GB830211A - Improvements relating to the measurement of fluid velocity - Google Patents

Abstract

830,211. Electric measuring devices. MINISTER OF POWER. June 28, 1956 [March 31, 1955], No. 9389/55. Class 40 (1). In apparatus for measuring the velocity of flow of a fluid of determined density, an elastic diaphragm, on which is mounted a number of resistor-type strain gauges, is disposed normal to the fluid flow, the strain thereby imparted to the diaphragm being measured to obtain an indication of flow velocity. A conical section may be attached to the apparatus to increase the flow velocity at the diaphragm, which may be of metal or of other resilient material and which may be protected from the action of the fluid by a heat-proof and moisture-proof covering, as may the strain gauges. The diaphragm may be rectangular, one side or two opposite sides being clamped to a fixed mounting, or trapesoidal, one of the parallel sides being clamped, or of any conveient shape (e.g. square or circular) and peripherally clamped. Fig. 7 shows a paddle-shaped diaphragm comprising a circular portion 1b which is presented to the fluid flow, and a stem 1a, on one or each of whose faces is mounted a strain gauge 3. Fig. 8 depicts a measuring head in which one end of a blade-like diaphragm 1 is clamped within a casing including a tube 4, from the mouth of which the free end of the diaphragm 1 extends into the stream of fluid A, strain gauges 3 being cemented to both faces of the enclosed part of the diaphragm 1 and connected by cables 5 in a bridge measuring circuit, or in series with a battery, the voltage changes across one resistance being measured. Use of a cathode-ray oscillograph for transient indication, and use of a pen recorder for continuous recording, are mentioned. The apparatus may be used to measure high velocity gas flows in e.g. windtunnels, gas turbine engines, aircraft (for determining air speeds) and explosions of gas and dusts, and may be adapted to measure low air velocities.