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Control Loops (control + loop)
Selected AbstractsOperative Platform Applied to Building AutomationCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2009João Figueiredo This structure is composed by three interrelated levels: the Operational level,where the field equipment is controlled, the Inter-Active level,where inhabitants communicate the building their preferences regarding control variables (lights, temperature, etc.), and the higher-level control, the Overall Building Well-Being Model, which manages the global building, taking into account the optimization of the inhabitants preferences, constrained by the available resources. At this third level, the inter-building communication is available. Each building has the capability to communicate with its neighbors, informing about fires, floods, security problems, power consumption expectations, and so on. This article implements one of the three above-referred interrelated control levels: the Operational-level control. This operative platform is structured over a cascade hierarchical control architecture where inner loops are performed by local PLCs (Programmable Logic Controllers), and the outer loop is managed by a centralized SCADA system (Supervisory Control and Data Acquisition) that interacts with the entire PLC network. The lower-level control loop assures high processing velocity tasks, the upper-level control loop updates the local references, knowing the complete system state. This operative model is tested on two prototypes, where all instrumentation in place is controlled by the industrial PLC network. Both prototypes worked perfectly showing the huge potential of communication systems between distributed processes. These communication systems allow intelligent centralized algorithms to manage decision-making problems in real-time environments. The system presented in this article combines several technologies (local PLCs, SCADA systems, and network communications) to reach the goal of efficient management of intelligent buildings. [source] Equivalent force control method for generalized real-time substructure testing with implicit integrationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2007Bin Wu Abstract This paper presents a new method, called the equivalent force control method, for solving the nonlinear equations of motion in a real-time substructure test using an implicit time integration algorithm. The method replaces the numerical iteration in implicit integration with a force-feedback control loop, while displacement control is retained to control the motion of an actuator. The method is formulated in such a way that it represents a unified approach that also encompasses the effective force test method. The accuracy and effectiveness of the method have been demonstrated with numerical simulations of real-time substructure tests with physical substructures represented by spring and damper elements, respectively. The method has also been validated with actual tests in which a Magnetorheological damper was used as the physical substructure. Copyright © 2007 John Wiley & Sons, Ltd. [source] Performance evaluation of TCP-based applications over DVB-RCS DAMA schemesINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 3 2009M. Luglio Abstract Transmission Control Protocol (TCP) performance over Digital Video Broadcasting,Return Channel via Satellite (DVB-RCS) standard is greatly affected by the total delay, which is mainly due to two components, propagation delay and access delay. Both are significant because they are dependent on the long propagation path of the satellite link. The former is intrinsic and due to radio wave propagation over the satellite channel for both TCP packets and acknowledgements. It is regulated by the control loop that governs TCP. The latter is due to the control loop that governs the demand assignment multiple access (DAMA) signalling exchange between satellite terminals and the network control center, necessary to manage return link resources. DAMA is adopted in DVB-RCS standard to achieve flexible and efficient use of the shared resources. Therefore, performance of TCP over DVB-RCS may degrade due to the exploitation of two nested control loops also depending on both the selected DAMA algorithm and the traffic profile. This paper analyses the impact of basic DAMA implementation on TCP-based applications over a DVB-RCS link for a large set of study cases. To provide a detailed overview of TCP performance in DVB-RCS environment, the analysis includes both theoretical approach and simulation campaign. Copyright © 2009 John Wiley & Sons, Ltd. [source] Position/Force Control of an Underwater Mobile ManipulatorJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 12 2003Lionel Lapierre This paper proposes a new control method applied to an underwater vehicle equipped with a robot manipulator. This