slc500 verse plc5

porky

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Oct 2002
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what would you do?????????

Hi all
here is a question that I need help in answering.... :oops:
we are due to replace our PLC3 ----my boss reckons that it should be replaced with a PLC5... I think that we could upgrade it to a SLC500..... My boss has the opinion that a PLC5 is more powerful than a SLC500......Personally I think that the PLC5 is outdated and that the SLC500 is just as good if not better as the latter.... what arguments could I use to convince him... or is he right ???????
 
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The PLC5 is more powerful especially when it comes to communication. The SLC is less expensive. If you want more powerful, go with control logix...
 
It really depends on your system. How many I/O? Analog? PID? Remote racks? There's more to getting the right hardware than just picking one out of a catalog.

Certain PLC5s are more capable than some SLC500s. The PLC5 is also more expensive. Do you absolutely need all of the power and communication options that a PLC5 has to offer? Can a SLC adequately handle your requirements? You haven't told us enough to evaluate...

However, unless there is a real good reason to stick with either of those platforms, I strongly recommend that you look at the ControlLogix platform. Much more power than a PLC5. The ControlLogix platform is the latest-greatest that AB has to offer. As such, it will have the longest life-expectancy before it is put out to pasture. (The PLC5 and SLC500 platforms are both 20 years old.) AB's R&D efforts and new developments will be all in the CLX line.

Perhaps your system would be such that you could actually get by with a CompactLogix, itself a very capable PLC inspite of the name "Compact".

It just depends on your system configuration and requirements. I don't think anyone here can accurately answer your question based on the information you've provided.
 
I would not go with PLC-5 or SLC. As others have indicated, the ControLogix / CompactLogix line is the way to go, the choice of which depending on your application. Both the PLC-5 and the SLC platform at at the end of the development cycle, and while they will be supported for many years they are obsolescent.

Since you have to buy new software anyway, that cost is a wash. The RSLogix 5000 may present some challenges because the file structure etc. is different. Overall, in my opinion, once you get past the learning curve it is faster to create programs and it is easier to integrate them with HMIs in 5000.

I suggest you get your local A-B rep in and discuss the pros and cons with them, and perhaps get alternate quotes.
 
Sorry Porky, but your boss is right. The SLC500 is an inferior platform the the PLC5 - and not just a bit. The PLC5 uses 1771 IO, which is an older IO family, but the processors are very powerful.

But lets look at the things that matter. You are replacing a PLC3. Obviously the PLC3 could do the job as it was doing it in the past. So instead of focusing on which processor is most powerful, focus on which processor will do the job most economically.

Both the PLC5 and the SLC500 are old systems. If I were to bet, I would wager however that the PLC5 will continue to be supported for longer than the SLC500 will be. But a PLC5 costs a lot more than a ControlLogix. Depending on what you need, a ControlLogix can be price competitive with a SLC. A CompactLogix system will likely cost you less than a SLC. And depending upon what your IO count is, a MicroLogix 1500 might just be the way to go. The SLC and PLC5 are legacy systems and prices have been structured to encourage customers to migrate to newer technology.


We do not do anything new with the PLC5 processor and the SLC processor line other than maintain the ones we already have. Anything new is a control logix, compact logix, or if we need a brick, a MicroLogix.
 
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I'd be interested in what is in the PLC3 as well, that needs to be replaced. I had experience with a GA basic module that handled several things, and the original programmer of that system told of one he did, at a customers' request:

One rung. The rest of the program was in the GA Basic module. I hope this isn't the one you have... You're looking at a rewrite any way you go, there are too many differences.

I second the Contrologix. You will fall in love with it. If you are of a mind to replace one central processor with several distributed, the Flexlogix line lets you put a lot of stuff into very small spaces. We use Flex I/O with PLC5 via Controlnet.

Good luck.
 
SLC vs PLC5

The SLC is OK for smaller systems. Its never just a question of what PLC to use. What are you going to program it with? AI? RS500? RS5? Is it communucating with another PLC? Is there motion control? How big is the budget? If the company has RS5 and PLC5s then a PLC5 is the way to go. If there are no other PLCs and the number of I/O is small then maybe the SLC is OK. The software is still needed to program it. Control logix is expensive, the software is expensive. It is good if you have the cash, the PLC5s are getting old. We still buy PLC5s, we have Control logix. All of our SLCs are used for small dedicated parts of our machines. We use one for controlling 4 axis motion on a machine with 19 axis. The main PLC is close to being maxed out, so the SLC was used to take the process load off it. First question, do you have programming software for the PLC? #2- will the PLC meet your I/O requirments? #3- Do you program at the PLC or at a remote location? #4- Is the PLC memory capable of holding the program for your project? In your case, if the 3 can handle the program both the SLC and the PLC5 will have no trouble. Decide how you are going to program the PLC. This alone might limit your options. Have a great weekend!!
 
I'm going to join the chorus and recommend the ControlLogix. Depending on the size of your PLC3 system, it may well be the only solution that can replace the PLC3 with a single processor. With the CLX, you can have as many RIO channels as the existing PLC3. I know of one PLC3 system that had 10 RIO channels configured. Using a ControlLogix and several DHRIO modules made the conversion easy. Switching all that I/O between the PLC3 and the new ControlLogix for testing only took a few minutes downtime.
 
---my boss reckons that it should be replaced with a PLC5...
The boss is your ultimate customer and thus politically is "always right". That said, a question not answered yet: For which platform will it be the easiest to translate the old PLC3 program? I think the PLC5 would be more similar in instruction set than the SLC or any of the newer platforms. That is just one consideration, and it could be an important one if it is a large complex program and you are doing the translating yourself. The "Latest and Greatest" system is not always best. Sometimes Easiest is best.
 
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