posted 27 July 1999 02:17 PM               

I'm not an MSA guru but my understanding is it doesn't matter which you use. See page 32 of the MSA manual. My understanding is that R&R is to be addressed as a per cent of tolerance.

As far as linearity, bias, and stability - I have seen auditors ask about them and expect, in some cases, to see calculations. I would bet 80%+ of the auditors will not have a good understanding of l,b,&s. In the MSA they talk about bias of a system - but the MSA discussion is vague to say the least. They talk about system bias but confuse you with instrument bias.

Part of the problem here is going to be writing a procedure to address these issues. These things are generally looked at during early APQP as part of a knowledge base. That is to say in some cases linearity may be an important study and in others it is not 'significant'. I wouldn't write a procedure - I would say something like "the need for linearity and bias and stability studies will be determined by the APQP team. Where linearity or bias or stabuility is deemed critical or important studies will be done in consenance with the AIAG MSA manual.

But again, QS says you have to follow the MSA. The thing is - do you know enough to be able to discuss? For example, uncertainty is generally given by gage manufacturers - can you show and discuss these issues?

Part of my problem comes from the way the MSA manual is written. You keep reading about 'Reference Values' and they say '...the reference values of the parts can be determined with tool room or layout inspection equipment...' which doesn't explain much. And what do you do when your measurements are all done with the layout equipment (this is an issue of gage precision)? How can you do these studies when the most sensitive gage you have (maybe a CMM) is what you use to measure everything.

posted 19 March 2000 04:59 PM               

>From: Pfscott2@aol.com
>
>List,
>
>I'm looking for practical examples of how a small machining company (50
>people, 2 in QA) can analyze the bias, linearity, and stability of its IMTE
>as required by QS-9000 3rd edition clause 4.11.4.
>
>Before you rush to suggest reading the MSA manual, I have......well, I have
>tried. The more I read it, the more I became confused.
>
>Thanks!
>Glover Enop

Date: Mon, 6 Mar 2000 10:07:40 -0500
To: jennejohnn@uwstout.edu
From: Philip Stein pstein@measurement.com
Subject: Re: Q: Measurement system bias, linearity, and stability /Enop
Cc: iso25@quality.org

I have cross-posted this on the ISO 25 (Testing and calibration) listserve in the hopes that you will get a wider range of answers.

posted 20 March 2000 11:15 AM               

Bias, Linearity and stability are covered by our calibration programme.
If the gauge is biased, this will show when it's checked against a traceable master - and we have a tolerance stated in our calibration procedure.

We check linearity by doing calibration checks through the working range of the gauge (i.e at 10, 20, 30 and 40 Nm)so if the gauge is out at one end of the working range we will know, and we have a tolerance.

If our guage is not stable over a long period we will notice a drift from one calibration check to the next. If it is not stable in the short term, our r & r system will identify this.
This is putting everything very simply - which is usually good enough for any auditor I've met.

Cheers

posted 03 April 2000 07:23 AM               

quote:

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Originally posted by Dawn:

The MSA book says to use parts when doing a linearity study. Does this mean we must use parts or would it not make more sense to use standards traceable to NIST/ That is what I'm currently doing.

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