METHOD FOR DETERMINING A FLOW RATE, FLOW SENSOR AND MEASURING SYSTEM WITH A FLOW SENSOR

Description

[0001] The invention relates to a method for determining a flow rate of a fluid through a flow sensor having a measuring channel according to claim 1, a flow sensor according to claim 9, a measuring system having a flow sensor according to claim 13 and a differential pressure sensor according to claim 15.

[0002] Flow measurements are used in a wide variety of applications, including ventilators, inhalers, oxygen concentrators, and anesthesia machines. Various measurement approaches exist: pressure-based, thermal, ultrasound, and variable-area flow measurements.

[0003] Most pressure-based approaches exploit the relationship between pressure and flow rate. In a Venturi meter, the flow channel is reduced in size, which changes the flow velocity in the channel. This in turn creates a pressure difference between the fast and slow flow regions. The resulting differential pressure between the fast and slow flow regions is now flow-dependent. Thus, the flow can be derived from the measured differential pressure. An alternative approach is to insert a resistor into the flow channel. This causes a certain proportion of the pressure to drop across the resistor. This creates a pressure difference before and after the resistor, which in turn is flow-dependent. This differential pressure is measured to determine the flow. There are various ways in which such a resistor can be constructed. For example, an orifice plate can be used as a resistor.Other flow measurements use sieves, honeycomb elements or linear flow elements as resistance.

[0004] Every resistance or differential pressure consists of two parts: a laminar part and a turbulent part. The laminar part has a linear relationship between the flow and the differential pressure in the measuring channel, while the turbulent part has a quadratic relationship between the flow and the differential pressure.

[0005] US6681189 A discloses a computer-assisted method for determining a flow rate of a fluid flowing through a conduit having an obstruction flowmeter, comprising: receiving a beta ratio value indicative of a beta ratio of the obstruction flowmeter; receiving a pressure differential value indicative of a pressure differential across the obstruction flowmeter; receiving a density value indicative of a density of the fluid; receiving a discharge coefficient formula for the obstruction flowmeter, the discharge coefficient formula being a function of the beta ratio of the obstruction flowmeter and an Euler number for the fluid flowing through the conduit; and determining the flow rate by the computer based on the received beta ratio value, the received pressure differential value, the received density value, and the received discharge coefficient formula.

[0006] CN212340332 U discloses a method for reducing interference in high-precision flow meters. The measuring device comprises a measuring tube with several pressure rings arranged in series, between which two differential pressure sensors are arranged. The differential pressure sensors measure two adjacent pressures between the adjacent pressure rings.

[0007] US2002 / 016688A1 discloses a method for accurately calculating gas and liquid mass flows in an extended venturi tube, comprising the use of four values ​​determined by testing: ΔP3 being the measured pressure difference across the venturi throat; ΔP2 being the measured pressure difference across the extended venturi neck; P being the absolute pressure upstream of the venturi tube; and T being the temperature of the upstream stream.

[0008] US2016341585A1 discloses a multiphase flowmeter comprising two resistive elements in series and in which three differential pressures are measured: dp1 and dp2 are measured across each resistive element, while dp3 is measured across both resistive elements.

[0009] The disadvantage of these known solutions is that they only cover a limited flow measurement range, which is also known as the turndown ratio. The turndown ratio is calculated by dividing the maximum measurable flow rate by the minimum measurable flow rate and thus characterizes the range capability of a flow measurement.

[0010] The object of the present invention is therefore to provide a method that eliminates at least one of the aforementioned disadvantages and, in particular, to provide an improved method, an improved flow sensor, or an improved measuring system that enables the flow rate to be evaluated over a larger flow measuring range with improved absolute resolution and measurement accuracy. Furthermore, a differential pressure sensor is to be created that can simultaneously measure multiple differential pressure ranges with improved resolution.

[0011] The problem is solved by the features of the independent claims. Advantageous further developments are set forth in the figures and in the dependent patent claims.

[0012] According to the method according to the invention for determining a flow rate of a fluid through a flow sensor with a measuring channel, the method comprises at least the following steps: a. Providing a fluid in the measuring channel of the flow sensor, wherein three resistance elements (20a-20c) are present in the measuring channel (19); b. Detecting at least one first differential pressure in the measuring channel, wherein the at least one first differential pressure is present in a first differential pressure range in the measuring channel, and wherein the first differential pressure is detected via the second resistance element (20b) or is detected via the second and third resistance elements (20b, 20c); c. Detecting at least one second differential pressure in the measuring channel, wherein the at least one second differential pressure is present in a second differential pressure range in the measuring channel and the differential pressure in the second differential pressure range comprises the differential pressure in the first differential pressure range; d. Transmitting the detected differential pressures to an evaluation unit; e. Determining a flow rate in the measuring channel using the evaluation unit on the basis of the detected differential pressures.

