Patent GB-703634-A (GB)
Title: Improvements in apparatus for establishing a fluid loading pressure bearing a functional relationship to a variable
IPC: G05B11/50
Filed: 1951-02-09
Abstract: 703,634. Automatic flow control systems. BAILEY METERS & CONTROLS, Ltd. Feb. 9, 1951 [Feb. 11, 1950], No. -3186/51. Class 38 (4). [Also in Group XXXVIII] In an automatically balanced potentiometric device 'for producing a fluid loading pressure corresponding to a variable, regulating means controlling the fluid loading pressure is driven by the potentiometer balancing device. Any desired functional relationship may be obtained between the variable and the fluid loading pressure, e.g. a linear, square or square root relationship, and the fluid loading pressure may be indicated, recorded or used to regulate the variable. The variable may be fluid-flow, temperature, pressure voltage, humidity or position, e.g. of a damper. In Fig. 1 the fluid flow in a pipe 2 produces by means of a manometer 3 a linear displacement of a transformer core 8 proportional to the pressure differential h at the orifice 1, i.e. proportional to the square of the fluid flow v. The transformer secondaries 10, 11 are in series opposition and produce a voltage E1 directly proportional to h. Normally E1 is balanced by the voltage drop.E2 across a resistor 24 series connected with a solenoid 16 and potentiometer 100 energized in phase with the transmitter transformer 9. A change in fluid flow upsets the balance ; the error voltage E1-E2 is amplified at 26, and through a control device 26A drives the movable arm of the potentiometer 100 to vary the current flow through resistor 24 until balance is restored. The force on the plunger 15 produced by the solenoid current is normally balanced by the air pressure P in a bellows 21. Variation in the solenoid current due to a change in the fluid flow v in pipe 2 operates a valve 18 which as disclosed in Specification 425,507, [Group XII], alters the air loading pressure P in a pipe 19, 20 until the plunger 15 is again balanced. The air pressure P which is thus a measure of E2, and hence of the fluid flow v in pipe 2, is measured on a meter 30 and may operate a control valve 31. In this case P αh<SP>2</SP>. i.e. P α v<SP>4</SP>. To make P α v<SP>2</SP>, the voltage E2, Fig. 2, is derived from the opposed secondaries 36, 37 of a transformer energized at 35 in phase with the transmitter. The error voltage E1-E2 through the amplifier 26 and control unit 26A varies the energization of differentially connected solenoid coils 44, 45 which move the plunger 46 to vary the air loading pressure P in pipe 49. This pressure is applied to the bellows 50 to balance the plunger 46 and also to a bellows 39 to move the core 38 of transformer 35 to vary E2 until it equals E1. The arrangement of Fig. 2 may be modified by using a single bellows to actuate both solenoid cores 38, 46, Fig. 3 (not shown). In a further modification of Fig. 2 the solenoid core 46, Fig. 4, also adjusts the moving contacts 59, 63 of potentiometers 58, 61 which reduce the output voltage E2 of the transformer 55 to a value e which is balanced against E1. In this case P α #h, i.e. P α v. In a modification of this arrangement, Fig. 5 (not shown), the transformer 55 has a movable core adjusted by the solenoid core 46 and one of the potentiometers 58, 61 is dispensed with.