Method for monitoring the metering of at least one liquid

Abstract

The invention relates to a method for monitoring the metering of at least one liquid within a metering station (1), the metering station (1) comprising: a material supply (2) of the liquid to be metered; a supply pump (3); a metering pump (4); and a delivery line (5) extending between the supply pump (3) and the metering pump (4), wherein: the supply pump (3) is suitable for delivering the liquid from the material supply (2) through the delivery line (5) to the metering pump (4); the metering pump (4) is designed to meter a specified amount of liquid; and a delivery capacity of the supply pump (3) is ascertained during a metering process, and the ascertained delivery capacity of the supply pump (3) is compared with a specified metering capacity of the metering pump (4).

Description

[0001] Method for monitoring the dosage of at least one liquid

[0002] Description

[0003] The invention relates to a method for monitoring the dosage of at least one liquid within a dosing station, wherein the dosing station comprises at least one supply pump and at least one dosing pump.

[0004] Dosing processes in a dosing station can be affected by errors in the control system of the dosing pump or by mechanical malfunctions of individual components, such as slipping couplings, broken shafts, or similar issues. Dosing inaccuracies or even dosing failures can occur. In these cases, the actual dosing rate does not match the dosing rate specified by the manufacturer for the specific dosing pump. Often, such errors can be detected by regularly weighing the dispensed material and, if necessary, corrected using an internal correction factor. However, a problem arises when several different materials, for example, two, are processed in a dosing station and are to be dispensed by two dosing pumps in a specific mixing ratio.If a dosing error occurs during the dispensing of one of the two components, weighing the mixture will not reveal which component was incorrectly dispensed. In mixtures with significantly different mixing ratios, an error in the dispensing of the smaller fraction can be compensated for by a slight inaccuracy in the dispensing of the larger fraction, so that the dosing error remains completely undetected.

[0005] It is generally known to install a flow meter at the outlet of the dosing pump to monitor the actual flow rate. However, it has been shown that such flow meters, especially in combination with materials containing a high proportion of solid fillers, are themselves very prone to malfunction and are therefore not suitable as a reliable monitoring device.

[0006] Dosing errors can have serious consequences in subsequent applications. This is especially true for safety-critical applications, such as in aerospace.

[0007] The invention therefore aims to provide a method by which the dosage of at least one liquid within a dosing station can be better monitored, so that dosing errors can be detected more reliably.

[0008] This problem is solved by a method with the features of claim 1. Specific embodiments and further developments of the invention are the subject of the dependent claims.

[0009] According to claim 1, the invention is a method for monitoring the dosing of at least one liquid within a dosing station, wherein the dosing station comprises: a supply of the liquid to be dosed, a supply pump, a dosing pump, and a delivery line extending between the supply pump and the dosing pump, wherein the supply pump is suitable for pumping the liquid from the supply through the delivery line to the dosing pump, and wherein the dosing pump is configured to dispense a predetermined quantity of liquid. The invention is characterized in that, during a dosing process, the delivery rate of the supply pump is measured and compared with a predetermined delivery rate of the dosing pump.

[0010] In other words, the method according to the invention provides that the delivery rate of the supply pump is incorporated as additional information into the evaluation of a dosing result. For the purposes of the invention, it is assumed that the liquid to be dosed is incompressible and is conveyed from the supply pump through the delivery line to the dosing pump at a substantially constant density. It can therefore be assumed that the quantity of liquid dispensed by the dosing pump during a dosing process corresponds exactly to the quantity of liquid that is fed from the material supply into the delivery line by the supply pump during the same time interval.By measuring the delivery rate of the supply pump, and thus the amount of liquid fed into the delivery line by the supply pump during a dosing process, it is possible to determine the actual amount of liquid dispensed by the dosing pump during that process. Comparing this actual dispensed amount of liquid with the amount that would be expected based on the manufacturer's specified dosing rate for the dosing pump, it can be determined whether a dosing error exists in the respective dosing pump.

