Mass flow meter

Abstract

The utility model proposes a mass flow meter, comprising a flow sensor, a temperature detection circuit, a flow detection circuit, a temperature sensor, a main control circuit and an adjustment circuit. The main control circuit determines the temperature and flow of a fluid through the temperature detection circuit and the flow detection circuit, and outputs an adjustment signal of corresponding size according to the ambient temperature detected by the temperature sensor. The adjustment circuit adjusts two heating resistors inside the flow sensor according to the adjustment signal, so that the current signal of the heating resistor changes in a positive correlation with the ambient temperature, so that the difference between the temperature of the heating resistor and the ambient temperature is within a preset temperature range, thereby realizing adaptive adjustment of the temperature of the heating resistor and improving the sensitivity and response speed of the mass flow meter.

Description

Technical Field

[0001] The utility model belongs to the technical field of mass flowmeters, in particular to a mass flowmeter. Background Art

[0002] As an instrument for measuring and controlling fluid flow, thermal MFC is widely used in semiconductor manufacturing, biopharmaceuticals, environmental monitoring and other fields that require precise control of fluid flow.

[0003] In the existing thermal MFC flow sensing technology, the core component is a group of heating resistors that provide a heat source higher than the environment. When the gas flow increases, heat is carried from the upstream resistor element to the downstream resistor element, thereby forming a temperature or power difference between the upstream and downstream resistor elements. The difference in this value is used for calculation to obtain the current gas mass flow rate passing through the sensor.

[0004] The operating environment of MFC is usually limited to 15℃~60℃, and after calibration, the flow accuracy cannot be guaranteed when the ambient temperature changes beyond a certain range. This is because the sensor sensitivity of thermal MFC is greatly affected by the difference between the working temperature of the resistance wire and the ambient temperature. When the ambient temperature changes greatly, since the heating temperature or power of the flow sensor is relatively fixed, the sensitivity and response speed of the flow sensor will deteriorate, and it cannot meet the requirements of high-precision scenarios. Utility Model Content

[0005] The utility model aims to provide a mass flow meter, aiming to solve the problems of low sensitivity and low response speed of traditional mass flow meters when the temperature changes.

[0006] A first aspect of an embodiment of the utility model provides a mass flow meter, comprising:

[0007] A flow sensor, wherein the flow sensor comprises two heating resistors, the two heating resistors are arranged at intervals along the flow direction of the fluid, and the flow sensor is used to detect the temperature or power of the two heating resistors and output a detection signal;

[0008] A temperature detection circuit connected to the flow sensor, the temperature detection circuit is used to determine the temperature of the fluid according to the detection signal and output a first temperature detection signal;

[0009] A flow detection circuit connected to the flow sensor, the flow detection circuit being used to determine the flow rate of the fluid according to the detection signal and output a flow detection signal;

[0010] The temperature sensor is used to detect the ambient temperature and output a second temperature detection signal;

[0011] a main control circuit, connected to the temperature detection circuit, the flow detection circuit and the ambient temperature sensor respectively, the main control circuit being used to determine the temperature and flow of the fluid according to the first temperature detection signal and the flow detection signal, and to output an adjustment signal triggered by the second temperature detection signal;

[0012] The adjustment circuit is connected to the flow sensor and the main control circuit respectively. The adjustment circuit is triggered by the adjustment signal to output a current signal of corresponding magnitude to the flow sensor to adjust the difference between the temperature of the two heating resistors and the ambient temperature within a preset temperature range. The current signal changes in a positive correlation with the ambient temperature.

[0013] Optionally, the adjustment circuit includes:

[0014] an output circuit, connected to the flow sensor, for converting the received voltage regulation signal into the current signal, wherein the current signal changes in a positive correlation with the voltage regulation signal;

[0015] A current detection circuit, connected to the output circuit, for detecting the current magnitude and outputting a current detection signal;

[0016] The gain adjustment circuit is connected to the main control circuit, the current detection circuit and the output circuit respectively. The gain adjustment circuit is used to amplify the voltage difference between the adjustment signal and the current detection signal, and output the voltage regulation signal.

[0017] Optionally, the output circuit comprises a voltage-controlled current source.

