CPU Work Load

Hi to all,

In my Automation system i've a CPU 319 3 PN-DP. now the client ask for the work load of the CPU.

My question:

is the Work load the fill rate of the CPU memory?

Othewise exist  another way to calculate the work load of the CPU?

Thanks in Advance.

Duccio.

Hello,

Perhaps the following topic might help:

How can you obtain an overview of the memory concept of SIMATIC S7-300 CPUs and C7 devices?

Hi Online tech,

Thanks for your reply, i've already seen that post, but my question is if i can consider the fill rate of the memory as a work load.

for example if the load memory is at 80% used, is correct to consider that as a work load of the CPU at 80%

Regards.

Duccio.

Duccio

...

for example if the load memory is at 80% used, is correct to consider that as a work load of the CPU at 80%

...

No. The memory load is 80%.

The "CPU load" of a PLC is always 100%, it is working different from PC CPU.

If you want Information about the remaining CPU - "power", the SCAN TIME is a good value to describe that.

Good Morning Sirs,

Thanks to all for the support.

IBN, when i check the scan time in the CPU, the biggest time showed, is the maxium cicle time for the CPU?

For example:

You have a bar graph with minimum 0ms and mximum 100ms, actual cicle is 20ms.

Is the 100ms the 100% of the CPU capacity?

BEst Regards.

Duccio. 

Duccio

Good Morning Sirs,

Thanks to all for the support.

IBN, when i check the scan time in the CPU, the biggest time showed, is the maxium cicle time for the CPU?

For example:

You have a bar graph with minimum 0ms and mximum 100ms, actual cicle is 20ms.

Is the 100ms the 100% of the CPU capacity?

BEst Regards.

Duccio. 

Hello Duccio,

no, the 100ms is just the longest scan time that was processed.

The "100% of the CPU capacity scan time" is NOT depending form CPU but depending from your application.

And the scan time itself is depending from speed of CPU.

Example:

A large programm on CPU 312 needs 20ms scan time.
The same program at CPU 319 perhaps just need 2 MS, so this CPU is 10 times faster.
But a veryvery large Programm may need 500ms even on CPU 319.

BUT if the machine running well with 20ms or it need a higher speed processing from i.e. 2ms is depending from your application.

Some slow application can work with scan time from 1000 ms, some fast application needs scan time faster than 5 ms...

So it is not possible to say what is 100% of CPU speed capacity.
You must ask, what is the maximum scan time that is allowed for your application.

So you have to take care selecting your CPU in that way, that it is fast enough for you application / machine.

"Dark and Dirty" Statement:

Mostly, scan times of 20ms and faster are fast enough for most applications.
and scan times much longer than 100ms may bring problems with a lot of applications.

Hi thanks for your explanation.

I'll try do explane that to my client.

Thanks a lot.

Duccio.