Type of Document Dissertation Author Hughes, Christopher Scott Author's Email Address email@example.com URN etd-041999-130738 Title Variable Sampling Rate Control Charts for Monitoring Process Variance Degree PhD Department Statistics Advisory Committee
Advisor Name Title Arnold, Jesse C. Committee Co-Chair Reynolds, Marion R. Jr. Committee Co-Chair Coakley, Clint W. Committee Member Foutz, Robert Committee Member Ye, Keying Committee Member Keywords
- Shewhart chart
- integral equation
- Markov chain
- CUSUM chart
- EWMA chart
Date of Defense 1999-04-13 Availability restricted AbstractIndustrial processes are subject to changes that can adversely
affect product quality. A change in the process that increases
the variability of the output of the process causes the output to
be less uniform and increases the probability that individual
items will not meet specifications.
Statistical control charts for monitoring process variance can be
used to detect an increase in the variability of the output of a
process so that the situation can be repaired and product
uniformity restored. Control charts that increase the sampling
rate when there is evidence the variance has changed gather
information more quickly and detect changes in the variance more
quickly (on average) than fixed sampling rate procedures. Several
variable sampling rate procedures for detecting increases in the
process variance will be developed and compared with fixed
sampling rate methods.
A control chart for the variance is usually used with a separate
control chart for the mean so that changes in the average level
of the process and the variability of the process can both be
detected. A simple method for applying variable sampling rate
techniques to dual monitoring of mean and variance will be
developed. This control chart procedure increases the sampling
rate when there is evidence the mean or variance has changed so
that changes in either parameter that will negatively impact
product quality will be detected quickly.
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