[0018] Optionally, the current detection circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor and a first operational amplifier;

[0019] The first end of the first resistor and the first end of the second resistor are connected to the output end of the output circuit, the second end of the first resistor and the first end of the third resistor are connected to the input end of the flow sensor, the second end of the second resistor and the first end of the fourth resistor are connected to the non-inverting input end of the first operational amplifier, the second end of the third resistor and the first end of the fifth resistor are connected to the inverting input end of the first operational amplifier, the second end of the fourth resistor is grounded, and the output end of the first operational amplifier and the second end of the fifth resistor are connected to form the output end of the current detection circuit.

[0020] Optionally, the gain adjustment circuit includes:

[0021] a subtractor circuit, wherein a first input end of the subtractor circuit is connected to an output end of the main control circuit, a second input end of the subtractor circuit is connected to an output end of the current detection circuit, and the subtractor circuit is used to calculate a voltage difference between the adjustment signal and the current detection signal, and output a voltage difference signal;

[0022] a signal amplifying circuit connected to the subtractor circuit, the signal amplifying circuit being used to amplify the pressure difference signal and output the amplified pressure difference signal;

[0023] The filter circuit is connected to the signal amplifying circuit and the output circuit respectively, and the filter circuit is used to filter the amplified pressure difference signal and output the voltage regulation signal.

[0024] Optionally, the subtractor circuit includes a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor and a second operational amplifier;

[0025] The first end of the sixth resistor constitutes the first input end of the subtractor circuit, the second end of the sixth resistor, the first end of the seventh resistor and the non-inverting input end of the second operational amplifier are connected, the second end of the seventh resistor is grounded, the first end of the eighth resistor constitutes the second input end of the subtractor circuit, the second end of the eighth resistor, the first end of the ninth resistor and the inverting input end of the operational amplifier are connected, and the output end of the operational amplifier and the second end of the ninth resistor are connected to constitute the output end of the subtractor circuit.

[0026] Optionally, the signal amplification circuit includes a third operational amplifier;

[0027] The non-inverting input terminal of the third operational amplifier constitutes the input terminal of the signal amplifying circuit, and the inverting input terminal of the third operational amplifier and the output terminal of the third operational amplifier are connected to constitute the output terminal of the signal amplifying circuit.

[0028] Optionally, the filtering circuit includes a tenth resistor and a capacitor;

[0029] The first end of the tenth resistor constitutes the input end of the filter circuit, the second end of the tenth resistor and the first end of the capacitor are connected to constitute the output end of the filter circuit, and the second end of the capacitor is grounded.

[0030] Optionally, the main control circuit includes:

[0031] an analog-to-digital conversion circuit, wherein the input end of the analog-to-digital conversion circuit is respectively connected to the temperature detection circuit, the flow detection circuit and the ambient temperature sensor, the output end of the analog-to-digital conversion circuit is connected to the main control circuit, and the analog-to-digital conversion circuit is used to perform analog-to-digital conversion on the first temperature detection signal, the flow detection signal and the second temperature detection signal and output the analog-to-digital conversion;

[0032] A main controller is connected to the analog-to-digital conversion circuit and the adjustment circuit. The main controller is used to determine the temperature and flow rate of the fluid based on the first temperature detection signal and the flow detection signal of the digital signal, and to output an adjustment signal triggered by the second temperature detection signal of the digital signal.

[0033] Optionally, the adjustment circuit further includes:

[0034] The digital-to-analog conversion circuit is connected between the gain adjustment circuit and the output circuit. The digital-to-analog conversion circuit is used to perform digital-to-analog conversion on the voltage adjustment signal output by the gain adjustment circuit, and output the voltage adjustment signal as an analog signal to the output circuit.

