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Please help finding control limits!!!

Six Sigma – iSixSigma Forums Old Forums General Please help finding control limits!!!

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  • #49496

    walden
    Participant

    Im stumped on finding the upper and lower control limits using 2 sigma limits and deciding what chart to use. All that is given is the product number then the number of defects per product…
    product#1=7 defects, 2=4,3=3,4=5,5=6,6=3,7=8,8=2, 9=7,10=2,11=3

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    #169198

    Savage
    Participant

    You might consider a c-chart. The standard method of computing the control limits will be at +/- 3 sigma, not 2, but you can adjust for this.

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    #169202

    Ron
    Member

    Shewhart control charts use an approximation methodolgy to calculate the upper and lower control limits. each type of chart has it’s own unique formula for calculating th SD approximation.
    Don’t try using SD from other than the proper formula for the specific chart you are trying to chart.
     
    The one you are looking for could be a C chart, a U chart or an ImR
    depending on the particulars.
     
     

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    #169204

    walden
    Participant

    Thanks. I guess I will use the c chart method and find the ucl and lcl. I was a little confused because all of the previous scenarios I came across mentioned a sample size and  this one had limited information. Plus this scenario used the 2 sigma instead of standard 3. 

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    #169206

    SiggySig
    Member

    Chris,
    Out of curiosity, what is the application of 2 sigma control limits? Messing with control limits can have some pretty disastrous consequences…

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