On 15 Mar 2019 at 15:25, RussellMc wrote:

> On Fri, 15 Mar 2019 at 01:36, David Van Horn <
> david.vanhorn@backcountryaccess.com> wrote:
>=20
> > Does anyone know if transistor gain variations for the same part, unit =
to
> > unit, are distributed flat across the min-max or gaussian?
> >
> > Related, but not pertinent :-)
>=20
> Exact detail of the "what I did" fades with time (about 11 years ago) but
> the 'story' is true.
>=20
> I was in a factory in China where a large number of NimH AA cells were in
> the store.
> All the boxes looked the same and while the factory said that supply had
> been from several batches they did not know how to distinguish between
> batches or know any details about quantities etc.
> Some batteries behaved in an acceptable manner and some were substandard.
> It appeared that this may be batch based but this was not certain. The
> differences appeared to be on a per box basis but this was not 100% certa=
in
> and testing 100% or even sampling per box was unattractive.
>=20
> Memory fades, but I found a way to ID boxes by batch externally but this
> was not enough to weed out good and bad boxes.
>=20
> I asked if they had any 'scales' and they produced a digital office scale
> with a resolution of (I think) 1 gram.
> I started to weigh boxes and it became obvious that there were noticeable
> differences.
> I grouped batteries by mass in 1 gram increments on a box by box basis
> (Each cell weighed in the order of 25-30 grams so not many groups would
> have been expected.
> One set of boxes had a single peak weight distribution with a semi gaussi=
an
> distribution.
> The other set had a double peak weight distribution with one somewhat
> higher than the other, significant separation and a noticeable dip betwee=
n.
>=20
> Low spec batteries came from the double dip boxes and (probably) low mass
> samples.
>=20
> Absolute weighing would have probably produced a similar result but the l=
ow
> tail of the 'good' batteries probably overlapped the low tail bad batteri=
es
> which would have hidden both the different-batch cause and given a mix of
> good and bad lower mass batteries.
>=20
> The factory were suitably impressed. Such somewhat fortunate results help
> one's image and credibility :-).

.... were they also impressed with the solution being to add a small weight =
to the low=20
weight boxes? ;-)


--=20
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