control method is based on force control to stabilize the platform when the manipulator works in free or constrained space. The torque produced by the arm on the platform is estimated with a force sensor installed between the base of the manipulator and the vehicle. This allows correcting the position errors of the platform using an external force control loop. This paper presents this control law and shows some simulation results. © 2003 Wiley Periodicals, Inc. [source] Elucidation and decisional risk in a multi-criteria decision based on a Choquet integral aggregation,a cybernetic frameworkJOURNAL OF MULTI CRITERIA DECISION ANALYSIS, Issue 5-6 2005J. Montmain Abstract The authors are developing multi-criteria Decision-making support systems (DMSS) for project teams in charge of selecting a technical solution among alternatives. They propose a cybernetic framework to emphasize the link between decision-making (DM) and knowledge management processes in such projects. These DMSSs rely on the tracking of the accompanying knowledge production of long-term decisional processes by a collective with many actors. Based on knowledge-production management, this paper explains how to design decisional risk evaluation, monitoring and control aids and traceability functions for strategic choices and logical argumentation. The DMSS is seen as a recommender system for the project manager. Each possible solution involved in the decision-making process (DMP) is evaluated by means of a set of criteria. The evaluation results from an interpretation of the knowledge items in terms of satisfaction scores of the solutions according to the considered criteria. Aggregating these partial scores provides a ranking of all the possible solutions by order of preference. As criteria are sometimes interacting, the aggregation has to be based on adapted operators, i.e. Choquet integrals. Evaluating possible solutions by the knowledge contained in the knowledge base (KB) opens the way to automating the argumentation of the project team's decisions: the argumentation principle underlying this approach is based naturally on coupling a knowledge dynamical management system (KDMS) with the DMSS. The DMSS also evaluates the decisional risk that reflects the eventuality of a wrong selection due to the insufficiency of available knowledge at a given time in order to adopt a reliable solution. Decisional risk assessment corresponds to sensitivity analyses. These analyses are then exploited to control the decisional risk in time: they enable to identify the crucial information points for which additional and deeper investigations would be of great interest to improve the stability of the selection in the future. The knowledge management of a collective project is represented as a control loop: the KDMS is the actuator, the risk accompanying the decision is the controlled variable and is strongly linked to the entropy of the KB managed by the KDMS. Each of the three phases,intelligence, design, choice,of the DMP is identified to a function of the control loop: actuator, process and regulator. This cybernetic framework for decision has its origin in knowledge management activities for a great-scale project,the EtLD project of the French Atomic Commission (CEA) that concerns the management of high-level long-life radioactive waste in France. Copyright © 2007 John Wiley & Sons, Ltd. [source] PID control performance assessment: The single-loop caseAICHE JOURNAL, Issue 6 2004Byung-Su Ko Abstract An iterative solution is developed for the calculation of the best achievable (minimum variance) PID control performance and the corresponding optimal PID setting in an existing control loop. An analytic expression is derived for the closed-loop output as an explicit function of PID setting. The resulting benchmark allows for realistic performance assessment of an existing PID control loop, especially when the control loop fails to meet the minimum variance performance. A PID performance index is then defined based on the PID performance bound, and its confidence interval is estimated. A series of simulated examples are used to demonstrate the utility of the proposed method. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1211,1218, 2004 [source] Modifications to improve the accuracy of a four-ball test apparatusLUBRICATION SCIENCE, Issue 1 2000P. I. Lacey Abstract The four-ball wear test machine is one of the most widely used tribological tools in both research and industry. In general, the test geometry is self-aligning and minimises the opportunity for random variation. Nonetheless, accurate control of the test parameters remains vital to repeatability and reproducibility. The present paper details a number of modifications to a commercially available test apparatus that have been found to improve accuracy. The applied load on some apparatus was found to vary from the correct value, probably due to frictional drag in the loading system. A feedback control loop was designed and fitted to the applied load mechanism, which resulted in significantly improved accuracy. Finally, the apparatus was fully automated, with complete computer control of all test parameters. Under this, following cleaning and assembly of the test specimens, the required test procedure could be selected from a menu of standard methods, and the computer program then adjusted the test parameters according to the method selected, greatly reducing the possibility of operator error. [source] Physiological Control of a Rotary Blood Pump With Selectable Therapeutic Options: Control of Pulsatility GradientARTIFICIAL ORGANS, Issue 10 2008Andreas Arndt Abstract A control strategy for rotary blood pumps meeting different user-selectable control objectives is proposed: maximum support with the highest feasible flow rate versus medium support with maximum ventricular washout and controlled opening of the aortic valve (AoV). A pulsatility index (PI) is calculated from the pressure difference, which is deduced from the axial thrust measured by the magnetic bearing of the pump. The gradient of PI with respect to pump speed (GPI) is estimated via online system identification. The outer loop of a cascaded controller regulates GPI to a reference value satisfying the selected control objective. The inner loop controls the PI to a reference value set by the outer loop. Adverse pumping states such as suction and regurgitation can be detected on the basis of the GPI estimates and corrected by the controller. A lumped-parameter computer model of the assisted circulation was used to simulate variations of ventricular contractility, pulmonary venous pressure, and aortic pressure. The performance of the outer control loop was demonstrated by transitions between the two control modes. Fast reaction of the inner loop was tested by stepwise reduction of venous return. For maximum support, a low PI was maintained without inducing ventricular collapse. For maximum washout, the pump worked at a high PI in the transition region between the opening and the permanently closed AoV. The cascaded control of GPI and PI is able to meet different control objectives and is worth testing in vitro and in vivo. [source] Generic UMTS test signal for RF bioelectromagnetic studiesBIOELECTROMAGNETICS, Issue 6 2004H. Ndoumbè Mbonjo Mbonjo Abstract This report outlines the characteristics of universal mobile telecommunications system (UMTS) signals and discusses the signal parameters with respect to their possible biological relevance in order to define a generic UMTS test signal (GUS) for experiments aiming at the investigation of biological effects of weak electromagnetic fields. The GUS includes features of a real UMTS signal and especially the characteristics of UMTS, which differ from those of already applied second generation mobile communication systems (GSM 900, DCS1800, PCS1900, IS-95). It has been specified on the basis of the recommendations of a working group of the German Forschungsgemeinschaft Funk (FGF) with a focus on the mechanisms of UMTS which are responsible for slow term signal contributions, i.e., low frequency variations of the radio frequency (RF) envelope, since the hypothetical possibility of biological relevance of weak electromagnetic fields is often attributed to time variations of the RF envelope with frequencies close to those of natural processes. In this respect, it is also shown that the mandatory power control loop in UMTS gives rise to very strong 1.5 kHz variations on the air interface. Based upon the concept of the GUS, a UMTS test signal generator (GUS6960S) is described. Bioelectromagnetics 25:415,425, 2004. © 2004 Wiley-Liss, Inc. [source] Twenty-four-well plate miniature bioreactor high-throughput system: Assessment for microbial cultivationsBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2007Kevin Isett Abstract High-throughput (HT) miniature bioreactor (MBR) systems are becoming increasingly important to rapidly perform clonal selection, strain improvement screening, and culture media and process optimization. This study documents the initial assessment of a 24-well plate MBR system, Micro (µ)-24, for Saccharomyces cerevisiae, Escherichia coli, and Pichia pastoris cultivations. MBR batch cultivations for S. cerevisiae demonstrated comparable growth to a 20-L stirred tank bioreactor fermentation by off-line metabolite and biomass analyses. High inter-well reproducibility was observed for process parameters such as on-line temperature, pH and dissolved oxygen. E. coli and P. pastoris strains were also tested in this MBR system under conditions of rapidly increasing oxygen uptake rates (OUR) and at high cell densities, thus requiring the utilization of gas blending for dissolved oxygen and pH control. The E. coli batch fermentations challenged the dissolved oxygen and pH control loop as demonstrated by process excursions below the control set-point during the exponential growth phase on dextrose. For P. pastoris fermentations, the µ-24 was capable of controlling dissolved oxygen, pH, and temperature under batch and fed-batch conditions with subsequent substrate shot feeds and supported biomass levels of 278 g/L wet cell weight (wcw). The average oxygen mass transfer coefficient per non-sparged well were measured at 32.6,±,2.4, 46.5,±,4.6, 51.6,±,3.7, and 56.1,±,1.6 h,1 at the operating conditions of 500, 600, 700, and 800 rpm shaking speed, respectively. The mixing times measured for the agitation settings 500 and 800 rpm were below 5 and 1 s, respectively. Biotechnol. Bioeng. 