Patent ID: 6386047
Filing Date: 2002-05-14
Classification: G01F

Abstract:
A method of transiting/receiving an ultrasonic wave at a constant angle &agr; in a direction similar or contrary to a flow velocity and measuring a flow velocity using an ultrasonic phase difference changed proportional to the flow velocity comprising:amplitude-modulating an ultrasonic wave of a carrier frequench Æ’C into an amplitude-modulation frequench Æ’M which is lower than the carrier frequench Æ’C; transiting the amplitude-modulated signals in directions similar and contrary to the flow velocity; demodulating the amplitude-modulated signals transited through an interval distance L and then detecting signals of the amplitude-modulation frequench Æ’M; measuring a phase difference &Dgr;&phgr;M1 between the signals of the amplitude-modulation frequench Æ’M transited and received in the direction similar to the flow velocity and a phase difference &Dgr;&phgr;M2 between the signals of the amplitude-modulation frequench Æ’M transited and received in the direction contrary to the flow velocity; obtaining multiples of m1 and m2 by &pgr; excluding different phase components &bgr;&pgr; and &ggr;&pgr; measured by at least two phase difference discriminators from phase differences &Dgr;&phgr;C1 and &Dgr;&phgr;C2 between the signals of an ultrasonic carrier frequench Æ’C transited and received in the direction similar to the flow velocity and between the signals of the carrier frequench Æ’C transited and received in the direction contrary to the flow velocity by the following expressions; Î”&varphi;C1Ï€=Î”&varphi;M1&it;fCÏ€&it;â€ƒ&it;fM=m1+Î²Î”&varphi;C2Ï€=Î”&varphi;M2&it;fCÏ€&it;â€ƒ&it;fM=m2+Î²wherein &bgr; is smaller than 1.0 and &ggr; is smaller than 1.0, storing m1 and m2 at the memory of a system, measuring the phase different components &bgr;&pgr; and &ggr;&pgr;, adding m1&pgr; and m2&pgr; to the phase different components to calculate the phase differences &Dgr;&phgr;C1 and &Dgr;&phgr;C2 and computing the flow velocity V based on the following expression: V=Ï€&it;â€ƒ&it;fC&it;Lcos&it;â€ƒ&it;Î±&it;(1Î”&varphi;C1-1Î”&varphi;C2)selecting the amplitude-modulation frequench Æ’M as follows: fM=n+a2&it;L&it;(Cmin-vmax)n=a&af;(Cmin-vmax)-b&af;(Cmin+max)Cmax-Cmin+2&it;vmax)storing n at the memory of the system as follows; and &Dgr;&phgr;M1=n&pgr;+a&pgr; &Dgr;&phgr;M2=n&pgr;+b&pgr;measuring the phase differences a&pgr; and b&pgr; measured by the phase discriminators in the above expression and adding n&pgr; to the phase differences a&pgr; and b&pgr; thereby to obtain the phase differences &Dgr;&phgr;M1 and &Dgr;&phgr;M2, wherein a<1.0 is a factor for selecting a maximum measuring range (a&pgr;)max of one of the phase difference discriminators, which is 0.95, and b<1.0 is a factor for selecting a maximum measuring range (b&pgr;)max of the other phase difference discriminator, which is about 0.2, Cmax and Cmin are maximum and minimum sound velocities, and &ugr;max=VmaxÃ—cos &agr; is a maximum flow velocity measuring range; the Vmax is a maximum flow velocity and the cos&agr; is a directivity angle of the ultrasonic wave.