Gas mass flow sensor and detection method

Abstract

The invention discloses a gas mass flow sensor and a detection method. The gas mass flow sensor comprises a base layer, a first detection unit and a second detection unit, the first detection unit comprises a first airflow channel, and a first heating element and a first temperature measuring element which are arranged in the first airflow channel; the second detection unit comprises a second airflow channel, and a second heating element and a second temperature measuring element which are arranged in the second airflow channel; the first detection unit is used for detecting small flow, and the second detection unit is used for detecting large flow. A first thermal isolation structure is arranged between the two detection units and is used for isolating temperature field thermal crosstalk between the detection units; a second thermal isolation structure is arranged in the base layer and used for isolating heat conduction from the detection unit to the position below the base layer. The gas mass flow sensor disclosed by the invention adopts an integrated structural design, the sensor structure is simplified, the processing difficulty is reduced, the problems of sensitivity dead zone, thermal crosstalk and the like of the gas mass flow sensor are solved, and the detection effect is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to a gas mass flow sensor. Background Art

[0003] The MEMS sensor based on the thermal temperature difference principle detects the gas flow rate by using the principle that the gas flow absorbs heat when passing through the heating element, thereby causing the thermal temperature difference. Since the amount of heat absorbed by the gas is directly causally related to its own specific heat capacity (CH4 content) and mass, it detects the mass flow rate of methane gas, and thus can more accurately reflect the amount of methane actually consumed by the user than the traditional volume flow detection method, and will not be affected by the volume expansion, pressure changes, different methane content in different gas fields and other factors that affect the accuracy of gas metering. Moreover, the gas mass flow sensor based on this principle can be manufactured using the MEMS process, and has the advantages of small size, light weight, low power consumption, compatibility with the Internet of Things, and easy integration of MEMS sensors. Therefore, once it was proposed, it was considered by the gas industry to be an ideal detection solution to solve the accurate measurement of gas and avoid measurement disputes.

[0004] However, the gas mass flow sensor based on this principle has a higher detection sensitivity when the gas flow is small; however, as the gas flow increases, the detection sensitivity of the sensor will drop rapidly and tend to 0, which is difficult to meet the actual needs of gas flow detection. Summary of the invention

[0005] Based on this, the present invention provides a gas mass flow sensor and a detection method to address the above problems.

[0006] A gas mass flow sensor, comprising:

[0007] Grassroots;

[0008] a first detection unit, disposed on the base layer, comprising a first airflow channel and a first heating element and a first temperature measuring element disposed in the first airflow channel, and the first temperature measuring element is disposed both upstream and downstream of the first heating element; and

[0009] The second detection unit is arranged on the base layer, the second detection unit comprises a second airflow channel and a second heating element and a second temperature measuring element arranged in the second airflow channel, and the second temperature measuring element is arranged upstream and downstream of the second heating element. The first detection unit is used to detect a small flow rate, and the second detection unit is used to detect a large flow rate.

[0010] Furthermore, it also includes a shell for accommodating the first detection unit and the second detection unit, and a first thermal isolation structure for isolating the thermal crosstalk of the temperature field between the first detection unit and the second detection unit is provided in the shell.

[0011] Furthermore, the first thermal isolation structure includes a first thermal insulation cavity and a closing plate, the first thermal insulation cavity is on the bottom surface of the shell and is located between the first airflow channel and the second airflow channel, and the two closing plates are arranged at both ends of the first thermal insulation cavity to form the first thermal isolation structure with the side walls of the first thermal insulation cavity and the top surface of the base layer.

[0012] Furthermore, the first detection unit and the second detection unit are arranged in parallel on the base layer.

[0013] Further, a cross-sectional area of ​​the first airflow channel is smaller than a cross-sectional area of ​​the second airflow channel.

[0014] Furthermore, a second thermal isolation structure is provided in the base layer, and the second thermal isolation structure is used to isolate the first detection unit and the second detection unit from heat conduction to the bottom of the base layer.

[0015] Furthermore, the base layer includes a substrate used as a support and a bottom plate arranged below the substrate, a second insulation cavity is arranged on the side of the substrate facing the bottom plate, and the bottom plate is arranged on the bottom surface of the substrate to seal the open end of the second insulation cavity to form the second thermal isolation structure.

[0016] Furthermore, it also includes a third temperature measuring element and a fourth temperature measuring element, and the third temperature measuring element and the fourth temperature measuring element are respectively located at the inlet ends of the first airflow channel and the second airflow channel.