[0013] A gas or a liquid can typically be used as the fluid. In particular, the flow sensor can be used to check the flow rate of the ventilation gas (as a fluid) through a ventilator. A differential pressure in the measuring channel is generated with the help of at least one resistance element in the measuring channel, since the resistance element creates a first pressure on a first side of the resistance element in the measuring channel and a second pressure on a second side of the resistance element. A differential pressure is created when the two pressures are measured and the measured pressures are subtracted from one another or the differential pressure is measured directly. Alternatively, a small amount of the fluid flows through a differential pressure sensor arranged on the measuring channel, whereby the differential pressure sensor measures the differential pressure directly.

[0014] The first differential pressure is different from the second differential pressure, with the first differential pressure being smaller than the second differential pressure. Combining two different measuring ranges, which at least overlap, with different differential pressures in the measuring channel of the flow sensor increases the resolution and accuracy across the entire measuring range relevant for the measurement, improves the determination of the flow rate in the measuring channel, and increases the turndown ratio. Resolution is defined here as the change in pressure difference per change in flow in the measuring channel.

[0015] Typically, it is desired that the resolution and accuracy are sufficiently high across the entire measuring range in the measuring channel. Two conditions are relevant for this: firstly, the differential pressure must be selected to be large enough at the maximum fluid flow, and secondly, the laminar part of the measurement must be as large as possible. This means that the resolution and the differential pressure are greater at small flow rates in the measuring channel. In general, both conditions or effects counteract each other. If the differential pressure is increased, primarily only the quadratic component of the differential pressure is increased, which in turn worsens the ratio of laminar to turbulent part in the measurement. If one attempts to keep the flow more laminar, the total differential pressure is reduced.

[0016] Another effect of the quadratic part of the measurement is that the resolution of the calculated flow rate is much higher at high flow rates than at low flow rates. Typically, one would want a higher absolute resolution at low flow rates, or at least the same absolute resolution as at high flow rates.

[0017] Instead of a single resistor, the measuring channel contains at least two resistors. The differential pressures across the resistors are added linearly, and the laminar component is increased proportionally to the number of resistors. Low flow rates are measured via a single differential pressure, specifically the sum of all differential pressures, while high flow rates are measured only via individual differential pressures, which may be lower. This creates multiple pressure ranges that can be measured individually. The flow rate range to be measured across and the number of differential pressure ranges can be freely selected.

[0018] The absolute resolution is better distributed across the entire measuring range thanks to the aforementioned method. On the one hand, high resolution and accuracy are achieved at low flow rates due to the large laminar flow rate; on the other hand, a similar resolution is also achieved at high flow rates because measurements are taken over fewer differential pressure ranges. In general, the aforementioned methods can be used to achieve any desired resolution and different turndown ratios, depending on requirements.

[0019] The direction of fluid flow through the measuring channel is irrelevant, so the aforementioned method can be used for bidirectional measurements. This means that it doesn't matter which direction the fluid flows through the measuring channel; the principle works exactly the same. Furthermore, this measurement method exhibits no hysteresis effects in the measurement.

[0020] The second differential pressure range encloses the first differential pressure range in the measuring channel, so that the internal measurement of the first differential pressure is protected from external turbulence by the external measurement of the second differential pressure, which occurs particularly at high flow rates. Furthermore, the total differential pressure is kept as low as possible.

[0021] Preferably, the first differential pressure and the second differential pressure are recorded simultaneously. The pressure is measured at four points in the measuring channel, and the first differential pressure and the second differential pressure are determined. This enables quick and simplified recording and evaluation of the data from both differential pressures.

[0022] Preferably, the first differential pressure range in the measuring channel comprises at least one resistance element, with differential pressures in the differential pressure range from -20 kPa to 20 kPa being present. This allows high flow rates in the measuring channel to be easily determined or measured.

[0023] In particular, differential pressures in the differential pressure range of -1.2 kPa to 1.2 kPa, preferably -0.5 kPa to 0.5 kPa, are required. Differential pressure sensors can be provided that measure in this range, have a standardized design, and are therefore cost-effective to manufacture.

[0024] Preferably, the second differential pressure range in the measuring channel comprises at least two resistance elements, with differential pressures in the differential pressure range from -100 kPa to 100 kPa. This allows smaller flow rates in the measuring channel to be easily determined with the necessary resolution.

