Method for prolonging the life of a thermal flow sensor, thermal flow sensor and thermal mass gas meter

Abstract

This invention provides a method for extending the service life of a thermal flow sensor. The method is applicable to a thermal flow sensor comprising a control module, a main flow channel, and two identical measurement channels, wherein the second measurement channel is connected to the main flow channel via a solenoid valve. Both measurement channels are equipped with MEMS thermal flow sensing chips. The method includes: a calibration phase where the solenoid valve is sequentially closed and opened to acquire the measurement model and dual-channel initial relationship model of the thermal flow sensor; a usage phase where the thermal flow sensor is controlled in a single-channel state, and flow measurement is performed based on the real-time temperature difference signal from the first MEMS thermal flow sensing chip and the measurement model; and a correction phase where the thermal flow sensor is controlled in a dual-channel state, and the measurement model of the thermal flow sensor is corrected based on the temperature difference signal acquired by the first and second MEMS thermal flow sensing chips and the dual-channel initial relationship model of the thermal flow sensor.

Description

Technical Field

[0001] This invention relates to a thermal mass gas meter, and more specifically, to a method for extending the service life of a thermal flow sensor, a thermal flow sensor, and a thermal mass gas meter. Background Technology

[0002] In recent years, the domestic gas meter market has reached tens of millions of units, with an estimated total market size exceeding 40 billion yuan. The gas meter market has broad prospects and great potential. Most existing gas meters on the market are diaphragm-type mechanical meters. With the rise of heat and energy metering methods, ultrasonic gas meters or thermal mass gas meters have also developed rapidly.

[0003] A thermal mass gas meter is an instrument that measures the mass flow rate of gas using the principle of thermal diffusion. It includes a micro-heater and a pair of symmetrically distributed upstream and downstream temperature sensors T1 and T2. At zero flow, the two temperature sensors are in the same temperature field. When gas flows through, the temperature sensors detect a change in the temperature field, and the temperature field corresponds to the flow rate as follows: Qm = K / Cp*ΔT, where Cp is the specific heat capacity of the gas at constant pressure, K is the overall coefficient of the equipment, ΔT = (T1 - T2), and Qm is the mass flow rate.

[0004] With technological advancements, thermal mass flow meters utilize MEMS thermal gas flow sensors based on current CMOS sensor technology as the gas flow detection element. This type of sensor is characterized by its exceptionally small size, high sensitivity, long lifespan, high stability, and high repeatability, making it widely used in precision measuring instruments. Flow meters employing this technology require no temperature or pressure compensation for gas flow measurement, offering convenient and accurate measurements, providing either mass flow rate or standard volumetric flow rate. Furthermore, this type of sensor exhibits a wide rangeability, capable of measuring gases with flow velocities ranging from 100 Nm / s to as low as 0.5 Nm / s. Thermal gas mass flow meters also possess excellent shock resistance; the sensor has no moving parts or pressure-sensitive components, rendering it unaffected by vibrations in terms of measurement accuracy.

[0005] In actual use, as the usage time of the thermal mass gas meter increases, a phenomenon of significantly lower meter readings appears. Through research and testing of the application products, we found that the cleanliness of the gas is not high, and it contains various impurities. During use, impurities, especially volatile organic compounds, adhere to the surface of the MEMS sensor, causing changes in the sensor sensitivity, thus resulting in metering deviations.

[0006] To ensure accurate product testing results, each company typically has its own calibration methods and procedures. Traditional calibration processes are complex and heavily influenced by the raw sensor signal from the MEMS silicon flow chip. For example, patent application number 201811117616.1 discloses a detailed calibration process. However, each calibration process requires manually inputting calibration parameters into the calibration software, resulting in low efficiency and a high risk of errors. Furthermore, if the raw sensor signal is discrete, the operational amplifier's amplification factor needs manual adjustment, leading to unstable accuracy and low calibration yield. Building on this, patent application number CN118032098A establishes a gas quality detection model based on LS-SVM. Before using the thermal flow sensor module, gas flow calibration is performed based on this model. The entire process is automated, requiring no manual intervention, significantly improving calibration efficiency and accuracy. However, this method is a centralized calibration method and cannot perform on-site calibration without disassembling the device.

[0007] In order to solve the above problems, people have been seeking an ideal technological solution. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for extending the service life of a thermal flow sensor, a thermal flow sensor, and a thermal mass gas meter.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A first aspect provides a method for extending the service life of a thermal flow sensor, the thermal flow sensor including a control module, a main flow channel and a first measurement channel, the first measurement channel being directly connected to the main flow channel, and a first MEMS thermal flow sensor chip communicatively connected to the control module being disposed in the first measurement channel.

