DD286299A5 - METHOD FOR CONTROLLING THE RENDER RATE OF HPLC PUMPS - Google Patents

Abstract

The invention relates to a method for controlling the delivery rate of HPLC pumps. According to the invention, the compression phase is divided into a phase of compression within the cylinder and a phase of delivery into the system and from the time of commencement of the phase of compression within the cylinder the volume increments resulting from the piston movement are counted up to the time of delivery into the system and saved. The beginning of this is determined by the time of the minimum pressure in the system and from the known size of the volume step, multiplied by the number of stored steps, relative to the cylinder volume, the effective compression of the liquid at the current working pressure and determined with this Groesze for the promotion reduces the applicable frequency. Thus, an exact correction of the Foerderrate is achieved with little effort. FIG {HPLC; Pump; Cam; Stepper motor; Pump control; Volume step; Promotion; Print; Compression; intake}

Description

For this 1 page drawing

Field of application of the invention

The invention relates to a method for controlling the delivery rate of HPLC pumps, in particular for single-piston pumps with a greatly reduced intake time

Characteristic of the known state of the art

In single-piston pumps with a cylinder containing the liquid and a piston movable in this cylinder, which is usually controlled by a cam disc, a distinction is made between an intake phase, a compression phase and a delivery phase.

At the higher pressures required by HPLC, as well as in pumps with increased demands on the accuracy of the actual delivery rate, the compressibility of the fluid in the system has a negative effect and must be corrected.

For this purpose, it is known to measure the pressure during the compression phase in the cylinder and thus to realize an electronic real-time compressibility compensation (Beckmann Bulletin 3-5953, Bulletin ^ ^r i-7396).

This technical solution has the disadvantage that in the cylinder a special measuring device must be atied, so that the pressure curve can be detected during the compression phase. This measuring device requires the highest precision and is very expensive.

Object of the invention

The aim of the invention is to increase the accuracy of the delivery rate and to reduce the technical effort required for this purpose.

Explanation of the essence of the invention

The invention is based on the object to derive characteristic values from the pump cycle in a simple manner and to use these to control the delivery rate.

According to the invention, this is achieved by dividing the compression phase into a phase of compression within the cylinder and a phase of delivery into the system with each delivery cycle and from the time of commencement of the phase of compression within the cylinder those resulting from piston movement Volume increments are counted and stored by the time of promotion into the system. The beginning of the phase of delivery into the system is determined by the time of the minimum pressure in the system and from the known size of the volume step multiplied by the number of stored steps relative to the cylinder volume becomes the effective compression of the fluid at the current working pressure determined and reduced with this size d <e promotion rate.

It has been found that, at the time of commencement of production into the system, the pressure reading downstream of the system Exhaust valve of the pump has a minimum and this time is so easy to determine, for. B. by using a Pressure transducer with Bourdon tube. It is possible to calculate the number of volume steps resulting from the pumping rate and the number of actual, real ones Represent volume steps as analog values and perform the comparison of these two values in analog form. It is advantageous to determine the compressibility from the effective compression in a known manner, to monitor and

if a tolerance stored in the memory is exceeded, a warning signal is triggered.

The inventive method allows for minimal technical effort high accuracy of Pump delivery. The method automatically considers the currently given pressures and therefore does not require any

manual intervention.

Ausführungsheispiel The invention will be explained in more detail below using an exemplary embodiment. The accompanying drawing shows a

Graphic representation of the pressure curve inside and outside the cylinder of a single-piston pump.

A piston is driven via a cam by a stepper motor, each step being a specific one Piston movement and thus causes a defined volume step. By an encoder on the cam is the Time 1 (Fig.) Signals the beginning of the intake. The stepper motor is at higher speed, the so-called. Ansauggeschwindigkoit operated. After completion of the suction phase, to Zoitpunkt 2, the cam starts the piston in the direction of compression

Press and the pressure in the cylinder rises. During the suction phase and the phase of the compression of the liquid in the cylinder, the pressure in the system behind the pump drops slightly despite an activated damping vessel. With the beginning of

Fluid delivery from the cylinder into the system also begins immediately to increase the pressure in the system, the pressure curve

shows a previous minimum 3. The time of the minimum is determined in a known manner, e.g. From the polarity reversal of the differentiated pressure signal.

Between times 2 and 3, the number η of the volume steps performed by the piston is counted and with the Ratio of step volume AV to volume of the cylinder contents V multiplied:

AV ^z = "-

By this number 7, the frequency f for controlling the piston steps is compared with that in the case of conveyance without compression f ", i. with non-pressurized delivery, reduced:

In a change in the pressure against which the pump has to work, the measured number n changes, thus the control frequency for the pump, and it is achieved independent of the back pressure delivery rate. The piston is driven from the end of the full compression, time 4, on with the new frequency f.

Furthermore, the number Z is divided by the measured value for the current pressure, and you get a statement about the compressibility of the pumped liquid

This is a material-specific size that is 10'Vbar for most fluids used. From the operator of the pump can z. Example, a range of 5 χ NT ⁶ or to 2 χ 10 ~ Vbar be selected. If the measured value C drops out of this range, a warning signal is triggered, because then it is certain that there is a malfunction, eg. B. by penetrating gases, can be closed.

Claims (3)

A method of controlling the delivery rate of HPLC pumps, comprising a suction, a compression and a delivery phase at each delivery cycle, characterized in that the compression phase is divided into a phase of compression within the cylinder and a phase of delivery into the system, from the time of commencement of the phase of compression within the cylinder, the volume steps resulting from the piston movement are counted and stored up to the time of delivery into the system, and the beginning of the phase of delivery into the system by the time of the minimum pressure in the system it is determined that from the known size of the volume step, multiplied by the number of stored steps, relative to the cylinder volume, the effective compression of the liquid at the current working pressure is determined and decreases with this size the applicable promotion frequency. 2. The method according to claim 1, characterized in that the number of resulting from the pumping rate steps and the number of actual, real volume steps are represented as analog values and the comparison of these two values is carried out in analog form. 3. The method according to claim 1, characterized in that from the effective compression in a known manner, the compressibility determined, this monitored and a warning signal is triggered when exceeding a stored in the memory tolerance.