Gas mass flow sensor

Abstract

The utility model provides a kind of gas mass flow sensor, including pedestal, shell, sensing pipe, first sensing winding, second sensing winding;The shell is integrally formed structure, the shell is closed cavity with pedestal buckling formation;The sensing pipe is bent and forms U type structure, two ends of the sensing pipe pass through pedestal and communicate with outside;The bending of the sensing pipe is wound and forms first dense winding section and second dense winding section, the first sensing winding and second sensing winding are wound in sensing pipe and located between first dense winding section and second dense winding section;It further includes the heat preservation layer for covering first sensing winding, second sensing winding and sensing pipe, can effectively reduce the heat dissipation area set heat dissipation rate of touch feeling winding, guarantee the balance and symmetry of sensing pipe wall heat distribution, reduce zero drift phenomenon.

Description

Technical Field

[0001] This utility model relates to a sensor, and more particularly to a gas mass flow sensor. Background Technology

[0002] Gas mass flow sensors measure gas flow rate using the principle of heat transfer, specifically the heat exchange between the flowing fluid and a heat source. The specific principle is as follows: Figure 9 As shown: After the airflow enters the intake pipe joint, most of the flow passes through the distributor channel, with only a small portion entering the capillary tube inside the sensor. Due to the special structure of the distributor channel, the flow rates of these two gas portions are directly proportional. The sensor is preheated, and its internal temperature is higher than the temperature of the incoming airflow. At this point, the mass flow rate of this small portion of gas is measured using the principle of capillary heat transfer and differential thermocalorimetry. Specifically: The sensor is typically composed of two sets of thermistor wires wound upstream and downstream of a stainless steel capillary tube. The thermistor wires, along with two other precision resistors, form a measuring bridge. During operation, the thermistors are heated by energizing them. When there is no gas flow in the capillary, the two sets of thermistors are at the same temperature, the bridge is balanced and there is no signal output; U=0 corresponds to a flow rate of zero. When gas flows through the capillary, the upstream and downstream windings experience different temperature changes, ΔT, causing different changes in the thermistor resistance. The measuring bridge outputs a difference signal UO>0, the magnitude of which is proportional to the mass flow rate through the sensor. The output voltage UO is linearly related to the mass flow rate qm of the gas flowing through the main channel. Figure 10 As shown.

[0003] Based on the above principles, existing gas mass flow sensors are prone to zero drift. Zero drift refers to the phenomenon where, within a certain time range, when no gas passes through the flow controller and external conditions (such as temperature and pressure) remain unchanged, the flow controller's output signal deviates from the initial zero position. This is a key factor affecting the accuracy of flow measurement. The factors causing zero drift are multifaceted, and the sensor's structure is one of the important factors. In existing technologies, the structure of the sensing tube, insulation structure, and housing structure in the sensor can all lead to zero drift. For example, in existing technologies, the sensing tubes on both sides of the sensing winding are straight tubes, which increases the heat dissipation of the sensing winding and makes it more susceptible to environmental interference.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a new technical approach. Utility Model Content

[0005] In view of this, the purpose of this utility model is to provide a gas mass flow sensor that optimizes the structure of the sensing tube so that the sensing tube has two closely wound sections and the two sensing windings are arranged between the two closely wound sections. This can effectively reduce the heat dissipation area and heat dissipation rate of the sensing windings, ensure the balanced and symmetrical heat distribution of the sensing tube wall, reduce zero drift, and the housing adopts an integral molding structure to avoid the problem of poor sealing caused by the split structure in the prior art, further suppressing the zero drift phenomenon.

[0006] This utility model provides a gas mass flow sensor, including a base, a housing, a sensing tube, a first sensing winding, and a second sensing winding;

[0007] The shell is a one-piece molded structure, and the shell and the base are fastened together to form a sealed cavity;

[0008] The sensing tube is bent into a U-shaped structure, and both ends of the sensing tube pass through the base and are connected to the outside.

