[802.3af] voltage offset proposal (was 1-point detection, monotonicity)
I have a proposal for the signature voltage offset requirement
as seen by the PSE. However, before I generate an official
comment to the editor, I am sending it to the reflector
for comment. I believe the proposal below is in
the spirit of our agreements, and it also eliminates
the one-point detection "loophole" in our former discussion.
The Proposal (in two parts):
Part 1: Change the valid detection signature maximum
voltage offset that the PSE might see to 2.8 volts,
instead of 1.5 volts (see p.8, l.11).
Part 2: Change the valid detection signature
voltage range for the PD V-I characteristic
to 2.7 - 10.1 volts, instead of 2.8 - 10 (see p.16, l.22).
Rationale for Part 1: the 2.8 volt offset:
Several meetings ago we agreed that the detection
test voltage would be 2.8 to 10 volts.
The 2.8 number was selected to allow for
voltage offsets.
Where did the 1.5 number come from?
I think this is what happened.
The PSE Detection Source Material gave its "must pass"
requirements in the form of circuits that could include
the "typical" two diodes. D1.2 put this into words.
Rationale for Part 2: the 2.7 - 10.1 PD voltage range:
This leaves a 100mV band for qualification testing,
and ensures that a slightly-out-of-spec PSE
will still detect a slightly-out-of-spec PD.
(Thanks, Dave D.)
John Jetzt