DESIGN AND DEVELOPMENT OF FLUID FLOW MEASURING SYSTEM USING ULTRASONIC SENSORS

Abstract

In recent years flow measuring systems using ultrasonic sensors are becoming more popular due to their inherent advantages such as low pressure loss, no hindrance, viscosity independence, linear and bidirectional operation. One of the most attractive features of ultrasonic sensors based flow measuring systems is that they measure the fluid flow non-invasively and hence they reduce the hazards of operating with poisonous, radioactive, explosive or corrosive fluids. Generally piezoelectric materials are used for the fabrication of ultrasonic sensors such as Quartz, Barium Titanate, PZT and PVDF etc. PZT-5 material is preferred due to its availability and properties best suits for flow measurement such as high value of coupling coefficient k and piezoelectric constant d & g. The backing material is taken as wrought iron, outer enclosure as stainless steal and matching layer as perfex. The frequency of operation is also an important parameter and the fabrication of ultrasonic sensors is done for 1 MHz frequency. For the development of flow measuring system an experimental setup has been designed to maintain different flow rates at elevated temperature up to 80°C. The flow rate up to 2.6 m/s can be achieved and flow rate can be changed in the whole range smoothly up to 80°C. Ultrasonic sensor based flow measuring systems work on either Doppler Effect or Transit Time principle. In these two, Transit Time principle is more popular. In transit time type flow measuring systems the time difference between transmitted and received pulses, in the direction of flow and in opposite direction of flow, is measured. Therefore to generate the burst of ultrasonic pulses and to detect the transmitted pulses, transmitter and receiver circuits have been designed. A microcontroller based circuit has also been designed to control the hardware and to measure the pulse count difference of downstream and upstream directions. The controller can be programmed through the Corn port of the PC directly. Pulses are transmitted and detected at the other side of the pipe by the microcontroller based control circuit. The flow rates have been measured with good accuracy.