FLOW SENSOR FOR DETERMINING THE FLOW RATE OF A FLUID FLOWING ALONG A DIRECTION

Description

Description:

[0001] The invention relates to a flow sensor for determining a flow rate of a fluid flowing along a flow direction and to a method for determining a flow rate of a fluid flowing along a flow direction.

[0002] A large number of flow sensors or flow meters are known from the state of the art.

[0003] Flow sensors based on an ultrasonic measuring principle, as explained for example by DE 10 2019 009 033 A1, usually have the problem that the flow rate can only be determined exactly for one specific fluid or a specific and previously known mixture.

[0004] Such sensors typically work by measuring two sound travel times in opposite directions along a measuring section inclined to the fluid flow direction. The difference between these travel times is determined as the differential travel time, and the flow rate is then calculated based on this differential travel time, for example, using a table. However, the table is limited to exactly one mixing ratio or a pre-known fluid mixture.

[0005] The fluids often consist of water and an antifreeze, such as glycol, although the mixing ratio can vary depending on the application and external factors. If the composition or mixture changes, the relationships shown in the table are no longer accurate, resulting in an incorrect flow rate reading. The greater the deviation of the actual mixture from the mixture assumed in the table, the larger the measurement error.

[0006] The ultrasonic flow sensor according to EP 2 641 071 B1 provides additional physical correction elements, such as heat flux, to correct the separately determined flow rate, which makes the flow sensor comparatively expensive.

[0007] EP 2 369 305 A1 discloses an ultrasonic flowmeter and a corresponding method for a liquid containing multiple components. An algorithm accesses a stored relationship between the mixing ratio, the speed of sound, and the liquid temperature and determines the mixing ratio.

[0008] The invention is therefore based on the objective of overcoming the aforementioned disadvantages and providing a cost-effective flow sensor which can determine the flow rate depending on the mixing ratio of the mixture.

[0009] This problem is solved by the combination of features according to claim 1 and claim 8.

[0010] According to the invention, a flow sensor is proposed for determining the flow rate of a fluid flowing along a flow direction, and in particular, the flow rate of a fluid flowing through the flow sensor. The fluid is a mixture mixed according to a specific ratio, preferably consisting of essentially two (main) components. In particular, the mixture can include water and an antifreeze agent, such as glycol, as components. For the purposes of this invention, "mixture" is also to be understood as meaning that it can consist of 100% of one component, and in particular, water. Accordingly, the fluid preferably consists of between 50% and 100% water, so that the proportion of antifreeze or glycol can be between 0% and 50%. Such a mixture or fluid can, however, preferably contain a small proportion of other components or impurities.The proposed flow sensor comprises a temperature module for measuring the fluid temperature, a first ultrasonic module, a second ultrasonic module, and an evaluation module. The evaluation module can also be understood as an evaluation unit or evaluation electronics. A measuring section extending through the fluid is located between the first and second ultrasonic modules, running at least partially in the direction of flow, i.e., obliquely to it. Preferably, the first ultrasonic module is therefore arranged upstream of the second ultrasonic module with respect to the flow direction. The first and second ultrasonic modules are configured to determine a first sound transit time along the measuring section from the first to the second and a second sound transit time along the measuring section from the second to the first.Furthermore, the evaluation module is designed to determine the fluid's mixing ratio from the temperature, the first sound transit time, and the second sound transit time. Based on this now known mixing ratio, the evaluation module is further designed to determine the flow rate from the mixing ratio, temperature, first sound transit time, and second sound transit time.

[0011] The first sound transit time can be determined by having the first ultrasound module generate a first ultrasound signal in a first direction along the measurement path and measuring its transit time from the first ultrasound module to the second ultrasound module. Similarly, the second sound transit time can be determined by having the second ultrasound module generate a second ultrasound signal in a second direction, opposite to the first, and measuring its transit time from the second ultrasound module to the first ultrasound module.

[0012] The transit time measurement can be performed jointly by the first and second ultrasound modules or by the evaluation module. For this purpose, the ultrasound modules can be directly connected to each other and / or at least one of the ultrasound modules can be connected to the evaluation module to enable data exchange.

[0013] The mixing ratio is then determined from the first and second run times as well as from the temperature, and from this, together with the run times, the flow rate is determined.

[0014] The basic idea of ​​the invention can therefore be summarized by the fact that the mixture and the flow rate of the mixture or the fluid are determined indirectly, i.e. implicitly, by the three related measured variables (first runtime, second runtime, temperature), whereby their relationships are stored in the evaluation module, for example, by a model, a formula, one or more graphs, or in tabular form.

[0015] In the case of a tabular presentation or a presentation as one or more graphs, the relationships stored therein may have been determined by previously carried out series of measurements and / or experiments.

