Root cause analysis in oscillatory control loops

Texas Tech University System Office of Technology Commercialization
posted on 07/15/2011

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Invention Title

Software for analyzing the root cause of oscillatory behavior in control loop systems.

Executive Summary

The invention described is a software based tool for use in diagnosing the cause of oscillation in systems using multiple control loops. The problem of oscillation in control loop systems leads to millions of dollars in additional operating expense for manufacturing plants yearly. Additionally, an oscillatory control loop limits the maximum quality achievable by the system. This software can detect oscillation in the control loops, and describe the root cause(s) of that oscillation without requiring costly offline time for the system. The additional ability of this software to differentiate between external causes, stiction, and poor tuning allows system managers to schedule maintenance and tuning intelligently as the system requires. All of these features allow the system to be adjusted more closely to the actual output required, because the need to account for standard error is nearly eliminated.

Product Description

The software described is based on an algorithm in which the only required input is commonly measured parameters around control loops. Consequently, the inventor has been allowed to test the software using measurement data from several manufacturing plants. The hardware requirements are minimal even for large control loop systems, allowing a manufacturing plant to run a simulation every night and adjust the control loops according to outputs read every morning. The advantages of this system over competing products are its ability to detect all three causes of oscillation and also to describe from which root causes individual control loops are suffering. Also, the algorithm can diagnose oscillation as due to multiple root causes simultaneously.

Inventor Background

Prof. Raghunathan Rengasamy is a researcher in the chemical engineering department at Texas Tech University. He has multiple research interests, including several inventions targeted at alleviating control loop oscillation problems in manufacturing plants. 

http://www.depts.ttu.edu/che/faculty/rrengasamy/interests.php

Publications

U. Nallasivam, B. Srinivasan and R. Rengaswamy, "Stiction Identification in Nonlinear Process Control Loops", accepted, Computers and Chemical Engineering, doi:10.1016/j.compchemeng.2010.02.040, 2010.

Ranganathan Srinivasan, Raghunathan Rengaswamy and Randy Miller, "A Modified Empirical Mode Decomposition (EMD) Process for Oscillation Characterization in Control Loops", Control Engineering Practice, 15(9), pp 1135-1148, 2007.