US3985467A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Constant pressure pump
Assignee: LDC Analytical Inc
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Filing: 1975-05-27
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Granted: 1976-10-12
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Expires: 1995-05-27
Abstract
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.
Inventors
- 👤 Peter Lefferson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 02:52
CPC Classifications
G; G05; G05D; G05D16/00; G05D16/20; G05D16/2006; G05D16/2066; F; F04; F04B; F04B49/00; F04B49/06; F04B2205/00; F04B2205/05
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
190 words
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.
Claim 2
Dependent Claim
190 words
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.
Claim 3
Dependent Claim
24 words
The control system recited in claim 1 wherein said set point signal is applied to control the gain of said first variable gain amplifier.
Claim 4
Dependent Claim
24 words
The control system recited in claim 1 wherein said actual pressure signal is applied to control the gain of said first variable gain amplifier.
Claim 5
Dependent Claim
52 words
The control system recited in claim 1 further comprising: a minimum gain loop connected in parallel with said first and second variable gain amplifiers and between said error amplifier and said motor, said minimum gain loop providing a small fixed gain between said error amplifier and said motor to facilitate motor startup.
Claim 6
Dependent Claim
65 words
The control system recited in claim 4 further comprising a second minimum gain loop connected in parallel with said second variable gain amplifier and between the output of said first variable gain amplifier and said motor, said second minimum gain loop thereby coupling the output of said first variable gain stage to said motor when said second variable gain stage is off during motor startup.
Claim 7
Dependent Claim
22 words
The control system recited in claim 1 wherein said first variable gain stage includes a transconductance amplifier controlled by input bias current.
Claim 8
Dependent Claim
43 words
The control system of claim 1 in combination with a metering pump comprising: a cylinder having a piston reciprocating therein, said cylinder having inlet and outlet ports, said piston transferring quantities of liquid between said inlet and said outlet as said piston reciprocates.
References Cited (Backward Citations)
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-10-12 | 1980-04-12 | 1980-10-12 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-10-12 | 1984-04-12 | 1984-10-12 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-10-12 | 1988-04-12 | 1988-10-12 | $7700.00 | Window Closed / Lapsed |