[0011] The method according to the invention can thus provide that a decision is made as to whether a dosing error exists by comparing the measured delivery rate of the supply pump with the predetermined dosing rate of the metering pump. For example, a threshold value can be defined for a deviation of the measured delivery rate of the supply pump from the manufacturer-specified dosing rate of the metering pump, whereby a dosing error is reported if this threshold value is exceeded. For this purpose, as will be explained in more detail below, the results of a position determination of the piston rod as a function of time can, for example, be supplied to a data processing unit, which first determines the delivery rate of the metering pump from the supplied data and compares it with the manufacturer-specified dosing rate of the metering pump.Subsequently, any deviation detected between the delivery rate of the supply pump and the dosing rate of the dosing pump can be compared to a predefined threshold value. If the threshold value is exceeded, a dosing error can be reported. Alternatively or additionally, the operation of the dosing station can be stopped immediately upon detection of a dosing error.

[0012] The essential aspect of the invention is the measurement of the delivery rate of the supply pump during a dosing process. For the purposes of this invention, the term "dosing process" encompasses both dosing over a predetermined time period and dosing of a predetermined quantity. For example, a deviation between the delivery rate of the supply pump and the dosing rate of the metering pump can be determined over a dosing period of 100 seconds. Alternatively, a deviation can also be measured with respect to a dosing quantity of, for example, 100 g or 100 m³. 3The accuracy can be determined. For very short dosing processes of just a few seconds and / or very small doses of just a few grams, the accuracy may not be sufficient to detect any deviations. Therefore, it may be necessary to record the flow rate of the supply pump and the dosing rate of the dosing pump over a predetermined minimum duration or minimum dose.

[0013] According to one embodiment of the inventive method, the supply pump is designed as a reciprocating piston pump with a piston and a piston rod rigidly connected to the piston, for example as a scoop piston pump, wherein the position of the piston rod is recorded at different times during the metering process in order to determine the delivery rate of the supply pump and wherein the quantity of liquid fed into the delivery line by the supply pump during the metering process is deduced from the recorded positions of the piston rod.

[0014] In other words, in this embodiment, the delivery rate of the supply pump is determined according to the invention by measuring the position of the piston rod of the reciprocating pump at different times during the metering process. Based on the distance traveled by the piston, which can be determined in this way, the quantity of liquid delivered by the supply pump during the metering process, and thus the delivery rate of the supply pump, can be directly inferred.

[0015] It can be provided that the position of the piston rod is detected during the dosing process at a sampling rate of at least 0.1 Hz, preferably at a sampling rate of at least 1 Hz. From the resulting profile of the piston rod's position over time, the quantity of liquid delivered by the supply pump within the specified period can be determined.

[0016] One embodiment of the method according to the invention provides that the position of the piston rod is detected by a Hall sensor measuring the magnetic field of a magnet connected to the piston rod and moving with the piston rod, whereby, based on a calibration, the position of the magnet and thus the position of the piston rod is deduced from the measured magnetic flux density.

[0017] In this variant, a magnet, for example a permanent magnet, is connected to the piston rod and moves up and down with it. The movement of the piston rod periodically moves the magnet past a stationary Hall sensor. The Hall sensor measures, for example at a sampling rate of 1 Hz, the magnetic flux density of the magnetic field generated by the magnet. This flux density changes depending on the position of the magnet relative to the Hall sensor. Based on calibration, the position of the magnet, and thus the position of the piston rod, can be determined from the output signal of the Hall sensor as a function of time.

[0018] Alternatively or additionally, the position of the piston rod can be detected according to another proposal by using an inductive sensor to measure the distance to the surface of a measuring body connected to and moving with the piston rod, wherein the measuring body is conical or wedge-shaped, so that the distance to the surface of the measuring body changes depending on the position of the measuring body, and wherein, based on a calibration, the position of the measuring body and thus the position of the piston rod is inferred from the measured distance.

[0019] In this design, a measuring element is rigidly connected to the piston rod and moves up and down periodically with it. During this movement, it passes a stationary inductive sensor, which measures the distance to the surface of the measuring element at a predetermined sampling rate. The measuring element is conical or wedge-shaped, so that the distance between the inductive sensor and the surface of the measuring element changes depending on the position of the measuring element. Based on a calibration, the position of the measuring element, and thus the position of the piston rod, can be determined from the output signal of the inductive sensor as a function of time.

