Ultrasonic Gas Flowmeter Research Articles

Ultrasonic dynamic gas flowmeter for medical applications

The principle of a dynamic flow measurement device is described, which allows the measurement of gas flow in the range of 1 to 150 1/min with time resolution of 1 msec. With two ring‐shaped transducers, the delay time upstream and downstream of ultrasonic pulses in the upper kilohertz and megahertz range is measured. In a process computer, the differences of the reciprocals of these values are obtained. These differences are proportional to the flow, not dependent on gas composition and temperature. For measurements with CO2 (and other 3‐atomic gases) air mixtures, the influence of the rotational absorption must be considered. This requires lower ultrasonic frequencies and greater lengths of the measuring path. The time resolution of the flowmeter is therefore reduced. First experimental results are presented.

Acoustic holography: Holotron Group UK patent 1263093 (1972) filed 6 March 1968

A microcomputer-based ultrasonic gas flowmeter with transit-time method is presented. Modules of the flowmeter are designed systematically, including the acoustic path arrangement, ultrasound emission and reception module, transit-time measurement module, the software and so on. Four 200 kHz transducers forming two acoustic paths are used to send and receive ultrasound simultaneously. The synchronization of the transducers can eliminate the influence caused by the inherent switch time in simple chord flowmeter. The distribution of the acoustic paths on the mechanical apparatus follows the Tailored integration, which could reduce the inherent error by 2–3% compared with the Gaussian integration commonly used in the ultrasonic flowmeter now. This work also develops timing modules to determine the flight time of the acoustic signal. The timing mechanism is different from the traditional method. The timing circuit here adopts high capability chip TDC-GP2, with the typical resolution of 50 ps. The software of Labview is used to receive data from the circuit and calculate the gas flow value. Finally, the two paths flowmeter has been calibrated and validated on the test facilities for air flow in Shaanxi Institute of Measurement & Testing.