[0011] The method includes:

[0012] A second measuring channel is added to the thermal flow sensor. The second measuring channel has the same structural dimensions as the first measuring channel and is connected to the main air channel through a solenoid valve. A second MEMS thermal flow sensor chip is disposed in the second measuring channel. The second MEMS thermal flow sensor chip is the same as the first MEMS thermal flow sensor chip.

[0013] The control module is connected to the solenoid valve and the second MEMS thermal flow sensor chip, and switches the working state of the thermal flow sensor by controlling the opening and closing of the solenoid valve; wherein, when the solenoid valve is open, the thermal flow sensor operates in a dual-channel state, and the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip simultaneously acquire temperature difference signals; when the solenoid valve is closed, the thermal flow sensor operates in a single-channel state, and the first MEMS thermal flow sensor chip acquires temperature difference signals.

[0014] The operation of the thermal flow sensor includes three stages:

[0015] Calibration phase: First, control the thermal flow sensor to single-channel state, introduce standard gas to obtain and store the measurement model of the thermal flow sensor; then control the thermal flow sensor to dual-channel state, introduce standard gas to obtain and store the initial relationship model of the dual-channel thermal flow sensor.

[0016] Usage phase: Control the thermal flow sensor to be in single-channel mode, and measure the flow rate based on the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the measurement model;

[0017] Correction phase: The thermal flow sensor is controlled to be in dual-channel state. The measurement model of the thermal flow sensor is corrected based on the temperature difference signal collected by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip and the initial relationship model of the dual-channel thermal flow sensor.

[0018] Preferably, the specific steps of controlling the thermal flow sensor in a single-channel state to obtain the measurement model of the thermal flow sensor, and then controlling the thermal flow sensor in a dual-channel state to obtain the initial relationship model of the dual-channel thermal flow sensor include:

[0019] The control module controls the solenoid valve to close, and the thermal flow sensor is in single-channel state; standard flow gas of standard flow rate is passed to the thermal flow sensor to obtain the real-time temperature difference signal of the first MEMS thermal flow sensor chip; according to the thermal flow measurement principle, a flow data model I is established when the first MEMS thermal flow sensor chip is used alone, and this flow data model I is the measurement model of the thermal flow sensor.

[0020] The measurement model is:

[0021] The control module controls the solenoid valve to open, and the thermal flow sensor is in dual-channel state; standard flow gas of standard flow is supplied to the thermal flow sensor, and the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip is obtained respectively. Based on the thermal flow measurement principle, a flow data model II is established when the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip work together.

[0022] Traffic data model II is

[0023] According to the flow continuity equation Q m =Q m_1 =Q m_2 Based on flow data model I and flow data model II, a dual-channel initial relationship model for the thermal flow sensor is established. The expression for the dual-channel initial relationship model is as follows:

[0024]

[0025] Among them, Q m_1 The total gas flow rate is the result of the first MEMS thermal flow sensor chip acting alone when the solenoid valve is closed.

[0026] Q m_2 The total flow rate of the gas meter is obtained when the solenoid valve is opened, and the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip work together.

[0027] Q m Standard flow rate;

[0028] f is the flow rate ratio between the measured flow channel and the main flow channel; K is the sensitivity of the MEMS thermal flow sensor chip; c p The heat capacity of the fluid;

[0029] △T a , △T b These represent the temperature difference obtained by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip when standard gas passes through; T 1标 For △T a The corresponding signal voltage, T 2标 For △T b The corresponding signal voltage;

[0030] x1 and x2 are the temperature differences between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip under a unit voltage, respectively. This represents the initial relationship between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip in the dual-channel state, i.e., the initial relationship between the two channels.

[0031] Preferably, the measurement model of the thermal flow sensor is corrected based on the temperature difference signal acquired by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip and the dual-channel initial relationship model of the thermal flow sensor, including:

[0032] Based on the initial relationship of the dual channels, the ideal voltage ratio measured by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip during the field correction phase is derived:

[0033]

[0034] Among them, T 1理 T represents the ideal signal voltage of the temperature difference measured by the first MEMS thermal flow sensor chip during the field correction phase. 2理 This represents the ideal signal voltage of the temperature difference measured by the second MEMS thermal flow sensor chip during the field correction phase.

[0035] Assuming the temperature difference signal voltage measured by the second MEMS thermal flow sensor chip during the field correction phase is an ideal signal voltage, the correction coefficient k is obtained based on the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase, the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase, and the aforementioned ideal voltage ratio. The expression for k is:

[0036]

[0037] Among them, T 1实 This represents the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase; T 2实 This indicates the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase.

