GB860485A - Improvements in or relating to automatic force balance apparatus - Google Patents

Abstract

860,485. Fluid-pressure servomotor-control systems. FOXBORO-YOXALL Ltd. April 20, 1959 [March 26, 1958], No. 9760/58. Class 135. An automatic force balance device for producing an output signal bearing a predetermined relationship to an input signal, comprises a lever mounted to rock about a fulcrum, means for applying two forces arranged to rock the lever in one direction about the fulcrum, means for applying two further forces arranged to rock the lever in the opposite direction about the fulcrum which is adjustable relative to the points of application of the forces, three of the force applying means being interconnected by means including at least one time delay device so as to transmit the input or output signal and the fourth force applying means serving to transmit the output or input signal respectively, the output signal being determined by means responsive to the position of the lever. In the first example, Fig. 1, the lever 1 is acted on by four bellows A, B, C, P at points 3 and 4 between which the fulcrum 2 is adjustable. The input signal is fed to bellows A which is connected via at least one variable resistor R to bellows B and C. The lever extension 12 cooperates with a nozzle 13, the back pressure of which constitutes the output signal and is fed to the bellows P via the relay 10. The position of the fulcrum 2 determines the gain and the phase angle of the output signal for input signals of a frequency within a limited range. In another embodiment, Fig. 6, the position of the fulcrum 2 is determined by a signal representing the error or a function of the error in the associated control loop and applied to the bellows 18. In order that this latter signal may be independent of the direction of the error, the use of the device illustrated in Fig. 27 is suggested. This device comprises a desired value bellows 30 and a measured value bellows 31 which position a lever 32 connected through the linkage 34, 38, 39, 40, 42 to the pneumatic relay 45. In another example, Fig. 18, an additional RC network is inserted between the relay 10 and the bellows P whereby the gain is multiplied by a predetermined factor. Specifications 670,427, 740,179, 740,238, 764,660 and 827,207 are referred to.