metering instrument

Abstract

This utility model belongs to the field of metering equipment technology and discloses a metering instrument, including a housing, a metering module, a first filter, a flow guide, and a second filter. The housing has a accommodating cavity, and an air inlet and an air outlet communicating with the accommodating cavity are also provided on the housing. The metering module is disposed within the accommodating cavity and has a metering channel. The metering module also has a metering inlet and a metering outlet communicating with the metering channel, and the metering outlet is connected to the air outlet. The first filter divides the accommodating cavity into a first flow chamber and a second flow chamber, with the metering inlet located in the first flow chamber. The flow guide is disposed between the air inlet and the metering module, and is used to at least partially deposit dust in the gas entering the accommodating cavity through the air inlet, and to guide the gas into the second flow chamber. The second filter is disposed at the metering inlet. The above-mentioned metering instrument has high anti-pollution performance, and the second filter requires low cleaning frequency.

Description

Technical Field

[0001] This utility model relates to the field of metering equipment technology, and in particular to a metering instrument. Background Technology

[0002] Ultrasonic gas meters are fully electronic instruments that use ultrasound to measure gas flow. Their core principle is to calculate the flow velocity by measuring the time difference between the forward and reverse propagation of ultrasound waves in the gas, thus determining the flow rate. However, natural gas, the main component of gas, contains a certain amount of dust (including but not limited to rust, paint residue, or dust particles that fall during pipeline transportation). When this dust flows through the ultrasonic gas meter, it deposits and adheres to the metering module, causing a localized reduction in the inner diameter of the metering channel, increased roughness, and distortion of the flow field velocity distribution profile. This ultimately reduces the metering accuracy of the module.

[0003] According to the requirements of GB / T39841-2021 Ultrasonic Gas Meters, ultrasonic gas meters are recommended to have anti-pollutant performance. Therefore, a filter is installed at the inlet of the metering module in these gas meters to intercept dust particles. However, if the mesh size of the filter is too high, the filter pores are easily clogged, requiring frequent disassembly and cleaning of the ultrasonic gas meter. If the mesh size is too low, the anti-pollutant performance of the ultrasonic gas meter will not meet the requirements. Therefore, how to reduce the frequency of filter cleaning while meeting the anti-pollutant performance requirements has become an urgent problem to be solved. Utility Model Content

[0004] The purpose of this invention is to provide a metering instrument that can reduce the frequency of filter cleaning while meeting the requirements for anti-pollution performance.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] A metering instrument includes a housing, a metering module, a first filter, a flow guide, and a second filter. The housing has a accommodating cavity and an air inlet and an air outlet communicating with the accommodating cavity. The metering module is disposed within the accommodating cavity and has a metering channel. The metering module also has a metering inlet and a metering outlet communicating with the metering channel, and the metering outlet communicating with the air outlet. The first filter divides the accommodating cavity into a first flow chamber and a second flow chamber, with the metering inlet located in the first flow chamber. The flow guide is disposed between the air inlet and the metering module, and is used to at least partially deposit dust in the gas entering the accommodating cavity through the air inlet and guide the gas into the second flow chamber. The second filter is disposed at the metering inlet.

[0007] In one embodiment, the flow guide includes a base plate facing the metering module, and the base plate has flow holes.

[0008] In one embodiment, multiple flow holes are provided, and the multiple flow holes are distributed in an array.

[0009] In one embodiment, the flow guide further includes baffles, and multiple baffles are staggered at positions opposite to the air inlet on the base plate to form multiple dust collection chambers in conjunction with the base plate.

[0010] In one embodiment, the guide member cooperates with the housing to form a guide cavity that communicates with the air inlet, and the guide cavity is connected to the second flow cavity through the flow hole.

[0011] In one embodiment, the first filter and the flow guide form a through hole, and the metering module passes through the through hole.

[0012] In one embodiment, the watch case includes a first housing and a second housing. The first housing is configured as a groove structure, and the air inlet is located at the bottom of the groove of the first housing. The second housing blocks the groove of the first housing and surrounds the first housing to form the accommodating cavity.

[0013] In one embodiment, one of the first filter screen and the watch case is provided with a slider, and the other of the first filter screen and the watch case is provided with a groove. The slider is slidably disposed in the groove along the length direction of the metering channel so as to contact the protruding top of the base plate to form the through hole.

[0014] In one embodiment, multiple first filters are spaced apart, and a support member is provided between adjacent first filters to support the metering module.

