Device for controlling a piston pump unit for liquid chromatography
First Claim
1. A device for controlling a piston pump unit for liquid chromatography comprising:
- (a) two phase-offset cyclically working piston-cylinder units that include two pistons, which produce a predefined flow of a liquid medium to be delivered at an outlet port, wherein a system pressure results at the outlet port, wherein, in a pre-compression phase of one cycle of at least one of the piston-cylinder units, an at least partially adiabatic compression of the medium from a starting pressure to the system pressure occurs, and wherein, in a following delivery phase of the one cycle, in which the flow is also determined by the piston-cylinder units, the medium, which is adiabatically heated during the pre-compression phase, is cooled during a transition phase of the delivery phase of the one cycle;
(b) a pressure sensor located within at least one of the piston-cylinder units configured to detect the pressure of the medium in a cylinder volume of the at least one of the piston-cylinder units; and
(c) a processor-controlled control unit, whichactivates a drive device for the two piston-cylinder units with respect to a speed, at which the two pistons of the piston-cylinder units are moved,detects a pressure of the medium in the cylinder volume of the at least one of the piston-cylinder units during the pre-compression phase of the one cycle in which a cooling of the adiabatically heated medium occurs,detects the pressure of the medium in the cylinder volume of the at least one of the piston-cylinder units during an initial phase of the pre-compression phase of the one cycle, in which substantially no heating of the medium by the adiabatic compression has yet occurred, and extrapolates a pressure profile as a function of a time or a position of the piston, and calculates a time t1 or a position of the piston xi, at which the extrapolated pressure profile, which represents an isothermal profile, reaches a value for the system pressure which would result in an idealized isothermal compression at an end of the pre-compression phase,ascertains a time t2 or a position xii of the piston at which the pre-compression phase is ended, andcontrols a piston speed of the two piston-cylinder units during the transition phase of the one cycle depending on at least one characteristic that includes a difference of the time t1 and the time t2 or a difference of the position xi and the position xii, such that variations of the system pressure as a result of the cooling of the adiabatically heated medium are at least partially compensated for.
1 Assignment
0 Petitions
Accused Products
Abstract
A control device of a piston pump unit comprising at least two piston-cylinder units that operate in a phase-shifted manner for the purpose of liquid chromatography and to a piston pump unit is described. The control device corrects fluctuations of the system pressure while switching from one piston cylinder unit to the respective other piston cylinder unit. The fluctuations can occur as a result of the cooling of the liquid medium that is heated in an adiabatic manner during a pre-compression phase in the working piston. The control unit controls the piston speed of at least one piston-cylinder unit during the transition phase depending on at least one characteristic, which is ascertained from chronologically previously detected pressure values, such that variations of the system pressure as a result of the cooling of the adiabatically heated medium are at least partially compensated for.
26 Citations
8 Claims
-
1. A device for controlling a piston pump unit for liquid chromatography comprising:
-
(a) two phase-offset cyclically working piston-cylinder units that include two pistons, which produce a predefined flow of a liquid medium to be delivered at an outlet port, wherein a system pressure results at the outlet port, wherein, in a pre-compression phase of one cycle of at least one of the piston-cylinder units, an at least partially adiabatic compression of the medium from a starting pressure to the system pressure occurs, and wherein, in a following delivery phase of the one cycle, in which the flow is also determined by the piston-cylinder units, the medium, which is adiabatically heated during the pre-compression phase, is cooled during a transition phase of the delivery phase of the one cycle; (b) a pressure sensor located within at least one of the piston-cylinder units configured to detect the pressure of the medium in a cylinder volume of the at least one of the piston-cylinder units; and (c) a processor-controlled control unit, which activates a drive device for the two piston-cylinder units with respect to a speed, at which the two pistons of the piston-cylinder units are moved, detects a pressure of the medium in the cylinder volume of the at least one of the piston-cylinder units during the pre-compression phase of the one cycle in which a cooling of the adiabatically heated medium occurs, detects the pressure of the medium in the cylinder volume of the at least one of the piston-cylinder units during an initial phase of the pre-compression phase of the one cycle, in which substantially no heating of the medium by the adiabatic compression has yet occurred, and extrapolates a pressure profile as a function of a time or a position of the piston, and calculates a time t1 or a position of the piston xi, at which the extrapolated pressure profile, which represents an isothermal profile, reaches a value for the system pressure which would result in an idealized isothermal compression at an end of the pre-compression phase, ascertains a time t2 or a position xii of the piston at which the pre-compression phase is ended, and controls a piston speed of the two piston-cylinder units during the transition phase of the one cycle depending on at least one characteristic that includes a difference of the time t1 and the time t2 or a difference of the position xi and the position xii, such that variations of the system pressure as a result of the cooling of the adiabatically heated medium are at least partially compensated for. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
Specification