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troubles with saving control chart--"control chart sigma" becomes "specified sigma"

New user here, previously used Minitab.

I'm having a strange issue where, after I generate an IR chart with process capabilities calculated and I save the report, when I reopen the report later on, "control chart sigma" becomes "specified sigma." Moreover, the control limits on the control chart are somewhat different from before the save event. If I try saving to a journal I get the same problem. Anyone seen this before? Am I doing something wrong? My JMP version is 9.0.0.

Thank you!

Patrick

8 REPLIES

Hi patlu,

Thanks for spotting this. I was able to reproduce the title problem when saving the report. JMP development team will fix this for the coming release of JMP. I also wanted to let you know a workaround. You can double click the title and type 'Control Chart Sigma in there. From my observation, there was no problem on the control limits themselves.

Thanks,

Jong-Seok Lee

swelish

Community Trekker

Joined:

Feb 24, 2014

I am using JMP 11 and it seems to me the above issue has not been resolved. I my script for an IR chart and capability analysis to use the Control Chart Sigma but it saves a Specified Sigma instead.

Regards

Sean

Jeff_Perkinson

Community Manager

Joined:

Jun 23, 2011

Hi Sean,

When saving a script there is sometimes a natural tension between wanting to save a script that reproduces the results, exactly as you saw them, and saving a script that reproduces the analysis, which may have different results depending on the data.

In the case of the Capability analysis in the Control Chart platform we're trying to meet both of those requirements, sort of.

The computed Control Chart sigma gets saved in the script so that the capability analysis is using the same parameters each time it's run. If you would rather use a computed Control Chart sigma when the script is run, simply edit the script to remove the Sigma() specification in the Capability section.

Control Chart(

       Group Size( 1 ),

       KSigma( 3 ),

       Chart Col(

            :DIAMETER,

            Individual Measurement,

            Moving Range,

            Capability(

                 Distribution(

                 Continuous Distribution(

                 Column( :DIAMETER ),

                 Quantiles( 0 ),

                 Summary Statistics( 0 ),

                 Outlier Box Plot( 0 ),

                 Normal Quantile Plot( 1 ),

                 Capability Analysis(

                      LSL( 5 ),

                      USL( 3.7 ),

                      Target( 4.2 ),

                      Sigma( 0.265048929559034 ) // Remove this line to use the Sigma calculated from the control chart

                      )

                  )

             )

       )

   ) 

);


-Jeff
swelish

Community Trekker

Joined:

Feb 24, 2014

Hi Jeff

Deleting the Sigma() specification in the Capability script removes the Specified Sigma capability statistics but does not replace it with the Control Chart Sigma capability statistics. Only the Long Term Sigma (Pp, Ppk) statistics remain. Ideally I would like to be able to display both the Ppk and Cpk.

Thanks!

Sean

Jeff_Perkinson

Community Manager

Joined:

Jun 23, 2011

Hi Sean,

Sorry for the confusion.

I started working on this at one point and then picked it back up again and thought I remembered correctly what I had learned. Obviously, I hadn't. ;-)

You're right, you need to remove more than just that one line.

Try something like this instead:

Control Chart(

  Group Size( 1 ),

  KSigma( 3 ),

  Chart Col(

     :DIAMETER,

     Individual Measurement,

     Moving Range,

     Capability(

                

        LSL( 5 ),

        USL( 3.7 ),

        Target( 4.2 )

                     

        )

     )

);

-Jeff
swelish

Community Trekker

Joined:

Feb 24, 2014

That worked perfectly,

Thank you!

Sean

kayne

Community Trekker

Joined:

Jan 20, 2016

Hi there,

Adding on, are there any ways to save/capture/copy the sigma value under the Control Chart Sigma's diagram?

I understand that the sigma value under the Long Term Sigma's diagram is simply the std dev which can be taken directly from the table summary.

But what about the sigma value under the Control Chart Sigma diagram? Does anyone have the formula to calculate it?

Thanks,

Kayne

louv

Staff

Joined:

Jun 23, 2011

Kayne,

The formulas can be found here

http://www.jmp.com/support/notes/36/484.html