Patent GB-1051831-A (GB)
IPC: F15C1/02
Abstract: 1,051,831. Fluid analogue inputers. YARROW & CO. Ltd. May 23, 1963 [May 23, 1962], No. 19924/62. Heading G3H. A fluid-pressure variable function generator comprises a chamber 2 having an inlet 3 through which there can be applied a fluid pressure can be introduced into the chamber and output means 5, 6 by which the fluid pressure within the chamber can be applied to a load, and a plurality of conduits 7 arranged in parallel and through which fluid can leak out of the chamber 2, each conduit 7 being provided with valve means 11 for preventing fluid from leaking out of the chamber through the conduit unless the fluid pressure within the conduit exceeds a certain value which is variable and/or different for different valve means, each conduit 7 being provided with an adjustable orifice means 10 in series with the associated valve means 11 for controlling the rate of leakage of fluid through the conduit when the associated valve is open, and the inlet 3 being provided with a constriction 4 so that, in operation, there is an appreciable pressure drop between the pressure applied to the inlet 3 and the pressure within the chamber 2 when fluid is leaking out of the chamber 2 through at least one of the conduits 7. The arrangement is such that the output fluid pressure is a function of the total rate of leakage of fluid out of the chamber 2 through the conduits 7 and of the input fluid pressure. Such a generator produces functions of negative curvature but when used as a feedback element around a high-gain amplifier functions of positive curvature are obtained, and when a second variable function generator is coupled to the input of the amplifier, functions of either positive or negative curvature and also functions of mixed curvature may be generated. The invention is described with particular reference to pneumatic variable function generators. Referring to Fig. 5, such a generator comprises a cylindrical metal casing in four parts 14, 15, 16, 17 between which are clamped flexible diaphragms 18, 19, 20 the areas of the upper and lower diaphragms 18, 20 being equal to one another and less than that of the intermediate diaphragm 19. The three diaphragms are rigidly interconnected by means of a vertical spindle 21. Situated in the chamber 22 above the diaphragm 18 is a spring 28 which bears downwardly onto the diaphragm 18, the force exerted being adjustable by means of a screw 29. The chamber 23 between diaphragms 18, 19 communicates through a conduit 31, in which there is an orifice 32, with the chamber 24 between diaphragms 19, 20 and has an inlet 30. A plurality of outlets 33 are formed in the wall of the chamber 24 and each is provided with a valve 34. Each valve 34 (Fig. 6) comprises an adjustable needle valve 35 screwed into an axial bore in a plug 36 which is screwed into the outlet 33, a coil spring 39 between the plug 36 and a non-return valve 38 urging the valve 38 against an annular seating. In operation, the valve 38 remains closed until the pressure within the chamber 24 exceeds a given value, which depends upon the setting of the plug 36, when the valve 38 opens and allows air to escape from the chamber 24 at a rate which depends upon the setting of the needle valve 35. In the wall of the chamber 25 beneath the diaphragm 20 is a bore 40 in which is fitted a nozzle 41 of which the inner end can be closed by the lower end of the spindle 21. A supply conduit 42 provided with a constriction 43 leads into the chamber 25, from which there is an output conduit 44. Air is supplied to the inlet 30 and air from the chamber 23 passes into the chamber 24 through the conduit 31 and orifice 32. In the steady state, the rate at which air enters the chamber 24 through the conduit 31 is equal to the total rate at which air leaks out of the chamber through the outlets 33 and associated valves 34. The air pressure within the chamber 25 represents the output variable and is equal to the pressure at which air is supplied to the conduit 42 less the pressure drop across the constriction 43, and this pressure drop is determined by the rate of escape of air through the nozzle 41 which in turn depends upon the position of the spindle 21. This position is determined by the air pressures within the chambers, 22, 23, 24 and by the setting of the adjusting screw 29.