Jagadeesh Kumar Varadarajan

This paper presents a novel resistance-to-digital converter (RDC) suitable for differential resistive sensors. The proposed RDC provides a digital output linearly proportional to the parameter being sensed by a differential resistive sensor not only for differential resistive sensors possessing linear characteristic but also for sensors possessing inverse characteristic. The proposed RDC is based on the sigma-delta type analog-to-digital converter (Σ-Δ ADC) principle and hence possesses all the advantages and limitations of a Σ-Δ ADC. Experimental results on a prototype built and tested gave a worst case error < 0.15 %, establishing the efficacy of the proffered RDC. ©2008 IEEE.

A scheme using the counter-timer 8253 in a microprocessor environment is described for deriving a synchronized time signal, whose frequency is an integral multiple of a given reference. Conventional PLL and associated circuitry are dispensed with. Errors arising out of the use of finite clock frequency and computational bit length are quantified. The scheme is also suitable for micro-controller-based applications. © 1992.

A feedback technique for phase sensitive detection (PSD) is developed, which is suitable for both synchronous and multiplier modes of implementation. The feedback-compensated PSD straightaway provides a dc output proportional to the amplitude of the measurand. The technique is very useful in a noisy environment where postprocessing of the in-phase and quadrature components would otherwise deteriorate the stability, accuracy, and sensitivity. © 1991 IEEE

Signal conditioning of inductive sensors so as to obtain an output proportional to just the change in the inductance alone is fraught with problems. The large value of self inductance that is present in a sensor coil and the change in the inductance being a small fraction of this large inductance coupled with the winding resistance of the sensor coil make signal conditioning of such inductive sensors a challenge. This paper presents a simple analog front-end suitable for signal conditioning of inductive sensors. The proposed signal conditioning circuit provides an output linearly related to the change in inductance due to the measurand alone, masking the large value of self (offset) inductance present in inductive sensors as well as the appreciable winding resistance. A prototype of the proposed signal conditioning circuit was developed and tested in the laboratory. Test results validate the efficacy of the technique presented herein. © 2013 IEEE.

The wave energy group at the Indian Institute of Technology, Madras, India, in coordination with the National Institute of Ocean Technology, Madras has successfully installed a pilot wave energy plant of the oscillating water column (OWC) type, at Vizhinjam, on the west coast of India. The wave energy plant (WEP) consists of a concrete caisson OWC pneumatically driving a Wells type turbine. The turbine is mechanically coupled to an Induction generator (IG). The stator of the IG is connected to the electrical grid of the Kerala State Electricity Board. This paper describes the control instrumentation and data acquisition aspects of the WEP. Sample data collected on the power module are also provided in the form of graphs.

An algorithm is presented for identification of ventricular ectopic beats (PVC) by performing a beat by beat analysis of Electrocardiogram (ECG). The discrete Cosine Transform (DCT) of a windowed ECG cycle is decomposed into spectra of system and excitatory functions representing action potential and excitation pattern of the heart muscle during cardiac cycle. The Autoregressive (AR) modeling of the system function provides necessary information for identification of PVC's. The partial energy spectrum derived from the DCT coefficients characterizes the decay rate of DCT of the system function and is related to bandwidths of resonances in the AR spectrum. The Algorithm was able to successfully identify PVC's from the recordings of MIT-BIH database. Under noisy conditions, the Algorithm clearly distinguishes PVC patterns from those of normal beats upto a signal to noise ratio (SNR) of 10 dB.

The problem of reducing the exciting current drawn by a winding for establishing flux in a magnetic core has been receiving considerable attention over the years. Conventionally, quality materials of high permeability and low loss have been employed for this purpose. `Two-stage' principle has also been applied along with buffer amplifiers for increasing the input impedance, especially of inductive voltage dividers. In this paper, we propose an alternative electronic feedback compensation technique employing an i-to-i converter for achieving the above goal in both single-core and two-stage arrangements. A quantitative analysis of the circuit is presented, to determine the factor of improvement attainable in the two cases. Experimental results on a model two-core arrangement are provided, to establish the feasibility of the proposed technique.

A novel, simple and high accuracy dual slope direct digital converter suitable for differential capacitive sensors is presented in this work. The proposed technique provides a linear digital output proportional to the parameter being sensed by differential capacitive sensors irrespective of the fact that the sensor could possess either a linear or an inverse characteristic. In the proposed technique, the output is dependent only on, apart from the sensitivity of the sensor, a single dc reference voltage. Thus by employing a precision dc reference voltage, high accuracy is easily achieved. The proposed direct capacitance to digital converter is based on the popular dual-slope analog to digital converter structure and hence possesses all the advantages of the dual-slope technique, namely, high resolution, accuracy and immunity to noise and component parameter variations. A prototype built and tested for a typical differential capacitive sensor with a nominal value of 250 pF gave a worst-case error less than 0.05 %. © 2009 IEEE.

A direct resistance-to-digital converter (RDC) that is suitable for differential resistive sensors is proposed and analyzed in this paper. The RDC presented here provides a digital output that is linearly proportional to the parameter being sensed by a differential resistive sensor possessing either linear or inverse characteristics. The RDC employs the sigma-delta analog-to-digital conversion (Σ-Δ ADC) principle and, hence, possesses all the advantages and limitations of such an ADC. Analysis shows that the proposed RDC has negligible sensitivity to variations in circuit parameters. Experimental results on a prototype built and tested gave a worst-case error < 0.15%, establishing the efficacy of the proffered RDC. © 2009 IEEE.

This paper presents a new technique based on comparison method of testing to distinguish an annealed magnetic sample from a non-annealed sample of same dimensions. In order to perform this test, a suitable magnetic fixture that can accommodate test samples of various inner and outer diameters has been developed and described in the paper. The paper also gives details of a virtual instrument that has been developed to perform the comparison method of testing for the annealed samples. Using the developed instrument, the samples can be tested after the manufacturing process without any further machining. The performance of the developed instrument has been verified by conducting measurements on different samples of known magnetic properties. The instrument developed distinguished the annealed samples from the non-annealed samples accurately. © 2011 IEEE.