DEVICE FOR CONTROLLING A PISTON PUMP UNIT FOR LIQUID CHROMATOGRAPHY

• US 20140193275A1
• Filed: 07/02/2012
• Published: 07/10/2014
• Est. Priority Date: 08/19/2011
• Status: Active Grant

• Current Assignee: Dionex Softron GmbH (Thermo Fisher Scientific Incorporated)
• Original Assignee: Dionex Softron GmbH (Thermo Fisher Scientific Incorporated)
• Inventors: Strobl, Christoph
• Granted Patent: US 10,801,479 B2
• Time in Patent Office: Days
• US Class Current: 417/12
• CPC Class Codes: F04B 11/0058 with piston speed control
• CPC Class Codes: G01N 2030/324 speed, flow rate
• CPC Class Codes: G01N 2030/326 pumps
• CPC Class Codes: G01N 30/34 of fluid composition, e.g. gradient G01N30/36 takes precedence
• CPC Class Codes: G01N 30/36 in high pressure liquid systems

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.

Claims

1. A device for controlling a piston pump unit for liquid chromatography comprising:

(a) at least two phase-offset cyclically working piston-cylinder units, 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,

(b) 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, in which the flow is also determined at least by the piston-cylinder unit, the medium, which is adiabatically heated during the pre-compression phase, is cooled during a transition phase of the delivery phase, and

(c) a control unit, which activates a drive device for the at least two piston-cylinder units with respect to the speed, at which the pistons of the piston-cylinder units are moved,

(d) the control unit detects a pressure of the medium in at least one of the piston-cylinder units during the pre-compression phase or during a part of the delivery phase in which a cooling of the adiabatically heated medium occurs,

(e) 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.

2. The device as claimed in claim 1, in that the control unit, while using the at least one characteristic, ascertains a correction guideline for the control of the piston speed of at least one of the piston-cylinder units during the transition phase, which determines the flow during the transition phase, wherein the correction guideline is superimposed by addition on an activation guideline for the piston, where the activation guideline does not include a compensation of the cooling of the adiabatically heated medium.

3. The device as claimed in claim 2, in that the correction guideline comprises a decreasing exponential function, the function including v_k=c·

exp [(t−

t₂)/τ

] or v_k=c·

exp [(x−

x_II)/ε

], wherein v_k designates the correction guideline to correct a piston speed of at least one of the piston-cylinder units, t designates a time, t₂ designates a chronological beginning of the transition phase of the delivery phase, c designates an amplitude of the function at the point in time t=t₂, τ

designates a time constant of the function, x designates a position of the piston, and x_II designates a starting position for the transition phase of the delivery phase.

4. The device as claimed in claim 2 in that the correction guideline further comprises a substantially ramped or stepped function, which has a stepped or ramped increase, a middle region having a substantially constant value of a determined maximum amplitude, and a stepped or ramped decrease in the piston speed.

5. The device as claimed in claim 4, in that a front flank of the ramped or stepped function is associated with a predefined piston position.

6. The device as claimed in claim 3 in that the control unit

(f) detects the pressure of the medium in a cylinder volume of a compressing piston-cylinder unit in an initial phase of the compression phase, in which substantially no heating of the medium by the adiabatic compression has yet occurred, and extrapolates the pressure profile as a function of the time or the position of the piston, and calculates a point in time t₁ or a position of the piston x_I, at which the extrapolated pressure profile, which represents an isothermal profile, where the pressure reaches a value for the system pressure which would result in an idealized thermal compression at an end of the compression phase,

(g) ascertains a point in time t₂ or a position x_II of the piston at which the pre-compression phase is ended, and

(h) uses, as the characteristic for determining at least one parameter of the correction guideline, a difference of the calculated time t₁ and the detected time t₂ or the difference of the calculated position x_I and the detected position x_II.

7. The device as claimed in claim 6, in that the control unit determines the point in time t₁ or the position of the piston x_I, at which the extrapolated pressure profile reaches the value for the system pressure which would result in the idealized, thermal compression at the end of the compression phase, detects the system pressure of the medium at the outlet of the pump unit in a range before the beginning of the delivery phase depending on the time or on the position of the piston and extrapolates it, and determines the intersection point of this extrapolated curve for the system pressure with the calculated curve, which represents the isothermal profile, for the pressure in the relevant volume of the compressing piston-cylinder unit.

8. The device as claimed in claim 6, in that the control unit determines the point in time t₁ or the position of the piston x, uses a constant value for the system pressure, which is supplied to the control unit or which the control unit detects during the compression phase.

9. The device as claimed in claim 8, in that,

(i) the control unit determines the point in time t₂ or the position x_II of the piston, detects the pressure during the pre-compression phase in a range in which an adiabatic heating occurs before the end of the compression phase, and extrapolates the pressure profile,

(j) the control unit detects the system pressure of the medium at the outlet of the pump unit, in a range before the beginning of the delivery phase and extrapolates it, and

(k) the control unit determines the point in time t₂ or the position x_II of the piston from the intersection point of the two extrapolated curves for the system pressure and the pressure in the volume of the piston-cylinder unit,

(l) wherein the control unit ascertains the correction guideline to control the drive device during a directly following delivery phase.

10. The device as claimed in claim 2, in that the control unit

(f) detects the system pressure of the medium during the transition phase, in which the cooling of the medium heated during the compression phase occurs, and

(g) uses a deviation of the system pressure, which is detected during the transition phase, from an idealized system pressure as the characteristic for determining at least one parameter of the correction guideline.

