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PlasticsDude

Most robust, industrial PLC

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Hello, I'm new to this forum. Seems like a great forum! I'm completely new to PLC's. What is the most robust, reliable and noise resistant PLC on the market? Thanks!

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Welcome! I vote for the PLC5 as being the best I have worked with. I have seen panels full of water, and all kinds of electrical problems, but never had a PLC5 I could not revive.

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Noise resistant in what sense.... if you are talking about analogue signals then it can simply come to your wiring...etc... also good electrical wiring practice and seperation etc all play a part... As for PLC etc all you will get are responses from people touting their favroutie brand... I for 1 would say that i have seen Omron and AB PLC's in $hitty enviroements plugging away for years....

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We use AB, Omron, Misubishi and getting more of Siemens. As a machine builder, we usually deal with new components (unless there are upgrades etc.) and maintenance is tipically handled by customers. PLCs are very reliable and long lasting, specially when considering life expectancy of some other electronics products. So far all of the PLC failures I witnessed in last ten years are AB and one HMI from Siemens. None of them ware in dirty or in harsh enviroment. Most of the failures ware out of box or relatively shortly after installation and those are always easiest to replace. Just few weeks ago had to replace SLC500 rack sent back by customer. This part quit working after two years. At the same time we found out that Siemens HMI was not ok, it was brand new MP277 that appeared ok but could not communicate on any port. Others failures I can remember ware SLC rack, SLC CPU, couple of SLC output cards (OB16, OB32, OW16...) that had one or two dead or "weak" output, ControlLogix Motion Cards (M02AE) etc. There was two new SLC CPUs that appeared non responsive at first until we noticed write protect jumpers ware not set correctly. I've never seen Omron or Mitsubishi fail (probably stricter QC).

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I doubt any of the 80s vintage PLC are CE rated.

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Just about any top brand will be reliable and robust. Take your pick.

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I agree with Ken. Any top brand PLC would be the best choice. The thing that I always look at is the Programming Software and the world wide recognition. No matter how good a PLC is, if the programming software is not user friendly, the programmer is going to struggle with programming the PLC. In my opinion, AB, Omron and Mitsubishi have the best programming software. I also like the Eaton ELC. The porogramming software is a lot like the Mitsubishi GX Developer. I hope all of the information that you receive from this forum will be helpful.

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I love Omron CX-One V2. New one on the way as well. Inexpensive compared to most and reasonable upgrade prices. The latest versions of CJ1 and CS1 serial cards include Modbus RTU slave at no extra cost or work. AB is expensive. Mitso GX-Developer is OK but the PLCs lack a lot of very useable functions. Siemens (Germans) have very much their own way of doing things and you either love it or hate it! I am of the latter.

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Perhaps one of the most important things to consider, especially for a newbie, is local support. It really doesn't matter what our preferences are if PlasticsDude can't get the parts or the help/training he needs. And for a newbie, it might be important to have a "real person" available - not just a phone number... I see lotsa people recommending Omron in here. I don't have local support for them here - closest support is > 200 miles away. Same with Mitsubishi and Siemens. So, PlasticsDude, what reps do you have in your area? All of the major players in the controls market have good quality PLCs.

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This brings back memories of "Atari vs. Commodore vs. Apple" debates from the 80s :) I only have experience with A-B, and I would have to agree that the PLC 5 and 1771 I/O is the most robust. If you question this, take a look at all the PLC-2 systems from the late 70s/early 80s that are still in service today. I wouldn't say that the SLC and Micrologix families are a bad product, but they just aren't designed for the type of abuse that the 1771-based systems stand up to. On the other hand, I just came back from a GE facility in Canada that has standardized on the TI/Siemens 545 PLC. Now, this was more of a laboratory environment than a factory, but nonetheless some of these PLCs had been in service for 20-25 years and they still were working fine. The systems resembled 1771 racks, but I would have to say that from what I saw, the processor programmed more like a PLC-2 than a PLC-5. I think just about every major PLC manufacturer has a rugged, robust product in their line. Just take a look at what brand is common for your area/industry, and research what they have to offer.

