| 摘要 |
PURPOSE:To enable execution of highly precise measurement by a method wherein a pressure in an internal space of a surrounding body is made to fluctuate at a prescribed frequency and the velocity of a fluid is calculated from a change in the pressure caused by a hole in a wall surface which is so disposed as to be in contact with the flow of the fluid. CONSTITUTION:A surrounding body 7 covers a hole 2 made in the wall surface of a pipe 1 from outside in an airtight manner and a sound pressure generating means 10 such as a thin-type speaker is so fitted as to form a part of the wall surface of the surrounding body 7. The means 10 is driven in a sine wave manner by a drive circuit 11 of which the frequency is set to be a Helmholtz resonance frequency determined by the capacity V of the surrounding body 7, the dimension of the diameter of the hole 2, etc., and the internal pressure of the surrounding body 7 is changed at the Helmholtz resonance frequency. A capacitor-microphone 8 is fitted inside the surrounding body 7 and detects a change in a sound pressure. A coefficient circuit 9 amplifies a detection output from the microphone 8 at a prescribed amplification rate, detects the velocity of an airflow in the pipe 1 and outputs it. |