[0025] In particular, differential pressures in the differential pressure range from -5 kPa to 5 kPa, preferably from -1.5 kPa to 1.5 kPa, are present. Several resistance elements can be provided in the measuring channel, their construction being identical and thus cost-effective to manufacture.

[0026] The more resistance elements arranged in series in the measuring channel, the more freedom there is for scaling the measurement. The pressure in the pressure differential areas in the measuring channel is determined by the number of resistance elements. In addition, the differential pressure or pressure drop across a resistance element can be kept smaller if multiple resistance elements are present in the measuring channel. For a resistance element with a small differential pressure or pressure drop, the laminar component is generally larger, which in turn improves the overall resistance. The first resistance element, as defined here, is the resistance element that is first detected by the fluid, depending on the direction of flow. The second resistance element in the measuring channel is therefore detected by the fluid at a later point in time. The resistance element can be a disk with a number of defined holes, possibly of different sizes, in the disk.

[0027] In particular, the first or second differential pressure is measured via at least the last resistance element, so that the measurement of the differential pressure is independent of the flow. The laminar part of the flow increases the more resistance elements are arranged in series in the measuring channel. The flow will therefore have the largest laminar component over the last resistance element. This improves the resistance characteristic of the last resistance element compared to the second resistance element. An improved resistance characteristic leads to a further improvement in resolution.

[0028] In particular, at least one resistance element is constructed differently from another resistance element. The exact differential pressure ranges can be designed individually, with the maximum differential pressure and the resolution being adjusted individually in each differential pressure range.

[0029] According to the invention, the first differential pressure in the measuring channel is detected via the second resistance element or via the second and third resistance elements. Thus, the measurement of the first differential pressure, i.e., the internal measurement, is protected by the external resistance elements, preventing turbulence, especially at high flow rates, and thus further improving the accuracy of the measurement process.

[0030] In particular, the second differential pressure in the measuring channel is recorded across all three resistance elements

[0031] Preferably, a storage unit is provided in which at least one first threshold value for the first differential pressure is stored. The at least one first threshold value serves as a determination criterion for detecting the second differential pressure in the second differential pressure range. If the at least one first threshold value for the first differential pressure is reached, it can be automatically determined whether and how the second differential pressure is measured. A simple switching of the measurements between the first and second differential pressures is possible depending on the flow rate.

[0032] Alternatively or additionally, at least one first threshold value for the second differential pressure is stored in the storage unit. The at least one first threshold value serves as a determination criterion for detecting the second differential pressure in the second differential pressure range. If the at least one first threshold value for the second differential pressure is reached, switching between the measurements can occur depending on the flow rate.

[0033] Preferably, at least one threshold value is retrieved from the storage unit and compared in the evaluation unit with at least one of the two measured differential pressures. The evaluation unit can independently detect the flow rate at which a switch in the measuring range is necessary.

[0034] Preferably, the first threshold value of the first differential pressure is compared with the currently measured first differential pressure. The measurement process can be shortened if the desired resolution is already sufficient for the existing flow rate. In particular, step c. is performed if the first threshold value is greater than the currently measured first differential pressure.

[0035] Preferably, at least one differential pressure sensor is present, wherein the at least one differential pressure sensor measures the first differential pressure and the second differential pressure and the measuring range of the at least one differential pressure sensor for the second differential pressure is smaller than the measuring range of the at least one differential pressure sensor for the first differential pressure.

[0036] Alternatively, a second differential pressure sensor is provided, wherein the at least one differential pressure sensor (inner) measures the first differential pressure in the first differential pressure range, and the second differential pressure sensor (outer) measures the second differential pressure in the second differential pressure range. The measuring range for the first differential pressure sensor is larger than the measuring range of the second differential pressure sensor (outer). This further increases the resolution and thus the accuracy at small flow rates.

[0037] Preferably, the measuring range of the at least one differential pressure sensor (inner) is in the range from -20 kPa to 20 kPa, in particular -1.2 kPa to 1.2 kPa, preferably from -0.5 kPa to 0.5 kPa.

[0038] Preferably, the measuring range of the second differential pressure sensor (outer) is in the range from -2.5 kPa to 2.5 kPa, in particular -0.5 kPa to 0.5 kPa, preferably from -0.125 kPa to 0.125 kPa.

[0039] Preferably, at least one fluid property of the fluid in the measuring channel is recorded and used in step e) to determine the flow rate in the evaluation unit. This further improves the determination of the flow rate with the desired accuracy, since this depends not only on the geometry in the measuring channel, but also on the fluid properties themselves.

