DEVICE FOR DETERMINING A FLOW PARAMETER OF A FLUID STREAM

Abstract

Device for determining a flow parameter (VD) of a fluid flow (FS), in particular a breathing gas flow, with a flow sensor (10) for generating an electrical signal (ΔTP) corresponding to the flow parameter (VD), which has a sensor chip (5, 5') having a substantially planar surface (2) on which a thermal membrane sensor element (12) is arranged, wherein the thermal membrane sensor element (12) has a first temperature sensor (7) and a second temperature sensor (7') as well as a heating element (3) arranged between the temperature sensors (7, 7'), and with a fluid channel (17) having a wall (4) for guiding the fluid flow in a flow direction (ST1), in which the surface (2) of the sensor chip (5, 5') is arranged, wherein the fluid channel (17) is designed such that the fluid flow (FS) flows along the same straight main flow line (HSL) on both sides of the sensor chip (5) when viewed in the flow direction (ST1), so that the fluid flow (FS) flows towards the sensor chip (5, 5') along a straight line, and that the fluid flow (FS) flows away from the sensor chip (5, 5') along the same straight line, wherein the surface (2) of the sensor chip (5, 5') is arranged parallel to the main flow line (HSL) and wherein a flow deflecting element (6) is associated with the surface (2) of the sensor chip (5, 5') which deflects at least one partial flow (UTS) of the fluid flow (FS) such that the partial flow (UTS) is directed obliquely towards the surface (2), wherein the flow deflection element (6) has a triangular shape in a section parallel to the main flow line (HSL) and perpendicular to the surface (2), wherein a point of the triangular shape faces the surface (2), wherein preferably a side of the triangular shape extending from the point intersects a straight line parallel to the main flow line (HSL) at an angle of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°.

Description

[0001] The present invention relates to a device for determining a flow parameter of a fluid flow.

[0002] Flow sensors for determining flow parameters, such as flow rate, mass flow, volumetric flow rate, or flow velocity of a fluid, are known in various designs and with different measuring principles from the prior art. The fluid can be a gas or a liquid. The gas or liquid can contain several different components or substances. Air, for example, can be such a gas or fluid containing water vapor.

[0003] Flow meters are used in a wide variety of technical fields, such as aerospace, vehicle and engine control, heating and ventilation technology, and industrial process engineering. If, for example, air is considered a fluid, such a flow sensor is often also referred to as an anemometer, an air mass meter, or an air volume flow sensor or air mass flow sensor.

[0004] Flow meters are also used in medical technology; for example, in spirometers, they are used to measure respiratory gases, i.e., the time-resolved measurement of the volume flow during inhalation and exhalation. Such a time-resolved measurement of the volume flow during inhalation and exhalation can be performed, for example, with thermal flow sensors, in particular with microelectromechanical membrane sensors (MEMS membrane sensors), in which the essential components such as heaters and temperature sensors are located on a thin membrane.

[0005] In general, thermal flow sensors have the advantage of high measurement sensitivity at low fluid flow velocities.

[0006] Respiratory gas measurement using thermal sensor elements, particularly MEMS membrane sensors, offers the advantages of high measurement sensitivity at low flow velocities for detecting the crucial reversal point between expiration (inhalation) and inspiration (exhalation) for mechanical ventilation, high measurement dynamics across the entire flow measurement range, and precise temporal resolution of highly dynamic respiratory curves. The lower the thermal mass of the sensor, the higher its temporal resolution, which is approximately 1 ms in the case of the MEMS sensor.

[0007] The technical challenge in measuring respiratory gases or reliable volumetric flow rates with thermal sensors lies in the fact that the exhaled gas is 100% saturated with water. This can lead to condensation and increased aerosol formation under adverse operating conditions, as the temperatures of the hoses and the measuring device can fall below the dew point.

[0008] MEMS sensors generally require significantly less energy than comparable thin-film sensors and are therefore particularly suitable for battery operation in portable devices. However, unlike thin-film sensors, their operating temperature is typically below 100°C, meaning that water droplets deposited on the sensor can have an uncompensable impact on the measurement signal, leading to inaccurate readings or even a complete signal loss. The heating energy emitted by the heating element during sensor operation is insufficient to heat away a large droplet within a reasonable timeframe. As a result, water accumulation on the sensor usually remains stable and does not evaporate. Evaporation can only occur during inspiration due to the maximum humidity during exhalation.Since a sensor failure during ventilation is critical to the system, a faulty measurement due to water accumulation should only occur rarely and then only for a short time (< 10s).

[0009] For several years now, the so-called chamber head sensor has become established as a MEMS immersion sensor for measuring the flow of dry gases, and it would also be suitable for use in ventilation technology. In this sensor, the sensor chip is located in a small flow channel integrated into the tip of a probe. For measurement, the probe, or rather its tip, is positioned with the chamber opening parallel to the gas flow (e.g., in a pipeline) so that a defined portion of the flow passes through the small flow channel and is measured there. This arrangement can also be described as a tube-in-tube bypass.

[0010] However, this measuring device is unsuitable in the presence of aerosols, as these can accumulate in the chamber via capillary action and disrupt the sensor signal. Furthermore, the entire measuring chamber, with its relatively high thermal mass, would have to be heated to a temperature above the dew point. This would significantly affect the temperature of the measured gas. Heating it even to the evaporation temperature would require considerably more energy.

[0011] According to DE 196 36 095 A1, a sensor for an air volume flow comprises a sensing device with a centrally mounted heating device located between two temperature-sensitive sensing elements along a current path, wherein the sensing device is essentially flat between a first and second point along the current path and the heating device and the sensing elements are all located between the first and second point;a streamlined body with a curved surface convex with respect to the sensing device, which is arranged facing the sensing device at a predetermined distance from it, wherein the curved surface extends from in front of the first point to behind the second point along the stream path, wherein the streamlined body is symmetrical with respect to a center of the heating element, and wherein the streamlined body causes a bidirectional airflow to strike the sensing device at an angle such that the airflow in the area of ​​the sensing elements is substantially turbulence-free.

[0012] From DE 102 53 691 A1, an air flow meter with a membrane sensor element is known. The sensor element is supported on a support element such that a sensor surface of the sensor element is parallel to the direction of airflow. The air flow meter has at least one device for protecting the sensor element from dust, such as foreign matter. The protective device is provided with an obstruction element, which is arranged upstream or downstream of the sensor element with respect to the direction of airflow. The sensor element is concealed behind the obstruction element. The obstruction element has gradually expanding or gradually converging surfaces along the direction of airflow. Alternatively, the protective device can be provided with a deflection device, a cover element, an air guide element, an inlet, or a dust collector.

[0013] WO 2013 / 030 198 A1 describes a device for determining a flow parameter of a fluid stream using a thermal MEMS sensor. This device provides an accurate mass flow signal even in the presence of dew or when water droplets are deposited on the sensor, for example, by entrained aerosols in the sample gas. This is achieved by a free-standing sensor finger positioned at an angle α of 5° to 75° to a main flow line of the fluid in the measuring channel and surrounded by the sample medium. In addition to the thermal sensor membrane for flow measurement, the MEMS sensor contains another membrane that can be used for dynamic temperature measurement of the breathing gas and for humidity detection. Additional condensate heaters can be used to supply the necessary amount of heat to briefly evaporate droplets or to raise the temperature of the entire sensor chip above the dew point.A bulk silicon-structured diode used for temperature measurement, together with the dynamic temperature measurement on the second membrane, provides the precise gas temperature. From the mass flow rate, gas temperature, and gas pressure (external sensor), the volumetric flow rate can be calculated using the real gas law due to the precise temporal measurement.

[0014] The flow sensor is positioned in the pipe-bound measuring section such that its sensitive measuring surface is angled α to the main flow direction of the fluid. This ensures that the fluid flows in a directed and largely turbulence-free manner across the measuring membrane in the thermal boundary layer region. The angled position reduces flow shadowing and turbulence propagating into the membrane region, which is generated by the leading edge, thus guaranteeing reliable flow measurements in the membrane region of the MEMS sensor. For bidirectional measurement of the flow parameter, two sensor chips are used, positioned at the same angle but with opposite signs.

[0015] From DE 601 12 002 T2, a flow meter unit is known, comprising a projecting part in at least one of the first and second sub-fluid channels. The projecting part acts as a flow resistance for the fluid flowing through the at least one sub-fluid channel. The flow channel losses of the first and second sub-fluid channels differ from one another as a result of the projecting part. Thus, when the fluid flow pulsates, the measured average flow rate is corrected to be either higher or lower by adjusting the flow channel losses of the first and second sub-fluid channels by changing the size and / or shape of the projecting part, without altering the length and / or the fluid channel area of ​​the sub-fluid channels.

[0016] A split-flow flow meter known from US 2002 / 0166376A1 comprises a detection element 2 facing a flow path and a Venturi structure 4 formed within a flow path 1 near the detection element 2. The Venturi structure 4 serves to throttle the flow directed towards the detection element 2, thereby reducing flow disturbances. It is positioned opposite the detection element 2 in the flow path 1 and has a projection 5 extending towards the detection element 2 in the flow path 1 of the split-flow flow meter.

