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Articles 1201 - 1230 of 1240

Full-Text Articles in Electrical and Computer Engineering

A Classification Of Techniques For The Compensation Of Time Delayed Processes. Part 1: Parameter Optimised Controllers, Aidan O'Dwyer, John Ringwood Jan 1999

A Classification Of Techniques For The Compensation Of Time Delayed Processes. Part 1: Parameter Optimised Controllers, Aidan O'Dwyer, John Ringwood

Conference papers

An extensive literature exists on the compensation of time delayed processes. It is possible to identify themes that are common to many of the available techniques. The intention of the two parts of this paper is to provide a framework against which the literature may be viewed; Part 1 of the paper considers the use of parameter optimised controllers for the compensation problem, with Part 2 of the paper considering the use of structurally optimised compensators. Conclusions are drawn at the end of Part 2.

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Estimation Of The Parameters Of A Delayed Process Using Open Loop Time Domain Techniques, Morena Stolfa, Aidan O'Dwyer Jan 1999

Estimation Of The Parameters Of A Delayed Process Using Open Loop Time Domain Techniques, Morena Stolfa, Aidan O'Dwyer

Conference papers

In this paper, we present three different approaches to fit the experimental data of a process with time delay in the time domain. Two of the proposed methods are based on the step response, and the third is based on the pulse response. The effectiveness of these techniques is verified by simulation results and by real-time experimental data. Only first order lag plus time delay models are considered in this paper.

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The Dynamic Properties Of 5cb Filled With Aerosil Particles Investigated By Pcs, F.M. Aliev, M. Kreuzer, Yuri Panarin Jan 1999

The Dynamic Properties Of 5cb Filled With Aerosil Particles Investigated By Pcs, F.M. Aliev, M. Kreuzer, Yuri Panarin

Articles

Nematic liquid crystal filled with Aerosil particles, a prospective composite material for optoelectronic application, has been investigated by static light scattering and Photon Correlation Spectroscopy (PCS). The Aerosil particles in filled nematic liquid crystals (FN) form a network structure with LC domains about 2500 Å in size with a random distribution of the director orientation of each domain. We found that the properties of 5CB are considerably affected by the network. The N-I phase transition in filled 5CB was found to be smeared out and depressed. PCS experiments show that two new relaxation processes appear in filled 5CB in addition …

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Robust Controller Design For Time Delay Systems Using H-Infinity Techniques, Susan Carr, Aidan O'Dwyer Jan 1999

Robust Controller Design For Time Delay Systems Using H-Infinity Techniques, Susan Carr, Aidan O'Dwyer

Conference papers

Using H-infinity control, the design problem is formulated in terms of user defined weighting polynomials on the process closed-loop sensitivity functions to achieve desired closed-loop performance and robust stability in the presence of process modelling error. In this paper stability conditions , in terms of the process sensitivity functions, are derived for processes containing a pure time delay for the following three design scenarios i) the time delay is neglected in the control design and is considered as part of the unmodelled process dynamics ii) A Pade approximation of the delay is included in the controller design and the effect …

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Pi And Pid Controller Tuning Rules For Time Delay Processes: A Summary. Part 2: Pid Controller Tuning Rules, Aidan O'Dwyer Jan 1999

Pi And Pid Controller Tuning Rules For Time Delay Processes: A Summary. Part 2: Pid Controller Tuning Rules, Aidan O'Dwyer

Conference papers

A summary of tuning rules for the PID control of single input, single output (SISO) processes with time delay, modeled in stable first order lag plus time delay (FOLPD) form, is provided in this part of the paper.

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A Classification Of Techniques For The Compensation Of Time Delayed Processes. Part 2: Structurally Optimised Controllers, Aidan O'Dwyer, John Ringwood Jan 1999

A Classification Of Techniques For The Compensation Of Time Delayed Processes. Part 2: Structurally Optimised Controllers, Aidan O'Dwyer, John Ringwood

Conference papers

Following on from Part 1, Part 2 of the paper considers the use of structurally optimised controllers to compensate time delayed processes.

