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Proceedings Paper

Wavelet packet time series analysis of aluminum electrolytic cells
Author(s): Arthur Johnson III; Ching-Chung Li
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Paper 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.

Paper Details

Date Published: 26 March 2001
PDF: 10 pages
Proc. SPIE 4391, Wavelet Applications VIII, (26 March 2001); doi: 10.1117/12.421204
Show Author Affiliations
Arthur Johnson III, Univ. of Pittsburgh (United States)
Ching-Chung Li, Univ. of Pittsburgh (United States)

Published in SPIE Proceedings Vol. 4391:
Wavelet Applications VIII
Harold H. Szu; David L. Donoho; Adolf W. Lohmann; William J. Campbell; James R. Buss, Editor(s)

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