1/5/2022 7:32 AM | |
Joined: 10/7/2005 Last visit: 11/6/2024 Posts: 3026 Rating: (1055)
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Hi sixthomas
Yes, as far as CPU choice is concerned
Not quite. I'd leave the Send clock at 1ms to more evenly distribute the load. Step 7 arguably misleads when it displays a lower bandwidth figure simply by setting the Send Clock to a longer value (as it seems to only base it on the Send Clock rather than the Netload that will be experienced). Next is to check what the update time is set to for every IO Device (8ms perhaps?) as it greatly affects the Netload (and the update time must not be confused with the Send Clock) . As luck would have it, https://www.felser.ch/profinet-manual/t_-_timing.html contains a table that is based on 60 Bytes I/O data per IO Device (close enough to your 64 Bytes) and different update times. As you can see (or extrapolate from it), with 8ms update time per IO Device, you'll end up with ~30% Netload. A quick check with PI's Netload calculation Excel tool as attached confirms this too (I assumed 4 I/O modules per Device). While 30% Netload doesn't sound too bad, you rally do want to stay below 20% as per PI guideline (which would mean going for 16ms update time for at least some of the IO Devices) Tools like Indu-Sol’s PROnetplan or Siemens SINETPLAN cater for detailed Netload calculation and also allow inclusion of non PN IO Devices that may - or may not - per part of the Network (e.g. HMI's, programming Laptops etc.). Although these tools cost money to buy and require time and effort, it is money and time well spent to get this aspect of the design sorted out properly.
Can't say I agree with the post you referenced and will argue that using DPRD_DAT and DPWR_DAT will NOT lead to additional PN traffic. Instead these will simply read/write the latest values from/to the PN I/O Controllers buffer as and when called. If your process Image is large enough (and you don't need to have the most current values throughout the cycle) there's no need for DPRD_DAT or DPWR_DAT. |
Cheers |
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1/5/2022 4:14 PM | |
Joined: 1/24/2014 Last visit: 10/29/2024 Posts: 127 Rating: (6) |
First, thank you for your time for this discussion, really thank you
Yes, I declared different hardware configuration, and that's what I observed :
That is what I thought. DPRD_DAT increases the cycle time (necessarily with 64Bytes * the number of devices + the function itself), but does not modify the process_image, nor its operation. |
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