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usage of X-bar R Xbar s chart

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  • #50353

    fresher
    Participant

    Hi Team ,
    will appreciate if any one help me in understanding the difference of -X bar R & Xbar s chart , and their usage, i mean when can u use which .
    regards
    fresher
     

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    #173076

    Bower Chiel
    Participant

    Hi FresherBoth chart pairs do the same job. In his book Introduction to SQC Doug Montgomery advises using Xbar and s charts rather than Xbar and R charts 1. When sample size is greater than 10 or so and 2. When sample size is variable.
    Best WishesBower Chiel

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    #173081

    fresher
    Participant

    hi Bower,
    tnx for u r input , so should i say for a varaible sample of more than 10 one should use Xbar-s & for lesser sample we should use Xbar-r ,
    hope i have understood u r guidance propely ,
    regarsds

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    #173082

    Ax Campos
    Participant

    Hello
    Another criteria is to use X-R charts whenever you have to make the calculations by hand directly at the work station. The reason for this is that it is a lot easier to calculate Range than Standard Deviation.

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    #173083

    fresher
    Participant

    thnks & whar abt for xbar -s

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    #173091

    Ron
    Member

    Xbar & R charts are useful… in any application however, when your sample size is greatewr than 25 -30 statistically you can actually calculate the standrard deviation versus estimating as the Xbar chart does.
    So use the Xbar & S when you have extremely large sample sizes.
     

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    #173240

    Bart
    Participant

     
    A nice definition from the Minitab help menu:
    Xbar S process behaviors charts display a control chart for subgroup

    means (an X chart) and a control chart for subgroup standard deviations (an S chart) in the same graph window. The X chart is drawn in the upper half of the screen; the S chart in the lower half. Seeing both charts together allows you to track both the process level and process variation at the same time, as well as detect the presence of special causes

    . See [31] for a discussion of how to interpret joint patterns in the two charts.
    X and S charts

    are typically used to track process variation for samples of nine or more, while X and R charts

    are used for smaller samples.
    BDR

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