[0020] Another embodiment involves detecting the piston rod's position alternatively or additionally by mechanically coupling a piston from an additional measuring cylinder, such as a pneumatic cylinder, to the piston rod of the supply pump. The position of the piston moving within the measuring cylinder is then detected by a sensor. In other words, this embodiment couples the supply pump's piston rod to a measuring cylinder containing a piston, for example, by pressing the supply pump's piston rod onto the pneumatic cylinder's piston via an intermediate spring, thus creating a force-fit connection between the two components. If the supply pump's piston rod moves up and down periodically, the piston in the pneumatic cylinder is also moved up and down by the spring force.Since pneumatic cylinders typically contain a magnet in the piston, the piston's movement within the cylinder can be detected using suitable magnetic sensors. Based on calibration, the position of the piston rod of the supply pump can then be determined from the detected position of the piston within the pneumatic cylinder.

[0021] According to one embodiment of the invention, the delivery rate of the supply pump can be determined, alternatively or additionally to determining the position of the piston rod, by measuring the position of a follower plate resting on the material reservoir at different times during the metering process. A follower plate is typically used in the processing of highly viscous liquids and is pressed onto the liquid level of the material reservoir held in a storage container to prevent the liquid in the reservoir from flowing unevenly into the delivery line after material has been dispensed, due to its high viscosity.During the dosing process, the liquid level, and consequently the follower plate, in the reservoir slowly descends. Knowing the reservoir's diameter, the follower plate's position can then be used as a measure of the amount of liquid dispensed from the reservoir into the delivery line by the supply pump. This, in turn, serves as a measure of the amount of liquid dispensed by the metering pump at the other end of the delivery line. However, because the follower plate typically descends very slowly due to its relatively large diameter, this method is generally unsuitable for monitoring low dosing rates. It is more appropriate for detecting long-term deviations between the actual delivery rate of the supply pump and the manufacturer's specified dosing rate of the metering pump.In particular, this method allows for the detection and subsequent adjustment of wear-related slippage in the supply pump. In addition to the methods already mentioned above for determining the supply pump's delivery rate by measuring the piston rod position, measuring the follower plate position can also be used for further calibration.

[0022] The position of the follower plate can be determined using a suitable displacement measuring system, for example using a cable pull sensor, a magnetic sensor and / or an optical sensor.

[0023] Another aspect of the invention provides that the quantity of liquid dispensed by the metering pump during a metering process is weighed, and the actual metering rate of the metering pump, derived from the weighed quantity of liquid, is compared with the delivery rate of the supply pump measured during the metering process and / or the predetermined metering rate of the metering pump. This allows for a further comparison of the individual methods. In one embodiment of the invention, the metering pump can be designed as a rotary pump, for example, as a gear pump or progressive cavity pump. For the method according to the invention, the combination of a metering pump designed as a rotary pump with a supply pump designed as a reciprocating pump, in which the piston performs a translational movement, has proven to be particularly advantageous.Since these two pump types are based on different operating principles, the probability of fault detection can be further increased. However, a metering pump can also be designed as a pump with a linear motion pattern, for example, as a piston metering pump.

[0024] According to a further embodiment of the method according to the invention, a first and a second liquid are dispensed in a predetermined mixing ratio in the dispensing station, wherein the dispensing station comprises: a first material supply of the first liquid to be dispensed, a first supply pump, a first dispensing pump, and a first delivery line extending between the first supply pump and the first dispensing pump, wherein the first supply pump is suitable for conveying the first liquid from the first material supply through the first delivery line to the first dispensing pump, and wherein the first dispensing pump is configured to dispense a predetermined quantity of liquid, wherein the dispensing station further comprises: a second material supply of the second liquid to be dispensed, a second supply pump,a second metering pump and a second delivery line extending between the second supply pump and the second metering pump, wherein the second supply pump is suitable for pumping the second liquid from the second material supply through the second delivery line to the second metering pump, and wherein the second metering pump is configured to dispense a predetermined quantity of liquid, wherein during a metering process a delivery rate of the first supply pump is recorded and the recorded delivery rate of the first supply pump is compared with a metering rate of the first metering pump, and that during the metering process a delivery rate of the second supply pump is recorded and the recorded delivery rate of the second supply pump is compared with a metering rate of the second metering pump.