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With out a doubt….Siemens S5 You can kick them, spit on them, curse them, blow snot on them, they just keep doing what they have been doing in the past (whether you like, it or not) The bad part is they are obsolete, so you will need to go to a sub tolerant level plc

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Ask a dozen automation engineers and you'll get a dozen answers this thread is proof of that. I must agree that any of the major industrial PLC's will prove reliable when installed and maintained well. YOu've read of PLC 2's from teh 70"s I've also seen Omron C500's from the 80's still plugging away.

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I was deciding whether or not to even mention the near-indestructible SLC 100 and 150, but they're WAY obsolete and not terribly enjoyable to program either!

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Even PLC-5's have trouble with water and dust eventually. In the foundry where I work, we've lost a couple that way. One of the biggest issues is buying NEMA 4 cabinets and then finding that somebody only loosely screwed down one single fastener because it "saves time"...it didn't save any down time last I checked... Over time, I've grown into the idea of simply ordering NEMA 4 cabinets (or NEMA 6 or NEMA 13 for the situations of definitely being underwater or soaked in oil on a regular basis) and placing the PLC's and the associated local IO inside. It seems like no matter which PLC you buy, the end result is the same when it gets hosed down with water or oil, or covered in dust to the point where it overheats. The only exceptions I can think of have to do with heat and vibration. I've had numerous problems with overheating I/O cards developed by hydraulics manufacturers. I've also had numerous problems with the current plant having gobs and gobs and gobs of linear power supplies (=relatively inexpensive PLC cabinet heaters) and "constant voltage" autotransformers (=relatively expensive PLC cabinet roasting equipment). All of these things can be avoided...buy hydraulics with on-board electronics (keeps the stuff away from the PLC and makes it easier to maintain), buy good quality switching power supplies, and use either good quality power conditioners as a minimum or else UPS's for all your PLC's. Yes, the PLC power supplies usually do a very good job of cleaning up crappy power but they will also shut down your PLC at the nearest hint of a voltage droop, causing needless troubleshooting and debugging nightmares. Noise resistance has almost NOTHING to do with a PLC. This is all the world of I/O design. Aside from networking, nearly everyone is using either 24VDC or 110 VAC. 24VDC is generally faster, lower power (heat), and more robust especially to coupling issues, but lacks drive current in most cases. You usually end up installing a lot of power supplies. 110 VAC has the advantage of direct drive for a lot of equipment but since it is usually not isolated (see clean power above) and can suffer inductive pickup (110VAC signal couples from one line to another in a long run), it has it's own problems as well. In almost all cases, the issues usually revolve around good designs. For instance, put in diodes and resistors where appropriate even if the relay doesn't come with it. Use solid state outputs if you don't want to spend a good deal of your life troubleshooting failed relays. Relay contacts have a finite life, and they are subject to various strange failures such as welded contacts, frozen contacts (outdoors), and the occasional grain of sand getting in there and driving you up the wall. Solid state outputs avoid all of those problems and seem to be much more robust, but recognize all the downsides of that decision as well (more heat, leakage voltages/currents will always be present, lower maximum output power). Unlike the relay case, these are all design issues that can be dealt with...the relay failure issues are inherent to the device. All this being said, there is one class of relatively recent vintage PLC's that I'm a bit concerned about. GE, National Instruments, and a few others are now selling "PAC's" ("super PLC's"). These are roughly 10-100x faster than the last generation of PLC's and they frequently have some amazing capabilities like user-programmable instruction sets. Many of them are based on the Pentium CPU and many of them require cooling fans. A fan has a sealed ball bearing which has a finite mechanical life...and well, you know how rugged that Pentium laptop is that you're using, right? If you treat these like office equipment...NEMA 4 enclosures, optionally with solid state air conditioning (Melcor is a good brand), UPS power supplies, etc....then it will probably have a good, long, productive life. The amount of horsepower you get with these is enough that you can potentially run an entire plant off just one or two of them (redundancy is frequently an option). At first this seems like an absolutely horrible idea...lose the one PLC and the whole plant goes down. But the advantage here is that you can go crazy putting in all kinds of redundancy, sealed and protected environments, etc., that you would never dream of doing for cost reasons on all PLC's in the plant. Yes, it's all your eggs in one basket. But oh what a sweet basket you can have.

