N. Thornhill

Publications (3)0 Total impact

• Conference Proceeding: Cause and effect analysis of chemical processes analysis of a plant-wide disturbance

  M. Bauer, N. Thornhill, A. Meaburn
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  ABSTRACT: In continuous chemical processes, disturbances in the process conditions can propagate widely and cause secondary upsets in remote locations. The aim of this paper is to apply some recent data-driven methods for detection and diagnosis of process disturbances using historical process data that have been proving successful in a range of applications. An industrial case study is presented in which a plant-wide control system disturbance caused by the presence of a recycle was successfully located and then verified by further plant testing.
  Control Loop Assessment and Diagnosis, 2005. The IEE Seminar on (Ref. No. 2005/11008); 07/2005
• Conference Proceeding: A governing equation based fault detection and diagnosis algorithmand its application in a chemical plant

  Jie Zhang, Suzhen Zhang, N. Thornhill
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  ABSTRACT: This paper describes a governing equation fault detection and diagnosis algorithm, which is based on Kramer's (1987) approach and extended it to deal with multiple faults. The algorithm is specifically designed to overcome disturbances and uncertainties in the process which might result in diagnostic instability. The approach is used to detect and/or diagnose the following faults: sensor faulty status of fails-high and fails-low, sticking valve, plant leaks, and other unanticipated or novel faults. The algorithm was installed on a distributed control system of a PET plant in Dec. 1995, and continues to be used thus demonstrating the success of the fault detection and diagnosis approach
  American Control Conference, 1998. Proceedings of the 1998; 07/1998
• Article: Diagnosis of a unit-wide disturbance caused by saturation in a manipulated variable

  T. Matsuo, I. Tadakuma, N. Thornhill
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  ABSTRACT: It is well known that faulty control valves with friction in the moving parts lead to limit cycle oscillations which can propagate to other parts of the plant. However, a control loop with healthy valve can also undergo oscillatory behavior. The root cause of a unit-wide oscillation in a distillation column was traced to a pressure control loop in a case study at Mitsui Chemicals. The diagnosis was made by means of a new technique of pattern matching of the time-resolved frequency spectrum using a wavelet analysis tool. The method identified key characteristics shared by measurements at various places in the column and quantified the similarities. Non-linearity was detected in the time trend of the pressure measurement, a result which initially suggested the root cause was a faulty actuator or sensor. Further analysis showed, however, that the source of non-linearlity was periodic saturation of the manipulated variable caused by slack tuning. The problem was remidied by changing the controller tuning settings and the unit-wide disturbance then went away.
  Matsuo, T. and Tadakuma, I. and Thornhill, N. (2004) Diagnosis of a unit-wide disturbance caused by saturation in a manipulated variable. In: APC 2004, IEEE Advanced Process Control Applications for Industry Workshop, 26-28 April 2004, Vancouver, Canada.