Host Engineering Forum
General Category => General Discussion => Topic started by: BobO on June 11, 2008, 06:15:29 PM
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Hey ya'll, we were chatting about which is the best form factor for a PLC system. Clearly there is really no right or wrong answer, just opinions...however...would you help us out by telling us which you like (or use) the most? I used pretty broad catagories on purpose, but if there is one you think I should add, please PM me. Feel free to elaborate on your choice...or defend it...with a comment below. Discussions are good!
Thanks a bunch!
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As far as stackable - if I correctly understand the term - the AB CompactLogix/ML1500 I/O can be the most confusing expecially when mounted on DIN rail. The modules APPEAR to be connected but unless the electrical connection tab is flipped over properly, they aren't. Forgetting the termination end plate can be frustrating also.
All form factors have their advantages somewhere.
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Clearly they all have advantages...which is why they all exist...but I am trying to get a clue as to what our customers like best. Us product design engi-nerds have our own opinions...which while interesting, are substantially irrelevant. Folks that actually buy controls, on the other hand, have opinions that should be forcefully considered.
Actually Bernie, I'm trying to get a fight started...makes for lots of site activity. The next poll will involve politics. ;)
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Looks like a three way tie, so you'll have to make at least one piece of each! I **strongly** dislike stackables for reasons I've already outlined. Completely modular ala DL205 is my favorite, but for small projects I certainly don't mind the expando-brick like the 06 or the early SLC's.
I like the idea of the a number of different slot-count bases, like the 205/305/405, etc. The only advantage (other than potentially cost) to the stackables is finer granularity of I/O count vs. cubic and square inches of panel space, and if you have 4/6/8 slot bases, at worst only 1 empty slot is forced upon them except in extremely small jobs. And don't forget, space for future expansion is generally considered an advantage, not a disadvantage.
I once had a guy from Grayhill trying to sell me on why it was good to use 1 or 2 point modules because you could build the machine with the exact I/O count. (Even though their cost/point was enough higher that all the money saved went to Grayhill, not to me, and at the cost of shafting my customer. They never seemed to notice that point.) Then they came out with 16-point modules. I asked (already knowing what answer I would get) why they thought 16-point modules would be a good idea. He said that the the cost/point was enough lower that I could save money overall, even if it meant I had to ship machines with unused I/O points. I asked him if this meant his competitors had had a superior product all along.
He said that no, low density modules were still superior to your high density ones, or AB's, due to their low point count, but that HIS multipoint ones had advantages over his low density ones, because of their higher point count. I went for a shovel.
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Hmmm...have to think upon the dis-logic of the Grayhill chap. Methinks he may have gotten hold of some bad juju... ::)
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I selected all of the above because, you have to "make the shoe fit". Application, price and size constraints choose which one to use. My preference is a card based system, zip link type IO with expandable racks. I think it provides the most flexibility, highest reliability in the smallest space. Stackable systems are ok if you follow the rules. With the CLX system, you have to careful about power supply sizing and where it goes. Adding a module in the middle may not be so easy with the wiring. They sell a blank module to hold that space open, but if you are doing that, what's the advantage? The connectors can be a reliablility issue too. A long while ago, I used to use the Omron S6, which was stackable and it would really act funky sometimes if there was a poor connection in the module chain. Also it was tough to replace one in the middle. The CLX solves that, but as b_carlton stated, its not always easy to see when something is not properly connected. With a rack system, it's usually pretty obvious if the card isn't seated and the power supplies increase with the rack size and you don't have to think about it most of the time. Also, The cost of a larger rack is usually minor. You only have to make sure to provide the space and for additional racks if required. Bricks are great in their place, but blow one output and you have to replace it all. I think the 06 was a nice fit to take care of applications that are more than a brick, not quite justified for a rack based system, but provides some expansion at an affordable cost.
