17 Multivariate process control
1988; Elsevier BV; Linguagem: Inglês
10.1016/s0169-7161(88)07019-1
ISSN1875-7448
Autores Tópico(s)Advanced Statistical Methods and Models
ResumoThere are many situations in which it is necessary to simultaneously monitor two or more correlated quality characteristics. Such problems are referred to as multivariate quality control problems. A manufacturing plant where the product is plastic film is considered to illustrate the need for a multivariate approach. The usefulness of the film depends on its transparency and its tear resistance. These two quality characteristics are jointly distributed as a bivariate normal, and is obtained and plotted against time on an EQ \x \to(x) -chart. The use of separate EQ \x \to(x) -charts is equivalent to plotting on a single chart formed by superimposing one EQ \x \to(x) -chart over the other. The use of separate control charts or the equivalent rectangular region can be misleading. It will be shortly demonstrated that the true control region is elliptical in nature, and the process is judged out of control only if the pair of means plots outside this elliptical region.
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