[0017] A thermal flow sensor known from US 2008 / 0 016 959 A1 comprises a base part arranged in the direction of fluid flow through a main channel and a sensor element mounted on the base part, the sensor element having an exothermic resistor formed on a substrate for detecting the fluid flow rate. The base part has a rectangular recess in which the sensor element is mounted such that the surface of the sensing area of ​​the sensor element is below the upper edge of the recess. A wall section of the measuring channel facing the sensor element is constricted. The exothermic resistor is arranged along the fluid channel and spaced from the upper edge of the recessed section on the upstream side. It is not significantly affected by a flow disturbance caused by a step formed between the upper edge of the recessed section and the surface of the detection area.

[0018] DE 26 53 359 A1 discloses a device for determining a flow medium flow and / or for carrying out a control dependent thereon, comprising a flow damming device and two heat-emitting elements which are mounted in a conduit in such a geometrically symmetrical manner that the heat-emitting elements are subject to the same heat losses when there is no flow medium in the conduit and that the flow damming device causes a differential influence of the flow medium flow on the heat-emitting elements when there is a flow medium in the conduit, wherein a circuit arrangement responsive to the ratio of the heat losses of the two heat-emitting elements is provided for determining the flow medium flow and / or for carrying out the control dependent thereon.

[0019] EP 2 236 996 A1 describes another flow metering device. A first and a second subsection of the passage are configured to each form layers on both sides of a partition. A linear passage section of a third subsection is designed such that its cross-section extends over a region across both sides of the partition in a direction perpendicular to a wall surface of the partition. The cross-section is measured in a direction perpendicular to the flow direction of a fluid flowing through the linear passage section. The partition separates the layer of the first subsection of the passage from the layer of the second subsection of the passage.A first connecting section, which enables the connection between the first and third subsections, describes a curve to change direction and connects a wall surface of the first subsection to a side wall of the third subsection via an inclined surface. The passage wall surface is defined by the partition wall.

[0020] DE 102 45 134 A1 discloses a further airflow measuring device. It has a component that defines a bypass channel. The bypass channel has a sensor channel in which a sensor tip is arranged. The sensor channel is limited at least in a lateral direction that is perpendicular to both a longitudinal direction of the sensor channel and to a perpendicular direction perpendicular to the surface of the sensor tip. This arrangement defines a relatively larger distance in the perpendicular direction at the sensor tip.

[0021] JP 2008-175780A describes a further thermal flow sensor equipped with a sensor chip in which at least one heat generator is formed on a surface of the semiconductor substrate and a flow meter is designed for measuring the fluid flow rate. It features a lead wire as an external connection, which is electrically connected to the sensor chip, and a sealing resin uniformly arranged such that the flow meter is exposed by covering a connection point between the sensor chip and the lead wire. The sealing resin forms the side surface of the sensor chip and covers the upstream side of the flow meter by contacting it in the direction of fluid flow, flushing the heat-generating surface of the sensor chip and the lateral covering portion of the sealing resin in a direction perpendicular to the heat-generating surface.

[0022] In a device for bidirectional measurement of the flow parameter using only one sensor chip, the sensor finger is installed at an angle of 45° in a 90° bent angled tube. This allows for directed flow from both sides.

[0023] However, increased vortex formation can be observed due to the impact of the main flow on the outer inner wall of the channel in the bend, which at certain speeds results in unfavorable feedback of the turbulence to the sensor surface, so that the required accuracy of the measured values ​​cannot be guaranteed over the entire speed range.

[0024] The object of the present invention is to improve such a device.

[0025] The problem is solved by a device for determining a flow parameter of a fluid flow according to claims 1-4.

[0026] The flow sensor for generating an electrical signal corresponding to the flow parameter is a thermal flow sensor, which is based on the fact that a temperature distribution in an area around a heating element changes when the area is in thermal contact with a flowing fluid.

[0027] The flow sensor comprises a sensor chip, which includes at least one thermal membrane sensor element configured to determine a fluid flow parameter. It can also be configured to determine a fluid temperature, such as a relative or absolute temperature. The thermal membrane sensor element has two temperature sensors. These sensors can be, for example, thermocouples, resistance strips (e.g., platinum or nickel), or groups of thermocouples, known as thermopiles. The thermal membrane sensor element has a membrane with two spaced-apart temperature sensors and a heating element located between them. Thus, the sensor chip includes a thermal membrane sensor element with two spaced-apart temperature sensors.

[0028] The first temperature sensor provides a first temperature-dependent signal, and the second sensor provides a second temperature-dependent signal. From these two temperature-dependent signals, the electrical signal corresponding to the flow parameter can then be derived. For example, the difference or quotient of the first temperature-dependent signal and the second temperature-dependent signal can be calculated and used as the electrical signal corresponding to the flow parameter. However, the two temperature-dependent signals can also be combined in other ways.

[0029] Thermal flow sensors, especially those with MEMS membrane sensors, offer the advantages of high measurement sensitivity at low flow velocities for detecting the crucial reversal point between expiration (inhalation) and inspiration (exhalation) for mechanical ventilation, high measurement dynamics across the entire flow measurement range, and precise temporal resolution of highly dynamic respiratory curves. The lower the thermal mass of the sensor, the higher its temporal resolution, which in the case of MEMS sensors can be around 1 ms or less.

[0030] The fluid channel, with a wall designed to guide the fluid flow in a specific direction, is configured such that the fluid flowing through it is reliably guided transversely to the flow direction. The fluid channel can, in principle, have a round or rectangular cross-section. However, other cross-sectional shapes are possible. The surface of the sensor chip is positioned within the fluid channel, so that the surface is in thermal contact with the fluid flow. The fluid channel is designed such that the fluid flow is guided along the same straight main flow line on both sides of the sensor chip. A main flow line can be understood as the center of gravity of the fluid flow. For example, if the fluid channel has a circular cross-section, the center of gravity line runs along the centers of the circles forming the cross-section.The fluid flows into the sensor chip along a straight line, and the fluid flows out of the sensor chip along the same straight line.

[0031] Designing the fluid channel such that the fluid flow approaches the sensor chip along a straight line, and that the fluid flow from the sensor chip flows along the same straight line, results in a compact design of the fluid channel, which facilitates the use of the device in medical practice. Furthermore, this design counteracts the formation of undesirable turbulence in the fluid flow in the area of ​​the sensor chip, which improves measurement accuracy and extends the measuring range to higher fluid velocities.

[0032] The wall of the fluid channel can be made of one piece or multiple pieces.

[0033] In the device according to the invention, the surface of the sensor chip is arranged parallel to the main flow line. Furthermore, a flow deflection element is associated with the surface of the sensor chip, which deflects at least a portion of the fluid flow such that this portion is directed obliquely towards the surface. In this way, a uniform fluid flow in contact with the surface of the sensor chip can be achieved, which, in particular, can be free of turbulence over a wide flow velocity range, thus ensuring stable thermal contact between the surface of the sensor chip and the fluid flow even at higher flow velocities. This ensures high measurement accuracy even at high flow velocities. Erroneous measured values, as well as a drop in the measurement signal, can be reliably prevented.

[0034] The flow deflection element can be formed integrally with the wall of the fluid channel or as a separate component.

[0035] In contrast to a flow guidance system with a chamber head sensor, the measuring device proposed here does not require side walls that could retain the (water) droplets via capillary action. Furthermore, unlike with the chamber head sensor, the thermal mass remains reduced to a minimum, since the sensor chip and the deflection element can be thermally decoupled, meaning that a low thermal power output is sufficient to raise the sensor temperature above the dew point.

[0036] According to an advantageous embodiment of the invention, the flow deflection element is designed such that the partial flow is directed obliquely towards the surface in both the first and opposite flow directions. This makes it possible to measure the flow parameter both when the fluid flows in the first direction and when the fluid flows in the second, opposite direction. The device is thus suitable for bidirectional measurement.

[0037] According to an advantageous embodiment of the invention, a gap between the surface and the flow deflection element is open in at least one direction perpendicular to the main flow line and parallel to the surface. This allows any condensate that accumulates in the gap to drain laterally out of the gap, thus preventing measurement errors caused by condensate.

[0038] According to a practical embodiment of the invention, the deflecting element is arranged centrally to the thermal membrane sensor element when viewed along the main flow line. This feature contributes to ensuring that the characteristic curve of the flow sensor is at least identical in magnitude in both flow directions, which simplifies the further processing of the electrical signal from the flow sensor.

[0039] According to a further advantageous embodiment of the invention, the flow deflection element is symmetrical in a section parallel to the main flow line and perpendicular to the surface with respect to an axis running perpendicular to the main flow line. This feature also contributes to the symmetrical characteristic curve.

