ElectronGuru

CompactLogix Point I/O Module Limits

9 posts in this topic

Hey guys,

I did a quick search here and didn't come up with anything, so hoping I'm not asking something that has already been answered.

I'm looking at automating an existing plant which currently has zero controls, so starting from scratch. The process isn't complicated but the equipment is a bit spread out over a two story facility. We're thinking about using a CompactLogix 1769-L32, physically located as central as possible, with ten four-slot 1734 Point I/O blocks. My concern is that many Allen Bradley controllers limit the number of I/O modules you can add to the project. Like some 1756 controllers are limited to 30 local and remote I/O modules, CompactLogix controllers may be limited to 16 local and who knows how many remotes, etc. I can't find anything that spells it out explicitly in the Design Considerations Manual. The CompactLogix 5370 User Manual only says it supports, "a limited number of Point I/O modules that can be used as local modules". Nothing about networked modules. The CompactLogix Selection Guide clearly defines the number of network nodes, but nothing about the number of modules.

Does anyone have any direct experience with this much Point I/O in a CompactLogix environment? I'm thinking that we're in an age of counting nodes, rather than modules but don't want to order the hardware without being 100% sure.

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@ElectronGuru you're not going to be concerned with module count, what you want to look for and it is in the manuals is the connections count.  Each module and/or each rack depending on Rack Optimization.  I know we hooked a controllogix L6x to 128 Gppro HMI back in the day and it took 7 ethernet modules because of connection counts per ethernet module.  You'll find your CPU has a connection limit and ethernet port has a connection limit as well and they aren't the same.  You'll also learn or take my word that once you're over 25% of limit things get sluggish at at 50% they get flaky.

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Posted (edited)

It's been about 12 years but I connected 5 small point IO racks to a Controllogix box that had two remote racks on it. All of the remote racks were on EN2T's (maybe ENBT's, I wouldn't use an ENBT). 

The link to the point IO racks was made with an MDS i-Net 900 MHz radios (one master and 5 slaves). Distance was a couple of miles. It worked great until the trees leafed out and the signal dropped out. I had to go back and raise the antennas

 

Edited by Michael Lloyd

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That's good advice, @BobLfoot. I am aware of connection counts but had no idea things slow down that much at such a low usage rate! 

Side-note: When going down this rabbit hole I found that the 1756-L8 controllers controllers have completely abandoned connection counts in lieu of Node limits. I'm wondering now if performance on the L8s deteriorates as quickly with added nodes as it does with connections. 

Thanks for the quick response! I can now proceed with confidence!!!

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@ElectronGuru please keep us posted how it goes and anything you learn.  Especially if you're using an L8x.

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Electron the easiest way is to build a project and add the AENTs.  It will then tell you what the max module limit is.  Again, as mentioned by others, you'll want to use rack optimization to reduce the connections.

But the real limitation, especially in the L32E is the number of TCP and EIP connections.

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It's very empirical and not particularly scientific, but we once built a system using an -L33ERM that did motion control of a single-axis Kinetix 6500 along with two PowerFlex 525 drives, an SMC valve bank, a Red Lion HMI, and a data exchange link with a ControlLogix -L71, all over the same Ethernet port. There were zero issues with communications lag or anything. The servo was a linear motor that was constantly cycling (synchronized with pneumatic cylinders controlled by the valve bank) and would move back and forth with one direction a fast move and the other direction having a slow section in the middle. Performance was flawless.

Where I am now, we have a large system with a bunch of CompactLogix processors (11 total). One is an -L24 with an HMI, a VFD, 2 servos, 2 1734 racks, and datalink to 2 other PLCs on the line. It's also handling it with no issues.

Without doing a node/connection count, I really don't think you're going to have any trouble at all. Only thing I would suggest is make sure you physically separate the office network from the machine, either using a managed switch or physical isolation. I have seen issues with that. We had a ControlLogix -L55 connected to an HMI and a single Flex-IO chassis (through an -ENBT) that would drop communications to the Flex chassis as soon as the office network was connected. We ended up adding a second -ENBT for the office network. Given today's security situation, that's probably a prudent idea anyway...

 

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Thanks for all the great feedback, guys! We're in the planning stages now and probably won't start building the system until this Fall, during this small manufacturer's normal slow season. I will revisit this thread and post anything we may learn.

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It’s been a while since I looked but Rockwell had an enet resource tool to build your system and test if the hardware would support the number of connections. Look on their IA site

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