Flow measuring apparatus

Claim 1

In fluid flow metering apparatus of the type wherein an elongate cylindrical element is inserted in a stream of fluid to produce at opposite sides of the element vortices which are shed in an alternating fashion with a frequency bearing a predetermined relationship to the velocity of the fluid stream, and wherein the inserted element is formed with interior cavities communicating with said fluid stream through openings at said opposite sides, said cavities being connected by an internal passageway permitting fluid to flow between said cavities and through said openings in an alternating fashion corresponding to the shedding of vortices, and wherein detection means are provided for detecting the frequency of vortex production to provide a measure of the velocity of the fluid stream; that improvement in such apparatus which comprises: pressure conduit means at least partly within said element connecting said cavities together through a fluid channel which is separate and distincti from said internal passageway, said fluid channel extending through a region which is remote from said cavity openings and also remote from said internal passageway, said pressure conduit means transmitting through said fluid channel to the remote region alternating fluid fluctuations produced by and corresponding in frequency to the shedding of vortices from said element; said detection means being located in said fluid channel in the remote region of said pressure conduit means and being responsive to the fluid fluctuations therein produced by the shedding of vortices adjacent said opposite sides of said element, whereby the detection means in said remote region remains substantially free of contaminants in the fluid stream; and sealing means between said openings and said pressure conduit region to isolate said detector from said fluid while permitting transmission to the detector of the fluid fluctuations produced by the shedding of vortices.