[0040] According to an advantageous embodiment of the invention, the flow deflection element has a triangular shape in a section parallel to the main flow line and perpendicular to the surface, with one apex of the triangular shape facing the surface, wherein preferably a side of the triangular shape extending from the apex intersects a straight line running parallel to the main flow line at an angle of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. The triangular shape of the flow deflection element facilitates the manufacture of the device and simultaneously achieves an irritant-free contact of the partial flow with the surface of the sensor.Surprisingly, experiments have shown that the speed range in which accurate measurements are possible is greatest when the sides of the triangular shape extending from the tip are angled at approximately 45° to the main flow line.

[0041] According to an advantageous embodiment of the invention, the flow deflection element has a trapezoidal shape in a section parallel to the main flow line and perpendicular to the surface, wherein a shorter base side of the trapezoidal shape faces the surface, and preferably, a side of the trapezoidal shape extending from the shorter base side intersects a straight line running parallel to the main flow line at an angle of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. The trapezoidal shape of the flow deflection element also facilitates the manufacture of the device and simultaneously achieves a turbulence-free contact of the partial flow with the surface of the sensor.Here too, experiments have surprisingly shown that the speed range in which accurate measurements are possible is greatest when the sides of the trapezoidal shape extending from the shorter base are angled at approximately 45° to the main flow line.

[0042] According to an advantageous embodiment of the invention, the flow deflection element has a hexagonal shape in a section parallel to the main flow line HSL and perpendicular to the surface, wherein a first side of the hexagonal shape is formed parallel to the surface and faces the surface, wherein preferably a side of the hexagonal shape extending from the first side intersects a straight line running parallel to the main flow line at an angle α of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. The hexagonal shape of the flow deflection element also facilitates the manufacture of the device and simultaneously achieves a turbulence-free contact of the partial flow with the surface of the sensor.Here too, experiments have surprisingly shown that the velocity range in which accurate measurements are possible is greatest when the sides of the hexagonal shape extending from the side parallel to and facing the surface are angled at approximately 45° with respect to the main flow line.

[0043] According to an advantageous embodiment of the invention, the flow deflecting element 6 has a rhomboid shape in a section parallel to the main flow line HSL and perpendicular to the surface 2, wherein one apex of the rhomboid shape faces the surface 2, wherein preferably a side extending from the apex of the rhomboid shape intersects a straight line running parallel to the main flow line HSL at an angle α of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. Here too, tests have surprisingly shown that the velocity range in which accurate measurements are possible is greatest when the sides of the rhomboid shape extending from the apex are angled at approximately 45° with respect to the main flow line.

[0044] According to an advantageous embodiment of the invention, the flow deflection element, in a section parallel to the main flow line, has a circular segment shape, wherein one arc of the circular segment faces the surface, or an elliptical segment shape, wherein one arc of the elliptical segment faces the surface. In this way, edges on the flow deflection element can be avoided, which can further counteract undesirable vortex formation.

[0045] According to an advantageous embodiment of the invention, the flow deflection element is arranged in the fluid channel such that a free cross-section exists between a side of the flow deflection element facing away from the sensor chip and the wall of the fluid channel, and / or that a free cross-section exists between a side of the sensor chip facing away from the flow deflection element and the wall of the fluid channel. In this way, only a small portion of the fluid flow passes through the gap between the surface of the sensor chip and the deflection element. The larger portion of the fluid flow can flow outside the gap. This results in minimal energy interference with the fluid flow, leading to low flow resistance and accurate measurement results.

[0046] According to an advantageous embodiment of the invention, the flow deflection element and / or the sensor chip is arranged in the fluid channel such that it forms part of the wall. This increases the stability of the device and simplifies its manufacture.

[0047] According to a preferred embodiment of the invention, the minimum distance between the surface and the deflecting element is at least 0.5 mm, preferably at least 0.6 mm, particularly preferably at least 0.8 mm, and / or at most 2.0 mm, preferably at most 1.5 mm, particularly preferably at most 1.2 mm. As experiments have surprisingly shown, particularly good results can be achieved, especially when measuring a flow parameter of a breathing gas, if the minimum distance between the surface and the deflecting element is in the range of approximately 1 mm. In this case, highly accurate measurements can be obtained over a wide velocity range, with hardly any disruptive condensation occurring.

[0048] According to an advantageous embodiment of the invention, the sum of the cross-sectional area of ​​the flow sensor in the fluid channel and the cross-sectional area of ​​the deflecting element in the fluid channel, in a plane perpendicular to the main flow line, is at most 50%, preferably at most 30%, and particularly preferably at most 10%, of the cross-sectional area bounded by the wall of the fluid channel. In this way, the energetic influence on the fluid flow can be reduced to a tolerable value.

[0049] According to an advantageous further development of the invention, the deflecting element is designed as a freestanding deflecting finger. This also further reduces the energetic influence on the fluid flow as well as the risk of condensation formation.

[0050] According to an advantageous embodiment of the invention, the thermal membrane sensor element is arranged on a freestanding sensor finger. This further reduces the energetic influence on the fluid flow as well as the risk of condensation. The freestanding sensor finger can be formed by the sensor chip itself.

[0051] It is also possible that the freestanding sensor finger is formed by a carrier for the sensor chip, for example made of glass, and by the sensor chip itself.

[0052] According to a further advantageous embodiment of the invention, the sensor finger's extension in a direction perpendicular to the main flow line and parallel to the surface is at least three times, preferably four times, and particularly preferably five times, as large as an extension of the sensor finger in a direction parallel to the main flow line. The sensor finger can be elongated, for example, with a longitudinal side extending perpendicular to the main flow line and parallel to the surface of 6 mm and a width parallel to the main flow line of 2 mm. In some embodiments, a longitudinal edge of the sensor finger is thus three times or even longer than the narrow side W of the sensor finger, in order to position the sensitive elements freely in the flow and outside the fluidically disruptive transition to the mechanical anchoring of the sensor finger.

[0053] According to a preferred embodiment of the invention, the membrane sensor element is arranged in a first third of the surface at a free end of the sensor finger, with the free end of the sensor finger being opposite a second end of the sensor finger to which electrical leads are connected. The active sensor elements can be arranged in the first third of the finger surface at the free end of the sensor finger. This minimizes the influence of the electrical or mechanical connection to the body or measuring head of the sensor finger housing on the flow measurement.

[0054] According to a practical embodiment of the invention, a side of the flow sensor facing the fluid flowing in the first direction and / or a side of the flow sensor facing the fluid flowing in the second direction is shaped such that the cross-section of the fluid channel narrows in the respective flow direction. In this way, a low energetic influence on the fluid flow can be achieved, resulting in low flow resistance and accurate measurement results.

[0055] According to a preferred embodiment of the invention, the flow parameter is a flow rate, mass flow rate, volume flow rate, and / or flow velocity of the fluid stream. The flow rate indicates the absolute quantity of fluid that has flowed through the device in a specific time interval. The mass flow rate indicates the mass of fluid flowing through the device per unit of time. Furthermore, the volume flow rate indicates the volume of fluid passing through the device per unit of time. Finally, the flow velocity indicates the speed at which the fluid stream flows.

[0056] The advantageous embodiments and further developments of the invention described above and / or described in the dependent claims can be used individually or in any combination, except, for example, in cases of clear dependencies or incompatible alternatives.

[0057] The invention and its advantageous developments and refinements, as well as their advantages, are explained in more detail below with reference to drawings.

[0058] They show, each in a schematic diagram: Fig. 1a a first view of a first embodiment of a device according to the invention, wherein a three-dimensional cutaway view of a bottom of the device is shown in a view from an oblique top; Fig. 1b a second view of the first embodiment of a device according to the invention, wherein a three-dimensional cutaway view of a top of the device is shown in a view from an oblique bottom; Fig. 2a a third view of the first embodiment of a device according to the invention, wherein a two-dimensional longitudinal section view is shown; Fig. 2b a fourth view of the first embodiment of a device according to the invention, wherein a two-dimensional cross-sectional view is shown; Fig. 2c a fifth view of the first embodiment of a device according to the invention, wherein a two-dimensional longitudinal section view is shown; Fig. 2d a sixth view of the first embodiment of a device according to the invention, wherein a two-dimensional cross-sectional view is shown; Fig. 3a a first view of a second embodiment of a device according to the invention, wherein a two-dimensional longitudinal section view is shown; Fig. 3b a second view of the second embodiment of a device according to the invention, wherein a two-dimensional cross-sectional view is shown; Fig. 3c a first view of a third embodiment of a device according to the invention, wherein a two-dimensional longitudinal section view is shown; Fig. 3d a second view of the third embodiment of a device according to the invention, showing a two-dimensional cross-sectional view; Fig. 3e a first view of a fourth embodiment of a device according to the invention, wherein a two-dimensional longitudinal section view is shown; Fig. 3f a second view of the fourth embodiment of a device according to the invention, wherein a two-dimensional cross-sectional view is shown; Fig. 4a a first view of a fifth embodiment of a device according to the invention, wherein a two-dimensional longitudinal section view is shown; Fig. 4b a second view of the fifth embodiment of a device according to the invention, showing a two-dimensional cross-sectional view; Fig. 4c a first view of a sixth embodiment of a device according to the invention, wherein a two-dimensional longitudinal section view is shown; Fig. 4d a second view of the sixth embodiment of a device according to the invention, showing a two-dimensional cross-sectional view; Fig. 5 a three-dimensional representation of the flow sensor of the preceding embodiments of the device; Fig. 6a-c a schematic representation of a sensor chip for a flow sensor according to the invention as well as a thermal membrane sensor element and a thermopile located thereon according to an embodiment of the present invention; Fig. 7 a diagram illustrating the operation of a thermal flow sensor according to Sven Zinober (Redundancy structures for increasing the safety and reliability of microsystems, dissertation, Albert-Ludwig-University Freiburg i. Breisgau, 09.07.2002); and Fig. 8 a diagram of simulator-determined characteristic curves different embodiments of the device according to the invention.