[0038] Substituting the correction coefficients into the measurement model of the thermal flow sensor, we obtain the corrected measurement model:

[0039]

[0040] A second aspect of the present invention provides a self-correcting thermal flow sensor, the thermal flow sensor comprising a control module, a main flow channel, and two identical measuring channels, wherein the first measuring channel is directly connected to the main flow channel; and the second measuring channel is connected to the main flow channel via a solenoid valve.

[0041] A first MEMS thermal flow sensor chip is installed in the first measurement flow channel, and a second MEMS thermal flow sensor chip is installed in the second measurement flow channel. The first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip are the same MEMS thermal flow sensor chip.

[0042] The control module is connected to the solenoid valve, the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip, and is equipped with a measurement model of the thermal flow sensor and a dual-channel initial relationship model.

[0043] The control module controls the closing of the solenoid valve to execute normal operation mode and correction mode;

[0044] In normal operating mode, the control module controls the solenoid valve to close and performs flow measurement based on the real-time temperature difference signal and measurement model of the first MEMS thermal flow sensor chip.

[0045] In correction mode, the control module controls the solenoid valve to open, and acquires the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip respectively. Based on the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip and the dual-channel initial relationship model, the measurement model of the thermal flow sensor is corrected.

[0046] Preferably, the measurement model of the thermal flow sensor is as follows:

[0047] The initial relationship model for the dual-channel thermal flow sensor is as follows:

[0048]

[0049] Among them, Q m_1 The total flow rate of the gas meter is obtained when the first MEMS thermal flow sensor chip is used alone.

[0050] f is the flow rate ratio between the measured flow channel and the main flow channel; K is the sensitivity of the MEMS thermal flow sensor chip. p The heat capacity of the fluid; ΔT a The temperature difference value obtained by the first MEMS thermal flow sensor chip when standard gas passes through; T 1标 For △T a The corresponding signal voltage is the real-time temperature difference signal of the first MEMS thermal flow sensor chip when the standard gas passes through.

[0051] T 2标 This is the real-time temperature difference signal of the second MEMS thermal flow sensor chip when standard gas passes through;

[0052] x1 and x2 are the temperature differences between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip under a unit voltage, respectively. The initial relationship between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip is the dual-channel initial relationship.

[0053] Preferably, the measurement model of the thermal flow sensor is corrected based on the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip, and the dual-channel initial relationship model, including:

[0054] The correction coefficient k is obtained based on the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase, the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase, and the dual-channel initial relationship model. The expression for k is:

[0055]

[0056] Among them, T 1实 This represents the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase; T 2实 This indicates the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase.

[0057] Substituting the correction coefficients into the measurement model of the thermal flow sensor, we obtain the corrected measurement model:

[0058]

[0059] A third aspect of the present invention provides a thermal mass gas meter, comprising an inlet, an outlet, a thermal flow sensor, a gas bladder, and a housing, wherein the thermal flow sensor is the aforementioned self-correcting thermal flow sensor.

[0060] This invention has outstanding substantive features and significant progress compared to the prior art. Specifically, this invention has the following advantages:

[0061] 1. The thermal flow sensor of the present invention includes two measuring channels and is coupled with two sets of thermal flow chips. An initial relationship model of the two sets of thermal flow chips is established through calibration, so that the gas meter can be periodically calibrated on site using air without disassembly, thereby achieving continuous and accurate measurement.

[0062] 2. By calibrating, a single-channel measurement model and a dual-channel initial relationship model are established. Different models are used in different modes to ensure the long-term stability and measurement accuracy of the initial relationship model.

[0063] 3. By driving the opening and closing of the solenoid valve, the airflow of the second measurement channel is cut off, preventing impurities in the sample gas from entering the second measurement channel and interfering with the second MEMS thermal flow sensor chip, thereby ensuring the durability of the second MEMS thermal flow sensor chip.

[0064] 4. The correction mode of this invention can be set to trigger according to actual needs, which is flexible and maintains the measurement accuracy of the instrument for a long time. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the thermal flow sensor described in Embodiments 1 and 2 of the present invention.

[0066] Figure 2 This is a schematic diagram of the workflow for obtaining the measurement model and the initial relationship model in Embodiment 1 of the present invention.

[0067] Figure 3 This is a schematic diagram of the workflow described in Embodiments 1 and 2 of the present invention.

[0068] Figure 4 This is a circuit diagram of the control module in Embodiment 2 of the present invention.

[0069] Figure 5 This is a schematic diagram of the structure of Embodiment 3 of the present invention.

[0070] In the diagram: 1. Inlet; 2. Measuring channel a; 3. Measuring channel b; 4. Throttling orifice plate; 5. Outlet connector; 6. Inlet; 7. Outlet; 8. Thermal flow sensor; 9. Airbag; 10. Housing. Detailed Implementation

[0071] The principle of bypass measurement in gas meters, especially in MEMS thermal mass gas meters, mainly relies on MEMS thermal flow sensors to detect the fluid flow and the fluid generated during heat exchange. These gas meters typically include a main flow path and a bypass flow path. The MEMS thermal flow sensor is installed in the bypass flow path to accurately measure the flow, while the main flow path carries the majority of the gas flow.