[0016] The flow rate is preferably understood to be the volume flow through the flow sensor, so that in determining it, in particular, a flow cross-section provided by the flow sensor and through which the fluid flows can also be taken into account.

[0017] The evaluation module is designed according to the invention to determine a total transit time as the sum of the first sound transit time and the second sound transit time.

[0018] Furthermore, the evaluation module is designed to store a tabular relationship between the mixing ratio, temperature, first sound transit time, and second sound transit time. This relationship is directly stored as a correlation between the mixing ratio, temperature, and total transit time, allowing the mixing ratio to be determined using a previously calculated total transit time and the fluid temperature. Preferably, this relationship applies to a combination of two components, such as a mixture of water and glycol. The evaluation module can also store additional relationships for other mixtures, enabling, for example, the setting during commissioning to specify the (main) components of the mixture flowing through the flow sensor.

[0019] According to the invention, a first table or matrix is ​​stored in the evaluation module as a relationship containing a multitude of mixing ratios as a function of temperature and total runtime, from which the mixing ratio of the mixture can be determined and / or interpolated. Thus, several tables can be stored in the evaluation module, and, for example, it is possible to select which table should be used to determine the mixing ratio during commissioning.

[0020] Once the total runtime and temperature have been determined, a mixing ratio can be calculated from the table. It is not necessary to have mixing ratios stored for every possible total runtime or temperature. Instead, the evaluation module can be configured to calculate intermediate values ​​from the stored values, i.e., to interpolate a mixing ratio from the known values.

[0021] For such a table, the components of the fluid are preferably known and predetermined. The first table therefore preferably considers the dependencies or relationships for a mixture of water and an antifreeze, such as glycol.

[0022] Furthermore, the evaluation module is designed to determine a differential transit time as the difference between the first and second sound transit times. Preferably, the shorter transit time is subtracted from the longer transit time. If the first ultrasonic module is arranged upstream of the second ultrasonic module along the flow direction or along the flow determined by the fluid, the differential transit time is thus determined by subtracting the first transit time from the second transit time. Regardless of which transit time is subtracted from the other, the absolute value can also simply be calculated.

[0023] The evaluation module also contains a tabular relationship between the mixing ratio, temperature, first sound transit time, second sound transit time, and flow rate. This relationship is directly stored as a correlation between the mixing ratio, temperature, and differential transit time, allowing the flow rate to be calculated from a previously determined mixing ratio, temperature, and differential transit time. Since the flow rate can be determined for various mixing ratios, the evaluation module can store a multitude of relationships, each applicable to a specific mixing ratio.

[0024] According to the invention, the evaluation module contains at least a second table or matrix in which a plurality of flow rates are stored as a function of the mixing ratio, temperature, and differential transit time, and from which the flow rate can be determined and / or interpolated. The flow rate corresponds in particular to the volumetric flow rate of the fluid through the flow sensor and can, for example, be specified in l / h. Preferably, a plurality of tables are stored from which the flow rate for different mixing ratios can be determined.

[0025] The evaluation module can also contain a correction value, which can be determined, for example, during commissioning of the flow sensor and indicates any deviation between a flow rate determined using the second table and an actual flow rate. This correction value is intended to compensate for component tolerances, particularly those caused by manufacturing, making it component-specific and allowing it to be determined during manufacturing or commissioning, as well as at intervals during operation. Accordingly, in an advantageous embodiment, the evaluation module is configured to apply the correction value to a flow rate determined from the second table, thereby calculating an actual flow rate from the (theoretical) flow rate derived from the second table.

[0026] The flow sensor or its evaluation module can also be designed to repeat the determination of the mixing ratio at predetermined and preferably regular intervals in order to detect changes in the mixing ratio and to take them into account when determining the flow rate.

[0027] Another aspect of the invention relates to a method for determining the flow rate of a fluid flowing along a flow direction through a flow cross-section. This method can be carried out, in particular, in or by the flow sensor according to the invention, which can be designed accordingly for this purpose. As already stated with regard to the flow sensor, the fluid is a mixture mixed according to a specific ratio, preferably consisting of essentially two (main) components. In particular, the mixture can comprise water and an antifreeze, such as glycol, as (main) components. For the purposes of this invention, "mixture" is also to be understood as meaning that it can consist of 100% of one component, and in particular water. The fluid preferably consists of between 50% and 100% water, so that the proportion of antifreeze or glycol can be 0% to 50%. Such a mixture, orThe fluid may also contain other components or impurities, preferably in small proportions. According to the method, the temperature of the fluid is determined, a first sound transit time is measured in a first direction along a measuring section running through the fluid and at least partially in the direction of flow, and a second sound transit time is measured in a second, opposite direction along the measuring section. The mixing ratio is then determined from the temperature, the first sound transit time, and the second sound transit time. Once the mixing ratio has been determined, the flow rate is calculated from the mixing ratio, the temperature, the first sound transit time, and the second sound transit time.