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After reading your type by type critique, I still can't figure out the scenario when you would find a stackable the best choice. All the stackable-specific comments seem to be negative. If I'm reading you wrong, try explaining in smaller words and then I'll probably get it. 8)
And as far as bricks go, if you're using a brick with every last output used, you've already set yourself up for trouble in the first place, so no, that particular brick is not a good choice for that particular project.
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I selected all of the above because, you have to "make the shoe fit".
I think that was the answer.
But what I also heard was...given the choice, he'd prefer modular...so in this context, I'd have to add an extra half vote to modular.
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Well, he said "make the shoe fit" but failed to describe the foot that would be best fit by a stackable, only feet belonging to modulars and expando-bricks as I did. Maybe you should rewrite the poll to allow votes for more than one type without voting for "all of the above". It also occurred to me that this is exactly the type poll you might find in Control Design or Control Engineering to use as a proxy if you're having trouble getting a statistically significant sample, but I did a quick search and didn't turn any up. Anyway, just my $0.000002 worth.
I hopped over to Control.com and didn't find any there either (didn't expect to, it's more of a Q&A forum), but I posted a thread asking for links to existing polls or failing that, for everyone to get over here and vote.
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Stackables make sense if the design is set in stone. Once the control package is produced, then it would never be altered. For instance, a standard piece of production machinery, ie. CNC, Molding, Stamping, PC board assembly, packaging etc. Machines like this are highly competitive and proprietary. The end user would not have access to the program, so it would never be changed. If you want something different, you have to order it special from the factory and that would be a different model. If you are a builder of this type of equipment then you want only exactly what is needed, spare slots are wasted space. The more compact the control panel is, the smaller the footprint which makes it more atractive. Floor space is money.
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Yeah, I guess I could change it to checkables. In truth, I wasn't looking for anything scientific...more just a general sense of how AD/Host customers feel about the problem. It is so easy to sit in our ivory towers (actually it's a 2 storey brick building on 50 acres of pasture in the foothills of the Smoky Mountains...not a tower in sight) and choose what people will like...or as they said at Siemens, 'vill like'. And it is equally easy to ask the marketing guys at AD what they think, and then drink the coolaid without question...and BTW, I like coolaid. However, I really want to balance my opinions and the opinions of AD with the opinions of our customers. Since I am stuck in the ivory tower...er, pasture...this forum is a great way to get a sanity check from actual users of our products.
So com'on...fight, argue, let the fur fly!! Express your opinions. We'll break into religion and politics shortly... ;D
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Ok...made the poll checkable...and removed 'all of the above', which kinda doesn't make sense with checkable. So if you 'all of the above' folks can re-vote...kinda like they do in Chicago...that'd be great.
Thanks!!
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I tried to vote, but I got confused and voted for Buchanan. But my vote should still count, right?
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Yes. For Buchanan. And don't even bring up that Chad guy... ;)
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I was working with a guy named Chad in Nov-Dec 2000 and we made sure he was always referred to as "Hanging Chad", "Swinging Chad", "Dimpled Chad" or best of all, "Pregnant Chad".
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Stackables make sense if the design is set in stone. Once the control package is produced, then it would never be altered. For instance, a standard piece of production machinery, ie. CNC, Molding, Stamping, PC board assembly, packaging etc. Machines like this are highly competitive and proprietary. The end user would not have access to the program, so it would never be changed. If you want something different, you have to order it special from the factory and that would be a different model. If you are a builder of this type of equipment then you want only exactly what is needed, spare slots are wasted space. The more compact the control panel is, the smaller the footprint which makes it more atractive. Floor space is money.
Thanks for the amplification.
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I really don't think there is much to argue about. They are what they are. If you want to start an argument, lets talk about native communciation ports on the PLC . RS232, USB, Ethernet, firewire? Why are we not seeing some of these higher speed connections directly on the CPU? Sure you can buy an adapter, but thats really turning down the throttle and you can't always add an ethernet card. Tell us why this is so.
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Hmmm...the prototype on my desk has three (3) fast ports, with the 115200 baud serial being the slowest of the three. ;)
It gets even more interesting when you put the new protocol's random access functions on those high speed ports. You'll like it. 8)
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Dangling those carrots out there again BobO?