[0017] Furthermore, the first heating element and the second heating element are both rectangular sheet-shaped resistance films; the first heating element and the second heating element are both arranged near the middle of the first airflow channel and the second airflow channel.

[0018] A method for detecting gas flow rate using the gas mass flow sensor as described above comprises:

[0019] The first heating element and the second heating element are energized to generate heat;

[0020] The gas enters the first air flow channel and the second air flow channel;

[0021] The first detection unit detects the gas flow in the first gas flow channel; the second detection unit detects the gas flow in the second gas flow channel;

[0022] A receiving end outside the sensor receives detection results of the first detection unit and the second detection unit;

[0023] The detection result of the first detection unit is used as the detection value when the flow rate is small, and the detection result of the second detection unit is used as the detection value when the flow rate is large, and the complete flow detection data is obtained by combining them.

[0024] Beneficial effects of the present invention:

[0025] The present invention discovers the problem of sensitivity dead zone of thermal temperature difference gas mass flow sensor and the cause of its occurrence, and designs a gas mass flow sensor and detection method to solve this problem, which not only solves the problem of sensitivity dead zone, but also solves the problem that the sensor is difficult to meet the actual needs of flow detection due to limited sensitivity of large flow detection. The gas mass flow sensor disclosed by the present invention, when in use, connects the gas mass flow sensor to the gas pipeline of the measured section, opens the gas valve to pass the gas into the first air flow channel and the second air flow channel, and allows the gas to flow normally in the channel for a period of time, waits for the air flow to stabilize before testing, obtains the test results in the first detection unit and the second detection unit respectively, takes the test result in the first detection unit as the test value at a small flow rate, takes the test result in the second detection unit as the test value at a large flow rate, and combines them to obtain complete flow detection data.

[0026] By adopting the above-mentioned gas mass flow sensor and detection method, since a first detection unit is provided for detecting a small flow rate, and a second detection unit is provided for detecting a large flow rate, when the design parameters of the first detection unit are optimized to improve the small flow rate detection sensitivity, the sensitivity of the second detection unit will not be affected; when the design parameters of the second detection unit are optimized to improve the large flow rate detection sensitivity, the sensitivity of the first detection unit will not be interfered with, thereby simultaneously improving the large flow rate detection sensitivity and the small flow rate detection sensitivity, solving the problem that the detection sensitivity of the thermal temperature difference MEMS gas mass flow sensor will drop rapidly and tend to 0, making it difficult to meet the actual needs of gas flow detection, and can meet the simultaneous consideration of large and small flow rate sensitivities, solving the problem of the dead zone of sensor sensitivity.

[0027] In addition, due to the technical solution disclosed in the present invention that the first detection unit and the second detection unit can be arranged on the same base layer, the overall structure of the sensor can be integrated, which simplifies the structure of the MEMS microsensor, simplifies the chip structure, reduces the processing difficulty, and is conducive to the mass processing and production of sensors when they are commercialized. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation of the present invention, the following will briefly introduce the drawings required for use in the specific implementation. In all the drawings, each element or part is not necessarily drawn according to the actual scale.

[0029] Figure 1 A temperature difference-flow curve diagram of a gas mass flow sensor with a traditional structure when detecting gas flow;

[0030] Figure 2 This is a temperature difference-flow curve diagram obtained by optimizing the parameters of a gas mass flow sensor with a traditional structure to improve the large flow detection sensitivity;

[0031] Figure 3 for Figure 1 and Figure 2 The partial enlarged comparison diagram of the small flow section curve marked by the middle ellipse;

[0032] Figure 4 is a three-dimensional schematic diagram of a gas mass flow sensor chip in one embodiment;

[0033] Figure 5 for Figure 4 A side view schematic diagram of a gas mass flow sensor chip shown;

[0034] Figure 6 for Figure 4 A three-dimensional schematic diagram of a housing assembly in a gas mass flow sensor is shown;

[0035] Figure 7 for Figure 4 A design diagram of related components in a gas mass flow sensor chip shown;

[0036] Figure 8 for Figure 4 A partial enlarged view of the geometric shape of a temperature measuring element in a gas mass flow sensor chip shown;

[0037] Fig. 9 for Figure 4 A comparison diagram of a temperature difference-flow curve of a gas mass flow sensor and a temperature difference-flow curve of a sensor with a traditional structure;

[0038] Reference numerals:

