Constant Temperature Anemometer With Fixed Calibration

Abstract

This thesis is a study of Constant Temperature Anemometer (CTA), and a proposal of architecture to enhance it’s property so as to increase the domain of application of the flow sensor.Constant Temperature Anemometer is one of the oldest and widely used technique to measure the flow of fluid because of its simple structure, principle and ease of operation, with energy spectrum of the measured flow covering wide ranges of frequencies in the range of 30KHz to 50 KHz.
However it has a drawback that it has to be calibrated each time it has to be used to measure the flow of different fluids.Also, it is not used frequently for measurement of flow of liquids in the industrial area because of the sensor’s dependency on the type of fluids used. Due to the sensors dependency on the type of fluids in contact with the liquids, there arises certain restrictions such as the use of specific type of probes, and also not all liquids give satisfactory output. So, the liquid flow measurement is somewhat deprived of the usage of such sensors.
Author here has proposed an architecture which allows only one type of fluids called the calibration fluid to interact with the hot-wire, thereby fixing the calibration. Architecture is so designed that the flow velocity of fluids whose flow has to be measured is transferred to the calibration fluids. The velocity of fluid and the calibration fluid then becomes the same, and the output due to calibration fluid gives the output of the fluid velocity. This technique hence reduces the usage of calibration each time the instrument has to be used to measure flow of different fluids. By, the proper selection of calibration fluids, it can be used to measure the velocity of almost any type of liquids.
Also, in this research work the circuit of anemometer has been made. Simulation of circuit with a energy spectrum of high frequency has been made.This circuit increases the frequency on which CTA works from 15 KHz to 40 KHz. Using the conventional technique of the use of power amplifier as a current feedback, a cheaper solution with RTD has been made, which has a poor sensitivity.
To increase the sensitivity with the available resources, conventional technique has been left out and the use of voltage to current converter in place of power amplifier has been used as current feedback which has increased the sensitivity of anemometer three folds. So, the main motive behind this research work is to use same Constant Temperature Anemometer for measurement of different fluid flow without the need of calibrating the device each time. Thus we can remove the major disadvantage associated with it, and with the robust arrangement, this device can be used and its advantages extracted by the industry.
Also, a circuit for hot-wire anemometer has been proposed which does not follow the conventional technique of use of power amplifier as current feedback, but uses Voltage to Current converter for the same. This decreases the dependency on the power amplifier ICs, and user can design CTA as per their requirement.