Causality of manufacturing processes  with significant time delays, TAPPI JOURNAL November 2015

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ABSTRACT: In this paper, the effects of flow rate, fiber consistency, and pressure fluctuation on basis weight variations were studied based on a set of paper mill operation data that include thick stock flow rate, consistency at eight different stock preparation stages, inlet and outlet pressure of the pressure pulsation attenuator, scanner position, β gauge, and scanner basis weight measurements. In order to focus on the important spectra and correlations within the low frequency range, a boxcar averaging procedure to eliminate high frequency extraneous information was employed. Moreover, two complete sets of data have been obtained for consistent and problematic operational conditions; namely, with and without a stuff box flow control system. The transfer function between the input and output spectra of certain components or processes within approach flow systems is also studied. Particular emphasis is placed on the synchronization procedure necessary for the study of low frequency range signals, as well as the correlation between two signals. All analysis results presented here are derived with an in-house developed program targeted for systems with significant time delays.

Application: This process control study has immediate application for streamlining and improving the operation of paper mills. The in-house developed software employed in this research can be used to monitor and study data and provide relevant recommendations with direct impact on mill operations.