Poll: PLC and I/O form factors...please vote!

[Controls Guy]

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.

[ATU]

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.

[BobO]

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. 

[ATU]

Dangling those carrots out there again BobO?

[Controls Guy]

It gets even more interesting when you put the new protocol's random access functions on those high speed ports. You'll like it. 

New protocol?  Random access functions?  Splain, please.

[Controls Guy]

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.

[ATU]

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.

[BobO]

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.

[Daddyo]

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

[Controls Guy]

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.

[stepheneltze]

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. 

Is it possible that one of these three ports might be USB, perhaps similar to the c-more?                (please say "yes"!!!!)

[BobO]

It is possible.

[Joe]

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.

[Paulyo]

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.   

[PLCGuy]

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.