[0040] In particular, the fluid property is recorded by a user and / or measured with a sensor and / or calculated in the evaluation unit. This allows the process to be further improved using empirical values, e.g., for a specific fluid type. For example, the fluid properties are stored as parameters in a lookup table in the evaluation unit and can thus be easily calculated based on user input or the (other) fluid properties measured by the sensor. Thus, the fluid properties are directly available in the process, allowing for a fast and cost-effective measurement process.

[0041] Preferably, the fluid property is comprised of at least one parameter from the group of absolute pressure, temperature, humidity, fluid type, viscosity, or density. These can be used individually or in combination directly to determine the flow rate, thus increasing the accuracy of the measurement process and, in particular, allowing conversion to different flow measurement standards. The fluid property parameters are mapped to at least one mathematical function, for example, a polynomial, and can be taken into account when determining the flow rate.

[0042] A flow sensor according to the invention for determining a flow rate of a fluid in a measuring channel, in particular using a method as described above, comprises a measuring channel with at least four channel sections which are arranged in series adjacent to one another in the flow sensor and at least one resistance element is arranged between the adjacent channel sections, wherein each of the four channel sections has at least one measuring connection for measuring a fluid pressure.

[0043] At least two channel sections define the first differential pressure range and at least three channel sections define the second differential pressure range. Each differential pressure in the measuring channel is generated using at least one resistance element in the measuring channel, as previously described. The first differential pressure is different from the second differential pressure, whereby the first differential pressure is in particular smaller than the second differential pressure. The combination of two different measuring ranges with different differential pressures in the measuring channel of the flow sensor increases the resolution across the entire measuring range relevant for the measurement and improves the determination of the flow rate in the measuring channel. An optimal resistance element has the largest possible laminar resistance component. This is desired so that the absolute resolution is as high as possible for small flow rates.

[0044] The absolute measurement resolution is better distributed across the entire measuring range due to the aforementioned geometry of the flow sensor. On the one hand, high resolution is achieved at low flow rates due to the large laminar portion; on the other hand, a similar resolution is also achieved at high flow rates because measurements are taken over fewer differential pressure ranges. In general, with the flow sensor disclosed here and the aforementioned method, any desired resolution can be set for determining the flow rate, depending on requirements. Furthermore, the flow sensor has no moving parts, making it robust, durable, and miniaturizable.

[0045] Arranging the resistance elements in series results in a beneficial addition of the resistance values, while maintaining the ratio of linear to quadratic components. This means that the resistance maintains the desired ratio and the total resistance increases.

[0046] Preferably, at least one housing component is provided in which the three channel sections are formed. The housing component can be easily manufactured using additive manufacturing processes and comprises both the at least three channel sections and the resistance elements installed therein, optionally permanently. This allows the flow sensor to be manufactured easily and cost-effectively. Furthermore, the manufactured flow sensors exhibit comparable characteristics, eliminating the need for subsequent adjustment of the geometry.

[0047] Preferably, a strainer is arranged in the first channel section so that the flow rate measurement is not disturbed by unwanted foreign matter or preceding turbulence. In particular, another strainer is also arranged in the last channel section. This provides bidirectional protection for the measuring channel.

[0048] Preferably, at least two housing components are provided, each of which contains at least one of the three channel sections. This provides a simple housing with few components and defined differential pressure ranges, enabling reproducible detection of the first and second differential pressures.

[0049] Preferably, the resistance elements are arranged in the measuring channel in an interchangeable manner. This makes the housing, for example, easy to manufacture, and depending on the application of the flow sensor, different resistance elements can be easily arranged in the measuring channel, for example, to adapt the resolution of the measuring method to the fluid type. In particular, defective resistance elements can be easily replaced, allowing the flow sensor to be used for different applications, thus protecting the environment.

[0050] Preferably, at least one resistance element is designed differently from another resistance element. This allows the laminar or turbulent part to be adapted depending on the fluid type used.

[0051] Preferably, at least one differential pressure sensor is arranged at at least two of the measuring connections. The measuring connections can protrude from the pressure measuring sensor or run as a stub line into the measuring channel, so that the differential pressure sensor is also located in the measuring channel and / or is arranged outside the measuring channel. The differential pressure sensor can have at least four pressure measuring connections for detecting the first differential pressure and for detecting the second differential pressure, which are directly or indirectly connected to the measuring connections. In particular, a further differential pressure sensor is provided, wherein the at least one differential pressure sensor is directly or indirectly connected to two measuring connections of the flow sensor and the further differential pressure sensor is connected to two further measuring connections of the flow sensor.