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It gets even more interesting when you put the new protocol's random access functions on those high speed ports. You'll like it. 8)
New protocol? Random access functions? Splain, please.
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I won't get mad at you just for offering a stackable, but I sure will if you deny me the right to buy a GOOD PLC because you're building stackables instead.
Now I've heard that stackables are less expensive to build, but we're going to take the country of origin into account when comparing alternatives, so if it costs you a little more to make them in Tennessee than an equivalent Chinese product, that won't necessarily rule you out. We derive our incomes from US manufacturing, so we'd be idiots not to support US manufacturing. I don't buy PLC Direct stuff primarily because of the cost, although it doesn't hurt. If I didn't like it I wouldn't buy it. If a particular project is a better fit for Allen Bradley or Siemens' capabilities, I put the money for that in the quote.
Case in point: You may ask if I truly prefer to buy US products and am not exclusively driven by price, why don't I buy Allen Bradley instead of PLC Direct. Well, they never had anything competitive with the 205 in terms of points/ rail inch, points/in^2, points/in^3, points / module, and types of I/O available. You say they have the Compact Logix and Micro 1200 now. I say they're stackable (and ugly). I'll take the Chinese modulars, thank you very much. (And at one point most of AB's low end stuff was non-US anyway. I don't know what they're doing now, but I presume it hasn't gotten any better.)
Oh, that's another thing. NO beige plastic or softly rounded surfaces! It should look like industrial control hardware, not an answering machine.
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Well, I don't believe they would turn their backs on that customer base and the already available line of I/O. Maybe down the road, I could see a stackable version, but I would expect them to get their feet wet and the bugs out first with a CPU that would slide right into a 205 rack. Just my guess.
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Ok, just to clarify. We are making a 205 based CPU, and are strongly leaning towards a Terminator version of the same. We are asking the questions regarding what folks do and don't like about I/O systems to get a better understanding of what might be built donw the road, if folks like the new CPU.
You find that integrators, end users, and OEMs all like something a bit different for different reasons. That why the market has bricks, modulars, and stackables. They all have advantages and disadvantages. My goal here is to stimulate the very discussions that are happening, so that we can make informed decisions.
Again, there are no right or wrong answers globally...although there are both locally...which is why each of the customer groups I described tend toward different solutions, as is appropriate. Rest assured, neither Host nor AD has ignored the needs of any of those three groups, and we're not about to start now.
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Way back when PLC's were new (mid 1980s) Square D sold a small type of PLC that each module looked like a relay. These units snapped onto a DIN rail and was connected across the top with a ribbon cable.
They were only 8 Input or 8 Output density (The CPU and Power Supply had the same form factor)
This was the 1st PLC I worked with, but through the years I have often thought of these units.
If they were upgraded to todays CPU cabilities and I/O density these would be a great form factor especially if they used a Can Bus cable
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The TI 500 (not 505) and the Siemens S5 modulars had a form factor that in one respect I always admired. You mounted the module base first, then wired to the base, then plugged the module onto the front of the base. (And no, I haven't forgotten that the S5 base sockets were stackable! :-[ )
Advantage: Module changeouts are slightly easier, as you don't have to remove the wiring arm first. Also, some panel builders string the wire from the wiring arm to about middle C, so sometimes it's really tough to get the connector off.
Disadvantage: You can't probe the terminals to check wire state if you're troubleshooting I/O. You can't add or change an I/O wire while the process runs.
I guess on balance I prefer the stuff you can do with the connector on the front as in the 205/405.
Hot pluggability of modules is a cool feature if it isn't extremely difficult or breaks other things.
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Hmmm...the prototype on my desk has three (3) fast ports, with the 115200 baud serial being the slowest of the three. ;)
It gets even more interesting when you put the new protocol's random access functions on those high speed ports. You'll like it. 8)
Is it possible that one of these three ports might be USB, perhaps similar to the c-more? (please say "yes"!!!!)
