iSixSigma

ImR charts

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  • #43973

    Kanwal Kapur
    Participant

    Do Individual and moving range charts go together like X barR charts or we can use any of the two to monitor variation.

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    #140170

    Hemanth
    Participant

    They go together, the moving range chart is used to monitor the variation.
    Hope this is helpful

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    #140188

    GAC
    Participant

    They go together.  The sigma is estimated from the moving range value assuming a pseudorange of two.  The results is a “sort of” time series in which the variation, batch to batch, or lot to lot is judged by the average difference between each consecutive value.
    The variation is judged from both the excursions above the UCL on the moving range chart, and the standard signals from the individuals chart.  The mR chart essentially provides a value (the UCL) that is the predictable maximum difference between any two consecutive values.  The X chart is providing the same view of process behavior as a Xbar chart but with some sacrifices in statistical power. 
    This isn’t terribly important if the process is in good control and capability is high.  But, for lesser processes, the ability to detect a shift in the mean or overall change in process behavior as quickly as in the Xbar chart could be a problem
    Hope that helps.
    GAC

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