Ancient EMC mythology, well proven to be wrong and so abandoned decades ago.
And still it pops on occasion and often with new twists to revive the
mythology.So it gets ignored as those new to the stories, such that they cannot
figure it out, will need the lessons of 'on the job training'.
ps. the proper terminology needed to clearly enunciate the concepts is not
settled.
The physics is plain and simple but to describe it takes a lot words due to a
lack of commonly understood terminology.
For example 'ground' serves as the catchall term, for shielding, signal return,
power return, zero reference, analog return, digital return, chassis, circuit,
logic, cable, AND for Safety as in earth ground.
Now Maxwell's law's (made up by a mad Scotman back in the 1800's) dictate that
a so-called signal must be accompanied by its return signal, and further more
that return signal will couple as close as possible to the original so-called
signal. The two parts are inextricably intertwined and cannot be considered
separately, without great risk to ones grasp of reality. Just as the alleged
E-field and H-field are two aspects of the same thing, which conveniently might
be called the Poynting Vector, and are related by the Impedance, the ratio of
the two fields, which in free space, well away from any conducting structures,
is approximately 377 ohms.
Now conducting structures, ones like a circuit 'ground', a chassis 'ground', a
shielding 'ground' and signal returns often called 'ground' and the concept of
'inside' verses 'outside' which seems to ignore Maxwell, are all going to make
for a rich realm of mythology which is not well defined and so, all sorts of
imaginings are created to fill all the constructed voids from using all these
artificial concepts, when one simple concept is necessary and sufficient to
complete the structure.
Aside: If that secret, the simple one, was to be 'leaked' to common knowledge,
we all would be out of a job in managing EMC since even the simple digital guys
could understand it. So we keep it under-wraps and obscure by using mysterious
language so that the neophytes and uninitiated think that they understand
and/or have no clue as to what is going on.
Always the correct answer: "It depends!"- Bill
From: "Grasso, Charles" <[email protected]>
To: [email protected]
Sent: Friday, June 23, 2017 10:53 AM
Subject: Re: [PSES] USB dongle connector shield filtered grounding
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{}#yiv4500181799 Hello John, Thank you – but the other half of the water
tank is not metal – it is plastic – a dongle after all. I am fully aware of
shielding and termination techniques – however I have not seen
a “filter” used to attach the connector shield to the circuit ground at the
dongle. I have also read that the industry convention now is to tie the
shield ground
and the circuit ground at the host only and “float” the peripheral connector
using the filter combo previously stated. Clearly (due to the lack of
response) no one else has run across this either! Thanks Charles
Grasso (w) 303-706-5467 From: John Woodgate
[mailto:[email protected]]
-
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