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ISA Transactions
Volume 44, Number 1
January 2005
A collection of articles about measurement and control systems in the process industries.



Characterization of a differential fiber Bragg grating sensor for oil-water boundary detection

By Peter LoPresti, Dilip Jali, Blake Carpenter, Michael Gersztenkorn
Department of Electrical Engineering, University of Tulsa, 600 South College Avenue, Tulsa, Oklahoma 74104, USA

Abstract
We investigate the operating characteristics of an oil-water boundary detector utilizing differential interrogation of fiber Bragg grating sensors. The system resolution is shown to be stable with respect to the choice of strain actuator and long-term temperature changes and changes in the initial strain on the fiber string. Fluid flow, particularly turbulent flow, is found to reduce system resolution significantly for the current system design. Improvements in the system design are required to minimize the effects of fluid flow and to accurately detect the presence of oil-water emulsions.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



A study of wavelet analysis based error compensation for the angular measuring system of high-precision test turntables

By Deng Huiyu, Wang Xinli, and Ma Peisun
Research Institute of Robot, Shang Hai Jiao Tong University, Shang Hai 200030, People’s Republic of China; Department of Electrical Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China

Abstract
An angular measuring system is the most important component of high-precision test turntables; its function and precision determine the turntable’s function and precision. The angular measuring system’s error was considered as a stationary signal in the past. An autocorrelation function and spectrum characteristics of the angular measuring system error are analyzed using the cyclostationary signal theory. The idea that the error in the angular measuring system is nonstationary is first put forward; theory is provided to reconstruct the angular measuring system’s error signal using wavelet analysis. The error signal is reconstructed using one-dimensional Mallat’s algorithm. The standard deviation between the reconstructed and the original signal is much less than the angular measuring system’s accuracy. The reconstruction signal is used to compensate the system error instead of the original error signal; the angular measuring system accuracy is improved.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Linear mass balance equilibration: A new approach for an old problem

By J. Ragot, D. Maquin, and M. Alhaj-Dibo
Centre de Recherche en Automatique de Nancy, CNRS UMR 7039, 2, Avenue de la Forıˆt de Haye, 54516 Vandoeuvre Cedex, France

Abstract
Interval analyses are well known in the mathematics literature but have found few applications in control engineering. Based on the interval concept, we present here a methodology for data reconciliation and mass balance equilibration which is a very classical problem in mineral and chemical engineering. Indeed, this problem is solved with the view of inequality constraints which allows us to represent measurements by interval without particular knowledge and hypothesis about the density probability function of the measurement errors. As a main result, the paper gives a set of solutions for the reconciled data under an interval form and not only one solution as is the case with classical approaches.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Observer design and stabilization for linear neutral delay systems


By Bing Chen, James Lam, and Zidong Wang|
Department of Mathematics, Bohai University, Liaoning 121003, People’s Republic of China; Department of Mechanical Engineering, University of Hong Kong, Hong Kong, Hong Kong; and the Department of Information Systems and Computing, Brunel University, Uxbridge UB8 3PH, United Kingdom

Abstract
This paper focuses on the state observer design problem as well as the observer-based stabilization problem for linear neutral delay systems. The purpose of the former problem is to design an observer that guarantees the asymptotic stability of the estimation error dynamics. The existence condition for such an observer is established. The latter problem, which is the main problem studied in this paper, aims at designing an observer-based feedback controller, such that the closed-loop system is asymptotically stabilized. It is shown that the desired controller can be easily designed if there are solutions to several linear matrix inequalities. Finally, two simulation examples are given to demonstrate the validity and effectiveness of the proposed approach.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Geometrical error compensation of machines with significant random errors

By Kok Kiong Tan, Sunan Huang
Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore

Abstract
In this paper, we present a new statistical approach towards soft geometrical error compensation of machines with significant errors. The approach, based on an analysis of the probability of the random error recurring, can reduce the adverse influence of random errors on the compensation of systematic errors. The proposed methodology is made up of three steps. First, error classes are defined from the error bands obtained from calibration. Second, the probability of the magnitude of random error belonging to each of these classes is computed based on the density of the data set within the class. Based on these probabilities, the most probable systematic part of the error measurement can be statistically deduced. Finally, the geometrical error compensation is carried out based on this value. Experimental results are provided for the linear error compensation of a single-axis piezo-ceramic motion system.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Adaptive control of uncertain continuously stirred tank reactors with unknown actuator nonlinearities


By T. Zhang, M. Guay
Department of Chemical Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6

Abstract
Adaptive nonlinear control is investigated for continuously stirred tank reactor (CSTR) systems using neural networks. The CSTR plant under study belongs to a class of nonaffine nonlinear systems, and contains an unknown parameter that enters the model nonlinearly. Using adaptive backstepping and neural network NN approximation techniques, an alternative adaptive NN controller is developed that achieves asymptotic output tracking control. A novel integral-type Lyapunov function, which includes both system states and control input as its arguments, is constructed to solve the difficulty associated with the nonaffine control problem. Numerical simulation is performed to show the feasibility of the proposed approach for chemical process control.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Continuous analysis of move suppressed and shifted DMC


By G. C. Kember, R. Dubay, and S. E. Mansour
Department of Engineering Mathematics, Dalhousie University, P.O. Box 1000, Halifax, NS, Canada, B3J 2X4; Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB, Canada, E3B 5A3

