features that are important to you.
If you're doing the comparison to choose the best PLC for your brother-in-law's application, compare the features that are important to him.

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These two are redundant... if the brother in law has enough knowledge to specify technical requirements of the PLC, he'll be specifying the PLC itself. If he doesn't, then most PLC's will meet the clients specification, which is usually "Make me money".

Local support is important too, does the end user have a good relationship with a distributor of either product? I would prefer a relatively local stocking distributor.

I agree with Travis and Steve. The most important feature is, who can help me if I have a problem. Whether that is telephone support or getting replacement parts. PLCs themselves generally have pretty similar capabilities.

If a Rockwell PLC can handle 500 I/O but the Siemens can only handle 480, does that make it better when my application only requires 200 I/O? Would a Siemens PLC be better because it has two ethernet ports (at a higher cost) if the similar Rockwell PLC only had one? Do you need two ethernet ports? Can I add one to the Rockwell at a comparable cost to the Siemens? These scenarios make it difficult to compare just based on features.

Another way to ask your question might be....What Siemens controller is comparable to a Rockwell CompactLogix? Otherwise it is like asking what features should I compare when selecting between Toyota and Ford.

OG

Also look at the Programming Software that is used to program the Processors. Siemens has always build great expensive Processors but never put a lot into the software. Rockwell put a lot into the software and the processors were a bit less impressive than Siemens. Both have gotten much better. I learned PLC's on Modicon, which I absolutely try to stay away from now.

I'm echoing what others have noted. First, the PLC platform has to function as needed. What about future changes? What about programming? What about support - either onsite or via phone? What about availability of spare hardware? Who and/or what is going to interface with it? Too many variables to give you a thumbs up/down on either platform. I prefer AB but that's because it's more common in my world.

For me it would have been a no-brainer a few years ago. Rockwell all the way because I hated the S7-300, but the new S7-1200 and S7-1500 are decent. You guys haven't heard rant and rave about S7s lately. I would like to program in Structured Text. The S7 may have an advantage here. For inexpensive the Koyo PLCs are good now. Again, I hated the old PLC programming where somethings were programmed in decimal, some in hex and some in octal. How brain dead is that. My guys tell me the software is much improved.



I would definitely look at the programming IDE if all the PLCs are capable of doing the application. I hate poor IDEs.

Peter Nachtwey said:

Again, I hated the old PLC programming where somethings were programmed in decimal, some in hex and some in octal. How brain dead is that.

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All of those are number representations... same number, different way of us understanding it. Same as you can program a number into a variable in c by using 0b, 0x, etc... prefixes to the number.
On Simatic Manager, you can right click on a number when online with the PLC and choose the representation you want to see it in.

Chuck Woodbury said:

Also look at the Programming Software that is used to program the Processors. Siemens has always build great expensive Processors but never put a lot into the software. Rockwell put a lot into the software and the processors were a bit less impressive than Siemens.

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Siemens processors, in terms of price, match Rockwell's... in the UK at least. As for the IDE and functionality, I think it's more of a personal opinion rather than being objectively better. I really dislike online editing and much prefer the option to download a piece of code onto the processor. Some people argue the opposite.

The fact that Rockwell doesn't have Function Blocks when most do is proof they're not that advanced. And no, AOI's are instructions (with the weaknesses that come with them), not function blocks.