A vibrating tube densitometer for small mass flow measurement

Abstract

The present invention discloses a vibrating tube densitometer for small mass flow measurement, which comprises a housing, a flange, a bracket, a vibrating tube assembly and a wiring sealing structure; the measuring tube includes an input pipeline, an output pipeline, a fluid flow tube, a flow equalizing tube and an accelerating tube, the flow equalizing tube includes a shunt inlet, a shunt outlet and a spiral tube, and a plurality of alternately connected first passages and second passages are arranged inside the accelerating tube. The liquid containing trace gas is first shunted through the flow equalizing tube to form small bubbles. Due to gravity, most of the liquid flows from the lower passage of the first passage to the second passage, and the bubbles in the fluid will float up, and a small part of the bubbles will adhere to the upper wall and stay in the first passage. After the fluid enters the second passage, a small amount of fluid passes through the upper passage of the second passage and causes the floating bubbles to stay. After multiple operations, the gas will not be discharged with the liquid, so that only the liquid part without gas is metered, thereby improving the metering accuracy.

Description

Technical Field

[0001] The present invention relates to a vibrating tube density meter, and more particularly to a vibrating tube density meter for measuring small mass flow rates. Background Art

[0002] A vibrating tube density meter is a device that directly measures the density of a fluid based on the principle that when a fluid of different densities is in a vibrating tube, there is a functional relationship between the simple harmonic vibration generated by the vibrating tube and the fluid density. It consists of a flow detection element and a converter. Specifically, in the vibrating tube density meter, the fluid performs simple harmonic vibration. When the fluid medium flows through the splitter at a certain speed, the medium vibrates synchronously (simple harmonic vibration) with the splitter. By detecting the resonant frequency signal, the density of the medium can be obtained.

[0003] Vibrating tube density meters can measure a wide range of fluids, including various liquids with high viscosity, slurries containing solids, liquids containing trace amounts of gas, and medium- and high-pressure gases with sufficient density. Currently, according to the number of vibrating tubes in the sensor, they can be divided into single-tube and double-tube types. The single-tube type instrument does not have flow splitting. According to the tube shape structure of the sensor, they can be roughly divided into straight-tube and bent-tube types. The straight-tube type instrument is not prone to gas accumulation, and the flow sensor has a small size and light weight. However, when measuring a liquid containing trace amounts of gas, since the straight-tube type instrument is not prone to gas accumulation, during measurement, the vibrating tube density meter installed on the output pipeline will measure the density of the fluid containing gas, thereby resulting in a problem of low measurement accuracy. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to solve the problem that in the existing vibrating tube density meter, due to the fact that the straight-tube type instrument is not prone to gas accumulation, during measurement, the vibrating tube density meter installed on the output pipeline will measure the fluid containing gas, thereby resulting in a problem of low measurement accuracy.

[0005] To solve the above technical problem, the present invention provides the following technical solutions:

[0006] A vibrating tube densitometer for small mass flow measurement, comprising a housing, flanges, a bracket, a vibrating tube assembly and a wiring sealing structure; there are two flanges, and the two flanges are respectively arranged on both sides of the housing; the vibrating tube assembly includes a joint and a measuring tube arranged in the housing; the measuring tube includes an input pipeline, an output pipeline and a fluid flow tube connected in series between the input pipeline and the output pipeline; one end of the input pipeline is connected to one flange through the joint, and one end of the output pipeline is connected to the other flange through the joint; the fluid flow tube is fixedly installed on the bracket, and the fluid flow tube is a continuous pipeline structure with a double loop formed by a single tube wound, and the fluid flow tube includes a continuously connected first loop, a crossover part and a second loop, and both the first loop and the second loop are "triangle" structures formed by connecting inclined straight pipe sections, elbow sections and horizontal straight pipe sections; the wiring sealing structure is connected to the housing; the measuring tube further includes a flow equalizing tube and an accelerating tube, and the flow equalizing tube and the accelerating tube are connected to form the horizontal straight pipe section;

