Patent GB-950452-A (GB)
Title: Improvements in apparatus for metering and proportioning materials
Inventor: MAPP ALFRED GEORGE
IPC: G05D11/13
Filed: 1959-03-02
Abstract: 950,452. Automatic fluid flow control; fluid-pressure servomotor systems. DOWTY ROTOL Ltd. June 2, 1960 [March 2,1959; June 17, 1959; March 7, 1960], Nos. 7220/59, 20818/59 and 7986/60. Headings G3P and G3R. Rate of fluid flow is automatically controlled in dependence on variations in the phase relationship between signals from a cyclic signal generator driven from a flow measuring device and signals from a master cyclic generator so that the phase relationship is maintained constant. In one embodiment three different fluids to be blended are pumped from storage tanks into ducts 31, 32, 33 supplying a common delivery duct 34. The three rates of flow are measured by positive displacement rotors 35, 36, 37 of the sliding vane eccentric type which drive three-phase alternators 38, 39, 40 the outputs of which energize one set of stator windings of phase comparators 25, 26, 27 of the type described in Specification 516, 613. Three electrical supplies having different predetermined frequencies corresponding to the desired rates of flow are produced from a frequency multiplier oscillator unit 11 by setting associated decade or continuously variable controls. After amplification and three-phase conversion in units 22, 23, 24, these supplies energize the other set of stator windings of phase comparators 25, 26, 27. The phase comparator rotors take up a position corresponding to the phase displacement between the two stator supplies and hence flow error. Such error is automatically corrected by causing the rotors to control the settings of fluid-operated valves such as valve 73, in the three ducts. To achieve this, phase comparator 25 controls, through a cam 51 and follower 52, a needle valve opening 54 in a bellows 56 supplied with compressed air through a conduit 61, so that the pressure applied to a diaphragm 66 is varied to cause operation of valve 73. A lever 59 interconnecting valve stem 59 and bellows 56 provides follow-up. A ganged frequency control associated with oscillator unit 11 may be operated to vary total rate of flow without altering relative rate of flow. Indication and recording of the rates of flow are referred to. In another embodiment applied to blending two fluids to be supplied to a fuel tanker at a wharfside, a rotor in each duct is associated with a high frequency electrical pulse generator, preferably of the striped disc-photocell type. The pulses from each generator are applied to separate decade counting tube units which repeatedly count a preset number of pulses corresponding to the desired rate of flow in the associated duct and the two counters control a diode co-incidence circuit which produces a D.C. signal of polarity and magnitude corresponding to the relative durations of the two counts. This signal is applied to control a reversible A. C. servomotor adjusting a valve in one of the ducts to maintain the desired relative rate of flow. Position and rate feedback is applied to the servomotor which may control the valve through a hydraulic servo-system. A Miller type integrating circuit included in the control circuit may also terminate automatic control or give a warning if error is unduly persistent. In a third embodiment applied to maintaining the flows from two aircraft fuel tanks in a desired proportion, the flow in each of two ducts is controlled and measured by a hydraulically driven vane type rotor corresponding in size to the size of the tank with which it is associated. Separate electrical generators driven with the rotors produce signals dependent on speed and position which are applied to comparators the outputs of which control a common electromagnetically operated valve, of the type described in Specification 730, 965, regulating the hydraulic drive of one of the rotors to maintain the desired relative rate of flow. By-passes and non-return valves associated with the rotors permit flow to continue if a rotor jams. Specification 931, 092 also is referred to.