Method for metering a liquid volume with a peristaltic pump

Abstract

The invention relates to a method for metering a volume of liquid with a peristaltic pump. The invention discloses a method for metering a volume of liquid with a peristaltic pump in an analyser, wherein the analyser is designed to determine a concentration of an analyte of a sample, wherein the peristaltic pump comprises at least one rotor with at least two rollers, the method comprising the steps of determining a position of the at least one roller of the peristaltic pump, moving the rotor of the peristaltic pump to an initial position if it is not already in the initial position, and metering the volume of liquid to be delivered by moving the rotor by counting the rollers passing a reference position. The invention also discloses an analyser for implementing the method.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for metering a liquid volume with a peristaltic pump in an analyzer, an analyzer, a computer program and a computer readable medium. BACKGROUND

[0002] In process measurement technology, for example in chemical, biotechnological, pharmaceutical and food technology processes, and in environmental metrology, such automatic analyzers, also called analysis devices, are used to determine measurands of liquid samples. The analyzer can be used, for example, to monitor and optimize the cleaning performance of a sewage treatment plant, to monitor drinking water or to monitor the quality of food. For example, the proportion of certain substances, also called analytes, in a sample fluid such as a liquid or a liquid mixture, an emulsion, a suspension, a gas or a gas mixture is measured and monitored. The analyte can be, for example, an ion such as ammonium, phosphate, silicate or nitrate, calcium, sodium or chloride, or a biological or biochemical compound, for example a hormone, or even a microorganism. Other parameters determined using an analyzer in process measurement technology, in particular in the field of water control, are parameters such as total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP) or chemical oxygen demand (COD). The analyzer can be designed, for example, as a cabinet device or as a buoy.

[0003] The sample to be analyzed is usually treated in the analyzer by mixing it with one or more reagents, thereby causing a chemical reaction in the reaction mixture. The reagents are preferably chosen such that the chemical reaction can be verified by physical methods, for example by optical measurement, using a potential or amperometric sensor or by conductivity measurement. By means of the measurement sensor, the measured value of the measurand, which is relevant to the analysis parameter actually to be determined, such as COD, is detected accordingly. The chemical reaction can, for example, result in a coloration or a change in color, which can be detected using optical means. In this case, the intensity of the color is a measure of the parameter to be determined. As a measurand related to the parameter to be determined, the absorbency or the extinction of the sample treated can be determined, for example, by a photometric device by feeding electromagnetic radiation, such as visible light, from a radiation source into the liquid sample and receiving it with a suitable receiver after transmission through the liquid sample. The receiver generates a measurement signal which depends on the intensity of the radiation received and from which the value of the parameter to be determined can be derived, for example, on the basis of a calibration function or a calibration table.

[0004] In analyzers for liquid analysis, both the sample to be analyzed and the reagents required for the reaction have to be dosed into the reaction vessel, for example cuvette or reactor. Peristaltic pumps are often used for this purpose. Usually, they dose small amounts of liquid with moderate accuracy and at the same time offer many advantages, such as self-priming and run-to-run safety.

[0005] However, in some areas of application of liquid analysis, the dosing accuracy of such peristaltic pumps is not good enough and must therefore be guaranteed by using additional components. These are usually things called dosing units, which consist of a number of elements (manifolds, valves, optical components, etc.). This ultimately makes it possible to dose very accurately. However, the cost of such a solution is correspondingly higher due to the greater number of components and thus has a negative impact on the equipment costs.

[0006] For many applications in the field of liquid analysis, it is not precise enough to dose the amount of liquid using only a peristaltic pump. This is firstly due to the pulsation of the peristaltic pump and secondly due to the increased tube wear and thirdly due to the fact that the volume actually dosed in a conventional peristaltic pump is unknown. The delivery volume per revolution can vary significantly due to the aging of the tube.

[0007] As mentioned before, peristaltic pumps usually pulsate very strongly. This is due to its principle of transport. In a peristaltic pump, the mounted tube is closed and compressed by rollers located on the rotor. When the rotor rotates, the rollers slide over the tube and displace the medium located in the tube in the direction of the pump outlet / pressure outlet. When the rollers leave the tube, the tube opens the chamber and causes a short-term volume backflow (corresponding to the volume of the tube piece that was pressed) and a pressure fluctuation. The application of the rollers at the pump inlet can likewise cause a volume flow that is temporarily moved in the opposite direction to the actual volume flow. Thus, pulsation occurs on the inlet side and on the outlet side of the peristaltic pump.

