Patent GB-891312-A (GB)
Title: Mass flowmeter
IPC: G01F1/82
Filed: 1960-05-20
Abstract: 891,312. Flow meters. GENERAL ELECTRIC CO. May 20, 1960 [May 21, 1959], No. 17871/60. Class 69 (1). [Also in Group XXXII] A fluid mass flow-meter has a resiliently restrained member which transmits to pick-up means deflections it makes due to the torque applied to a single rotatable impeller in a housing by drive means in the same housing and is characterized by an error-eliminating member which is close to the impeller and which, due to viscous coupling with the impeller imparts to the deflectable member movement in a direction opposite to that imparted by the impeller drive means. In a split housing 10 a stator 18 of an electric motor is mounted in a fluid-tight casing 40 on bearings 26. Webs 20, 22 connect the stator to bosses 30 in which is journalled a rotor 39 which carries an impeller 32 with longitudinal channels 36 through which the fluid is propelled. The outer wall 38 of the channels is a cylindrical magnet with a plurality of poles. A flattened tubular coil-spring 46 connects a shaft 42 extending from one boss 30 with a fairing 44 fixed on the housing 10. A projecting annulus on the other boss 30 carries magnets 64 which transmit deflections of the stator to magnets 62 on the shaft of an electrical pick-off housed in another fixed fairing 58. The fairings 44 and 58 are supported in the housing 10 on vanes 14 and 12 which serve as flow straighteners. The electrical leads 52 to the motor are carried inside the hollow tube 50 of the spring 46 (Fig. 2). The distance the stator assembly 18, 20, 22 deflects against the spring 46 due to reaction arising from the momentum the impeller imparts to the fluid is subject to additive errors due to viscous drag between the impeller and the casing 10 and to friction in the bearings. The proximity of the surfaces at 38 and 40 gives rise to a contrary viscous drag which cancels the error due to that from the casing. Similarly, the frictional effects in the bearings of the armature and the rotor are in contrary directions and cancel each other. Errors are thus eliminated from the deflection which the stator signals to the pickoff 56. Alternatively, both the stator and the rotor of the motor may be housed inside a fluid-tight cylinder on the outside of which an annular impeller assembly is mounted for rotation from the rotor by magnets. A sleeve, either fixed on the outside of the stator by way of the cylinder wall, or rotated through the wall by magnets on a rotatable stator, concentrically shrouds the periphery of the impeller and gives rise to the required compensating drag (Figs. 3 and 6, not shown). The electric leads may come from the motor independently of the coil spring. Fig. 9 shows an embodiment in which the motor 234 is fixed in the housing 220 and drives a shaft 242 through gears 236 and magnets 238, 240. The shaft 242 rotates the impeller 262 through a gear train 246, 250, 252. Part 250 of the train is mounted on a disc 272 which is journalled at 268 in the housing and which bears against the force of a coil spring 274 the reactive force due to the drive from the motor to the impeller. A sleeve 270 on the disc 274 closely surrounds the periphery of the impeller and is subject to a compensating counterrotation due to viscous drag. The consequent nett deflection of the disc 274 is conveyed by magnets 280, 282 to a pick-off 284. To allow for local turbulence or for gear ratio the axial lengths of the sleeve 270 and outer surface of the impeller may be made to differ. Adjusting vanes 230, 232 may correct for alignment of the flow straightening vanes 226 and 228.