[0009] The bending section of the sensing tube is wound to form a first dense winding section and a second dense winding section. The first sensing winding and the second sensing winding are wound on the sensing tube and located between the first dense winding section and the second dense winding section.

[0010] It also includes an insulation layer for covering the first sensing winding, the second sensing winding, and the sensing tube.

[0011] Furthermore, the number of turns in the first and second closely wound sections is 2 or 3.

[0012] Furthermore, the insulation layer includes a PU film and an aerogel felt filled between the PU films;

[0013] The insulation layer is folded in half to form a U-shaped structure, and the first sensing winding, the second sensing winding, and the sensing tube are embedded in the internal space of the U-shaped structure.

[0014] Furthermore, pins are provided at both ends of the sensing tube;

[0015] The outer surface of the pin is cylindrical, and the inner surface of the pin has an embedding hole and an airflow hole. The end of the sensing tube is embedded in the embedding hole and communicates with the airflow hole. The outer wall of the sensing tube and the inner wall of the embedding hole are filled with solder filler.

[0016] Furthermore, the airflow hole is a trumpet-shaped structure with a diameter that gradually decreases from the outside to the inside, and the inclination angle of the airflow hole is 10°.

[0017] Furthermore, it also includes a PCB, which is disposed inside the housing and is equipped with a temperature sensor;

[0018] The PCB board is also provided with pads for electrical connection with the first sensing winding and the second sensing winding. The temperature sensor and the pads are electrically connected to external devices through metal cables, which pass through the housing and are electrically connected to the external devices.

[0019] Furthermore, the base has a central protrusion forming an embedded part, which is embedded in the housing. The bottom of the embedded part is provided with a first annular groove, and the edge of the housing is embedded in the first annular groove.

[0020] Furthermore, the side of the embedded part is recessed to form a second annular groove, and a sealing ring is provided in the second annular groove.

[0021] Furthermore, the base is provided with a through hole for mounting the pin, and a sealing ring is provided between the pin and the through hole.

[0022] The beneficial effects of this utility model are as follows: By optimizing the structure of the sensing tube, the sensing tube has two closely wound sections, and the two sensing windings are arranged between the two closely wound sections. This can effectively reduce the heat dissipation area and heat dissipation rate of the tactile windings, ensure the balanced and symmetrical heat distribution of the sensing tube wall, reduce the zero drift phenomenon, and the shell adopts an integral molding structure, avoiding the problem of poor sealing caused by the split structure in the prior art, further suppressing the zero drift phenomenon. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0024] Figure 1 This is a schematic diagram of the structure of this utility model.

[0025] Figure 2 for Figure 1 The sectional view in the image.

[0026] Figure 3 This is a schematic diagram of the base structure.

[0027] Figure 4 Schematic diagram of pin structure

[0028] Figure 5 This is a schematic diagram of the sensor tube structure.

[0029] Figure 6 This is a schematic diagram of the insulation layer structure.

[0030] Figure 7 This is a schematic diagram of the shell structure.

[0031] Figure 8 for Figure 7 A schematic diagram of the structure viewed from below.

[0032] Figure 9This is a schematic diagram illustrating the working principle of a gas mass flow sensor.

[0033] Figure 10 This is a schematic diagram of a gas mass flow sensor measuring temperature. Detailed Implementation

[0034] The present invention will be further described in detail below:

[0035] The present invention provides a gas mass flow sensor, including a base 1, a housing 3, a sensing tube 26, a first sensing winding 22, and a second sensing winding 23;

[0036] The shell 3 is a one-piece molded structure, and the shell 3 and the base 1 are fastened together to form a sealed cavity;

[0037] The sensing tube is bent to form a U-shaped structure, and both ends of the sensing tube 26 pass through the base and communicate with the outside.

