Controllogix – Controller sizing/IO cards/Power questions

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  • #3298
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      Hi guys,

      This is my first time working on panel design and working with AB. This is a food industry application, most of the components I am wiring are either switches and solenoids.

      I need to specify the various components I would need and need to prepare associated drawings. I have a couple of questions, really hoping someone could point me in the right direction.

      I need to use controllogix. I have about 35DIs, 35DOs and 2AIs. Power coming in is 120VAC.  I was thinking to use:

      1756-IA32 (qty 2)

      1756-OA16 (qty 3 as there doesn’t seem to be an option for 32)

      17556-IF6CIS (qty 1)


      There are some devices that use Ethernet/IP for communication

      1. Is there an online tool that we can use for sizing controllers. I am trying to figure out how much memory I would need.
      2. I am considering Controllogix 5580 controller. What does the attribute in the manual means? like 1756-L84E, is this an extra component that I would need to get based on how much memory I require?
      3. Looks like the IO modules need external power so I will be bringing the 120VAC. Yet it also seems that sometimes they can be power through the backplane. I found that for the backplane my options seemed limited to 24VDC
      4.  Is there a place online where I could get the io cards template so I can wire my devices to it?

      I know these are lots of questions, but I am honestly out of my comfort zone and just trying to learn by means of the internet. If anybody can help me out I would appreciate it. thank you!



        Hi Antuaneth and welcome to the forums!

        The type of I/O modules you spec are going to correspond to the voltage of the I/O components you will be using. For example, the voltage of your solenoids, proximity switchs etc. If this is something that you will be choosing also, then you may want to look at the 24VDC options, as most controls are moving to the 24VDC variety for safety, variety as well as other reasons.

        As for the catalog number of the various controllers, this largely corresponds to the memory size of the given processor. You mentioned the 5580 series, I actually did an article that compares these different processors, . You may want to give it a read.

        As far as software tools go to help you layout/design your system at a high level you could look into Studio 5000 Architect. It is designed exactly for this. You can check it out here: Of course this is not a free tool as far I know.

        Based on your IO estimates I don’t suspect you are going to need a lot of horsepower in that regard and could possibly look at the CompactLogix line of controllers if your project will allow it. There’s some cost savings there if you can, and it still uses the Studio 5000 programming environment.

        Most IO modules you will provide field supplied power to (120VAC or 24VDC), with some exceptions of course. My advice for any particular IO module is to go to the Rockwell website and search for the particular module. Here is the Product Configuration Assistant page for ControlLogix modules.

        On this page just click on the module you want to see and it will bring you to the associated drawings and wiring diagrams for that module. Also you’ll note a tab for “Documentation” in here you can download the user manuals for all sort of modules for more indepth understanding.

        Hope that helps!


          Karma: 187
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          I would certainly be wary of using 120VAC fo the control system. I am not sure where this system is to be installed but many PLC Programmers and Controls Tech types are not Licensed Electricians. Many states required a license to work on voltage of 120VAC and this will mean your contractors and installers need to be as well.

          I know that there are many different components that rockwell offers, and I am not totally sure of your application however, I make it a rule to always use the 24VDC High Density I/O cards for DI’s and DO’s then drive 120 or whatever voltage I need using Relay’s or if I have 120 coming back from the field, use an interposing relay to switch back down to 24VDC. Also High Density I/O is not often a huge difference in price, and makes a difference down the road when you need “JUST ONE MORE DI” for some crap management has decided they want to see of the SCADA. Literally been the song and dance for the last 2 projects ive done, and the answer was to add a RIO to add on the one more DI and 2 DO’s. Just something to consider.

          This also makes building the panel easier, as all of your field wiring can be brought into terminal blocks and shop testing / FAT is much easier.

          However, rockwell has alot of tools including the Product Selector that you can utilize or call the Tech Connect number, they can give you 100% of the engineering limitations of any piece of hardware.

            Karma: 171
            Rank: Jedi

            Antuaneth hi, and welcome to the forum. As Sean said, 120 V control creates some problems. I worked for years in the seafood industry in Alaska as an industrial electrician/PLC programmer. I had to work on a lot of European equipment that used 230 VAC control power, and they were very dangerous and parts were hard to get.

            In my job now, my company almost exclusively uses 24 VDC. Easy to work with and safe to troubleshoot. If you do need 120 for say hydraulic solenoids or other high current devices, you may want to check the current rating on the output cards (modules) and possibly use interposing relays for the outputs. I’ve also had to install surge suppressors on the 24 VDC relays to keep them from having current spike issues when de-energizing. I had a lot of trouble with that on some totalizers one time.

            Lastly, unless the customer requests otherwise, we supply sink/source modules for everything, mainly because it is easier to configure the wiring for a device that’s changed from say PNP to NPN than it is to change a module if a device cannot be found or is hard to get. And, I’m not into hardware design much; I did some as a favor a couple years back and although I learned a lot, it’s not for me. Good luck and if this was any help at all, then you made progress!!

              Karma: 129
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              Hello Antuaneth,

              I would Highly suggest using the Rockwell Integrated Architecture tool.

              This is a free download and will allow you to put in you I/O count and it will design a working system for you. Check out this Video from Amy Carter at Gerrie, She does a great job demoing the tool.



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