[0015] In one embodiment, the metering instrument further includes a foreign object shield, which is installed inside the air outlet.

[0016] The beneficial effects of this utility model are as follows: The above-mentioned metering instrument has a flow guide between the metering module and the air inlet. After the gas enters the flow guide cavity through the air inlet, the dust in the gas collides with the flow guide, resulting in kinetic energy loss and causing some larger dust particles to be deposited on the flow guide. At the same time, due to the setting of the flow guide, the gas flows towards the second flow cavity, which prolongs the flow path of the gas. The gas enters the metering channel through the second filter after being filtered by the first filter. That is, before passing through the second filter, the dust has already been deposited and filtered by the first filter. Therefore, the amount of dust carried by the gas flowing to the second filter is reduced, and the amount of dust accumulated at the second filter is also significantly reduced. Under the premise of meeting the anti-pollution performance, the cleaning frequency of the second filter is reduced. Attached Figure Description

[0017] Figure 1 This is a three-dimensional structural diagram of the measuring instrument in the embodiment of this utility model;

[0018] Figure 2 This is a cross-sectional view of the measuring instrument from one angle in an embodiment of this utility model;

[0019] Figure 3 This is a cross-sectional view of the measuring instrument from another angle in an embodiment of this utility model;

[0020] Figure 4 This is an exploded view of the metering instrument in an embodiment of this utility model;

[0021] Figure 5 This is a three-dimensional structural diagram of the guide component at one angle in an embodiment of this utility model;

[0022] Figure 6 This is a three-dimensional structural diagram of the guide component from another angle in an embodiment of this utility model;

[0023] Figure 7 This is a schematic diagram of the structure of the first filter screen in an embodiment of this utility model;

[0024] Figure 8 This is a schematic diagram of the structure of the first housing in an embodiment of this utility model;

[0025] Figure 9 This is a gas flow path diagram in an embodiment of this utility model.

[0026] In the picture:

[0027] 1. Case; 11. First housing; 111. Snap-fit ​​component; 112. Connecting post; 12. Second housing; 121. Slider; 13. Second sealing ring; 14. Partition; 15. Air inlet; 16. Air outlet; 17. First flow passage; 18. Second flow passage; 19. Guide cavity; 110. Air outlet; 2. Guide component; 21. Base plate; 211. Blocking part; 212. Rectifying part; 213. Extension part; 214. Flow passage hole; 22. Enclosure plate; 23. Baffle; 24. Snap-fit ​​component; 25. Top; 3. Metering module; 31. Metering channel; 32. Metering inlet; 33. Metering outlet; 4. First filter screen; 41. Slide groove; 5. Second filter screen; 6. Foreign object protection cover; 7. Valve assembly; 8. Support component; 9. Adhesive plate. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, not the entire structure.

[0029] In the description of this utility model, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0030] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0031] In the description of this embodiment, the terms "upper," "lower," "left," and "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. In addition, the terms "first" and "second" are only used for distinction in description and have no special meaning.

[0032] refer to Figures 1-9As shown in the embodiment of this utility model, a metering instrument is proposed for measuring the flow rate of gases including but not limited to fuel gas. The metering instrument includes a housing 1, a metering module 3, a flow guide 2, a first filter 4, and a second filter 5. The housing 1 has a accommodating cavity, within which the metering module 3, flow guide 2, first filter 4, and second filter 5 are all disposed. To facilitate timely cleaning and maintenance of the first filter 4, second filter 5, and metering module 3, the housing 1 includes a detachably connected first housing 11 and second housing 12, which together form the aforementioned accommodating cavity. An air inlet 15 and an air outlet 16 communicating with the accommodating cavity are provided on either the first housing 11 or the second housing 12. The metering module 3 can be an ultrasonic metering module. The metering module 3 has a metering channel 31, and a metering inlet 32 ​​and a metering outlet 33 communicating with the metering channel 31. The metering outlet 33 is connected to the air outlet 16. The first filter 4 divides the accommodating cavity to form a first flow chamber 17 and a second flow chamber 18. The metering inlet 32 ​​is located in the first flow chamber 17. The guide member 2 is disposed between the air inlet 15 and the metering module 3. The guide member 2 is used to deposit at least part of the dust in the gas entering the accommodating cavity through the air inlet 15 and guide the gas into the second flow chamber 18. The second filter 5 is disposed at the metering inlet 32 ​​of the metering module 3, and is not limited to stainless steel mesh, nylon mesh, etc.