[0072] Specifically, MEMS thermal flow sensors can calculate the flow rate within the measurement channel by measuring the temperature difference. Therefore, the total flow rate through the gas meter is Q. m =(f+1)q m K represents the sensitivity of the MEMS thermal flow sensor chip, and c p is the heat capacity of the gas fluid; f is the flow rate ratio between the main gas path and the bypass gas path.

[0073] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0074] Example 1

[0075] This embodiment provides a method for extending the service life of a thermal flow sensor. The thermal flow sensor includes a control module, a main airflow channel, and a first measurement channel. The first measurement channel is directly connected to the main airflow channel, and a first MEMS thermal flow sensor chip that is communicatively connected to the control module is disposed in the first measurement channel. It is understood that, under normal circumstances, the thermal flow sensor should include a throttling orifice plate 4, an outlet connector 5, and an inlet end 1.

[0076] The method includes:

[0077] A second measuring channel is added to the thermal flow sensor. The second measuring channel has the same structural dimensions as the first measuring channel and is connected to the main airflow channel via a solenoid valve. A second MEMS thermal flow sensor chip, identical to the first MEMS thermal flow sensor chip, is disposed within the second measuring channel. For ease of understanding, the first measuring channel is designated as measuring channel a2, and the second measuring channel as measuring channel b3. Specifically, the final structural diagram of the thermal flow sensor described in this embodiment is as follows: Figure 1 As shown.

[0078] The control module is connected to the solenoid valve and the second MEMS thermal flow sensor chip, and switches the working state of the thermal flow sensor by controlling the opening and closing of the solenoid valve; wherein, when the solenoid valve is open, the thermal flow sensor operates in a dual-channel state, and the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip simultaneously collect temperature difference signals; when the solenoid valve is closed, the thermal flow sensor operates in a single-channel state, and the first MEMS thermal flow sensor chip collects temperature difference signals.

[0079] The operation of the thermal flow sensor includes three stages:

[0080] Calibration phase: such as Figure 2 As shown, first, the thermal flow sensor is controlled to be in single-channel mode, and standard gas is introduced to obtain and store the measurement model of the thermal flow sensor; then, the thermal flow sensor is controlled to be in dual-channel mode, and standard gas is introduced to obtain and store the dual-channel initial relationship model of the thermal flow sensor.

[0081] The specific steps of controlling the thermal flow sensor in a single-channel state to obtain the measurement model of the thermal flow sensor, and then controlling the thermal flow sensor in a dual-channel state to obtain the initial relationship model of the dual-channel thermal flow sensor, include:

[0082] The control module controls the solenoid valve to close, and the thermal flow sensor is in single-channel state; standard flow gas of standard flow rate is passed to the thermal flow sensor to obtain the real-time temperature difference signal of the first MEMS thermal flow sensor chip; according to the thermal flow measurement principle, a flow data model I is established when the first MEMS thermal flow sensor chip is used alone, and this flow data model I is the measurement model of the thermal flow sensor.

[0083] The measurement model is:

[0084] The control module controls the solenoid valve to open, and the thermal flow sensor is in dual-channel state; standard flow gas of standard flow is supplied to the thermal flow sensor, and the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip is obtained respectively. Based on the thermal flow measurement principle, a flow data model II is established when the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip work together.

[0085] Traffic data model II is

[0086] According to the flow continuity equation Q m =Q m_1 =Q m_2 Based on flow data model I and flow data model II, a dual-channel initial relationship model for the thermal flow sensor is established. The expression for the dual-channel initial relationship model is as follows:

[0087]

[0088] Among them, Q m_1 The total gas flow rate is the result of the first MEMS thermal flow sensor chip acting alone when the solenoid valve is closed.

[0089] Q m_2 The total flow rate of the gas meter is obtained when the solenoid valve is opened, and the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip work together.

[0090] Q m Standard flow rate;

[0091] f is the flow rate ratio between the measured flow channel and the main flow channel; K is the sensitivity of the MEMS thermal flow sensor chip; c p The heat capacity of the fluid;

[0092] △T a , △T b These represent the temperature difference obtained by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip when standard gas passes through; T 1标 For △T a The corresponding signal voltage, T 2标 For △T b The corresponding signal voltage;

[0093] x1 and x2 are the temperature differences between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip under a unit voltage, respectively. This represents the initial relationship between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip in the dual-channel state, i.e., the initial relationship between the two channels.

