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Linearity Problem (MSA - Measurement System Analysis)

Rameshwar25

Quite Involved in Discussions
#1
Whenever i have done linearity study, my calculated values never satisfied following criteria:
R-Sq to be more than 75%
Zero line to be within confi intervals
ta and tb to be less than t-value (2.001717 for gm=60, alpha=0.05)

can some1 look into my study data attached and tell me what is wrong here?

Can some1 share study data meeting these requirements?

Further, I would say that the examples given in MSA manual for Bias, Linearity, GRR - all are very unrealistic. for example, if we look into bias data given in manual, against reference value of 6.0, the reading vary from 5.6 to 6.4. For the same ref value of 6, how the actual measurements can vary to this extent.
In case of linearity, the readings for ref value 4 vary from 3.8 to 5.1. Is is practically possible to vary to this extent? Even if someone use an instrument with high least count (like measuring tape), this much variation seems impracticable?

I want covers' views on this matter..



Rameshwar
 

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Rameshwar25

Quite Involved in Discussions
#4
My question still goes unanswered. This is very important issue. I have discussed with some TS auditors and asked whether they have seen a measuring system without linearity problem.There was no clear answer.
The quality people said that they tried but never got OK result therefore discontinued.
My feeling is getting stronger that world's all measurement system's have linearity problem. .
Now we should discuss whether there is problem with the measuring systems or problem with formula/ requirements of AIAG manual.

I want MSA experts, who have always responded to my posts positively, to respond to this thread also. I am not finding any other way to clear my doubts.

Regards
rameshwar
 

Marc

Hunkered Down for the Duration with a Mask on...
Staff member
Admin
#5
I'm bumping this thread again. My Thanks in advance to anyone who can help.
 
#6
Whenever i have done linearity study, my calculated values never satisfied following criteria:
R-Sq to be more than 75%
Zero line to be within confi intervals
ta and tb to be less than t-value (2.001717 for gm=60, alpha=0.05)

can some1 look into my study data attached and tell me what is wrong here?

Can some1 share study data meeting these requirements?

Further, I would say that the examples given in MSA manual for Bias, Linearity, GRR - all are very unrealistic. for example, if we look into bias data given in manual, against reference value of 6.0, the reading vary from 5.6 to 6.4. For the same ref value of 6, how the actual measurements can vary to this extent.
In case of linearity, the readings for ref value 4 vary from 3.8 to 5.1. Is is practically possible to vary to this extent? Even if someone use an instrument with high least count (like measuring tape), this much variation seems impracticable?

I want covers' views on this matter..



Rameshwar
Hi.
I think nothing is wrong basically in your evaluation .
In the real world the linearity is not perfect ,with Rsq > 0,75 and slope = 0 ;
I finded in my activity some examples of gages with linearity with slope very close to zero and others with slope and t coefficients out of critical value .
But , in my opinion the true question is : "is the gage, with this linearity ( evaluated ) , acceptable for my use? "
The theoretical and matematical level of acceptability for linearity is very tight , is true .
The statistic expert say : linearity non acceptable !
The engineer say : if the maximum bias not overcome the admitted error
in the process the linearity is acceptable .
I compare the admitted error in the process for my gage ; if the maximum bias is less then the value of MPE ,
the gage can be used in the process.
I make a GRR study with this linearity , if the result is acceptable ,the gage can to be used in the process .
Strictly speaking , the bias line with zero slope is an abstract ,difficult to realize in a real industrial situation.
T
 
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