[0025] In other words, the method according to the invention is particularly suitable for monitoring the mixing ratio in a dosing station where two different liquids are dispensed in a predetermined mixing ratio. For this purpose, the actual delivery rate of the associated supply pump is recorded for each of the two liquids as described above and compared with the predetermined dosing rate of the respective dosing pump. In this way, it can be determined whether the individual fractions are actually being dispensed according to the respective intended dosage amounts. In particular, it is possible to detect even a very small fraction whether a dosing error has occurred.Signal evaluation using reciprocating pumps can be performed as follows: The position of the piston rods of both reciprocating pumps is recorded in a measurement process whenever, according to the control system of the metering pumps, a complete gram of the liquid mixture to be metered has been dispensed by the metering pumps. By comparing the recorded position of the piston rod of a reciprocating pump with the position recorded in the previous measurement process, both the magnitude and direction of the change in position of the piston rod can be determined. Multiplying the magnitude of the change in position by a stored factor, which specifies the delivery rate in grams per millimeter of piston travel, yields the delivery rate fed by the respective supply pump into the associated delivery line per gram dispensed by the metering pumps.Since the delivery rates of the supply pumps can vary slightly depending on the direction of the piston movement, two different factors can be stored for each supply pump, with one factor being used for a determined upward movement of the piston and the other factor for a determined downward movement of the piston.

[0026] Due to the switching process of the internal pump valves, deviations from the otherwise essentially uniform linear motion profile of the piston rods can occur, particularly at the upper and lower switching points of the reciprocating pumps. This can lead to excessively high flow rates being determined in the switching point ranges using the procedure described above, exceeding the actual flow rate. To account for this, a limit value can be defined that specifies the maximum permissible flow rate delivered by a supply pump per gram of liquid mixture dispensed by the metering pumps. If the flow rate detected based on the piston rod position exceeds this limit value, the defined limit value can be used for further evaluation instead of the measured flow rate.

[0027] For example, based on the last 100 g of dispensed liquid mixture, moving averages can now be calculated for the individual measured flow rates. The following iterative formula can be used for this purpose: Average (flow rate n) = 0.01 * (flow rate n) + 0.99 * (average (flow rate n-1)). For each measured flow rate, here referred to as flow rate n, an average is calculated by multiplying flow rate n by a factor of 0.01 and adding this to 0.99 times the average of the preceding flow rate n-1, which was determined in the same way. Each individual flow rate refers to 1 g of the target quantity dispensed by the dosing station. The moving average refers to each component to be dosed individually.

[0028] Finally, the total delivery rate of each piston pump, derived from the moving averages, is compared with the respective target value of the associated metering pump. If the deviation exceeds a predefined threshold, an alarm can be triggered and the metering operation rejected.

[0029] In principle, the method according to the invention can also be used to monitor the dosage of more than two different liquids in a predetermined mixing ratio in the manner described above.

[0030] The invention will now be explained in more detail with reference to exemplary embodiments and the accompanying drawings. These show:

[0031] Figure 1: side view of an embodiment of a dosing station in which the method according to the invention is used;

[0032] Figure 2: the dosing station from Figure 1 in a rear view;

[0033] Figure 3: a view of a detail of a dosing station in which a first embodiment of the method according to the invention is used;

[0034] Figure 4: a view of a detail of a dosing station, in which a second

[0035] A variant of the inventive method is used;

[0036] Figure 5: a view of a detail of a dosing station in which a third embodiment of the method according to the invention is used.

[0037] Figures 1 and 2 show a dosing station, labeled 1, which is used for dosing two highly viscous liquids. A first supply of material 2 of a first liquid, not shown in the figures, is held in a first storage container, also labeled 2, while a second supply of material 20 of a second liquid, not shown in the figures, is held in a second storage container, also labeled 20.

[0038] Using the dosing station 1, the two liquids can be dispensed into a collection vessel 15 in a predetermined mixing ratio. For this purpose, a first supply pump 3 delivers the liquid from the first material reservoir 2 into a first delivery line 5. The first delivery line 5 extends between the first supply pump 3 and an associated first dosing pump 4. A predetermined quantity of the first liquid is dispensed into the collection vessel 15 via the first dosing pump 4. Similarly, a second supply pump 30 delivers the liquid from the second material reservoir 20 into a second delivery line 50. The second delivery line 50 extends between the second supply pump 30 and an associated second dosing pump 40. A predetermined quantity of the second liquid is dispensed into the collection vessel 15 via the second dosing pump 40.

