FLOW SENSOR AND METHOD FOR MEASURING A FLOW

Description

[0001] The present invention relates to a flow sensor for measuring a flow difference and a method for measuring a flow difference.

[0002] In particular, the present invention relates to a magnetic inductive sensor for measuring the difference in a flow of fluid streams flowing through two measuring chambers or channels.

[0003] The flow difference (inlet minus outlet) (also known as flow balance) of fluids is an important parameter, for example, in dialysis treatments. It is important that the water balance of dialysis patients is not negatively affected during treatment, but rather that the treatment supports the achievement of a healthy water balance. To achieve this, the patient's fluid balance must be known as accurately as possible.

[0004] In principle, the flow difference can be measured directly or determined by calculating two absolute flow measurements. A direct differential flow measurement is more accurate (or more cost-effective) than an indirect differential measurement by combining two absolute measurements whose difference is calculated, because absolute measurements are inherently very complex in terms of measurement accuracy and are also more error-prone. A direct differential measurement, on the other hand, can achieve greater accuracy with less effort because the measurement errors (per channel) occurring in the absolute measurement cancel each other out. Nevertheless, measurement accuracy continues to be a problem with known differential flow sensors, such as the generic flow sensor known from JP5467576 (B2).

[0005] Based on this, advantageous further developments were disclosed, for example, in WO 2015 / 197424 and EP 3 254 066 B1, from which disposable sensor cassettes with electrodes for arrangement in a magnetic yoke are known.

[0006] The measuring principle consists of two measuring channels, each penetrated by a magnetic field perpendicular to the flow direction, and two or more electrodes (arranged perpendicular to the magnetic field and flow direction). The magnetic field separates unlike charge carriers in the fluid (Hall effect) and transports them perpendicular to the magnetic field vector and the flow direction.

[0007] In the case of the solutions disclosed in WO 2015 / 197424 and EP 3 254 066 B1, electrodes are located at the two channel edges, intended to measure the potential resulting from charge separation. The electrical potential in the liquid resulting from charge separation is measured using these measuring electrodes. Further prior art is represented by documents DE102010003642A1 and US2015 / 135848A1.

[0008] However, these known sensors have the problem that they do not guarantee sufficient measurement accuracy over time for extracorporeal blood treatment, especially dialysis.

[0009] This is because even microscopic displacements or vibrations of the sensor cassette are sufficient over time to lead to intolerable measurement errors: Since the magnetic field in the known sensors is not perfectly homogeneous, the two measuring chambers or channels are penetrated differently by field lines of a magnetic field.

[0010] Temperature changes and vibrations are therefore sufficient for existing sensors to push the measurement accuracy beyond the tolerable range for dialysis. Vibrations occur, for example, from pumps (e.g., roller pumps, diaphragm pumps), from inherent vibration, or from pressure pulses on the fluid flowing through the measurement channels. In the case of dialysis, movement of the lines by a patient can also lead to further displacement of the sensor, thus further deteriorating measurement accuracy.

[0011] The present invention is based on the object of mitigating or even completely eliminating the problems known from the prior art and, in particular, of providing an improved differential flow sensor that offers sufficient measurement accuracy over a measurement period of several hours. This object is achieved by a flow sensor, a blood treatment device, and a system according to the independent claims. Further advantageous developments of the invention are the subject of the dependent claims.

[0012] A flow sensor according to the invention for measuring a flow difference comprises: at least two measuring chambers through which fluid can be conducted; at least one means for generating a magnetic field for charge separation in a fluid flowing through the at least two measuring chambers; and at least one means for measuring an electrical potential in the fluid flowing through the at least two measuring chambers. The at least two measuring chambers are arranged such that the same magnetic field line of the magnetic field for charge separation passes through them. The flow sensor also comprises a temperature sensor for measuring the temperature of a fluid.

[0013] In other words, according to the invention, in a flow sensor, the arrangement of the measuring chambers (or channels) is such that the geometric regions of both measuring channels in which the flows of the fluid are measured are arranged such that they are penetrated by the same magnetic field lines.

