Hello, Doug. As you know, the 'spherical model' is a classic joke about
physicists, but only half-joking because they do workas long as you
don't 'push' the model too far. Take a human of 80 kg who just floats,
they seem to have a 'spherical' capacitance of 300 pF (but I don't
trust my arithmetic this early in the morning).
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2018-06-20 00:10, Doug Smith wrote:
Hi John and the group,
Actually I was just kidding everyone. But I am going to start telling
everyone my body is about 24 pF/ns and see what happens. I will keep
an eye open for the men in the white coats with nets. Actually I have
been watching for them for some time now. Just completed a run at 100
F. Will be running in 111+ F on Thursday at the peak of the afternoon.
Some day I will act my age.....
Doug
On Tue, 19 Jun 2018 22:29:44 +0100, John Woodgate wrote:
I think the model should assume a spherical body of the relevant mass,
which capacitance in the archaic unit 'centimetres' is equal to its
radius in cm, and 1 cm = 1.13 pF. With all respect to Doug, I think
the BCI is about as scientific as BMI, which is at least a pressure
(kg/metre-squared) of some sort. I'm not sure what pF/ns would represent.
Of course the capacitance of a spherical grandmother of any radius is
1 nanafarad.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associateswww.woodjohn.uk
Rayleigh, Essex UK
On 2018-06-19 22:06, Doug Smith wrote:
Hi Ken and the group,
The model started out in IEC 801-2 which had a 150 Ohm, 150 pF model.
This eventually became IEC 6000-4-2 at 330 Ohms and 150 pF. Both were
meant to model a piece of metal in a human hand. Such a discharge is
an order of magnitude more severe, even for a tiny piece of metal in
one's hand, than a discharge directly from a human hand if one
measures the radiated EMI from these events.
The R and C above were the result of many measurements on people. The
first engineers to describe the IEC 61000-4-2 pulse as it is today,
with the sharp peak at the start, was Michael King and David Reynolds
back when dinosaurs roamed the earth in the last century.
There is a semiconductor device handling spec called "Human Body
Model" using 100 pF and 1500 Ohms. But, for me, there are no good HBM
simulators on the market as they all have metallic tips. They need a
tip composed of material that has the same volume and surface
resistivity as a human finger. There it goes, now no one can patent
the idea...it is now in the public domain.
Since capacitance goes by surface area, we may need a new capacitance
value as the population has gained weight. I propose we replace BMI
(Body Mass Index) with the BCI (Body Capacitance Index) a combination
of body free space capacitance in pF of a person and the number of
nanoseconds (at one foot per nanosecond) it takes for light to go from
head to foot. Like BCI = [body capacitance]/[body length in
nanoseconds at the speed of light]. For me that might be about 25
pF/ns. Some of my friends might be about 45 pF/ns.
Wow, two ideas in the same email!
Doug
On Tue, 19 Jun 2018 15:34:57 -0500, Ken Javor wrote:
What with Doug Smith being active in this sort of standard writing
activity, I doubt it’s simply inertia.
Ken Javor
Phone: (256) 650-5261
------------------------------------------------------------------------
*From: *John Woodgate <[email protected]>
*Date: *Tue, 19 Jun 2018 21:26:38 +0100
*To: *Ken Javor <[email protected]>,
<[email protected]>
*Subject: *Re: [PSES] ESD question
Probably handed down on a stone tablet in 1910 and no-one had the
courage to challenge it yet. (;-)
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk <http://www.woodjohn.uk>
<http://www.woodjohn.uk>
Rayleigh, Essex UK
On 2018-06-19 21:18, Ken Javor wrote:
ESD question Anyone out there know the origins of the 150 pF/330
ohm gun model used in EN61000-4-2 and derivative standards? It
seems it ought to be a human body model, but it isn't.
Ken Javor
Phone: (256) 650-5261 -
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