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FAQ

Sampling Plan

Sampling plans in the form of published standards are used in industry world-wide as a means of assisting quality assurance personnel to decide whether to accept or reject product lots presented for inspection. There are a number of standards available.

The SGS inspections in generally use the following sampling plans if there is no special requirement from the client.

Standard	ANSI/ASQ Z1.4-2008	/
Sampling Plan Class	Single Sampling Plans	/
Inspection Level	Level 2 Normal	/
AQL	Critical Defect	Not Allow
	Major Defect	2.5
	Minor Defect	4

Standard
ANSI/ASQ Z1.4-2008 Sampling Procedures and Tables for Inspection by Attributes is a sampling system to be used for Acceptance Quality Limit (AQL) specified. It provides tightened, normal, and reduced plans to be applied for attributes inspection for percent nonconforming or nonconformities per 100 units.
Sampling Plans Class
A lot acceptance sampling plan (LASP) is a sampling scheme and a set of rules to facilitate decision making. Based on the number of defective samples, the accepting sampling plan will advise on accepting/rejecting the lot or for multiple or sequential sampling schemes, to take another sample and then repeat the decision process. LASPs fall into the following categories: Single sample plans: One sample of items is selected at random from a lot and the disposition of the lot is determined from the resulting information. These plans are usually denoted as (n,c) plans for a sample size n, where the lot is rejected if there are more than c defective samples. These are the most common (and easiest) plans to use although not the most efficient in terms of average number of samples needed. Double sample plans: After the first sample is tested, there are three possibilities: Accept the lot Reject the lot No decision If the outcome is (3), and second sample is taken, the procedure is to combine the results of both samples and make a final decision based on that information. Multiple sampling plans: This is an extension of the double sampling plans where more than two samples are needed to reach a conclusion. The advantage of multiple sampling is smaller sample sizes.
Inspection Level
Three general and four special inspection levels are commonly used. The general inspection levels (1 to 3) are typically used for non-destructive inspection. Level 2 is considered the norm (except for small sample sizes). Level 1 requires 40 percent less samples for inspection than level 2 and can be used where less discrimination is needed. Level 3 demands 160 percent more samples than level 2 inspection. Since a larger number of sample is needed, level 3 will give a lower risk of accepting a lot with excessive number of defects.
AQL (Acceptance Quality Limit)
Acceptance Quality Limit (AQL) sampling inspection is the most widely accepted sampling inspection protocol for inspection by attributes. The AQL is the quality level which is the worst tolerable process average when a continuing series lots is submitted for acceptance sampling.
Defect
A "defect" is any non-conformance of the unit of product against the specified requirements. A "defective" is a unit of product which contains one or more defects. Below are the different defect level definitions: Critical Defect: A "Critical" defect is on one's judgment and experience indicates is likely to: (1) Result in hazardous or unsafe use, operation, or maintenance of the product, or (2) Prevent performance of the principal function of a major end product. Major Defect: A "Major" defect is one other than critical, that is likely to result in the failure/reduction of the usability of the product for its intended purpose. Minor Defect: A "Minor" defect is one that is not likely to reduce substantially the usability of the unit of product for its intended purpose or is a departure from established standards having little bearing on the effective use or operation of the unit of product. Example: Lot or batch size: 3000 pcs Sampling plan standard: ANSI / ASQ Z1.4-2008 Sampling plan class: Single Sampling Plans Inspection Level: Level II Normal AQL: Critical defect: Not Allow Major defect: 2.5 Minor defect: 4.0 Sample size is 125 pcs It will be accepted if the major defective samples are bellow 7 pieces or minor defect one are bellow 10 pieces. It will be failed if the major defects samples reach to 8 pcs or minor defect one reach to 11 pieces.