P Chart With Variable UCL

[Former Member]

Hello,

I am trying to use an iSPCChart in P mode. My sample size varies per point and I am specifying a Sample Size Column on the display template's Data Mapping tab. I have the box checked to Calculate Control Limits on the Limits tab.

My problem is that the upper control limit does not show up on the chart even though I have Show Control Limits checked on the Upper Chart tab. The lower control limit does show up.

Is there a way to get the UCL to show up on the P chart when it is calculated and it varies due to varying sample sizes?

Thanks,

Mike

[agentry_src]

Mike,

There may not be a simple answer without more information. What is the UCL that is not displaying (value)?

Under Upper Chart Axes, what are the settings? What is your overall data range? How many lines are you displaying? What else can you tell us about the data being displayed?

Thanks,

Mike

[Former Member]

The chart is autoscaling and zero relative. The Y axis goes from 0 to 0.05. The UCLs that are not showing range from 0.02 to 0.05 (depending on the sample size corresponding to the given P value). The P values vary from 0.0 to 0.04 and the sample sizes (derived from a column as stated above) vary from 20 to 101.

Show control limits is checked on the upper chart tab.

I am only trying to display 3 lines, P, LCL, and UCL. The first two are showing up. UCL is not.

I am guessing this may have something to do with the fact that the UCL is not static but it sure seems like it should show up anyway.

Thanks,

Mike

[agentry_src]

Mike,

Try turning on the Server Scaling and maybe the zero relative. I found out the hard way that the zero mid point check box in line charts does not work or at least it didn't with the rest of my settings. I am working with 12.0.2 right now and there were several issues with display templates that were supposed to be fixed in Service Release 3 and possibly 4, but I have not tested them.

I have not used the P charts much and not since 11.0. I know from my experience with line and other standard charts that the behaviors have changed at least a little bit with virtually every new version, so there is always some trial and error testing to do. You did move up to 12.0, didn't you? Which of the service releases are you using?

Thanks,

Mike

[Former Member]

Hi Mike,

Thanks for trying to help. Unfortunately your suggestions did not make any difference. We are running 11.5.3 b66.

Thanks,

Mike

[Former Member]

Check the SPC Results detail for your data set by right clicking on the chart applet --> Data --> SPC... and see if the limits are being calculated or not.

I suspect in your case they are not being calculated (you will see an NA against those in the data detail).

Visit http://www.sixsigmafirst.com/controlcharts1.htm awhere they have explained the calculations behind the p - chart among others.

[Former Member]

Hi Udayan,

It appears that the UCL is being calculated. If I do a right-click on the applet and then Data -> SPC Results Detail, each position has a UCL listed. They range from 0.02 to 0.05 (depending on the sample size).

In the summary section at the top of the SPC Details, however, it says NA for UpperChartUCL. I think this is because I did not specify a static UCL in the template.

Also, on my chart one of my plotted points is red indicating that the upper control limit alarm point has been exceeded. The control limit alarm is the only alarm I have turned on.

So, I think it is calculating the UCL properly and that it is using it properly in terms of assessing the alarm conditions but, for some reason, it is not drawing the UCL on the chart.

Thanks for your help.

Mike

[Former Member]

So does anyone know if this is a documented bug or not? Our six sigma deptartment posed the same question to me today regarding variable UCLs and I ran into the same problem. We are running version 12.

[agentry_src]

Mike/Matt,

I would suggest opening a CSS ticket so it can be worked on.

Regards,

Mike

[Former Member]

Hi Matt,

I opened a ticket on this and it resulted in SAP Note 0001225959 "SPC Variable Control Limits" being written. The bottom line is that it is not supported at this time. There is partial workaround using a line chart that is documented in the note. It also contains a 12.0 project that shows how to use the workaround.

I have also asked that this feature be supported in 12.1 if possible.

Mike

[Former Member]

Hi All,

Does anyone have an update on this?

I am using 12.0.6 and am experiencing a similar problem as Mike: UCL and LCL are not being drawn, though they are being calculated (and used in alerts) in the "SPC Results" -> "SPC Detail".

I do notice however, like Mike, that the "SPC Results" -> "SPC Summary" UpperControlLimit and LowerControlLimit are NA. I presume that this is related to the problem. I can fix the control limits and they display in the chart OK.

Thanks again.