All inspectors use the MIL STD 105E tables, which are recognized standards by every industrial company.
This American standard now has equivalents in all national and international standardization organisations (ANSI/ASQC Z1.4, ISO 2859, NF06-022, BS 6001, DIN 40080).
This standard is a proven method to accept or reject a production lot by inspecting a randomly selected number of products.
This method is called ‘AQL’(acceptable quality level):
Uses the Acceptable Quality Level (AQL) to establish a maximum allowable error rate or variation from the standard. Acceptance testing will cease immediately if the failure rate of the product being tested exceeds the minimum Acceptable Quality Level.
NB: It is important to note that Acceptance Sampling cannot provide 100% perfect products. The only way of achieving this is to produce 100% perfect products.
MIL STD 105E table:
Practically, the MIL STD 105E tables are summarised below:
Table A :
Table B:
NB: What can I find out from the AQL tables?
Let's take a lot of 3,000 units to inspect, with an AQL of 2.5%.
According to Table B, the sample size is therefore 125 units, and the corresponding acceptance number is 7.
In other words:
If the number of defective units is more than 7, the lot has to be rejected
If the lot is accepted, it is commonly perceived that there is a maximum of 2.5% of defective units in the lot (with a failure risk percentage of less than 5%). |
发表于 2007-4-27 18:48:50
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