[0035] Compared with the prior art, the beneficial effects of the embodiments of the utility model are as follows: the above-mentioned mass flow meter includes a flow sensor, a temperature detection circuit, a flow detection circuit, a temperature sensor, a main control circuit and an adjustment circuit. The main control circuit determines the temperature and flow of the fluid through the temperature detection circuit and the flow detection circuit, and outputs an adjustment signal of corresponding size according to the ambient temperature detected by the temperature sensor. The adjustment circuit adjusts the two heating resistors inside the flow sensor according to the adjustment signal, so that the current signal of the heating resistor changes in a positive correlation with the ambient temperature, so that the difference between the temperature of the heating resistor and the ambient temperature is within a preset temperature range, thereby realizing adaptive adjustment of the temperature of the heating resistor and improving the sensitivity and response speed of the mass flow meter. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0037] Figure 1 A first structural schematic diagram of a mass flow meter provided in an embodiment of the utility model;

[0038] Figure 2 A second structural schematic diagram of a mass flow meter provided in an embodiment of the utility model;

[0039] Figure 3 A third structural schematic diagram of a mass flow meter provided in an embodiment of the utility model;

[0040] Figure 4 A fourth structural schematic diagram of a mass flow meter provided in an embodiment of the utility model;

[0041] Figure 5 A circuit diagram of a current detection circuit provided by an embodiment of the utility model;

[0042] Figure 6 A fifth structural schematic diagram of a mass flow meter provided in an embodiment of the utility model;

[0043] Figure 7 A schematic diagram of the circuit structure of a gain adjustment circuit provided in an embodiment of the utility model. DETAILED DESCRIPTION

[0044] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0046] The first aspect of an embodiment of the utility model proposes a mass flow meter 1, which can be applied to a variety of different fields and is used to measure the flow rate of a fluid 2, which can be a liquid, a gas, etc. For example, it is applied to the field of semiconductor manufacturing. In the semiconductor manufacturing process, precise control of the gas flow rate is crucial to ensuring the consistency and quality of the process. The flow sensor 10 can be used to monitor and control the flow in the gas delivery system to ensure high accuracy and low power consumption within different flow ranges.

[0047] It can also be applied to the biopharmaceutical field. In the biopharmaceutical process, the precise control of liquid and gas flow has an important impact on the production process and product quality. The mass flow meter 1 can be used in pharmaceutical equipment to monitor and adjust the flow of drug solution and culture medium in real time to ensure the stability and reliability of the process.

[0048] It can also be applied to the field of environmental monitoring. The mass flow meter 1 is used to monitor air quality, greenhouse gas emissions, etc. The mass flow meter 1 can be installed in environmental monitoring equipment to monitor the concentration of pollutants in the air in real time and provide high-precision data to support environmental protection and governance.

[0049] It can also be applied to the field of industrial automation. In industrial automation systems, the precise control of gas and liquid flow has a direct impact on the efficiency of the production line and product quality. The mass flow meter 1 can be integrated into the automation control system for real-time monitoring and adjustment of flow to ensure efficient operation of the production process.

[0050] It can also be used in the field of HVAC systems (heating, ventilation and air conditioning), which require precise control of the flow of air and refrigerant to achieve energy saving and a comfortable environment. Mass flow meters 1 are used to monitor and control air flow and refrigerant flow to optimize system performance and reduce energy consumption.

[0051] It can also be applied to the automotive industry. In automobile engines and emission control systems, the mass flow meter 1 is used to monitor the flow of fuel and exhaust gas. The mass flow meter 1 can be used in the intake and exhaust systems of automobile engines to provide real-time flow data, optimize engine performance and reduce emissions.

[0052] It can also be applied to the chemical industry. The chemical production process requires precise control of gas and liquid flow rates to ensure the stability of reaction conditions and product quality. The mass flow meter 1 can be used in chemical equipment to monitor and adjust the flow rate in real time to improve production efficiency and safety.

[0053] It can also be applied to the field of laboratory research. In scientific research experiments, precise control of gas and liquid flow is crucial to the accuracy and repeatability of experimental results. The mass flow meter 1 can be used in laboratory equipment to provide high-precision flow measurement and control to support various scientific research.

