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What to do with moving average chart after machine malfunction?

Discussion in 'SPC - Statistical Process Control' started by Future engineer, Jan 13, 2021.

  1. Future engineer

    Future engineer Member

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    Exactly, what to do? A cumsum chart is "restarted", beginning production after malfunction is a new "0 point". Should I do the same with a MA chart? Sources which I've found don't tell anything about that but there isn't written that it's prohibited, too. In fact a "pick" caused by unproper work of the machine may create a false perception of a process instability.
     
  2. Bev D

    Bev D Moderator Staff Member

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    typically you wouldn’t re-calculate the LIMITS. (You never recalculate limits after setting the baseline unless you have made an intentional improvement. There are some specialty charts that recalculate limits based on unique systems, but these have limited applicability) You would simply continue calculating the average and plot it. The moving average would have a blank for the first average after a reset. You can’t plot the moving average until you have 2 sequential averages...
     

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