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Apparatus for controlling a pump to account for compressibility of liquids in obtaining steady flow

  • US 4,797,207 A
  • Filed: 09/30/1986
  • Issued: 01/10/1989
  • Est. Priority Date: 09/30/1986
  • Status: Expired due to Term
First Claim
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1. An apparatus for causing controlled flow of a solvent composition through a liquid chromatography column comprising:

  • means for pumping a solvent composition comprised of one or more solvents through said column at a constant pressure determined by a pressure control signal including a dual piston pump means for pumping said solvent composition at a pressure determined by said pressure control signal where said dual pistons each have their own cylinder and are driven by the same rotating shaft and an associated drive mechanism such that said pistons have an associated overlap interval in the rotation of said rotating shaft during which both pistons are pushing said solvent composition out their respective cylinders, and where each piston has an intake interval in the rotation of said rotating shaft during which said solvent composition is being drawn by each respective piston into the associated cylinder, said intake interval including a linear interval defined by a constant piston velocity, and further including control means including transducer means for detecting data indicating the actual pressure at the output of said means for pumping, said control means for comparing the actual pressure detected by said transducer means to the desired pressure as determined by said pressure control signal and for controlling the speed of rotation of said rotating shaft during intervals including said overlap interval such that the actual pressure at the output of said means for pumping equals the desired pressure; and

    computer means for for receiving data defining the desired flow rate and for determining a correction factor determined by the compressibility of the solvent composition by computing the ratio of the duration of a first interval during which said rotating shaft is moving said pistons through said overlap interval for the current solvent composition and the current actual constant pressure to the duration of a second interval during which said rotating shaft is moving said pistons through said overlap interval for incompressible solvent pumped at a constant pressure, each said first and second intervals being normalized to the time it takes said rotating shaft to rotate through a predetermined angle during which the corresponding one of said pistons moves during the corresponding one of said respective linear intervals, where said predetermined angle is equal to the angle through which said rotating shaft moves while said pistons are in said overlap interval, and said computer means for subtracting one from each said normalized first and second interval before computing said ratio and for multiplying said ratio times a volume factor equal to the amount of volume displaced by one of said pistons during said overlap interval to derive a product and for subtracting said product from said volume factor to derive said correction factor, and for updating said pressure control signal by multiplying the value of the old pressure control signal times the quantity equal to the correction factor plus 1.

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