Uncertainty measurements for a 6 inch caliper

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Curtis317

#1
As many of you are aware we are just beginning in our adventure to become an A2LA lab. In working towards the goal of establishing the uncertainty for our measurements we are starting with a 6 in caliper (mm measurements) and pin gauges. My question is do we measure 10 times over the length of the calibrate range of the calipers? We use gage blocks and stack them 250 mm until we get the range of the caliper. For pins do we measure 3 places, top middle and bottom 10 times to establish the standard deviation? I am just looking for a reasonable way to do the uncertainty measurements.
 
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C

Curtis317

#4
So you only evaluate the uncertainty for one measurement? Just 2 inches? or 100 mm? Not the whole range of the caliper that would be calibrated?
 

dgriffith

Quite Involved in Discussions
#5
We perform uncertainty analysis at the test point level- the test point result is either in or out of tolerance (or indeterminate), and the uncertainty for that point is estimated. That was just an example for one test point. We did several across the range. You want to pick points that require the fewest gage block combinations while still providing good coverage throughout the range. Most block sets provide good coverage using 3 or less blocks (don't want to be wringing too many together if you don't need to).
 
C

Curtis317

#6
Thanks I am gaining a better understanding about how to perform the uncertainty evaluations. I would also think that for a gage pin you would do much the same thing. Evaluate two diameters on a gage pin for measurements. Correct?
 
S

sitapaty

#7
Uncertainity measurement of a caliper requires knowledge of such a complex statistical theory what about much more precision instruments? We end up spending more time in calculations than production.Could we not simplify things to avoid all these rocket science subjects in our work.
 
#8
Uncertainity measurement of a caliper requires knowledge of such a complex statistical theory what about much more precision instruments? We end up spending more time in calculations than production.Could we not simplify things to avoid all these rocket science subjects in our work.
Not if you want to do the job properly! It's not "rocket science", when you understand it.
 
S

sitapaty

#9
I appriciate we shuld posses knowledge and expertise on complex subjects especially statistics but cannot we exemt GRR for items like measuring tapes and steel rules,and calipers.
 
#10
I appriciate we shuld posses knowledge and expertise on complex subjects especially statistics but cannot we exemt GRR for items like measuring tapes and steel rules,and calipers.
If you can justify why you want to exclude them, after performing a study, why not? But you have to perform the study to show why uncertainty isn't a factor. You can't simply exclude something because it looks like hard work!
 
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