Hi Peter,
going through your presentation for next Wednesday’s meeting I have some comments:
Looking on slides 4 and 5 (and also the other slides in your presentation), it seems, that you modified the “N” value in the alien noise limits depending on where the measured IL exceeds 16 dB or 21 dB and not depending on which is the IL of the link segment at a fixed frequency of 20 MHz. In the alien noise limits I suggested the factor “N” is changed from 0 to 1, if the IL at 20 MHz is above 16 dB and changed to 2, if the IL at 20 MHz is above 21 dB. This is valid for the complete limit curve and not adding frequency dependent “edges” into the limit curve, like shown in the graphs in your presentation.
I hope, that this significantly reduces your concerns, as there are no IL(f) dependent changes in the alien noise limits, once the factor N has been evaluated for a link segment.
Regarding your concerns related to AN, I agree that we have a lower plateau for the short link segments of 50 dB (for approx. up to 300 m) or 55 dB (for approx. up to 400 m) instead of 60 dB as for 10BASE-T1L.
For the low speed AN signal we have a very low communication signal frequency (625 kHz Nyquist frequency). Even at a 50 dB plateau and assuming 2.4 Vpp disturbers and only 1 Vpp for the AN signal we have more than 38 dB margin (50 dB – 4 dB (IL for 300 m @ 625 kHz) – 7.6 dB (2.4 Vpp vs. 1 Vpp) = 38.4 dB), which is close to a factor of 80 in amplitude between noise and AN signal. Thus I do not expect the lower plateau to be critical for AN.
Comparing the IL limit of a 10BASE-T1L segment at 625 kHz, which is 12.5 dB with the 4 dB IL of a 300 m 100BASE-T1L link segment at 625 kHz (which is close to 16 dB IL at 20 MHz), we gain 8.5 dB, thus I would expect the 50 dB plateau for 100BASE-T1L 300 m link segments to provide a similar noise immunity than the 60 dB plateau for 10BASE-T1L.
Related to the suggested TCL values of up to 60 dB (for E1 and E2) and coupling attenuation values of up to 60 dB (for E1 and E2) or 70 dB (for E3) I personally see these high TCL/coupling attenuation values technically critical, and this not only for e.g. the DIN rail terminals, but also for the complete system.
Even if it is possible to meet these values using a good cable, from my perspective it would become pretty “hard” for the complete system to meet these requirements (e.g. a signal isolation transformer instead of capacitive coupling would be required, there is need for low tolerance components in the power and signal coupling networks, a very carefully designed symmetric layout is needed, shielded connectors might be needed, etc.).
EFT testing for 100BASE-T1L is expected to be significantly more critical than for 10BASE-T1L, but this is mainly caused by the higher communication frequency of 100BASE-T1L compared to 10BASE-T1L, which is much closer to the ringing frequency of an EFT impulse on the line and thus cannot easily be filtered out by the PHY receiver. Thus having 10 dB better system TCL values would lead to an improvement, but likely not prevent telegrams from being corrupted during EFT testing and on the other side lead to significant side effects in system design (as not only the cable needs to be improved, but the whole system).
Thanks.
Regards,
Steffen
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