Patent GB-900941-A (GB)
Title: Apparatus for adjusting the rate of flow of a fluid flowing through a passage
IPC: G05D7/06
Filed: 1959-03-02
Abstract: 900,941. Controlling fluid flow. SULZER FRERES S.A. March 2, 1959 [March 3, 1958], No. 7216/59. Class 40 (1). [Also in Groups XX, XXIX and XXXVI] The rate of flow of fluid past a throttling point in a passage is controlled in accordance with a control signal J(st) by measuring the pressure difference dp across the point, combining this signal with the control signal to give a corrected adjustment signal and using this to adjust the flow cross-section at the throttling point. Preferably the pressure difference signal is used as its square root J(#dp), and a third signal J(F) representing the rate of flow is combined with the other two in various ways. In Fig. 2 the pressure difference at 2 is measured by a device 5 and a signal representing the square root of this is generated at 60. A further signal is generated at 8 representing the aperture of the throttle (and hence the rate of flow) and these signals are multiplied together in unit 9. The product is compared at 10 with the control signal and the resultant moves the slider of a centre-tapped potentiometer 11 to energize a motor 3 and adjust the throttle aperture until the output from 10 is zero. In Fig. 3 (not shown), the quotient of J(st) and #dp is applied to one end of a beam and J(F) to the other. Deflection of the beam closes one or other of two pairs of contacts to energize the motor 3. The arrangement of Fig. 5 employs two automatically-balanced Wheatstone bridges. The first bridge ABCD has a resistor A adjusted by a diaphragm 22 responsive to the pressure difference across the aperture 2. Any unbalance energizes a servomotor 26 which rebalances the bridge at B and D and also adjusts a resistor B<SP>1</SP> in the second bridge. Since B and D are always equal and C is constant, B (and therefore B<SP>1</SP>) is proportional to the square root of A and hence to #dp. The control signal J(st) is applied at A<SP>1</SP> and any unbalance of the second bridge energizes the motor 3 to adjust the throttle aperture and simultaneously rebalance the bridge at D<SP>1</SP>. The latter resistor (Fig. 7, not shown) is tapered to be geometrically similar to the valve which controls the flow at 2 so that its resistance value represents the cross-section available for flow and the desired relationship between the quantities is obtained. It is possible (Fig. 8, not shown) to adjust the resistor C in accordance with the density or the reciprocal of the density of the fluid, to give a corrected value for the mass or volume rate of flow. A simplification (Fig. 9, not shown) uses only one bridge with the resistor A tapered as for D<SP>1</SP> in Fig. 5. The rebalancing motor can be electro-hydraulic. Fig. 11 shows a similar device using electromagnets instead of resistors. The pressure difference across 2 deflects a beam 60 and produces a signal from the differential pick-up 70. This is amplified at 91, rectified (not shown) and passed to series fixed and moving coils 81, 82 to give a restoring force proportional to the square of the current, so that the amplifier output represents #dp. A similar pick-up 8 gives a signal representing the flow-aperture J(F) and these are multiplied in the fixed and moving coil arrangement 85, 86 to deflect the beam 90 in accordance with J(F.#dp). This is sensed by a differential feed-back system 83 and the resulting signal passed to a magnetic amplifier 93, which is controlled by the signal J(st). The output of the magnetic amplifier energizes the motor 3 to adjust the aperture 2 accordingly. A modification of this system using A.C. signals is given in Fig. 12 (not shown). Instead of combining a signal with the square root of another signal, it is possible to combine the second signal with the square of the first. It is also possible to modify the system in cases where the rate of flow is not strictly proportional to the square root of the pressure difference across the aperture. It is also stated that it is possible to compare J(#dp) with the quotient of J(st) and J(F), and an hydraulic system for carrying out this method is described (see Group XXIX).