I-Chart and X bar Chart Control limits

G

G.Pito

#1
Dear experts,
I am trying to provide a SW tool oriented to MSA and I have a simple questions:

1) Does I-Chart (individual Observation chart) need always to be associated with MR Chart? I need MR chart in order to calculate I Chart control limits UCL and LCL don't I? Does it make sense to show only I-Chart witl UCL and LCL = Mean +/- 3 sigma?

2) Same question for Xbar-chart: does it need alway R-Chart to be associated with?

Thank you for supporting a newbie :)
 
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Miner

Forum Moderator
Staff member
Admin
#2
Re: I-Chart and Xbar-Chart Control limits

The quick answer is:

1) The MR chart provides redundant information and is not necessary. That is, anything unusual in the MR chart is also apparent in the I chart.

2) The R chart is necessary because it does provide information about subgroup variation that is not found in the Xbar chart.
 

Statistical Steven

Statistician
Staff member
Super Moderator
#3
The short answer is you need the movR to calculate the control limits for the individual chart, even if you do not plan to chart movR values on a separate chart. Simply using +/-3S limits will give you wider limits than using 2.66*movR.

With subgroups greater than 2, the xbar and R (or S) chart is imperative as was stated, it contains useful information, as well as being able to calculate the Xbar control limits.


Dear experts,
I am trying to provide a SW tool oriented to MSA and I have a simple questions:

1) Does I-Chart (individual Observation chart) need always to be associated with MR Chart? I need MR chart in order to calculate I Chart control limits UCL and LCL don't I? Does it make sense to show only I-Chart witl UCL and LCL = Mean +/- 3 sigma?

2) Same question for Xbar-chart: does it need alway R-Chart to be associated with?

Thank you for supporting a newbie :)
 
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