US 3,985,467 AGranted

Constant pressure pump

AssigneeMilton Roy Company

InventorPeter Lefferson

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Abstract

A controller maintains a constant desired fluid pressure in a fluid load driven by a variable flow fluid pump with a variable speed motor. A set point signal representing desired pressure and a signal from a pressure transducer representing actual pressure are applied to an error amplifier. The resulting error signal is applied through a variable gain stage to the motor control. The variable gain stage includes first and second variable gain amplifiers the first of which has a gain which is controlled inversely to pressure. The second variable gain amplifier has a gain which is controlled in proportion to flow. In this manner, the gain of the controller changes in inverse proportion to the restriction of the fluid load. This makes the performance of the controller independent of changes in the fluid load by keeping the total loop gain constant.

Claims7

Dependent claims

A control system for maintaining a constant desired fluid pressure in a fluid load driven by a variable flow fluid pump having a variable speed motor comprising:

means for generating a set point signal representing said desired pressure;
a pressure transducer responsive to said fluid load for generating an actual pressure signal;
an error amplifier, said set point signal and said actual pressure signal being applied to said error amplifier to produce an error signal;
a variable gain amplifier stage including first and second variable gain amplifiers, said error signal being applied to said variable gain stage, the output of said variable gain stage being applied to control the speed of said motor, a signal proportional to pressure being applied to said first amplifier to change the gain thereof in inverse proportion to said pressure;
and
means for generating a signal representing fluid flow in said load, said signal representing flow being applied to said second variable gain amplifier to control the gain thereof in proportion to said flow so that the gain of said amplifier stage is controlled in inverse proportion to the variable restriction of said fluid flow.

3 more elements

Dependencies are inferred from the claim text.