[0038] The bending portion of the sensing tube 26 is wound to form a first closely wound section 24 and a second closely wound section 25. The first sensing winding 22 and the second sensing winding 23 are wound around the sensing tube and located between the first closely wound section 24 and the second closely wound section 25. Figure 5 As shown, the tightly wound section of the sensor tube is formed by winding the sensor tube itself. The so-called tightly wound section means that the adjacent turns of the sensor tube are tightly fitted together after winding, minimizing gaps.

[0039] It also includes an insulation layer 6 for covering the first sensing winding, the second sensing winding, and the sensing tube. Through the above structure, the structure of the sensing tube is optimized, resulting in two closely wound sections with the two sensing windings positioned between them. This effectively reduces the heat dissipation area and heat dissipation rate of the tactile windings, ensuring a balanced and symmetrical heat distribution on the sensing tube wall, reducing zero drift. Furthermore, the housing adopts a one-piece molded structure, avoiding the poor sealing problems caused by the split structure in existing technologies, further suppressing zero drift.

[0040] In this embodiment, the number of turns in the first tightly wound section 24 and the second tightly wound section 26 is 2 or 3 turns. When the number of tightly wound turns of the sensing tube 26 increases from 1 turn to 2 turns, the heat dissipation area decreases by 40% and the measurement sensitivity increases by 15%. When the number of winding turns increases from 2 turns to 3 turns, the heat dissipation area decreases by 50%, but the sensitivity improvement decreases to 5%. Moreover, too many turns will lead to a significant increase in airflow resistance, thereby reducing accuracy. Therefore, the optimal number of turns is 2 or 3 turns. Through the above structure, both gas flow during the measurement process is ensured and heat loss is reduced, thereby improving measurement accuracy.

[0041] In this embodiment, the insulation layer 6 includes a PU film 30 and an aerogel felt 29 filled between the PU films;

[0042] The insulation layer 6 is folded in half to form a U-shaped structure. The first sensing winding, the second sensing winding, and the sensing tube are embedded in the internal space 31 of the U-shaped structure. Through the above structure, heat loss can be effectively reduced and the accuracy of measurement can be ensured.

[0043] In this embodiment, pins are provided at both ends of the sensing tube 26;

[0044] The outer surface of the pin 10 is cylindrical, and the inner surface of the pin has an embedding hole 21 and an airflow hole 20. The end of the sensing tube 26 is embedded in the embedding hole 21 and communicates with the airflow hole 20. The outer wall of the sensing tube and the inner wall of the embedding hole are filled with solder filler 9, which means that the pin and the end of the sensing tube are fixedly connected by soldering, which not only ensures the sealing performance, but also effectively prevents aging from affecting the sealing performance, thereby reducing heat loss. The pin and the through hole of the base form an interference fit, and the upper end of the pin has a protrusion 19 on the side wall.

[0045] Specifically: the airflow hole 20 is a trumpet-shaped structure with a diameter that gradually decreases from the outside to the inside. The tilt angle of the airflow hole 20 is 10°. This structure can improve the airflow state, maintain the laminar flow state, reduce the interference of vortices on the temperature field, avoid excessive airflow acceleration, and avoid local airflow abrupt changes that would lead to a decrease in accuracy.

[0046] In this embodiment, a PCB board 12 is also included. The PCB board 12 is disposed inside the housing and is fixedly connected to the embedded part of the base by screws 8. The PCB board 12 is provided with a temperature sensor 7.

[0047] The PCB board 12 is also provided with pads for electrical connection with the first sensing winding and the second sensing winding. The temperature sensor 7 and the pads are electrically connected to external devices through a metal cable 4. The metal cable 4 passes through the housing and is electrically connected to the external devices, that is, it is connected to the outside through the groove 28 on the edge of the housing. The function of the temperature sensor is to detect the internal temperature for temperature compensation calculation. Moreover, the signal is transferred through the PCB board to avoid the phenomenon of temperature loss due to direct electrical connection between the two sensing windings and the external devices, thereby ensuring measurement accuracy.