[0014] The two measuring chambers or the areas of the measuring chambers are arranged, for example, one above the other, one below the other, or even next to each other. The arrangement is arbitrary, as long as it is ensured that both measuring chambers or the areas of the measuring chambers in which the fluid flows are measured are traversed by the same magnetic field lines.

[0015] A flow sensor with such an arrangement is robust against temperature changes, vibrations and other environmental influences because both measuring chambers or channels are always affected by the environmental influences to the same extent.

[0016] This means that in a differential measurement the changes are not significant, since the same conditions regarding the magnetic field prevail in both measuring chambers or the magnetic field in both measuring chambers is influenced to the same extent by the environmental influences.

[0017] The means for measuring an electrical potential preferably comprises one or more measuring electrodes. Preferably, each measuring chamber or channel has two measuring electrodes.

[0018] In other words, according to a preferred embodiment, each of the two measuring chambers is assigned a means for measuring an electrical potential and the at least two measuring chambers and / or the means for measuring an electrical potential assigned thereto are aligned with one another.

[0019] In a particularly preferred embodiment, the measuring electrodes of both channels are arranged in alignment or in such a way that their projection onto a plane (running parallel to the flow of the fluid and perpendicular to the magnetic field) is exactly congruent.

[0020] As a result, the flow sensor or the cassette containing it is designed in such a way that it can be inserted into a magnetic yoke, for example of a blood treatment device, in such a way that the measuring areas in both channels are penetrated by exactly the same field lines.

[0021] The method by which the electrical potential resulting from the magnetically induced charge separation is measured is arbitrary. For example, electrodes in direct contact with the fluid can be used, or it can be measured indirectly using capacitive methods. Furthermore, the shape, number, and positioning of the measuring devices, especially the measuring electrodes, are arbitrary. More than two electrodes can also be used.

[0022] An indirect measurement of the potential would also be conceivable: Here, for example, the electric field is measured capacitively. In a capacitive measurement, the measuring devices for measuring the electric field are not located in the fluid, but are arranged outside it (separated by an insulator). A flow sensor according to the invention is preferably a magnetic-inductive differential flow sensor.

[0023] Two synergistic advantages arise when a temperature is also measured in the flow sensor: First, temperature measurement of the fluids or liquids is usually required for extracorporeal blood treatments. If the flow sensor also integrates the temperature measurement, an additional sensor, which would otherwise record additional fluid volume, can be advantageously eliminated.

[0024] Secondly, with knowledge of the temperature, a correction of flow measurements or the measurement accuracy can be made.

[0025] Preferably, a flow sensor, which also serves as a temperature sensor, is used in conjunction with an extracorporeal blood treatment device, in particular a dialysis machine.

[0026] According to a preferred embodiment, a treatment machine into which the cassette with the flow sensor according to the invention can be inserted comprises an infrared diode and an evaluation device that evaluates the light measured by the diode and thus determines the temperature of a medium or fluid located in front of the diode. A recess or a type of "window" corresponding to the diode is provided in the flow sensor cassette.

[0027] The wall thickness in the window area is preferably approximately 300 µm–600 µm, especially approximately 500 µm. Other thicknesses are conceivable. Alternatively, a PT1000 sensor, for example, can be used for temperature measurement.

[0028] The temperature sensor is preferably integrated and / or permanently installed in a cassette containing the flow sensor. In this case, an associated evaluation device is preferably also integrated into the cassette. Alternatively or additionally, the temperature sensor and / or the evaluation device can also be provided by the blood treatment device and assigned to or connected to the cassette.

[0029] Alternatively or additionally, the flow sensor can comprise a conductivity sensor for measuring the conductivity of a fluid. The conductivity sensor is also preferably integrated and / or permanently installed in a cassette containing the flow sensor. In this case, an associated evaluation device is preferably also integrated into the cassette.

[0030] Alternatively or additionally, the temperature sensor and / or the evaluation device can also be provided by the blood treatment device and assigned to or connected to the cassette.

