Acceptance Sampling for Variables: ANSI/ASQ Z1.9
William A. Levinson, P.E., FASQ, CFPIM is the principal of Levinson Productivity Systems, P.C. He is an ASQ Certified Quality Engineer, Quality Auditor, Quality Manager, Reliability Engineer, and Six Sigma Black Belt, and the author of several books on quality, productivity, and management.
This webinar will show how to use ANSI/ASQ Z1.9 (formerly MIL-STD 414) to define sampling plans for products with continuous-scale (variables) data, and use the accompanying switching rules to move between normal, reduced, and tightened inspection as required by the publication.
ANSI/ASQ Z1.9 (formerly MIL-STD 414) is a widely accepted standard for sampling by variables (continuous scale measurements). The sample size n is defined by the plan's requirements including the sampling level, lot size, and acceptable quality level. The sample's average and standard deviation (or the known standard deviation of the process) are used to determine whether the lot meets the plan's acceptance criteria, and can also be used to estimate the nonconforming fraction in the lot. Switching rules define when the sampling plan must be performed under normal or tightened conditions, and when a reduced inspection is acceptable.
- Selection of the sample code letter and tabulated acceptable quality level (AQL) according to their sampling plan requirements along with the lot size
- Definition of the sample size (n) and acceptability constant k depending on whether the variation is known or unknown, and whether the specification is one-sided or two-sided
- Calculation of the acceptability criterion (standard deviations between the specification and the specification limit), also known as the quality index
- Estimation of the nonconforming fraction of the lot, and comparison to the tabulated acceptable value to determine whether the lot should be accepted (Form 2 method)
- Also, know that these plans rely on the assumption that the critical to quality (CTQ) characteristic follows the normal or bell curve distribution
- The appendix in the pdf handout provides technical details as to how the operating characteristic curve (OC curve, a plot of the chance of acceptance versus the nonconforming fraction ) is derived for cases in which the variation is known and when it must be estimated from the sample standard deviation. This is for attendees who want to know the details, but this information is not necessary to use ANSI/ASQ Z1.9
Who Should Attend
Quality Managers, Engineers, and Technicians.