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The Appearance Of Ferrielectric Phases In Confined Liquid Crystal Studied By Photon Correlation Spectroscopy, Yuri Panarin, Fouad M. Aliev, Charles Rosenblatt Jan 1999

The Appearance Of Ferrielectric Phases In Confined Liquid Crystal Studied By Photon Correlation Spectroscopy, Yuri Panarin, Fouad M. Aliev, Charles Rosenblatt

Articles

The influence of confinement on the dynamic properties and appearance of ferrielectric phases has been investigated by dynamic light scattering, performed in the bulk AFLC as well as confined in 200 8, and 2000 8, cylindrical pores. The analysis of the experimental results shows that the ferrielectric phases are not formed in 200 A pores, while they appear in 2000 8, pores as well as in bulk.

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The Dynamic Properties Of Confined Antiferroelectric Liquid Crystal Investigated By Photon Correlation Spectroscopy, Yuri Panarin, C. Rosenblatr, F.M. Aliev Jan 1999

The Dynamic Properties Of Confined Antiferroelectric Liquid Crystal Investigated By Photon Correlation Spectroscopy, Yuri Panarin, C. Rosenblatr, F.M. Aliev

Articles

Dynamic light scattering was used to examine ferrielectric liquid crystalline phases in porous media. Whereas in larger pores (200 Å) ferrielectric phases were observed, they were not found in the smallest pores (200 Å). Additionally, the temperatures of SmC - SmA phase transition were found to be suppressed in the pores relative to bulk, while SmCA - SmCγ phase transition is not affected by the confinement. These observations have been explained by the structural aspects of antiferroelectric liquid crystalline materials in a confined geometry and show the importance of long range electrostatic interaction for existence of ferrielectric phases.

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Compensation Of Processes With Time Delays, Thomas Heeg, Aidan O'Dwyer Jan 1998

Compensation Of Processes With Time Delays, Thomas Heeg, Aidan O'Dwyer

Conference papers

Methods which allow comparisons in the use of PI and PID controller strategies for the control of first order lag plus time delay processes (FOLPD) are worthy of investigation because of the relative lack of work done in this area. In this paper, strategies for comparing performance and robustness for a PI or PID controlled FOLPD process are analysed and designed. The use of different PID controller structures for processes with time delay is also worth considering in detail. Various PID controller structures are compared by means of servo and regulator time responses, Bode plots and Nyquist plots.

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The Identification And Control Of Processes With Time Delay, Susan Carr, Aidan O'Dwyer Jan 1998

The Identification And Control Of Processes With Time Delay, Susan Carr, Aidan O'Dwyer

Conference papers

The identification of the frequency response and process model parameters of systems with time delay using frequency domain techniques is evaluated in this paper. The performance of both Fourier Transform and Power Spectral Density techniques is considered. The benefits of employing modern model based design and delay compensation techniques, based on the identified process data, are assessed.

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Performance And Robustness Issues In The Compensation Of Folpd Processes With Pi And Pid Controllers, Aidan O'Dwyer Jan 1998

Performance And Robustness Issues In The Compensation Of Folpd Processes With Pi And Pid Controllers, Aidan O'Dwyer

Conference papers

This paper will discuss the compensation of first order lag plus time delay (FOLPD) processes using PI and PID controllers whose parameters are specified using appropriate tuning rules. The gain margin, phase margin and maximum sensitivity of the compensated system as the ratio of time delay to time constant of the process varies, are used as ways of judging the performance and robustness of the system.

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The Gain Scheduled Piece-Wise Adaptive Digital Control Of A Ph Process, Eugene O'Shaughnessy, Aidan O'Dwyer Jan 1998

The Gain Scheduled Piece-Wise Adaptive Digital Control Of A Ph Process, Eugene O'Shaughnessy, Aidan O'Dwyer

Conference papers

The compensation of a pH process is complicated by the non-linear nature of the process titration curve and the significant time delays that typically exist in such processes. This paper will propose the use of a gain scheduled piecewise adaptive PI controller to compensate the process. A pilot plant is controlled, with the control algorithm implemented on a programmable controller. SCADA software displays and trends the plant and controller signals.

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The Investigation Of The Relaxation Process In Antiferroelectric Liquid Crystals By Electro-Optic Spectroscopy, Yuri Panarin, O. Kalinovskaya, J.K. Vij Jan 1998

The Investigation Of The Relaxation Process In Antiferroelectric Liquid Crystals By Electro-Optic Spectroscopy, Yuri Panarin, O. Kalinovskaya, J.K. Vij

Articles

Electrooptic spectroscopy of an antiferroelectric liquid crystal is carried out over a range of frequencies from 1 Hz to 100 kHz. In the antiferroelectric SmCA phase two relaxation processes are found, one at the fundamental frequency of a mode and the second at twice the frequency of a different mode. A comparison of the results of the electro-optic spectroscopy with a theoretical study of the motion of the director of an antiferroelectric helix subject to a weak alternating field enables a determination of the origin of the relaxation processes in antiferroelectric phases. © 1998 American Institute of Physics.

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A Comparison Of Some Low Cost Laminates For Antennas Operating In The 2.45 Ghz Ism Band, Max Ammann Jan 1998

A Comparison Of Some Low Cost Laminates For Antennas Operating In The 2.45 Ghz Ism Band, Max Ammann

Conference papers

An evaluation of some low-cost laminates suitable for microstrip patch antennas is presented. Criteria for the selection of substrates for antenna fabrication are given careful consideration. A coaxial-probe fed linearly-polarized rectangular microstrip patch operating at a frequency of 2.45 GHz was fabricated on four different low cost laminates. The substrates used were polyester, epoxy glass (FR-4), a ceramic filled PTFE composite and a woven glass-reinforced hydrocarbon and ceramic thermoset material. Material properties are discussed and the antenna performances are evaluated and compared to one fabricated on a thick glass-loaded microfiber PTFE substrate. An evaluation of some inexpensive microstrip antenna CAD …

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The Development Of Electromechanical Batteries For Power System Support And For Short-Term Standby Power, Michael Peter O'Leary Dec 1997

The Development Of Electromechanical Batteries For Power System Support And For Short-Term Standby Power, Michael Peter O'Leary

Masters

The slow move from a fossil-fuel powered society to a renewable-energy powered society is creating and will continue to create a demand for good energy storage techniques. The electromechanical battery (EMB), comprising a flywheel energy storage system with electrical input and output, is one of the many candidate technologies. Two different EMB types are evaluated in this present project. The first is a ring (or annular) flywheel to be constructed using fibre composite materials and to rotate at high speed in a vacuum. Energy is to be imported and exported electromagnetically based on linear electrical machine principles. Confinement of the …

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Observation And Investigation Of The Ferrielectric Subphase With High Qt Parameter, Yuri Panarin, O. Kalinovskaya, J.K. Vij, J.W. Goodby Jan 1997

Observation And Investigation Of The Ferrielectric Subphase With High Qt Parameter, Yuri Panarin, O. Kalinovskaya, J.K. Vij, J.W. Goodby

Articles

Dielectric relaxation processes in an antiferroelectric liquid crystal (AFLC) have been investigated over a wide range of frequencies from 1 Hz to 1 GHz. The AFLC under investigation possesses a variety of different ferrielectric, ferroelectric, and antiferroelectric phases. Dielectric and polarization measurements under direct bias voltage have been made with a view to clarifying the origin of the high-temperature ferrielectric phase, which appears between the AF and smectic-C phases. This phase is assigned to an unstable ferrielectric phase with qT parameter greater than 1/2 (according to the Ising model) or a doubly modulated incommensurate phase (according to the expanded Landau …

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Observation And Investigation Of The Ferrielectric Subphase With Qt>1/2, Yuri Panarin, O. Kalinovskaya, J. K. Vij Jan 1997

Observation And Investigation Of The Ferrielectric Subphase With Qt>1/2, Yuri Panarin, O. Kalinovskaya, J. K. Vij

Articles

The high-temperature femelectric phase with qT > 1/2 has been found to exist in a antiferroelectric liquid crystal. This phase has been identified using dielectric spectroscopy and conoscopy.

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Closed Loop Time Domain Gradient Methods For Parameter And Time Delay Estimation, M, Behan, M Cahill, M. Carry, G Clausen, V. Dooley, N. English, W. Grainger, D. O'Connor, Aidan O'Dwyer, John Ringwood Jan 1997

Closed Loop Time Domain Gradient Methods For Parameter And Time Delay Estimation, M, Behan, M Cahill, M. Carry, G Clausen, V. Dooley, N. English, W. Grainger, D. O'Connor, Aidan O'Dwyer, John Ringwood

Conference papers

This paper discusses the estimation of process parameters and time delay, in a Smith predictor structure, using gradient algorithms in the time domain. A number of estimation algorithms are outlined and applied in simulation to the estimation of the parameters of an appropriate process model. An analytical exploration of the technique is also provided.

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Investigation Of The Ferrielectric Subphase With Qt>1/2 Under Bias Voltage, Yuri Panarin, O.E. Kalinovskaya, J.K. Vij Jan 1997

Investigation Of The Ferrielectric Subphase With Qt>1/2 Under Bias Voltage, Yuri Panarin, O.E. Kalinovskaya, J.K. Vij

Articles

The properties of Femelectric phase with qT > 112 have been investigated using broadband dielectric spectroscopy and polarization measurements under the bias voltage. The field -induced sequence of phase transitions is found to be different fiom those of the conventional femelectric phases with qTS 112

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A Study Of Antiferroelectric Liquid Crystals Using The Pyroelectric Technique, J.W. O'Sullivan, Yuri Panarin, J.K. Vij, A.J. Seed, M. Hird, J.W. Goodby Jan 1997

A Study Of Antiferroelectric Liquid Crystals Using The Pyroelectric Technique, J.W. O'Sullivan, Yuri Panarin, J.K. Vij, A.J. Seed, M. Hird, J.W. Goodby

Articles

Antiferroelectric liquid crystals are studied using the pyroelecmc technique. The effects of temperature and applied voltage on the pyroelectric signal are examined. The pyroelecmc signal can detect phase changes that occur due to temperature and bias voltage. A high temperature femelecmc phase FiLC is found and the stability of this phase under different bias voltages is examined

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The Control Of A Process With Time Delay By Using A Modified Smith Predictor Compensator, Aidan O'Dwyer, John Ringwood Jan 1996

The Control Of A Process With Time Delay By Using A Modified Smith Predictor Compensator, Aidan O'Dwyer, John Ringwood

Conference papers

A modification is proposed to the Smith predictor compensator structure for the control of a process with time delay. The modification facilitates the achievement of an improved closed loop system regulator response, with little degradation in the corresponding servo response. The compensator design procedure is discussed, and simulation results are provided to demonstrate the applicability of the method.

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Theoretical Investigations Of Electro-Optical Synchonisation Of Self-Pulsating Laser Diodes, A. Egan, P. Rees, J. O'Gorman, M. Harley-Stead, Gerald Farrell, Joe Hegarty, P. Phelan Jan 1996

Theoretical Investigations Of Electro-Optical Synchonisation Of Self-Pulsating Laser Diodes, A. Egan, P. Rees, J. O'Gorman, M. Harley-Stead, Gerald Farrell, Joe Hegarty, P. Phelan

Articles

The synchronisation mechanism of selfpulsating laser diodes is determined and it is shown how this results in a frequency-dependent phase difference between the electrical input and optical output. The time-to-lock of the electrical input to the optical output is examined, particularly with regard to the importance of the initial phase difference between the signals. The effect of synchronisation on timing jitter in self pulsating lasers is also investigated.

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Model Parameter And Time Delay Estimation In The Frequency Domain, Aidan O'Dwyer, John Ringwood Jan 1995

Model Parameter And Time Delay Estimation In The Frequency Domain, Aidan O'Dwyer, John Ringwood

Conference papers

This paper discusses the estimation of the parameters (including the time delay) of single input, single output (SISO) process models from an appropriate number of arbitrarily specified points on the process frequency response. The method involves combining an analytical approach with a least squares approach using a gradient algorithm, to provide accurate and robust estimates of the parameters.

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Instability In Self-Pulsation In Laser Diodes And Its Effect On All-Optical Synchonization, Jonathan Hyland, Gerald Farrell Dec 1994

Instability In Self-Pulsation In Laser Diodes And Its Effect On All-Optical Synchonization, Jonathan Hyland, Gerald Farrell

Articles

The effect of short- and long-term frequency instability in self pulsation on all-optical synchronization using a twin-section laser diode is experimentally investigated. Short-term frequency instability broadens the unlocked full width at half maximum (FWHM) of the fundamental of the rf spectrum of the self-pulsating laser diode. We show experimentally that the value of the unlocked FWHM, and thus the level of short-term instability, has a direct effect on the optical power required to maintain synchronization. A novel means of reducing the FWHM is presented based on a reflective transmission line stub connected to the absorber of the twin-section self-pulsating laser …

