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shahprabal
1 Posts |
 Posted - 26 Jul 2006 : 12:32:19
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I am recommending this control to my boss to purchase. He needs the following info before we can be sure this control will meet our needs :
- Does it calculate Cp and Cpk?
- Does it allow us to set Control Limits and Spc Limits optionally?
- Can the user click on any data point and get what values make up the sub group and what rules are violated (if any)?
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quinncurtis
1164 Posts |
Posted - 04 Aug 2006 : 16:12:55
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| We have updated the software to include the Process Capability Ratios Cp, Cpu, Cpl, and Cpk, Cpm, and the Process Performance Indices Pp, Ppu, Ppl and Ppk. Any downloads after 8/4/2006 will include these statistics. |
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Josh
23 Posts |
Posted - 30 Apr 2008 : 16:01:33
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Would you mind providing a sample of how perform and get the results of the calculations?
I'm creating an SPCBatchVariableControlChart object and after adding all my SampleRecords I call the Auto.... methods. After that I have the following line to get an SPCProcessCapabilityRecord object which I would expect to contain the results of the calculation.
Dim cpk As New SPCProcessCapabilityRecord(Me.ChartData, LSL, USL, SPCProcessCapabilityRecord.SPC_CPK_CALC, 5, "CPK")
LSL & USL are doubles which contain the Upper and Lower spec limits. I've tried calling cpk.CurrentValue (as well as other properties), but it only contains 0.0.
Thanks. |
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quinncurtis
1164 Posts |
Posted - 03 May 2008 : 18:21:40
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It is not clear, are you working with one of our many example programs that demonstrate how the process performance indices are added to a chart (displayed in the table section) ? I don't believe any of them do what you are doing. Look at TimeVariableControlCharts.XBarRChart
Me.ChartData.ProcessCapabilityLSLValue = 27
Me.ChartData.ProcessCapabilityUSLValue = 35
Me.ChartData.AddProcessCapabilityValue(SPCProcessCapabilityRecord.SPC_CPK_CALC)
Me.ChartData.AddProcessCapabilityValue(SPCProcessCapabilityRecord.SPC_CPM_CALC)
Me.ChartData.AddProcessCapabilityValue(SPCProcessCapabilityRecord.SPC_PPK_CALC)
If you want to retreive the values, use the ChartData.GetProcessCapabilityRecord method
' Retrieve in the order they were added.
Dim cpk As SPCProcessCapabilityRecord = Me.ChartData.GetProcessCapabilityRecord(0)
Dim cpm As SPCProcessCapabilityRecord = Me.ChartData.GetProcessCapabilityRecord(1)
Dim ppk As SPCProcessCapabilityRecord = Me.ChartData.GetProcessCapabilityRecord(2)
Dim pcvalue As Double = cpk.CurrentValue |
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Josh
23 Posts |
Posted - 05 May 2008 : 10:04:35
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| Works perfectly. Thank you for your help. |
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sfy
14 Posts |
Posted - 29 Jul 2008 : 04:39:36
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I added hundreds of subgroups(each made up of 5 samples) to the Xbar-R chart,How can I get the Cpk and Ppk value calculated from all of the subgroups on the chart which makes out the capability of process?
Thanks a lot.
go |
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quinncurtis
1164 Posts |
Posted - 29 Jul 2008 : 08:57:48
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| It seems like this thread already answers your question. It covers how to add process performance indices to the chart (repeating information described in the manual), and how to retrieve the values in your program, after they are calculated. Can you describe in more detail how the responses on this thread do not answer your question. |
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sfy
14 Posts |
Posted - 30 Jul 2008 : 03:43:57
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On the Xbar-R chart,there is Cpk and Ppk for every subgroup,for example,the subgroup on time 16:15 has 5 samples(1.51,1.54,1.48,1.49,1.52),
Does the calculation of it's Cpk only use the sample data in subgroup(16:15)?
BTW:the subgroup before 16:15 is 16:00,and the next one is 16:30.
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in the QCSPCChartNetManual.pdf,about page 159/380(SPC Variable Control Charts 153),there is the title "Process Capability Ratios and Process Performance Indices",on the next few page(156 SPC Variable Control Charts),it writes:
Cp = (USL ¨C LSL) / (6 * RBar/d2)
Cpl = (XDoubleBar ¨C LSL) / (3 * RBar/d2)
Cpu = (USL - XDoubleBar) / (3 * RBar/d2)
Cpk = MINIMUM (Cpl, Cpu)
=
X = XDoubleBar - Mean of sample subgroup means (also called the grand average)
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R = RBar ¨C Mean of sample subgroup ranges
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I was deeply confused,the Cpk value of subgroup(16:15) on the chart,how this value calculated?The raw data used to calculate it is only the samples of this subgroup(1.51,1.54,1.48,1.49,1.52)?
Thanks a lot.
go |
Edited by - sfy on 30 Jul 2008 03:51:18 |
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quinncurtis
1164 Posts |
Posted - 30 Jul 2008 : 09:02:46
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No, the calculation does not use just the data of a sample subgroup.
For a sample interval, the calculation of the process performance indices uses all of the past data, including all previous sample intervals, to calculate the mean (average of the sample subgroup means) and range (mean of sample subgroup ranges) of the process.
So the process performance indices for the LAST sample subgroup of the chart represent the overall process performance indices for the entire run of the process. That seems to be the value you are looking for. |
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sfy
14 Posts |
Posted - 30 Jul 2008 : 10:41:26
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For example,there are 100 subgroups on the batched Xbar-R chart(id:1~100),the calculated Cpk/Ppk value on the subgroup(id:100) is 0.228/0.231,you mean,the raw data used to calculate the Cpk/Ppk value(0.228/0.231) includes subgroups(id:1~100)? If yes,okey,it is what I want.
Thanks a lot.
go |
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quinncurtis
1164 Posts |
Posted - 30 Jul 2008 : 10:49:19
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| Yes. |
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sfy
14 Posts |
Posted - 12 Aug 2008 : 21:40:55
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In this library,is there any statistic util class/function we can call directly to get the "Process Capability Ratios and Process Performance Indices"(Cp, Cpl, Cpu, Cpk, Cpm, Pp, Ppu,Ppl, Ppk) without initiating the chart's GUI?
for example,the following subgroup data,we now want to get the final value of Cp,Cpl,Cpu,Cpk,Cpm,Pp,Ppu,Ppl and Ppk calculated by the whole subgroups:
subgroup 1 : 5.51,5.50,5.52,5.49
subgroup 2 : 5.50,5.48,5.54,5.47
subgroup 3 : 5.47,5.52,5.51,5.48
...
subgroup n : 5.49,5.50,5.52,5.47
If can,would you please show me some sample code?
Thanks a lot.
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Edited by - sfy on 12 Aug 2008 21:55:11 |
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quinncurtis
1164 Posts |
Posted - 12 Aug 2008 : 22:09:13
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| The process performance and process capability statistics can only be calculated as a result of creating an SPC chart as previously described. There are no standalone functions you can call that will calculated those values for an arbitrary set of sampled data. |
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Can .NET SPC Control used to calculate cp and cpk?
