Economic Design of – Control Charts Under Weibull Shock Models

Abstract

In this article, a moditied version of Duncan's (1956) model for the economic design of -control charts is extended to deal with situations involving the Weibull shock model. In the traditional Duncan approach to Markovian shock models, the length of sampling intervals is kept constant. When the process-failure mechanism follows a Weibull model or some other model having an increasing hazard rate. however, it may be desirable to have the frequency of sampling increased with the age of the system. This study proposes a cost model that uses variable sampling intervals as opposed to sampling intervals of fixed length. The computational results indicate that the proposed model under variable sampling intervals provides a lower cost than those obtained by using the existing model developed by Hu (1984) for a Welbull shock model having sampling intervals of fixed length.

KEY WORDS:

• Constant integrated hazard
• Intervals
• Process control
• Variable sampling