DD286301B5 - METHOD FOR CONTROLLING HPLC PUMPS - Google Patents

Description

For this 1 page drawing

Field of application of the invention

The invention relates to a method for controlling 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, occurs at each delivery cycle in the intake phase, a pressure drop. It is known to reduce this pressure drop through a reservoir (damping vessel) as far as possible until the pump again promotes directly into the system. In addition, it is known to greatly shorten the duration of the suction, thereby further reducing the pressure drop. This suction phase is followed by a period of time during which the liquid in the pump is compressed.

For this purpose, it is known to determine the periods for suction and compression and set permanently. This has the effect that ink flows which affect a change in compressibility can not be taken into account.

According to EP-PS 106009 is known to measure the pressure behind the outlet valve of the pump at a time-predetermined Stolle the delivery cycle and store. During the compression period, the prevailing pressure is measured and compared with the stored value. If the two values are the same, the compression period is ended and the pump is switched from cW to previously increased delivery rate to normal delivery.

This technical solution has uen disadvantage that on the one hand a highly sensitive measuring system must be used for the pressure, but on the other hand, the degree of the realized damping falsified the measured actual value and reduces the control accuracy based thereon.

Furthermore, it is known to measure the pressure in the pump cylinder and to derive control variables for the pump control from these measured values. Although this method reduces the influence of the attenuator on the pressure measurement, it increases the internal volume of the cylinder and requires a costly special measuring device instead of the otherwise common pressure transducer.

Object of the invention

The aim of the invention is to reduce the technical complexity of the pump control.

Explanation of the essence of the invention

The invention has for its object to make the control of the underlying pressure measurement outside the cylinder and thereby reduce the influence of the usedon damping on the pump control. According to the invention, this is achieved by counting and storing, in the case of the iodine delivery cycle, the volume steps theoretically resulting from the start of the intake phase from the pumping rate. Since HPLC pumps are usually operated with stepper motors, each step of the motor corresponds to a defined, conveyed volume (volume step). The term "pump rate" here means the amount of liquid to be delivered in the unit of time measured as volume. The grain compression phase is divided into a phase of compression within the cylinder and a phase of delivery into the system. The beginning of the phase of promotion in the system is determined by the time of a pressure minimum in the system

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certainly. From this point onwards, the volume steps are counted and with the number in memory

Volume steps compared. The phase of rapid promotion is limited until the time when the number of

actual, real volume steps corresponds to the number of stored, theoretical volume steps. Then it switches to continuous production.

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. In drive systems with DC motor, the control is often done with analog control variables. It can do that

Methods according to the invention are used in that the volume sizes are represented as analog values and also the comparison is carried out with the aid of the analog technique.

embodiments

The invention will be explained in more detail below by exemplary embodiments. The accompanying drawing shows a graphic representation of the pressure curve inside and outside the cylinder of a single-piston pump.

1. A piston is driven via a cam by a stepper motor, each step causes a certain piston movement and thus a defined volume step. An encoder on the cam signalizes the time 1 (FIG. 1) of the start of the intake phase. From this point in time 1, the number of control pulses applied to a constant flow is fed to a counter. The stepper motor is operated at a higher speed, the so-called intake speed.

After completion of the suction phase, at time 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, the pressure in the system also begins to increase immediately,

the pressure curve shows a previous minimum 3. The time of the minimum is determined in a known manner, e.g. B. from the

Polarity reversal of the differentiated pressure signal. From this point on, the control pulses supplied to the stepper motor are fed to a second counter. The content

Both counters are compared continuously. When equality is achieved, time 4, the fast run is ended and the

Stepper motor continue to operate at the speed corresponding to the selected river. Thereafter, both counters are switched to zero and are thus ready for the control of the next intake. In the Figure is the constant flux pulses 5 input to counter 1 from time 1 to time 4,

and the control pulses for the stepping motor 6, which are input from the time 3 to time 4 in the counter 2, shown in a dashed line.

2. In a variant, the two counters of Example 1 are replaced by an up-down counter and the constant-flow control pulses are fed to the up-count input and the step-motor control pulses are applied to the down-count input.

The switching of the stepping motor from the fast to the speed corresponding to the flow occurs at zero crossing of the counter, after which the counter for the next suction is provided.

3. In a further variant, the tasks of the two counters or the pre-Pückwärtszählers and the switching of the stepping motor to the different speeds are adopted by a digital computer.

Claims (2)

1. A method for controlling HPLC pumps, with a suction, a compression and a delivery phase at each pump cycle, characterized in that from the time of the beginning of the intake phase, the resulting from the pumping rate volume steps are counted and stored, the compression phase in dividing a phase of compression within the cylinder and a phase of delivery into the system and determining the beginning of the phase of delivery into the system by the time of a pressure minimum in the system, and from that point on the volume increments are counted and counted in number Memory volume steps are compared and the phase of the rapid promotion is limited to the time at which the number of actual, real volume steps of the number of stored, theoretical volume steps corresponds and that is then switched to a continuous production. 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.