Karman vortex flowmeter

Abstract

A Karman vortex flowmeter for deriving the velocity or quantity of fluid flow is comprised of an upstream pillar for producing Karman's vortex streets or paths that has a substantially isosceles triangle cross section, a downstream pillar for producing Karman's vortex paths that has a substantially isosceles trapezoidal cross section, a vibration chamber, and a vibrator member supported in the vibration chamber in a state of mass equilibrium relative to a revolving shaft passing through its center of gravity such that it can vibrate torsionally about the revolving shaft. The base of the upstream pillar is substantially equal to the base of the downstream pillar, and the pillars are positioned so that the bases are parallel to each other and perpendicular to the direction of the fluid flow. The vibrator member is preferably provided with a pair of taut bands supporting the vibrator member which form the revolving shaft and a frame which supports the bands. The taut bands may be pressed by a spring member to ensure uniform tension in the face of temperature changes, and may be damped with suitable elastic material. The flowmeter is provided with a photoelectric detector to detect the vibration of the vibrator member as it vibrates in response to pressure variations attributable to the Karman streets produced by the pillars. The detector preferably includes an integrator and comparator which cooperate to derive only effective frequency components.