[0039] 100, base layer; 110, second thermal insulation cavity; 120, substrate; 130, bottom plate; 200, first detection unit; 210, first air flow channel; 220, first heating element; 230, first temperature measuring element; 240, third temperature measuring element; 250, first terminal; 300, second detection unit; 310, second air flow channel; 320, second heating element; 330, second temperature measuring element; 340, fourth temperature measuring element; 350, second terminal; 400, first thermal isolation structure; 410, first thermal insulation cavity; 420, closed plate. DETAILED DESCRIPTION

[0040] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0041] The MEMS sensor based on the thermal temperature difference principle detects the gas flow rate by using the principle that the gas flow absorbs heat when passing through the heating element, thereby causing the thermal temperature difference. Since the amount of heat absorbed by the gas is directly causally related to its own specific heat capacity (CH4 content) and mass, it detects the mass flow rate of methane gas, and thus can more accurately reflect the amount of methane actually consumed by the user than the traditional volume flow detection method, and will not be affected by the volume expansion, pressure changes, different methane content in different gas fields and other factors that affect the accuracy of gas metering. Moreover, the gas mass flow sensor based on this principle can be manufactured using the MEMS process, and has the advantages of small size, light weight, low power consumption, compatibility with the Internet of Things, and easy integration of MEMS sensors. Therefore, once it was proposed, it was considered by the gas industry to be an ideal detection solution to solve the accurate measurement of gas and avoid measurement disputes.

[0042] However, the inventors discovered during their research that the gas mass flow sensor based on this principle has a higher detection sensitivity when the gas flow is small; however, as the gas flow increases, the detection sensitivity of the sensor decreases rapidly and tends to 0, making it impossible to detect, that is, a sensitivity dead zone occurs in large flow detection.

[0043] As we all know, it is difficult to meet the actual needs of gas flow metering if only a small flow rate can be detected. In order to solve this problem, we first need to find the reason why the sensitivity of the gas mass flow sensor based on the thermal temperature difference principle tends to 0. Therefore, the inventors derived its mathematical model based on the detection principle of this type of sensor. After research, it was found that the mathematical relationship between the thermal temperature difference and the gas flow rate obtained by the mass flow sensor based on the thermal temperature difference principle is as shown in formula (1):

[0044]

[0045] Where: ΔT is the thermal temperature difference, q is the gas flow rate, and K is a constant.

[0046] That is, the temperature difference-flow curve is a square root function curve opening to the right, rather than a straight line, such as Figure 1 When the flow rate is small, the slope of the square root function curve will be relatively high, that is, the sensitivity of the sensor will be relatively high; when the flow rate is large, the slope of the square root function curve will drop rapidly and tend to be horizontal, the sensitivity tends to 0, and it cannot be detected. This is the fundamental reason for the large flow detection sensitivity dead zone.

[0047] Because this problem is determined by its detection principle, it is inevitable and difficult to completely eliminate. However, it is possible to improve the detection sensitivity at high flow rates by optimizing the design of sensor parameters. Therefore, the inventors optimized the design parameters of the sensor chip to improve the sensitivity at high flow rates, and finally obtained the following Figure 2 Results shown: From Figure 2 It can be clearly seen from the temperature difference-flow curve in that the slope (sensitivity) of the curve at large flow is indeed improved. However, when the inventor further studied the detailed data of the curve, he found that after the detection sensitivity of large flow was improved, a sensitivity dead zone of small flow detection appeared, such as Figure 3 shown. Figure 3 yes Figure 1 and Figure 2 The partial enlarged comparison diagram of the small flow section curve marked by the ellipse circle in the middle, from Figure 3 It can be clearly seen that after the large flow rate sensitivity is improved, its small flow rate sensitivity has dropped to a very low level.

[0048] This research result shows that it is difficult to effectively solve the problem of sensitivity dead zone by optimizing the design of parameters alone, and a new technical solution must be proposed. This research result has important guiding significance for the design and improvement of sensors.

[0049] See also Figure 4 Based on the above research results, the present invention proposes a new technical solution and discloses a gas mass flow sensor, wherein the sensor is configured as an integrated structure consisting of a first detection unit 200 and a second detection unit 300. The first detection unit 200 is used to detect a small flow rate, and the second detection unit 300 is used to detect a large flow rate. By optimizing the design to improve the small flow detection sensitivity of the first detection unit 200 and the large flow detection sensitivity of the second detection unit 300, the purpose of simultaneously improving the large flow detection sensitivity and the small flow detection sensitivity can be achieved, thereby solving the problem of sensitivity dead zone. Specifically:

[0050] Please also read Figures 4 to 8 The gas mass flow sensor includes a substrate 100, a first detection unit 200, and a second detection unit 300. The first detection unit 200 is disposed on the substrate 100, and the first detection unit 200 includes a first airflow channel 210, and a first heating element 220 and a first temperature measuring element 230 disposed in the first airflow channel 210. The second detection unit 300 is disposed on the substrate 100, and the second detection unit 300 includes a second airflow channel 310, and a second heating element 320 and a second temperature measuring element 330 disposed in the second airflow channel 310. The first detection unit 200 is used to detect a small flow rate, and the second detection unit 300 is used to detect a large flow rate.