[0059] The Fig. Figure 1a shows a first view of a first embodiment of a device 1 according to the invention for determining a flow parameter of a fluid flow, in particular a breathing gas flow, wherein a three-dimensional sectional view of a bottom side of the device 1 is shown in a view from an oblique top. Furthermore, the Fig. 1b A second view of the first embodiment of a device 1 according to the invention, wherein a three-dimensional sectional view of a top surface of the device 1 is shown from a low oblique angle. The flow sensor 10 is shown to illustrate its position in the device 1, both in the Fig. 1a as well as in the Fig. 1b shown. In fact, the device 1 of the first embodiment comprises only a flow sensor. The entire device according to the invention is obtained by combining the components shown in the Fig. 1a shown underside and the one in the Fig. The top side shown in 1b is joined together.

[0060] The device 1 for determining a flow parameter VD of a fluid flow FS, in particular a breathing gas flow, thus comprises a flow sensor 10 for generating an electrical signal corresponding to the flow parameter VD, which has a sensor chip 5 having a substantially planar surface 2 on which a thermal membrane sensor element 12 is arranged, wherein the thermal membrane sensor element 12 has a first temperature sensor, a second temperature sensor and a heating element arranged between the thermocouples.

[0061] Furthermore, the device 1 comprises a fluid channel 17 with a wall 4 for guiding the fluid flow FS in a flow direction ST1, in which the surface 2 of the sensor chip 5 is arranged, wherein the fluid channel 17 is designed such that the fluid flow FS, viewed in the flow direction ST1, flows to both sides of the sensor chip 5 along the same straight main flow line HSL.

[0062] The surface 2 of the sensor chip 5 is arranged parallel to the main flow line HSL, and a flow deflection element 6 is assigned to the surface 2 of the sensor chip 5, which deflects at least a partial flow of the fluid flow FS such that the partial flow is directed obliquely towards the surface 2.

[0063] The flow sensor 10 for generating an electrical signal corresponding to the flow parameter VD is a thermal flow sensor 10, which is based on the fact that a temperature distribution in a region around a heating element 3 changes when the region is in thermal contact with a flowing fluid. The flow sensor 10 is described below with reference to the Fig. 5 and Fig. 6 explained in more detail.

[0064] According to a preferred embodiment of the invention, the flow parameter VD is a flow rate, a mass flow rate, a volumetric flow rate VD, and / or a flow velocity of the fluid stream FS. The flow rate indicates the absolute quantity of fluid that has flowed through the device in a specific time interval. The mass flow rate indicates the mass of fluid flowing through the device per unit of time. Furthermore, the volumetric flow rate VD indicates the volume of fluid passing through the device 1 per unit of time. Finally, the flow velocity indicates the speed at which the fluid stream FS flows.

[0065] The fluid channel 17, with a wall 4 for guiding the fluid flow FS in a flow direction ST1, is designed such that the fluid flowing through it is reliably guided transversely to the flow direction ST1. The fluid channel 17 can, in principle, have a round or a rectangular cross-section. However, other cross-sectional shapes are possible. The surface 2 of the sensor chip 5 is arranged within the fluid channel 17, so that the surface 2 is in thermal contact with the fluid flow FS. The fluid channel 17 is designed such that the fluid flow FS is guided along the same straight main flow line HSL on both sides of the sensor chip 5. A main flow line HSL can be understood as a center of gravity line of the fluid flow FS. For example, if the fluid channel 17 has a circular cross-section, the center of gravity line runs along the centers of the circles forming the cross-section.The fluid flows into sensor chip 5 along a straight line, and the fluid flows out of sensor chip 5 along the same straight line.

[0066] Designing the fluid channel 17 such that the fluid flow FS flows towards and away from the sensor chip 5 along a straight line results in a compact design for the fluid channel 17, which facilitates the application of the device 1 in medical practice. Furthermore, this design counteracts the formation of undesirable turbulence in the fluid flow FS in the area of ​​the sensor chip 5, thus improving measurement accuracy and extending the measuring range to higher fluid velocities.

[0067] The wall 4 of the fluid channel 17 can be formed in one piece or in multiple pieces.

[0068] In the device 1 according to the invention, the surface 2 of the sensor chip 5 is arranged parallel to the main flow line HSL. Furthermore, a flow deflection element 6 is associated with the surface 2 of the sensor chip 5, which deflects at least a partial flow of the fluid flow FS such that the partial flow is directed obliquely towards the surface 2. In this way, a uniform fluid flow FS in contact with the surface 2 of the sensor chip 5 can be achieved, which can be free of turbulence, particularly over a wider flow velocity range, so that stable thermal contact between the surface 2 of the sensor chip 5 and the fluid flow FS is ensured even at higher flow velocities. This ensures high measurement accuracy even at high flow velocities. Erroneous measured values, as well as a drop in the measurement signal, can be reliably prevented.

[0069] The flow deflection element 6 can be formed integrally with the wall 4 of the fluid channel 17 or as a separate component.

[0070] In contrast to a flow guide with a chamber head sensor, the measuring device 1 proposed here does not require side walls that could retain the (water) droplets by capillary action. Furthermore, unlike with the chamber head sensor, the thermal mass remains reduced to a minimum, since the sensor chip 5 and the deflecting element 6 can be thermally decoupled, so that a low thermal power is sufficient to raise the temperature of the sensor chip 5 above the dew point.

[0071] Fig. Figure 2a shows a third view of the first embodiment of a device 1 according to the invention, wherein a two-dimensional longitudinal section view is shown. Fig. Figure 2b shows a fourth view of the first embodiment of a device according to the invention, wherein a two-dimensional cross-sectional view of the device 1 is shown. Fig. 2a is shown.

[0072] According to an advantageous embodiment of the invention, a gap 14 between the surface 2 and the flow deflection element 6 is open towards the surface in at least one direction perpendicular to the main flow line HSL and parallel to the surface 2. This allows any condensate that accumulates in the gap 14 to flow laterally out of the gap 14, thus preventing measurement errors caused by condensate.

[0073] According to a further advantageous embodiment of the invention, the flow deflection element 6 is symmetrical in a section parallel to the main flow line HSL and perpendicular to the surface 2 with respect to an axis running perpendicular to the main flow line HSL. This feature also contributes to the symmetrical characteristic curve of the flow sensor 10. Exemplary such characteristic curves are shown below. Fig. 8 explained.

[0074] According to an advantageous embodiment of the invention, the flow deflection element 6 has a trapezoidal shape in a section parallel to the main flow line HSL and perpendicular to the surface 2, wherein a shorter base side 29 of the trapezoidal shape faces the surface 2, and preferably a side 15 extending from the shorter base side 29 of the trapezoidal shape intersects a straight line running parallel to the main flow line HSL at an angle α of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. The trapezoidal shape of the flow deflection element 6 facilitates the manufacture of the device and simultaneously achieves a vortex-free contact of the partial flow with the surface 2 of the sensor 10.Surprisingly, experiments have shown that the velocity range in which accurate measurements are possible is greatest when the sides of the trapezoidal shape extending from the shorter base 29 are angled at approximately 45° with respect to the main flow line HSL.

[0075] According to an advantageous embodiment of the invention, the flow deflection element 6 is arranged in the fluid channel 17 such that a free cross-section 18 exists between a side of the sensor chip 5 facing away from the flow deflection element and the wall 4 of the fluid channel. In this way, only a small partial flow UTS of the fluid flow FS flows through the gap 14 between the surface 2 of the sensor chip 5 and the deflection element 6. The larger part GTS of the fluid flow FS can flow outside the gap 14. This results in minimal energy interference with the fluid flow FS, leading to low flow resistance and accurate measurement results.

[0076] According to an advantageous embodiment of the invention, the flow deflection element 6 is arranged in the fluid channel 17 such that it forms part of the wall 4. In this way, the stability of the device 1 is increased and its manufacture is simplified.

[0077] According to a preferred embodiment of the invention, the minimum distance between the surface 2 and the deflecting element 6 is at least 0.5 mm, preferably at least 0.6 mm, particularly preferably at least 0.8 mm, and / or at most 2.0 mm, preferably at most 1.5 mm, particularly preferably at most 1.2 mm. As experiments have surprisingly shown, particularly good results can be achieved, especially when measuring a flow parameter VD of a breathing gas, if the minimum distance between the surface 2 and the deflecting element 6 is in the range of approximately 1 mm. In this case, highly accurate measurements can be obtained over a wide velocity range, with hardly any disruptive condensation occurring.