[0008] Therefore, depending on the position of the rollers, a volume flow standstill and a time-dependent dosing inaccuracy occur. However, a uniform flow rate is very important for the accurate dosing of liquids. There are now several solutions to prevent pulsation. These include, for example, passive and active pulsation damping, combination of pulsating volume flow or a greater number of rollers.

[0009] To meter a volume using a peristaltic pump, the rotational speed of the pump motor is adjusted and the pump is operated for a specific predetermined time. If the pump runs longer or faster, more medium is delivered. If the rotational speed (or the rotational angle performed) deviates from the target during the predetermined time, the metered volume is inevitably wrong. Since in conventional peristaltic pumps the volume is metered using only time to set, or in the case of a stepper motor using the number of steps, but there is never any feedback about how many turns or steps have actually been performed in that time, the actually metered volume is unknown. However, the behavior of the pump changes due to aging, in particular the aging of the tube. If the same time is continued to be set, different volumes will be delivered as the peristaltic pump ages. Therefore, the pump must be calibrated periodically so that for a given delivery amount, the pump actually runs for the correct time. With the help of such a calibration, a relatively accurate metering is possible. However, the problem of the feedback of the actually performed rotational angle remains unsuccessful. Therefore, it is not known at all whether and how much the pump has rotated.

[0010] However, all solutions are typically only implementable or associated with high costs in the case of high technical effort. SUMMARY

[0011] It is an object of the present invention to improve the metering accuracy of a peristaltic pump in an analyzer in process automation.

[0012] The object is achieved by a method for a universal analyzer having a peristaltic pump, wherein the peristaltic pump comprises at least one rotor having at least two rollers, wherein the method comprises the steps of determining the position of the at least one roller of the peristaltic pump, moving the rotor of the peristaltic pump to an initial position if it is not already in the initial position, and metering the amount of liquid to be delivered by moving the rotor by counting the rollers passing a reference position.

[0013] Counting the rollers passing a reference position should be considered equivalent to counting the number of rotations.

[0014] Therefore, the position of the rollers within the peristaltic pump is detected and the magnitude and number of the inevitable pulsations in each of the metering steps can be predicted and taken into account. This enables an accurate metering of the amount of liquid.

[0015] If there are multiple amounts of liquid to be delivered, the absolute volume is less important than the ratio. For example, if a first amount of liquid of 1 ml and a second amount of liquid of 2 ml are required, a double number of rollers passing is used for the second amount of liquid.

[0016] The smallest reasonable amount that can be metered in this case is the volume in the tube during the passage of a roller. If the amount of liquid to be metered cannot be metered in an integer multiple of this smallest amount that can be metered, the amount of liquid to be metered is in one embodiment increased or decreased to an integer multiple of this smallest amount that can be metered, depending on the application. For example, if 1.1 ml is to be metered, but the smallest amount that can be metered is 0.25 ml, the volume to be metered is for example reduced to 1.0 ml, so that this can be metered in an integer multiple of the smallest amount that can be metered, namely in this case 4*0.25 ml. As mentioned above, it is not the absolute volume that is important, but the ratio of the different amounts of liquid to be metered.

[0017] One embodiment provides that the method comprises the step of discarding the contents of the tube in the region of the tube on the outlet side before reaching the initial position.

[0018] The object is also achieved by an analyser comprising at least one peristaltic pump having a rotor with at least two rollers, and a data processing unit designed to carry out the method steps as explained above.

[0019] One embodiment provides that the analyser comprises a counting unit for counting the passage of a roller through a reference position.

[0020] One embodiment provides that the counting unit comprises a switch which is closed when a roller passes.

[0021] One embodiment provides that the at least one roller comprises a magnet and the counting unit comprises a magnetic sensor, in particular a reed contact or a Hall effect sensor.

[0022] One embodiment provides that the counting unit comprises a light barrier.

[0023] The object is also achieved by a computer program comprising commands which cause an analyser to carry out the method steps as described above.

[0024] The object is also achieved by a computer-readable medium on which a computer program is stored. BRIEF DESCRIPTION OF DRAWINGS

[0025] This will be explained in more detail with reference to the following drawings.

[0026] Figure 1 The claimed automatic analyser is illustrated in a symbolic sketch.