[0033] The aforementioned metering instrument has a guide member 2 between the metering module 3 and the air inlet 15. After the gas enters the guide cavity 19 through the air inlet 15, the dust in the gas collides with the guide member 2, resulting in kinetic energy loss and causing some larger dust particles to be deposited on the guide member 2. At the same time, due to the setting of the guide member 2, the gas flows towards the second flow cavity 18, extending the gas flow path. After the gas passes through the first filter screen 4, it enters the metering channel 31 through the second filter screen 5. That is, before passing through the second filter screen 5, the dust has already been deposited and filtered by the first filter screen 4. Therefore, the dust carried by the gas flowing to the second filter screen 5 is reduced, and the amount of dust accumulated at the second filter screen 5 is also significantly reduced. Under the premise of meeting the anti-pollution performance, the cleaning frequency of the second filter screen 5 is reduced. It can be understood that the second filter screen 5 can be cleaned either when it is installed on the metering module 3 or after it is removed from the metering module 3. In the current embodiment, the second filter screen 5 is installed on the metering module 3 by a snap-fit ​​method. In other embodiments, the second filter 5 may also be fixed to the metering inlet 32 ​​of the metering module 3 in a detachable manner, not limited to bolt connection.

[0034] Specifically, because the received ultrasonic signal is affected by fluctuations in gas flow rate, large fluctuations in gas flow rate can lead to a decrease in the measurement accuracy of the metering instrument. Therefore, refer to Figure 2 , Figure 3 and Figure 8As shown, a partition 14 is provided inside the casing 1, which divides the accommodating cavity into an air inlet chamber and an air outlet chamber 110. The air inlet chamber is connected to the air inlet 15, and the air outlet chamber 110 is connected to the air outlet 16. The metering module 3 is mounted on the partition 14 and is fixedly connected to the partition 14 by means of bolts or snap-fit. The metering inlet 32 ​​is located in the air inlet chamber, and the metering outlet 33 is located in the air outlet chamber 110. A first sealing ring is provided between the metering module 3 and the side of the partition 14 facing the air inlet 15, so that the gas can only flow to the air outlet chamber 110 through the metering module 3. The air inlet chamber can buffer the pressure of the gas entering the casing 1 before allowing the gas to enter the metering channel 31 for metering. It has a good suppressive effect on the pressure fluctuation of the upstream gas. The air outlet chamber 110 can buffer the pressure fluctuation generated by the load, that is, it has a good suppressive effect on the pressure fluctuation of the downstream gas, avoiding the impact of load instability on the accuracy of the metering results. Based on this, the guide 2 is disposed in the air intake chamber, and the first flow chamber 17 and the second flow chamber 18 both belong to the air intake chamber.

[0035] refer to Figure 5 and Figure 6 As shown, the flow guide 2 includes a base plate 21 facing the metering module 3. A flow hole 214 is provided on the side of the base plate 21 opposite to the second flow cavity 18. The gas flowing out from the flow hole 214 is directed to the side of the casing 1 away from the air inlet 15, thereby impacting the surface of the casing 1 and the metering module 3 to generate secondary sedimentation, and then flows to the metering inlet 32 ​​of the metering module 3, further reducing the dust flowing into the metering channel 31.

[0036] More specifically, multiple flow holes 214 are formed on the base plate 21, and these multiple flow holes 214 are arranged in an array on the base plate 21. At this time, the multiple flow holes 214 can rectify and discretize the gas, resulting in a more uniform gas velocity distribution. Moreover, the pore size of the flow holes 214 is at least smaller than the particle size of some dust particles, so the flow holes 214 can also filter the gas. It can be understood that the pore size of the flow holes 214 is larger than the pore size of the filter holes on the first filter screen 4, and the pore size of the filter holes on the first filter screen 4 is larger than the pore size of the filter holes on the second filter screen 5. The gas is filtered layer by layer through the guide element 2, the first filter screen 4, and the second filter screen 5, adopting a multi-stage filtration design of "coarse first, then fine", which ensures the filtration effect while avoiding excessive gas pressure loss. Obviously, since both the first filter screen 4 and the second filter screen 5 are provided with multiple filter holes, the first filter screen 4 and the second filter screen 5 not only have a filtering function, but also a rectification effect, which can make the airflow into the metering channel 31 more stable and uniform, and further improve the metering accuracy of the metering module 3.