[0031] A preferred embodiment for a conductivity measuring arrangement comprises three electrodes arranged one behind the other in the fluid channel (in contact with the fluid) in the direction of flow. The middle electrode is preferably designed as a flat rectangle, and the other two electrodes are each designed as a "U" enclosing the fluid channel. All three electrodes are preferably made of stainless steel.

[0032] During measurement, a voltage is applied to the center electrode such that a current flows through the fluid to the downstream and upstream electrodes. The two outer electrodes are grounded. The voltage drop between the center electrode and the outer electrodes is measured, as is the flowing current. The conductance is measured from the current and voltage drop. With knowledge of the geometry, the conductivity of the fluid can be determined.

[0033] The evaluation device, which determines conductivity from the electrical measurements at the electrodes, is preferably part of the treatment machine, not the flow sensor cassette. This allows the sensor cassette to be designed particularly cost-effectively, allowing it to be designed as a disposable item.

[0034] In principle, the flow sensor and / or the cassette containing it can be designed as a disposable or as a multiple item.

[0035] A further aspect of the present invention relates to a blood treatment device, in particular a dialysis machine, which is designed to be used with a flow sensor according to the invention or which has a flow sensor according to the invention.

[0036] It has proven advantageous in practice if the blood treatment device is designed to at least partially detachably receive a flow sensor according to the invention and is preferably equipped with a receptacle for the flow sensor for this purpose.

[0037] The receptacle can be designed in any way. For example, the receptacle for the blood treatment device can be designed like a pair of forceps (preferably with internal electrical contacts) or as a recess, such as a slot.

[0038] It is also conceivable for the receptacle to be in the form of a recess that can be closed by a door when the sensor cassette is inserted into the recess. The door can be designed, e.g., pre-tensioned, to keep the recess closed unless a user actively opens the door.

[0039] Locking elements can also be provided to hold the sensor cassette on or in the blood treatment device.

[0040] Furthermore, it has proven advantageous if the at least one means for generating a magnetic field for charge separation in a fluid flowing through the at least two measuring chambers is arranged on the side of the blood treatment device. In other words, one or more magnets are preferably provided on the blood treatment device.

[0041] Preferably, the at least one means for generating a magnetic field for charge separation comprises at least two magnetic poles arranged on opposite sides of a receptacle for the flow sensor or sensor cassette. This embodiment is particularly advantageous when the flow sensor is designed as a disposable device. Alternatively, two electromagnets can also be used.

[0042] A further aspect of the invention relates to the use of a flow sensor according to the invention and / or a blood treatment device according to the invention for blood-to-blood balancing. Due to the compact design of the flow sensor according to the invention, only a small amount of blood is required for the measurement, which is why the flow sensor according to the invention is particularly suitable for such an application.

[0043] For example, WO 2019 / 139671 A1 discloses a treatment that involves "donating" the dialysis capacity of a healthy kidney of a first person to a second person with renal insufficiency. A dialyzer can also be used in this case. A balance sensor according to the invention can be used in various ways to measure changes in the fluid balance (water balance) of the person with renal insufficiency.

[0044] For example, a flow sensor according to the invention can be used to measure the fluid balance (inlet minus outlet) of the dialyzer for a person with renal insufficiency. This assumes that the healthy person can regulate their water balance independently.

[0045] Optionally, a second balance sensor could be used to complete the system, which determines the fluid balance (input minus output) of the dialyzer for the healthy person.

[0046] Alternatively, two flow sensors according to the invention can be used for blood-to-blood balancing. Preferably, a differential flow sensor according to the invention is used at each of the dialyzer inlet and outlet. In this embodiment of using a flow sensor presented here, the fluid balance for the two dialyzer halves or for the two people would be determined in a second step: In the first step, an "input balance" (the input flow of person 1 into the dialyzer is measured differentially compared to the input flow of person 2 into the dialyzer) is measured by a first sensor, and simultaneously, an "output balance" is measured at the dialyzer outlet. From these two balances, a fluid balance for both people can be calculated in a second step, for example, by subtracting the "output balance" from the "input balance."