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It is possible. ;)
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I like both the bricks and the modular depending on the application. The brick if the job is small and dedicated. The modular works well for bigger jobs and if seems that the operators over the years their needs and wants change, so it nice to have room to expand functions. Sometimes it only software changes, especially if you have a HMI. We still use some Sq D PLC's and one thing I like, I can make very small changes in some instances on the fly while machine is running. Even on machines purchased from the manufacturer I have been able to modify the programs and add functionally. One time on a brick (Mitsubishi) an output went bad and I was able to move to and unused I/O until we could get a new unit in.
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Well, I know that the whole stackable vs dedicated base is all debatable.
Maybe you should do both. Have stackable bases that the cards plug into or buy a pre-assembled "rack" that the same intelligent modules could plug into. that way you could please both parties. In the future if one is out-selling the other or if you are getting to many serivice calls because someone forgot to plug it in correctly you could phase out the problem design but it doesn't change the modules or the PLC.
I have had problems with the AB flex I/O and the Compactlogix with bent pins and other problems mentioned above.
The AB Point I/O on the other hand has been reliable. I've also used Beckhoff I/O also that works well. both assemble easy and have interfearing pins that mate. The point i/o has wiring bases and smart modules. Beckhoff modules don't have detachable terminals.
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I only used the brick once and never again. If an output goes, you have to replace the whole plc. I use the DL205 and love it. The ability to change or add modules is nice. The only down side is all the rack you do not use, taking up space. I just recently tried the Click, I suppose that is stackable. Nice though, again you have I/O on the cpu section. You blow an output, you are in the same situation with the brick, reprogram cpu because the I/O is on the CPU. I sticking to the DL205 system for now.
And why is ladder logic winning? I would bet if those voting for ladder would even try the stage program, they would not go back. C'mon guys try something new.
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I like the modular set up, the bricks are good for small simple apps. But then again I started out on the slc100 kinda like a brick, then the micro logics came along, did a few of those. I don't get to do too much programming execpt for what I practice on here at the house and that's just to keep from forgetting how to do it. I think it all depends on the application, I have never got to anything more than a 05 or an slc 1000. I have at the house to play with is an slc 5/03 with 13 slots, 4 are analog, a micrologics 1000 unit, and a D0-05DR. I have been spending more time with the 05, I like it, it has more potentinal that the AB brick.
I used to use the PCIS software for the slc 100/ 150's till the slc 5 came out then the software was too exspensive for the company to buy. Learned about DS through my brother and been learning it for the past year or so.
BobO,
Where in TN. are you? I'm about 53 miles South of Knoxville, BTW, I have noticed that are more "ville"s here that anywhere I have seen.
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Vern, we're in the Tri Cities...specifically...Sulphur Springs, a suburb of a suburb of Johnson City.
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I have been spending more time with the 05, I like it, it has more potentinal that the AB brick.
One huge advantage of the 05 over the AB micros is online edits. With the AB stuff you have to make changes offline, redownload, then switch back to run mode, so you can't do it while the PLC is running a process, because it will lose track of where it is and/or the process will go out of control during the amount of time it takes to do all that.
The thing I DON"T like about the 05's is the lack of PNP outputs, so I use the relay units (DR's), and if they wear out, I guess I'll buy a new one. I find most of my applications take at least an 06, so it's hardly ever an issue anyway.
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I have had to repair some AB cards, the guy before me didn't fuse any of the outputs, had a coil short and burn a trace on the card. I worked in a Dairy (milk plant) awhile back that had an Omron PLC on on a cart loader, the relays would go out once in awhile, that was easy to fix because they just pop out and pop a new one in on the card.
