on 10-08-2015 11:36 AM
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
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
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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
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
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
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
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
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
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