Re: "human" topload

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

The biggest factor affecting body C is going to be distance from ground.
For the purposes of ESD testing, they use a model consisting of a 100 pF cap
in series with 1.5 k.  Note, however, that the model was developed in the
19th century for investigating explosive gas mixtures in mines.  They still
use it because all the specs and test procedures are written in terms of
this, and when it comes right down to it, it probably doesn't make much
difference (unless you are trying make cheap IC's)

There is also a "machine model" (i.e. if your equipment gets a static zap
from a "box") which is 200 pF in series with 0.5 uH.

For what it's worth, a sphere 1 meter radius in free space has a capacitance
of about 110 pF.  If it is close (within 5 radii) of a grounded surface, the
C is going to rise.  The mathematically inclined (and masochistic) can do
this by considering the ground as a reflector and calculating the
capacitance between two spheres separated by 2d, where d is the distance to
ground.  This in itself is non trivial (there isn't a closed form solution).

I think the best way to measure it (which is the ultimate answer) is to set
up a tuned circuit where the Cbody is the dominant C, and measure the
frequency.  For completeness, one should use a number of test subjects
ranging in size from, say 3-4 kg (newborn) to 200 kg, and of varying
stature(both height and diameter).  One would also wish to have them placed
in various positions, and both clothed and nude, to identify any variations
due to clothing (which is both a dielectric, and a semiconductor).  I should
think that one could make a fine PhD thesis out of this, if you were
inclined....

Actually, has anyone ever scrounged up a mannikin and painted it with
conductive paint for their top load.. you could "animate" it with some air
cylinders so it's arms could raise and lower, etc....

Even an inflatable doll might work.  Hmm... my daughters have this 4 foot
inflatable alien that came from a trade show....Hallowe'en is coming.....
-