Multiple Sampling Plan for Defective Units

Sampling Plan Analyzer Help System

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Multiple Sampling Plans for Defective Units

Characteristic:

Defective units

Assumptions:

(1) Representative sample

Parameters:

S = number stages, integer satisfying Sł2
ni = sample sizes, integers satisfying ni>0
ai = accept numbers, integers satisfying aiłai-1 where a0=-1. Entering a # sign is interpreted as -1.
ri = reject numbers, integers satisfying riłri-1 where r0=1 and riłai+2 except rS=aS+1
Must also satisfy riŁn1+...+ni+1 except rSŁn1+...+nS

Procedure:

(1) Take a representative sample of n1 units from the lot to be inspected.
(2) Count the number of defective units in this sample.
(3) If this count is less than or equal to a1, accept the lot.
(4) If this count is greater than or equal to r1, reject the lot.
(5) Otherwise, set i=2.
(6) Take an additional representative sample of ni units from the lot.
(7) Count the total number of defective units in the combined sample of n1+...+ni units.
(8) If this count is less than or equal to ai, accept the lot.
(9) If this count is greater than or equal to ri, reject the lot.
(10) Otherwise, increase i by 1 and go back to step 6.

This procedure always terminates on the S-th stage because of the restriction rS=aS+1.

Sometimes the accept or reject decision is determined before all units are inspected. In this case, the inspection can be curtailed. For multiple sampling plans for defective units you can curtail on both acceptance and rejection during any stage as follows:

Curtail on Rejection during i-th Stage: Stop the inspection and reject as soon as ri defective units are found.
Curtail on Acceptance during i-th Stage: Stop the inspection and accept as soon as n1+...+ni - ai good units are found.