Charles, sounds like your power units went through a 100% sort and those out of spec were corrected.  A "Bimodal distribution" is one that has 2 peaks, which suggests you have parts from two populations in those measured.  

You can get Cpk for non-normal distributions.  Statistical software packages like Statistica or Minitab can do it for you.  But for a truncated distribution like you describe, I'd guess there is no really valid method.

Lou Hart

----------
From:   Charles Law[SMTP:[log in to unmask]]
Sent:   Tuesday, May 16, 2000 4:38 AM
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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