[0094] Usage phase: such as Figure 3 As shown, the thermal flow sensor is controlled to be in single-channel mode, and flow measurement is performed based on the real-time temperature difference signal and measurement model of the first MEMS thermal flow sensor chip.

[0095] Revision phase: such as Figure 3 As shown, the thermal flow sensor is controlled to be in dual-channel mode. The measurement model of the thermal flow sensor is corrected based on the temperature difference signal collected by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip and the initial relationship model of the dual-channel thermal flow sensor.

[0096] The measurement model of the thermal flow sensor is corrected based on the temperature difference signal acquired by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip, and the dual-channel initial relationship model of the thermal flow sensor. This includes:

[0097] Based on the initial relationship of the dual channels, the ideal voltage ratio measured by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip during the field correction phase is derived:

[0098]

[0099] Among them, T 1理 T represents the ideal signal voltage of the temperature difference measured by the first MEMS thermal flow sensor chip during the field correction phase. 2理 This represents the ideal signal voltage of the temperature difference measured by the second MEMS thermal flow sensor chip during the field correction phase.

[0100] Assuming the temperature difference signal voltage measured by the second MEMS thermal flow sensor chip during the field correction phase is an ideal signal voltage, the correction coefficient k is obtained based on the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase, the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase, and the aforementioned ideal voltage ratio. The expression for k is as follows:

[0101]

[0102] Among them, T 1实 This represents the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase; T 2实 This indicates the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase.

[0103] Substituting the correction coefficients into the measurement model of the thermal flow sensor, we obtain the corrected measurement model:

[0104]

[0105] It is important to note that the thermal flow sensor does not need to be disassembled in either normal or correction mode. In correction mode, it is also unnecessary to input standard flow gas into the thermal flow sensor; instead, ambient air is used directly. The flow rate obtained by the second MEMS thermal flow sensor chip when both MEMS thermal flow sensor chips are operating simultaneously is used as the standard flow rate to correct the measurement model of the thermal flow sensor on-site, resulting in low cost. Since the second MEMS thermal flow sensor chip is located in the measurement flow channel of the solenoid valve, and the solenoid valve is normally closed, it is in a non-operating state during normal operation. This state aims to maintain the original characteristics of the second MEMS thermal flow sensor chip as a standard source; therefore, the second MEMS thermal flow sensor chip only enters the operating state after receiving a calibration command.

[0106] Example 2

[0107] This embodiment provides a self-correcting thermal flow sensor. For example... Figure 1 As shown, the thermal flow sensor includes a control module, a main airway, and two identical measurement channels. The first measurement channel is directly connected to the main airway, and the second measurement channel is connected to the main airway via a solenoid valve. For ease of understanding, the first measurement channel is designated as measurement channel a 2, and the second measurement channel is designated as measurement channel b 3.

[0108] A first MEMS thermal flow sensor chip is installed in the measuring flow channel a 32, and a second MEMS thermal flow sensor chip is installed in the measuring flow channel b 3. The first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip are the same MEMS thermal flow sensor chip.

[0109] The control module is connected to the solenoid valve, the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip, and is equipped with a measurement model of the thermal flow sensor and a dual-channel initial relationship model.

[0110] like Figure 3 As shown, the control module controls the closing of the solenoid valve to execute the normal operation mode and the correction mode;

[0111] In normal operating mode, the control module controls the solenoid valve to close and performs flow measurement based on the real-time temperature difference signal and measurement model of the first MEMS thermal flow sensor chip.

[0112] In correction mode, the control module controls the solenoid valve to open, and acquires the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip respectively. Based on the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip and the dual-channel initial relationship model, the measurement model of the thermal flow sensor is corrected.

[0113] Specifically, the control module of the thermal flow sensor is as follows: Figure 4 As shown, it includes: two flow detection circuits, a solenoid valve drive circuit, a power supply module, and a microcontroller (MCU).

[0114] The flow monitoring circuit uses a differential amplifier circuit to amplify the weak voltage signal output by the MEMS thermal flow sensor, and uses a high-speed, high-resolution ADC to convert the analog signal into a digital signal, thereby realizing signal reading.

[0115] The solenoid valve drive circuit switches the solenoid valve on and off according to the measurement requirements, thereby realizing the gas path switch of the second measurement flow channel.

[0116] The storage circuit is used to store the measurement model of the thermal flow sensor, the initial relationship model between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip and the standard flow, as well as calibration parameters, etc.

[0117] In normal operating mode, the microcontroller (MCU) outputs the total flow rate of the gas meter based on the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the measurement model. In correction mode, the measurement model of the thermal flow sensor is corrected based on the real-time temperature difference signals of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip, and the dual-channel initial relationship model.

