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SIMATIC S7-1500: Ai 8XU/I Hs Smoothing Duration quantification

Hello All,
I use a CPU 1513-1 PN CPU equipped on the same backplane with a AI 8XU/I HS analog input card (531-7NF10-0AB0). I only have one TP1200 and 3 S120 VFDs on this network. No isochronous mode has been set up (as I know of)
I have an unstable signal on the input due to the previous equipment in the acquisition chain. Nothing to do on that side.
I found out the "Smoothing" function in the hardware configuration of the card. I set it to Strong (k=32).
I would like to quantify this time window. In the manual the following formula is used :
"Smoothing time = number of module cycles (k) x cycle time of the module." (
Manual, 12/2016, A5E03484886-AE)
I am unable to find out what is the "cycle time of the module"
Is it the " Basic execution time of the module (all channel released) => 62.5 us
Or the "Isochronous mode Bus cycle time (TDP), min" => 250us
Or the "CPU cycle time" like for oversampling for example? => variable depending on OB1 or 10ms if OB35 used at 10ms
Thank you in advance for your answers.
Regards
Victor

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Answers(1)

Understanding Smoothing Time Calculation for AI 8xU/I HS (531-7NF10-0AB0)

Dear Victor,

You are correct to question the "cycle time of the module" for the smoothing function calculation. For the AI 8xU/I HS module, use the Basic execution time of the module (all channels released) which is 62.5 µs. This value represents the time the module needs for one complete scan of all channels, and is the correct basis for the smoothing time calculation.

Here's why the other options are not suitable:

  • Isochronous mode Bus cycle time (TDP): This applies only when isochronous mode is active, which you've confirmed is not the case.
  • CPU cycle time: While the CPU cycle time impacts overall performance, the smoothing function operates at the module level, not the CPU level.

Therefore, with your setting of k=32 (Strong smoothing), the Smoothing Time = 32 * 62.5 µs = 2000 µs or 2ms.

For further details, refer to the A5E03484886-AE manual section on Analog Input Modules and the Smoothing Function Siemens Industry Online Support.

Sincerely,
Siemens Self Support

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