Abstract: An instrument for measuring simultaneously the flow rate and density of a moving fluid includes means for measuring the frequency and amplitude of vortices shed by interaction of the fluid with a bluff body. Typically the sensing means includes an optical fibre movable in response to pressure changes in the fluid. Computation of the mass flow rate of the fluid can be effected.In one embodiment a light signal from a transmitter (41) is modulated via a sensor (42) and is then fed via a detector (45) and A to D converter (46) to a microprocessor (47) where demodulation and computation of mass flow rate is effected. The microprocessor also provides neative feedback to maintain the output level of the transmitter substantially constant.

Abstract: A vortex flowmeter including a single optical fiber into one end of which a light signal can be transmitted from a source to the other fiber end where it is vortex modulated. Modulated light at the other end is then reflected to a receiver back along the same optical fiber. Relative movement between the other fiber end and a reflector serves to modulate the light signal. Embodiments are disclosed in which the other fiber end moves and the reflector is stationary. In the alternative case, the other fiber end is stationary and the reflector moves.

Abstract: An elongate body extends as a bar across a fluid flow passage and has a vortex shedding tapered head portion pointing upstream and a tail portion downstream of the head. The head has an axial length equal to or less than half the head width. The tail has a width less than head width throughout its length. A sensor is arranged downstream of the head. For example, the sensor may be in the tail portion of the body such as to sense the vortices produced alternately on the side surfaces. The frequency output of the sensor is proportional to the relative speed between the elongate body and the fluid. The arrangement can be used as a fluid flowmeter or a ship's log.