[0054] Among them, Figure 1 As shown, in this embodiment, the mass flow meter 1 includes:

[0055] The flow sensor 10 includes two heating resistors, which are arranged at intervals along the flow direction of the fluid 2. The flow sensor 10 is used to detect the temperature or power of the two heating resistors and output a detection signal;

[0056] The temperature detection circuit 20 is connected to the flow sensor 10, and is used to determine the temperature of the fluid 2 according to the detection signal and output a first temperature detection signal;

[0057] A flow detection circuit 30 is connected to the flow sensor 10, and is used to determine the flow rate of the fluid 2 according to the detection signal and output a flow detection signal;

[0058] The temperature sensor 50 is used to detect the ambient temperature and output a second temperature detection signal;

[0059] The main control circuit 60 is connected to the temperature detection circuit 20, the flow detection circuit 30 and the ambient temperature sensor 50 respectively. The main control circuit 60 is used to determine the temperature and flow rate of the fluid 2 according to the first temperature detection signal and the flow detection signal, and to output an adjustment signal triggered by the second temperature detection signal;

[0060] The adjustment circuit 40 is connected to the flow sensor 10 and the main control circuit 60 respectively. The adjustment circuit 40 is triggered by the adjustment signal to output a current signal of corresponding size to the flow sensor 10 to adjust the difference between the temperature of the two heating resistors and the ambient temperature within a preset temperature range. The current signal changes in a positive correlation with the ambient temperature.

[0061] In this embodiment, the flow sensor 10 includes two heating resistors, which can be defined as an upstream heating resistor 11 and a downstream heating resistor 12 according to their installation positions. The upstream heating resistor 11 and the downstream heating resistor 12 are arranged at intervals along the flow direction of the fluid 2. The upstream heating resistor 11 is closer to the inflow position of the fluid 2 to be measured than the downstream heating resistor 12, and the downstream heating resistor 12 is closer to the outflow position of the fluid 2 to be measured than the upstream heating resistor 11. The adjustment circuit 40 serves as a power output module, which is directly or indirectly connected to the two heating resistors and outputs current signals. After receiving the current signals, the two heating resistors are heated and generate heat.

[0062] The temperature of the heating resistor is greater than the ambient temperature. When the ambient temperature remains unchanged and the gas flow rate increases, the heat of the upstream heating resistor 11 is transferred to the downstream heating resistor 12 through the fluid 2, and the temperature or power of the downstream heating resistor 12 increases, thereby forming a temperature difference or power difference between the two heating resistors. The flow sensor 10 detects the temperature or power of the two heating resistors in real time. When the temperature or power of the two heating resistors changes, the detection signal generated by the flow sensor 10 changes, and the detection signal is output to the temperature detection circuit 20 and the flow detection circuit 30. The temperature detection circuit 20 processes the detection signal and determines the temperature of the fluid 2, and generates a first temperature detection signal corresponding to the temperature of the fluid 2 to the main control circuit 60. The main control circuit 60 determines the temperature of the current heating resistor based on the received first temperature detection signal. The main control circuit 60 can also perform closed-loop temperature control based on the temperature of the current heating resistor and the preset temperature, and output an adjustment signal to the adjustment circuit 40 to adjust the output current signal size so that the temperature of the heating resistor is maintained at the preset temperature.

[0063] At the same time, the flow detection circuit 30 determines the flow of the fluid 2 according to the detection signal output by the flow sensor 10, and outputs the flow detection signal to the main control circuit 60. The main control circuit 60 determines the flow of the fluid 2 and displays or plays the current flow data of the fluid 2.

[0064] The temperature sensor 50 detects the current ambient temperature in real time. When the ambient temperature rises, the temperature of the fluid 2 itself rises. When it exceeds the temperature of the current heating resistor, when the flow rate of the fluid 2 changes, the measured temperature difference or power difference is affected by the temperature of the fluid 2, resulting in abnormal measurement of the fluid 2, and the sensitivity and response speed of the mass flowmeter 1 are reduced. At this time, the main control circuit 60 adjusts the output adjustment signal size according to the ambient temperature, and the adjustment signal triggers the adjustment circuit 40 to increase the output current signal, thereby increasing the operating temperature of the heating resistor, so that the temperature of the heating resistor exceeds the temperature of the fluid 2 and forms a preset temperature difference with the ambient temperature. When the flow rate of the fluid 2 changes, it is not affected by the current ambient temperature, thereby improving the sensitivity and response speed of the mass flowmeter 1.