[0047] Using the flow sensor at the inlet of the dialyzer, the difference in flow at the inlet of the dialyzer for the healthy person and the person with renal insufficiency is determined.

[0048] Similarly, at the outlet of the dialyzer, the difference in flow from the dialyzer for the healthy person and the person with renal insufficiency is determined.

[0049] From both differences, one can infer the net water flow of both persons.

[0050] A further aspect of the invention relates to a method for measuring a flow difference of a fluid, preferably with a flow sensor according to the present invention, comprising the steps: Conducting fluid through at least two measuring chambers or channels, generating a magnetic field for charge separation in the fluid, measuring an electrical potential in the fluid flowing through the at least two measuring chambers, wherein the magnetic field for charge separation is generated such that the same magnetic field line of the magnetic field for charge separation passes through the at least two measuring chambers, and

[0051] Detecting the temperature of the fluid, preferably by means of a temperature sensor integrated into the flow sensor.

[0052] Preferably, the method also comprises the upstream step of inserting a flow sensor cassette into a corresponding receptacle of a blood treatment device according to the invention.

[0053] Alternatively or additionally, the method also comprises the step of detecting the conductivity of the fluid, preferably by means of a conductivity sensor integrated into the flow sensor.

[0054] Further advantages, features, and effects of the present invention will become apparent from the following description of preferred embodiments with reference to the figures. Identical or similar components are designated by the same reference numerals in the drawings. Here: Fig. 1 a cross-section of a flow sensor according to the invention; Fig. 2 a further cross-section of a flow sensor according to the invention; Fig. 3 a longitudinal section of a flow sensor according to the invention; and Fig. 4 a diagram illustrating the use of a sensor according to the invention for blood-blood balancing.

[0055] As in Fig. 1As shown, a flow sensor 1 according to the invention has two measuring chambers or channels 2 through which a fluid flows during the measurement. A measuring electrode 3 is arranged on opposite sides of each measuring chamber 2 to measure an electrical potential resulting from charge separation in the fluid.

[0056] The sensor is inserted into a magnetic yoke 4, which has two magnetic coils 5, which are connected to each other by a bracket 6. Magnetic poles 7 are arranged between the coils 5 and the measuring chambers 2. A magnetic field is generated by means of the magnets, the magnetic field vector of which is determined by the Fig. 1 The magnetic field vector is orthogonal to the flow direction of the fluid in the measuring chambers, which is shown in Fig. 1 runs orthogonal to the plane of the paper.

[0057] In Fig. 2The fluid flow direction is indicated by two opposing arrows. The magnetic field vector is orthogonal to the fluid flow direction.

[0058] Fig. 3 Figures 3a and 3b show a longitudinal section of a flow sensor according to the invention. The illustration in Figure 3b ) is compared to the representation in Figure 3a ) was turned.

[0059] The Fig. 3 The flow sensor shown is not only designed for differential flow measurement, but also has an integrated temperature sensor and an integrated conductivity sensor.

[0060] As shown in Figures 3a and 3b, a flow sensor according to this embodiment has three electrodes for conductivity measurement. These are designated by reference numerals 1a, 1b, 1c, and 2a, 2b, and 2c, respectively. The electrode designated by reference numeral 1a or 2a serves as the ground electrode for conductivity measurement. The electrode designated by reference numeral 1c or 2c serves as the hot electrode for conductivity measurement. The electrode designated by reference numeral 1b or 2b is also used for conductivity measurement.

[0061] Electrodes 1cl and 1cr preferably serve as measuring electrodes for flow measurement and are arranged to the left (1cl) and right (1cr) of a measuring chamber, respectively. Electrodes 2cl and 2cr preferably serve as measuring electrodes for flow measurement and are arranged to the left (2cl) and right (2cr) of a measuring chamber, respectively.

[0062] The reference symbols 1cl and 2cl each designate the left measuring electrode and the reference symbols 1cr and 2cr each designate the right measuring electrode.

[0063] Fig. 4 a diagram illustrating the use of a sensor according to the invention for blood-blood balancing.