[0007] The flow equalizing tube includes a flow dividing inlet, a flow dividing outlet and a spiral tube; the flow dividing inlet is a tubular structure with a hollow interior, and the interior of the flow dividing inlet is equally divided into three fluid inlet holes by three partitions, the flow dividing outlet is a tubular structure with a hollow interior, and the interior of the flow dividing outlet is equally divided into three fluid outlet holes by three partitions; there are three spiral tubes, and the three spiral tubes are wound around each other and twisted into a "twisted" shape, and the inlet ends of the three spiral tubes are respectively communicated with the three fluid inlet holes of the flow dividing inlet, and the outlet ends of the three spiral tubes are respectively communicated with the three fluid outlet holes of the flow dividing outlet;

[0008] The interior of the accelerating tube is provided with a plurality of alternately communicated first passages and second passages. The first passage is a passage structure with a low starting end and a high ending end. The starting end of the first passage is communicated with the flow dividing outlet, and a first stop block is arranged in the first passage. The first stop block divides the interior of the first passage into upper and lower two-layer passages; the second passage is a passage structure with a high starting end and a low ending end, and a second stop block is arranged in the second passage. The second stop block divides the second passage into upper and lower two-layer passages.

[0009] The present invention uses a flow equalizing tube and an accelerating tube to form a horizontal straight pipe section of a double pipeline of a fluid flow tube. When measuring a liquid containing a small amount of gas, the liquid containing a small amount of gas is first shunted through the flow equalizing tube, which can evenly divide the larger bubbles in the liquid to form small bubbles, making the gas in the liquid more uniform. Immediately afterwards, the evenly divided liquid is introduced into the accelerating tube. First, the liquid enters the first passage. Due to gravity, most of the liquid flows from the lower passage of the first passage to the second passage, and the bubbles in the fluid will float upwards. Some bubbles will follow a small part of the liquid through the upper passage of the first passage, while a small number of bubbles will stick to the upper wall and remain in the first passage. Similarly, after the fluid enters the second passage, a small amount of the fluid passes through the upper passage of the second passage and causes the floating bubbles to remain. After multiple operations, before the liquid is discharged, the gas floats to a sufficient distance from the outlet of the accelerating tube, so that it will not be discharged with the liquid. In this way, only the liquid part without gas is measured, thereby improving the measurement accuracy.

[0010] In the prior art, usually two tubes are used as the fluid flow tube, but there is a problem of uneven shunting in the two tubes, and a flow dividing cone is required to guide at the inlet and outlet. However, the manufacturing difficulty of a small flow dividing cone is high. Therefore, the present invention uses a single tube wound into a fluid flow tube with a double loop, eliminating the installation and use of the flow dividing cone.

[0011] Preferably, the housing includes a front shell and a rear shell, and after the front shell and the rear shell are snap-fitted and fixed, they are fixedly connected through a shaft pin.

[0012] Preferably, an air pipe, a one-way valve and a connection hole are provided on the front shell, and internal threads are provided on the inner wall of the connection hole.

[0013] Preferably, the first loop and the second loop are located above the bracket and extend from the bracket; the cross-connecting part is located below the bracket and extends from the bracket.

[0014] Preferably, the first loop is in a first plane, the second loop is in a second plane, and the first plane and the second plane are substantially parallel.

[0015] Preferably, a number of second stoppers are connected to each of the spiral tubes, and both ends of the second stoppers are communicated with the spiral tubes.

[0016] Preferably, it further includes a connecting member, a magnetic steel and a coil; the connecting member is a screw structure, and both ends of the connecting member are respectively connected to the first loop and the second loop; the magnetic steel is sleeved on the connecting member; the coil is installed in the middle of the connecting member.

[0017] Preferably, weights are sleeved at both ends of the magnetic steel.

