Patent GB-764476-A (GB)
Title: Improvements relating to fluid-flow measuring or control apparauts of the force-balanced type
IPC: G01F1/38
Filed: 1953-03-11
Abstract: 764,476. Electric fluid flow gauges. ELECTROFLO METERS CO., Ltd., and ENGEL, F. V. A. E. June 4, 1954 [March 11, 1953], No. 6734/53. Class 40 (1). [Also in Groups XIX and XL (b)] A measuring or controlling apparatus responsive to fluid flow comprises a rockable balance element acted on by a force caused by pressure in a fluid flow metering device of the diaphragm or ring balance type and a counterbalancing force exerted by an electromagnetic means, an optical system comprising a light source, lightsensitive cell and reflecting or obturating means on the element to control the incidence of light on the cell and means to change variations in light caused by unbalance of the element into a current in the electromagnetic means which is a function of the pressure. In Fig. 1 the two sides of a constriction in a tube are communicated to opposite sides of diaphragm 3 to rock beam 8. The beam bears a mirror 11 cooperating with light source 13, 14 and stationary mirror 15 to vary the amount of light falling on a photo-cell 17 forming part of a potentiometer across the anode supply of amplifier 35, in accordance with the extent of beam deflection. The consequent change in cell resistance varies the grid voltage of amplifier 35 to alter the current through the D.C. winding of saturable reactor 24. The R.C. network 19, 20, 21 smooths out any rapid fluctuations due to A.C. energization of the light source. The current in the A.C. winding of the saturable reactor, the amplitude of which corresponds to the current in the D.C. winding flows through a winding embracing the potmagnet 32 and armature 33 fixed to the beam to produce a restoring force on the beam proportional to the square of the current. The current when the beam is balanced, which is recorded, indicated and integrated at 30, 29, 28 is thus directly proportional to rate of flow in the tube. To allow use of D.C. instruments a rectifier may be provided in series with winding 31, in which case the armature is replaced by a permanent magnet. The positions of magnet and winding may be interchanged. In a second embodiment a ring balance pivoted on crossed leaf springs 9 attached to a fixed casing is used, the difference in pressure applied to the liquid on opposite sides of diaphragm 37 via holes 38a, 38b altering the level of liquid in the two limbs to produce a torque. The beam 8 attached to the tube carries a screen or shutter 39 which, in accordance with beam deflection, varies the amount of light falling on photo-cell 17 to vary the grid voltage of amplifier 35, the anode current of which flows through a winding 31 co-operating with soft iron armature 33 fixed to the beam, and through indicating, integrating, recording and possibly also controlling devices. Alternatively, the screen may be mounted adjacent the pivot point 9 on a beam which is rocked by beam 8 to produce an amplified movement or both screen and armature may be directly mounted on the tube. Means for making connection to holes 38a, 38b each comprise a helical spring tube 54, Fig. 3, fixed on and coaxial with the beam and joined to the casing near the pivot point, L-shaped connectors 55, 57 and tube 56. The ring balance may be used with the diaphragm at the lowest point where differential liquid heads are being measured, the space above the liquid being filled with compressed gas or a liquid lighter than and immiscible with the liquid on which measurements are being made (e.g. decahydronaphthalene with water).