ControlLogix Flavors

How many different variants are there, how do they differ, and how do you decide which is best for your application?

Is it just speed and memory and tag list size?

As far at the 1756 ControlLogix the L7x the only differences is memory size from the L71 to the L75. Speeds I believe are the same. So basically memory will limit how much you can do with an L71 vs an L75. The L8x series have a 1GB embedded Ethernet port and are significantly faster than the L7x. There are some limitations with the L8's like they don't support redundancy which was covered in another post. Integrated Architecture Builder has a tool that might help size a controller.

If this is a new system, one thing to keep in mind is the total cost to build out the processor and Ethernet communications. Generally when you get a processor, you need communications as well. I have spent some time looking at the differences between the L7X and L8X series. I currently run mostly L72 processors and a 1756-EN2T card for communications. When they released the L8X series, I got quotes for the 1756-L82E processor expecting a big price gap. I was surprised when I got the price back and it was less than the the L72 and EN2T card. My initial hesitation was that they were new so I waited to get one.

Three months ago I finally decided to swap a 1756-L72 with the new 1756-L82E due to the expansion of the system and the amount of PIDE Loops I had running. I have been happy with the performance difference as well as getting a slot back on the rack because the EN2T was no longer needed. My overall scan times went from 23ms to 4ms. The 23ms scan wasn't a problem, it just buggged me to see it that high.

The one downfall is that I needed to update the SCADA Kepserver software version to support the new processor and I am now running version 30 of Studio 5000. Don't get me started on Rockwell's version control! That's for another thread all together!

The other variant is whether you want guardlogix for safety or a standard processor

Wow! Thanks! Great info! 4 millisecond scan time ... that's crazy!

For safety, we've typically used a standard processor. Don't know anything about guardlogix yet.