11. The device as claimed in claim 10, in that the control unit determines the idealized system pressure during the transition phase according to one where:

(h) the control unit uses a constant value for the system pressure, which is supplied to the control unit or which the control unit detects during the compression phase, or

(i) the control unit detects the system pressure of the medium, at the outlet of the pump unit, in a range before the beginning of the delivery phase and extrapolates the pressure profile.

12. The device as claimed in claim 11, in that the control unit determines a maximum deviation of the detected system pressure from the idealized system pressure and determines at least one parameter of the correction guideline based on the maximum deviation.

13. The device as claimed in claim 12, in that the control unit uses the correction guideline ascertained in the control of the drive device during at least one delivery phase, which follows the delivery phase, the transition phase of which is used to determine the at least one parameter of the correction guideline.

14. The device as claimed in claim 13, in that the control unit determines the value of the at least one parameter iteratively in such a manner that in transition phases of successive cycles, one value for the parameter is determined and combined by a computer.

15. (canceled)

16. (canceled)

17. A method to control a piston pump for liquid chromatography, the piston pump including at least two phase-offset cyclically working piston-cylinder units, which produce a predefined flow of a liquid medium to be delivered at an outlet port, wherein a constant system pressure results at the outlet port, the method comprising:

in a pre-compression phase of one cycle of at least one of the piston-cylinder units, compressing a piston in the piston-cylinder unit;

measuring a first pressure at a first time and a second pressure at a second time during the pre-compression phase in which an adiabatic heating effect is negligible in the piston-cylinder unit;

extrapolating the first pressure at the first time and the second pressure at the second time to determine a calculated time in which the pressure of the piston-cylinder unit will be at the constant system pressure;

determining a detected time in which the pressure of the piston-cylinder unit is measured with a pressure sensor to be at the constant system pressure;

calculating a time difference based on the calculated time and the detected time; and

calculating a first correction amplitude of the piston speed for at least one piston-cylinder unit based on the time difference.

18. The method of claim 17 further comprising:

opening an outlet valve on the piston-cylinder unit when the pressure of the piston-cylinder unit is at the constant system pressure to begin a delivery phase;

applying a first corrected piston speed to at least one piston-cylinder unit during the delivery phase, in which the delivery phase is subsequent to the pre-compression phase, the first corrected piston speed is based on the calculated first correction amplitude of the piston speed.

19. The method of claim 17, in which a piston speed is constant during the pre-compression phase.

20. The method of claim 17, in which the first pressure ranges from 2 MPa to 10 MPa and the second pressure ranges from 10 MPa to 20 MPa.

21. The method of claim 17, in which the calculated first correction amplitude of the piston speed is based on a decreasing exponential function.

22. The method of claim 21, in which the decreasing exponential function comprises an equation, the equation including:

v_k=c·

exp [(t−

t₂)/τ

]

wherein v_k is the first corrected piston speed for at least one of the piston-cylinder units, c is the first correction amplitude of the piston speed, t is a time, t₂ is the detected time, τ

is a time constant.

23. The method of claim 21, in which the decreasing exponential function comprises an equation, the equation including:

v_k=c·

exp [(x−

x_II)/ε

],

wherein v_k is the corrected piston speed for at least one of the piston-cylinder units, c is the first correction amplitude of the piston speed, x is a position of the piston, and x_II is a position of the piston at the detected time.

24. The method of claim 17 further comprising

calculating a second correction amplitude of the piston speed based on a characteristic selected from the group consisting of a magnitude of the first correction amplitude, the constant system pressure, and a combination thereof.

25. The method of claim 24 further comprising:

applying a second corrected piston speed to at least one piston-cylinder unit during the delivery phase, the second corrected piston speed is based on the calculated second correction amplitude of the piston speed.

26. The method of claim 25, in which the calculated second correction amplitude of the piston speed is based on a stepped or rectangular function.

27. A method to control a piston pump for liquid chromatography, the piston pump including at least two phase-offset cyclically working piston-cylinder units, which produce a predefined flow of a liquid medium to be delivered at an outlet port, the method comprising:

in a first pre-compression phase of one cycle of at least one of the piston-cylinder units, compressing a piston in the piston-cylinder unit;

measuring a pressure profile at the outlet port during the pre-compression phase, wherein a system pressure at the outlet port increases linearly;

opening an outlet valve on the piston-cylinder unit to begin a first delivery phase of the liquid medium;

linearly extrapolating the pressure profile at the beginning of the first delivery phase;

calculating a first pressure difference between the linearly extrapolated pressure profile at the beginning of the first delivery phase and a measured system pressure during the first delivery phase; and

calculating a first correction amplitude of the piston speed based on the first pressure difference.

28. The method of claim 27 further comprising:

applying a first corrected piston speed to at least one piston-cylinder unit during the first delivery phase, in which the first delivery phase is subsequent to the pre-compression phase, the corrected piston speed is based on the calculated first correction amplitude of the piston speed.

29. The method of claim 28 further comprising:

in a second pre-compression phase of one cycle of at least one of the piston-cylinder units, compressing the piston in the piston-cylinder unit;

opening the outlet valve on the piston-cylinder unit to begin a second delivery phase of the liquid medium;

linearly extrapolating the pressure profile at the beginning of the second delivery phase;

calculating a second pressure difference between the linearly extrapolated pressure profile at the beginning of the second delivery phase and a measured system pressure during the second delivery phase; and

calculating a second correction amplitude of the piston speed based on the second pressure difference;

adding the first correction amplitude and the second correction amplitude to form a summation; and

applying a second corrected piston speed to at least one piston-cylinder unit during the second delivery phase, in which the second delivery phase is subsequent to the second pre-compression phase, the second corrected piston speed is based on the summation.