[0052] Preferably, at least one absolute pressure sensor and / or one temperature sensor and / or one humidity sensor is present in the measuring channel. This allows additional fluid properties to be measured, improves the accuracy of determining the flow rate, and enables conversion to different flow rate measurement standards.

[0053] A measuring system according to the invention for determining a flow rate using a flow sensor, in particular using a flow sensor as described above and using at least one differential pressure sensor, comprises an evaluation unit connected at least to the at least one differential pressure sensor in order to detect at least a first differential pressure in the measuring channel of the flow sensor and to detect a second differential pressure in the measuring channel of the flow sensor. The differential pressure sensor is thus arranged between the measuring connections of the flow sensor and the evaluation unit, which can be seen at least from an electrical engineering perspective - in particular when the differential pressure sensor is arranged in the measuring channel of the flow sensor. In particular, the evaluation unit is designed to carry out the aforementioned method. Due to the aforementioned method, the absolute resolution is better distributed across the entire measuring range.On the one hand, high resolution and accuracy are achieved at low flow rates due to the large laminar flow rate. On the other hand, a similar resolution is also achieved at high flow rates because measurements are taken over fewer differential pressure ranges. In general, the aforementioned measuring system can be used to achieve any desired resolution, depending on the requirements.

[0054] Preferably, a display unit is provided to display at least the flow rate, so that a direct reading of the measured flow rate and / or the other aforementioned fluid properties on the measuring system is possible.

[0055] In particular, the flow rate can be displayed graphically, so that, for example, the temporal progression of the flow rate can be shown.

[0056] Preferably, a memory unit is provided in which at least a first threshold value is stored. This allows the previously described at least first threshold value to be easily and reproducibly retrieved and used in the evaluation unit.

[0057] Alternatively or additionally, at least one interface is available for reading recorded values ​​of differential pressures or flow rates. The recorded values ​​can then be transferred to an external evaluation device. The interface can be wireless or wired, so that a physical connection between the measuring system and the external evaluation device can be omitted. Alternatively or additionally, an interface is available for reading evaluated data.

[0058] A differential pressure sensor according to the invention for a flow sensor, in particular a flow sensor as described above, comprises four pressure measuring connections for detecting two different differential pressures in a measuring channel. Such a differential pressure sensor requires only one power supply and one housing, thus offering a simple and cost-effective design. The required readout protocol can be kept simple, and only one interface, such as a data bus, is required, simplifying the installation and maintenance of the differential pressure sensor.

[0059] The measuring range (inner) is preferably in the range from -20 kPa to 20 kPa, in particular -1.2 kPa to 1.2 kPa, preferably from -0.5 kPa to 0.5 kPa.

[0060] The measuring range (outer) is preferably in the range from -2.5 kPa to 2.5 kPa, in particular -0.5 kPa to 0.5 kPa, preferably from -0.125 kPa to 0.125 kPa.

[0061] Further advantages, features and details of the invention will become apparent from the following description, in which embodiments of the invention are described with reference to the drawings.

[0062] The list of reference symbols, like the technical content of the patent claims and figures, is part of the disclosure. The figures are described coherently and comprehensively. Identical reference symbols indicate identical components; reference symbols with different indices indicate functionally identical or similar components.

[0063] They show: Fig. 1 shows a flow sensor according to the invention in a schematic sectional view, Fig. 2 shows a measuring system according to the invention with a flow sensor according to Fig. 1 in a schematic side view, Fig. 3 the measuring system according to Fig. 2in a further schematic side view, Fig. 4 a flow diagram for a method according to the invention with a measuring system according to Fig. 2 or Fig. 3 , and Fig. 5 a differential pressure sensor according to the invention for a flow sensor according to Fig. 1 .

[0064] Fig. 1shows a flow sensor 15 with a housing component G for determining a flow rate of a fluid F in a measuring channel 19. The flow sensor 15 has a first connection 16 and a second connection 17 for connecting fluid hoses, wherein the measuring channel 19 extends between the first and second connections 16, 17. Sieves 24a, 24b are arranged at the two connections 16, 17 to protect the measuring channel from foreign bodies and to calm the flow of the fluid, thus enabling a reproducible measurement. The measuring channel 19 has four channel sections 18a-18d, which are arranged adjacent to one another in series in the flow sensor 15 and at least one resistance element 20a-20c is arranged in series between the adjacent channel sections 18a-18d. The flow sensor 15 has a first differential pressure region 22 and a second differential pressure region 23.The first differential pressure region 22 can also be referred to as the inner differential pressure region and comprises the two channel sections 18b and 18c, as well as the resistance element 20b. The second differential pressure region 23 can also be referred to as the outer differential pressure region and comprises the four channel sections 18a-18d, as well as the resistance elements 20a-20c. Each of the channel sections 18a-18d has a measuring connection 21a-21d for measuring a fluid pressure of the fluid F flowing through the measuring channel.

