Patent ID: 6226598
Filing Date: 2001-05-01
Classification: G01F

Abstract:
A method of measuring the propagation time of a sound signal in a fluid flow between a first transducer acting as a transmitter and a second transducer acting as a receiver and situated at a determined distance from the first transducer, the sound signal transmitted by the first transducer being constituted by at least one pulse transmitted at a determined sound frequency Fa, and the sound signal received by the second transducer comprising a series of characteristic oscillations of amplitude that increases initially over several periods, and then decreases over several following periods, the envelope of the characteristic oscillations being bell-shaped, the method consisting in sampling the received sound signal at a sampling frequency Fe, in digitizing the sampled received sound signal, and in seeking the first meaningful zero-crossing of the characteristic oscillations of the received sound signal by analyzing the sampled and digitized received sound signal,wherein in order to seek the first meaningful zero-crossing of the characteristic oscillations of the received sound signal, an ideal characteristic first period is initially defined for determining the first zero-crossing of characteristic oscillations of the received sound signal, with said ideal characteristic first period being characterized by an ideal amplitude ratio .DELTA. between the maximum amplitudes Pi- and Pi+ of the two lobes of said ideal characteristic first period, and then for each period of the received sound signal as sampled and digitized, the maximum amplitudes P- and P+ of the two lobes of the period under examination are determined, a ratio of said maximum amplitudes P- and P+ is compared with the ratio of the ideal amplitudes corresponding to the ideal period, and then if the result of the comparison is greater than a threshold value G.sub.s, the period under consideration is considered as being an interference period corresponding to noise, whereas if the result of the comparison is less than said threshold value G.sub.s, the period under examination is considered as being a characteristic, in which case the zero-crossing between the two lobes of said characteristic period is determined, which zero-crossing is determined as being the first meaningfuil zero-crossing of the characteristic oscillations of the received sound signal.