Flow sensor and photoacoustic detector

Abstract

The invention relates to a flow sensor and a photoacoustic detector. The invention relates to a flow sensor comprising a substrate (2) with grooves (4), in which a resistive serpentine (3) consisting of a plurality of platinum film tracks having a web (6) spanning the grooves (4) is arranged on the substrate (2), in which a cover (16) covering the resistive serpentine (3) is arranged on the substrate (2), the cover having grooves (4) aligned with the grooves (4) in the substrate (2), these grooves (4) forming flow channels for the medium, one or more holes (5) are provided in the base plate (2) and / or in the cover (16) for lateral flow of media into the recess (4), characterized in that one hole (5) in the cover (16) and one hole (5) in the base plate (2) are arranged such that media entering the recess (4) through one of the holes (5) sweeps over or all of the screens (6) before reaching the other hole (5).

Description

Technical Field

[0001] The invention relates to a flow sensor and a photoacoustic detector. Background Art

[0002] Flow sensors based on the anemometer principle are widely used and easy to use in many areas. This principle is based on the effect that a heated body or surface can release energy into the environment. The surrounding medium can be gaseous, liquid, or solid. The energy dissipated depends on the surface and physical properties of the medium, as well as the flow rate and flow type (turbulent or laminar) through the medium. At zero flow, the energy output is determined solely by convection, the physical properties of the medium, and the surface of the heated body.

[0003] Flow sensors operating according to the anemometer principle are described in numerous patent applications and patents. DE 42 24518 C2 describes a silicon device in which a meandering resistor structure is partially mounted on a dielectric support structure having flow channels extending through the silicon body. DE 10 2013 209 951 A1 describes a device for temperature detection using thermocouple pairs. DE 10 2009 029 169 A1 describes a device with an attached vortex flow body. DE 10 210 042307 A1 describes a device in which a heater and temperature sensor are mounted separately.

[0004] Flow sensors are also known to detect gas flows in the detector chamber of miniature photoacoustic detectors. These flows are generated by the expansion of a preferably gaseous medium due to energy absorption. However, known solutions using pressure sensors are often too insensitive. The use of miniature microphones is limited by a high lower cutoff frequency of approximately 50 Hz to 100 Hz. Flow sensors used in large, classical photoacoustic detectors are too large to fit within the envisioned detector chamber. Summary of the Invention

[0005] The purpose of the present invention is to provide a novel flow sensor and a novel photoacoustic detector.

[0006] According to the present invention, this object is achieved by a flow sensor and a photoacoustic detector according to the set of appended claims.

[0007] Advantageous embodiments of the invention are subject matter of the dependent claims.

[0008] A flow sensor is proposed, comprising a grooved substrate on which a resistive meander comprising several platinum thin film tracks is arranged. These tracks have a web that crosses the grooves. The grooves can be closed at their ends. In particular, the grooves in the substrate can be initially continuous and then closed during installation of the flow sensor to change the flow direction.

[0009] According to the present invention, a cover is placed on the substrate, covering the resistive meander. The cover has grooves aligned with the grooves in the substrate, so that these grooves form flow channels for the medium. The grooves can be closed at their ends. In particular, the grooves in the cover can initially be continuous and then closed when the flow sensor is installed.

[0010] According to the invention, one or more holes are arranged in the base plate and / or the cover for allowing the medium to flow laterally into the recess.

[0011] According to the invention, the holes in the cover and the holes in the base are arranged so that the medium entering the groove through one of the holes sweeps over several or all of the stencils before reaching the other hole and exiting from there.

[0012] In one embodiment, a temperature sensor is arranged on the substrate, which may also serve as a heater.

[0013] In one embodiment, the stencil width is approximately 10 μm and / or the thickness is approximately 1 μm, and / or 5 to 10 stencils are provided. Technically, a stencil width of 5 μm and a thickness of approximately 0.8 μm can be achieved. The number of stencils can be as high as 100 or more.

[0014] In one embodiment, the substrate is designed as a ceramic substrate.

[0015] In one embodiment, the substrate has dimensions of 2 mm x 2 mm x 1 mm; dimensions of 1 mm x 1 mm x 0.5 mm are also useful.

[0016] In one embodiment, the screens span the grooves at right angles or approximately right angles. The openings may, for example, open into the grooves at right angles or approximately right angles. The screens may be connected in parallel or in series, or a combination of the two.

[0017] According to one aspect of the invention, a photoacoustic detector is proposed, comprising a closed, optically sealed, and gas-tight housing (this sealing should be maintained during the service life of the detector), the housing enclosing a detector chamber and a buffer chamber, the buffer chamber being separated from the detector chamber by an optically sealed partition wall having a bore, wherein a transparent inlet window is arranged in the housing between the environment and the detector chamber, through which the detector chamber and the medium located therein can be irradiated, the buffer chamber being designed as a Helmholtz resonant cavity, the flow sensor being arranged in or on the partition wall as described above and positioned such that changes in the medium pressure in the detector chamber caused by the irradiation result in an equalizing flow via the flow sensor into the buffer chamber. The irradiation is pulsed, for example, at a frequency of approximately 5 Hz to 10 Hz.

