Imperial College London
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Professor Nina F. Thornhill

Faculty of Engineering, Department of Chemical Engineering

Emeritus Professor of Process Automation
 
 
 
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Contact

 

n.thornhill

 
 
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Location

 

ACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

212 results found

Choudhury MAAS, Kariwala V, Shah SL, Douke H, Takada H, Thornhill NFet al., 2005, A simple test to confirm control valve stiction, Pages: 81-86, ISSN: 1474-6670

Stiction is a common problem in the widely used spring-diaphragm type control valves in the process industry. Several methods are available for detecting stiction in control valves. After detection of stiction, a test is required to confirm that the valve in question is indeed suffering from stiction. This paper presents a simple closed loop test, based on changing only the controller gain, for confirming the presence of stiction. The method does not require that the loop be put in manual, which can otherwise upset the plant. The usefulness of this test is demonstrated through simulation studies and an industrial application. Copyright © 2005 IFAC.

Conference paper

Anaparthi KK, Chaudhuri B, Thornhill NF, Pal BCet al., 2005, Coherency identification in power systems through principal component analysis, IEEE Transactions on Power Systems, Vol: 20, Pages: 1658-1660, ISSN: 0885-8950

Journal article

Choudhury MAAS, Shah SL, Thornhill NF, 2004, Diagnosis of poor control-loop performance using higher-order statistics, AUTOMATICA, Vol: 40, Pages: 1719-1728, ISSN: 0005-1098

Journal article

Thornhill NF, Choudhury MAAS, Shah SL, 2004, The impact of compression on data-driven process analyses, JOURNAL OF PROCESS CONTROL, Vol: 14, Pages: 389-398, ISSN: 0959-1524

Journal article

Choudhury MAAS, Shah SL, Thornhill NF, 2004, Detection and quantification of control valve stiction, Pages: 865-870, ISSN: 1474-6670

Stiction is one of the most common problems in the spring-diaphragm type control valves, which are widely used in the process industry. Although there have been many attempts to understand and detect stiction in control valves, none of the current methods can simultaneously detect and quantify stiction. There is thus a clear need in the process industry for a non-invasive method that can not only detect but also quantify stiction so that the valves that need repair or maintenance can be identified, isolated and repaired. This work describes a method that can detect and quantify stiction that may present in control valves using routine closed loop operating data obtained from the process. No additional excitation or experimentation with the plant is required. Over a dozen industrial case studies have demonstrated the wide applicability and practicality of this method as an useful diagnostic aid in control-loop performance monitoring.

Conference paper

Choudhury MAAS, Thornhill NF, Shah SL, 2004, A data-driven model for valve stiction, Pages: 245-250, ISSN: 1474-6670

The presence of nonlinearities, e.g., stiction, hysteresis and backlash in a control valve limits control loop performance. Stiction is the most common problem in spring-diaphragm type valves, which are widely used in the process industry. Though there have been many attempts to understand the stiction phenomena and model it, there is lack of a proper model which can be understood and related directly to the practical situation as observed in real valves in the process industry. This study focuses on the understanding, from industrial data, of the mechanism that causes stiction and proposes a new data-driven model of stiction, which can be directly-related to real valves. It compares simulation results generated using the proposed model with industrial data.

Conference paper

Law VJ, Kenyon AJ, Thornhill NF, Pagliarani A, Lea L, Watkins Met al., 2004, A frequency domain measurement diagnostic technique for plasma-tools, MEASUREMENT SCIENCE AND TECHNOLOGY, Vol: 15, Pages: 231-236, ISSN: 0957-0233

Journal article

Bauer M, Thornhill NF, Meaburn A, 2004, Specifying the directionality of fault propagation paths using transfer entropy, 7th International Symposium on Dynamics and Control of Process Systems (DYCOPS 7)

In continuous chemical processes, variations of process variables usually travel along propagation paths in the direction of flow. The aim of this study was to find a data-driven method for identifying the direction of variation propagation using historical process data. Transfer entropy is a recently proposed method based on the probability density function (PDF) that measures directionality of variation with respect to time. An industrial case study illustrates the method which detects the influence of a temperature controller on downstream temperature measurements. A reversal of directionality was noted during a disturbance and a physical explanation offered.

