Flow stability reporting system for a liquid chromatography system

An apparatus for testing the flow stability in a column of liquid in a liquid chromatography system comprising:

• means for pumping liquid through the column of said liquid chromatography system using a pump controlled by a control system that generates a control signal in the form of a target pressure which is compared to the actual pressure at said column for purposes of controlling the shaft speed of said pump to obtain a desired flow rate wherein said target pressure is updated one or more times during each revolution;
• means for storing the maximum value and minimum value of said target pressure a plurality of times during each revolution for each of a plurality of revolutions, where the number of revolutions during which the maximum and minimum values are recorded is varied according to the flow rate, where the stored maximum and minimum values represent a measure of a degree of variations of the flow rates of the liquid;
• and
• means for calculating a flow stability criterion using the following formula:
• ##EQU2## wherein:
• max=the maximum of maximum values for said target pressure over all the revolutions for which maximum values were measured since the last calculation of said flow stability criterion;
• min=the minimum of the minimum values for said target pressure over all the revolutions for which minimum values were measured since the last calculation of said flow stability criterion.

A method of measuring flow stability in a liquid chromatography system having a pump and a column comprising the steps of:

• controlling the shaft speed of said pump using a target pressure at the column compared to the actual pressure at the column to control the flow rate by controlling the pump speed;
• measuring the maximum value of said target pressure and the minimum value for said target pressure during each revolution for a plurality of revolutions at the same flow rate;
• recording said maximum and minimum values;
• calculating a flow stability criterion using the following relationship:
• ##EQU3## where, max=the maximum of the maximum values for said control signals over all the recorded values for all the revolutions tested, and
• min=the minimum of the minimum values for said control signals over all the recorded values for all the revolutions tested.