[0018] In one embodiment, the detector chamber and / or the buffer chamber has a width less than 1 cm 3closed volume.

[0019] The present invention provides a flow sensor capable of detecting a gas flow between a detector chamber and a buffer chamber caused by expansion of a medium due to energy absorption in a micro photoacoustic (PA) detector.

[0020] The flow sensor can be designed to detect a flow with a cutoff frequency of 0 to 50 Hz, in particular 5 Hz to 10 Hz, and a size of, for example, 2 mm x 2 mm x 1 mm. The measurement sensitivity can be: less than 1 cm 3 The pressure change caused by the energy input in the closed volume results in a measurable flow at the sensor, and this can be converted into a corresponding output voltage that is related to the energy consumption of the PA sensor. For this purpose, the measurement current can be pulsed. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Examples of embodiments of the present invention will be described in more detail below with reference to the accompanying drawings, in which

[0022] Figure 1 is a schematic diagram of the flow sensor, and

[0023] Figure 2 is a schematic diagram of a photoacoustic detector.

[0024] Corresponding parts are marked with the same reference symbols in all figures. DETAILED DESCRIPTION

[0025] Figure 1 is a schematic diagram of the flow sensor 1.

[0026] For example, a flow sensor 1 may include a substrate 2, such as a ceramic substrate 2. A resistive meander 3 (e.g., produced in a batch process) consisting of several freely suspended platinum thin film tracks is arranged on the substrate 2. The resistive meander has a mesh 6 that extends over a groove 4 in the substrate 2 at an angle of, for example, 90° and is therefore cooled by the medium flowing through the groove 4 (also referred to as a flow channel). To generate turbulence in the medium, one or more holes 5 are arranged in the substrate 2, for example, at right angles to the groove 4. The fluid can be directed through these holes into the groove 4, thereby generating eddies at tear edges 15. These eddies are amplified at the mesh 6 and result in additional eddies and turbulence, thereby improving energy transfer from the medium to the mesh 6. The tear edges 15 are edges at which the flow is deflected by 90 degrees. This can also be created by a constriction in the groove 4. A cover 16 may be arranged on the substrate 2, having a groove 4 aligned with the groove 4 so that the groove 4 forms a flow channel for the medium. Holes 5 can also be arranged in the cover 16, for example at right angles to the groove 4, through which the fluid can be directed to the groove 4, so that eddies can be generated at the tear edge 15, which are amplified at the mesh 6 and cause additional eddies and turbulence, thereby making it possible to improve the energy transmission from the medium to the mesh 6. The holes 5 in the cover 16 and the holes 5 in the base plate 2 can be arranged so that the medium entering the groove 4 through one of the holes 5 sweeps over several meshes 6 or all meshes 6 before it reaches another hole 5.

[0027] In order to suppress and / or compensate for temperature influences, a temperature sensor 7 is formed on the flow sensor 1, in particular on the substrate 2. The temperature sensor 7 can also be used as a heater to keep the temperature of the flow sensor 1 constant. The temperature sensor 7 can be made of platinum and covered by a glass layer or a glass passivation layer to be protected.

[0028] For example, the width of the mesh 6 of the resistive meandering portion 3 may be about 10 μm and the thickness may be about 1 μm. For example, 5 to 10 or more meshes 6 may be provided.

[0029] exist Figure 1 In FIG, the ends of the groove 4 are shown as open. If the flow sensor 1 is manufactured in a batch process, this may be due to the manufacturing process. For application of the flow sensor 1, the ends of the groove can be closed. Alternatively, the flow sensor 1 can be manufactured so that the groove is closed at the ends.

[0030] Figure 2Figure 8 is a schematic diagram of a photoacoustic detector 8, which includes a housing 9, in particular a gas-tight housing, which encloses a detector chamber 10 and a buffer chamber 11. The buffer chamber 11 is separated from the detector chamber 10 by a partition wall 14 having a borehole 17. Furthermore, an inlet window 12 is arranged in the housing 9 between the environment 13 and the detector chamber 10, through which the detector chamber 10 and the medium located therein can be irradiated. The inlet window 12 is transparent to infrared radiation, which can be absorbed by the irradiated medium. The buffer chamber 11 is designed as a Helmholtz resonator and is shielded from the irradiation by the partition wall 14. Figure 1 The flow sensor 1 is arranged in or on the partition wall 14. The medium can flow from the detector chamber 10 via the bore 17 into the hole 5 in the base plate 2, from there further into the groove 4 in the base plate 2 and the cover 16 and along the mesh 6 to the hole 5 in the base plate 2 and the cover 16 and from there into the buffer chamber 11 or in the opposite direction.

