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Hi Chad and George,
We slightly off in calculations but I am not sure if you have the same cable length (48.5m from PSE to first MPD and then 0.1m between 16 MPDs). If possible, please send me your file and I review it to understand why we have slightly different results. Thanks a lot for reviewing our calculation and proposed annex and please let me know if you have any questions. Best Regards Arkadiy From: Chad Jones (cmjones) <cmjones@xxxxxxxxx>
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Arkadiy, George did not say it wasn’t a good idea to have informative annexes - he said we are late in the process and anything we add needs to be fully fleshed out and hopefully peer reviewed. The downside is
adding something that then requires more review stretches out the process. There are other avenues to publish this material, EA being one example. For BT, the EA published a white paper where the BT editorial team tried to translate the standards language
into plain English. But to your presentation, I too have made a spreadsheet to calculate all the details of each node. Michael Paul has a simulator that we’ve correlated such that I have confidence in my spreadsheet. In my spreadsheet,
I brute force calculate each node. To find the mixing segment current, I enter the cable resistances, the MPD power, guess a current (similar to your method but you're guessing final PD voltage), and then I use goal seek to find what mixing segment current
gives me zero current out the last node. For the Type 0 one, I get 1.06 A on the mixing segment (1.06245, so not 1.07 like you have), and my initial MPD voltage is 17.48V with the final MPD voltage of 16.12V. So we are slightly off. Even if I make the current
1.07 A in my sheet, I get 16.08 V at the last MPD. For Type 1, my MPSE current is 1.741 A and my last MPD voltage is 36.03 V. Again, we are slightly off. Before I’d agree to publish anything, I’d want to figure out why our numbers don’t better match. Yes, they are close but it appears one of us has an error. I was hoping Michael could pull numbers from his sim to
be the tie breaker. I’m happy to send you my spreadsheet if you want to look it over to see how our two methods might differ. (And to have a call to explain how my spreadsheet works). Regards, Chad Jones Principal Engineer, Cisco Systems Executive Secretary, IEEE 802.3 Working Group Chair, IEEE P802.3da Task Force Principal, NFPA 70 CMP3 To unsubscribe from the STDS-802-3-SPMD list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=STDS-802-3-SPMD&A=1 |
Attachment:
Annex 189 A rev 0.1 .docx
Description: Annex 189 A rev 0.1 .docx