[0065] A first differential pressure sensor 25 is arranged at the measuring ports 21b and 21c. The measuring ports 21b and 21c protrude from the flow sensor 15. The differential pressure sensor 25 has two pressure measuring ports 26a and 26b and detects the first differential pressure in the first differential pressure range 22. The measuring range of the first differential pressure sensor 25 is in the range from -0.5 kPa to 0.5 kPa.

[0066] A second differential pressure sensor 27 is arranged at the measuring ports 21a and 21d on the flow sensor 15. The measuring range of the second differential pressure sensor 27 is in the range from -0.125 kPa to 0.125 kPa. The measuring ports 21a and 21d protrude from the flow sensor 15. The differential pressure sensor 27 has two pressure measuring ports 28a and 28b and detects the second differential pressure in the second differential pressure range 23.

[0067] The first differential pressure is measured via measuring ports 21b and 21c, and the second differential pressure is measured via measuring ports 21a and 21d. The first differential pressure is different from the second differential pressure, with the first differential pressure being, in particular, smaller than the second differential pressure.

[0068] The flow sensor 15 has a further measuring connection 30, which protrudes from the housing component G and is arranged on the channel section 18d. An absolute pressure sensor 35, which measures the absolute pressure in the fluid, is arranged at this measuring connection 30. The absolute pressure sensor has a measuring range of 0.5 to 2 mbar.

[0069] The flow sensor 15 has a holding device 40 arranged on the channel section 18d. A temperature sensor 41 and a humidity sensor 42, which measure the temperature and humidity in the fluid, are arranged on this holding device 40. These sensors are arranged in the measuring channel 19 via a holding device 40 and are electrically connected to an evaluation unit, as shown below.

[0070] The Fig. 2 and Fig. 3 show a measuring system 115 for determining a flow rate with the flow sensor 15 in a housing 116, as previously described according to the Fig. 1described. The differential pressure sensors 25 and 27, the absolute pressure sensor 35, the temperature sensor 41, and the humidity sensor 42 are electrically connected to an evaluation unit 120 for exchanging the respective measurement data. The evaluation unit 120 is thus connected to the differential pressure sensors 25 and 27 in order to detect the first differential pressure in the measuring channel 19 of the flow sensor 15 and to detect the second differential pressure in the measuring channel 19 of the flow sensor 15. The differential pressure sensors 25 and 27 are thus arranged between the measuring connections 21a-21d of the flow sensor 15 and the evaluation unit 120. The evaluation unit 120 has a memory unit 125 and a computing unit 130. Various mathematical functions (polynomials, lookup tables) for the temperature, the humidity for different fluid types, as well as various limit values ​​for the differential pressures are stored in the memory unit 125.The computing unit 130 is connected to the storage unit 125 for the exchange of data, wherein the detected differential pressures and the method described below are executed in the computing unit 135 of the evaluation unit 120.

[0071] A display unit 140 is provided to display at least the determined flow rate and / or the measured parameters of the temperature sensor 41, the humidity sensor 42, and / or the absolute pressure sensor 35. The display unit can comprise a simple display and input buttons or a touch display 141 for selecting individual programs, functions, or data. The display is configured to graphically represent the flow rate.

[0072] The measuring system features several interfaces 150 for reading recorded values ​​or differential pressure data. The recorded values ​​can thus be transferred to an external evaluation device. The interfaces shown are USB interfaces and RS232 interfaces. At least one interface 150a is a wireless interface, such as Bluetooth®.

[0073] Fig. 4 shows a flow diagram which includes a method for determining the flow rate, wherein the device features refer to the measuring system 115 according to the Fig. 2 and Fig. 3 reference is made.