[0051] It should be noted that, in this embodiment, the number of detection units may be further increased according to actual needs to further expand the detection range of the sensor, or to further subdivide the detection flow segment of the sensor to further improve the detection sensitivity and accuracy.

[0052] In this embodiment, the cross-sectional area of ​​the second airflow channel 310 is generally larger than the cross-sectional area of ​​the first airflow channel 210. For example, the width of the first airflow channel 210 is preferably 4 to 6 mm, and the height is 8 to 12 mm; the width of the second airflow channel 310 is preferably 8 to 12 mm, and the height is 10 to 14 mm. In specific implementation, the length, width and cross-sectional area of ​​the two airflow channels should be selected according to actual conditions.

[0053] In the present embodiment, the first heating element 220 and the second heating element 320 are used to heat the airflow in the first airflow channel 210 and the second airflow channel 310, respectively. In the specific implementation, the first heating element 220 and the second heating element 320 can be respectively arranged close to the middle of the first airflow channel 210 and the second airflow channel 310, so as to avoid the opening ends before and after the two airflow channels from affecting the temperature distribution. Of course, the specific positions of the first heating element 220 and the second heating element 320 can also be adjusted according to actual needs. In addition, the first heating element 220 and the second heating element 320 can both preferably be rectangular sheet-shaped resistor films. Of course, the first heating element 220 and the second heating element 320 can also be in a zigzag shape or other shapes.

[0054] It should be noted that the two heating elements are used as heat sources for the first detection unit 200 and the second detection unit 300, respectively, and can be made of platinum material. In specific implementation, it is better when the width dimension of the first heating element 220 is generally larger than the width dimension of the second heating element 320; it is better when the length dimension of the first heating element 220 is generally smaller than the length dimension of the second heating element 320. For example: it is preferred that the length dimension of the resistor film in the first airflow channel 210 is 0.4-0.6mm, and the width dimension is 80-150μm; it is preferred that the length dimension of the resistor film in the second airflow channel 310 is 0.15-0.35mm, and the width dimension is 600-1200μm.

[0055] In this embodiment, a first temperature measuring element 230 is provided upstream and downstream of the first heating element 220, and a second temperature measuring element 330 is provided upstream and downstream of the second heating element 320. The gas flow is detected by using the temperature difference measured by the upstream and downstream temperature measuring elements.

[0056] In this embodiment, the upstream and downstream temperature measuring elements in the two air flow channels are spaced apart from the heating element. In specific implementation, the spacing between the heating element 220 in the first air flow channel 210 and the two first temperature measuring elements 230 is preferably 0.3-1 mm; the spacing between the heating element 320 in the second air flow channel 310 and the two second temperature measuring elements 330 is preferably 0.4-1.2 mm.

[0057] It should be noted that, in this embodiment, all temperature measuring elements can be arranged in a broken line shape. All temperature measuring elements can be preferably made of thermosensitive materials with high temperature coefficient and good linearity, such as platinum, nickel and alloys thereof.

[0058] The design of the two detection units disclosed in this embodiment provides a possibility for solving the problem that high flow sensitivity and low flow sensitivity cannot be achieved at the same time. However, the inventors found in further research that this solution also leads to a new problem, namely, the thermal crosstalk problem of the temperature field between the two detection units will disturb the original real thermal temperature difference in the first detection unit 200 and the second detection unit 300, seriously damaging the accuracy of the thermal temperature difference detection by the first detection unit 200 and the second detection unit 300. Specifically:

[0059] The two detection units are set up as one. Since heating elements need to be set in both detection units, the heat between the detection units will be transferred to each other. Since the temperature field is non-uniformly distributed, this thermal crosstalk will cause the temperature field distribution in the chip detection area to be extremely complex, destroying the original temperature difference distribution, and thus destroying the accuracy of temperature difference detection. If the distance between the two detection units is set far away, the mutual heat conduction between the detection units can be alleviated, but this will cause the overall size of the entire sensor to be too large and cannot be miniaturized; if the distance between the detection units is set small, the mutual thermal crosstalk between them will be enhanced, and the thermal crosstalk effect will seriously interfere with the accuracy of temperature difference detection by each detection unit. Therefore, solving the thermal crosstalk problem is another key to the success of the design of the two detection units.

