Vortex shedding flowmeter
First Claim
1. In a flowmeter for monitoring the vortex shedding frequency of a fluid flow, said flowmeter comprising a tensioned optical fibre sensing element arranged to extend transversely to the fluid flow so as to oscillate in response to vortex shedding, a light source for illuminating the optical fibre, and a photodetector for sensing an output of the fibre sensing element and producing an electrical signal corresponding to the vortex shedding frequency, the improvement wherein said sensing element comprises at least part of a single mode optical fibre forming a signal arm of an interferometer which also includes means for deriving a reference signal from the illuminating light source, said interferometer producing an interference signal which corresponds to the optical phase difference between the signal light beam and the reference signal and which is modulated by oscillation of the sensing element in response to vortex shedding, and said photodetector being arranged to sense the modulated interference signal and produce an electrical signal having a modulation frequency corresponding to the vortex shedding frequency.
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Accused Products
Abstract
A flowmeter for measuring the velocity of fluid flow by monitoring the vortex shedding frequency of the fluid flow comprises a single mode optical fibre sensing element (1) for detecting vortex shedding and utilizes interferometric techniques for producing an electrical output signal corresponding to the vortex shedding frequency. The sensing element (1) comprises at least part of the signal arm (2) of an interferometer (3) which also includes means (12) for deriving a reference signal from the illuminating light source (4). The flow induced oscillation of the sensing element (1) caused by vortex shedding produces modulations of the interferometer output which is monitored by a photodetector (14) which, in turn, produces a modulated electrical output signal which can be processed by a signal processing system (16-19) to identify the vortex shedding frequency and, hence, produce a measurement of the flow velocity.
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Citations
9 Claims
- 1. In a flowmeter for monitoring the vortex shedding frequency of a fluid flow, said flowmeter comprising a tensioned optical fibre sensing element arranged to extend transversely to the fluid flow so as to oscillate in response to vortex shedding, a light source for illuminating the optical fibre, and a photodetector for sensing an output of the fibre sensing element and producing an electrical signal corresponding to the vortex shedding frequency, the improvement wherein said sensing element comprises at least part of a single mode optical fibre forming a signal arm of an interferometer which also includes means for deriving a reference signal from the illuminating light source, said interferometer producing an interference signal which corresponds to the optical phase difference between the signal light beam and the reference signal and which is modulated by oscillation of the sensing element in response to vortex shedding, and said photodetector being arranged to sense the modulated interference signal and produce an electrical signal having a modulation frequency corresponding to the vortex shedding frequency.
Specification