Noise classification in the aluminum reduction process

Cell "noise" is monitored by virtually all reduction cell control systems, and is generally used as one of the control variables for anode movement. High noise levels are thought to reduce cell current efficiency and are generally combated by increasing anode-cathode distance. However, exactly what constitutes "noise" and how noise is measured varies from controller to controller. Cell control algorithms are universally proprietary and little has been published on the correlation between voltage noise and current efficiency. In this study, three types of frequently observed cell noise are presented, and corresponding noise metrics are proposed. The characteristics and possible causes of the three types of noise are discussed. We show that not all types respond to anode movement, and posit that a better understanding of noise type is necessary for effective control of the cell.