[0118] The power module adopts a low-power design. By selecting appropriate chips for the total power consumption of all circuits and adjusting the circuit's operating mode, the power consumption is reduced to ensure the lifespan of the instrument battery.

[0119] Furthermore, before leaving the factory, the measurement model and dual-channel initial relationship model of the thermal flow sensor need to be obtained through calibration with standard gas and stored in the storage circuit.

[0120] Specifically, such as Figure 2 As shown, the steps for obtaining the measurement model and the dual-channel initial relationship model of the thermal flow sensor are as follows:

[0121] The control module controls the solenoid valve to close, and supplies a standard flow rate of standard gas to the thermal flow sensor. At this time, the thermal flow sensor only has standard gas flowing through the measuring flow channel a2 and the main flow channel, and obtains the real-time temperature difference value ΔT of the first MEMS thermal flow sensor chip. a Based on the principle of thermal flow measurement, a flow data model I is established when the first MEMS thermal flow sensor chip operates alone. This flow data model I is the measurement model of the thermal flow sensor.

[0122] The expression for the measurement model is:

[0123] Among them, Q m_1 When the solenoid valve is closed, the total gas flow rate is the result of the first MEMS thermal flow sensor chip operating alone; f is the flow rate ratio between the measured flow channel a2 and the main flow channel; K is the sensitivity of the MEMS thermal flow sensor chip; c p The heat capacity of the fluid; ΔT a This represents the temperature difference obtained by the first MEMS thermal flow sensor chip when standard gas passes through it.

[0124] The measurement model of the thermal flow sensor is stored in the storage circuit for use in subsequent normal operation modes.

[0125] Then, the control module controls the solenoid valve to open, and standard flow gas of standard flow rate is introduced into the thermal flow sensor. At this time, airflow passes through the measuring channel a2, the measuring channel b3 and the main flow channel.

[0126] The real-time temperature difference signal ΔT between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip was acquired respectively. a and △T b A flow data model II is established based on the principle of thermal flow measurement when the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip work together.

[0127] The expression for Flow Data Model II is:

[0128] Among them, Q m_2 The total flow rate of the gas meter is obtained when the solenoid valve is opened, and the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip work together.

[0129] During initial calibration, the standard flow rate Q is supplied to the thermal mass gas meter. m Therefore, the total gas flow rate Q obtained by the solenoid valve in both open and closed states is... m_2 and Q m_1 All of these should be equal to the standard flow rate, thus yielding the flow continuity equation Q. m =Q m_1 =Q m_2 .

[0130] Based on the flow continuity equation and flow data model I and flow data model II, a dual-channel initial relationship model for the thermal flow sensor is established. The expression for the dual-channel initial relationship model is as follows:

[0131]

[0132] x1 and x2 are the temperature differences between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip under a unit voltage, respectively. The parameter ratio of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip is also the initial relationship between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip, i.e., the initial relationship of the dual channels.

[0133] The initial relational model is then stored in the storage circuit for use in subsequent correction modes.

[0134] Specifically, the steps for obtaining the initial relational model are as follows:

[0135] Based on the flow continuity equation, establish the correspondence between data model I and data model II, namely:

[0136]

[0137] The above equation can be simplified to:

[0138] By performing a simple transformation on the simplified equation, we get:

[0139]

[0140] It can be seen that different models are used under different modes to ensure the long-term stability and measurement accuracy of the initial relationship model.

[0141] Furthermore, based on the real-time temperature difference signals of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip, and the initial relationship between the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip and the preset flow rate, the measurement model of the thermal flow sensor is corrected, including:

[0142] The correction coefficient k is obtained based on the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase, the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase, and the dual-channel initial relationship model. The expression for k is as follows:

[0143]

[0144] Among them, T 1实 This represents the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase; T 2实 This indicates the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase.

[0145] Substituting the correction coefficients into the measurement model of the thermal flow sensor, we obtain the corrected measurement model:

[0146]

[0147] After obtaining the calibrated measurement model, the solenoid valve is closed again, and subsequent flow measurements are performed using the calibrated measurement model.

[0148] Specifically, the steps for obtaining the correction coefficients based on the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase, the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase, and the dual-channel initial relationship model include:

[0149] Based on the initial relational model, the ideal voltage ratio of the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase and the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase are derived:

[0150]

[0151] Among them, T 1理 T represents the ideal voltage of the flow signal measured by the first MEMS thermal flow sensor chip during field calibration. 2理 This represents the ideal voltage of the flow signal measured during the field calibration of the second MEMS thermal flow sensor chip.