[0078] According to an advantageous embodiment of the invention, the membrane sensor element 12 is formed on a freestanding sensor finger 5. This further reduces the energetic influence on the fluid flow FS as well as the risk of condensation. In the first embodiment, the sensor finger 5 is formed by the sensor chip 5 itself. However, it would also be possible for the freestanding sensor finger to be formed by a carrier for the sensor chip 5, for example made of glass, and by the sensor chip 5 itself.

[0079] According to an advantageous embodiment of the invention, the flow deflection element 6, in a section parallel to the main flow line HSL and perpendicular to the surface 2, has a triangular shape, in contrast to the first embodiment, wherein one apex of the triangular shape faces the surface 2, and preferably, a side extending from the apex of the triangular shape intersects a straight line running parallel to the main flow line HSL at an angle α of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. The triangular shape of the flow deflection element 6 also facilitates the manufacture of the device and simultaneously achieves an irritant-free contact of the partial flow with the surface 2 of the sensor chip 5.Surprisingly, experiments have shown that the speed range in which accurate measurements are possible is greatest when the sides of the triangular shape extending from the tip are angled at approximately 45° to the main flow line HSL.

[0080] According to an advantageous embodiment of the invention, the flow deflection element 6, in a section parallel to the main flow line HSL, has, in a modification to the first embodiment, a circular segment shape, wherein a circular arc faces the circular segment shape of the surface 2, or an elliptical segment shape, wherein an elliptical arc faces the elliptical segment shape of the surface 2. In this way, edges on the flow deflection element 6 can be avoided, which can further counteract undesirable vortex formation.

[0081] According to an advantageous further development of the invention, the deflecting element 6 is designed as a freestanding deflecting finger 6, in a modification to the first embodiment. This also further reduces the energetic influence on the fluid flow FS as well as the risk of condensation formation.

[0082] Fig. Figure 2c shows a fifth view of the first embodiment of a device 1 according to the invention, wherein a two-dimensional longitudinal section view is shown. Fig. Figure 2d shows a sixth view of the first embodiment of a device one according to the invention, wherein a two-dimensional cross-sectional view of the device 1 is shown. Fig. 2c is shown. Unlike in the Fig. 1a, Fig. 1b, Fig. 2a and Fig. 2b Here the fluid flow FS flows in a second flow direction ST2, which is opposite to the first flow direction ST1.

[0083] According to an advantageous embodiment of the invention, the flow deflection element 6 is designed such that the partial flow UTS is directed obliquely towards the surface 2 in both the flow direction ST1 and the opposite flow direction ST2. In this way, a measurement of the flow parameter VD is possible both when the fluid flows in the first flow direction ST1 and when the fluid flows in the opposite second flow direction ST2. The device is thus suitable for bidirectional measurement.

[0084] According to a practical embodiment of the invention, the deflecting element 6 is arranged centrally to the thermal membrane sensor element 12 when viewed along the main flow line HSL. This feature contributes to ensuring that the characteristic curve of the flow sensor 10 is at least identical in magnitude in both flow directions ST1 and ST2, which simplifies the further processing of the electrical signal from the flow sensor.

[0085] Fig. Figure 3a shows a first view of a second embodiment of a device 1 according to the invention, wherein a two-dimensional longitudinal section view is shown. Fig. Figure 3b shows a second view of the second embodiment of a device according to the invention, showing a two-dimensional cross-sectional view.

[0086] According to an advantageous embodiment of the invention, the flow deflection element 6 is arranged in the fluid channel 17 such that a free cross-section 16 is present between a side of the flow deflection element 6 facing away from the sensor chip 5 and the wall 4 of the fluid channel.

[0087] According to an advantageous embodiment of the invention, the sum of the cross-sectional area 20 of the flow sensor 10 in the fluid channel 17 and the cross-sectional area 21 of the deflecting element 6 in the fluid channel 17, in a plane perpendicular to the main flow line HSL, is at most 50%, preferably at most 30%, and particularly preferably at most 10% of the cross-sectional area bounded by the wall 4 of the fluid channel 17. In this way, the energetic influence on the fluid flow FS can be reduced to a tolerable value.

[0088] Fig. Figure 3c shows a first view of a third embodiment of a device according to the invention, wherein a two-dimensional longitudinal section is shown. Furthermore, it shows Fig. Figure 3d shows a second view of the third embodiment of a device according to the invention, in which a two-dimensional cross-sectional view is shown. According to an advantageous further development of the invention, a side 26 of the flow sensor 10 facing the fluid flowing in the first flow direction ST1 and / or a side 26' of the flow sensor 10 facing the fluid flowing in the second flow direction ST1 is shaped such that the cross-section of the fluid channel 17 narrows in the respective flow direction ST1; ST2. In this way, a low energetic influence on the fluid flow can be achieved, leading to low flow resistance and accurate measurement results. Otherwise, the third embodiment corresponds to the second embodiment.

[0089] Fig. Figure 3e shows a first view of a fourth embodiment of a device according to the invention, wherein a two-dimensional longitudinal section is shown. Furthermore, it shows Fig. Figure 3f shows a second view of the fourth embodiment of a device according to the invention, in which a two-dimensional cross-sectional view is shown. According to an advantageous further development of the invention, in the fourth embodiment, the flow deflecting element 6 has a hexagonal shape in a section parallel to the main flow line HSL and perpendicular to the surface 2, wherein a first side 28 of the hexagonal shape is formed parallel to the surface 2 and faces the surface 2, wherein preferably a side 27 extending from the first side 28 of the hexagonal shape intersects a straight line running parallel to the main flow line HSL at an angle α of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. Otherwise, the fourth embodiment corresponds to the second embodiment.

[0090] The hexagonal shape of the flow deflection element 6 also facilitates the manufacture of the device and simultaneously achieves a vortex-free contact of the partial flow with the surface 2 of the sensor 10. Here too, experiments have surprisingly shown that the velocity range in which accurate measurements are possible is greatest when the sides 27 of the hexagonal shape extending from the side 28, which is parallel to and facing the surface, are angled at approximately 45° with respect to the main flow line HSL.

[0091] According to a similar advantageous embodiment of the invention (not shown), the flow deflecting element 6 has a rhomboid shape in a section parallel to the main flow line HSL and perpendicular to the surface 2, wherein one apex of the rhomboid shape faces the surface 2, wherein preferably a side extending from the apex of the rhomboid shape intersects a straight line running parallel to the main flow line HSL at an angle α of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. Tests have also surprisingly shown that the velocity range in which accurate measurements are possible is greatest when the sides of the rhomboid shape extending from the apex are angled at approximately 45° with respect to the main flow line.The diamond-shaped form is basically obtained when the sides of the hexagonal shape, arranged parallel to the main flow line HSL in the fourth embodiment, are omitted.

[0092] Fig. Figure 4a shows a first view of a fifth embodiment of a device 1 according to the invention, wherein a two-dimensional longitudinal section view is shown. Fig. Figure 4b shows a second view of the fifth embodiment of a device 1 according to the invention, wherein a two-dimensional cross-sectional view is shown.

[0093] According to an advantageous embodiment of the invention, the sensor chip 5 is arranged in the fluid channel 17 such that it forms part of the wall 4. This increases the stability of the device and simplifies its manufacture.

[0094] Fig. Figure 4c shows a first view of a sixth embodiment of a device according to the invention, wherein a two-dimensional longitudinal section is shown. Furthermore, it shows Fig. Figure 4d shows a second view of the sixth embodiment of a device according to the invention, in which a two-dimensional cross-sectional view is shown. According to an advantageous further development of the invention, a side 26 of the flow sensor 10 facing the fluid flowing in the first flow direction ST1 and / or a side 26' of the flow sensor 10 facing the fluid flowing in the second flow direction ST1 is shaped such that the cross-section of the fluid channel 17 narrows in the respective flow direction ST1; ST2. In this way, a low energetic influence on the fluid flow can be achieved, leading to low flow resistance and accurate measurement results. Otherwise, the sixth embodiment corresponds to the fifth embodiment.

[0095] As in the Fig. As shown in Figure 5, the flow sensor 10 can have a sensor chip 5 which can be attached to a measuring head 13 which has corresponding electrical connections 11, wherein during operation of the flow sensor 10 the sensor chip 5 is connected to the thermal membrane sensor element 12 ( Fig. 6) as a freestanding sensor finger 5 around which the fluid flow FS flows. The flow sensor 10 can taper from the measuring head 13 towards the sensor chip 5. The flow sensor 10 with the sensor chip can be positioned freely in the fluid channel 17, as shown in the preceding figures, as a "naked chip" around which the fluid flows, in order to determine a flow parameter of the fluid more accurately, e.g., with a lower error rate, in a larger measuring range, or with higher measurement dynamics. The flow sensor can be a microelectromechanical semiconductor (MEMS) sensor. That is, the sensor chip 5 can, for example, be a silicon semiconductor chip 5 that has been structured using microsystems technology. The use of other semiconductor materials is also conceivable, such as silicon carbide, gallium arsenide, indium phosphide, etc., which are used in semiconductor technology and in microelectromechanics.Glass, ceramics or similar materials can also serve as a substrate for the flow sensor or sensor chip according to the invention.