[0027] Figure 2 The system design of the claimed analyser is illustrated.

[0028] Figure 3a / b shows two positions of the rollers of the peristaltic pump.

[0029] Figure 4a / b shows an embodiment of the peristaltic pump in the first position and the second position.

[0030] Figure 5a / b shows an embodiment of the peristaltic pump in the first position and the second position.

[0031] In the drawings, identical features are identified by the same reference signs. DETAILED DESCRIPTION

[0032] The overall claimed automatic analyzer is denoted by reference sign 1 and is shown in Figure 1 Fig. 1.

[0033] To be measured is, for example, the direct absorbance of a substance or the intensity of a color, which is generated by the conversion of the substance to be determined into a color complex by means of a reagent. Further possible measurands that act according to similar principles are turbidity, fluorescence, etc. An application example is the measurement of the chemical oxygen demand (COD), wherein COD is a parameter, which means that the measured value results from the sum of substances and cannot be attributed to a single substance. In this measurement method, a color change is generated in a reactor; see below. Other possible parameters are, for example, total carbon, total nitrogen or ion concentrations, such as of ammonium, phosphate, nitrate, etc.

[0034] From the medium 15 to be analyzed, for example a liquid or a gas, a sample 13 is taken. Usually, the taking of the sample 13 takes place completely automatically, for example by means of the analyzer itself, by means of subsystems 14 such as pumps, tubes, valves, etc. For the determination of a certain kind of substance content, one or more reagents 16 are mixed with the sample 13 to be measured, which are specifically developed for the respective substance content and are available in the housing of the analyzer. This is shown in a symbolized manner in Figure 1 Fig. 2. In reality, different containers are provided with different reagents, which are extracted and mixed as required by means of the aforementioned pumps, tubes and valves, etc. This is shown in Figure 2 Fig. 3. It is also possible to use separate pumps, tubes and valves for each process (taking of the sample, mixing of the reagents, etc.).

[0035] The color reaction of the mixture thus caused is then measured by means of a suitable measuring device such as a photometer 17. For this purpose, the sample 13 and the reagent 16 are mixed, for example in a measuring chamber 8, and an optical measurement is carried out using light of at least one wavelength using the transmission method. In this method, light is transmitted by a transmitter 17.1 through the sample 13. A receiver 17.2 for receiving the transmitted light is assigned to the transmitter 17.1, wherein an optical measurement path 17.3 (by means of the sample 13) is formed between the transmitter 17.1 and the receiver 17.2. The measurement result is output to a control unit 18, which is connected to the photometer 17 and to the subsystems 14. Figure 1The light (indicated by the dashed line in Fig. 1) travels from the sender 17.1 to the receiver 17.2. The sender 17.1 comprises, for example, one or more LEDs, i.e. one LED per wavelength, or a suitable light source with a broadband excitation. Alternatively, a broadband light source is used, whose front is placed with a corresponding filter, which can also be installed directly in front of the receiver, depending on the application. The receiver 17.2 can comprise, for example, one or more photodiodes.

[0036] The measured values are generated by the receiver on the basis of the light absorption and the stored calibration function. The analyser 9 comprises a transmitter 10 with a microcontroller 11 and a memory 12. The analyser 9 can be connected to a field bus via the transmitter 10. In addition, the analyser 9 is controlled via the transmitter 10. Thus, for example, the taking of the sample 13 from the medium 15 is initiated by the microcontroller 11 by means of suitable control commands to the subsystem 14. The measurement by the photometer 17 is also controlled and adjusted by the microcontroller. The metering of the sample 13 can also be controlled by the transmitter 10. A computer program for controlling the analyser, for example for metering, then runs on the transmitter 10. A computer-readable medium is also located on the transmitter 10 or can be inserted into the transmitter 10.

[0037] The taking of the sample 13 is now described in principle. For the taking of the sample 13 from the medium 15, a sample taking device is used, which can comprise, for example, a pump 4, here a peristaltic pump. The sample 13 enters the metering device 1 via a medium line. As mentioned above, the analyser 9 comprises liquid containers, which contain reagents 16 to be added to the sample 13 for determining the measurand of the analyser 9, and standard solutions for calibrating and / or adjusting the analyser 9. The peristaltic pump 4 pumps the sample 13 into the metering device 1.

