| 摘要 |
PURPOSE:To measure a mass flow rate directly utilizing an ultrasonic wave by including a comparison amplifying means adapted to apply an excitation signal to an excitation means so that the amplitude of a detection output signal from a detection means equals a fixed reference value. CONSTITUTION:An excitation means 3, a detection means 4 and an amplification circuit 52 forms a self-exciting loop to generate a vibration at a resonance frequency determined by the representative length (e.g. diameter) of a pipeline and the sound velocity of a fluid. At this point, a feedback control is done to make the amplitude of a detection output signal Sr equal the reference value R. As a result, a stationary wave 7 with a fixed amplitude is generated in a passage 11 to confine the ultrasonic energy to a fixed area. As the ultrasonic energy drains with the movement of a fluid, the ultrasonic energy in the area decreases. Thus, to keep the stationary wave excited at a fixed amplitude, the power proportional to the flow rate is needed and the flow rate can be determined by measuring variations in the exciting power. |
