00228 c833f71b9f2a382663c8b3b0c1f1814

230

Baxley

Figurę 9. Example of Manuał Implementation of EWMA Control.

risk as shown by prior simulation studies [Baxley(1990)| where o_r / a_a = 1.05 so that, with no special causes present and the EWMA algorithm in operation, a = P^|F| - Target| > 3o_a) = 2G>(-2.85) = 0.005. When there is a violation of the

Shewhart limits on Kj , the EWMA is not updated, thereby preventing an adjustment from being madę and instead requiring that troubleshooting be done.

Experiences with this method during the first year have been favorable. Although it is too early to estimate the reduction of variability in Yj, there have been no instances of large, unwarranted adjustments to pump RPM. On several occasions, following senes of upward adjustments to pump RPM, the machinę operators used troubleshooting procedures to detect a plugged filter in the supply linę. Subseąuently, it was decided to employ troubleshooting in lieu of the second straight upward RPM adjustment, thereby correcting pluggage problems early. In order to avoid freąuent troubleshooting, the algorithm was tuned by changing X to .15 and the EWMA limits to ± .025 (L = 2.2). This reduced the adjustment freąuency without increasing the process