[0060] In order to solve this problem and ensure that the technical solution of the two detection units can be successfully implemented, the present invention discloses a first thermal isolation structure 400 composed of "solid-vacuum / gas-solid" to solve the mutual thermal crosstalk problem after the two detection units are integrated. Specifically:

[0061] The sensor disclosed in the present invention further comprises a housing covering the first detection unit 200 and the second detection unit 300. A first thermal isolation structure 400 is disposed in the housing to isolate thermal crosstalk between the first detection unit 200 and the second detection unit 300.

[0062] In the present embodiment, the first thermal isolation structure 400 includes a first thermal isolation cavity 410 and two closed plates 420. The first thermal isolation cavity 410 is arranged between the first airflow channel 210 and the second airflow channel 310, and the two closed plates 420 are arranged at both ends of the first thermal isolation cavity 410, and are surrounded by the base layer 100 to form a closed first thermal isolation structure 400 for isolating thermal crosstalk and improving detection accuracy. In the specific implementation, the first thermal isolation cavity 410 is evacuated to a vacuum for better thermal insulation effect. Of course, other gases with smaller specific heat capacity can also be injected. It should be noted that the first thermal isolation structure 400 is generally set to be equal in length to the two airflow channels. Of course, its length dimension can also be adjusted to be not equal in length to the two airflow channels according to actual needs; its width dimension can also be appropriately increased or decreased.

[0063] In this embodiment, the first thermal isolation structure 400 preferably has a through-hole thermal insulation cavity design. Of course, it can also be appropriately changed according to actual needs, such as: a non-through-hole design can be adopted, or a plurality of partitions can be arranged in the through-hole thermal insulation cavity to form a multi-layer partition structure with a plurality of cavities connected in series.

[0064] It should be noted that, in this embodiment, the positional relationship between the first detection unit 200 and the second detection unit 300 can be arranged in parallel left and right, in parallel front and back, or in a stacked arrangement of two layers.

[0065] In addition, further research also found that: because MEMS sensors are micro sensors, the geometric structure of the micro size is too complex to be processed, or even impossible to process. Therefore, it is necessary to simplify the overall structure of the sensor. To simplify the overall structure of the sensor, we must first consider the relative positions and size settings of the two detection units. In terms of the relative positions and size settings of the first detection unit 200 and the second detection unit 300, if the two are arranged side by side on the same base plane, the overall structure of the sensor can be effectively simplified. However, new problems will also arise: the heat between the two detection units arranged side by side on the same base plane is easier to propagate to each other, which increases the two-way mutual series effect of the temperature and affects the detection accuracy.

[0066] If the two are designed in the upper and lower layers respectively, the temperature of the lower detection unit will propagate to the upper layer due to the rise of hot air, but the temperature of the upper detection unit propagates to the lower layer more slowly, and the heat conduction is closer to unidirectional propagation, which weakens the bidirectional crosstalk effect and can alleviate the complexity of the thermal crosstalk effect to a certain extent. However, this design will lead to the following disadvantages of the sensor: First, the complexity of the sensor geometry is increased. The upper and lower layers need to design two layers of support base and two layers of gas flow channels in the vertical direction, and the two layers of support base, two layers of air flow channels and two detection units are integrated into an integral structure through an integrated design. This design scheme significantly increases the complexity of the sensor structure, which is not conducive to the simplification of the sensor structure. The complex micro-size structure significantly increases the difficulty and cost of processing and is not easy to implement; second, from the perspective of sensor performance, due to the rise of hot air, the temperature generated by the lower detection unit is more likely to propagate to the upper layer, which can easily lead to inconsistent performance of the two detection units and increase the difficulty of thermal isolation between the detection units; third, the chip size problem, the design of two air flow channels in the vertical direction will cause its height size to be too large, which is not conducive to the stability of the chip during installation and use.

[0067] Therefore, in order to solve this problem, in the specific implementation, it is preferred to arrange the first detection unit 200 and the second detection unit 300 side by side on the same base plane. Because the first thermal isolation structure 400 disclosed in the present invention is adopted, the thermal crosstalk problem between the first detection unit 200 and the second detection unit 300 can be solved, and physical conditions are provided for the first detection unit 200 and the second detection unit 300 to be arranged side by side on the same base plane. Furthermore, since the first detection unit 200 and the second detection unit 300 can be arranged side by side on the same base plane, the sensor can be designed into an integrated overall structure, which can simplify the geometric structure of the sensor, making it easy to process, which is conducive to mass processing and production of the sensor when it goes commercial.

