GB850221A - Improvements in or relating to pneumatic force-balance controllers - Google Patents

Abstract

850,221. Fluid-pressure servomotor-control systems. CHELTENHAM AUTO CONTROLS Ltd. Dec. 24, 1956 [Dec. 23, 1955], No. 36872/55. Class 135. A pneumatic force-balance controller 10 comprises a sensing device 12 to which a gas pressure of the desired value is applied in direct opposition to the signal or measured value pressure so that deviation between the two pressures causes movement of an element 19, 19a to vary the gap 36 at the tip of a nozzle 32 which is fed with 'compressed air. The resulting variable nozzle pressure is transmitted via relay valve means 13 to a pneumatic regulator 49. The desired value pressure enters the controller 10 'through the port 30 and acts on the outside of bellows 15 to the inside of which the measured value pressure is applied via port 31. Attached to the bellows 15 is a rod 19 which upon movement of the bellows varies the gap 36 at the nozzle 32 which is supplied with air at constant pressure via a restriction 34 and bleeds to atmosphere via passage 28. The nozzle pressure is thus varied in accordance with the relationship between the desired value and measured value pressures and is applied to the outside of a bellows 39, 40 in a chamber 37. The inside of the bellows 39, 40 has an inlet valve 44 supplied from the constantpressure source and an outlet valve 47 exhausting to atmosphere via passage 48. Upon increase of nozzle pressure consequent on increase of the measured value pressure the bellows plate 40 is moved upwardly to open the inlet valve 44 so that the pressure in the bellows 39 builds up and upon decrease of nozzle pressure the exhaust valve 47 is opened to reduce the pressure in bellows 39 which is connected via pipes 46, 50 to the regulating unit 49. The lower end of the rod 19 is attached to a proportioning bellows 21, 22 in a chamber 51. The bellows 21, 22 is connected to the output from bellows 39. A variable proportion of this output pressure, obtained by a fixed restrictor 53 and a variable needle valve 54, is applied to the chamber 51. Integral action is obtained by a restrictor and capacity 59, 60, respectively, the pressure in the capacity 60 acting on a diaphragm 65 to vary the proportional pressure fed to the chamber 51. Sealing bellows 23, 24, 25 and 41 constitute exhaust channels.