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February 2012

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From:
"Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES]" <[log in to unmask]>
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TechNet E-Mail Forum <[log in to unmask]>, Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES] <[log in to unmask]>
Date:
Fri, 17 Feb 2012 14:54:39 -0600
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Hi Rich,

I am working right now on the approval of a non-standard cleaning process for one of the NASA projects and have been wrestling with a similar topic. What I want to do is to use the ROSE Test as a Process Control tool but want to use Statistical Process Control to do it so that I can see and react to trends over time.

The biggest problem that I have encountered is that the community uses the ROSE test in different ways. Some of us establish a time limit 10-15 minutes and some others let the test run until the reading stabilizes. Of course you are going to get two different type of results. Statistically speaking these are two completely different approaches.

If anybody is doing it I would really like to know how they are using SPC Tools to monitor ROSE test results:
- What are the test conditions for the ROSE Test?
- What type of SPC chart are they using?
- What specification limits?

Once you can frame the process like this, coming up with valid Cpk data is a breeze.

I believe the trick to avoid the data to be skewed are the considerations for the test. Please correct me if I am wrong but something like limiting the duration of the test will do just that, skew the data.

Rigo

Sr. Quality Assurance Engineer
Workmanship Standards, Code 300 
NASA, Goddard Space Flight Center
Greenbelt, MD  20771
Phone. (301) 286-6129
Fax.       (301) 286-6576

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard Kraszewski
Sent: Friday, February 17, 2012 3:22 PM
To: [log in to unmask]
Subject: Re: [TN] Correlation Factors for ROSE Testing & Cpk

Thanks to all who responded to this string. Realized it could strike a chord. 


To carry this a step further on a very related topic... 

Any of you guys ever try to run a Cpk on ROSE data sets?  Most of the times I've tried to over the years, the data sets have been non-normal, single tailed distributions, with highest counts near zero and then tailing off towards 10.06. (Similar to having only the right side half of a normal distribution curve).  They have defied data transformation to a normal distribution, hence can't really run a proper capability analysis (data of course must be normal for a Cpk).  

You could of course (at least within Minitab) try to run as a non-normal distribution and just report a PpK, however with such a high count near zero it's next to impossible to find a statistically supportable non-normal distribution. 

I would appreciate any related experiences and/or thoughts on this topic.  


Rich Kraszewski

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Richard Kraszewski
Sent: Thursday, February 16, 2012 2:00 PM
To: [log in to unmask]
Subject: [TN] Correlation Factors for ROSE Testing

While I realize that IPC specifically and the industry in general, does not support the use of ROSE correlation factors for the various testers, I have a need to see the official document that at one time quoted these specifically allowed factors.

I took a cursory look though all 230 pages of IPC TR 583 and didn't see that table. 

I seem to recall a military specification that had that table. Was it 454? 28809, 2000?

Does anyone recall?


Rich  Kraszewski / PLEXUS
 



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