| 摘要 |
PURPOSE:To enhance a detection speed, by providing a frequency selecting means in a positive feedback loop consisting of a speaker for ultrasonic radiation arranged on one side of a passage pipe, a microphone arranged on the opposite side, and an output amplifying circuit. CONSTITUTION:When the gain of the positive feedback loop constituted with a speaker 2 arranged in a passage pipe 1, a microphone 3, and an amplifying circuit 4 is set to a value very larger than one and a white noise is used as a trigger signal to oscillate a fluid, a frequency where a length L between the speaker 2 and the microphone 3 is N times as high as the wavelength of acoustic waves in the fluid is oscillated. Since an oscillation frequency (f) is changed as a primary function of a fluid speed V, the speed V is obtained on a basis of the frequency (f), and the sectional area of the pipe 1 is multiplied to obtain a flow rate. Meanwhile, since the number of frequencies (f) is infinite, the narrow- band microphone 3, the narrow-band speaker 2, or the like is used as the frequency selecting function means to specify preliminarily one value as N. |
