Real Time PC-Based Flow Measurement Technique Using Optical Channel as a Signal Transmitting Media

Abstract

A PC based cost effective electro-optic type flow measurement technique is designed and developed. The anemometric principle i.e. the effect of heat loss on a heating element due to flowing fluid is utilized for the measurement of flow rate of liquid in the process industry. A constant voltage p-n junction diode is used as a basic sensing element and the output of the sensing element is amplified and conditioned with the help of the instrumentation amplifier and signal conditioning circuit. Transmission of electrical signals in remote locations suffers from measurement errors due to electromagnetic induction effect, stray capacitance effect etc. The transmission of electrical signal is also not safe for the industries where an inflammable area is present between fields to remote locations and optical transmission is preferred in such areas. To overcome these, an electro-optical system has been developed. The process variable is first sensed electrically. This electrical signal of the transducer is converted into an optical signal using an electro-optic amplitude modulator and then it is transmitted in the form of an optical signal from field to control room through inflammable areas. The modulated signals are demodulated in the control room or remote location and then send to the PC through an optoisolator circuit and DAS card. The experiment has been performed and the theory as well as the mathematical equation has been derived to explain the operation of the proposed system. The overall PC based flow indicator system is also found to have linear characteristics with very good repeatability within tolerable percentage error.The experimental result is reported in the paper.