[0068] In addition, the study also found that heat conduction from the sensor detection unit to the bottom of the base layer 100 is an important factor affecting thermal temperature difference detection. Reducing heat conduction to the bottom of the base layer 100 is a key issue in ensuring and improving the sensor detection accuracy.

[0069] To solve this problem, the present invention discloses a design scheme of setting a second thermal isolation structure below the first detection unit 200 and the second detection unit 300, which is used to isolate the heat conduction from the first detection unit 200 and the second detection unit 300 to the bottom of the base layer to solve this problem and improve the detection accuracy. Specifically:

[0070] See also Figure 4The base layer 100 includes a substrate 120 used as a support and a bottom plate 130 disposed below the substrate 120. A second heat insulation cavity 110 is disposed on the side of the substrate 120 facing the bottom plate 130, and the bottom plate 130 is disposed on the bottom surface of the substrate 120 to seal the open end of the second heat insulation cavity 110 to form a second thermal isolation structure.

[0071] In this embodiment, the length dimension setting of the second thermal insulation cavity 110 in the second thermal isolation structure in the x direction should generally be equal to or slightly larger than the length dimension of the first detection unit 200 and the second detection unit 300 in the x direction; the length dimension setting in the y direction should generally be larger than the length dimension of the first detection unit 200 and the second detection unit 300 in the y direction. Of course, its specific length can be adjusted according to actual needs. In specific implementation, it is better to evacuate the second thermal insulation cavity 110 in the second thermal isolation structure. Of course, other gases with smaller specific heat capacity can also be injected.

[0072] Similarly, the second thermal isolation structure disclosed in the present invention solves the influence of heat conduction from the first detection unit 200 and the second detection unit 300 to the bottom of the base layer 100 on the detection accuracy of the sensor, and provides a basic condition for the first detection unit 200 and the second detection unit 300 to be arranged side by side on the same base layer plane. Similarly, since the first detection unit 200 and the second detection unit 300 can be arranged side by side on the same base layer plane, the sensor can be designed into an integrated overall structure, which can simplify the geometric structure of the sensor, making it easy to process, which is conducive to mass production of the sensor when it goes commercial.

[0073] In specific implementation, the substrate 120 may preferably be a single crystal silicon plate; the bottom plate 130 may preferably be a quartz glass plate. Of course, the substrate 120 may also be other semiconductor chip substrates, such as silicon dioxide substrates, ceramic substrates, etc.; the bottom plate 130 may also be made of other solid materials with low thermal conductivity, such as organic resin plates, etc.

[0074] It should be noted that, in specific implementation, the size of the first thermal isolation structure 400 and the second thermal isolation structure is preferably set to be consistent with the size of the sensor detection area. Of course, it can also be adjusted according to actual needs.

[0075] Similarly, in the specific implementation, for the convenience of processing, the second thermal isolation structure is preferably designed as a through-hole thermal insulation cavity, and sealed with a closing plate at both ends of the through-hole. Of course, appropriate changes can also be made according to actual needs, such as: a non-through-hole design can be adopted, or a plurality of partitions can be arranged in the through-hole thermal insulation cavity to form a multi-layer partition structure with a plurality of cavities connected in series.

[0076] Please note that Figure 4 and Figure 7The electrical leads and terminals at the ends of all heating elements and temperature measuring elements in the present invention should extend to the outside of the shell to facilitate external wiring and daily maintenance.

[0077] See also Fig. 9 , Fig. 9 This is a comparison chart of the temperature difference-flow curve of a gas mass flow sensor based on the thermal temperature difference principle disclosed in the present invention and the temperature difference-flow curve of a thermal temperature difference gas mass flow sensor of a traditional structure. Fig. 9 The curve comparison results in the figure clearly show that the sensitivity (curve slope) of the thermal temperature difference gas mass flow sensor of the traditional structure decreases significantly with the increase of the detected flow rate; while the temperature difference-flow curve of a gas mass flow sensor in the present embodiment maintains a high sensitivity (curve slope) in both the small flow segment and the large flow segment, which solves the problem of sensitivity dead zone, also solves the problem of thermal crosstalk, and simplifies the overall structure of the sensor.

