One,random testDefinition of

Sample testing is done in accordance with certainsampling programIn addition, a portion of the randomly selected samples from a batch of products for testing, through the test results of the sample to infer whether the entire batch of product quality is qualified as a test method.

II. Principles of sampling and testing

Example: for a batch of foreign trade large shipments of washing machines, we can not be every washing machine for product testing, but to extract a certain number of washing machines for quality inspection, according to the inspection data of these washing machines to speculate on the quality of the whole batch of large shipments of washing machines.

III. Classification of sampling tests

1. Classification by number of samples

   • One sample test:Only one sampling is performed, and the entire batch is judged to be qualified based on the test results of the sample.
   • Secondary sampling and testing:Carry out two sampling, after the first sampling if you can not judge whether the whole batch of products are qualified, and then the second sampling, and then a combination of the results of the two sampling judgment.
   • Multiple sample tests:Carry out multiple sampling, after each sample according to certain rules for judgment, until you can determine whether the whole batch of products are qualified.

2. Classification by quality characteristics

   • Count sampling test:Applicable to products whose quality characteristics are counted, such as the number of nonconforming products and the number of defects in a product. Judge whether the whole batch of products is qualified according to the number of defective products in the sample.
   • Measurement sampling and testing:It is applicable to products whose quality characteristics are measured values, such as the size, weight and strength of the product. Through the statistical analysis of the measurement data of the sample, to determine whether the whole batch of products meet the quality requirements.

IV. Steps for sampling and testing

1. Determination of sampling program

   • Define the quality characteristics of the test and the acceptable quality level (AQL), which is the upper limit of the acceptable quality level below which the batch is considered to be acceptable.
   • According to the batch size of the product, the degree of rigor of the inspection and other factors, select the appropriate sampling program, including sample size and sampling method.

2. take a sample

   • Randomly select samples from the entire batch in accordance with the selected sampling method. Ensure the randomness and fairness of the sampling process to ensure a representative sample.

3. test sample

   • Inspection of samples taken, each sample being tested or measured individually according to predetermined quality characteristics and test criteria.

4. Determine if the entire batch is acceptable

   • According to the test results of the sample, in accordance with the determination rules in the sampling plan, to determine whether the whole batch of products is qualified.
   • If the number of nonconforming products in the sample or the statistical value of quality characteristics is within the acceptable range, the whole batch of products is judged to be qualified; otherwise, the whole batch of products is judged to be unqualified.

5. Handling of test results

   • For qualified products, they can be packaged, shipped or put into use.
   • Unqualified products need to be further analyzed and processed. Measures such as rework, rework, downgrading for use or scrapping can be taken.

V. Advantages and disadvantages of sampling tests

1. vantage

   • Saving inspection costs and time: compared to the full inspection, sampling test only need to test a part of the sample, greatly reducing the workload and cost of inspection, but also shorten the inspection time.
   • With a certain degree of scientificity and reliability: through a reasonable sampling program and statistical analysis methods, the quality of the entire batch of products can be inferred at a certain level of confidence, with a certain degree of scientificity and reliability.
   • Suitable for large-scale production and inspection: for larger batches of products, sampling inspection is a very effective means of quality control.

2. drawbacks

   • There is a risk of misjudgment: Since only a portion of the sample is tested, misjudgment may occur. When the sample does not fully represent the quality of the entire batch, there is a risk that a qualified product will be judged as unqualified, or a failed product will be judged as qualified.
   • Higher requirements for the design of the sampling program: the design of the sampling program needs to take into account a number of factors, such as the quality characteristics of the product, batch size, inspection costs, etc., if the design is not reasonable, it may affect the accuracy of the test results.

VI. Application of sampling tests in practice

1. service industry

   • In the manufacture of electronic products, the quality of electronic components is sampled and inspected, such as whether the parameters of resistors and capacitors comply with the standards.
   • In automobile manufacturing, the size and strength of components are sampled to ensure the quality and safety of the entire vehicle.

2. Food industry

   • Sampling and testing of hygiene indicators and nutritional content of food products to ensure food safety.
   • The sealing and printing quality of food packaging are sampled and inspected to ensure the quality of food packaging.

3. import and export trade

   • In the inspection of import and export commodities, sampling inspection is a commonly used method. Customs and inspection and quarantine agencies carry out sample tests on imported and exported commodities to determine whether the commodities comply with national quality standards and relevant regulations.