Patent GB-737281-A (GB)
Title: Fluid flow measuring system
IPC: G01F1/88
Filed: 1953-01-30
Abstract: 737,281. Electric indicating systems. BENDIX AVIATION CORPORATION. Jan. 30, 1953 [Feb. 26, 1952], No. 2783/53. Class 40 (1). A fluid flow measuring apparatus. comprises an electrodynamic device operated in response to fluid flow and energized correspondingly to the fluid density to produce an electric signal proportional to the mass rate of fluid flow which drives a variable speed electric motor coupled to a rate generator producing a feedback signal proportional to the speed of the motor, .the latter being energized by the differential signal arising between the rate of flow signal and the feedback signal and driving a rotational speedmeasuring device which indicates the mass rate of fluid flow. Fig. 1 shows apparatus for measuring mass flow of a fluid in a conduit 19 wherein the pressure across a venturi 21 in the conduit is applied respectively to differentially connected expansible spring-loaded bellows 14, 16 and linked to rotate proportionately to the rate of flow across the venturi, a gear sector 26 meshing with a pinion 29 rotating secondary winding 32 relatively to stationary primary winding 34 of a transformer energized from an A.C. source through plural series calibrated resistances 40 of a densitometer 36, which are selectively short-circuited by switches 44 operated by corresponding hydrometer floats 42 of graduated densities arranged to operatively rise (or fall) in succession according to the density of the fluid flowing through the conduit. The excitation voltage of the primary winding 34 is variable proportionally to the square root of the fluid density p, and the voltage induced therefrom into winding 32 is proportional to the square root of the pressure drop #P across the venturi and it is shown that the mass flow rate of fluid W F =K#p ##P where K is a constant. Thus, the output voltage of winding 32 is proportional to the mass flow rate, and through the output winding 50 of an A.C. rate signal generator 51 having a continuously A.C. energized exciting winding 62 it excites amplifier 46 over connection 48 to energize winding 66 of a two-phase variable speed A.C. motor 58 whose fixed phase winding 59 is energized continuously from an A.C. source through a phase-shifting condenser. The motor drives rate generator 51 through gearing 60 to-develop a rate signal at the input of amplifier 46 in antiphase with the output of winding 32 so that the speed of rotation of the motor 58 is controlled at a value proportionately to the mass flow rate signal. An integrating counter 63 driven by motor 58 records the total mass flow over an interval while a pointer 70 driven against a hair-spring 69 by a magnetic slip coupling 65 indicates the instantaneous mass flow rate on a scale 71. A reset switch 55 between the amplifier and the motor is operable to disconnect the mass flow rate signal and energize both motor windings in quadrature from an A.C. source to zeroize the integrating counter. In a modification (Figs. 4, 5), a propeller 98 rotated by the fluid flow in the conduit drives a tachometer generator 99 having an output winding 102 and an input winding 100 connected to the secondary winding of a variable densitometer transformer 74 which is energized from the secondary of an A.C. energized power transformer 78 while the primary 75 is energized from a tap thereon. A mass 81, submerged in the fluid in a housing 86 connected by ports with the conduit 19 and mounted on a lever 82 rotates a shaft 84 against a hair-spring 89 in accordance with the fluid density, which is linked by a magnetic coupling 91, 92 through the non-magnetic wall of the housing to correspondingly rotate the secondary 73 relatively to the primary 75. It is shown that since the excitation of winding 100 of generator 99 is proportional to the fluid density and the generator output is proportional to the propeller speed and thus to the volumetric rate of fluid flow, the output voltage of winding 102 is proportional to the mass flow rate and operates the indicating apparatus over connection 48 as above. In a further modification (Figs. 2, 3, not shown), the latter type of densitometer may be used to energize the primary of the now responsive transformer in Fig. 1.