
206 Control for Aluminum Production
(anode spike and anode effect fault models) showed that the related scores
entered the“anode spike” area or “problem area” in theunderlying PCA
plot. The operator’s screen indicated this situation by a changein the
color of button for pot 2003 from green to red,the status of the process
from IN CONTROL to OUT OF CONTROL,andthe statusofthe anode
spike detection from NO to YES (Figure12.19).
In this investigation, the time when the scores of the above samples
entered the “problem area” was compared with the time the anode spike
was detected by the operators. There were three time periods prior to the ...