[0039] The two supply pumps 3, 30 are each designed as piston pumps with a piston running in a cylinder and a piston rod rigidly connected to the piston. The piston performs a stroke movement in a manner known per se, such that in a first stroke, liquid is drawn from the material reservoir 2, 20 into the cylinder through an opening inlet valve, and in a second stroke, the drawn-in liquid is forced out of the cylinder through an outlet valve into the delivery line 5, 50.

[0040] The dosing rates of the dosing pumps 4 and 40 are generally specified by the manufacturer, for example, such that a certain operating time of the dosing pump corresponds to a specific dosing quantity. However, it has been shown that dosing errors cannot be ruled out and that these are difficult to detect based on the dispensed mixture. For this reason, the dosing process is monitored by recording the flow rates of the supply pumps 3 and 30 during a dosing operation and comparing these flow rates with the specified dosing rates of the associated dosing pumps 4 and 40. By comparing the recorded flow rates of the supply pumps 3 and 30 with the specified dosing rates of the dosing pumps 4 and 40, it can be determined whether a dosing error has occurred.

[0041] For this purpose, the position of the piston rod of the supply pump 3, 30, which is rigidly connected to the piston, is recorded at different times during the metering process. Based on the distance traveled by the piston, which can be determined in this way, the quantity of liquid fed into the delivery line 5, 50 by the supply pump 3, 30 during the metering process can be directly deduced.

[0042] Furthermore, it can be assumed that the liquids to be metered are incompressible and are conveyed at essentially constant density from the supply pumps 3, 30 through the delivery lines 5, 50 to the respective metering pumps 4, 40. Under this assumption, the quantity of liquid dispensed by a metering pump 4, 40 during a metering process corresponds exactly to the quantity of liquid that is fed from the material reservoir 2, 20 into the associated delivery line 5, 50 by the respective supply pump 3, 30 in the same time interval. By measuring the delivery rate of the supply pump 3, 30 and thus the quantity of liquid fed from the supply pump 3, 30 into the delivery line 5, 50 during a metering process, the actual quantity of liquid dispensed by the respective metering pump 4, 40 during the metering process can be determined.By comparing this actually dispensed amount of liquid with the amount of liquid that would be expected based on a dosing capacity specified by the manufacturer for the dosing pump 4, 40, it can be decided whether there is a dosing error in the respective dosing pump 4, 40.

[0043] Figures 3 to 5 each show a view of a detail of a dosing station 1, where the section shown in Figures 3 to 5 corresponds approximately to the area 100 shown as a dashed line in Figure 1.

[0044] The following section explains various design options for determining the position of the piston rod of the supply pump with reference to Figures 3 to 5. The explanations and figures refer to the first supply pump 3, but apply analogously to supply pump 30 as well.

[0045] In a first embodiment shown in Figure 3, the position of the piston rod 6 of the supply pump 3 can be detected by a stationary Hall sensor 7 detecting the magnetic field of a magnet connected to the piston rod 6 and moving with the piston rod 6.

[0046] 8 measures. The movement of the piston rod 6 is indicated by an arrow in Figure 3. The movement of the piston rod 6 periodically moves the magnet 8 past the Hall sensor 7. The Hall sensor 7 measures, for example at a sampling rate of 1 Hz, the magnetic flux density of the magnetic field generated by the magnet 8. This changes depending on the position of the magnet 8 relative to the Hall sensor 7. Based on a calibration, the position of the magnet 8, and thus the position of the piston rod 6, can be determined from the output signal of the Hall sensor 7 as a function of time.

[0047] From the resulting profile of the position of the piston rod 6 as a function of time, it is possible to deduce the amount of liquid pumped by the supply pump 3 in the specified period.

[0048] Alternatively or additionally, the position of the piston rod 6 can be detected according to a further embodiment shown in Figure 4 by means of a stationary inductive sensor.

[0049] 9 measures the distance to the surface 10 of a measuring body 11 that is rigidly connected to the piston rod 6 and moves periodically up and down with the piston rod 6 in the direction of the arrow shown. In the embodiment shown here, the measuring body 11 is conical, so that the distance of the sensor 9 to the surface 10 of the measuring body 11 changes depending on the position of the measuring body 11. Based on suitable calibration, the position of the measuring body 11, and thus the position of the piston rod 6, can be determined from the distance measured, for example, at a sampling rate of 1 Hz.