2007;98: 1017,1028. © 2007 Wiley Periodicals, Inc. [source] Manoeuvring and vibration reduction of a flexible spacecraft integrating optimal sliding mode controller and distributed piezoelectric sensors/actuatorsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 6 2007Qinglei Hu Abstract This investigation is to apply optimal sliding mode (OSM) control theory and distributed piezoelectric sensor/actuator technology to vibration control of a flexible spacecraft. An approximate analytical dynamic model of a slewing flexible spacecraft with surface-bonded piezoelectric sensors/actuators is developed using Hamilton's principle with discretization by assumed model method. To satisfy pointing requirements and simultaneously suppress vibration, two separate control loops are adopted. The first uses the piezoceramics as sensors and actuators to actively suppress certain flexible modes by designing a positive position feedback (PPF) compensators that add damping to the flexible structures in certain critical modes in the inner feedback loop; then a second feedback loop is designed using OSM control to slew the spacecraft. The OSM controller minimizes the expected value of a quadratic objective function consisting of only the states with the constraints that the error states always remain on the intersection of sliding surfaces. The advantage in this method is that the vibration reduction and attitude control are achieved separately in the two separate feedback loops, allowing the pointing requirements and simultaneous vibrations suppression to be satisfied independently of one another. An additional attraction of the design method is that the selection of PPF gain is determined by introducing a cost function to be minimized by the feedback gains which are subject to the stability criterion at the same time, such that the feedback gains are selected in a more systematical way to avoid the arbitrary selecting of feedback gains. The proposed control strategy has been implemented on a flexible spacecraft, which is a hub with a cantilever flexible beam appendage and can undergo a single axis rotation. Both analytical and numerical results are presented to show the theoretical and practical merits of this approach. Copyright © 2006 John Wiley & Sons, Ltd. [source] A reference model approach to performance monitoring of control loops with applications to irrigation channelsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 10 2005P. Zhang Abstract In this paper a new method for detection of oscillatory and sluggish controllers is developed. The method is aimed at control systems where rejection of measured load disturbances is the main control objective, and it is based on comparing the actual system output with the output of a reference model. A number of performance indicators are defined taking the most important factors from a control perspective into consideration. Based on the performance indicators, the performance of the control loops is evaluated. The developed method has been successfully applied to real data from an irrigation channel. The method correctly detected the control loops which needed retuning, and it provided useful information about several aspects of the control performance such as speed of response, oscillations and interactions between control loops. Copyright © 2005 John Wiley & Sons, Ltd. [source] Analysis of multivariable controllers using degree of freedom dataINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 7-9 2003T. J. Harris Abstract Most approaches for monitoring, diagnosis and performance analysis of multivariable control loops employ time series methods and use non-parametric statistics to analyse the process inputs and outputs. In this paper, we explore the use of a discrete variable that summarizes the status of the constraint set of the controller to analyse the long run behaviour of control systems. We introduce a number of waiting and holding time statistics that describe the status of this data, which we call the degree of freedom data. We demonstrate how Markov Chains might be used to model the status of the degree of freedom data. This model-based approach has the potential to provide considerable