[0078] In addition, the present invention discloses a gas mass flow sensor, in which the number of detection units and the number of thermal isolation structures provided can be increased or decreased according to actual needs, and the length, width and other dimensions of each detection unit and the relative positions of the detection units (such as: parallel left and right, parallel front and back, stacked up and down, etc.) as well as the length, width and other dimensions of each thermal isolation structure and the morphological structure of the thermal isolation structure (such as: through-hole type, non-through-hole type, multi-layer partition type, etc.) can be adjusted according to actual needs to meet requirements such as different detection sensitivities, different detection ranges or different detection accuracies.

[0079] See also Figure 4 and Figure 7 The present invention also provides a method for detecting gas flow rate, which uses the above-mentioned gas mass flow sensor and comprises the following steps:

[0080] Step S110: the first heating element 220 and the second heating element 320 are powered on to generate heat;

[0081] Step S120 : the gas enters the first air flow channel 210 and the second air flow channel 310 .

[0082] Specifically, the gas mass flow sensor is connected to the gas pipeline of the measured section, the gas valve is opened to allow the gas to flow into the first gas flow channel 210 and the second gas flow channel 310, and the gas is allowed to flow normally in the channel for a period of time, and then the detection is performed after the gas flow is stable.

[0083] Step S130 : the first detection unit 200 detects the gas flow in the first air flow channel 210 ; the second detection unit 300 detects the gas flow in the second air flow channel 310 .

[0084] Specifically, since the first detection unit 200 and the second detection unit 300 are both provided with a heating element and upstream and downstream temperature measuring elements, before the gas enters the first detection unit 200 and the second detection unit 300, the temperature field in the first detection unit 200 and the second detection unit 300 is symmetrically distributed with the heating element as the center. After the gas enters the first detection unit 200 and the second detection unit 300, the gas upstream of the heating element brings the heat of the heating element to the downstream of the heating element, forming an upstream and downstream thermal temperature difference. Since the upstream and downstream of the heating element in the first detection unit 200 and the second detection unit 300 are both provided with a temperature measuring element composed of a thermistor, the temperature measuring element composed of a thermistor can quickly detect the corresponding temperature values ​​at the upstream and downstream. By calculating the temperature difference between the upstream and downstream, and comparing the temperature difference-flow relationship curve, the flow value of the measured gas can be obtained.

[0085] Step S140: The receiving end outside the sensor receives the detection results of the first detection unit 200 and the second detection unit 300;

[0086] Specifically, since the first temperature measuring resistor in the first detection unit 200 and the second temperature measuring resistor in the second detection unit 300 are both made of thermistors with high temperature coefficients and good linearity, when the gas temperature in the first detection unit 200 and the second detection unit 300 changes, the resistance of the thermistors will change accordingly. The first temperature measuring resistor and the second temperature measuring resistor are connected to the bridge circuit located outside the sensor chip through the first terminal 250 and the second terminal 350 at the end of the electrical lead of the first temperature measuring resistor and the second temperature measuring resistor. The bridge circuit will output an electrical signal due to the change in the resistance of the thermistor, and the detection results in the first detection unit 200 and the second detection unit 300 can be obtained.

[0087] Step S150: Use the detection result in the first detection unit 200 as the detection value at a small flow rate (such as 0-500 mL / min), and use the detection result in the second detection unit 300 as the detection value at a large flow rate (such as above 500 mL / min), and combine them to obtain complete flow detection data.

[0088] Specifically, the temperature difference-flow data in the first detection unit 200 obtained in step S140 (such as: temperature difference-flow data at 0-500 mL / min) and the temperature difference-flow data in the second detection unit 300 (such as: temperature difference-flow data above 500 mL / min) are combined together to obtain complete temperature difference-flow data.

[0089] The present invention discovers the problem of sensitivity dead zone of thermal temperature difference gas mass flow sensor and its cause, and designs a gas mass flow sensor and detection method to solve this problem, which not only solves the problem of sensitivity dead zone, but also solves the problem that the sensor is difficult to meet the actual needs of flow detection due to limited sensitivity of large flow detection. Therefore, the gas mass flow sensor and detection method disclosed by the present invention have the following advantages:

[0090] 1. Since the present invention discloses and sets a first detection unit 200 for detecting a small flow rate and a second detection unit 300 for detecting a large flow rate, when the design parameters of the first detection unit 200 are optimized to improve the small flow rate detection sensitivity, the sensitivity of the second detection unit 300 will not be affected; when the design parameters of the second detection unit 300 are optimized to improve the large flow rate detection sensitivity, the sensitivity of the first detection unit 200 will not be interfered with, thereby simultaneously improving the large flow rate detection sensitivity and the small flow rate detection sensitivity, solving the technical bottleneck problem of the sensitivity dead zone of the thermal temperature difference gas mass flow sensor.