[0037] The guide component 2 also includes baffles 23. Multiple baffles 23 are staggered at the positions opposite to the bottom plate 21 and the air inlet 15 to form multiple dust collection chambers with the bottom plate 21, further reducing the possibility of dust flowing to the second flow chamber 18 through the flow hole 214, and causing more dust to accumulate on the guide component 2.

[0038] Specifically, the baffle 23 is divided into a first baffle and a second baffle. Both the first baffle and the second baffle are perpendicular to the bottom plate 21. The first baffle extends along the length of the metering channel 31. Multiple first baffles are spaced apart along the length of the metering channel 31. The second baffle is perpendicular to the first baffle. Multiple second baffles are spaced apart along the length of the metering channel 31. The height of the second baffle is lower than that of the first baffle. Therefore, compared with the direction perpendicular to the metering channel 31, the resistance to gas flow along the direction of the metering channel 31 is smaller, which is more conducive to the flow towards the flow hole 214.

[0039] It is understandable that the orthogonal projection of the guide component 2 toward the metering module 3 will inevitably partially overlap with the metering module 3. In order to further improve the utilization rate of the internal space of the casing 1 and allow dust to accumulate better on the guide component 2, the base plate 21 includes a blocking part 211, a rectifying part 212, and an extension part 213. The blocking part 211 is arranged opposite to the air inlet 15 and perpendicular to the axis of the air inlet 15, so that the dust can better impact the blocking part 211. The rectifying part 212 is connected to the blocking part 211 near the metering module. On one side of the outlet 33, the flow hole 214 is opened on the rectifier 212. At least one of the other sides of the blocking part 211 is connected to the extension part 213. The extension part 213 gradually extends away from the air inlet 15 in a direction away from the blocking part 211. The orthographic projection of the extension part 213 onto the metering module 3 does not coincide with the metering module 3. That is, the groove depth of the position of the rectifier 212 opposite to the metering module 3 is shallower than the groove depth of the part of the rectifier 212 whose orthographic projection does not coincide with the metering channel 31.

[0040] refer to Figure 2 and Figure 9As shown, to maximize the flow of gas through the guide member 2 and thus improve its flow capacity, the guide member 2, in conjunction with the casing 1, forms a guide cavity 19 that connects to the air inlet 15. The guide member 2 also has a flow passage 214, through which the guide cavity 19 connects to the second flow passage 18. In this case, the air inlet chamber is divided into the guide cavity 19 and the flow passage by the guide member 2, and the flow passage is further divided into a first flow passage 17 and a second flow passage 18 by the first filter 4. Therefore, the air inlet chamber includes the guide cavity 19, the first flow passage 17, and the second flow passage 18. Furthermore, the guide member 2 may also include a surrounding plate 22. The surrounding plate 22 surrounds the base plate 21, creating a groove-shaped structure with the opening of the guide member 2 facing the air inlet 15. This, in conjunction with the casing 1, forms the guide cavity 19. The surrounding plate 22 increases the contact area between the guide member 2 and the casing 1, which is beneficial for forming a relatively closed guide cavity 19.

[0041] In other embodiments, the guide member 2 has a guide cavity 19 that connects to the air inlet 15 inside, and the guide member 2 is also provided with a flow hole 214. The guide cavity 19 is connected to the second flow cavity 18 through the flow hole 214. For example, the flow member is set as a hollow tubular structure. Of course, the hollow tubular structure here can be a square tube or a round tube, and no specific limitation is made here.

[0042] In some embodiments, the flow guide 2 is detachably connected to the first housing 11 to facilitate timely removal of dust from the flow guide cavity 19. Specifically, refer to... Figure 2 As shown, to reduce the difficulty of assembling and disassembling the flow guide 2 and the first housing 11, the flow guide 2 is provided with a first connecting hole and a snap-fit ​​component 24 at opposite ends. The first housing 11 is provided with a second connecting hole corresponding to the first connecting hole, and a snap-fit ​​fitting component 111 is provided corresponding to the snap-fit ​​component 24. The flow guide 2 is initially positioned by the snap-fit ​​component 24 and the snap-fit ​​fitting component 111, and then further fixed by connectors passing through the first and second connecting holes. The connectors can be screws or screws used with nuts. Clearly, compared to using only snap-fit ​​connections, the connection between the flow guide 2 and the first housing 11 is more stable, and compared to connections with multiple connectors, the assembly and disassembly of the flow guide 2 and the first housing 11 are faster.