[0018] Preferably, the wiring sealing structure includes a junction box, a junction box cover, a wiring board assembly, a wiring terminal, a clamp and a positioning plate; the junction box cover is covered on one side of the junction box to form a cavity structure inside the junction box; the wiring board assembly is arranged inside the cavity, and the wiring board assembly is connected to the inner wall of the junction box by screws; one end of the wiring terminal is connected to the outer end of the junction box through a clamp, the other end of the wiring terminal is provided with an external thread, and the other end of the wiring terminal is inserted into the connection hole and threadedly connected to the connection hole; the positioning plate is arranged inside the junction box; a cable connector is arranged at the lower end of the junction box.

[0019] Preferably, the wiring sealing structure further includes a sealing ring, and the sealing ring is arranged at the connection between the junction box and the junction box cover.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] 1. The present invention adopts a horizontal straight pipe section of a double pipeline formed by connecting a flow equalizing pipe and an accelerating pipe to form a fluid flow pipe. When measuring a liquid containing trace amounts of gas, the liquid containing trace amounts of gas is first shunted through the flow equalizing pipe, which can make the larger bubbles in the liquid evenly divided into small bubbles, making the gas in the liquid more uniform. Immediately afterwards, the evenly divided liquid is introduced into the accelerating pipe. First, the liquid enters the first passage. Due to gravity, most of the liquid flows from the lower passage of the first passage to the second passage, and the bubbles in the fluid will float upwards. Some bubbles will follow a small part of the liquid through the upper passage of the first passage, while a small number of bubbles will stick to the upper wall and stay in the first passage. Similarly, after the fluid enters the second passage, a small amount of the fluid passes through the upper passage of the second passage and makes the floating bubbles stay. After multiple operations, before the liquid is discharged, the gas floats up to a sufficient distance from the outlet of the accelerating pipe, so that it will not be discharged with the liquid. In this way, only the liquid part without gas is measured, thereby improving the measurement accuracy.

[0022] 2. In the prior art, usually two pipes are used as the fluid flow pipe, but there will be a problem of uneven shunting in the two pipes, and a shunt cone is needed to guide at the inlet and outlet. However, the manufacturing difficulty of a small shunt cone is high. Therefore, the present invention uses a single pipe wound into a fluid flow pipe with a double loop, eliminating the installation and use of the shunt cone. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of a Coriolis mass flowmeter for measuring small mass flow rates according to an embodiment of the present invention;

[0024] Figure 2 It is a schematic structural diagram of the housing according to an embodiment of the present invention;

[0025] Figure 3Schematic diagram of the connection structure of the flange, bracket and vibration tube assembly according to an embodiment of the present invention;

[0026] Figure 4 Schematic diagram of the structure of the vibration tube assembly according to an embodiment of the present invention;

[0027] Figure 5 Front view structure schematic diagram of the vibration tube assembly according to an embodiment of the present invention;

[0028] Figure 6 Schematic diagram of the structure of the flow equalizing tube and the acceleration tube according to an embodiment of the present invention;

[0029] Figure 7 Schematic diagram of the connection structure of the flow equalizing tube and the acceleration tube according to an embodiment of the present invention;

[0030] Figure 8 Schematic diagram of the structure of the wiring sealing structure according to an embodiment of the present invention;

[0031] Figure 9 Schematic diagram of the connection structure of the housing and the wiring sealing structure according to an embodiment of the present invention;

[0032] Figure 10 Enlarged structure schematic diagram of A according to an embodiment of the present invention.

