SOP on Types of Sampling Plan

SOP on Types of Sampling Plan
1.0 Purpose: This SOP describes the number of samples to be taken for analysis.
2.0 Scope: This SOP applies to Quality Control staff.
3.0 Responsibility: Quality Control Manager is responsible for ensuring that this procedure is followed.
4.0 Materials and Equipment: None
5.0 Procedure: Sampling plan may be of three types – 
5.1 Single sampling plan: In such a type of plan, decision to accept or reject a lot is taken on the basis of the results of first sample. In general a large sample is used but in certain cases decision can be taken on the basis of even a small sample.
5.2 Double sampling plan: Sometimes it becomes difficult to decide, on the basis of first sample, whether it is good or bad. This happens in case of borderline cases. Number of defectives may be very close to upper control limit. Under such circumstances, it becomes necessary to inspect another sample. A second sample, therefore, is drawn, inspected, added to first sample and on the basis of combined result, decision regarding acceptance or rejection of lot is taken. The following procedure is followed under this plan –
a. take first sample, find out number of defectives in that sample. Compare the number with two acceptance number C1 & C2.
b. If the number of defectives is less than C1, accept the lot and if it is more than C2, reject the lot.
c. If the number of defectives is between C1 & C2, take a second sample. Find out the number of defectives in the combined sample. Compare the number with two acceptance number C1 and C2.
d. If the number of defectives is less than C2, accept the lot and if it exceeds C2, reject the lot.
5.3 Multiple sampling plan: Under this plan, several samples are taken until a decision to accept or reject a lot is reached. it should be noted that if first few items are found defective, lot could be rejected without further inspection.

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