[0096] In Fig. Figure 6 shows a top view of a sensor chip 5 with varying levels of detail for the individual elements. The figure shows... Fig. 6a the top view of a microscope image of sensor chip 5, and the Fig. 6b is a schematic representation of the top view of a membrane 9 or the thermal membrane sensor element 12 with the heaters 3 and the two opposing temperature sensors 7, 7', each configured as a thermocouple group 7, 7'. Furthermore, the Fig. Figure 6c shows a detailed view of a thermocouple group 7' with the thermocouples connected in series.

[0097] The flow sensor 10 comprises a sensor chip 5, which includes at least one thermal membrane sensor element 12 configured to determine a flow parameter VD of the fluid. Furthermore, it can additionally be configured to determine a fluid temperature, for example, a relative fluid temperature or an absolute fluid temperature. The thermal membrane sensor element 12 has two temperature sensors 7, 7'. These temperature sensors 7, 7' can be, for example, thermocouples 8, 8', resistance strips (e.g., made of platinum or nickel), or groups of thermocouples 7, 7', so-called thermopiles 7, 7'. The thermal membrane sensor element 12 has a membrane comprising two spaced-apart temperature sensors 7, 7' and a heating element 3 arranged between the temperature sensors 7, 7'.The sensor chip 5 therefore has a thermal membrane sensor element 12 with two temperature sensors 7, 7' spaced apart from each other.

[0098] The sensor chip 5 can be, as in the Fig. Figure 6a shows an elongated sensor finger 5, where, for example, the long side L is 6 mm and the width W is 2 mm. In some embodiments, a long edge of the sensor finger or sensor chip 5 is three times or more longer than the narrow side W of the sensor finger or sensor chip 5, in order to position the sensitive element 12 freely in the flow FS and outside the flow-disrupting transition to the mechanical anchoring of a measuring head 13. The electrical leads 19 are located at an end face of the sensor finger or sensor chip 5 and are connected there to the measuring head (not shown in Figure 6a). Fig. 6a) connected. The active sensor elements 12 can be arranged in the first third of the surface 2 of the sensor finger 5 at the free end 5a of the sensor finger 5. This minimizes the influence of the connection to the body or measuring head 13 of the flow sensor 10 on the flow measurement.

[0099] Under the supervision of Fig. Figure 6b shows the thermal membrane sensor element 12 with its associated heater 3. The temperature sensors 7 and 7' are each configured as thermocouple groups 7, 7'. The thermocouples 8 and 8' are connected in series on their respective sides and combined to form thermopiles 7, 7'. The individual thermocouples 8 and 8', and the thermopiles 7, 7', each have thermocouple junctions 8a and 8b, which are arranged on the sensor membrane 9, and corresponding second thermocouple junctions 8c and 8d, which are arranged on the chip frame and the silicon bulk, respectively. Both the heating elements 3 and the thermocouples 8, 8' have corresponding electrical leads 19. Fig. Figure 6c shows a partial view of the thermopile 7' with the thermocouple junctions 8b and 8d. The figure shows the thermocouple junctions 8b, which comprise aluminum 24 and polysilicon 25 and are arranged on the membrane 9, and also the thermocouple junctions 8d, which likewise comprise polysilicon 25 and aluminum 24, and which are formed on the silicon bulk or sensor chip frame.

[0100] During operation, when the heater 3 heats the environment, the thermocouple junctions 8b of the thermopile 7' reach a higher temperature T warm exhibiting a lower temperature T than the corresponding thermocouple junctions 8d of the thermopile 7'. kalt The membrane 9 has a low thermal mass, so that when the heating element is heated, the membrane 9 will relatively quickly assume the temperature generated by the heater, whereas the temperature on the silicon chip or the sensor chip frame will be lower.

[0101] According to a further advantageous embodiment of the invention, an extent L of the sensor chip or sensor finger 5 in a direction perpendicular to the main flow line HSL and parallel to the surface 2 is at least three times as large, preferably four times as large, and particularly preferably five times as large, as an extent W of the sensor chip 5 or sensor finger 5 in a direction parallel to the main flow line HSL. The sensor chip 5 or sensor finger 5 can be an elongated sensor chip 5 or sensor finger 5, in which, for example, the longitudinal side running perpendicular to the main flow line and parallel to the surface is 6 mm and the width running parallel to the main flow line is 2 mm. In some embodiments, therefore, a longitudinal edge of the sensor chip 5 or sensor finger 5 is three times or even longer than the narrow side W of the sensor chip or sensor finger 5.Sensor fingers to enable the sensitive elements 12 to be placed freely in the flow and outside the flow-disrupting transition to the mechanical anchoring of the sensor chip or sensor finger 5.

[0102] According to a preferred embodiment of the invention, the membrane sensor element 12 is arranged in a first third of the surface 2 at a free end 5a of the sensor chip 5 or sensor finger 5, wherein the free end 5a of the sensor chip 5 or sensor finger 5 is opposite a second end 5b of the sensor chip 5 or sensor finger 5, to which electrical leads 19 are connected. The active sensor elements 12 can be arranged in the first third of the chip area 2 at the free end 5a of the sensor chip 5 or sensor finger 5. This minimizes the influence of the electrical or mechanical connection to the body or measuring head 13 of the sensor finger housing on the flow measurement.

[0103] In Fig. Figure 7 shows the operating principle of a thermal flow sensor 5 in a diagram from the dissertation by Sven Zinober, “Redundancy Structures for Increasing the Safety and Reliability of Microsystems”, dissertation, Albert-Ludwig-University of Freiburg im Breisgau, 2002. The solid curve in Fig. Figure 7 shows the schematic temperature profile along a fluid channel wall 4 on a sensor surface 2 for a stationary medium or fluid and the dashed curve for an assumed flow rate of a fluid in the flow direction ST1 indicated by the arrow from left to right.

[0104] In a stationary medium, the heating of the sensor membrane at point X0 by the heater 3 results in a uniformly decaying temperature distribution in the direction of thermocouples 8 and 8'. This means that in a stationary flow, if the distances -X1 and +X1 between thermocouples 8 and 8' are identical, the heater 3 will measure the same temperature. Therefore, when the flowing medium is stationary, the active sensor area is heated by heat conduction in the membrane and the medium. The corresponding temperature is then detected by thermocouples 8 and 8'. When a flow begins in the direction indicated by the arrow, a temperature distribution develops as shown by the dashed curve. In the event of flow, the heat distribution field is shifted towards thermocouple 8', which is furthest from the flow.

[0105] Fig. Figure 7 shows the schematic temperature profile at the sensor level with the two thermocouples 8, 8' and the heater 3 arranged between them, and the shift of this profile as a function of the flow velocity of the fluid flowing over it, where in Fig. Figure 7 shows that the heater 3 is heated to a constant temperature (also known as constant-temperature anemometry, CTA). Depending on the requirements or the flow parameter to be measured, the heater 3 can also be heated in different ways, i.e., with constant power, constant voltage, or constant current (constant-current anemometry, CCA), or, for example, periodically or pulsed. A measuring head with a free-standing sensor finger can thus be arranged in a flowing fluid such that the flowing fluid first flows around a first thermocouple 8, then around the heater 3, and then around the second thermocouple 8'.

[0106] The temperature differences ΔT1 and ΔT2 represent the difference between the respective hot contacts 8a, 8b of the thermocouples 8, 8' facing the heater 3 and the ends 8c, 8d of the thermocouples 8, 8' facing away from the heater 3, which are located on the silicon bulk and can therefore be described as cold contacts. ΔT1 is the temperature difference at the upstream sensor 8 and ΔT2 at the downstream sensor 8'. When the flow medium is at rest, the active sensor area is heated by heat conduction in the membrane and the medium. When flow begins, here in the flow direction from left to right, this heat distribution field shifts to the right. The thermocouples 8, 8' can again be connected in series to form thermopiles 7, 7'. The flow medium or fluid first reaches the upstream thermopile 7, cools it, is then heated at the heater 3 and carries this heat with it.This causes the hot contacts 8b of the downstream thermopile 7' facing away from the flow to be heated more intensely. The difference in temperature at thermopiles 7 and 7', i.e., ΔT2 - ΔT1, is then the temperature difference between the downstream thermopile 7' and the upstream thermopile 7, which depends on the flow velocity. Thus, the temperature profile between the membrane center with the heater and the silicon bulk can be measured.

[0107] The above measuring principle allows for the construction of flow sensors 10 with high dynamic ranges, e.g., from 1:10 to 1:10000. When used for liquid measurements, the flow sensor 10 should have a dense passivation of the thermopile structures and their leads to prevent an electrical short circuit of the active sensor elements. The flow sensor 10 is suitable for gases and liquids, or fluids in general, and can be used, for example, in an anemometer or a calorimeter.

