ANALYSIS AND APPLICATION OF THERMISTOR BRIDGE CIRCUITS IN FLOW MEASUREMENT

Abstract

The dissertation deals with the analysis and applications of thermistor bridge circuits. All important and useful thermistor bridge circuits namely Wheatstone (WB), Astable multivibrator (AMB), and Astable Monostable multivibrators (AMB—MMB) have been considered for analysis. It has been mentioned that AMB—MMB circuit is more sensitive and linear as compared to V1B and AMB circuits for similar input/output conditions. Some useful mathematical relations have been derived for 4x5 combinations of transducers circuit by carrying out generalized analysis. Expressions are given for the thermistor resistance for linearizing and balancing conditions for five different transducer probe configurations P-iecewise linearized model approach has been applied to a WB circuit by dividing R—T characteristic of an actual NTC thermistor in three segments. The flow rate has been related to thermistor parameter change for showing its application in flow metering. The response time and sensitivity considerations have been investigated using a numerical analysis method. It has been shown that there is decrease in the rise time with increase in velocity. Some other interesting applications of thermistor bridge circuits are also given. Lastly, the conclusions drawn from the present work and the problems to be solved in future are given.