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Difference between Control Limits and Historical Deviation

Discussion in 'Gage R&R and MSA - Measurement Systems Analysis' started by kyleruppelt, Nov 29, 2020.

  1. kyleruppelt

    kyleruppelt Member

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    Hi all, I am having difficulty understating something and battling to find clarity on what is required and why it is required.

    So in the MSA section the requirement is to use Control Limits and not specification limits on the MSA before SOP. To my knowledge Conrol limits are calculated by CL=m + or - 3*std deviation?
    What global is saying, is we must redo the study but use Historical Standard deviation from our SPC done with line side data collection.

    So when we redo the MSA using the same data from original MSA (using full range) instead if giving the Spec limits in minitab, we use the historical standard deviation option.

    1. What is the outcome of redoing or doing the MSA with Control limits and/or Historical deviation?
     
    kyleruppelt, Nov 29, 2020
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  2. Bev D

    Bev D Moderator Staff Member

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    Note that when using the historical standard deviation in your MSA study, you are not necessarily using statistical control limits. The historical SD in an MSA is the total standard deviation of the individual measurements. Control Limit formulas are dependent on the subgrouping/charting schema you use.
     
    Bev D, Nov 30, 2020
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    Andy Nichols likes this.