12.1: SPC Chart - Calculate Control Limits logic/rules?

[Former Member]

Hi,

I'm using 12.1 SP4 Patch 4 currently.

1. For SPC charts, there is a checkbox for Calculate Control Limits under the Control Limits for the Upper Chart Tab. What rules/formula does MII use for calculating the control limits? (I tried it and it looked correct but users want to verify how it calculates). See link for example: http://gunston.gmu.edu/708/XmR.asp?E=0

2. What does it do if Limits already exist for the input data set? Ignore the calculation?

3. Can this be set dynamically and refresh the SPC chart? (Set the Calculate Control Limits

UpperCalculateControlLimits Boolean property and refresh the chart? I've sometimes had issues setting these dynamic properties and having them take effect in charts so want to verify)

Thanks,

Kerby

[jcgood25 · Accepted solution]

1. I think you would already have the SPC help PDF document that has the formulas in it - Rob or Leey? In general, 3 sigma or standard deviation above and below the centerline(mean) based entirely upon the dataset returned by the underlying query template.

2. The Auto-Calc will take precedence over static limits, and the chart will use them accordingly. I'm not entirely sure, but if you look at the Summary Statistics popup from the applet you'll see EFFECTIVE and EST properties that will vary based upon the Auto Calc being enabled.

3. Yes, you should be able to 'check' the box through JavaScript and have the chart update with them. If you have issues with specific script then go ahead and post that snippet as a separate thread.

Regards,

Jeremy

[Former Member · Accepted solution]

Thanks Jeremy,

Alonso was able to find the SPC help document with the formulas after a bit of digging.

This looks like a good option for us and we'll adjust the display template depending on whether the static limits already exist for the specific parameter being charted.

Kerby

[former_member1170711 · Accepted solution]

Can someone please tell me where to find the PDF document referred to in this thread? I need the nitty gritty details on how the SPC is implemented.  I am trying to use MII to duplicate something we already have in Minitab and I am getting different results.  For example, the calculated control limits are not exactly the same in MII and Minitab for the same data.

Thank you,

Mike

[jcgood25 · Accepted solution]

Mike - it has been added into the online help documentation (under Actions, Quality, SPC Algorithms)

Message was edited by: Jeremy Good (sorry - the hyperlink was acting strange)...

[former_member1170711 · Accepted solution]

Got it.  Thanks Jeremy!