[0050] The resulting profile of the piston rod 6's position over time allows conclusions to be drawn about the quantity of liquid pumped by the supply pump 3 within the specified period. In principle, a wedge-shaped measuring element can be used instead of a conical, rotationally symmetrical measuring element 11. However, with such a design, due to the lack of rotational symmetry of the measuring element, particular care must be taken to ensure that the measuring element does not rotate relative to the sensor.

[0051] According to a third embodiment, shown in Figure 5, the position of the piston rod 6 can alternatively or additionally be detected by mechanically coupling a piston 12 of an additional measuring cylinder 13 to the piston rod 6 of the supply pump 3 (not shown in Figure 5). The position of the piston 12, which runs in the measuring cylinder 13 and synchronously with the piston rod 6, is detected by means of a stationary sensor 14. In a preferred embodiment, the measuring cylinder 13 is a pneumatic cylinder 13. A magnet is typically installed in the piston 12 of pneumatic cylinders 13, so that the movement of the piston 12 in the pneumatic cylinder 13 can be detected by means of a sensor 14 designed as a magnetic sensor.From the position of the piston 12 within the pneumatic cylinder 14, which is recorded, for example, with a sampling rate of 1 Hz, the position of the piston rod 6 of the supply pump 3 can be deduced based on a calibration.

[0052] From the resulting profile of the position of the piston rod 6 as a function of time, it is possible to deduce the amount of liquid pumped by the supply pump 3 in the specified period.

[0053] Alternatively or additionally to the methods described above, the position of a follower plate resting on the material reservoir 2 (not shown in the figures) can be recorded at different times during the metering process to determine the delivery rate of the supply pump 3. A follower plate resting on the liquid level of the material reservoir 2 in the reservoir lowers slowly along with the liquid level during the metering process. Therefore, if the diameter of the reservoir is known, the position of the follower plate can be used as a measure of the amount of liquid metered from the material reservoir 2 into the delivery line 5 by the supply pump 3, and thus simultaneously as a measure of the amount of liquid metered at the other end of the delivery line 5 by the metering pump 4.As already explained above, this method variant is particularly suitable as a supplement to the previously described methods for determining the delivery rate of the supply pump 3 by means of determining the position of the piston rod 6.

[0054] The position of the follower plate can be determined using a suitable displacement measuring system, for example, using a cable-extension sensor, a magnetic sensor, and / or an optical sensor. Finally, particularly for further comparison with the aforementioned methods, the quantity of liquid dispensed by the metering pumps 4, 40 during a metering process can be weighed using a scale 16 shown in Figure 1.

[0055] In the embodiment of the metering station 1 shown in Figures 1 and 2, the metering pumps 4, 40 are designed as progressive cavity pumps and thus as rotary pumps. The combination of metering pumps 4, 40 designed as rotary pumps with supply pumps 3, 30 designed as piston pumps, in which the piston performs a translational movement, is particularly advantageous because these two pump types are based on fundamentally different operating principles, which can further increase the probability of fault detection.

[0056] Reference symbol list

[0057] 1 dosing station

[0058] 2. Material stock / storage container

[0059] 3 Supply pump

[0060] 4 Dosing pump

[0061] 5 Conveyor line

[0062] 6 piston rod

[0063] 7 Hall sensor

[0064] 8 Magnet

[0065] 9 Inductive sensor

[0066] 10 surface

[0067] 11 measuring bodies

[0068] 12 pistons

[0069] 13 Measuring cylinders / pneumatic cylinders

[0070] 14 Sensor

[0071] 15 Collection container

[0072] 16 Scales

[0073] 20 Material stock / storage container

[0074] 30 Supply pump

[0075] 40 metering pump

[0076] 50 Conveyor line

Claims

Patent claims 1. Method for monitoring the dosage of at least one liquid within a Dosing station (1), wherein the dosing station (1) comprises: a material supply (2) of the liquid to be dosed, a supply pump (3), a metering pump (4) and a delivery line (5) extending between the supply pump (3) and the metering pump (4), wherein the supply pump (3) is suitable for pumping the liquid from the material supply (2) through the delivery line (5) to the metering pump (4) and wherein the metering pump (4) is designed to dose a predetermined quantity of liquid, characterized in that during a metering process a delivery rate of the supply pump (3) is recorded and the recorded delivery rate of the supply pump (3) is compared with a predetermined metering rate of the metering pump (4).