[0048] In this embodiment, the base 1 has a central protrusion forming an embedded part, which is embedded in the housing. The bottom of the embedded part is provided with a first annular groove 18, and the edge of the housing is embedded in the first annular groove 18. Of course, the housing and the protrusion of the base are fixedly connected by screws 2. The housing is provided with mounting holes 27, and the screws 2 pass through the mounting holes 27 and are fixedly connected to the base.

[0049] The side of the embedded part is recessed to form a second annular groove 17. A sealing ring is provided in the second annular groove. Through the above structure, the gap between the base and the shell can be well sealed to avoid heat loss. The embedded part is provided with a mounting part 15 for mounting the PCB board (the mounting part has an embedded groove). The mounting part 15 has a PCB board mounting hole 14. The base is also provided with a mounting hole 16 for mounting the shell. The screw 2 is threadedly engaged with the mounting hole 16.

[0050] In this embodiment, the base 1 is provided with a through hole 13 for mounting the pin, and a sealing ring 5 is provided between the pin 10 and the through hole 13. The through hole is a stepped hole, and the upper end of the through hole 13 is rigidly fitted with the pin, but the lower end diameter of the through hole is larger than the outer diameter of the pin, so as to seal through the sealing ring. This structure can not only facilitate the heat preservation of the inside of the shell to ensure the final measurement accuracy, but also facilitate the installation.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this utility model without departing from the spirit and scope of the technical solutions of this utility model, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A gas mass flow sensor, characterized in that: Includes a base, housing, sensing tube, first sensing winding, and second sensing winding; The shell is a one-piece molded structure, and the shell and the base are fastened together to form a sealed cavity; The sensing tube is bent into a U-shaped structure, and both ends of the sensing tube pass through the base and are connected to the outside. The bending section of the sensing tube is wound to form a first dense winding section and a second dense winding section. The first sensing winding and the second sensing winding are wound on the sensing tube and located between the first dense winding section and the second dense winding section. It also includes an insulation layer for covering the first sensing winding, the second sensing winding, and the sensing tube.

2. The gas mass flow sensor according to claim 1, characterized in that: The number of turns in the first and second densely wound sections is 2 or 3.

3. The gas mass flow sensor according to claim 1, characterized in that: The insulation layer includes a PU film and an aerogel felt filled between the PU films; The insulation layer is folded in half to form a U-shaped structure, and the first sensing winding, the second sensing winding, and the sensing tube are embedded in the internal space of the U-shaped structure.

4. The gas mass flow sensor according to claim 1, characterized in that: The sensing tube is provided with pins at both ends; The outer surface of the pin is cylindrical, and the inner surface of the pin has an embedding hole and an airflow hole. The end of the sensing tube is embedded in the embedding hole and communicates with the airflow hole. The outer wall of the sensing tube and the inner wall of the embedding hole are filled with solder filler.

5. The gas mass flow sensor according to claim 4, characterized in that: The airflow hole is a trumpet-shaped structure with a diameter that gradually decreases from the outside to the inside, and the tilt angle of the airflow hole is 10°.

6. The gas mass flow sensor according to claim 1, characterized in that: It also includes a PCB, which is disposed inside the housing and is equipped with a temperature sensor; The PCB board is also provided with pads for electrical connection with the first sensing winding and the second sensing winding. The temperature sensor and the pads are electrically connected to external devices through metal cables, which pass through the housing and are electrically connected to the external devices.

7. The gas mass flow sensor according to claim 1, characterized in that: The base has a central protrusion forming an embedded part, which is embedded in the housing. The bottom of the embedded part is provided with a first annular groove, and the edge of the housing is embedded in the first annular groove.

8. The gas mass flow sensor according to claim 7, characterized in that: The side of the embedded part is sunken to form a second annular groove, and a sealing ring is provided in the second annular groove.

9. The gas mass flow sensor according to claim 4, characterized in that: The base is provided with a through hole for mounting the pin, and a sealing ring is provided between the pin and the through hole.

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