Question

Samples of fabric from a textile mill, each 100 m", are selected, and the number of occurrences of foreign matter is recorded. Data for 25 samples are shown in Table 8-9. Construct a c-chart for the number of nonconformities, Table 8-9 Foreign Matter Data Sample Nonconformities Sample Nonconformities 1 5 a O oto- Desktop Links

Answer 1

The upper and lower control limits for the c-chart are given by UCL = 7+3Vē = 15.8086 LCL =z 3Mã = 0 The c-chart is displayed in Figure 5.24, which indicates that the sample number 9 is out-of-control. 1 Count of Nonconformities HLCL 5 20 25 10 15 Sample Number FIGURE 5.24: c-chart for foreign matter data. Assuming special causes for the out-of-control point (sample 9 is deleted), the revised centerline and control limits for

the c-chart are CL = [= 7.20833 UCL = [ +377 = 15.2628 LCL = – 3 % = 0 The revised c-chart is given in Figure 5.25, which shows that all the remaining points fall within the control limits. Count of Nonconformities LCL 10 15 Sample Number FIGURE 5.25: Revised c-chart for foreign matter data.

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