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SAP QM - 3 sigma limits in Control Charts

Former Member
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Dear QM gurus,

In the control charts which we get thru QGC1/2/3, can we set a 3 sigma limits ?

My customer wants the chart to be setup so that they can plot with 3 limits +/- with target line.

At the moment I can see in the chart is that limits can be changed only as below

upper action limit

upper warning limit

target

Lower warning limit

Lower action limit

Im looking for 1 more limit up and down, is this possible ?

Thanks

Mudassar

Accepted Solutions (1)

Accepted Solutions (1)

former_member42743
Active Contributor
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Ok.. I'm not a statistical guru but I think you mixed terms.  Maybe Martin can weight in on this one.

When you want 3 sigma limits it means that you want multiple limit calulated as a wider range, say as opposed to 2 sigma or 1 sigma and is related to the number of standard deviations.

When you specify warning limits and action limts you are specifying values at which you want something done.  You have two now.. and you are asking that you add a third?  How many warnings do your operators need? 

Craig

Martin_H
Contributor
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Craig, Mudassar,

I would go into the same direction: challenge your business colleagues about the sense of another limit. What do the want to do with it? One for warning, one for action (or similar, depends on the control chart type) is usual.

You might want to get familiar with the different approaches of control charts in general, and also on the way SAP implemented some of them in the QM module. A list of the control charts available can be seen e.g. on SAP help:

http://help.sap.com/saphelp_erp60_sp/helpdata/en/06/8bba53422bb54ce10000000a174cb4/content.htm?curre...

Best regards

MH

Former Member
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Craig,

What I understand from your comments is that for a 3 sigma limit - SAP has a standard way to calculate. Will it show the chart with 3 sigma limits.

Kindly review the attached image sent by my client and suggest further ....

This is what my client wants to see in SAP SPC Control charts.

Martin_H
Contributor
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You are confusing a 3-sigma limit (which is used to setup upper and lower
control limits for a process in SPC) with the requirement to have a third area (and therefore a third limit value beside the standard two that e.g. exist for a shewart card) on a quality control chart.

To answer your question: yes, SAP can display a chart that has a control limit calculated based on 3-sigma. But it will not look like your screenshot.

Regards

MH

Former Member
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So,

Is there any other way to have a chart to show the below limits?

SpecLimit

Warning Limit

control limit

Mudassar

Martin_H
Contributor
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Did you check if any of the control chart types that SAP provides support more than two limits?

MH

former_member42743
Active Contributor
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I think you could, but I think you might have to copy the FM used for one of the control charts and modify it.  You could probably modifiy it to calculate the warning limits and put them on the charat automatically since they seem to consistently be based on 1-sigma, 2-sigma and 3-sigma.  (that's not often the case for many processes).  You'll also probably need to copy/modify and ceate several other FM's to get the full functionality, i.e for instance evaluting the inspection lot based on the rules shown in  your graphic and triggering alerts or actions at each warning level.

Craig

anand_rao3
Active Contributor
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Hi Craig, Martin

I think the FM in control chart track mainly decides how the control limits are to be calculated. Does it create any new control limits in addition to the existing 5? I was exploring this in customization and observed that there is one functionality called whole number parameters but could not understand it correctly. Do you have any idea about it?

Thanks,

Anand

Martin_H
Contributor
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Hi Anand,

I am more into the quality part of SPC and normally do not dive too deep into the coding, especially not into the FMs. But basically you would create a whole new control chart type with the introduction of a third limit, and to me this sounds like a quite difficult thing.

Beside the technical part (the SAP implementation) I would expect other important things to be defined in advance, e.g. rules on the evaluation and the definition of actions. Most of the existing control charts have these rules already (or kind of best practice recommendations), like (just a hypothetical example) "if the warning limit has been exceeded 2 times in 4 hours you need to do a readjustment of the process". Mudassar still did not tell us why his business requires these 3 limits, which makes it difficult to judge what they want to achieve with them at all.

Regards

MH

Martin_H
Contributor
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To be a bit more precise: the "whole number parameters" seem to be two more constants in the customizing that are used by some of the control charts only.

As an example you can check the "moving average chart" (control chart type 520 (QRKT_MOVING_AVERAGE_2)). There one of the parameters is used for the moving range (number of samples).

Regards

MH

Answers (0)