insight into the behaviour of a model based control scheme with relative ease. We demonstrate the methodologies on simulated and industrial data. Copyright © 2003 John Wiley & Sons, Ltd. [source] Control of induction motors: an adaptive passivity MIMO perspectiveINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 4 2003Manuel A. Duarte-Mermoud The design of two multiple-input multiple-output (MIMO) controllers for induction motors, based on adaptive passivity, is presented in this paper. The controller design method is based on concepts of equivalence passivity via adaptive feedback, previously developed by the authors. Robustness under variations of the motor-load parameters is guaranteed and the knowledge of such a parameters is not needed in the design. Simple proportional controllers for the torque, rotor flux and stator current control loops are used, due to the control simplification introduced by the use of feedback passive equivalence. A principle called ,Torque-Flux Control Principle' is used in this article introducing a considerable simplification in the resultant controller. Because of the employment of this principle, the control efforts are diminished and rotor flux estimation (or measurement) is avoided. Copyright © 2003 John Wiley & Sons, Ltd. [source] Mixture-based adaptive probabilistic controlINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 2 2003Miroslav Kárný Abstract Quasi-Bayes algorithm, combined with stabilized forgetting, provides a tool for efficient recursive estimation of dynamic probabilistic mixture models. They can be interpreted either as models of closed-loop with switching modes and controllers or as a universal approximation of a wide class of non-linear control loops. Fully probabilistic control design extended to mixture models makes basis of a powerful class of adaptive controllers based on the receding-horizon certainty equivalence strategy. Paper summarizes the basic elements mentioned above, classifies possible types of control problems and provides solution of the key one referred to as ,simultaneous' design. Results are illustrated on mixtures with components formed by normal auto-regression models with external variable (ARX). Copyright © 2003 John Wiley & Sons, Ltd. [source] Self-tuning PID controller using , -model identificationINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 6 2002Vladimír Bobál Abstract This contribution presents an application of a self-tuning digital PID controller for process control modelled by , -models. The process is identified by the regression (ARX) model using the recursive least-squares method (RLSM) with LD decomposition and applied directional forgetting. Controller synthesis is designed on the basis of a modified Ziegler,Nichols criterion for digital PID control loops. The ultimate (critical) proportional gain and period of oscillations have been derived for the second-order , -model. Control results obtained using digital PID controller on the basic ,-models and z -models are compared. Copyright © 2002 John Wiley & Sons, Ltd. [source] Distributed model predictive control of nonlinear process systemsAICHE JOURNAL, Issue 5 2009Jinfeng Liu Abstract This work focuses on a class of nonlinear control problems that arise when new control systems which may use networked sensors and/or actuators are added to already operating control loops to improve closed-loop performance. In this case, it is desirable to design the pre-existing control system and the new control system in a way such that they coordinate their actions. To address this control problem, a distributed model predictive control method is introduced where both the pre-existing control system and the new control system are designed via Lyapunov-based model predictive control. Working with general nonlinear models of chemical processes and assuming that there exists a Lyapunov-based controller that stabilizes the nominal closed-loop system using only the pre-existing control loops, two separate Lyapunov-based model predictive controllers are designed that coordinate their actions in an efficient fashion. Specifically, the proposed distributed model predictive control design preserves the stability properties of the Lyapunov-based controller, improves the closed-loop performance, and allows handling input constraints. In addition, the proposed distributed control design requires reduced communication between the two distributed controllers since it requires that these controllers communicate only once at each sampling time and is computationally more efficient compared to the corresponding centralized model predictive control design. The theoretical results are illustrated using a chemical process example. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Leptin-Target Neurones of the Rat Hypothalamus Express Somatostatin ReceptorsJOURNAL OF NEUROENDOCRINOLOGY, Issue 9 2003Z. Stepanyan Abstract Hypothalamic leptinoceptive neurones can be visualized by histochemical demonstration of leptin-induced nuclear translocation of the signalling molecule STAT3. We investigated the relationship of the leptinoceptive neurones to the somatostatin signalling system. With double-labelling immunohistochemistry, we studied the colocalization of leptin-activated transcription factor, STAT3, with somatostatin receptor subtypes, sst1, sst2A, sst2B, sst3 and sst4, or the neuropeptide itself, in the rat hypothalamus. Immunoreactivity for all the entities was widely distributed throughout the entire hypothalamus. Despite the wide distribution, only few cases of colocalization of somatostatin with leptin-activated STAT3 were detected in the paraventricular, arcuate and dorsomedial nuclei. A moderate to high degree of colocalization of nuclear STAT3 and all investigated subtypes of somatostatin receptors was found in the lateral and dorsal hypothalamic areas and in the dorsomedial hypothalamic nucleus. Immunoreactivity for sst1, sst2B and sst4 was present in STAT3-containing nuclei of the paraventricular, periventricular, arcuate and ventromedial hypothalamic neurones, as well as in the retrochiasmatic and posterior hypothalamic areas. Despite the wide distribution of sst2A in the rat hypothalamus, few events of colocalization with leptin-activated STAT3 were observed in the dorsomedial nucleus and in the lateral and dorsal hypothalamic areas only. Many leptin-responsive neurones of the dorsal, lateral, periarcuate, perifornical and posterior hypothalamic areas, as well as in the ventromedial and dorsomedial hypothalamic nuclei, displayed sst3 immunoreactivity at their neuronal cilia. These results provide strong anatomical evidence for the direct interaction of leptin and the somatostatin systems in neuroendocrine control loops such as the energy homeostasis, growth or stress response. [source] Accidents, often the result of an ,uncontrolled business process',a study in the (Dutch) chemical industryQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 3 2003P. J. M. Sonnemans Abstract Often companies in the (petro-) chemical industry claim that all possible countermeasures against potential accidents have been taken and therefore accidents are unforeseeable. In this paper we question this statement by analysing the pre-warning signals (precursors) preceding a number of industrial accidents. 17 accidents that occurred in the (petro-) chemical industry have been investigated by exploring FACTS, an accident database containing information about industrial accidents worldwide. This paper will demonstrate that the existence of precursor information could have been used to foresee and even prevent these accidents if a proper control action had been initiated. The accidents are analysed further, according to a control model, which was adapted from that of C. Argyris. It demonstrates the ineffectiveness of several elements of business process control loops and that the so-called ,double-loop learning' cycle is more important than the ,single-loop learning' cycle if one considers safety improvement. Copyright © 2003 John Wiley & Sons, Ltd. [source] A Short Note About Energy-Efficiency Performance of Thermally Coupled Distillation SequencesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2006Juan Gabriel Segovia-Hernández Abstract In this work, we present a comparative study of the energy-efficiency performance between conventional distillation sequences and thermally coupled distillation arrangements (TCDS) for the separation of ternary mixtures of hydrocarbons under the action of feedback control loops. The influence of the relative ease of separation of the feed mixture and its composition was analyzed. The feedback analysis was conducted through servo tests with individual changes in the set points for each of the three product streams. Standard PI controllers were used for each loop. The results show an apparent trend regarding the sequence with a better dynamic performance. Generally, TCDS options performed better for the control of the extreme components of the ternary mixture (A and C), while the conventional sequences offered a better dynamic behaviour for the control of the intermediate component (B). The only case in which there was a dominant structure for all control loops was when the feed contained low amounts of the intermediate component and the mixture had similar relative volatilities. The Petlyuk column provided the optimal choice in such case, which contradicts the general expectations regarding its control behaviour. In addition, the energy demands during the dynamic responses were significantly lower than those observed for the other distillation sequences. TCDS options, therefore, are not only more energy efficient than the conventional sequences, but there are cases in which they also offer better feedback control properties. On présente