PLC Learning

I've designed complex control systems but PLCs weren't part of the situation. So, I've not used PLCs hands-on but the concepts of how they
work, etc. seems easy enough. I'm trying to learn more about PLCs so I might be able to help improve an existing system. I've not seen any documentation for the system and have doubts regarding the quality and completeness of what I'll find.
One question that comes to mind that seems typical of processors in general is "how do you program these things?" I *don't* mean what does a ladder diagram look like or how it's interpreted. I mean:
What interfaces and tools are used?
It appears that RS232 might be a typical physical interface and ethernet another. So, if that's the case then some command line interface must exist and even a GUI interface for programming.
OK .... with that:
I have an existing system that has a couple of PCs set up for monitoring and some simple controls. Would I expect to find PLC programming tools on one of the PCs? What might I be looking for?
No, I'm not going to muck about in something I don't understand... I *am* going to learn something though.
A couple of good references would be appreciated.
Thanks,
Fred
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Most communication though similar is manufacture, model and version dependant. CH has a nice simple shoe box device with limited I/O called the D-50. Only problem is there are at least 3 versions of the programming software that it will accept. One is DOS only, one is Win98 and DOS and one is Windows above NT only. Sadly the programs are not backwards compatible. No one in their right mind would use this processor for much. I am using it as a example only. I used to work for CH and used this processor almost exclusively for main-tie-main situations. When the project needed more than that we used the GE Modicon series. All of the more complex stuff CH sold was a Toshiba brand labeled. At the time we were moving away from ladder, to function block programming. The guys on the east coast had a lot of success with the function block programming. I am in the west and my clients were not at all happy with function block. Most had problems understanding ladder.
Look for the software and a special cord to connect to the PLC. Some manufactures sell hand held programmers. I certainly want to look at more than one contact or one rung at a time.
I move back and forth now from GE to ABB a lot. Keeping the key strokes separate for the programs is the hardest part. I always leave a copy of the program in paper and electric form. Not that any one can remember where they are or how to use them. Helps keep the bills paid.
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Just to get started, you may want to checkout automationdirect.com. You should be able to get a small PLC, software and cable for less than $200. PLCs are cheap (and dirty), software is cheap and works on current Windows versions, you can make a cable yourself or buy theirs for 30 bucks, and you can order it all online without setting up an account with an industrial distributor.
Being as you are new to PLCs, I might recommend a newer generation PLC. Take the Siemens S7-200 for instance. The high level instruction set and the advanced capabilities of their programming software allows you to accomplish complicated tasks with much more ease that with traditional software. Most PLCs require you do all this octal addressing and looking at special flags when using various operations. The Siemens software allows you to build your own function blocks, declare local variables, whip through floating point math, separate and reuse blocks of code, etc. Allen Bradley (and surely others) have similar strengths, but you don't even want to know the price of their software. Siemens handed me a copy of the S7-200 software at a training seminar. The PLCs are fairly competitively priced (more than Automation Direct, though), but you will need a Siemens cable (basically RS-485) to communicate with the PLC. The cable is over $100 for RS-232 and much higher for USB. Set up a couple of eBay saved searches to email you for "SIMATIC S7-200" and for "STEP-7 MICRO/WIN"
One thing to be aware of... most PLCs require your computer to have a serial port; most new laptops do not. If you need a serial port and have a laptop built in the last 5 years, I recommend the Keyspan USB to serial adapter.
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Thanks for the answers and suggestions!
If I find out what mfr. of PLCs are in use here I'll re-post to see if there are other recommendations.
I saw the PLC Twido training kit and GE Fanuc Series 90 training kit on ebay. Comments on those? I'll set the searches too.
One minor concern: if I start with the Siemens S7-200 will I go down a path that's not similar to what I'll probably find in the field here. I better go look!
Fred
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Definitely want to find out what you will be working with. If you start with S7-200, you may find it difficult to accomplish those same tasks with a more rudimentary package.
The problem with the GE Series 90 is which programming package you will be using. We mostly use Logicmaster 90 a.k.a. LM90, which is a DOS application; you probably ought to find a Windows 95 or 98 laptop to run that... (and you still may have difficulty capturing your serial port.) After that was a package called VersaPro, and then CIMplicity, and now I think it's called Proficy. The newer packages run from $2500 to $5000, more if you have a lot of I/O, plus "runtime" packages if you integrate a PC.
Not familiar w/ Twido.
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Fred Marshall wrote:

Twido is a reasonable small PLC but the software is quite clunky (it looks like a Windows port of the DOS software used by Twido's predecessor the Nano)
The Twido software is a free download from Schneider Electric, so you can download and have a play with no financial outlay.
The next size up PLC from Schneider, the TSX37 Micro is (IMO) a much superior product, both software and hardware, but with a significantly higher price.
Checking what is currently in use locally is defintely a good plan.
Cheers
Chris
--
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gnoge wrote:

Just one thing with USB to serial adaptors, make sure its running on the right protocol. We've had trouble the pass couple weeks as some automation devices use RS-485, not RS-232; because the common adaptors you buy from the shops are RS-232.
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do a search on iTrilogy
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Most PLCs (and drives and other devices) that use RS-485 provide (more like sell) some sort of adapter, since they know you probably won't have a 485 port on your PC. Some of the newer PLCs have available a USB converter cable, or better yet an ethernet port. Do your background check to make sure what all is needed to program a particular PLC: software, cables, converters, memory chips, batteries, etc. And also watch out for those like Allen Bradley that want to charge you $50 for their "special" programming cable that's actually just a 9-pin null modem serial cable.
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I have ended up with 4 different cord/software combos I am sure there are more out there these seem to cover the popular stuff installed locally.
I once had the Omron rep send me instructions in Japanese or Chinese. He maintained that I did not ask for English instructions. I brought the ~12k of parts back in unopened boxes and placed the boxes in the middle of his desk. It only took 2 days for the English instructions to show up, gratis. Even got a nice lunch at Hooters out of the deal.
Software and cords have a habit of changing from model to model in the same manufacture.
Are we having fun yet?
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