Contents
- Index
Double Sampling Plan for Defects Per Unit
Characteristic:
Defects Per Unit
Assumptions:
(1) Representative sample
Parameters:
n1 = first sample size, integer satisfying n1>0
a1 = first accept number, integer satisfying a1³0
r1 = first reject number, integer satisfying r1³a1+2
n2 = second sample size, integer satisfying n2>0
a2 = second accept number, integer satisfying a2³r1-1
Sometimes a sixth parameter, r2 = second reject number, is given. The parameter r2 is always equal to a2+1 and is redundant.
Procedure:
(1) Take a representative sample of n1 units from the lot to be inspected.
(2) Count the number of defects 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, take a second representative sample of n2 units from the lot.
(6) Count the total number of defects in the combined sample of n1+n2 units.
(7) If this count is less than or equal to a2, accept the lot. Otherwise, reject the lot.
Sometimes the accept or reject decision is determined before all units are inspected. In this case, the inspection can be curtailed. For double sampling plans for defects you can curtail on rejection during both stages as follows:
Curtail on Rejection during First Stage: Stop the inspection and reject as soon as r1 defects are found.
Curtail on Rejection during Second Stage: Stop the inspection and reject as soon as a2+1 defects are found.