[0038] The metering device 1 comprises a metering chamber 2, which is designed, for example, as a cuvette, and at least one metering light barrier 3. Figure 2 Three light barriers 3 are shown, of which two of them serve as measurement light barriers for measuring a certain amount of liquid, and the top one serves as a safety light barrier. If the liquid to be measured in the metering chamber 2 reaches the top light barrier, an alarm is triggered and the metering is stopped. The light barriers 3 can also be designed as infrared light barriers with a daylight filter. A valve 21 for ventilation is also connected to the metering device 1. A pump 5, more precisely a displacement pump, more precisely a piston pump, is also connected to the metering device 1. The piston pump 5 pumps the liquid from the metering chamber 2 into the measuring chamber 8. This happens because air is sucked in during the lifting of the piston pump 5, and this air column pushes the liquid in front of it from the metering chamber 2 to the measuring chamber 8.

[0039] The metering device 1 is connected to the measuring chamber 8, also called the reactor 8, by means of a line 6. The line 6 is designed as a tube or a pipe.

[0040] The reactor 8 comprises a valve 19 on one side of the line 6 and a valve 20 on the other side for venting.

[0041] The reagent 16 or the container comprising the reagent 16 is connected to the metering device 1 via a liquid line. There is a suitable valve 22 for opening and closing the line. In addition, there is also an outlet 18 which comprises a valve if applicable and serves as a drain.

[0042] Figure 3a / b shows the peristaltic pump 4 of the analyzer 9. In this example, the pump comprises three rollers 23, 24, 25 on a rotor 26. To address the disadvantages of the peristaltic pump described above, it is proposed to detect at least one of the rollers 23, 24, 25 inside the peristaltic pump 4.

[0043] Generally, a peristaltic pump is a displacement pump in which the volume of liquid to be conveyed is forced through a tube 27 by external mechanical deformation of the tube. The volume of liquid to be metered flows in through an inlet 32 and out through an outlet 33. In each case, the tube 27 is supported on the outside of the housing of the pump head and clamped from the inside by rollers or shoes rotating on the rotor 26. Here, this movement causes the clamping point to move along the tube 27 and thus to push the volume of liquid to be conveyed forward.

[0044] Figure 3a A first position of the rotor 26 is shown in Figure 3b A second position is shown in Figure 3a The position of the at least one roller 23, 24, 25 is determined in Figure 3a The counting unit 29 (see below for details; the counting unit is symbolically represented as a rectangle in

[0045] If it is recognized that the rotor 26 is already in the initial position, metering can be started immediately (see below). If the rotor 26 is not in the initial position (as is the case in Figure 3a it is first moved to the initial position. For example, Figure 3b This initial position is shown in

[0046] If the position at the beginning of the metering step is known, that is, due to this initial position, a software algorithm stored in the transmitter 10 can be used to configure the number of revolutions required so that for a certain liquid quantity, always the same number of pulses occurs - that is, the roller passes the counting unit 29. This ensures that the metered volume is always approximately constant. In order to make this compensation method applicable to every tube type and every tube wear degree, the transported volume is measured at regular intervals during the metering step and the peristaltic pump is thus calibrated.

[0047] If it is determined that the rotor 26 is not in the initial position, the liquid quantity located in the section closer to the output 33 is discarded. In Figure 3a In this case, this is the part of the tube 27 behind the roller 25 in the direction 33. In one embodiment, it is followed by a "flushing" with air or nitrogen, more generally with a flushing medium, so that it is ensured that the tube 27 is empty or free of undesirable medium.

[0048] The unit that determines the position of the roller at the beginning does not necessarily have to be the unit that counts the roller passes. However, this unit is preferably constructed as a single unit, namely the counting unit 29.

[0049] Figure 4a / b shows an embodiment that detects the initial position and / or counts the roller passes. Figure 4a shows the first position, Figure 4b shows the initial position. In this example and the next example, the peristaltic pump 4 has four rollers 23, 24, 25, 28. In this embodiment, the detection takes place by means of a switch 30. The rollers 23, 24, 25, 28 of the peristaltic pump 4 close the switch mechanism when they pass the switch 30. This produces an electrical connection that generates a signal for the transmitter 10. In this way, the position of the rollers can be processed.

[0050] In one embodiment, the detection takes place by means of a magnetic switch. Here, the reference position of the roller is detected via a magnetic contact. A magnetic switch fixed in the appropriate position on the outside of the rotor 26 is actuated by means of a magnet located on the rotor 26 of the peristaltic pump 4 at every rotation. The switch is configured as, for example, a magnetic sensor, for example, a reed contact or a Hall effect sensor. This produces an electrical signal that can be processed by the software and the corresponding algorithm.