[0065] When the ambient temperature drops, the temperature of the fluid 2 itself drops, and most of the heat of the heating resistor will be absorbed by the fluid 2. When the flow rate of the fluid 2 changes, the heat generated by the upstream heating resistor 11 may not be transferred to the downstream heating resistor 12, resulting in inaccurate measurement, and the power consumption of the mass flowmeter 1 increases and the service life decreases. At this time, the main control circuit 60 adjusts the size of the adjustment signal output according to the ambient temperature. The adjustment signal triggers the adjustment circuit 40 to reduce the output current signal and reduce the temperature of the heating resistor, so that the temperature of the heating resistor forms a preset temperature difference with the ambient temperature. When the flow rate of the fluid 2 changes, it is not affected by the current ambient temperature, thereby reducing the power consumption of the mass flowmeter 1 and increasing the service life of the mass flowmeter 1.

[0066] At the same time, the main control circuit 60 performs closed-loop control on the required temperature of the heating resistor through the temperature detection circuit 20 to improve the temperature control accuracy.

[0067] The mass flowmeter 1 adaptively adjusts the output current signal according to the ambient temperature and changes the temperature of the heating resistor. The sensitivity and response speed of the mass flowmeter 1 are not affected by the ambient temperature. The operating temperature of the heating resistor of the mass flowmeter 1 is quickly detected, judged and adjusted by the adjustment circuit 40, thereby improving the ambient temperature adaptability range of the mass flowmeter 1 and expanding its potential application areas.

[0068] Among them, the temperature detection circuit 20 and the flow detection circuit 30 can use corresponding signal conversion circuits to convert the detection signals output by the flow sensor 10 respectively, and output the temperature detection signal representing the temperature of the heating resistor and the flow detection signal representing the flow of the fluid 2 to the main control circuit 60, so as to determine the temperature of the heating resistor and the flow of the fluid 2.

[0069] The main control circuit 60 may adopt a corresponding controller, processor, etc. In an optional embodiment, as shown in FIG. Figure 2 As shown, the main control circuit 60 includes:

[0070] The analog-to-digital conversion circuit 61, the input end of the analog-to-digital conversion circuit 61 is respectively connected to the temperature detection circuit 20, the flow detection circuit 30 and the ambient temperature sensor 50, the output end of the analog-to-digital conversion circuit 61 is connected to the main control circuit 60, and the analog-to-digital conversion circuit 61 is used to perform analog-to-digital conversion on the first temperature detection signal, the flow detection signal and the second temperature detection signal and output them;

[0071] The main controller 62 is connected to the analog-to-digital conversion circuit 61 and the adjustment circuit 40. The main controller 62 is used to determine the temperature and flow rate of the fluid 2 according to the first temperature detection signal and the flow detection signal of the digital signal, and to output the adjustment signal triggered by the second temperature detection signal of the digital signal.

[0072] In this embodiment, the analog-to-digital conversion circuit 61 performs analog-to-digital conversion on different signals output by the temperature detection circuit 20, the flow detection circuit 30 and the temperature sensor 50, and outputs each signal of the digital signal type to the main controller 62. The main controller 62 can adopt MCU, CPU, etc. The main controller 62 executes the function of the main control circuit 60, and determines the temperature and flow of the fluid 2 according to the received signals, and outputs an adjustment signal of a corresponding size to the adjustment circuit 40, thereby correspondingly changing the output current of the adjustment circuit 40 and the temperature of the heating resistor, thereby realizing adaptive temperature regulation.

[0073] The adjustment circuit 40 may adopt a corresponding power output circuit 41, a gain adjustment circuit 43, etc., and adjust the current signal and the heating temperature of the heating resistor by changing the output power or current of the power output circuit 41. In an optional embodiment, the adjustment circuit 40 includes:

[0074] The output circuit 41 is connected to the flow sensor 10 and is used to convert the received voltage regulation signal into a current signal, and the current signal changes in a positive correlation with the voltage regulation signal;

[0075] The current detection circuit 42 is connected to the output circuit 41 and is used to detect the current and output a current detection signal;

[0076] The gain adjustment circuit 43 is connected to the main control circuit 60, the current detection circuit 42 and the output circuit 41 respectively. The gain adjustment circuit 43 is used to amplify the voltage difference between the adjustment signal and the current detection signal, and output a voltage adjustment signal.

