Abstract: An ultrasonic flow velocity measuring method using a transit time difference of continuous sine waves without transmitting/receiving an ultrasonic pulse comprises steps of amplitude-modulating a continuous ultrasonic sine wave carrier into a lower frequency and transiting the amplitude-modulated signal, whenever the ultrasonic transit time is measured; demodulating the amplitude-modulated signal; detecting or discriminating the amplitude-modulated signal from the demodulated signal and measuring a time interval from the moment that the ultrasonic sine wave is amplitude-modulated till the amplitude-modulated signal is demodulated.

Abstract: An ultrasonic flow velocity measuring apparatus measures a transit time under the condition a synchronization of an ultrasonic signal having a modulated frequency by PN (pseudo noise) code of a diffusion band at a transmitting side is locked at a receiving side, and prevents an excessive measurement error exceeding allowable error range. If the installation positions of the ultrasonic transducers of upper and lower stream sides are moved, an ultrasonic transit time can be precisely measured by using a different signal series PN code without changing an electronic component and a program. In addition, the ultrasonic flow velocity measuring apparatus installs a plurality of ultrasonic transducers according to various distances from the bottom of a fluid passage, and accurately measures average flow velocity which is variable in response to the height in a curved fluid passage.

Abstract: An ultrasonic flow velocity measuring method comprises a phase difference flow velocity measuring method irrelevant to the change of the sound velocity, if a flow velocity is measured based on a phase difference method without transmitting/receiving an ultrasonic pulse in a river, an open sluice channel or a pile having a large inner diameter, including amplitude-modulating at least one continuous ultrasonic sine waves of a carrier frequench ƒC into signals of an amplitude-modulated frequench ƒM, if at least one phase difference &Dgr;&phgr;C transited and received in directions similar and contrary to the flow velocity is equal to n&pgr;+a&pgr;, obtaining n&pgr;, using the signal of the amplitude-modulation ƒM; and measuring a part of a&pgr;<&pgr;, obtaining the phase difference between the signals of the carrier frequench ƒC and obtaining the total phase differences &Dgr;&phgr;C precisely.

Abstract: An ultrasonic flow velocity measuring apparatus includes two transducers arranged to form a certain angle to a flow velocity direction to measure flow velocity of a fluid, the two transducers transmitting and receiving an ultrasonic beam relative to each other to allow ultrasonic beam transmitting time to be measured to compute the flow velocity, wherein the transducers are connected to a transducer switching portion, which is connected to an outputting amplifier, which is connected to a frequency modulation oscillator, which is connected to a one shot multivibrator, which is connected to a control square pulse generating portion, which is connected to the transducer switching portion and an output switching portion, the outputting switching portion is connected to the receiving amplifier, the an attenuator, and to the frequency discriminator, which is connected to a pulse shaping portion to shape the output of the frequency discriminator into a square pulse, the pulse shaping portion is connected to a time i

Abstract: A method of measuring a horizontal average flow velocity at a plurality of depths using an ultrasonic beam to obtain the flowrate of a river comprises steps of emitting continuous ultrasonic beams along a selected flowrate measuring free crosssection from one skirt of a river and measuring a moving distance of paired ultrasonic receiving transducers spaced away in an interval from each other until the outputting voltages of the paired ultrasonic receiving transducers become equal to each other and then measuring a horizontal average flow velocity, in which the paired ultrasonic receiving transducers are electrically connected to differential amplifiers in order to measure the position at a moment that their outputting voltage differences becomes zero, and furthermore steps of testing and correcting an apparatus for performing the method.