Patent GB-1344278-A (GB)
Title: Method and devices for regulating the pressure and its rate of variation in a chamber
IPC: G05D16/20
Filed: 1971-04-19
Abstract: 1344278 Automatic control of pressure; fluid pressure servomotor systems SOC NATIONALE INDUSTRIELLE AEROSPATIALE and SEMCA SOC ANON DES ATELIERS SEMCA 19 April 1971 [4 Feb 1970] 20756/71 Heading G3P and G3R In a method of regulating the pressure in an aircraft cabin &c. to which air or other pressure fluid is continuously supplied and which is situated in an atmosphere of variable pressure, the control is obtained from a single pressure sensor 1, Fig. 1 within the chamber which provides an electrical output proportional to the sensed pressure, the output being used to generate a control signal for at least one electric torque motor a valve which vents the chamber to atmosphere. In the embodiment described the sensor 1 may be of the membrane type functioning on the differential electrical capacitance principle to modulate the current from a 100 kHz oscillator 2a providing one input to a summing amplifier 15 from which a "corrected error signal" output controls the motor 29 through a further control amplifier 28 Fig. 2, modulator (30) Fig.3 (not shown) and tuned "power amplifier" (31). A valve position sensor 18a provides a feed-back control to the amplifier 28 in a circuit which includes rate gain and position gain potentionmetric circuits 25, 26 and a differentiating feed-back circuit 60, 24 whereby the control of the motor 29 is electrically damped to provide linearised progressive control. The pressure sensor 1 in Fig. 1 may alternatively consist of a strain-gauge bridge on a pressure sensitive membrane producing variable D.C. current proportional to the pressure and coupled directly to a preamplifier 3. Sensor temperature compensation may be obtained by a unit 4. The output is fed through a differentiating amplifier 5 and filtering amplifier 6 to provide one input to the summing "error signal" amplifier 15. A second input is provided via a further differentiating amplifier 7 to give an "anticipation signal". The third input to the amplifier is a "corrected preset rate signal" initiated by a D.C. signal from a pressure preset circuit 9 operating in conjunction with a compensating amplifier 8 and switching relays 10, 11 to provide inputs to an "adding and rate presetting adjustable potentiometric circuit 13. The servomotor may control a butterfly valve, but in the particular embodiment applied to a system used to control the pressure in an aircraft cabin by the movements of a pneumatic servo-control valve, Fig. 4, the electric torque motor 29 opens or closes jets 37, 38 associated respectively with the higher pressure in the chamber to be controlled and with a preset lower pressure as determined by an over-pressure valve 40. Controlled opening of the jets 37, 38 varies the pressure in valve chamber 43 whereby movable bell-shaped valve plate 43b mounted on guide rod 43j sealed by flexible annular membranes 43e, 43h, may open against spring 43s to vent the pressurised chamber through grid space 43f and venturi 52. The underside of plate 43b is maintained at the pressure of the chamber through vents 43i. The plate 43b is coupled to a position sensor 18a forming part of the feed-back circuit. Fig. 2 The valve plate 43b may also be forcibly opened and closed by a power operated means comprising rack and pinion system 46, 46a driven by a separate electric motor (not shown), the rack being held in the open position by a latch 49 under the control of a microswitch 53 when the aircraft cabin is to be ventilated on the ground with its doors open. The microswitch 53 also controls reversing of the motor driven rack and pinion system 46, 46a whereby in the event of the aircraft alighting on the sea the rack 46a may be driven to an irreversibly locked position to hold the valve 43b against water pressure. Capsule valves 45, 47 mounted on the fixed top plate 43a with their capsules connected to the pressurised chamber and their casings vented to the external atmospheric are provided to limit the chamber pressure to a preset excess overpressure and automatically vent the valve chamber 43 to the low pressure system 40 and thereby cause the valve 43b to open . A capsule or bellows valve 48 vented internally to atmosphere and having its casing connected to the pressurised chamber similarly prevents underpressure in the pressurised chamber. In this event the valve 48 opens to vent the chamber 43 to the controlled pressurised chamber whereby the valve 43b is caused to close. Further since the vent passageways are of larger crosssection than that of the total cross-sections communicating with the low pressure system 40 the valve 43b remains closed below a preset altitude. Valve 43b is further caused to open automatically in the event of a rapid descent of the aircraft when the pressure in the cabin becomes lower than the outside pressure. In this event check valve 42 closes and the valve chamber 43 is connected to the cabin interior via valve 39, the lower pressure system no longer being operable. The valve 43b is thereby caused to open due to the external pressure acting on plate 51 which engages the underside of plate 43b.