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Quick Switching Systems

Summary: Quick switching systems (QSSs) are used to make accept/reject decisions when inspecting a series of lots. QSSs change the number of units inspected and the acceptance criteria based on past results, in order to provide extra protection during periods of poor quality while reducing the cost of inspection during periods of good quality. This article shows how to evaluate the protection provided by QSSs during periods of both constant and changing quality, as well as how to select QSSs based on the protection they provide. QSSs are compared with single, double, chain, and variables sampling plans as well as the MIL-STD 105E switching systems. It is concluded that QSSs are superior to chain sampling plans and can dramatically reduce the amount of inspection compared to single and double sampling plans, but at the cost of increased complexity. Further, MIL-STD-105E switching systems can be replaced with far simpler QSSs that require the same number or fewer samples and that offer equivalent protection during periods of constant quality, but increased protection against isolated or initial bad quality lots. QSSs prove especially useful for processes running at low levels of defects where small sample sizes and high sensitivity to problems are desired.

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  • Topics: Sampling
  • Keywords: Short runs,Switching rules,Operating Characteristic (OC) curve,Sampling plans
  • Author: Taylor, Wayne A.
  • Journal: Journal of Quality Technology