Performs the "acceptance sampling plan" of the standard
ANSI/ASQ Z1.9 [2003; ISO, 2007] —here, a previous version [1980,
p 38 ff]. The base case is Example B-4 [op. cit., p 40],
"double specification limit, variability unknown, standard deviation method,
different AQL values for upper and lower specification limits". The inspected
variable is assumed Gaussian.
For a settled specification limit (or just "spec") L (or U),
let the customer state his lot size, N, and AQL. To decide whether
a lot will be accepted or rejected : from N obtain
(Table A-2) the sample size, n; from the sample, compute
QL = (Xbar − L)
⁄ s [or
QU = (U − Xbar)
⁄ s]. If the quality index QL
(or QU), say Q (the greater the better),
is Q ≥ k (Table B-1) for the AQL and n chosen,
the lot is accepted, otherwise it is rejected. This is
Form 1. Also, Form 2, below, can be used in this single spec case,
with only one condition (for L or U) tested.
If both specs, L and U, are present, compute
(or from Table B-5) the ω's, "estimates of the (lower, upper)
lot fraction nonconforming": from
QL and n, ωL; and
from QU and n, ωU. If
ωL ≤ ML,
ωU ≤ MU, and
ωL+ωU ≤
max(ML, MU), simultaneously,
the lot is accepted, otherwise it is rejected.
NB: in this Plate, ω is just roughly computed
(under contruction). |
|
• "American National Standard
– Sampling procedures and tables for inspection by variables for
percent nonconforming, Z1.9-1980", 1980, American Society for Quality Control,
Milwaukee, WI (USA) (Newsletter.pdf,
1983).
• "ANSI/ASQ Z1.9-2003: sampling procedures and tables for inspection by variables for
percent nonconforming", 2003, American Society for Quality,
Milwaukee, WI (USA).
• ISO 3951-3:2007, 2007, "Sampling procedures for inspection by variables
— Part 3: Double sampling schemes indexed by acceptance quality limit
(AQL) for lot-by-lot inspection", www.iso.org. (See also Parts 1 and 2.) |