[0043] In the current embodiment, the snap-fit ​​component 111 is a protrusion provided on the first housing 11, and the snap-fit ​​component 24 of the guide component 2 is a snap block, which has a guide surface that gradually approaches the protrusion in a direction away from the air inlet 15. When the guide component 2 is assembled on the housing 1, the snap block gradually approaches the air inlet 15 from a direction away from the air inlet 15 until the snap block is engaged on the side of the protrusion facing the air inlet 15.

[0044] The first filter, screen 4, obviously also needs to be cleaned regularly. (Refer to...) Figure 4 and Figure 7As shown, to reduce the difficulty of disassembling and assembling the first filter 4, the first filter 4 is designed to be approximately U-shaped and fits against the inner wall of the casing 1. The first filter 4 and the guide member 2 together form a through hole, through which the metering module 3 passes. Simultaneously, the first housing 11 is designed as a groove structure, with the air inlet 15 located at the bottom of the groove. The partition 14 is integrally formed with the first housing 11 to reduce the difficulty of sealing between the air inlet chamber and the air outlet chamber 110. The second housing 12 blocks the groove of the first housing 11, thus forming a groove with the first housing 11. When disassembling and assembling the first filter 4, first remove the second housing 12 from the first housing 11, and then move the first filter 4 away from the first housing 11 to detach it from the metering module 3. The disassembly and assembly are simple.

[0045] For example, the air outlet 16 is also located on the same side of the first housing 11, that is, the air inlet 15 and the air outlet 16 are located on the same side of the first housing 11, so as to reduce the difficulty of connecting the metering instrument to external equipment. After the metering instrument is assembled, the air inlet 15 and the air outlet 16 are both located on the top of the housing 1, so the dust is more likely to accumulate in the guide cavity 19 under the action of gravity.

[0046] Specifically, the first housing 11 and the second housing 12 are bolted together. To reduce the thickness of the first housing 11 while still satisfying the bolted connection requirements, thereby lowering the manufacturing cost of the metering instrument and also for miniaturization, multiple arc-shaped connecting posts 112 are spaced apart on the inner wall of the first housing 11. Each connecting post 112 has a third connecting hole along its axial direction, while the second housing 12 has a fourth connecting hole. The second housing 12 and the first housing 11 are fixedly connected by connectors passing through the third and fourth connecting holes. Here, the connector refers to a threaded rod, meaning that at least the first connecting hole is a threaded hole.

[0047] Furthermore, the casing 1 also includes a second sealing ring 13. A mounting groove is provided on the first casing 11 or the second casing 12. The second sealing ring 13 is embedded in the mounting groove and presses against the first casing 11 and the second casing 12 to form an effective seal. It is worth emphasizing that the second sealing ring 13 is figure-eight shaped to correspond to the arrangement of the partition 14, ensuring that gas can only transfer from the inlet chamber to the outlet chamber 110 through the metering module 3, thereby further improving metering accuracy.

[0048] To limit the position of the first filter 4 and allow it to form a through hole with the flow guide 2, a slider 121 is provided on one of the first filter 4 and the second housing 12, and a groove 41 is provided on the other. The slider 121 is slidably disposed in the groove 41 along the length of the metering channel 31. The first filter 4 and the second housing 12 slide in cooperation with the slider 121 through the groove 41, thereby limiting the position of the first filter 4 on the second housing 12. Specifically, the flow guide 2 also includes a top abutment 25 protruding from the lower surface of the base plate 21. When the first filter 4 slides relative to the second housing 12, it abuts against the top abutment 25 to form a through hole.

[0049] refer to Figure 2 As shown, the slider 121 is disposed on the second housing 12. Compared with the slide groove 41, the thickness of the second housing 12 can be reduced, thereby reducing the manufacturing cost of the metering instrument. Specifically, the two ends of the slider 121 are respectively connected to the inner wall surface of the second housing 12 and the partition 14, and at least two sliders 121 are provided along the length direction perpendicular to the metering channel 31. Correspondingly, at least two slide grooves 41 are also provided to improve the stability of the first filter screen 4 on the second housing 12.

[0050] refer to Figure 7 As shown, the first filter screen 4 has multiple perforations spaced between the flow holes 214 and the metering inlet 32 ​​to further improve the dust filtration effect. It is understandable that, based on the different cross-sectional areas at different locations of the metering module 3, the area of ​​the through holes on different first filter screens 4 will also vary.