Conference paper

Thornhill NF, Cox JW, Paulonis MA, 2003, Diagnosis of plant-wide oscillation through data-driven analysis and process understanding, CONTROL ENGINEERING PRACTICE, Vol: 11, Pages: 1481-1490, ISSN: 0967-0661

Journal article

Law VJ, Thornhill NF, Kenyon AJ, Paglirani A, Lee K, Watkins M, Lea Let al., 2003, Harmonic monitoring of the switched silicon etched process, JOURNAL OF PHYSICS D-APPLIED PHYSICS, Vol: 36, Pages: 2146-2151, ISSN: 0022-3727

Journal article

Thornhill NF, Huang B, Shah SL, 2003, Controller performance assessment in set point tracking and regulatory control, INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Vol: 17, Pages: 709-727, ISSN: 0890-6327

Journal article

Thornhill NF, Huang B, Zhang H, 2003, Detection of multiple oscillations in control loops, JOURNAL OF PROCESS CONTROL, Vol: 13, Pages: 91-100, ISSN: 0959-1524

Journal article

Apelt TA, Asprey SP, Thornhill NF, 2002, Inferential measurement of SAG mill parameters III: inferential models, MINERALS ENGINEERING, Vol: 15, Pages: 1055-1071, ISSN: 0892-6875

Journal article

Apelt TA, Asprey SP, Thornhill NF, 2002, Inferential measurement of SAG mill parameters II: state estimation, MINERALS ENGINEERING, Vol: 15, Pages: 1043-1053, ISSN: 0892-6875

Journal article

Thornhill NF, Shah SL, Huang B, Vishnubhotla Aet al., 2002, Spectral principal component analysis of dynamic process data, CONTROL ENGINEERING PRACTICE, Vol: 10, Pages: 833-846, ISSN: 0967-0661

Journal article

Dobson JP, Thornhill NF, 2002, Analysis of plant-wide disturbances using conditional entropy, IEEE International Conference on Control Applications, Publisher: IEEE, Pages: 687-688

Plant-wide disturbances in chemical plants have an impact on product quality and running costs, thus there is a need for automated diagnosis of the root cause. This short paper reports work in progress and preliminary results from a novel signal processing application using conditional entropy. It analyses measurements from normal process operations in a chemical plant to determine cause and effect relationships. The method suggests which measurement is the root cause of a plant-wide disturbance and, additionally, maps the physical structure of the plant.

Conference paper

Choudhury MAAS, Shah SL, Thornhill NF, 2002, Detection and diagnosis of system nonlinearities using higher order statistics, Pages: 337-342, ISSN: 1474-6670

This paper is concerned with the statistical analysis of closed loop data for diagnosing the causes of poor control loop performance. Higher Order Statistical (HOS) techniques have been developed over the last two decades, but until now have not been applied to the area of process monitoring. The main contribution of this work is to utilize the higher order statistical tools such as cumulants and their frequency domain counterparts (bispectrum, bicoherence, trispectrum) to detect and quantify the non-Gaussianity and nonlinearity of regulated processes or control error variables which are sometimes the main contributors to the poor performance of many of the control loops. The bicoherence index together with the process and manipulated variable plots are used to diagnose the sources of system nonlinearities. Successful application of the proposed method is demonstrated on simulated as well as industrial data.

Conference paper

Thornhill NF, Xia C, Howell J, Cox J, Paulonis Met al., 2002, Analysis of plant-wide disturbances through data-driven techniques and process understanding, Pages: 399-404, ISSN: 1474-6670

Plant-wide disturbances can have an impact on product quality and running costs. Thus there is a motivation for automated detection of a plant-wide disturbance and for diagnosis of the root cause. In this article, data-driven techniques are used to analyze plant-wide disturbances caused, for instance, by limit cycle oscillation in a control loop. The control loops participating in the disturbance are detected and displayed on a process schematic. Other numerical signatures derived from the data trends are utilized for the diagnosis of the root cause. The outcome is a visual display that integrates process understanding and data-driven analysis.

Conference paper

Wang M, Thornhill NF, Huang B, 2002, Closed loop identification based on quantization, Pages: 319-324, ISSN: 1474-6670

This paper proposes a new closed-loop identification scheme for a single-input-single-output control loop. It is based upon a quantizer inserted into the feedback path. The quantizer can be used to generate an equivalent persistently exciting signal with which the well known two-stage and/or two-step method can be used directly. Simulation examples and an experimental demonstration are used to illustrate the proposed scheme.

Conference paper

Tan CC, Thornhill NF, Belchamber RM, 2002, Principal component analysis of spectra with application to acoustic emissions from mechanical equipment, TRANSACTIONS OF THE INSTITUTE OF MEASUREMENT AND CONTROL, Vol: 24, Pages: 333-353, ISSN: 0142-3312

Journal article

Law VJ, Kenyon AJ, Thornhill NF, Seeds AJ, Batty Iet al., 2001, Rf probe technology for the next generation of technological plasmas, JOURNAL OF PHYSICS D-APPLIED PHYSICS, Vol: 34, Pages: 2726-2733, ISSN: 0022-3727

Journal article

Apelt TA, Asprey SP, Thornhill NF, 2001, Inferential measurement of SAG mill parameter', MINERALS ENGINEERING, Vol: 14, Pages: 575-591, ISSN: 0892-6875

Journal article

Wang M, Saleem S, Thornhill NF, 2001, Time series reconstruction from quantized measurements, University of Texas at Austin, Chemical Process Control VI (CPC6), Publisher: CACHE Corporation, Pages: 448-452

Conference paper

Law VJ, Kenyon AJ, Thornhill NF, Srigengan V, Batty Iet al., 2000, Remote-coupled sensing of plasma harmonics and process end-point detection, VACUUM, Vol: 57, Pages: 351-364, ISSN: 0042-207X

Journal article

Pate ME, Turner MK, Thornhill NF, Titchener-Hooker NJet al., 1999, The use of principal component analysis for the modelling of high performance liquid chromatography, BIOPROCESS ENGINEERING, Vol: 21, Pages: 261-272, ISSN: 0178-515X

Journal article

Koh ATC, Thornhill NF, Law VJ, 1999, Principal component analysis of plasma harmonics in end-point detection of photoresist stripping, ELECTRONICS LETTERS, Vol: 35, Pages: 1383-1385, ISSN: 0013-5194

Journal article

Yeung KSY, Hoare M, Thornhill NF, Williams T, Vaghjiani JDet al., 1999, Near-infrared spectroscopy for bioprocess monitoring and control, BIOTECHNOLOGY AND BIOENGINEERING, Vol: 63, Pages: 684-693, ISSN: 0006-3592

Journal article

Thornhill NF, Oettinger M, Fedenczuk P, 1999, Refinery-wide control loop performance assessment, JOURNAL OF PROCESS CONTROL, Vol: 9, Pages: 109-124, ISSN: 0959-1524

Journal article

Pate ME, Thornhill NF, Chandwani R, Hoare M, Titchener-Hooker NJet al., 1998, Pre-processing of chromatographic data for principal component analysis, BIOPROCESS ENGINEERING, Vol: 19, Pages: 297-305, ISSN: 0178-515X

Journal article

Alheritiere C, Thornhill NF, Fraser S, Knight MJet al., 1998, Cost benefit analysis of refinery process data: Case study, COMPUTERS & CHEMICAL ENGINEERING, Vol: 22, Pages: S1031-S1034, ISSN: 0098-1354

Journal article

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