Patent GB-1389762-A (GB)
Title: Fluid operated apparatus for use in process instrumentation system
IPC: G05B11/44
Filed: 1973-01-17
Abstract: 1389762 Fluid-pressure servomotor systems; fluidic elements FOXBORO CO 17 Jan 1973 [2 Feb 1972] 2391/73 Headings G3H and G3P Fluidic controller for use in process instrumention systems has a flapper valve 14, Fig. 1, having a number of flapper sections 30, 32, 34 integral with a common pivot region, and a cutout region 36 located opposite a fixed support arm 38. The controller produces an output pressure determined by the difference in pressure between a process measurement signal in line 70 and a set pressure signal in line 68. The differential pressure causes the flapper 30, 32, 34 to pivot about axis 22 of its common pivot region to control flow from nozzle 62 and thereby control the back pressure communicated through negative feedback lines 64, 74 and relay 72, whereby the flapper is restored to its equilibrium position. The consequent new output pressure from relay 72 represents the output signal for appropriate adjustment of a process valve. The controller includes means for producing a reset function in its output signal, including a positive feedback circuit through which fluid flows through line 76, a variable reset restrictor 78, tank 84 and damping restrictor 85 to one side of a hinged element 16 controlling the restriction of a vent on its opposite side to produce a pressure on that side equal to the reset pressure for applying a positive feedback via pressure-dropping restrictor 90 and damping restrictor 91. Branch line 93 leading to a second adjustable restrictor 92 provides means for varying the magnitude of the positive feedback pressure. The flapper is of laminar construction comprising a rubber diaphragm 20 sandwiched between two metal plates 12A, 12B. The controller comprises a number of plates and gaskets with numerous flow passages therethrough, secured together with the flapper sandwiched therebetween, Figs. 3A to 31 (not shown). In another embodiment, Figs. 4 and 5, in which the output signal bears a predetermined but adjustable ratio with respect to an input signal, the various sections 106, 118, 120, 122, 124 of the flapper are associated with sealed chambers (140), Fig. 7 (not shown) 142, 144, 146, 148 having inlets 150, 152, 154, 156, 158. Suitable adjustment of valves 160, 162, 164, 166 determines which of the chambers are communicated with pressure line 168 and which are vented to atmosphere, thereby determining the nett input torque to the flapper. The consequent pivoting of the flapper about axis 108 restricts a vent 170 and causes pressure build-up in chamber (140) supplied with pressure fluid via inlet 150 which has a branch line (174), forming the output line of the controller. The area of one flapper section may be one half of that of the next and so on, thereby providing binary-digital input to analog output. Controllable pressure chambers may be provided above the flapper sections as well as below, Figs. 8 and 9 (not shown). For digital applications the input flapper sections may be arranged to move through a relatively large angle between adjustable stops to a zero input torque position or a position of predetermined input torque, Fig. 10 (not shown).