SherV

CPU Load Calculation

12 posts in this topic

Dear All,

My client ask me to estimate and calculate the S7-400 CPU Load based on IO Signals for generating the official document and I searched the Internet for siemens CPU load calculator in excel but can not find any. can you guys help me with this situation to find the solution and calculate that for my project?

Best Regards

SherV

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what do you mean by "Load based on IO Signals "? 

 

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I mean the cpu load calculation is based on Input/Output signals and loops type quantity and i need the calculator include this parameter and shown that in the tables 

thank you again for your asking and respond

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SherV

What cpu?

Its more complicated than just I/O,

How big will your program be?, how many pid loops?, how many bits, math instructions etc etc 

look at page 239 for example 

https://adegis.com/media/asset/62980bffb9be8c695300a7be8205648169ddffc9cc372fb8d47fb759915f9ddc.pdf#page231

Possibly make a spreadsheet from the instruction times on your cpu type

 

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Hi there,

i saw what you send to me and that was a good tip for me appreciate that, but as you know many parameter i should consider for that i just want to know do you have any calculator in excel file or something like that to add this parameters and calculate that or not because i see that file for another brands like honeywell or Emerson

thank you again for your respond 

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What information would you enter in for Emerson or Honeywell?

I would like to see details. Please post a pic of their spreadsheet 

Those are DCS systems. For Siemens you would use PCS7

Edited by jrw

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I have never heard of an Excel sheet for calculating CPU load... and I've been at this for 25 years.

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DCS platforms have relatively rigid configuration structures for large numbers of process loops at relatively slow update rates (1 second and 10 second, typically).  With such a background, and if the user sticks to it, a spreadsheet is not unreasonable for forecasting.

Totally useless with devices as flexible as PLCs.

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actually, I just saw that file and have not accessed that excel file from Honeywell to send you that information, and the problem is I should calculate the Memory and CPU Load before the project begins and document that for the client. if you have the solution on a manual that can help me with this situation or if there is a tool to do that I will appreciate that 

thank you again guys for your kind attention.

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Morning,

I never saw an excel tool to calculate cpu load for Siemens S7-300/400 Plcs. The only thing you could do is calculate yourself by adding instructions time for each instruction of your program according to your processor. Its a titanic job that is completly useless because I doubt you will ever meet a cpu load issue, except if your program is absolutely gigantic, and gigantic is weak :)

JC

Edited by acpi

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Write a sample program with one process loop with the features you need and all of the necessary overhead code. Compile it and note how much memory it uses.  Use the instruction documentation to estimate the execution time.  Place this into a spreadsheet as your "baseline" with x=1.  Copy the code and data elements to make it support 10 process loops.  Compile it and note how much memory it uses.  Examine the code to estimate execution time.  Add this into your spreadsheet with x=10.  Repeat a couple times with various values of x.

Extrapolate from there.  Add engineering margin to both CPU time and memory usage to account for user interface code and data.  (+100% would not be unreasonable.)

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Instruction execution time is also based on cpu type. So add a column for each cpu

Unless this is a huge process, this is a waste of time 

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