[0028] To determine the mixing ratio, the sum of the first and second sound transit times is calculated as the total transit time, and then the mixing ratio is determined from the temperature and the total transit time. A first table is provided for this purpose, from which the mixing ratio for a mixture of two preferably known components can be determined as a function of the total transit time and the temperature.

[0029] To determine the flow rate, the difference between the first and second sound transit times is calculated as the differential transit time. The flow rate is then determined from the mixing ratio, temperature, and differential transit time. A second table is provided for this purpose, from which the flow rate can be determined as a function of the differential transit time and temperature for the previously determined mixing ratio.

[0030] The values ​​stored in the table can take into account, in particular, the flow velocity of the fluid determined by the differential transit time, the density of the fluid determined by temperature and mixing ratio, and the flow diameter of the flow sensor through which the fluid flows.

[0031] To determine the mixing ratio, it is intended that this ratio be read from the first table. Alternatively, the mixing ratio stored for the closest values ​​(temperature, total runtime) can be used. Furthermore, multiple mixing ratios can be determined for several closest values, and the mixing ratio for the actual values ​​can be interpolated or extrapolated.

[0032] The same applies analogously to the determination of the flow rate using the relationship provided for this purpose or the second table.

[0033] The features disclosed above can be combined in any way, provided that this is technically possible and they do not contradict each other.

[0034] Other advantageous embodiments of the invention are characterized in the dependent claims or are described in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. The figures show: Fig. 1 schematic diagram of a flow sensor; Fig. 2 schematic diagram of the process by which the evaluation module determines the flow rate.

[0035] The figures are schematic examples. Identical reference symbols in the figures indicate identical functional and / or structural features.

[0036] The in Figure 1The illustrated flow sensor 1 has a temperature sensor or temperature module 10 for determining the temperature T of the fluid flowing through the flow sensor 1 in the flow direction S. Furthermore, two ultrasonic modules 11 and 12 are provided, which span a measuring section X between them. The fluid flows through this section obliquely to the flow direction S, so that the measuring section X extends partially along the flow direction S. The first ultrasonic module 11 is arranged upstream of the second ultrasonic module 12 with respect to the flow direction S, and the second ultrasonic module 12 is arranged downstream of the first ultrasonic module 11.

[0037] Even conventional flow sensors based on the ultrasonic measurement principle already incorporate such ultrasonic modules, which allow the sound transit times of an ultrasonic signal in both directions along the measuring section X to be determined. However, the flow rate cannot be precisely determined based on these sound transit times if the mixture flowing through the flow sensor 1 is unknown or changes.

[0038] Therefore, it is proposed that the flow sensor 1 has an evaluation module 13 which is configured to determine a mixing ratio of the fluid or mixture flowing through the flow sensor 1 and to determine the flow rate based on this.

[0039] For this purpose, the evaluation module 13 is connected to the temperature sensor 10 and at least one of the ultrasound modules 11, 12, enabling data exchange. In the Figure 1In the variant shown, the evaluation module 13 is connected to both ultrasound modules 11, 12, whereby a data connection between the ultrasound modules 11, 12 is only absolutely necessary if they are not both connected to the evaluation module 13.

[0040] The first ultrasound module 11 and the second ultrasound module 12 are jointly designed to generate an ultrasound pulse or an ultrasound signal in both directions along the measuring distance X and to measure the first sound transit time t1 of the ultrasound signal in a first direction from the first ultrasound module 11 to the second ultrasound module 12 as well as the second sound transit time t2 of the ultrasound signal in a second direction from the second ultrasound module 12 to the first ultrasound module 11.

[0041] Furthermore, the evaluation module 13 is designed to determine the mixing ratio of the fluid or mixture and the flow rate based on the temperature T and the first sound transit time t1 as well as the second sound transit time t2, as described in Figure 2 is shown schematically.

[0042] For this purpose, at least one first table 21 is stored in the evaluation module 13, which specifies a fluid mixing ratio for a multitude of pairs of total runtime Σt and temperature T. The first table 21 then refers to a mixture of two known components, and in particular to a mixture of water and glycol. The evaluation module 13 can also store several first tables 21, each for a mixture of two components. In this case, the first table 21 to be used, or rather the components of the mixture, are configured, particularly during the commissioning of the flow sensor 1.