[0077] In this embodiment, in the initial state, the main control circuit 60 outputs an adjustment signal according to the current ambient temperature. The adjustment signal is a voltage signal. The voltage signal is amplified by the gain adjustment circuit 43 and outputs the voltage adjustment signal to the output circuit 41. The output circuit 41 converts the received voltage adjustment signal into a current signal. The current signal triggers the heating resistor to heat. When the ambient temperature remains unchanged and the gas flow increases, the heat of the upstream heating resistor 11 is transferred to the downstream heating resistor 12 through the fluid 2. The temperature or power of the downstream heating resistor 12 rises, thereby forming a temperature difference or power difference between the two heating resistors. The flow sensor 10 detects the temperature or power of the two heating resistors in real time. When the two heating resistors are When the temperature or power of the resistor changes, the detection signal generated by the flow sensor 10 changes, and the detection signal is output to the temperature detection circuit 20 and the flow detection circuit 30. The temperature detection circuit 20 processes the detection signal and determines the temperature of the fluid 2, and generates a first temperature detection signal corresponding to the temperature of the fluid 2 to the main control circuit 60. The main control circuit 60 determines the current temperature of the heating resistor based on the received first temperature detection signal. The main control circuit 60 can also perform closed-loop temperature control based on the current temperature of the heating resistor and the preset temperature, and output an adjustment signal to the gain adjustment circuit 43 to adjust the output current signal through the output circuit 41 so that the temperature of the heating resistor is maintained at the preset temperature.

[0078] At the same time, the flow detection circuit 30 determines the flow of the fluid 2 according to the detection signal output by the flow sensor 10, and outputs the flow detection signal to the main control circuit 60. The main control circuit 60 determines the flow of the fluid 2 and displays or plays the current flow data of the fluid 2.

[0079] The current detection circuit 42 detects the output current of the current output circuit 41, and outputs the current detection signal to the gain adjustment circuit 43 and the main control circuit 60. The main control circuit 60 performs a closed-loop output of the current signal according to the current detection signal, and in a stable state, the magnitude of the current signal remains unchanged, that is, the magnitude of the current detection signal output to the gain adjustment circuit 43 remains unchanged, and finally the magnitude of the voltage adjustment signal output to the output circuit 41 remains unchanged.

[0080] When the ambient temperature rises, the temperature of the fluid 2 itself rises. When it exceeds the temperature of the current heating resistor, when the flow rate of the fluid 2 changes, the measured temperature difference or power difference is affected by the temperature of the fluid 2, resulting in abnormal measurement of the fluid 2. The sensitivity and response speed of the mass flowmeter 1 are reduced. At this time, the main control circuit 60 increases the output adjustment signal according to the ambient temperature, the voltage difference input by the gain adjustment circuit 43 becomes larger, and the output voltage adjustment signal becomes larger. Correspondingly, the current signal of the output circuit 41 becomes larger, thereby increasing the operating temperature of the heating resistor, so that the temperature of the heating resistor exceeds the temperature of the fluid 2 and forms a preset temperature difference with the ambient temperature. When the flow rate of the fluid 2 changes, it is not affected by the current ambient temperature, thereby improving the sensitivity and response speed of the mass flowmeter 1.

[0081] When the current signal becomes larger, the current detection signal becomes larger, and the voltage difference of the gain adjustment circuit 43 becomes smaller. At this time, the main control circuit 60 increases the size of the output adjustment signal to ensure that the output voltage difference is maintained at the preset voltage difference, so that the output current signal is maintained at the increased preset current.

