Subhankar Bandyopadhyay

True RC integrators with very large and very small time constants using active control of capacitance and/or resistance

Two novel active RC integrator schemes with time-constant enhancement as well as depletion facility are presented. One of the schemes uses a capacitor multiplication technique for time-constant enhancement; the other uses a negative immittance converter to enhance or lower resistance for integrator time-constant control. Both schemes have been tested and the results are found to corroborate the theoretical values. Pertinent discussions relating to their performance have been appended. >

Performance of Nanocrystalline PbS Gas Sensor with Improved Cross-Sensitivity

Development of nanostructure gas sensing materials is gaining considerable attention at present times. In this light, the present article reports on the synthesis and detailed characterization of nanocrystalline lead sulplide (PbS) as gas sensors. Sol-gel technique was used in preparing undoped PbS nanocrystalline material at two different reaction temperatures (60°C and 90°C) and was characterized by x-ray diffraction (XRD) as well as scanning electron microscopy (SEM). Results of XRD showed respective crystallite sizes of 17.81 nm and 14.5 nm. Synthesized PbS materials on SEM analysis further showed agglomerated crystalline structure. Response of these materials was studied in presence of water vapors as well as various other gases and vapors of organic solvents at various temperatures (25°C to 90°C). The gas sensing behavior showed that the synthesized nanocrystalline materials were influenced predominantly by NH3 and NO2 amongst many other gases at room temperature.

New improved bipolar and bilateral voltage to current converters

Some improved bipolar, bilateral voltage-source-to-current-signal converter schemes, using operational amplifiers (OA) as active devices, are described. Some of them are derived from an earlier scheme that uses the OAs in summing mode, and the others are derived from the conventional technique of using the OAs in current output configurations. Except for one scheme that uses a single OA for the realization, the others have ideal voltage-to-current transfer ratio and characteristics. The realization constraints in each case have considerable degrees of flexibility, and there is no effect of load variation as long as the OAs used in the schemes are not saturated due to increased input conditions. The admittance matrices, constraints of realizations, and sensitivity to passive parameters for the different schemes are tabulated for ready reference. It is shown that the schemes can be used as V-I and I-V converters with scaling facility of the conversion factors. >

Instrumentation for continuous in situ monitoring of water quality

A continuous river water-pollution level monitoring system using a comprehensive instrumentation package coupled with a microprocessor ( mu P)-based data logger and telelink is described. The instrumentation package along with a power supply unit and a mu P-based converter and transmitter set is housed in a floating buoy, and on-shore receiving is effected through another mu P-based system. A retransmission is performed next, and data are received at a station sufficiently remote from the river banks, where the data are stored as well as processed for further use. Bench-level tests and in situ experiments have shown promising results for long-term monitoring of water-quality parameters of a river. >

Frequency independent phase shifter circuit

In this paper we have proposed an electronic circuit, which can be used to introduce a phase lead independent of frequency. The design is achieved using a simple frequency to voltage converter and using it to control the resistance of a voltage controlled resistor, which has linear dependence. Previous efforts in building such a circuit were capable of providing a constant phase lag only. Thus, only half the problem was solved, since we did not have any method when the application demanded a constant phase lead. The proposed network is both a practical and relatively simple to understand, at least at functional level. The blocks used, along with the previous attempts have been cited and the results presented, using a standard and well known circuit simulation software. With a slight modification the proposed work can be translated to provide both a phase lead and lag of desired values. Thus, in short a multipurpose objective has been satisfied. The performance of the circuit has been graphically presented for different parameters of the circuit, over a wide range of frequencies. The performance is satisfactory and can be used for introducing frequency independent constant phase lead in various control circuit applications.

A novel approach in filter designing using a dual feedback operational amplifier

In this paper we have proposed a new analog filter. It uses a dual feedback op amp in series with an inductor and a resistor. The proposed filter shows a high roll-off and unlike the previous attempts at building a high roll off analog filters, it does not distort the pass band frequencies. A brief comparison has been done, to explain the superiority of the proposed filter compared to the other high roll analog filter existing till now. A mathematical analysis of the filter along with the simulated result has been presented in this paper.

A Self-Tuning Controller Based on PI Algorithm

A simple self-tuner algorithm based on the tuning of the proportional band of a conventional Proportional Integral mode action is proposed. The algorithm, based on intuitive reasoning as adopted by process experts is simpler than many of its type specially from the viewpoint of implementation on a 8 or 16-bit microprocessor. It has been tested in a stable second order process model as also in an actual second order thermal process. Test results show that the proposed algorithm has an edge over its conventional discrete counterpart even when the latter is perfectly tuned.

Linear Speed Control of Strip-Like Materials with a Variable Slope Current Ramp Excitation

A very elegant method of linear speed control for strip-like materials is presented. When the strip thickness does not vary an open loop system is shown to achieve the objective with a separately excited dc motor drive whose field coil is energized with a current varying in proportion to time. For varying thickness of the strip, feedback is incorporated, resulting in precise and accurate control of linear speed by suitably modifying the excitation current. Simulated results have shown excellent corroboration of the theory. A prototype has then been constructed and a set of results obtained with it has also shown good correspondence with the theory.