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Inspection in China
PRO QC International.

Sampling Plan
We use the recognized international quality control standards to conduct inspections. We refer to the most widely accepted sampling plans such as MIL-STD-105E, ABC-STD-105, ISO2859, DIN40.080, BS6001, NFK06-021/022 etc.

They are based on mathematical theories of probability and offer the advantage of clearly defining the number of samples to be drawn for inspection from a given lot or consignment. They also limit the allowable maximum number of defect in the sample size.
Unless otherwise instructed, our inspectors will usually use the MIL-STD 105E sampling plan & the Single Sampling Plan General Inspection Level II. This is generally applied for products manufactured in Chinese factory. (See Table I & II below)

For example ( as highlighted above), if a lot merchandise of quantity 3,201-10,000 will be inspected, using general inspection level II , on the table I the sample size code will be L , and in table II sample size 200 will be according to the code L . If AQL will be 2.5, so the found defect number 10 will be acceptable and 11 will be rejected.

You can use above table I & II to calculate the number of sample drawn depending on the shipment quantity.

Acceptable Quality Level (AQL)
As MIL-STD-105E is based on random sampling, therefore a few defectives are considered acceptable. The AQL only limit the allowable maximum number of defect in the inspection.

Different AQL may be designated for different defects such as Critical, Major and Minor defects. The AQL should be agreed upon between buyer and supplier before the start of production.

Defects Classification
Defects detected during the inspection are classified within 3 categories: 
“Critical”, “Major” and “Minor”:
Critical: likely to result in unsafe condition or contravene mandatory regulation   (no critical defect is accepted)
Major: reduces the usability of the product or is an obvious appearance defect
Minor: doesn't reduce the usability of the product, but is a defect beyond the   defined quality standard.

The following AQL's are usually applied by us unless otherwise instructed by the client:
For high valued products:
Critical defects: no critical defect is accepted
Major defects    : AQL 1.5    
Minor defects   : AQL 2.5

For low valued products:
Critical defects: no critical defect is accepted
Major defects   : AQL 2.5
Minor defects   : AQL 4.0

Acceptable quality level (AQL) sampling inspection methods have been proven to be accurate for long time worldwide. However, the quality level of merchandise at destination may be lower than the per-shipment inspection results. This may be due to transport, handling, change in environment and /or reliability problems. Buyer is therefore advised to take this into consideration when deciding the AQL level.

The client can specify the AQL referring to the sampling plan specified and what points are minor, major or critical defect. But we would suggest the client make an agreement about quality condition, such as product specification, defective definition, sampling plan & AQL etc. with the supplier/ manufactory before starting of production