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Simpson & Keats

Table 1. Explanation of Model Terms

Symbol    Description

a.    Number of assignable causes per hour

i    Expected time of occurrence of the    assignable cause    (a function    of X)

s    Expected number of samples taken    while in-control    (a function    of X)

T₀ Expected search time when false alarm T j Expected time to discover the assignable cause T2 Expected time to repair the process E Time to sample and chart one item Cq Quality cost/hr while producing in control C j Quaiity cost/hr while producing out-of-control W    Cost for search/repair

a    Fixed cost per sample

b    Variable cost per unit

Y    Cost per false alarm

A Mean shift - number of standard deviations slip when out-of-control n    Sample size

h Hours between samples or sampling interval k    CUSUM reference value

H    CUSUM decision interval

L X-chart - niunber of standard deviations from control limits to center linę

81    FlagTor whether production continues during searches (1 -yes, 0-no)

82    Flag for whether production continues during repairs (1 -yes, 0-no)

ARL1    In-controi average mn length

ARL2    Out-of-control average run length

n, k, H, and shift in the process mean (A) were developed and a file lookup techniąue was used for the optimization runs.

Sensitivity Analysis Study

By examining the cost equation for the LV model it is evident that, although the terms fully describe the economics of the control chart process, there are many parameters to estimate. The purpose of the sensitivity analysis