The viscosity of a chemical product is read every two minutes. Some data from this process are shown in Table 10E.11 (read down, then across from left to right).
(a) Is there a serious problem with autocorrelation in these data?
(b) Set up a control chart for individuals with a moving range used to estimate process variability. What conclusion can you draw from this chart?
(c) Design a cusum control scheme for this process, assuming that the observations are uncorrelated. How does the cusum perform?
(d) Set up an EWMA control chart with λ = 0.15 for the process. How does this chart perform?
(e) Set up a moving center line EWMA scheme for these data.
(f) Suppose that a reasonable model for the viscosity data is an AR (2) model. How could this model be used to assist in the development of a statistical process-control procedure for viscosity? Set up an appropriate control chart and use it to assess the current state of statistical control.
TABLE 1 0 E .11
Chemical Product Viscosity
29.330
33.220
27.990
24.280
19.980
30.150
24.130
22.690
25.760
27.080
29.200
26.600
29.000
33.660
34.300
28.860
31.030
36.580
26.410
28.270
32.680
29.040
28.780
28.170
33.560
28.080
21.280
28.580
27.500
30.280
21.710
30.760
26.750
29.350
21.470
30.620
30.550
33.600
24.710
20.840
28.940
30.290
33.610
16.560
28.500
20.110
36.540
25.230
28.190
17.510
35.700
31.790
26.130
23.710
33.680
32.520
27.790
24.220
29.290
27.630
32.430
25.120
26.140
29.890
32.440
27.230
19.030
28.180
29.390
30.610
24.340
26.650
23.450
29.060
31.530
30.010
23.620
28.480
31.950
30.800
28.120
32.010
31.680
30.450
29.940
31.890
29.100
36.610
30.560
31.720
23.150
31.400
32.300
29.090
26.740
30.830
31.580
31.920
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