dans ce travail une étude comparative de la performance d'efficacité d'énergétique entre les séquences de distillation conventionnelles et les configurations de distillation couplées thermiquement (TCDS) pour la séparation de mélanges ternaires d'hydrocarbures sous l'action de boucles de contrôle d'asservissement. L'influence de la facilité relative de séparation du mélange d'alimentation et de sa composition est analysée. L'analyse de rétroalimentation est réalisée grâce à des tests d'asservissement avec des changements individuels dans les points de consigne pour chacun des trois courants de produits. Des contrôleurs PI standards ont été utilisés pour chaque boucle. Les résultats montrent une tendance apparente pour la séquence ayant une meilleure performance dynamique. Généralement, les options TCDS sont meilleures pour le contrôle des composantes extrêmes du mélange ternaire (A et C), tandis que les séquences conventionnelles offrent un meilleur contrôle dynamique pour le contrôle de la composante intermédiaire (B). Le seul cas où il y a une structure dominante pour toutes les boucles de contrôle, c'est lorsque l'alimentation contenant de faibles quantités de la composante intermédiaire et le mélange ont la même volatilité relative. La colonne Petlyuk est le choix optimal dans un tel cas, ce qui contredit les attentes générales concernant son comportement de contrôle. En outre, les demandes d'énergie pendant les réponses dynamiques sont significativement plus faibles que celles observées pour les autres séquences de distillation. Ainsi, non seulement les options TCDS sont plus efficaces que les séquences conventionnelles, mais il y a des cas où elles offrent également de meilleures propriétés de contrôle d'asservissement. [source] Enhancing Controller Performance via Dynamic Data ReconciliationTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2005Shuanghua Bai Abstract Measured values of process variables are subject to measurement noise. The presence of measurement noise can result in detuned controllers in order to prevent excessive adjustments of manipulated variables. Digital filters, such as exponentially weighted moving average (EWMA) and moving average (MA) filters, are commonly used to attenuate measurement noise before controllers. In this article, we present another approach, a dynamic data reconciliation (DDR) filter. This filter employs discrete dynamic models that can be phenomenological or empirical, as constraints in reconciling noisy measurements. Simulation results for a storage tank and a distillation column under PI control demonstrate that the DDR filter can significantly reduce propagation of measurement noise inside control loops. It has better performance than the EWMA and MA filters, so that the overall performance of the control system is enhanced. Les valeurs mesurées des variables de procédé sont affectées par les bruits de mesure. La présence de bruit de mesure force de régler à la baisse les régulateurs afin de prévenir des mouvements excessifs des variables manipulées. Des filtres numériques, tels que les filtres à moyenne mobile pondérée exponentiellement (EWMA) et les filtres à moyenne mobile (MA), sont communément utilisés pour atténuer le bruit de mesure avant les régulateurs. On présente dans cet article une autre approche, soit un filtre dynamique de réconciliation de données (DDR). Ce filtre emploie des modèles dynamiques discrets qui peuvent être phénoménologiques ou empiriques comme contraintes pour réconcilier les mesures bruitées. Les résultats de simulation pour un réservoir de stockage et une colonne à distiller utilisant un régulateur PI montrent que le filtre DDR peut réduire de manière significative la propagation du bruit de mesure dans les boucles de régulation. Sa performance est meilleure que celles des filtres EWMA ou MA, et par conséquent la performance globale du système de commande s'en trouve accrue. [source] P/Pd Types Of Override Control SystemsASIAN JOURNAL OF CONTROL, Issue 4 2002Yaw-Ying Tsai ABSTRACT The override control provides protective action against abnormal operation and/or incipient process failure. In terms of control theory, it is a logic-based switching system and, in terms of operation, it is usually activated between the soft constraint and the hard constraint. It is used in all process industries, and most PID control loops are patched with some type of override system. Despite widespread application, little research has been done to analyze override control systems. In this work, the properties of the override control are explored. The stability of the override control is also studied. Counter to intuition, many well-known override systems may exhibit instability and lead to oscillatory responses as the process approaches constraints. Approaches are proposed for the design of override control systems to ensure inherent safe operation. [source] | |||||||||||||||||||