Chromatographic pumping method
First Claim
1. A method of operating a chromatograph in a constant flow rate mode comprising the steps of:
- selecting a rate of flow of liquid into a column;
representing the flow rate in a digital code in terms of a number of pulses for each cycle of a reciprocating pump;
measuring the rate of movement of a piston in the reciprocating pump only in the direction in which it is pumping liquid into a chromatographic column;
filling the cylinder of the reciprocating pump in a stroke in a return direction of the piston with effluent to be pumped into the chromatographic column with a motion in the return direction being controlled by a motor which accelerates starting at a time during the return cycle and ending at a time during a pumping stroke related to the preset rate of flow into the chromatographic column, wherein the rate of acceleration is controlled from a sample and hold circuit representing the motor current;
adjusting the signal in the sample and hold circuit by a value set empirically to avoid cavitation;
the signal being applied to a motor driver circuit to accelerate the motor for a predetermined time controlled by a timer set by the rate of flow; and
causing the flow from the pump to communicate with the inlet of a chromatographic column, whereby a relatively smooth and constant flow of influent into the column is provided.
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Abstract
To provide smooth constant flow from a pump, a chromatographic system comprises: a chromatographic column having an inlet; a pump for supplying fluid to the inlet of the chromatographic column; a power means for the pump motor; positive and negative feedback loop means for controlling said power means; means for energizing and de-energizing said positive and negative feedback control means; said negative feedback control means receiving a signal from said means for measuring flow rate and including means for comparing said signal with said corrected flow rate reference signal while said second feedback loop is energized to generate an error signal controlling said power means; and said positive feedback control means applying an acceleration voltage to said motor from a time a preset period after the initiation of a return stroke of said piston until after a timed duration.
77 Citations
19 Claims
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1. A method of operating a chromatograph in a constant flow rate mode comprising the steps of:
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selecting a rate of flow of liquid into a column; representing the flow rate in a digital code in terms of a number of pulses for each cycle of a reciprocating pump; measuring the rate of movement of a piston in the reciprocating pump only in the direction in which it is pumping liquid into a chromatographic column; filling the cylinder of the reciprocating pump in a stroke in a return direction of the piston with effluent to be pumped into the chromatographic column with a motion in the return direction being controlled by a motor which accelerates starting at a time during the return cycle and ending at a time during a pumping stroke related to the preset rate of flow into the chromatographic column, wherein the rate of acceleration is controlled from a sample and hold circuit representing the motor current; adjusting the signal in the sample and hold circuit by a value set empirically to avoid cavitation; the signal being applied to a motor driver circuit to accelerate the motor for a predetermined time controlled by a timer set by the rate of flow; and causing the flow from the pump to communicate with the inlet of a chromatographic column, whereby a relatively smooth and constant flow of influent into the column is provided. - View Dependent Claims (2)
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3. A method for controlling the speed of a motor which drives a direct displacement reciprocating pump in a chromatographic system having a chromatographic column, comprising the steps of:
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driving a pump at a constant rate of pumping for a first time period; driving said pump with an acceleration during a second time period which acceleration is related to the constant rate of pumping, whereby the rate of acceleration of said rate of pumping is larger for large constant pumping rates than for small constant pumping rates; and controlling the rate of acceleration so as to be below the rate at which cavitation of liquids occurs during a refill portion of a pumping cycle and in which time of acceleration of the pumping action is controlled by a rate of constant flow of liquid to the chromatographic column during a constant flow portion of a pumping cycle.
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4. A method of operating a liquid chromatographic system having a chromatographic column comprising the steps of:
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setting a flow rate; pumping water through said liquid chromatographic system; during a refill signal of a chromatographic pump in said chromatographic system, accelerate a motor and locate an acceleration which does not cause cavitation and reduces noise and is as high as possible; pump fluid during a delivery stroke at said preset flow rate; at a predetermined time after the end of the delivery stroke begin accelerating the motor and continue accelerating at a rate below a preset maximum rate of cavitation but adjusted for flow rate speed and for a time duration related to the flow rate; and when said time duration is completed, terminate acceleration and continue pump motion at said preset flow rate, whereby said acceleration may continue into a pumping stroke or terminate below a pumping stroke to minimize pulsations in an output flow from the chromatographic pump.
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5. A method of operating a chromatographic system having a pump motor and chromatographic column, said pump motor having a rate of acceleration, comprising the steps of controlling the speed of the pump motor during a first time period at a rate which results in a constant flow rate into the chromatographic column;
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controlling the speed of the pump motor in a second time period at a rate which avoids cavitation during refilling of the pump and for a time period that is related to the rate of pumping during the first period and in which the motor pumps with a pumping cycle portion and a refilling cycle portion for a duration of the first time period related to the rate of acceleration and for a second time period to cause the flow into the pump during the refilling cycle to be equal to the flow out of the pump during the pump cycle. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification