Random sampling methods:
Simple random sampling: random number table method, dice rolling method.
Periodic systematic sampling: method of sampling using certain intervals.
Stratified sampling: from an inspection lot can be divided into different sub-lots (or called layer), according to the specified proportion of samples taken from different layers.
Sampling and inspection standards and their systems
1, counting and measuring sampling and inspection standards
Counting and sampling inspection standards are counting the results of the sampling test as an indicator of the quality characteristics of the judgment, has developed national standards:
a) GB2828-1987 "batch-by-batch inspection counting and sampling procedures and sampling table (applicable to consecutive batches of)"
This is the first time in the history of the National Institute of Standards and Technology. Inspection)
b)GB2829-1987 Cycle Inspection Counting Sampling Procedures and Sampling Tables (Applicable to Production Process Stability Inspection)
c)GB8051-1987 Counting Sequential Sampling Inspection Procedures and Tables
d)GB8052-1987 Single-Level and Multi-Level Counting Successive Sampling Inspection Procedures and Tables
Measurement sampling inspection standard is to count the results of the sampling test as an indicator of the quality characteristics of the judgment, has formulated national standards:
a) GB6378-1986 "non-conformity rate of the measurement of the sampling inspection procedures and tables"
b) GB8053-1987 "the rate of non-conformity of the measurement of the standard-type sampling inspection procedures and tables
c)GB/T8054-1995 "the average value of the measurement of the standard type of sampling and inspection procedures and tables"
ACCEPTANCE QUALITY LIMIT (referred to as AQL): acceptance quality limit, is the daily inspection of the goods, the level of sampling standards, that is, when a series of consecutive batches are submitted to acceptance, the worst permissible process Average Quality Level. AQL is commonly used in the export of clothing, textile inspection, different AQL standards applied to different substances on the test.
In AQL sampling, the same number of samples are taken, and the smaller the value of AQL followed by the smaller the number of defects allowed, indicating that the higher the quality requirements, the relatively more stringent inspection.
Expanded:
AQL inspection related terms:
Unit product inspection: in order to implement the need for inspection and division of the basic unit. Inspection lot: a batch of unit products need to be tested. Abbreviated lot. Unit products constituting the test lot should not be essentially different, there can only be random fluctuations. Therefore, an inspection lot should be in the basic conditions of production and in about the same period of time, the production of the same type, the same level of unit products.
Lot inspection: the number of units contained in a batch to be inspected.
Fatal Defect: a defect that may cause a hazardous or unsafe condition to the use and maintenance of the product or to persons concerned with it; or a defect that damages the important, ultimate essential function of the product.
Serious Defects: Defects that are different from Fatal Defects, but that can cause failure or significantly reduce the expected performance of the product.
Minor Defects: Defects that do not significantly degrade the intended performance of the product, or defects that deviate from the standard but only slightly affect the effective use or operation of the product.
Product inspection classification: full inspection, sampling inspection, purchase inspection, intermediate inspection, finished product inspection, factory inspection, inventory inspection, supervision and inspection, counting inspection, measurement inspection, destructive testing, non-destructive testing.
Sampling test is often used in the following cases:
a) the test is destructive;
b) the test, the object of inspection is a continuum;
c) a large number of products;
d) the test items;
e) hope that the test cost is small;
f) as a test of the production process process control.
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