Wavelet packet time series analysis of aluminum electrolytic cells

Arthur Johnson III; Ching-Chung Li

doi:10.1117/12.421204

26 March 2001 Wavelet packet time series analysis of aluminum electrolytic cells

Arthur Johnson III, Ching-Chung Li

Proceedings Volume 4391, Wavelet Applications VIII; (2001) https://doi.org/10.1117/12.421204
Event: Aerospace/Defense Sensing, Simulation, and Controls, 2001, Orlando, FL, United States

Abstract

For decades the process of aluminum electrolysis has facilitated the production of aluminum. The process occurs within aluminum electrolytic cells, where alumina (Al₂O₃) is dissolved in liquid cryolite (Na₃AlF₆). The dissolved alumina is reduced by the carbon anode and forms carbon dioxide. Complexes containing aluminum ions migrate to the cathode surface (bath-metal interface) where aluminum metal is produced. The monitoring of the electrolysis process is done through the use of the cell resistance. Using resistance set point values that are indirectly related to the desired alumina concentration in the bath (cryolite), the computed resistance can indicate if the cell is operating within acceptable production conditions. The resistance time series is a nonstationary random process. We have applied the principal component method to shortsegments of each time series to identify key components. However the principal components are data dependent. In order to study the time series' localized structure we use a wavelet packet based approach to analyze this nonstationary process. We use Daubechies 3 orthonormal wavelet and scaling function as our basis functions and model each short segment of the resistance time series as a locally stationary wavelet process. The use of wavelet packets increases the separability of the innovations into individual packets. Hence each wavelet packet time series represents a single subprocess. The analysis of individual subprocesses yields information for making inference of how the process evolves during unstable operating conditions.

Citation Download Citation

Arthur Johnson III and Ching-Chung Li "Wavelet packet time series analysis of aluminum electrolytic cells", Proc. SPIE 4391, Wavelet Applications VIII, (26 March 2001); https://doi.org/10.1117/12.421204

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