[0043] The evaluation module 13 then calculates the total transit time Σt as the sum of the first sound transit time t1 and the second sound transit time t2. Subsequently, the mixing ratio is determined for the pair of values ​​consisting of temperature T and total transit time Σt. Figure 2 An example is shown with a proportion of 50% glycol in the mixture, so that the mixing ratio of water and glycol is 50 / 50.

[0044] Although presented as a table, the relationship between temperature T and total runtime Σt for determining the mixing ratio can also be represented, for example, as a formula, matrix, two-dimensional or three-dimensional graph.

[0045] Furthermore, in evaluation module 13, it is not necessary to specify mixing ratios for every possible pair of values. Rather, a mixing ratio for a pair of values ​​can be interpolated or extrapolated from the mixing ratios of neighboring pairs of values ​​stored in the first table 21.

[0046] Based on the determined mixing ratio, a second table 22 stored in the evaluation module 13 is then determined from a large number of second tables 22, which describe the flow rates Y in relation to the determined mixing ratio.

[0047] The relationships described in the second table 22 do not have to be stored in tabular form, but can also be stored as a formula, matrix, two-dimensional or three-dimensional graph in the evaluation module 13.

[0048] The evaluation module 13 is designed to determine the differential transit time Δt from the difference between the first sound transit time t1 and the second sound transit time t2. Subsequently, the flow rate Y, for example in l / h, can be determined from the pair of values ​​for temperature T and the differential transit time Δt.

[0049] In general, it can be stated that the flow velocity of the fluid through the flow sensor 1 can be deduced from the differential transit time Δt through the evaluation module 13. Furthermore, the density of the fluid can be determined from the temperature T in the evaluation module 13 and the mixing ratio, and together with a flow diameter stored in the evaluation module 13, the volume of the fluid flowing through the flow sensor 1 in a predetermined time can be determined. These relationships can be included in the second table 22 and thus taken into account.

[0050] The invention is not limited in its implementation to the preferred embodiments specified above. Rather, a number of variants are conceivable which make use of the solution presented even in fundamentally different designs.

Claims

1. A flow sensor (1) for determining a flow rate (Y) of a fluid flowing along a flow direction (S) which is a mixture mixed according to a mixing ratio, wherein the flow sensor (1) comprises a temperature module (10) for measuring a temperature (T) of the fluid, a first ultrasonic module (11), a second ultrasonic module (12), and an evaluation module (13), wherein a measuring section (X) which extends at least partially in the flow direction (S) and through the fluid is spanned between the first ultrasonic module (11) and the second ultrasonic module (12), wherein the first ultrasonic module (11) and the second ultrasonic module (12) are designed to determine a first acoustic travel time (t1) along the measuring path (X) from the first ultrasonic module (11) to the second ultrasonic module (12) and a second acoustic travel time (t2) along the measuring path (X) from the second ultrasonic module (12) to the first ultrasonic module (11), wherein the evaluation module (13) is designed to determine the mixing ratio of the fluid from the temperature (T), the first acoustic travel time (t1), and the second acoustic travel time (t2), wherein the evaluation module (13) is further designed to determine the flow rate (Y) from the mixing ratio, the temperature (T), the first acoustic travel time (t1), and the second acoustic travel time (t2), wherein the evaluation module (13) is designed to determine a total travel time (Σt) as the sum of the first acoustic travel time (t1) and the second acoustic travel time (t2) as well as a differential travel time (Δt) as the difference between the first acoustic travel time (t1) and the second acoustic travel time (t2), characterised in that a first table (21) is stored in the evaluation module in which a multiplicity of mixing ratios as a function of the temperature (T) and the total travel time (Σt) are stored and from which the mixing ratio can be determined and / or interpolated, and a second table (22) is stored in the evaluation module (13) in which a multiplicity of flow rates (Y) as a function of the mixing ratio, the temperature (T), and the differential travel time (Δt) are stored and from which the flow rate (Y) can be determined and / or interpolated.

2. A method for determining a flow rate (Y) of a fluid flowing along a flow direction (S) which is a mixture mixed according to a mixing ratio, wherein a temperature (T) of the fluid is determined, wherein a first acoustic travel time (t1) is determined in a first direction along a measuring section (X) which extends through the fluid and at least partially in the flow direction (S) and a second acoustic travel time (t2) is determined in a second, opposite direction along the measuring section (X), characterised in that the sum of the first acoustic travel time (t1) and the second acoustic travel time (t2) is determined as the total travel time (Σt), and the mixing ratio is determined from the temperature (T) and the total travel time (Σt) using a first table (21), and the difference between the first acoustic travel time (t1) and the second acoustic travel time (t2) is determined as the differential travel time (Δt), and the flow rate (Y) is determined from the mixing ratio, the temperature (T), and the differential travel time (Δt) using a second table (22).