[0152] Assuming the temperature difference signal voltage measured by the second MEMS thermal flow sensor chip during field calibration is an ideal voltage, the correction coefficient k is obtained by comparing the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip during the field correction phase, the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip during the field correction phase, and the aforementioned ideal voltage ratio. The expression for k is as follows:

[0153]

[0154] As can be seen, the thermal flow sensor of the present invention includes two measuring channels and couples two sets of thermal flow chips. An initial relationship model of the two sets of thermal flow chips is established through calibration, so that the gas meter can be periodically calibrated on-site using air without disassembly, based on the initial relationship model, to achieve continuous and accurate measurement.

[0155] By driving the opening and closing of the solenoid valve, the airflow of the measurement channel b3 is cut off, preventing impurities in the field environment from entering the measurement channel b3 and interfering with the second MEMS thermal flow sensor chip, thereby ensuring the durability of the second MEMS thermal flow sensor chip.

[0156] Example 3

[0157] This embodiment provides a thermal mass gas meter, such as Figure 5 As shown, it includes an air inlet 6, an air outlet 7, a thermal flow sensor 8, an air bladder 9, and a housing 10. The thermal flow sensor is the self-correcting thermal flow sensor described in Example 2.

[0158] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for prolonging the service life of a thermal flow sensor, the thermal flow sensor comprising a control module, a main flow air duct, and a first measuring flow channel, the first measuring flow channel being directly communicated with the main flow air duct, and a first MEMS thermal flow sensor chip being arranged in the first measuring flow channel and being in communication connection with the control module; characterized in that, The method comprises: A second measuring flow channel is added on the thermal flow sensor, which has the same structure size as the first measuring flow channel and is communicated with the main flow channel through a solenoid valve; a second MEMS thermal flow sensor chip is arranged in the second measuring flow channel, which is the same as the first MEMS thermal flow sensor chip; The control module is connected with the solenoid valve and the second MEMS thermal flow sensor chip, and switches the working state of the thermal flow sensor by controlling the opening and closing of the solenoid valve; when the solenoid valve is opened, the working state of the thermal flow sensor is a double-channel state, and the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip simultaneously collect temperature difference signals; when the solenoid valve is closed, the working state of the thermal flow sensor is a single-channel state, and the first MEMS thermal flow sensor chip collects temperature difference signals; The working process of the thermal flow sensor comprises three stages: The calibration stage: first, control the thermal flow sensor to be in a single-channel state, and pass in standard gas to obtain a measurement model of the thermal flow sensor and store it; then, control the thermal flow sensor to be in a double-channel state, and pass in standard gas to obtain a double-channel initial relationship model of the thermal flow sensor and store it; The use stage: control the thermal flow sensor to be in a single-channel state, and measure the flow according to the real-time temperature difference signal of the first MEMS thermal flow sensor chip and the measurement model; The correction stage: control the thermal flow sensor to be in a double-channel state, and correct the measurement model of the thermal flow sensor according to the temperature difference signals collected by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip and the double-channel initial relationship model of the thermal flow sensor.

2. The method of extending the life of a thermal flow sensor of claim 1, wherein, The specific steps of controlling the thermal flow sensor to be in a single-channel state to obtain a measurement model of the thermal flow sensor, and then controlling the thermal flow sensor to be in a double-channel state to obtain a double-channel initial relationship model of the thermal flow sensor comprise: The control module controls the solenoid valve to be closed, and the thermal flow sensor is in a single-channel state; standard gas with a standard flow is passed into the thermal flow sensor to obtain a real-time temperature difference signal of the first MEMS thermal flow sensor chip, and a flow data model I when the first MEMS thermal flow sensor chip acts alone is established according to the thermal flow measurement principle, which is the measurement model of the thermal flow sensor; The measurement model is: The control module controls the solenoid valve to be opened, and the thermal flow sensor is in a double-channel state; standard gas with a standard flow is passed into the thermal flow sensor to obtain real-time temperature difference signals of the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip, respectively, and a flow data model II when the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip act together is established according to the thermal flow measurement principle; The flow data model II is According to the flow continuity equation Q m = Q m_1 = Q m_2 and the flow data model I and the flow data model II, a two-channel initial relationship model of the thermal flow sensor is established, and an expression of the two-channel initial relationship model is as follows: wherein Q m_1 is the total flow of the gas meter when the solenoid is closed, the first MEMS thermal flow sensor chip acting alone. Q m_2 For the electromagnetic valve is opened, the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip jointly obtained when the total flow of the gas meter; Q m is the standard flow rate; f is the flow ratio of the measuring flow channel to the main flow channel; K is the sensitivity of the MEMS thermal flow sensing chip, c p is the heat capacity of the fluid; △T a , △T b These represent the temperature difference obtained by the first MEMS thermal flow sensor chip and the second MEMS thermal flow sensor chip when standard gas passes through; T 1标 For △T a The corresponding signal voltage, T 2标 For △T b The corresponding signal voltage; x1 and x2 are temperature difference values of the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip at a unit voltage, respectively, is the initial relationship of the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip in the dual-channel state, i.e., the dual-channel initial relationship.