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Comparison Of Self Pulsation In Multisection Lasers With Distributed Feedback And Intracavity Satuarable Absorbers, P. Phelan, D. Mcdonald, A. Egan, Joe Hegarty, R. O'Dowd, Gerald Farrell, S. Lingren Jan 1994

Comparison Of Self Pulsation In Multisection Lasers With Distributed Feedback And Intracavity Satuarable Absorbers, P. Phelan, D. Mcdonald, A. Egan, Joe Hegarty, R. O'Dowd, Gerald Farrell, S. Lingren

Articles

The authors report a comparison of the self-pulsing characteristics of two types of semiconductor laser. They show that the self-pulsing frequency of the DFB laser is decoupled from the resonance frequency. They discuss the various characteristics, their significance in relation to optical synchronisation, and use the results to suggest a possible explanation for the mechanism for self-pulsation in the DFB laser.

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A Frequency Domain Based Self-Tuning Pid Controller, John Ringwood, Aidan O'Dwyer Jan 1994

A Frequency Domain Based Self-Tuning Pid Controller, John Ringwood, Aidan O'Dwyer

Conference papers

Traditionally, both explicit and implicit self-tuning controllers have employed time domain techniques for the identification and tracking of plant and controller parameters. The use of the frequency domain provides concise information on the dynamics of the process which has led to its wide acceptance as a domain for controller design. This paper demonstrates a method employing recursive, on-line measurement of the process frequency response, with a straightforward calculation of PID controller parameters. The computational effort involved is comparable with that of a time domain technique.

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Model Parameter And Time Delay Estimation Using Gradient Methods, Aidan O'Dwyer, John Ringwood Jan 1994

Model Parameter And Time Delay Estimation Using Gradient Methods, Aidan O'Dwyer, John Ringwood

Conference papers

A number of approaches have been proposed for parameter and time delay estimation of process models in single input, single output (SISO) control systems using gradient descent algorithms; some of these approaches involve the selection of a rational polynomial that is used to approximate time delay variations. This paper takes a generalised approach to the investigation of the most appropriate choice of the rational polynomial, and the gradient descent algorithm, to be used.

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All Optical Timing Extraction With Frequency Division Using A Twin Section Laser Diode, Gerald Farrell, P. Phelan, Joe Hegarty, J. A. Shields Jan 1993

All Optical Timing Extraction With Frequency Division Using A Twin Section Laser Diode, Gerald Farrell, P. Phelan, Joe Hegarty, J. A. Shields

Articles

All-optical timing extraction from a coded line signal with division of the extracted clock frequency is demonstrated using a single twin-section self-pulsating laser diode. Either the bit-rate clock or a submultiple of the bit-rate clock can be extracted, depending only on the dc biases applied to the self-pulsating laser diode. Timing extraction is carried out for the first time without optical injection locking of the self-pulsating laser diode by the optical data source.

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The Influence Of The Unlocked Characteristics Of A Self-Pulsating Laser Diode On Synchronisation, Gerald Farrell, P. Phelan, Joe Hegarty Jan 1993

The Influence Of The Unlocked Characteristics Of A Self-Pulsating Laser Diode On Synchronisation, Gerald Farrell, P. Phelan, Joe Hegarty

Articles

All-optical synchronization and timing extraction based on self-pulsating twin section lasers has been demonstrated. We investigate the variation of the unlocked full-width at- half-maximum of the fundamental of the RF spectrum of a self-pulsating laser diode. We show for the first time that the value of the unlocked FWHM has a direct influence on the power required to maintain synchronization. We also show that the variation of the FWHM with frequency is dependent on the slope of the absorber bias versus self-pulsation frequency characteristic. The results have important implications for the design and selection of self-pulsating laser diodes for synchronization …

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A Comparison Of Techniques For Time Delay Estimation, Aidan O'Dwyer Jan 1993

A Comparison Of Techniques For Time Delay Estimation, Aidan O'Dwyer

Conference papers

This paper reviews some of the techniques used for the identification of unknown lumped time delays in single input, single output (SISO) control systems and evaluates a number of these techniques in simulation and in implementation. Both off line and on line identification techniques are considered.

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