Sensor Configuration and Flow Rate Characteristics of Ultrasonic Flowmeter for Very Low Liquids Flow Rate

In this study, small disk ultrasonic transducers were used to develop a very small ultrasonic flowmeter with a pipe diameter of 0.53mm ID. The feasibility of using a practical ultrasonic flowmeter to measure a liquid flow rate below 1mL/min was investigated experimentally.The minimum flow rate of an ultrasonic flowmeter depends on the resolution of the transit time measurement and the zero flow rate stability. The former can be improved by applying the high measurement resolution of propagation time of an ultrasonic pulse with advanced electronics. However, the latter gives rise to a serious problem for low flow rate measurements. One of the causes of the zero flow rate instability is that the superposition of reflected pulses or remaining pulses affects the main pulses. This problem can be easily avoided by carefully selecting the sensor material or appropriate sensor location. The other cause of the zero flow rate instability is the different thermal characteristics of the two sensors. In order to solve the above problem, in this study, a newly designed ultrasonic flowmeter was developed.A glass tube was used as the measuring pipe of an ultrasonic flowmeter. Detected signals of ultrasonic pulses were processed by applying the zero-cross method and the cross-correlation method for comparison. The performance of the developed ultrasonic flowmeter was examined, in particular, the measurement resolution and the zero flow rate stability were carefully evaluated. Results of the flowmeter calibration were scattered within the range predicted from its measurement resolution. It shows that the flow rate more than 0.2mL/min can be measured by the developed flowmeter. This suggests to be able to measure a very low flow rate range useful for semiconductor, medical and chemical industries.