22 ZACHARY G STOUMBOS AND MARION R REYNOLDS IR pling rate and the same average frequency of false probability ratio test (SPRT)chart,defined as a se A dis charts that the qence of SPRT unpredictable,and these sampling points may not is on targt correspond I periods in the process,such the mean is not on target.The time interval d as work s or th amount T's(from raw materials.The disadvantage of unpredictabl is a sequential hypothesis test.and for the be tak samples allowed between these fixed times when nec pendix A. (1993).Baxley(1995).and tion for the SPRT Another a be tested in a very short (negligible)time using a case every hot the he r,fo the pro That is after a sample is taken the ald be size of the n mple shoud e is a ll if th sured one resistor at a time. cdcaoofap applying an SPRT for an FSS chart for a certain application takes samples If ing th the be SPRT of 5 ob vations,then a Schart for this applica null hypothesis that the mean resistance is on tar. get. anothe one hou Sawalapurkar-Powers.Reynolds,and Arnold (1990) D.L 199 s(1).Costa signal that corrective action shoud be taken. this example,d is one hour. and Runger (1994).Reynolds (1996b),and Stoum vit h bos and Reynolds(1996b. 1996c).A VSS chart has oli nte tim can a VSS chart in the usual sense.In a VSS chart,the has shown that, current sampl mine on av age.the VSS feature will ubstantially FSS ch the current sampling point depends on the data o amp erage sampling rate and the same average frequenc the ysst ontrol charts is given in the ditional reduction in the ave nex ection time of section.Note that Daudin(1992)proposed the ingthe m at FSI's based on data from the current sampling The purpose of this paper is to provide an FSI point This chart assumes that two successive sam procedure for monitoring the me pr 91 and n2.resp can b time to tae an individual observation is The double sampling chart varies the sample size time at each sampling point be ween two pr short that it can be neglected. The idea is to var in zero sample s ly at ea the SPRT chart the sa size can be integer. pling point.by sampling sequentially one observatio at a time.Hence,this paper develops the sequential The SPRT chart is especially appropriare for ap- Journal of Quality Technology Vol.29,No.1.January 1997 Reproduced with permission of the copyright owner.Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission