Bhaswati Goswami

Fabrication of a Fractional Order Capacitor With Desired Specifications: A Study on Process Identification and Characterization

This paper reports the fabrication of a fractional order element (FOE) with predefined specifications. The FOE is a circuit element similar to resistance, capacitance, and inductance generally used in electrical network. The specifications of integer order elements, i.e., inductance, resistance, and capacitance, are defined by the magnitude only as their exponents are of fixed value, namely, - 1, 0, and +1, respectively. The specialty of FOE is that both its magnitude and exponent value have to be defined, where the value of the exponent dictates the behavior. This paper elaborately discusses the methodology of realizing a fractional order capacitor named here as FOE (or, in general, FOE). It has been found that a FOE can be realized by dipping a capacitive-type probe, coated with a porous film of polymer of particular thickness, into a polarizable medium. The thickness, uniformity, and stability of the porous film, on the electrode, are responsible for different exponent values.

Design of a Fractional Order Phase Shaper for Iso-Damped Control of a PHWR Under Step-Back Condition

Phase shaping using fractional order (FO) phase shapers has been proposed by many contemporary researchers as a means of producing systems with iso-damped closed loop response due to a stepped variation in input. Such systems, with the closed loop damping remaining invariant to gain changes can be used to produce dead-beat step response with only rise time varying with gain. This technique is used to achieve an active step-back in a Pressurized Heavy Water Reactor (PHWR) where it is desired to change the reactor power to a pre-determined value within a short interval keeping the power undershoot as low as possible. This paper puts forward an approach as an alternative for the present day practice of a passive step-back mechanism where the control rods are allowed to drop during a step-back action by gravity, with release of electromagnetic clutches. The reactor under a step-back condition is identified as a system using practical test data and a suitable Proportional plus Integral plus Derivative (PID) controller is designed for it. Then the combined plant is augmented with a phase shaper to achieve a dead-beat response in terms of power drop. The fact that the identified static gain of the system depends on the initial power level at which a step-back is initiated, makes this application particularly suited for using a FO phase shaper. In this paper, a model of a nuclear reactor is developed for a control rod drop scenario involving rapid power reduction in a 500 MWe Canadian Deuterium Uranium (CANDU) reactor using AutoRegressive Exogenous (ARX) algorithm. The system identification and reduced order modeling are developed from practical test data. For closed loop active control of the identified reactor model, the fractional order phase shaper along with a PID controller is shown to perform better than the present Reactor Regulating System (RRS) due to its iso-damped nature.

Network Control System Applied to a Large Pressurized Heavy Water Reactor

The advent of low latency message passing has opened up the possibility of using distributed real-time controllers to be used for process control applications. The paper presents the use of embedded controllers over a network for control of a Pressurized Heavy Water Nuclear Reactor. The reactor which is physically divided into 14 physical zones is represented by a system having 56 state variables, 14 inputs which correspond to the reactivity applied to each zone and 14 outputs which represent the power produced by the individual zones. For the present paper, it is assumed that the system is controllable and observable and the sensors along with the controllers are integrated over a 100 Mbps Ethernet LAN with UDP/IP as the communication protocol. A linear state feedback controller is implemented over network and the response is found satisfactory. The results have been compared to results reported in published papers using centralized control

Robustness and Sensitivity Metrics for Tuning the Extended Kalman Filter

In this paper, a robustness metric and a sensitivity metric have been defined, which can be used to determine a suitable combination of the filter tuning parameters of the extended Kalman filter. These metrics are related to the innovation covariance and their derivation necessitates a change of paradigm from the estimated states to the estimated measurements. The characteristics of these metrics have been inferred in detail and these have been used to predict the root-mean-squared error (RMSE) performances in a 2-D falling body problem. To do so, a general method has been proposed in this paper to obtain an initial choice of the filter tuning parameters based on the available literature. The RMSE performances are then obtained for a range of variation of the most critical tuning parameter, namely the filter process noise covariance. In general, the characteristics predicted from the metrics correlate significantly with the RMSE performances, and hence these can be used to obtain the desired tradeoff between robustness and sensitivity in various filter applications.

Fractional order phase shaper design with Bode’s integral for iso-damped control system

The phase curve of an open loop system is flat in nature if the derivative of its phase with respect to frequency is zero. With a flat-phase curve, the corresponding closed loop system exhibits an iso-damped property i.e. maintains constant overshoot with the change of gain. This implies enhanced parametric robustness e.g. to variation in system gain. In the recent past, fractional order (FO) phase shapers have been proposed by contemporary researchers to achieve enhanced parametric robustness. In this paper, a simple methodology is proposed to design an appropriate FO phase shaper to achieve phase flattening in a control loop, comprising a plant controlled by a classical Proportional Integral Derivative (PID) controller. The methodology is demonstrated with MATLAB simulation of representative plants and accompanying PID controllers.

