
92 Control for Aluminum Production
number of sick pots. The extra attention needed by section operators or
pot controllers to tend sick pots has a negative inuence on the other
pots, with a general reduction in current efciency, plus attendant loss of
control of carbon and energy usage, and sometimes safety.
The analysis with respect to the above situation, therefore, is focused
on three issues:
1. The failure of the basal automated control loops: The change in the
sensed variable (for example voltage instability or noise) is not
actually diagnosed in terms of its cause. Rather, the use of a com-
parator against a target value or limit for t ...