[0091] 2. Since the present invention discloses a first thermal isolation structure and is arranged between the first detection unit 200 and the second detection unit 300, and discloses a second thermal isolation structure and is arranged below the base layer 100, it not only isolates the thermal crosstalk of the temperature field between the two detection units, avoids the interference of the thermal crosstalk on the real thermal temperature difference in each detection unit, and ensures that the design scheme of the two detection units can be successfully implemented; it also isolates the heat conduction of the two detection units to the bottom of the base layer 100, and avoids the interference of the heat conduction to the bottom of the base layer 100 on the real thermal temperature difference in each detection unit. This technical solution disclosed by the present invention not only improves the detection accuracy of the sensor, but also provides the possibility that the two detection units can be arranged side by side on the same base layer plane to simplify the overall structure of the sensor.

[0092] 3. Since the first detection unit 200 and the second detection unit 300 of the sensor disclosed in the present invention can be arranged side by side on the same base plane, the overall structure of the sensor is easy to integrate, the structure of the MEMS microsensor is simplified, the chip structure is simplified, the processing difficulty is reduced, and it is conducive to the mass processing and production of the sensor when it goes commercial.

[0093] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A gas mass flow sensor, characterized in that: include: Grassroots; a first detection unit, disposed on the base layer, comprising a first airflow channel and a first heating element and a first temperature measuring element disposed in the first airflow channel, and the first temperature measuring element is disposed both upstream and downstream of the first heating element; and The second detection unit is arranged on the base layer, the second detection unit comprises a second airflow channel and a second heating element and a second temperature measuring element arranged in the second airflow channel, and the second temperature measuring element is arranged upstream and downstream of the second heating element. The first detection unit is used to detect a small flow rate, and the second detection unit is used to detect a large flow rate.

2. The gas mass flow sensor according to claim 1, characterized in that: It also includes a shell covering the first detection unit and the second detection unit, wherein a first thermal isolation structure is disposed in the shell to isolate the first detection unit from thermal crosstalk of the temperature field between the first detection unit and the second detection unit.

3. The gas mass flow sensor according to claim 2, characterized in that: The first thermal isolation structure includes a first thermal isolation cavity and a closing plate. The first thermal isolation cavity is located on the bottom surface of the shell and between the first airflow channel and the second airflow channel. The two closing plates are arranged at both ends of the first thermal isolation cavity to form the first thermal isolation structure with the side walls of the first thermal isolation cavity and the top surface of the base layer.

4. The gas mass flow sensor according to any one of claims 1 or 3, characterized in that: The first detection unit and the second detection unit are arranged in parallel on the base layer.

5. The gas mass flow sensor according to claim 1 or 3, characterized in that: A cross-sectional area of ​​the first airflow channel is smaller than a cross-sectional area of ​​the second airflow channel.

6. The gas mass flow sensor according to claim 1, characterized in that: A second thermal isolation structure is disposed in the base layer, and the second thermal isolation structure is used to isolate the first detection unit and the second detection unit from heat conduction to the bottom of the base layer.

7. The gas mass flow sensor according to claim 6, characterized in that: The base layer includes a substrate used as a support and a bottom plate arranged below the substrate, a second insulation cavity is arranged on the side of the substrate facing the bottom plate, and the bottom plate is arranged on the bottom surface of the substrate to seal the open end of the second insulation cavity to form the second thermal isolation structure.

8. The gas mass flow sensor according to claim 1, characterized in that: It also includes a third temperature measuring element and a fourth temperature measuring element, and the third temperature measuring element and the fourth temperature measuring element are respectively located at the inlet ends of the first airflow channel and the second airflow channel.

9. The gas mass flow sensor according to claim 1, characterized in that: The first heating element and the second heating element are both rectangular sheet-shaped resistance films; the first heating element and the second heating element are both arranged near the middle of the first airflow channel and the second airflow channel.

10. A method for detecting gas flow rate using the gas mass flow sensor according to any one of claims 1 to 9, characterized in that: include: The first heating element and the second heating element are energized to generate heat; The gas enters the first air flow channel and the second air flow channel; The first detection unit detects the gas flow in the first gas flow channel; the second detection unit detects the gas flow in the second gas flow channel; A receiving end outside the sensor receives detection results of the first detection unit and the second detection unit; The detection result of the first detection unit is used as the detection value when the flow rate is small, and the detection result of the second detection unit is used as the detection value when the flow rate is large, and the complete flow detection data is obtained by combining them.

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