Sampling Inspection involves inspecting a relatively small number of items from a batch or lot and then using the results of this sample to either accept or reject the entire lot. The accept/reject criteria is the number of defective items found in the sample.Sampling inspection relies on statistical probability and it is possible that a good batch will be wrongly rejected, or a bad batch will be wrongly accepted. This can have significant economic consequences and so it is usual to use a published sampling plan.
The sampling either for the grading or for checking the correctness of the grading should be done most accurately, because unless the sample is truly representative of the entire lot, correct grading can not be done. The general characteristics of the commodity should be preliminarily inspected before drawing samples from the lot.In the case of packed material or the packing material, stitching of the bags or metallic linings, the gross and net weight of the contents etc., should be invariably noted and verified.
Sampling must be appropriate to the application, cost effective, and integrated well into the quality system. A policy of 100% inspection tends to promote the status quo. Two kinds of sampling are used in inspection as a device for improvement and to reduce the amount of inspection: Product Control (acceptance of unique lots) and Process Control (acceptance of a process).The objective of process control is to characterize the process and not necessarily the product. Therefore, the sampling procedures are not necessarily those appropriate for random sampling from the lot of product produced over a given period. Rather, the samples are structured to give signals about the process. In contrast, random samples are used in acceptance sampling to characterize the population of product produced throughout a given period of production.
Sampling inspection is always used in plastic products inspection during the process.
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