Abstract
‘‘Shifted DMC’’ (shifted dynamic matrix control) has been empirically shown to have significant improved closed-loop control characteristics over ‘‘move-suppressed DMC’’ where, in the latter, diagonal terms of the dynamic matrix DMC prediction model are augmented to reduce numerical ill conditioning. An added benefit of shifted DMC was that the so-called ‘‘shifting parameter,’’ replacing the move suppression parameter, was easily found from the open-loop response. Therefore a novel analytical method, based on a closed form, continuous approximation to closed-loop DMC control, is introduced here and used to quantify the previous empirical results. The dependence of slow and fast time scales of the closed-loop response on the parameters is examined for move-suppressed and shifted DMC methods. It is found that in move-suppressed DMC the slow control time scale is sharply dependent upon the sampling time and move-suppression parameter and that these difficulties are eliminated in shifted DMC.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Design of controller using variable transformations for a nonlinear process with dead time


By R. Anandanatarajan, M. Chidambaram, and T. Jayasingh
Pondicherry Engineering College, Pondicherry, India; IIT, Chennai, India; St. Xaviers College of Engineering, Nagercoil, India

Abstract
In this work, a globally linearized controller (GLC) for a first-order nonlinear system with dead time is proposed. This is similar to the GLC proposed by Ogunnalke [Ind. Eng. Chem. Process. Des. Dev. 25, 241–248 (1986)] for nonlinear systems without dead time. Two methods are proposed. One is based on the Smith prediction from the model in the transformed domain and the other is based on Newton’s extrapolation method. The simulation study is made on the conical tank level process and the results are compared with those obtained using a conventional PI controller and the Smith PI controller based on the transfer function model about the operating point 39%. Finally, experimental results on the laboratory conical tank level process are also given.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Digital redesign of observer-based weighting switch controller for cascaded analog systems with state saturation and external loads


By J. S. H. Tsai, H. Cheng, M. M. Moussighi, and L. S. Shieh
Control System Laboratory, Department of Electrical Engineering, National Cheng Kung University, Tainan 701, Taiwan, R.O.C.; Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, 77204-4005, USA

Abstract
This paper presents an observer-based weighting switch controller for dealing with the problem of cascaded systems with state saturation and external loads. This method improves the generally poor transition response and output deviation caused by state saturation and external loads. In order to maintain the state-saturation limits, we adopt the evolutionary programming optimal search technique to find the optimal switching parameters for the weighted switch controller. Also, a digital redesign method is utilized to replace a designed high-gain analog controller with a low-gain digital controller. It is shown that the digitally redesigned outputs closely track the analogously controlled outputs. The digital redesign technique is then extended to find the digital version of the continuous-time observer. An illustrative example is demonstrated to show the effectiveness of the proposed procedure.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Second-order sliding mode controllers for nonlinear singular perturbation systems


By J. Wang, K. M. Tsang
Department of Electrical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong

Abstract
Nonlinear systems are decomposed into slow and fast response subsystems using the singular perturbation theory and second-order sliding mode controllers are designed for each of the subsystems. The combined control action forms a suboptimal controller that can eliminate chattering in the continuous control output. Simulated examples are included to demonstrate the effectiveness of the proposed algorithm.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Multi-model direct adaptive decoupling control with application to the wind tunnel system


By Xin Wang, Shaoyuan Li, Wenjian Cai, Heng Yue, Xiaojie Zhou, Tianyou Chai
Institute of Automation, Shanghai Jiao Tong University, Shanghai, 200030, People’s Republic of China; School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore; Research Center of Automation Northeastern University, Shenyang, 110004, People’s Republic of China

Abstract
In this paper, a new multi-model direct adaptive decoupling controller is presented for multivariable processes, which includes multiple fixed optimal controllers, one free-running adaptive controller, and one re-initialized adaptive controller. The fixed controllers provide initial control to the process if its model lies in the corresponding region. For each controller selected, the re-initialized adaptive controller uses the values of this particular controller to improve the adaptation speed. This controller may replace the fixed controller at a later stage according to the switching criterion which is to select the best one among all controllers. A free-running adaptive controller is also added to guarantee the overall system stability. Different from the multiple models adaptive control structure proposed in Narendra, Balakrishnan, and Ciliz [Adaptation and learning using multiple models, switching, and tuning. IEEE Control Syst. Mag. 15, 37–51 (1995)], the method not only is applicable to the multi-input multi-output processes but also identifies the decoupling controller parameters directly, which reduces both the computational burden and the chances of a singular matrix during the process of determining controller parameters. Several examples for a wind tunnel process are given to demonstrate the effectiveness and practicality of the proposed method.

© 2005 ISA—The Instrumentation, Systems, and Automation Society.



Design and analysis of controllers for a double inverted pendulum


By Henrik Niemann, Jesper Kildegaard Poulsen
Ørsted-DTU, Automation, Technical University of Denmark, Building 326, DK-2800 Lyngby, Denmark; Intentia Danmark A/S, Borupvang 5 D-E, DK-2750 Ballerup, Denmark

Abstract
A physical control problem is studied with the H and the u methodology. The issues of modeling, uncertainty modeling, performance specification, controller design, and laboratory implementation are discussed. The laboratory experiment is a double inverted pendulum placed on a cart. The limitations in the system with respect to performance are the limitation in the control signal and the limitation of the movement of the cart. It is shown how these performance limitations will effect the design of H and u controllers for the system.



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