Abstract: The noise will directly affect the accuracy of the ultrasonic flow meter. The sources of noise inside the small pipe ultrasonic flow meter were analyzed. Considering the critical real-time measurement for the flow meter, a method of directly denoising the transit-time difference data was proposed. It avoided sampling and analyzing the original ultrasonic signal, which might lead to the poor performance of real-time measurement. For different noise sources, two different kinds of filters were applied. The wavelet filter was chosen as the first denoisng filter, which used a hard thresholding to reduce error from the random noise. A median filter and a mean filter were combined as the second denoisng filter to reduce error from the acoustic noise. The flow rate measurement experiment was implemented to verify the validity of the proposed denoising method. The results show that the instantaneous measurement error can be less than 1% after denoising.

Key words: Ultrasonic flow meter, In-orbit refueling, Wavelet filter, Median and mean filter, Spacecraft