Automatic control of semi-autogenous grinding (SAG) mills has often been considered complex. Recent experiences at Century Zinc (world's second largest open pit zinc mine) refute this. Together with operating knowledge and appropriate control techniques high quality control is achievable. In this application model-based, constraint, and multiple output control were employed._x000D_
The control was implemented using standard blocks in the plant DCS. The resulting overall control strategy fulfils the operating objectives and controls the mill with minimal operator involvement over 95 per cent of the time._x000D_
Previous campaigns using expert systems and complex DCS based control have lacked durability. Their fall into disuse is briefly discussed.