[0051] Given that multiple first filters 4 are provided, in order to reduce the deformation of the first filters 4 and ensure the filtration effect, a support member 8 is provided between adjacent first filters 4. The support member 8 is used to support the metering module 3. The support member 8 is provided with a support groove to increase the contact area between the support member 8 and the metering module 3 and improve the support capacity.

[0052] In one embodiment, a portion of the first filter screen 4 faces the connecting post 112. In order to increase the contact area between the first filter screen 4 and the casing 1, and thereby reduce the possibility that gas will enter the first flow cavity 17 directly from the second flow cavity 18 without passing through the first filter screen 4, an arc-shaped bonding plate 9 is provided on the side of the first filter screen 4 facing the connecting post 112, and the bonding plate 9 is bonded to the connecting post 112.

[0053] refer to Figure 2 and Figure 4 As shown, the metering instrument also includes a valve assembly 7, which is also located inside the housing 1 and connected to the air outlet 16. To prevent foreign objects from entering the housing 1 from the air outlet 16, the metering instrument also includes a foreign object shield 6, which is installed inside the air outlet 16.

[0054] Obviously, the above embodiments of this utility model are merely examples for clearly illustrating the present utility model, and are not intended to limit the implementation of the present utility model. Those skilled in the art can make various obvious changes, readjustments, and substitutions without departing from the protection scope of this utility model. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this utility model should be included within the protection scope of the claims of this utility model.

Claims

1. A measuring instrument, characterized in that, include: The watch case (1) has a cavity inside, and the watch case (1) also has an air inlet (15) and an air outlet (16) that communicate with the cavity. A metering module (3) is provided in the accommodating cavity. The metering module (3) is designed with a metering channel (31). The metering module (3) is also provided with a metering inlet (32) and a metering outlet (33) that connect the metering channel (31). The metering outlet (33) connects to the air outlet (16). The first filter screen (4) is divided into a first flow chamber (17) and a second flow chamber (18) within the accommodating cavity, and the metering inlet (32) is located in the first flow chamber (17). A flow guide (2) is disposed between the air inlet (15) and the metering module (3). The flow guide (2) is used to deposit at least part of the dust in the gas entering the accommodating cavity through the air inlet (15) and to guide the gas into the second flow cavity (18). The second filter (5) is located at the metering inlet (32).

2. The metering instrument according to claim 1, characterized in that, The flow guide (2) includes a base plate (21) facing the metering module (3), and the base plate (21) has flow holes (214).

3. The metering instrument according to claim 2, characterized in that, Multiple flow holes (214) are provided, and the multiple flow holes (214) are distributed in an array.

4. The metering instrument according to claim 2, characterized in that, The flow guide (2) also includes baffles (23), and multiple baffles (23) are staggered at positions opposite to the bottom plate (21) and the air inlet (15) to form multiple dust collection chambers in conjunction with the bottom plate (21).

5. The metering instrument according to claim 2, characterized in that, The flow guide (2) cooperates with the housing (1) to form a flow guide cavity (19) that communicates with the air inlet (15), and the flow guide cavity (19) is connected to the second flow passage cavity (18) through the flow passage hole (214).

6. The metering instrument according to claim 5, characterized in that, The first filter (4) and the guide (2) together form a through hole, and the metering module (3) passes through the through hole.

7. The metering instrument according to claim 6, characterized in that, The watch case (1) includes a first housing (11) and a second housing (12). The first housing (11) is configured as a groove structure. The air inlet (15) is located at the bottom of the groove of the first housing (11). The second housing (12) blocks the groove of the first housing (11) and surrounds the first housing (11) to form the accommodating cavity.

8. The metering instrument according to claim 7, characterized in that, One of the first filter screen (4) and the watch case (1) is provided with a slider (121), and the other of the first filter screen (4) and the watch case (1) is provided with a groove (41). The slider (121) is slidably disposed in the groove (41) along the length direction of the metering channel (31) so as to surround the through hole with the top abutment (25) protruding from the bottom plate (21).

9. The measuring instrument according to any one of claims 1-8, characterized in that, Multiple first filters (4) are spaced apart, and a support member (8) is provided between adjacent first filters (4). The support member (8) is used to support the metering module (3).

10. The measuring instrument according to any one of claims 1-8, characterized in that, The metering instrument also includes a foreign object shield (6), which is installed inside the air outlet (16).

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