[0074] The method for determining a flow rate of a fluid through a flow sensor 15 with a measuring channel 19 comprises at least the following steps: Providing a fluid in the measuring channel 19 of the flow sensor 15 (step 301); Detecting at least one first differential pressure in the measuring channel 19, wherein the at least one first differential pressure is present in a first differential pressure range 22 in the measuring channel 19 (step 302); Detecting at least one second differential pressure in the measuring channel 19, wherein the at least one second differential pressure is present in a second differential pressure range 23 in the measuring channel 19 and the differential pressure in the second differential pressure range 23 comprises the differential pressure in the first differential pressure range 22 (step 303); Transmitting the detected differential pressures to an evaluation unit 120; Detecting the temperature and / or the humidity with the temperature sensor 41 (step 304); Detecting the absolute pressure with the absolute pressure sensor (step 305); Determining the density orthe viscosity, which is a function of the fluid type, the temperature, the humidity, and the absolute pressure (step 306); determining a first flow rate based on the first differential pressure determination in the first differential pressure range 22, the density, and the viscosity in the computing unit of the evaluation unit 120 (step 307); determining a second flow rate based on the second differential pressure determination in the second differential pressure range 23, the density, and the viscosity in the computing unit of the evaluation unit 120 (step 308); determining the flow rate in the measuring channel 19 using the evaluation unit 120 based on the detected differential pressures or the first and second flow rates determined therefrom (step 309).

[0075] When the fluid is provided, a fluid type is selected in the evaluation unit (step 301). The fluid type is selected by a user on the display and entered using the input buttons. The fluid type is stored in a lookup table in the memory unit of the evaluation unit 120.

[0076] The differential pressures in measuring channel 19 are generated by the resistance elements 20a-20c in measuring channel 19 and are measured directly by the differential pressure sensors 25, 27. The first differential pressure differs from the second differential pressure, with the first differential pressure being, in particular, smaller than the second differential pressure. The second differential pressure region 23 encloses the first differential pressure region 22 in measuring channel 19, so that the internal measurement of the first differential pressure is protected from external turbulence by the external measurement of the second differential pressure, which occurs particularly at high flow rates.

[0077] In the first differential pressure range 22 in the measuring channel 19, first differential pressures in the differential pressure range from -0.5 kPa to 0.5 kPa are recorded. In the second differential pressure range 23 in the measuring channel 19, second differential pressures in the differential pressure range from -1.5 kPa to 0.5 kPa are recorded.

[0078] Before step 302, a first threshold value can be retrieved from the memory unit 125 in the computing unit 130, which serves as the determination criterion for detecting the second differential pressure in the second differential pressure range 23. If at least the first threshold value for the first differential pressure is reached, it can be automatically determined whether and how the second differential pressure is measured. The first threshold value of the first differential pressure is compared in the computing unit with the currently detected first differential pressure.

[0079] Steps 302 to 309 may be performed multiple times before a flow rate is displayed on the display unit 140 (step 310).

[0080] Fig. 5 shows a differential pressure sensor 160 for a flow sensor 15 according to Fig. 1 , which comprises four pressure measuring connections 162a-d for detecting two different differential pressures in a measuring channel 19. The differential pressure sensor 160 requires only one power supply 165 and one housing 161, thus being simple and cost-effective. The required readout protocol can be kept simple, and only one interface 150, for example, a data bus, is required, simplifying the installation and maintenance of the differential pressure sensor.

[0081] The first measuring range of the differential pressure sensor 160 is in the range from -0.5 kPa to 0.5 kPa. The second measuring range of the differential pressure sensor 160 is in the range from -0.125 kPa to 0.125 kPa. List of reference symbols

[0082] 15 Flow sensor 16 First connection 17 Second connection 18a-18d Channel sections 19 Measuring channel 20a-20d Resistance elements 21a-21d Measuring connection 22 First differential pressure range 23 Second differential pressure range 25 First differential pressure sensor 26a-26b Pressure measuring connections 27 Second differential pressure sensor 28a-28b Pressure measuring connections 30 Measuring connection 35 Absolute pressure sensor 40 Holding device 41 Temperature sensor 42 Humidity sensor 115Measuring system 116Housing 120Evaluation unit 125Storage unit 130CPU 140Display unit 141Touch display 150-150aInterfaces 160Differential pressure sensor 161Housing 162a-162dPressure measuring connections 165Power supply 301-310Process steps GGossing component FFluid (gas / liquid)

Claims

1. A method for determining a flow rate of a fluid through a flow sensor (15) with a measurement channel (19), in particular a flow sensor for testing a respirator, wherein the method comprises at least the following steps: a. providing a fluid in the measurement channel (19) of the flow sensor (15); b. capturing at least one first differential pressure in the measurement channel (19), wherein the at least one first differential pressure is present in a first differential-pressure area (22) in the measurement channel (19); c. capturing at least one second differential pressure in the measurement channel (19), wherein the at least one second differential pressure is present in a second differential-pressure area (23) in the measurement channel (19) and the differential pressure in the second differential-pressure area (23) comprises the differential pressure in the first differential-pressure area (22); d. transmitting the captured differential pressures to an evaluation unit (120); e. determining a flow rate in the measurement channel (19) by means of the evaluation unit (120) based on the captured differential pressures, characterized in that three resistance elements (20a-20c) are provided in the measurement channel (19), and in that the first differential pressure is captured via the second resistance element (20b), or is captured via the second and third resistance elements (20b, 20c).

