Hi,

If I understood right the supplys where the output voltage where out of
tolerance where re-adjusted and output voltages at the patch varies from
minimum tolerance to maximum tolerance. Of course the distribution is not
normal, it is something else. Maybe there is a way to calculate the Cpk, but
that is not a problem as I think. If we look the problem from the customer
point, is the output voltage just inside the tolerance better than a output
voltage just out of tolerance? And the power supply will be installed to a
some system where the other parts has also variation. To ensure that all the
parts works well together, the target value and tolerances for the
parameters are set. If all the parts uses the they tolerance ranges like
your supply, do you think that the system will work well?

If you like to improve the quolity and assure the customer satisfaction, do
not screen off just the unit, where the output voltage is out of tolerance
but try to narrow the distribution improving you first
adjustment/calibration so that that the deviation from the target is minimal
with reasonable cost and ensure that the first time cpk is over 1.33.

B.R.
Jarmo Kiiski

> -----Original Message-----
> From: Charles Law [SMTP:[log in to unmask]]
> Sent: 16. toukokuuta 2000 11:38
> To:   [log in to unmask]
> Subject:      [TN] Distribution Mode for Trimmed parameter
>
>      Hi,
>
>      I believe that all of you must have some ideas on the term "Normal
>      Distribution".
>      What I am now facing is a population from batch of power supply
> output
>      voltage.  Since some power supplies had failed in meeting the
> customer
>      specification at their initial measurement, output were then adjusted
>      by tuning the trim-pot in the power supplies.  After that, I measured
>      the output voltage of all the power supplies then drew the
>      distribution graph.  You can see that the distribution is now clipped
>      at both ends.  Does anyone knows how this kind of distribution
> called?
>      And, if I cannot use the formula for a normal distribution to
>      calculate the cpk , what can I use to measure the process capability
>      under this condition?
>      Besides, does anyone know something about "Bimodal Distribution" and
>      how is it defined?
>      Comments are welcome.
>
>      Best Regards,
>      Charles
>
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