76/211/EEC Criteria for Non-Destructive Testing



According with the 76/211/EEC for non-destructive testing
Number in Criteria __* Acceptance

100 to 500(inclusive) * x_average >=Qn —0.503s

>500 _____________* x_average >=Qn —0.379s for destructive testing

Number in Criteria ___* sample Acceptance

(=100) ____________* x_average >=Qn —0.640s

Does anybody know where does 0.503, 0.379 and 0.64 come from?

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Rick Goodson


I am not familiar with that spec, but have a feeling it has to do with the area under the curve for a distribution. It looks like a comparison of an empirical reading to a calculated number that reflects a point on the curve. What is Qn?



Sorry, I found it

In this formula:
Qn =the nominal quantity of the prepackage,
n =the number of prepackages in the sample for this check,
s =the estimated standard deviation of the actual contents
of the batch,
t (1 —alfa )=0.995 confidence level of a Student distribution with ν
=n —1degree of freedom.

Qn — s/sqrt(n) * t (1 —alfa )

In the table

for non destructive and
Units/batch (100-500] , the samle must be 30
for [500..), the sample must be 50
and for non destructive, Sample size must be 20

So in Excel,
tinv(0.1,30-1)/sqrt(30)= 0.503
tinv(0.1,50-1)/sqrt(50)= 0.379
tinv(0.1,20-1)/sqrt(20)= 0.640
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