The CUSUM chart detects changes in the process mean by accumulating the sum of deviation of observed sample means X_1,..., X_t from a reference value. The CUSUM function about reference value k at time t is S_t = sum from i = 1 to t of (X-bar_i - k) = S_(t-1) + (X-bar_t - k) with S_0 = 0. An upward shift is detected when S_t > = h or vice versa with S_t < = - h. The two parameters in the CUSUM plan are k and h. k is usually set at the process mean mu and h is taken as 10k, 20k,...50k. In this paper h = 10k since higher values of h incurred too many cycles.
展开▼