[0108] The Fig. Figure 8 shows a diagram of simulated characteristic curves of different embodiments of the device according to the invention.

[0109] The diagram of Fig.Figure 8 shows the values ​​of the electrical signal ΔTP in millivolts (mV) of a flow sensor 10 of an exemplary device 1 as a function of a volumetric flow rate VD in standard liters per minute (slpm), which corresponds to a function ΔTP (VD). The values ​​of the electrical signal ΔTP are shown as the difference from a value measured without flow.

[0110] A first characteristic curve ΔTP1 refers to a simulation of the device 1 of the first embodiment, where the flanks of the trapezoidal deflecting element 6 are angled at 45°. A second characteristic curve ΔTP2 refers to a simulation of the device 1 of the first embodiment, where the flanks of the trapezoidal deflecting element 6 are angled at 21°. One side of the diagram applies when the fluid flow FS flows in the first flow direction ST1. Conversely, the other side of the diagram applies when the fluid flow FS flows in the opposite flow direction ST2. The direction is represented by the sign of the volumetric flow rate VD and the electrical signal ΔTP.

[0111] The characteristic curves ΔTP1 and ΔTP2 are essentially point-symmetric about the zero point.

[0112] While the measuring range for a deflection element 6 with flanks angled at 21° extends only from approximately -125 slpm to approximately +125 slpm, the measuring range for a deflection element 6 with flanks angled at 45° extends from approximately -300 slpm to approximately +300 slpm. The measuring range is the range in which a unique inverse function VD (ΔTP) can be derived from the function ΔTP (VD).

[0113] The present invention comprises, in one embodiment, a device 1 with a directed flow towards the freestanding sensor finger 5 for the bidirectional measurement of moist gases in the main flow FS, which lies in an externally straight measuring channel 17, which, according to the current state of the art, is preferred in practice as a flow measuring device 1.

[0114] Since the MEMS flow sensor 10, immersed in the main flow FS, only measures at a single point in a pipe-bound measuring section, i.e. at one location, preferably in the center of the pipe, a consistent distribution of the flow velocity profile across the entire measuring range must be ensured in order to be able to deduce the flow rate in the entire pipe cross-section from the local measurement information at the sensor 5 and at the same time achieve the required measurement accuracy.

[0115] The design of the measuring section can contribute to a smoothing of the flow profile, for example by narrowing the pipe cross-section in a Venturi shape and by installing additional flow straighteners, such as grids, sieves or honeycomb structures.

[0116] Therefore, in one embodiment of the invention, the following solution for installing the sensor finger in a straight pipe is proposed: A narrowing of the flow channel on one side by a wedge-shaped edge with 45° flanks, which generates a directed gap flow above its breaking edge. At a defined distance from the wedge-shaped edge, the sensor finger 5, which is oriented longitudinally to the main flow FS, can be positioned symmetrically and parallel to its longitudinal axis, so that its sensitive surface 2 is subjected to a defined flow of the medium deflected obliquely over the flank. This achieves the desired gap flow UTS above the sensor 5 without excessively influencing the main flow FS (energetically), as would be the case, for example, with a 90° deflection, and without generating undesirable turbulence.

[0117] Unlike a flow path in a tube-in-tube bypass (the chamber head described above), which also generates the desired gap flow, the measuring device proposed here has no side walls that could retain (water) droplets by capillary action. Instead, droplets can run out or drip off in the laterally open structure. The thermal mass remains reduced to a minimum, since only part of the sensor chip is located in the housing, so that low thermal power is sufficient to keep the sensor above the dew point.

[0118] The measuring device 1 for determining a flow parameter VD of a fluid FS can have the following features: Centrally symmetrical placement of a (preferably) wedge-shaped flow guide 6 over the sensitive elements 12 of a flow sensor 10, which is suitable to generate the desired plane-parallel gap flow UTS over the boundary layer of the sensor surface 2; wherein the flow guidance 6 can be designed in such a way that it can be bidirectionally directed in both pipe directions ST1, ST2 and generate the gap flow above the sensor chip 5; The flow guide can have 45° inclined flanks, but can also be designed as another advantageous flow body such as a round or oval profile according to the required flow measurement range, wherein the flow guide 6 can be installed in the smooth channel wall 4 with the side facing away from the sensor 10 and can thus accelerate and align the main flow FS in the sense of a (one-sided) channel narrowing, wherein the flow guide 6 can also be arranged freestanding in the middle of the channel as a bypass in the main channel 17 together with the sensor chip 5 and can thus represent a separate sensor assembly, wherein the sensor chip 5 itself can be installed flush in the channel wall 4 and the preferred flow path can also be positioned freely in the main channel as a bypass division spaced away from the sensor surface 2, wherein the sensor chip 5 can be placed symmetrically and parallel to its longitudinal axis at a defined distance from the flow guide 6 along the main flow FS and whose sensitive surface 2 can be subjected to a defined flow of the medium deflected obliquely over the flanks of the flow guide 6, the desired gap flow above the sensor chip 5 can be achieved without energetically influencing the main flow FS too much and without generating unwanted turbulence.

[0119] The device 1 for determining a flow parameter VD of a fluid FS may further have the following features: a sensor chip 5, with a thermal membrane sensor element 12, which is configured to determine the flow parameter of the fluid FS in a measuring range and / or to determine a fluid temperature of the fluid FS; wherein the thermal membrane sensor element 12 can have two thermocouple junctions 8, 8' spaced apart from each other and a heating element 3 arranged between the thermocouple junctions; wherein the sensor chip 5 can be configured to be surrounded by the fluid FS as a freestanding sensor finger when the flow sensor is in operation; wherein the sensor chip 5 can be freely attached to a measuring head 13; and wherein a length L of the sensor chip 5 can be at least three times as long as a width W of the sensor chip 5, so that the membrane sensor element 12 can be freestanding in the flow and placed outside of a flow-disrupting transition to a mechanical anchoring of the measuring head 13; wherein the membrane sensor element 12 can be arranged in a first third of the chip area 2 at a first end 5a of the sensor chip 5, and wherein the first end 5a of the sensor chip can be opposite a second end 5b of the sensor chip 5, to which electrical leads 19 are connected with the measuring head 13; and where the flow parameter VD can be a flow rate, a mass flow rate, a volume flow rate VD, a flow velocity, a flow direction, a fluid temperature or a fluid state parameter. Reference symbol list: 1 Device for determining a flow parameter of a fluid flow 2 Surface of the sensor chip 3 heating elements 4 wall 5 Sensor chip, sensor finger 5a free end 5b attached end 6 Flow deflection element 7 first temperature sensor, first thermocouple group 7' second temperature sensor, second thermocouple group 8 first thermocouples 8' second thermocouples 8a Hot contact of the first thermocouple 8b Hot contact of the second thermocouple 8c cold contact of the first thermocouple 8d cold contact of the second thermocouple 9 Membran 10 flow sensors 11 electrical connections 12 thermal membrane sensor element 13 Measuring head 14 columns 15th side of the trapezoidal shape 16 free cross-section 17 Fluid channel 18 free cross-section 19 electrical supply lines 20 Cross-sectional area of ​​the flow sensor in the fluid channel 21 Cross-sectional area of ​​the deflection element in the fluid channel 24 Aluminum 25 Polysilicon 26 beveled flanks 27 slanted side 28 parallel page 29 shorter base side FS Fluid Flow HSL main flow line UTS redirected partial flow GTS non-redirected partial flow ST1 first flow direction ST2 second flow direction ΔTP electrical signal VD Volume flow rate SA axis of symmetry L longer base of the sensor finger W shorter base of the sensor finger