2. Method according to claim 1, characterized in that a decision is made as to whether a dosing error exists by comparing the measured delivery rate of the supply pump (3) and the predetermined dosing rate of the dosing pump (4).

3. Method according to claim 1 or 2, characterized in that the supply pump (3) is designed as a reciprocating piston pump with a piston and a piston rod (6) rigidly connected to the piston and that, in order to determine the delivery rate of the supply pump (3), the position of the piston rod (6) is determined at different times during the metering process, wherein the quantity of liquid fed into the delivery line (5) by the supply pump (3) during the metering process is deduced from the determined positions of the piston rod (6).

4. Method according to claim 3, characterized in that the position of the piston rod (6) is detected during the metering process with a sampling rate of at least 0.1 Hz, preferably at least 1 Hz.

5. Method according to claim 3 or 4, characterized in that the position of the piston rod (6) is detected by a Hall sensor (7) measuring the magnetic field of a magnet (8) connected to and moving with the piston rod (6), wherein the position of the magnet (8) and thus the position of the piston rod (6) is inferred from the measured magnetic flux density.

6. Method according to any one of claims 3 to 5, characterized in that the position of the piston rod (6) is detected by an inductive sensor (9) measuring the distance to the surface (10) of a measuring body (11) connected to and moving with the piston rod (6), wherein the measuring body (11) is conical or wedge-shaped is designed such that the distance to the surface (10) of the measuring body (11) changes depending on the position of the measuring body (11), and wherein the position of the measuring body (11) and thus the position of the piston rod (6) is inferred from the measured distance.

7. Method according to one of claims 3 to 6, characterized in that the position of the piston rod (6) is detected by mechanically coupling a piston (12) of an additional measuring cylinder (13) to the piston rod (6) of the supply pump (3), wherein the position of the piston (12) is detected by means of a sensor (14) and wherein the position of the piston rod (6) is inferred from the position of the piston (12).

8. Method according to one of claims 1 to 7, characterized in that, in order to detect the delivery rate of the supply pump (3), the position of a follower plate resting on the material supply (2) is detected at different times during the dosing process.

9. Method according to one of claims 1 to 8, characterized in that the quantity of liquid dispensed by the metering pump (4) during a metering process is weighed and the weight of the dispensed quantity of liquid is compared with the delivery rate of the supply pump (3) and / or the predetermined metering rate of the metering pump (4) as measured during the metering process.

10. Method according to one of claims 1 to 9, characterized in that the metering pump (4) is designed as a rotary pump.

11. A method according to any one of claims 1 to 10, characterized in that a first and a second liquid are dispensed in a predetermined mixing ratio in the dispensing station (1), and wherein the dispensing station (1) comprises: a first material reservoir (2) of the first liquid to be dispensed, a first supply pump (3), a first dispensing pump (4), and a first delivery line (5) extending between the first supply pump (3) and the first dispensing pump (4), wherein the first supply pump (3) is suitable for pumping the first liquid from the first material reservoir (2) through the first delivery line (5) to the first dispensing pump (4), and wherein the first dispensing pump (4) is configured to dispense a predetermined quantity of liquid, wherein the dispensing station (1) further comprises: a second material reservoir (20) of the second liquid to be dispensed, a second supply pump (30),a second metering pump (40) and a second delivery line (50) extending between the second supply pump (30) and the second metering pump (40), wherein the second supply pump (30) is suitable for supplying the second liquid from the second material supply (20) through the second delivery line, (50) to the second metering pump (40) and wherein the second metering pump (40) is configured to dispense a predetermined quantity of liquid, wherein during a metering process a delivery rate of the first supply pump (3) is recorded and the recorded delivery rate of the first supply pump (3) is compared with a predetermined metering rate of the first metering pump (4) and wherein during the metering process a delivery rate of the second supply pump (30) is recorded and the recorded delivery rate of the second supply pump (30) is compared with a predetermined metering rate of the second metering pump (40).

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