[0033] Explanation of the reference numerals in the drawings:

[0034] 1. Housing; 11. Front shell; 12. Rear shell; 13. Axle pin; 14. Air pipe; 15. Check valve; 16. Connecting hole; 2. Flange; 3. Bracket; 4. Vibration tube assembly; 41. Joint; 42. Measuring tube; 421. Input pipeline; 422. Output pipeline; 423. Fluid flow tube; 4231. First loop; 4232. Cross-connecting part; 4233. Second loop; 424. Flow equalizing tube; 4241. Shunt inlet; 4242. Shunt outlet; 4243. Spiral tube; 425. Acceleration tube; 4251. First passage; 4252. Second passage; 4253. First stop block; 4254. Second stop block; 5. Wiring sealing structure; 51. Junction box; 52. Junction box cover; 53. Wiring board assembly; 54. Wiring terminal; 55. Clamp; 56. Positioning plate; 57. Cable connector; 58. Sealing ring; 6. Connecting piece; 7. Magnet; 8. Coil; 9. Counterweight. Detailed implementation manners

[0035] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings and embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0036] Embodiment 1

[0037] As Figures 1-10 shown, this embodiment provides a Coriolis mass flowmeter for measuring small mass flow rates, which includes a housing 1, a flange 2, a bracket 3, a vibrating tube assembly 4, a wiring sealing structure 5, a connector 6, a magnet 7, a coil 8 and a counterweight 9.

[0038] As Figure 1 、 Figure 2 shown, the housing 1 of this embodiment includes a front housing 11 and a rear housing 12. After the front housing 11 and the rear housing 12 are clamped and fixed together, they are fixedly connected through a shaft pin 13. The front housing 11 is provided with an air pipe 14, a one-way valve 15 and a connection hole 16, and an internal thread is provided on the inner wall of the connection hole 16; a nameplate and a flow direction mark are also provided on the surface of the front housing 11 of this embodiment.

[0039] As Figure 1 、 Figure 3 shown, this embodiment is provided with two flanges 2, and the two flanges 2 are respectively located on both sides of the housing 1. A DN15 dust cover made of PVC (polyvinyl chloride) material is provided at the outlet end of the flange 2 of this embodiment.

[0040] As Figure 1 、 Figure 3 、 Figure 4 and Figure 5As shown, the vibrating tube assembly 4 includes a joint 41 and a measuring tube 42 disposed within the housing 1; the measuring tube 42 includes an input pipeline 421, an output pipeline 422, and a fluid flow tube 423 connected in series between the input pipeline 421 and the output pipeline 422; one end of the input pipeline 421 is connected to a flange 2 through the joint 41, and one end of the output pipeline 422 is connected to another flange 2 through the joint 41; the fluid flow tube 423 is fixedly installed on the bracket 3, and the fluid flow tube 423 is a continuous pipeline structure formed by a single tube wound into a double loop. The fluid flow tube 423 includes a continuously connected first loop 4231, a bridging portion 4232, and a second loop 4233. Both the first loop 4231 and the second loop 4233 are "triangle" structures formed by connecting inclined straight pipe segments, elbow pipe segments, and horizontal straight pipe segments; the first loop 4231 and the second loop 4233 are located above the bracket 3 and extend from the bracket 3; the bridging portion 4232 is located below the bracket 3 and extends from the bracket 3; the first loop 4231 is in a first plane, the second loop 4233 is in a second plane, and the first plane and the second plane are substantially parallel.

[0041] As Figure 5 , Figure 6 and Figure 7 The measuring tube 42 further includes a flow equalizing tube 424 and an accelerating tube 425, and the flow equalizing tube 424 and the accelerating tube 425 are connected to form a horizontal straight pipe segment;

[0042] The flow equalizing tube 424 includes a flow splitting inlet 4241, a flow splitting outlet 4242, and a spiral tube 4243; the flow splitting inlet 4241 is a tubular structure with a hollow interior, and the interior of the flow splitting inlet 4241 is equally divided into three fluid inlet holes by three partitions. The flow splitting outlet 4242 is a tubular structure with a hollow interior, and the interior of the flow splitting outlet 4242 is equally divided into three fluid outlet holes by three partitions; there are three spiral tubes 4243, and the three spiral tubes 4243 are wound around each other and twisted into a "twisted" shape. The inlet ends of the three spiral tubes 4243 are respectively communicated with the three fluid inlet holes of the flow splitting inlet 4241, and the outlet ends of the three spiral tubes 4243 are respectively communicated with the three fluid outlet holes of the flow splitting outlet 4242; a number of second stoppers 4254 are connected to each spiral tube 4243, and both ends of the second stoppers 4254 are communicated with the spiral tube 4243;