Multi-loop networked process control: a synchronized approach.

Modern day process control uses digital controllers which are based on the principle of distributed rather than centralized control. Distributing controllers, sensors and actuators across a plant entails considerable wiring which can be reduced substantially by integrating the components of a control loop over a network. The other advantages include greater flexibility and higher reliability with lower hardware redundancy. The controllers and sensors are on a network and can take over the function of a failed component automatically, without the need of manual reconfiguration, thus eliminating the need of having a redundant component for each and every component. Though elaborate techniques have been developed for Single Input Single Output (SISO) systems, the major challenge lies in extending these ideas to control a practical process plant where de-centralized control is actually achieved through control of individual SISO control loops derived through de-coupling of the original system. Multiple loops increase network load and hence the sampling times associated with the control loops and makes synchronization difficult. This paper presents a methodology by which network based process control can be applied to practical process plants, with a simple direct synchronization mechanism.

Middle aortic syndrome as a cause of heart failure in children and its management.

Two cases of middle aortic syndrome in children are described along with two other cases reported earlier. In childhood, this disease may present as incipient or overt cardiac failure. Surgical treatment should be undertaken based on an objective assessment of the severity of the stricture and after taking into account the future growth of the child.

Performance of a constant phase element (CPE) sensor to detect adulteration in cow-milk with whey

In this paper, the performance of a constant phase element (CPE) sensor has been studied for detecting adulteration of cow-milk with whey. Addition of whey in milk increases its volume and makes it acidic but the percentage of lactose content does not change significantly. Hence, addition of neutralizers like NaOH will balances the pH value of the adulterated milk and increases the shelf life. Sometimes cheap muriatic acid (used for cleaning purpose) is added to the milk to prepare whey. Both muriatic acid and NaOH causes serious health hazards. In this work, the CPE sensor has been used to detect the adulteration of cow-milk with whey which contains muriatic acid and the neutralizer, NaOH. The sensor performances are observed in pure milk (pH- 6.74), milk adulterated with 60%, 120% and 180% of whey (pH value of whey is 6.02). The pH value of adulterated milk with 180% whey is 6.44. Finally NaOH is added to bring back the pH value to 6.74. At every stages of adulteration the CPE sensor is used and the results show that the sensor can successfully detect them. Finally, an electrical equivalent circuit of the sensor dipped-in the adulterated milk is proposed through complex non-linear least square (CNLS) method to facilitate the design of suitable signal conditioning circuit.

Design of Transducers for Resonance Frequency Measurement to assess the Dental Implant Stability in vitro

The objective of the present study is to assess the performance of various designs of a transducer for determining the Dental Implant stability using Resonance Frequency Analysis (RFA) technique. Three different designs of the transducer have been presented in this article. The resonance frequency response of each transducer design was measured and analyzed in vitro. For this purpose, the transducer was attached to the implant with the help of a screw and this was placed in the dental plaster mixture. The dental plaster mixture gradually hardens with time resulting in a change in the resonance frequency of the system. Analysis of the results helps in identification of the transducer design showing more consistent results as compared to the other two designs. The proposed transducer initially shows a slight increase in RF, followed by a fall of the RF as the dental plaster hardens. Subsequently, the RF slightly increases to a nearby high value, finally becoming steady.

Determination of Stability of Dental Implant from Impedance Studies Using Resonance Frequency Analysis

A new method is being proposed in this paper to ascertain the stability of the dental implant after its placement in situ. One of the established methods of doing this is by monitoring the change of resonance frequency of the system with time which is typically referred to as Resonance Frequency Analysis [1]. Traditionally, the resonance frequency is identified from the magnitude of measured voltage using a two piezo arrangement in which one piezo acts as the source for the mechanical vibration transmitted into the system while the second piezo acts as the pick up [2]. In the present work, the resonance frequency has been identified separately by analysing the magnitude as well as the phase plots of the impedance of the (single piezo) transducer attached to the total system. A comparative study has been done of the magnitude and the phase of the impedance of the total system as the resonance frequencies change with time. From this study, it is observed that the phase of the impedance is a more reliable indicator for inferring the stability of the dental implant.