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paulengr: Also, to make the image totally complete: In civilized countries, we use 230VAC instead of 110VAC.

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I have used OMRON, Allen Bradley, and now SIEMENS. I enjoy the SIEMENS for the fact that it is like the Rolls Royce of plc's, and it nice and complicated. I figure if I can master SIEMENS then all the others will be easier to use. But that just me thinking. Edited by mr_electrician

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I think that for robustness allmost all PLC's of major brands are ok. The local support organisation, the availability at long term and the upwards compatibility are another thing. There you will find big differences between the brands. For instance, if you have an Omron C200HS (80's) and you want to replace it by the latest Omron PLC you will probably (if you don't have a lot of special cards like motion or exotic communications) make the software change in a couple of hours. The hardware is of course another thing but even then you could be lucky if you choose well (even the IO-cards could be compatible if you take a CS1). Siemens on the other hand is the opposite. There are even incompatible versions between S7 PLC's not to mention S5-S7 compatibility. Also for availability there are big differences between brands but there it is more about peripherals then about the PLC's themselves. most major brands have older products available for quite some time....

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In my experience over 30 years the most reliable, easiest to use and readily upgradeable in order best to worst of the PLC's I have used:- OMRON - #1 ROCKWELL - #2 IDEC - #3 GE - #4 And at rock botton SIEMENS #*******

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These are the ones I have had experience with: AB PLC5: Very good reliability. Only the achilles heel of this platform is the connector between CPUs/Modules and the backplane. We have had a number of issues there. AB SLC500. Very good reliability, only a little less than PLC5. It seems to get a bit more hot than PLC5. I have had a number of SLC500 CPUs fail, but then they where situated in a quite hot environment. Siemens S5. Very good reliability. We are getting a steady flow of queries from old customers for spares or upgrades. But then again, these are PLCs that have been running for 15 maybe 20 years. Siemens S7. Very good reliability, but our experience is from the last 6 years only, so the final verdict is not clear. I have only had a single CPU fail, and that one had been used in a test environment (abused ?). paulengr, nice to see another person working in the foundry business :) BITS N BYTES, what has "easiest to use and readily upgradeable " got to do with the question ?

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IMHO OMRON has been the "easiest to use and readily upgradeable " PLC on the market. By "Easiest to use" I mean programming. Siemens is the least friendly in this respect. By "readily upgradeable" I am commenting on the fact that over the years when OMRON produces new PLC's they do a great job at being able to import old programs into new platforms - not perfectly but dang CLOSE.

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I am sure that Omron make good PLCs and they are advantageous for a number of reasons, but IMHO "easy to upgrade" is not what is meant with "robust, reliable and noise resistant".

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If you want noise resistance, Omron is not that bad either. I had a customer where the plc (CQM1) was at 30cm of at 1000A contactor running without problems while the contactor switched on a regular base. At another company where they do induction melting of different metals, Siemens did not want to sell PLC's, The Omron C200HE's are still running. At other sites I had OMRON PLC's in an open board where you could not see the leds anymore due to the wood dust all over the PLC. They might not be the most progressive at Omron but they are reliable....

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Jesper... BitNBytes said "Most relibable, Easiset to use and readliy upgradable" Most reliable infers most robust and niose resistant also doen;t it ?

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Sleepy. How does one know if Omron made it to the top because it was best on all accounts, on some of the accounts, on one of the accounts or despite of an account ? How did the others make it to their places in the list ? Can you tell ? I can guess, but I dont like to guess. But OK it was not me that asked in the 1st place, maybe it doesnt matter.

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Boy!!! Which side of the be d did you get out of today! Looks to me that Sleepy is more awake than you are [and certainly a lot easier going].!!

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