[0043] Inside the accelerating tube 425, there are multiple alternately connected first passages 4251 and second passages 4252. The first passage 4251 has a passage structure with a lower starting end and a higher terminating end. The starting end of the first passage 4251 is connected to the shunt outlet 4242, and a first stop block 4253 is arranged inside the first passage 4251. The first stop block 4253 divides the interior of the first passage 4251 into upper and lower two-layer passages. The second passage 4252 has a passage structure with a higher starting end and a lower terminating end, and a second stop block 4254 is arranged inside the second passage 4252. The second stop block 4254 divides the second passage 4252 into upper and lower two-layer passages.

[0044] On the fluid flow tube 423 of this embodiment, a thin-film platinum resistor is tied with an imide tape having a thickness of 0.06 and a width of 8. The specifications of the thin-film platinum resistor are 3*15*500 (3W, three-wire system), IST (-200°C to 300°C).

[0045] As Figure 1 、 Figure 8 and Figure 9 shown, the wiring and sealing structure 5 is connected to the housing 1. The wiring and sealing structure 5 of this embodiment includes a junction box 51, a junction box cover 52, a wiring board assembly 53, a wiring terminal 54, a clamp 55, and a positioning plate 56. The junction box cover 52 covers one side of the junction box 51, causing a cavity structure to be formed inside the junction box 51. The wiring board assembly 53 is arranged inside the cavity, and the wiring board assembly 53 is connected to the inner wall of the junction box 51 by screws. One end of the wiring terminal 54 is connected to the outer end of the junction box 51 through the clamp 55. The other end of the wiring terminal 54 is provided with an external thread. The other end of the wiring terminal 54 is inserted into the connection hole 16 and is threadedly connected to the connection hole 16. The positioning plate 56 is arranged inside the junction box 51. A cable connector 57 is arranged at the lower end of the junction box 51. The wiring and sealing structure 5 further includes a sealing ring 58, and the sealing ring 58 is arranged at the connection between the junction box 51 and the junction box cover 52.

[0046] As Figure 3 、 Figure 4 and Figure 10 shown, there are multiple groups of the connecting members 6 in this embodiment. Specifically, the connecting member 6 is a pan head screw M2×12. The two ends of the connecting member 6 are respectively connected to the first loop 4231 and the second loop 4233. Spring washers and flat washers are sequentially sleeved on the connecting members 6 on both sides of the counterweight 9, and the end of the connecting member 6 is locked by a nut.

[0047] As Figure 10 shown, the magnet 7 is sleeved on the screw 61; the coil 8 is installed in the middle of the connecting member 6; counterweights 9 are sleeved at both ends of the magnet 7.

[0048] Adopt argon arc welding and use SS-ER304 stainless steel welding wire to weld the housing 1 on the bracket 3 step by step. Specifically, adopt argon welding technology and use SS-ER304 stainless steel welding wire. First, weld the air pipe 14, one-way valve 15 and terminal on the front shell 11. Use a spot welder to spot-weld the pressure wire piece on the front shell 11 and slip on a yellow wax tube. Then, step by step weld the previously welded front shell 11, shaft pin 13 and rear shell 12 on the bracket 3 that has been marked naked. It is required that the surface weld is flat without concavity or convexity and can withstand the specified pressure. The inside of the shell is evacuated, and the vacuum degree is 0.06 MPa.

[0049] Use SS-ER304 stainless steel welding wire to spot-weld the vibration tube assembly 4 on the bracket 3. Apply BN12 Eric brazing paste evenly on the joints that need to be brazed, clean them up, and put them into a vacuum brazing furnace for vacuum brazing. Bind the IST thin-film platinum resistance with imide tape and bond it with 1596F silicone rubber planar sealant Q / SJTSX003.

