CONTROL CHARTS APPLYING A SEQUENTIAL TEST AT FIXED SAMPLING INTERVALS plications where testing is destructive and /or expen 1.2 Each sample (X. .X.is assumed t such as in deployment-rate testing of autome be taken in negligible time.Assume that the process 0.but no observation s It should be noted that a deploved airbag is not pling interval between observations X reusable and airbags are costly.Also onote that the will be d requ ag I deploy for/P and o That is,d is the een samp to the int the sampling times,which are usually no more of ation of from o in terms of units of and let In such practical Assume that observations within siAt nport of the The organization of the remainder of this eresidd is as follow A description of the SPRT char +上(2-以.ii=1 compared to the standard and CUSUM charts and VSI feature Uy= (1 to the when th 5 an ar f1=23 that the SPRT chart i than both the X and CUSUM charts,even when VSS for i=1. N.where uo 0.h denotes the and/or Then,gud specified starting value of the control statistic,and tive example is provided.In Appendix A,the defini- he tion of an SPRT for the mean of a normal variable rom a constant multiple)in the SPRT for testing the ties of the sprt char are developed in Appendix Bin terms of integral o versusH:=o 270,where each SPRT is equations gible time.with The SPRT Chart 1 abhewehetXrepn ng the observations from sample (A, its te that if SPRT chart is defined to e,et a target value uo (i)stop sampling and signal if U.h: the case will be considered here where shifts from otoand stays at he shi ) andor from past data,but for simplicity,it will be assumed here that go and 2 are known. e SPRT's dise per one-sided SPRT chart see Figure la.where.fo utive satules (X. urPposesofYisual arity,the tim of observations taken sequen atively large. 1+2 el where N.denotes the num Similarly.let the coutrol statistic of the lowerone ber of observations in sample )for i= sided SPRT chart for detecting a decrease in u be Vol.29.No.1.January 1997 Quality Technolog Reproduced with permission of the copyright owner.Further reproduction prohibited without permission.Reproduced with permission of the copyright owner. Further reproduction prohibited without permission