It's far and few between I get to work with PLC's in the real world but, what I have seen so far is that with an 05, is that it has built in motion control. I like the fact that, that empty slot has many uses, analog, eathernet, ect, try that with a slc1000. More bang for the buck with the 05-06's, not that I have had to use an 06 yet. Not to mention that the service is unmatched between Host and ADC, everyone else wants you to buy a subscription and I pray that ADC never does that to us. As for modular units, we have a 205 ( I think) on a g-normis vacuum machine, I have had to in the past make some edits, no big deal easy. Tried to do it with an AB unit, it didn't like anything I tried, had to call Rockwell, and wait, and wait, and......well you get it. As for looks, I like the way the AB slc 5/xxxx series look, the ADC stuff looks fragile no offence, ADC still my choice though.
You guys in suburb of suburbs, I live in a rual area, Englewood, same for y'all ;D ? BTW, what contitutes a "ville" anyway, population?
Happy ThanksGiving guys, Enjoy this time, I know I have a lot to be thankful for :)
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I called AB not too long ago with a hardware problem on a SLC and before they'd help me they wanted a SOFTWARE service contract no. My software IS under contract, but I refused to give them the number, because I don't think they should get away with trying to tie hardware warranty support to ownership of a software service contract. They eventually helped me with the hardware (rightly), but not without dragging their feet. What about users who own PLC's and no software? Is AB saying they don't have a right to warranty coverage on the hardware as a consequence?
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What about users who own PLC's and no software? Is AB saying they don't have a right to warranty coverage on the hardware as a consequence?
Good question, You buy a machine, it has a AB unit, it crashes, your tech works on it, no contract, now what? Buy a new unit, software,contract, and out source the program to some guy who likes to use his/her birthday as files........
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Yep Vern, there are a great many 'villes' around here. Went to Knoxville for Thanksgiving dinner, and on the way back I noted Knoxville, Maryville, Sevierville, Asheville, Rogersville, and Greeneville...and that was just over a 100 mile drive. I'm sure there are even more.
And yes, even with terrorism, wars, taxes, a crazy congress, a rockstar president, and a pitiful economy...true thankfulness is about focusing on what we do have, not obsessing about what we don't. Clothes, food, a warm place to sleep, safety, friends, family, churches, jobs, hope...given what we do have, complaining about the rest just seems petty, doesn't it?
Happy Thanksgiving all!!
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I was born in S.Cali. mostly named after long ago hespanic people, El Monte, La Puente, went to an elementry school named Cortez....... Not sure who they were. Most of the cities ther are named like that, moved here about 15 years ago and noticed that everything or just about had a "ville" after it, no big deal, just curious thought it was funny.
BTW, how many of you guys are hooking Chrismas lights to a plc? or have you done it yet? And if you do, what do(did) your nieghbors think?
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I have to agree with the "Shoe fits" comment. Back in the early days of PLC's
the cost of the PLC was a major component to the project, so designs would center around the one unit. Now, putting several small PLC's or remote I/O throughout an installation with comm links in between is cost effective and makes constuction much simpler. I've used an 05/06 combination on a machine and I'm in the process of adding another feature, controlled by another 05. Using the 05 has been easier since the option cards have been added. In the beginning of that series, there wasn't much to choose from. Now 05 06 and 205 coupled with a micro-graphic panel can handle most control applications. The nice thing about all of these products is that they work when you connect them together, the parts are less expensive than AB (for example) and the support hardware/software doesn't cost and arm and a leg (and a few other body parts) to have. Ok, enough on my rant. Keep up the good work! If I come up with any feature ideas, I'll be sure to add on.
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Modular gets my vote. I have had I/O go bad on the bricks and have had to move the I/O assignment or replace the PLC. When you have a system w/ many sites, are trying to maintain a programming standard, it's nice to replace a card and be done.
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I voted "other", the fact is, I dislike all three.
I suffer from a protracted and severe case of "Control Cabinet Anorexia". My ideal machine uses 100% remote IO, IP-67 rated, mounted directly where used and networked back to the PLC via fieldbus. No sub-panels either. Sub-panels make me sad.
I would like to see increased support for fieldbus. Modbus TCP is great, but let's see CanOpen, Profibus, Ethercat. It would also be a great way to add servo support in software without needing to add additional hardware to the product line.
My 2 bits (bits, get it? hah!)