GB721779A - Improvements in fluid-pressure analogue computers - Google Patents

Abstract

721,779. Fluid-pressure. servomotor control systems. FOXBORO CO. May 22, 1952, No. 13055/52. Class 135. An analogue computer includes a fluidpressure-responsive device for applying an indication of the value of a variable to a lever which constitutes the baffle-plate of a nozzlebaffle leak valve, a pressure-responsive means for applying the nozzle back pressure to the lever as a negative feed-back, and a resilient element co-operating with one of the pressureresponsive devices in such manner that the moment applied to the lever by the pressure in question is modified variably over the operating range. The invention is described in connection with the determination of the heat removed from an air stream in passing through a process unit, the final result being given by the computer from automatic measurements by sensing elements of the rate of flow of the air stream, its static pressure and temperature, and the temperature difference in the air stream across the process unit. A pressure corresponding to the linear value of a variable is applied to the inside of a bellows 33, Fig. II, which acts on a lever 28, pivoted at 29 ; and the response due to the pressure can be varied by adjusting the bellows along a slot 38 parallel to the lever. The lever acts as a baffle plate for a nozzle 53 which is supplied with pressure air from a pipe 55 past a restriction 56. The ensuing output pressure, i.e. the back pressure at the nozzle, is taken off at 57 and is also applied to act on a bellows 44, the latter being connected by a leaf spring 50 to the lever to give to the latter a neutralizing or balancing effect. As the pressure acting on bellows 44 increases, spring 50 contacts screw abutments 51 in succession so that the value of the output pressure will follow a function differing from the linear function of the value of the input pressure. In the embodiment described, the abutments are adjusted to an output which is a logarithm of the input to any convenient base. In a construction where the absolute pressure is required, the input pressure is applied to a bellows of which the free end, besides being connected to the lever, also constitutes the movable end of an absolute pressure bellows, the feed-back pressure is applied to the inside of the balancing bellows, and the lever is adjustably loaded by a further leaf spring. Where the input comprises two variables, e.g. the differential pressures obtained when the air stream is passed through an orifice, these two pressures are applied to similar bellows acting on opposite sides of the lever 28. The bases chosen for the logarithmic functions followed by the various output pressures may vary from variable to variable, but the output pressures are all combined to give a single, final output following a logarithmic function in a device comprising a lever 77, Fig. VI, acted on by bellows 79-81, the lever constituting a baffleplate to a nozzle 95 supplied with fluid under pressure from a line 96, past a restriction 96a. The output pressure taken off at 98 is also applied to a bellows 93 to act on the lever 77 to neutralize or balance the latter.