| 摘要 |
PURPOSE:To reduce a noise caused by disturbance force, to improve an S/N ratio, and also to make vibration resistance satisfactory, in a flow speed and flow rate measuring device for measuring a flow speed or a flow rate by detecting the variation frequency of pressure working on an object by a Karman's vortex, and fetching it as a vortex signal. CONSTITUTION:When a measuring fluid flows to a duct, a Karman's vortex is generated by a force receiving body 2. When this Karman's vortex is generated, a pressure difference is generated on the side of the force receiving body 2. Seal diaphragms 32, 33 are displaced by this pressure difference, and a gap between the seal diaphragms 32, 33 and a fixed capacity electrode 311 is varied. Vortex generation frequency can be detected by detecting the number of times of this variation as an electrostatic capacity variation. On the other hand, as for a disturbance signal caused by vibration of the duct, force F30 working on a measuring diaphragm 30 becomes like F30=(M-rhoHAe)alpha (provided that M: mass of a center plate 301, H: height of charged waves 36, 37, rho: density of the charged waves 36, 37, Ae: an effective area of the measuring diaphragm 30, alpha: acceleration of disturbance caused by vibration f the duct). When the mass M of the center plate 301 is set so as to be M=rhoHAe in advance, force generated by the disturbance acceleration alpha always becomes zero, and no error is generated by the disturbance accleration alpha. |
