The concentration of a chemical product is measured by

Chapter 15, Problem 76E

(choose chapter or problem)

The concentration of a chemical product is measured by taking four samples from each batch of material. The average concentration of these measurements for the last 20 batches is shown in the following table:

                                                         

                                                         

(a) Suppose that the process standard deviation is \(\sigma=8\) and that the target value of concentration for this process is 100. Design a CUSUM scheme for the process. Does the process appear to be in control at the target?

(b) How many batches would you expect to be produced with off-target concentration before it would be detected by the CUSUM control chart if the concentration shifted to 104 ? Use Table 15-10.