[0050] Adopt argon welding to weld the flange 2 on the joint 41 with SS-ER304 stainless steel welding wire. It is required that the single-sided welding has double-sided forming, the surface weld is flat without concavity or convexity and can withstand the specified pressure. Use SS-ER304 stainless steel welding wire to spot-weld the input pipeline 421, output pipeline 422 and fluid flow pipe 423 on the bracket 3 and joint 41. Apply BN12 Eric brazing paste evenly on the joints that need to be brazed, clean them up, and put them into a vacuum brazing furnace for vacuum brazing.

[0051] The present invention adopts a double pipeline horizontal straight pipe section formed by connecting the flow equalizing pipe 424 and the accelerating pipe 425 to form the fluid flow pipe 423. When measuring a liquid containing trace gas, the liquid containing trace gas first passes through the flow equalizing pipe 424 for flow splitting, which can make the larger bubbles in the liquid evenly divided into small bubbles, resulting in more uniform gas in the liquid. Immediately afterwards, the evenly divided liquid flows into the accelerating pipe 425. First, the liquid enters the first passage 4251. Due to gravity, most of the liquid flows from the lower passage of the first passage 4251 to the second passage 4252, and the bubbles in the fluid will float up. Some bubbles will follow a small part of the liquid through the upper passage of the first passage 4251, while a small number of bubbles will stick to the upper wall and stay in the first passage 4251. Similarly, after the fluid enters the second passage 4252, a small amount of fluid passes through the upper passage of the second passage 4252 and makes the floating bubbles stay. After multiple operations, before the liquid is discharged, the gas floats up to a sufficient distance from the outlet of the accelerating pipe 425, so that it will not be discharged with the liquid. In this way, only the liquid part without gas is metered, thereby improving the metering accuracy.

[0052] In the prior art, a double tube is usually used as the fluid flow tube 423. However, there is a problem of uneven flow splitting in the double tube, and a flow splitting cone is required to guide at the inlet and outlet. Since it is difficult to manufacture a small flow splitting cone, the present invention uses a single tube wound into a fluid flow tube 423 with a double loop, eliminating the installation and use of the flow splitting cone.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A vibrating tube density meter for small mass flow measurement, comprising a housing (1), flanges (2), a bracket (3), a vibrating tube assembly (4) and a wiring sealing structure (5); two flanges (2) are provided, and the two flanges (2) are respectively arranged on both sides of the housing (1); the vibrating tube assembly (4) includes a joint (41) and a measuring tube (42) arranged in the housing (1); the measuring tube (42) includes an input pipeline (421), an output pipeline (422) and a fluid flow tube (423) connected in series between the input pipeline (421) and the output pipeline (422); one end of the input pipeline (421) is connected to one flange (2) through the joint (41), and one end of the output pipeline (422) is connected to the other flange (2) through the joint (41); the fluid flow tube (423) is fixedly installed on the bracket (3), and the fluid flow tube (423) is a continuous pipeline structure with a double loop formed by winding a single tube, and the fluid flow tube (423) includes a continuously connected first loop (4231), a cross-connecting part (4232) and a second loop (4233), and both the first loop (4231) and the second loop (4233) are "triangle" structures formed by connecting inclined straight pipe sections, bent pipe sections and horizontal straight pipe sections; the wiring sealing structure (5) is connected to the housing (1); Characterized in that: The measuring tube (42) further includes a flow equalizing tube (424) and an accelerating tube (425), and the flow equalizing tube (424) and the accelerating tube (425) are connected to form the horizontal straight pipe section; The flow equalizing tube (424) includes a flow dividing inlet (4241), a flow dividing outlet (4242) and a spiral tube (4243); the flow dividing inlet (4241) is a tubular structure with a hollow interior, and the interior of the flow dividing inlet (4241) is equally divided into three fluid inlet holes by three partitions, the flow dividing outlet (4242) is a tubular structure with a hollow interior, and the interior of the flow dividing outlet (4242) is equally divided into three fluid outlet holes by three partitions; three spiral tubes (4243) are provided, and the three spiral tubes (4243) are wound around each other and twisted into a "twisted" shape, and the inlet ends of the three spiral tubes (4243) are respectively communicated with the three fluid inlet holes of the flow dividing inlet (4241), and the outlet ends of the three spiral tubes (4243) are respectively communicated with the three fluid outlet holes of the flow dividing outlet (4242); Inside the acceleration tube (425), there are multiple alternately connected first passages (4251) and second passages (4252). The first passage (4251) has a passage structure with a lower starting end and a higher ending end. The starting end of the first passage (4251) is connected to the shunt outlet (4242), and a first stop block (4253) is arranged inside the first passage (4251). The first stop block (4253) divides the inside of the first passage (4251) into upper and lower two-layer passages. The second passage (4252) has a passage structure with a higher starting end and a lower ending end, and a second stop block (4254) is arranged inside the second passage (4252). The second stop block (4254) divides the second passage (4252) into upper and lower two-layer passages. The housing (1) includes a front housing (11) and a rear housing (12). After the front housing (11) and the rear housing (12) are snap-fitted and fixed, they are fixedly connected by a shaft pin (13). The first loop (4231) and the second loop (4233) are located above the bracket (3) and extend from the bracket (3). The bridging part (4232) is located below the bracket (3) and extends from the bracket (3).

