ANALYSIS AND PERFORMANCE IMPROVEMENT OF INDUCTIVE TRANSDUCERS AND THERMISTORS

Abstract

Transducers are widely used for measurement of physical quantities in Biomedical, Aerospace, Meteorological, Industrial and Process Instrumentation systems. These are essential link between the physical systems and electronic signal processing, conditioning, and handling units. Commonly encountered problem with transducers is variation in their performance characteristics due to changes in excitation parameters and in internal and surrounding environmental conditions. The responses of most of the transducers are non-linear throughout their operating range. There is also another problem of stability in their long term use. Thus, there is continual effort by the researchers right from the beginning to improve the performance characteristics of transducers either by developing a new transducer or by improving the design of existing transducer. In view of the importance of this area, for this thesis work, two types of transducers have been selected for the improvement of their performance characteristics. Differential inductive transducers have been selected due to their extensive use in the measurement of large number of physical parameters, namely displacement, thickness, force, pressure, flow, level, velocity, acceleration, vibration, torque etc. NTC thermistors have been selected as the other transducer as these are most commonly used for the measurement of temperature due to their convenient shape, size and high order of sensitivity. (vi) The emphasis has been placed on the improvement of performance of differential inductive transducers by providing selfcompensation as these are used in almost all types of environ ments including hostile conditions. The response linearization of thermistors have been taken as the parameter of interest as this is the main problem encountered in their use. In the first part of the work, three type of inductive transducers have been developed with improved performance characteristics, one based on linear variable differential transformer (LVDT) principle and other two based on ratio and differential combinations of two inductive coils. The LVDT has been developed using dual set of secondary windings for self-compensation. This transducer is immune to variations in excitation conditions and changes in environmental tempera tures. The output voltage signal from one set of secondary windings is taken as difference of induced voltages and is termed as the differential output, whereas the output signal from other set of the secondary windings is taken as the sum of the induced voltages and is termed as areference *h. ratio of these two output output.