Claims

Device for determining a flow parameter (VD) of a fluid flow (FS), in particular a respiratory gas flow, comprising a flow sensor (10) for generating an electrical signal (ΔTP) corresponding to the flow parameter (VD), the sensor chip (5, 5') having a substantially planar surface (2) on which a thermal membrane sensor element (12) is arranged, the thermal membrane sensor element (12) comprising a first temperature sensor (7) and a second temperature sensor (7') as well as a heating element (3) arranged between the temperature sensors (7, 7'), and comprising a fluid channel (17) with a wall (4) for guiding the fluid flow in a flow direction (ST1) in which the surface (2) of the sensor chip (5, 5') is arranged, the fluid channel (17) being configured such thatthat the fluid flow (FS) flows in the flow direction (ST1) on both sides of the sensor chip (5) along the same straight main flow line (HSL), such that the fluid flow (FS) flows towards the sensor chip (5, 5') along a straight line, and that the fluid flow (FS) flows away from the sensor chip (5, 5') along the same straight line, wherein the surface (2) of the sensor chip (5, 5') is arranged parallel to the main flow line (HSL) and wherein a flow deflecting element (6) is associated with the surface (2) of the sensor chip (5, 5') which deflects at least a partial flow (UTS) of the fluid flow (FS) such that the partial flow (UTS) is directed obliquely towards the surface (2), wherein the flow deflecting element (6) has a triangular shape in a section parallel to the main flow line (HSL) and perpendicular to the surface (2), wherein one apex of the triangular shape of the surface (2) is facingwherein preferably a side of the triangular shape extending from the tip intersects a straight line running parallel to the main flow line (HSL) at an angle of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. Device for determining a flow parameter (VD) of a fluid flow (FS), in particular a respiratory gas flow, comprising a flow sensor (10) for generating an electrical signal (ΔTP) corresponding to the flow parameter (VD), the sensor chip (5, 5') having a substantially planar surface (2) on which a thermal membrane sensor element (12) is arranged, the thermal membrane sensor element (12) comprising a first temperature sensor (7) and a second temperature sensor (7') as well as a heating element (3) arranged between the temperature sensors (7, 7'), and comprising a fluid channel (17) with a wall (4) for guiding the fluid flow in a flow direction (ST1) in which the surface (2) of the sensor chip (5, 5') is arranged, the fluid channel (17) being configured such thatthat the fluid flow (FS) flows in the flow direction (ST1) on both sides of the sensor chip (5) along the same straight main flow line (HSL), such that the fluid flow (FS) flows towards the sensor chip (5, 5') along a straight line, and that the fluid flow (FS) flows away from the sensor chip (5, 5') along the same straight line, wherein the surface (2) of the sensor chip (5, 5') is arranged parallel to the main flow line (HSL) and wherein a flow deflecting element (6) is associated with the surface (2) of the sensor chip (5, 5') which deflects at least a partial flow (UTS) of the fluid flow (FS) such that the partial flow (UTS) is directed obliquely towards the surface (2), wherein the flow deflecting element (6) has a trapezoidal shape in a section parallel to the main flow line (HSL) and perpendicular to the surface (2), wherein a shorter base (29) of the trapezoidal shape of the surface (2) is facing,wherein preferably a side (15) of the trapezoidal shape extending from the shorter base side (29) intersects a straight line running parallel to the main flow line (HSL) at an angle (α) of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. Device for determining a flow parameter (VD) of a fluid flow (FS), in particular a respiratory gas flow, comprising a flow sensor (10) for generating an electrical signal (ΔTP) corresponding to the flow parameter (VD), the sensor chip (5, 5') having a substantially planar surface (2) on which a thermal membrane sensor element (12) is arranged, the thermal membrane sensor element (12) comprising a first temperature sensor (7) and a second temperature sensor (7') as well as a heating element (3) arranged between the temperature sensors (7, 7'), and comprising a fluid channel (17) with a wall (4) for guiding the fluid flow in a flow direction (ST1) in which the surface (2) of the sensor chip (5, 5') is arranged, the fluid channel (17) being configured such thatthat the fluid flow (FS) flows in the flow direction (ST1) on both sides of the sensor chip (5) along the same straight main flow line (HSL), such that the fluid flow (FS) flows towards the sensor chip (5, 5') along a straight line, and that the fluid flow (FS) flows away from the sensor chip (5, 5') along the same straight line, wherein the surface (2) of the sensor chip (5, 5') is arranged parallel to the main flow line (HSL) and wherein a flow deflecting element (6) is associated with the surface (2) of the sensor chip (5, 5') which deflects at least a partial flow (UTS) of the fluid flow (FS) such that the partial flow (UTS) is directed obliquely towards the surface (2), wherein the flow deflecting element (6) has a hexagonal shape in a section parallel to the main flow line (HSL) and perpendicular to the surface (2), wherein a first side (28) the hexagonal shape is formed parallel to the surface (2) and facing the surface (2),wherein preferably a side (27) of the hexagonal shape extending from the first side (28) intersects a straight line running parallel to the main flow line (HSL) at an angle (α) of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. Device for determining a flow parameter (VD) of a fluid flow (FS), in particular a respiratory gas flow, comprising a flow sensor (10) for generating an electrical signal (ΔTP) corresponding to the flow parameter (VD), the sensor chip (5, 5') having a substantially planar surface (2) on which a thermal membrane sensor element (12) is arranged, the thermal membrane sensor element (12) comprising a first temperature sensor (7) and a second temperature sensor (7') as well as a heating element (3) arranged between the temperature sensors (7, 7'), and comprising a fluid channel (17) with a wall (4) for guiding the fluid flow in a flow direction (ST1) in which the surface (2) of the sensor chip (5, 5') is arranged, the fluid channel (17) being configured such thatthat the fluid flow (FS) flows in the flow direction (ST1) on both sides of the sensor chip (5) along the same straight main flow line (HSL), such that the fluid flow (FS) flows towards the sensor chip (5, 5') along a straight line, and that the fluid flow (FS) flows away from the sensor chip (5, 5') along the same straight line, wherein the surface (2) of the sensor chip (5, 5') is arranged parallel to the main flow line (HSL) and wherein a flow deflecting element (6) is associated with the surface (2) of the sensor chip (5, 5') which deflects at least a partial flow (UTS) of the fluid flow (FS) such that the partial flow (UTS) is directed obliquely towards the surface (2), wherein the flow deflecting element (6) has a rhomboid shape in a section parallel to the main flow line (HSL) and perpendicular to the surface (2), wherein a tip of the diamond-shaped surface (2) is facing,wherein preferably a side of the rhomboid shape extending from the tip intersects a straight line running parallel to the main flow line (HSL) at an angle (α) of at least 20°, preferably at least 30°, particularly preferably at least 40°, and / or at most 70°, preferably at most 60°, particularly preferably at most 50°. Device according to one of the preceding claims, wherein the flow deflection element (6) is designed such that the partial flow (UTS) is directed obliquely towards the surface (2) in the flow direction (ST1) and in an opposite flow direction (ST2). Device according to one of the preceding claims, wherein a gap (14) between the surface (2) and the flow deflection element (6) is open in at least one direction perpendicular to the main flow line (HSL) and parallel to the surface towards the surface (2). Device according to one of the preceding claims, wherein the deflecting element (6) is arranged centrally to the thermal membrane sensor element (12) when viewed along the main flow line (HSL). Device according to one of the preceding claims, wherein the flow deflection element (6) is symmetrical in a section parallel to the main flow line (HSL) and perpendicular to the surface (2) with respect to an axis of symmetry (SA) perpendicular to the main flow line (HSL). Device according to one of the preceding claims, wherein the flow deflection element (6) is arranged in the fluid channel (17) such that a free cross-section (16) is provided between a side of the flow deflection element (6) facing away from the sensor chip (5, 5') and the wall (4) of the fluid channel (17), and / or wherein a free cross-section (18) is provided between a side of the sensor chip (5, 5') facing away from the flow deflection element (6) and the wall (4) of the fluid channel (17). Device according to one of the preceding claims, wherein the flow deflection element (6) is arranged in the fluid channel (17) such that it forms part of the wall (4), and / or wherein the sensor chip (5') is arranged in the fluid channel (17) such that it forms part of the wall (4). Device according to one of the preceding claims, wherein a minimum distance between the surface (2) and the deflecting element (6) is at least 0.5 mm, preferably at least 0.6 mm, particularly preferably at least 0.8 mm, and / or at most 2.0 mm, preferably at most 1.5 mm, particularly preferably at most 1.2 mm. Device according to one of the preceding claims, wherein the sum of the cross-sectional area (20) of the flow sensor (10) in the fluid channel (17) and the cross-sectional area (21) of the deflecting element (6) in the fluid channel (17) in a plane perpendicular to the main flow line (HSL) is at most 50%, preferably at most 30%, particularly preferably at most 10%, of the cross-sectional area bounded by the wall (4) of the fluid channel (17). Device according to one of the preceding claims, wherein the deflecting element (6) is designed as a freestanding deflecting finger (6). Device according to one of the preceding claims, wherein the thermal membrane sensor element (12) is arranged on a freestanding sensor finger (5). Device according to claim 14, wherein an extension (L) of the sensor finger (5) in a direction perpendicular to the main flow line and parallel to the surface is at least three times as large, preferably four times as large, particularly preferably five times as large, as an extension (W) of the sensor finger (5) in a direction parallel to the main flow line. Device according to claim 14 or 15, wherein the membrane sensor element (12) is arranged in a first third of the surface (2) at a free end (5a) of the sensor finger (5), and wherein the free end (5a) of the sensor finger (5) is opposite a fixed (5b) end of the sensor finger (5) to which electrical leads (19) are connected to the sensor finger (5). Device according to one of the preceding claims, wherein a side (26) of the flow sensor (10) facing the fluid flowing in the first flow direction (ST1) and / or a side (26') of the flow sensor (10) facing the fluid flowing in the second flow direction (ST1) is shaped such that the cross-section of the fluid channel (17) narrows in the respective flow direction (ST1; ST2). Device according to one of the preceding claims, wherein the flow parameter (VD) is a flow rate, a mass flow rate, a volume flow rate (VD) and / or a flow velocity of the fluid flow.

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