[0051] In Figure 5a In the embodiment in / b, the detection takes place by means of a light barrier 31. Figure 5a shows the first position, Figure 5bThe initial position is shown. For detection by means of the light barrier 31, the sender and the receiver are placed at the initial position to be determined. The light emitted by the sender is interrupted at the moment when the rollers 23, 24, 25, 28 of the peristaltic pump 4 pass the light barrier 31 and thus can no longer be detected by the receiver sensor. The position of the rollers 23, 24, 25, 28 is then considered to be detected.

[0052] This results in a method for increasing the metrological accuracy of the peristaltic pump 4 by detecting the initial position of the rollers 23, 24, 25, 28 in the interior of the peristaltic pump 4. If the position of the rollers is known before the start of the metrological step (initial position), the number of pulsations occurring can be predicted and taken into account accordingly when calculating the volume in order to carry out the metrology. This detection can be done by means of, for example, a switch, a magnetic switch or a light barrier.

[0053] List of reference signs

[0054] 1 metrological device

[0055] 2 metrological chamber

[0056] 3 metrological light barrier

[0057] 4 peristaltic pump

[0058] 5 piston pump

[0059] 6 line

[0060] 8 measuring chamber / reactor

[0061] 9 analyzer

[0062] 10 sender

[0063] 11 microcontroller

[0064] 12 memory

[0065] 13 sample

[0066] 14 subsystem of 9

[0067] 15 medium

[0068] 16 reagent

[0069] 17 photometer

[0070] 17.1 sender

[0071] 17.2 receiver

[0072] 17.3 optical measurement path

[0073] 18 outlet / drain

[0074] 19 valve

[0075] 20 valve

[0076] 21 valve

[0077] 22 valve

[0078] 23 roller

[0079] 24 roller

[0080] 25 roller

[0081] 26 rotor

[0082] 27 tube

[0083] 28 roller

[0084] 29 counting unit

[0085] 30 switch

[0086] 31 light barrier

[0087] 32 inlet

[0088] 33 outlet

Claims

1. A method for metering a volume of liquid with a peristaltic pump (4) in an analyzer (9), wherein the analyzer (9) is designed to determine a concentration of an analyte of a sample, wherein the peristaltic pump (4) comprises at least one rotor (26) having at least two rollers (23, 24, 25, 28), the method comprising the steps of: - determining a position of at least one roller (23, 24, 25, 28) of the peristaltic pump (4), - moving the rotor (26) of the peristaltic pump (4) to an initial position, if not already in the initial position, and - metering a volume of liquid to be delivered by moving the rotor (26) by counting a passage of a roller through a reference position by a counting unit (29), wherein the counting unit (29) comprises a switch (30) or a light barrier (31) passed by the roller (23, 24, 25, 28).

2. The method according to claim 1, further comprising the step of: - discarding a content of a tube of the peristaltic pump (4) in a region of the tube on an outlet side before reaching the initial position.

3. An analyzer (9) for determining a concentration of an analyte of a liquid sample, at least comprising - a peristaltic pump (4) having a rotor (26) with at least two rollers (23, 24, 25, 28), - a data processing unit designed to carry out the steps of the method according to claim 1 or 2, and - a counting unit (29) for counting the passages of the roller through a reference position, wherein the counting unit (29) comprises a switch (30) or a light barrier (31) passed by the roller (23, 24, 25, 28).

4. The analyzer (9) according to claim 3, wherein the switch (30) is closed when the roller (23, 24, 25, 28) passes.

5. The analyzer (9) according to claim 4, wherein at least one roller (23, 24, 25, 28) comprises a magnet and the switch is configured as a magnetic sensor.

6. The analyzer (9) according to claim 5, wherein the switch is configured as a reed contact or a Hall effect sensor.

7. An apparatus for metering a volume of liquid with a peristaltic pump (4) in an analyzer (9), comprising instructions causing the analyzer (9) according to any one of claims 3 to 6 to carry out the steps of the method according to claim 1 or 2.

8. A computer readable medium, instructions are stored on the computer readable medium, causing the analyzer (9) according to any one of claims 3 to 6 to carry out the steps of the method according to claim 1 or 2.

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