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• Conference paper
  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.

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  • Citations: 23
• Journal article
  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
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• 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
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  • Citations: 176
• 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
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  • Citations: 43
• Journal article
  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
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  • Citations: 6
• Conference paper
  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.

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• Journal article
  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
  • Author Web Link
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  • Citations: 98
• 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
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  • Citations: 2
• 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
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  • Citations: 19
• 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
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  • Citations: 153
• 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
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  • Citations: 8
• 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
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  • Citations: 21
• 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
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  • Citations: 101
• Conference paper
  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.

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• 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.

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  • Citations: 1
• 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.

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  • Citations: 11
• Journal article
  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
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  • Citations: 6
• 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
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  • Citations: 15
• 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
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  • Citations: 29
• Conference paper
  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
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