CPU Loading: Control Logix PLC with Flex IOs

[MAKSM]

Hello Experts,

Can any one please tell me how to calculate CPU loading for L73 controller with flex IOs. I want to calculate the CPU loading before any programming. Thanks in advance.

Thanks,
MAKSM

 

[Bob O]

I Can't help with your CPU loading question specifically but
Integrated Architecture Builder may help


https://www.rockwellautomation.com/...-Tools&docid=01503dfdb8a20bf09c86944a6f44364b

 

[drbitboy]

Maybe I don't understand the question, but without knowing what the program is doing, how would someone calculate the load? Maybe you mean you know instructions the program will comprise but have not actually done the programming of the hardware yet.


There is some documentation related to the topic here, https://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm005_-en-p.pdf, though not much detail.



Specifically, that does not have specifics on per-instruction execution time. That type of information is available in this MicroLogix manual, https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1763-rm001_-en-p.pdf







I did some work with this on a MicroLogix 1100 and found that the published execution times seemed to be conservative i.e. longer than they actually take by a few tens of percents. I doubt that could be used directly for ControlLogix, but perhaps with some experiments on ControlLogix hardware you could get an idea of scaling between MicroLogix and ControlLogix, whether it was consistent across different instructions, etc.


Anything you do would be at best an estimate, of course.


I'm not saying anything earth-shaking here; this is just basic engineering i.e. multiplying by unity.

 

[the_msp]

Just adding IO eats up processor resources. I once IAB'd a 1,400 IO system and on a, think it was an L7X processor, would require 4MB memory with no code.

 

[drbitboy]

https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1756-rm087_-en-p.pdf


I stumbled onto that, and the title looks promising:


Estimated Execution Time and Memory Use for Logix5000 Controller Instructions