[0031] The flow sensor 1 is capable of detecting the flow of a medium (in particular a gas) in a detector chamber 10 in a (micro)photoacoustic detector 8 , the flow being generated by the expansion of the medium due to energy absorption (irradiation).

[0032] The flow sensor 1 can be designed to detect a flow rate with a cutoff frequency of 0 to 50 Hz and a size of, for example, 2 mm x 2 mm x 1 mm. The measurement sensitivity can be such that the distance between the detector chamber 10 and the buffer chamber 11 is less than 1 cm. 3 The pressure change caused by the energy input in the closed volume results in a measurable flow at the flow sensor 1, which can be measured as a resistance change of the flow sensor 1, which is converted into a voltage through a bridge circuit with a reference sensor, which is related to the energy absorption of the photoacoustic detector 8.

[0033] The temperature sensor 7 , which can also serve as a heater, can be used to keep the average temperature of the medium in the detector chamber 10 and / or the buffer chamber 11 constant.

[0034] The flow sensor 1 is positioned in the housing 9 so that the pressure changes in the detector chamber 10 caused by the absorption of energy by the medium can flow via the flow sensor 1 and the partition wall 14 with the bore 17 into the unirradiated buffer chamber 11. For this purpose, the electrical connections 18 of the flow sensor 1 for the resistance meander 3 and / or the temperature sensor 7 are led out of the housing 9.

[0035] Reference Signs List

[0036] 1 flow sensor

[0037] 2Substrates, ceramic substrates

[0038] 3. Resistor winding part

[0039] 4 grooves

[0040] 5 holes

[0041] 6 stencils

[0042] 7 Temperature sensor

[0043] 8 Photoacoustic detector

[0044] 9 Shell

[0045] 10 detector chamber

[0046] 11 Buffer Room

[0047] 12 entrance windows

[0048] 13 Environment

[0049] 14 Next Door

[0050] 15 Torn Edge

[0051] 16 covers

[0052] 17 Drilling

[0053] 18 Electrical connections

Claims

1. A flow sensor (1), comprising a substrate (2) with a groove (4), wherein a resistive meander (3) comprising a plurality of platinum thin film tracks is arranged on the substrate (2), the tracks having a mesh (6) spanning the groove (4), wherein a cover (16) covering the resistive meander (3) is arranged on the substrate (2), the cover having a groove (4) aligned with the groove (4) in the substrate (2), so that the groove (4) forms a flow channel for a medium, and one or more holes (5) are arranged in the substrate (2) and / or the cover (16) for the medium to flow laterally into the groove (4), characterized in that One hole (5) in the cover (16) and one hole (5) in the base plate (2) are arranged so that a medium entering the groove (4) through one of the holes (5) sweeps over several or all of the stencils (6) before it reaches the other hole (5).

2. The flow sensor (1) according to claim 1, wherein a temperature sensor (7) is arranged on the substrate (2), said temperature sensor also being able to serve as a heater.

3. The flow sensor (1) according to claim 1, wherein the width of the web (6) is 5 μm to 10 μm and / or the thickness is 0.8 μm to 1 μm and / or 5 to 10 or up to 100 webs (6) are provided.

4. The flow sensor (1) according to one of the preceding claims, wherein the substrate (2) is designed as a ceramic substrate (2).

5. The flow sensor (1) according to any of the preceding claims, wherein the substrate (2) has dimensions of 2 mm x 2 mm x 1 mm or 1 mm x 1 mm x 0.5 mm.

6. A flow sensor (1) according to any one of the preceding claims, wherein the mesh (6) spans the groove (4) at a right angle or approximately a right angle and / or wherein the hole (5) opens into the groove (4) at a right angle or approximately a right angle.

7. A photoacoustic detector (8) comprising an airtight housing (9) which encloses a detector chamber (10) and a buffer chamber (11), the buffer chamber being separated from the detector chamber (10) by a partition wall (14) with a borehole (17), wherein a transparent inlet window (12) is arranged in the housing (9) between the environment (13) and the detector chamber (10), through which the detector chamber (10) and the medium located therein can be irradiated, wherein the buffer chamber (11) is designed as a Helmholtz resonance cavity, wherein a flow sensor (1) according to one of the preceding claims is arranged in or on the partition wall (14) with the borehole (17) and is positioned such that a pressure change of the medium in the detector chamber (10) caused by the irradiation leads to an equilibrium flow via the flow sensor (1) into the buffer chamber (11).

8. The photoacoustic detector (8) according to claim 7, wherein the detector chamber (10) and / or the buffer chamber (11) has a diameter of less than 1 cm 3 closed volume.

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