V. Jagadeesh Kumar

Virtual Instrument for the Measurement of Haemo-dynamic Parameters Using Photoplethysmograph

This paper presents the design and development of a virtual instrument for the measurement of haemodynamic parameters namely, pulse rate and oxygen saturation in arterial blood based on the popular photoplethysmographic (PPG) principle. A clip-on sensor, housing red and infrared (IR) light emitting diodes and suitable photo detectors is developed. The sensor is interfaced to a PC utilizing the audio channel of the sound card, thus dispensing with expensive analog to digital converter hardware. Since the frequency response of the audio channel is not suitable for the PPG waveforms of red and IR, FM modulation and demodulation are employed. An empirical relationship is developed for the computation of the oxygen saturation in arterial blood using the red and IR PPG data and the well-known and well-established extinction coefficients of haemoglobin with and without oxygen. Data acquisition and processing are accomplished under LabVIEW virtual environment

Linearising dual slope digital converter suitable for a thermistor

To measure temperature using a thermistor as the sensing element, linearization to compensate for the inverse exponential nature of the resistance-temperature characteristic of the thermistor is required. A linearizing dual-slope digital converter (LDSDC) that accepts a thermistor sensor as input and provides a digital output that is directly proportional to the temperature being sensed is presented here. A logarithmic amplifier at the input of the LDSDC compensates for the exponential characteristics. The conversion logic of the underlying dual-slope converter is suitably modified to implement the required inversion and offset correction and thus obtain linearization over a wide range of input temperature. The efficacy of the proposed LDSDC is established through simulation studies and its practicality demonstrated with experimental results obtained on a prototype unit built and tested. Analysis of the proffered method to identify possible sources of errors is also presented.

Fiber sensor for the simultaneous measurement of current and voltage in a high-voltage system

A sensor employing a single monomode low-birefringence fiber, excited with a 632.8-nm He-Ne laser, has been developed for the simultaneous measurement of current and voltage in an energy system. The piezoelectric effect for the voltage and the magnetic stress for the current are utilized. The current and voltage signals are separated at the detector end by suitable self-tracking tuned filters. Experimental results from a laboratory model demonstrate the feasibility of the sensor for field application in high-voltage systems.

A multiple loop vehicle detection system for heterogeneous and lane-less traffic

This paper presents a novel inductive loop sensor which detects large (e.g., bus) as well as small (e.g., bicycle) vehicles and help a traffic control management system in optimizing the best use of existing roads. To accomplish the sensing of large as well as a small vehicle, a multiple loop inductive sensor system is proposed. The proposed sensor structure not only senses and segregates the vehicle type as bicycle or motor cycle or car or bus but also enables accurate counting of the number of vehicles that too in a mixed traffic flow condition. A prototype of the multiple loop sensing system has been developed using a virtual instrumentation scheme and tested. Field tests indicate that the prototype successfully detected all types of vehicles and counted, correctly, the number of each type of vehicles. Thus the suitability of the proposed multi loop sensor system for any type of traffic has been established.

Digital Converter for Differential Capacitive Sensors

A capacitance to digital converter that directly translates the changes in a differential type capacitive sensor to a proportional digital value is described in this work. The proposed method employs a suitably modified, dual-slope, analog to digital conversion technique. Error analysis and results obtained from a prototype built around a micro-controller establish the efficacy of the proposed method.

Data processing of stress ECGs using discrete cosine transform

The signal processing steps for the analysis of stress ECGs are aimed at improving the signal to noise ratio (SNR) of recordings in addition to eliminating artifacts due to respiration, movement of arms, etc. In this paper, we bring forth two important applications of the discrete cosine transform (DCT) for noise suppression and removal of baseline wander. The noise suppression algorithm has been framed on the basis of a two step procedure involving singular value decomposition (SVD) smoothing operation in transform domain followed by that in time domain. The mean square error (MSE) resulting from the first step is shown to effectively follow the trend obtained by using an ideal Wiener filter using DCT. In the second step, the degree of closeness to the minimum mean square error (MMSE) of the ideal Wiener filter is improved by subjecting the filtered outputs to a second SVD smoothing operation in time domain. Application of this scheme to noisy records has resulted in near perfect reproduction of the original noise free ECG without significant alterations in its morphological features.

A Linear Variable Differential Capacitive Transducer for Sensing Planar Angles

A linear variable differential capacitive transducer for the measurement of planar angles from 0deg to 360deg is presented in this paper. The sensor part of the transducer consists of parallel plates of standard and easy to fabricate shapes and the signal conditioning electronics is made of a couple of simple relaxation oscillators. The output of the transducer is dictated only by a couple of dc reference voltages and hence high accuracy and linearity over the entire 0deg to 360deg are obtained easily by the use of precision dc reference voltages. Error analysis indicates that the sensitivity of the transducer for parameter variation is minimal. Test results obtained from a prototype indicated that the worst-case error was less than 0.1 %

A novel method for the measurement of the C-V characteristic of a solar photovoltaic cell

A novel method for obtaining the capacitance - voltage (C-V) characteristic of single crystalline or polycrystalline silicon solar photovoltaic (SPV) cells is demonstrated. Measurement of the C-V characteristics of an SPV cell is hindered by the presence of leakage resistance. The proposed method compensates the parallel leakage resistance of a SPV cell with the addition of a negative resistance of equal value. Test results obtained through experimentation validate the efficacy of the proposed method.

Direct digital converter for a single active element resistive sensor

A direct digital converter that provides a digital output, proportional to the measurand being sensed by a single active element resistive sensor is presented in this paper. To accomplish this task, the structure and the switching sequence of a conventional dual slope, analog to digital converter (DSADC) is appropriately altered so that the altered DSADC accepts the resistance of the sensor as an integral part and provides a digital output that is linearly proportional to the physical quantity being sensed by the resistive sensor. Since the output of the dual slope resistance to digital converter (DSRDC) is dictated only by the magnitudes of a pair of DC reference voltages, a fixed value resistor and the transformation constant of the sensor, the error in the output is minimal. Hence, a high level of linearity and accuracy is achieved. Simulation studies establish the efficacy of the proposed scheme.

Contact-less, Multi-Spectral Imaging of Dermal Perfusion

Photoplethysmography (PPG) has come to be accepted as a common, non-invasive method for measuring the level of oxygen saturation in arterial blood. This paper describes a variation of the accepted PPG technique, to provide a contact-less and non-invasive method of characterizing dermal perfusion. It employs a 3-CCD, multi-spectral camera, to image the selected area. The acquired images are analysed by making use of the fact that the absorption co-efficient of oxygenated blood is more in the infra-red (IR) region of the spectrum, when compared to the red region. This fact is utilised to characterize the extent of dermal perfusion in the selected area of the skin.