3. The method of extending the life of a thermal flow sensor of claim 2, wherein, According to the temperature difference signal collected by the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip and the double-channel initial relationship model of the thermal flow sensor, a measurement model of the thermal flow sensor is corrected, including: Based on the double-channel initial relationship, an ideal voltage ratio of the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip measured in the field correction stage is derived: Wherein, T 1理 represents the temperature difference value ideal signal voltage measured by the first MEMS thermal type flow sensor chip in the field correction stage, T 2理 represents the temperature difference ideal signal voltage measured by the second MEMS thermal type flow sensor chip in the field correction stage; Assuming that the temperature difference signal voltage measured by the second MEMS thermal flow sensing chip in the field correction stage is an ideal signal voltage, a correction coefficient k is obtained according to the temperature difference signal voltage measured by the first MEMS thermal flow sensing chip in the field correction stage, the temperature difference signal voltage measured by the second MEMS thermal flow sensing chip in the field correction stage, and the ideal voltage ratio, and the expression of k is: wherein, T 1实 represents the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip in the field correction stage; T 2实 represents the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip in the field correction stage; The correction coefficient is substituted into the measurement model of the thermal flow sensor to obtain a corrected measurement model:

4. A self-correcting thermal flow sensor characterized by, The thermal flow sensor includes a control module, a main flow channel, and two identical measurement channels, wherein the first measurement channel directly communicates with the main flow channel; and the second measurement channel communicates with the main flow channel through an electromagnetic valve. The first measurement channel is provided with the first MEMS thermal flow sensing chip, and the second measurement channel is provided with the second MEMS thermal flow sensing chip, wherein the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip are the same MEMS thermal flow sensing chip. The control module is connected with the electromagnetic valve, the first MEMS thermal flow sensing chip, and the second MEMS thermal flow sensing chip, and is provided with a measurement model of the thermal flow sensor and a double-channel initial relationship model. The control module controls the closing of the electromagnetic valve to perform a normal working mode and a correction mode. In the normal working mode, the control module controls the closing of the electromagnetic valve, and performs flow measurement according to the real-time temperature difference signal of the first MEMS thermal flow sensing chip and the measurement model. In the correction mode, the control module controls the opening of the electromagnetic valve, and respectively obtains the real-time temperature difference signals of the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip, and corrects the measurement model of the thermal flow sensor based on the real-time temperature difference signals of the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip and the double-channel initial relationship model.

5. The self-correcting thermal flow sensor of claim 4, wherein: The measurement model of the thermal flow sensor is The double-channel initial relationship model of the thermal flow sensor is: wherein Q m_1 is the total flow of the gas meter when the first MEMS thermal flow sensing chip acts alone; f is the flow ratio of the measuring flow channel to the main flow channel; K is the sensitivity c of the MEMS thermal flow sensing chip p Cf is the heat capacity of the fluid; ΔT a T is the temperature difference obtained by the first MEMS thermal flow sensing chip when the standard gas passes through; T 1标 T is the temperature difference obtained by the first MEMS thermal flow sensing chip when the standard gas passes through; T a The corresponding signal voltage, that is, the real-time temperature difference signal of the first MEMS thermal flow sensing chip when the standard gas passes through; T 2标 is the real-time temperature difference signal of the second MEMS thermal flow sensing chip when the calibration gas passes through; x1 and x2 are temperature difference values of the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip at a unit voltage, respectively, is the initial relationship of the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip, i.e., the dual-channel initial relationship.

6. A self-correcting thermal flow sensor according to claim 5, wherein, The measurement model of the thermal flow sensor is corrected based on the real-time temperature difference signals of the first MEMS thermal flow sensing chip and the second MEMS thermal flow sensing chip and the double-channel initial relationship model, including: According to the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensing chip in the field correction stage, the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensing chip in the field correction stage, and the double-channel initial relationship model, a correction coefficient k is obtained, and an expression of k is: wherein, T 1实 represents the temperature difference signal voltage measured in real time by the first MEMS thermal flow sensor chip in the field correction stage; T 2实 represents the temperature difference signal voltage measured in real time by the second MEMS thermal flow sensor chip in the field correction stage; The correction coefficient is substituted into the measurement model of the thermal flow sensor to obtain a corrected measurement model:

7. A thermal mass gas meter, comprising an air inlet, an air outlet, a thermal flow sensor, an air bag and a housing, wherein the thermal flow sensor is the self-correcting thermal flow sensor according to any one of claims 4-6.

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