GB699065A - Improvements in air operated automatic controller mechanisms - Google Patents

Abstract

699,065. Fluid-pressure servomotor-control systems. KENT, Ltd., G. March 24, 1948 [March 28, 1947], No. 7255/52. Divided out of 699,011. Class 135 An air pressure controller mechanism of the integral and proportional, or integral, proportional and derivative type, has means for influencing the pilot valve, e.g. a flapper controlling a nozzle. by a movement derived from the pressure in the integral bellows whereby the offset is substantially eliminated. A meter float 2 actuates, through one end 2A of a floating lever 1 and sensitivity adjusting link 5, a flapper 4 controlling a nozzle 3 fed with pressure air at 12 through a resistance 13, for controlling, e.g. a liquid level by a valve 11. The other end 2B of the lever is moved through a link 19 and bell-crank 14, 18, by a bellows 6, one side of which, fed with air at 8, provides a proportional chamber, and the other side, fed through an integral resistance 9, provides an integral chamber. A derivative resistance 10 may be incorporated as shown. Normally when a prolonged error is counteracted, the meter float detects a small offset in the controlled variable which slightly displaces the flapper in the nozzle throttling range in order to produce the control effect. In the invention, no offset is needed because the flapper is slightly displaced by being fulcrumed on a frame 21 which is pivoted about the .point 22 by a diaphragm, bellows or Bourdon tube 23 having a preselected spring rate and pressure-fed from the integral bellows.