2. The method according to claim 1, characterized in that the first differential pressure and the second differential pressure are captured simultaneously.

3. The method according to claim 1 or 2, characterized in that the first differential-pressure area (22) in the measurement channel (19) comprises at least one resistance element (20a-20c), wherein there are differential pressures in a differential-pressure range from -20kPa to 20kPa, in particular -1.2kPa to 1.2kPa, preferably from -0.5kPa to 0.5kPa.

4. The method according to one of the preceding claims, characterized in that the second differential-pressure area (23) in the measurement channel (19) comprises at least two resistance elements (20b, 20c), wherein there are differential pressures in a differential-pressure range from -100kPa to 100kPa, in particular -5kPa to 5kPa, preferably from -1.5kPa to 1.5kPa.

5. The method according to one of the preceding claims, characterized in that the second differential pressure is captured via all three resistance elements (20a-20c).

6. The method according to one of the preceding claims, characterized in that a memory unit (125) is provided, in which at least a first threshold value for the first differential pressure is stored and / or at least a first threshold value for the second differential pressure is stored.

7. The method according to one of the preceding claims, wherein at least one differential-pressure sensor (25, 27) is provided, characterized in that the differential-pressure sensor (25) measures the first differential pressure and the second differential pressure, or in that preferably a second differential-pressure sensor is provided, wherein the at least one differential-pressure sensor measures the first differential pressure and the second differential-pressure sensor measures the second differential pressure, wherein the measurement range for the first differential pressure is greater than the measurement range for the second differential pressure.

8. The method according to one of the preceding claims, characterized in that at least one fluid property of the fluid in the measurement channel (19) is captured and used in step e) during the determination of the flow rate, wherein the fluid property is captured by means of a user and / or is measured with a sensor and / or is calculated in the evaluation unit (120) and preferably the fluid property is comprised by at least one parameter from the group consisting of absolute pressure, temperature, humidity, fluid type, viscosity or density.

9. A flow sensor for determining a flow rate of a fluid in a measurement channel (19), in particular with a method according to at least one of claims 1 to 8, characterized in that the measurement channel (19) comprises at least four channel sections (18a-18d), which are arranged in the flow sensor (15) adjacent to one another in series and at least one resistance element (20a-20c) is respectively arranged between the adjacent channel sections (18a-18d), wherein each of the channel sections (18a-18d) has at least one measurement connection (21a-21d) for measuring a fluid pressure.

10. The flow sensor according to claim 9, characterized in that at least one housing part is provided in which the four channel sections (18a-18d) are formed, wherein a sieve (24a) is preferably arranged in the first channel section (18a).

11. The flow sensor according to claim 9 or 10, characterized in that the resistance elements (20a-20c) are arranged in a replaceable manner in the measurement channel (19), and preferably at least one resistance element (20b) is designed differently from the other resistance elements (20a, 20c).

12. The flow sensor according to one of claims 9 to 11, characterized in that at least one differential-pressure sensor (25, 27) is arranged on at least two of the measurement connections (26a, 26b, 28a, 28b) and preferably at least one absolute-pressure sensor (35) and / or one temperature sensor (41) and / or one humidity sensor (42) is provided in the measurement channel (19).

13. A measuring system (115) for determining a flow rate with a flow sensor, in particular a flow sensor (15) according to one of claims 9 to 12, and with at least one differential-pressure sensor, characterized in that an evaluation unit (120) is provided, which is connected at least to the at least one differential-pressure sensor (25, 27) in order to capture at least a first differential pressure in the measurement channel (19) of the flow sensor (15) and a second differential pressure in the measurement channel (19) of the flow sensor (15), wherein the evaluation unit (120) is designed to carry out a method according to one of claims 1 to 8, and preferably a display unit (120) is provided in order to display at least the flow rate, wherein in particular the flow rate can be represented graphically.

14. The measurement system according to claim 13, characterized in that a memory unit (135) is provided in which at least a first threshold value is stored and / or at least one interface for reading out captured values and / or evaluated data is provided.

15. A differential-pressure sensor (160) for a flow sensor (15) according to one of claims 9 to 12, with four pressure-measurement connections (162a-162d) for capturing two different differential pressures in a measurement channel (19) according to a method according to one of claims 1 to 8.