2. A vibrating tube density meter for small mass flow measurement according to claim 1, characterized in that: The front housing (11) is provided with an air pipe (14), a one-way valve (15) and a connection hole (16). The inner wall of the connection hole (16) is provided with internal threads.

3. A vibrating tube density meter for small mass flow measurement according to claim 1, characterized in that: The first loop (4231) is in a first plane, the second loop (4233) is in a second plane, and the first plane and the second plane are substantially parallel.

4. A vibrating tube density meter for small mass flow measurement according to claim 1, characterized in that: Each of the spiral tubes (4243) is connected with a plurality of second stop blocks (4254), and both ends of the second stop blocks (4254) are communicated with the spiral tubes (4243).

5. A vibrating tube density meter for small mass flow measurement according to claim 1, characterized in that: It further includes a connecting piece (6), a magnet (7) and a coil (8). The connecting piece (6) includes a screw (61). Both ends of the screw (61) are respectively connected to the first loop (4231) and the second loop (4233). The magnet (7) is sleeved on the screw (61). The coil (8) is installed in the middle of the screw (61). Weights (9) are sleeved at both ends of the magnet (7).

6. A vibrating tube density meter for small mass flow measurement according to claim 5, characterized in that: Spring washers (62) and flat washers (63) are respectively sleeved on both sides of the weight (9) on the screw (61).

7. A vibrating tube density meter for small mass flow measurement according to claim 2, characterized in that: The wiring sealing structure (5) includes a junction box (51), a junction box cover (52), a wiring board assembly (53), a wiring terminal (54), a clamp (55), and a positioning plate (56); the junction box cover (52) covers one side of the junction box (51) and causes a cavity structure to be formed inside the junction box (51); the wiring board assembly (53) is arranged inside the cavity, and the wiring board assembly (53) is connected to the inner wall of the junction box (51) by screws; one end of the wiring terminal (54) is connected to the outer end of the junction box (51) through a clamp (55), the other end of the wiring terminal (54) is provided with an external thread, and the other end of the wiring terminal (54) is inserted into the connection hole (16) and is threadedly connected to the connection hole (16); the positioning plate (56) is arranged inside the junction box (51); a cable connector (57) is arranged at the lower end of the junction box (51).

8. A vibrating tube density meter for small mass flow measurement according to claim 7, characterized in that: the wiring sealing structure (5) further includes a sealing ring (58), and the sealing ring (58) is arranged at the connection between the junction box (51) and the junction box cover (52).

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