[0064] In the Fig. 1 In the setup shown, the dialysis capacity of a healthy kidney of a person P2 is made available to a person with renal insufficiency P1. A dialyzer 7 with a membrane 8 is used.

[0065] A balance sensor according to the invention can be used in various ways to measure the change in the fluid balance or water balance of the person with renal insufficiency P1.

[0066] For example, a balance (input minus output of the dialyzer) for the person P1 with renal insufficiency is determined using a flow sensor 1 according to the invention. This balance is shown in Fig. 4indicated as ellipse 9. Here, it is assumed that the healthy person P2 regulates his or her water balance independently. The balance (input minus output of the dialyzer) for the healthy person P2 is therefore in Fig. 4 shown as a dashed ellipse 10.

[0067] The balance for the healthy person can be determined by means of a second flow sensor 1, which balances the inlet against the outlet on the side of the dialyzer assigned to the healthy person P2.

[0068] In Fig. 4 Two sensors 1 according to the invention are shown. However, this is merely an example, and only one flow sensor 1 may be provided, which determines the fluid balance of person P1 or person P2.

Claims

1. A flow sensor (1) for measuring a flow difference, comprising at least two measurement chambers (2) through which fluid is conductible; at least one means for producing a magnetic field for charge separation in a fluid flowing through the at least two measurement chambers (2); and at least one means for measuring an electric potential in the fluid flowing through the at least two measurement chambers, wherein the at least two measurement chambers (2) are arranged such that they are run-through by the same magnetic field line of the magnetic field for charge separation, characterized in that the flow sensor (1) additionally has a temperature sensor for measuring the temperature of a fluid.

2. A flow sensor in accordance with claim 1, characterized in that the flow sensor (1) is a magnetically inductive differential flow sensor.

3. A flow sensor (1) in accordance with one of the preceding claims, characterized in that the flow sensor (1) additionally has a conductivity sensor for measuring the conductivity of a fluid.

4. A flow sensor (1) in accordance with one of the preceding claims, characterized in that each of the two measurement chambers (2) has a means for measuring an electric potential associated with it and the at least two measurement chambers (2) and / or the means for measuring an electric potential associated with them are aligned with one another.

5. A flow sensor (1) in accordance with one of the preceding claims, characterized in that the flow sensor (1) is designed as disposable.

6. A blood treatment device, in particular a dialysis machine, having a flow sensor (1) in accordance with one of the claims 1 to 5.

7. A blood treatment device, in particular a dialysis device in accordance with claim 6, characterized in that the blood treatment device is adapted to at least partly releasably receive a flow sensor (1) in accordance with one of the claims 1 to 5 and is preferably equipped with a mount for the flow sensor for this purpose.

8. A system having a blood treatment device and a flow sensor (1) in accordance with one of the claims 1 to 5, characterized in that the at least one means for producing a magnetic field for charge separation is arranged at the side of the blood treatment device in a fluid flowing through the at least two measurement chambers (2).

9. A system in accordance with claim 8, characterized in that the at least one means for producing a magnetic field for charge separation comprises at least two magnetic poles that are arranged at mutually opposite sides of a mount for the flow sensor (1).

10. Use of a flow sensor(1) in accordance with one of the claims 1 to 6 and / or of a blood treatment device in accordance with one of the claims 6 to 7 for blood-blood balancing.

11. A method of measuring a flow difference of a fluid, preferably using a flow sensor (1) in accordance with one of the claims 1 to 6, comprising the steps: conducting fluid through at least two measurement chambers (2); producing a magnetic field for charge separation in the fluid; and measuring an electric potential in the fluid flowing through the at least two measurement chambers (2), wherein the magnetic field for charge separation is produced such that the same magnetic field line of the magnetic field for charge separation runs through the at least two measurement chambers, further comprising the step: detecting the temperature of the fluid, preferably by means of a temperature sensor integrated in the flow sensor.

12. A method in accordance with claim 11, further comprising the step: detecting the conductivity of the fluid, preferably by means of a conductivity sensor integrated in the flow sensor.