[0082] When the ambient temperature drops, the temperature of the fluid 2 itself drops, and most of the heat of the heating resistor will be absorbed by the fluid 2. When the flow rate of the fluid 2 changes, the heat generated by the upstream heating resistor 11 may not be transferred to the downstream heating resistor 12, resulting in inaccurate measurement, and the power consumption of the mass flow meter 1 increases and the service life decreases. At this time, the main control circuit 60 reduces the output adjustment signal according to the ambient temperature, the voltage difference input by the gain adjustment circuit 43 becomes smaller, and the output voltage adjustment signal becomes smaller. Correspondingly, the current signal of the output circuit 41 becomes smaller, thereby reducing the working temperature of the heating resistor, so that the temperature of the heating resistor forms a preset temperature difference with the ambient temperature. When the flow rate of the fluid 2 changes, it is not affected by the current ambient temperature, thereby reducing the power consumption of the mass flow meter 1 and increasing the service life of the mass flow meter 1.

[0083] When the current signal becomes smaller, the current detection signal becomes smaller, and the voltage difference of the gain adjustment circuit 43 becomes larger. At this time, the main control circuit 60 reduces the size of the output adjustment signal to ensure that the output voltage difference is maintained at the preset voltage difference, so that the output current signal is maintained at the increased preset current.

[0084] At the same time, when the ambient temperature rises or falls rapidly, the current detection circuit 42 directly acts on the gain adjustment circuit 43. When the ambient temperature rises rapidly, the temperature difference between the heating resistor and the ambient temperature decreases rapidly, and the current detection circuit 42 detects a rapidly decreasing current signal. At this time, the current detection signal decreases, the voltage difference of the gain adjustment circuit 43 increases, the voltage regulation signal received by the output circuit 41 increases, and the output current signal increases, thereby ensuring the sensitivity and response speed of the mass flowmeter 1.

[0085] When the ambient temperature drops rapidly, the temperature difference between the heating resistor and the ambient temperature rises rapidly, and the current detection circuit 42 detects a rapidly rising current signal. At this time, the current detection signal becomes larger, the voltage difference of the gain adjustment circuit 43 becomes smaller, the voltage adjustment signal received by the output circuit 41 becomes smaller, and the output current signal becomes smaller, thereby ensuring that the sensitivity of the mass flowmeter 1 is maintained within the preset range.

[0086] Among them, the output circuit 41 performs voltage-to-voltage conversion and can use power tubes, current sources, etc. In an optional embodiment, the output circuit 41 includes a voltage-controlled current source, which is used to adjust the current of the flow sensor 10, thereby changing the power of the heating resistor and using the sensitivity and response speed requirements under different ambient temperature scenarios. The voltage-controlled current source is a type of current source that can control its own output current by input voltage.

[0087] Since the voltage-controlled current source receives an analog signal, and the signal output by the gain adjustment circuit 43 is a digital signal, in order to achieve signal matching, in an optional embodiment, as Figure 4 As shown, optionally, the adjustment circuit 40 further includes:

[0088] The digital-to-analog conversion circuit 44 is connected between the gain adjustment circuit 43 and the output circuit 41 . The digital-to-analog conversion circuit 44 is used to perform digital-to-analog conversion on the voltage adjustment signal output by the gain adjustment circuit 43 , and output the voltage adjustment signal of the analog signal to the output circuit 41 .

[0089] The current detection circuit 42 may be a current transformer, a sampling resistor, etc. In an optional embodiment, Figure 5 As shown, the current detection circuit 42 includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5 and a first operational amplifier U1;

[0090] The first end of the first resistor R1, the first end of the second resistor R2, and the output end of the output circuit 41 are connected, the second end of the first resistor R1, the first end of the third resistor R3, and the input end of the flow sensor 10 are connected, the second end of the second resistor R2, the first end of the fourth resistor R4, and the non-inverting input end of the first operational amplifier U1 are connected, the second end of the third resistor R3, the first end of the fifth resistor R5, and the inverting input end of the first operational amplifier U1 are connected, the second end of the fourth resistor R4 is grounded, and the output end of the first operational amplifier U1 and the second end of the fifth resistor R5 are connected to form the output end of the current detection circuit 42.

[0091] In this embodiment, the first resistor R1 is a sampling resistor, which converts the output current signal into a voltage signal. The second resistor R2, the third resistor R3, the fifth resistor R5 and the first operational amplifier U1 constitute a signal amplification unit, and amplify the voltage signal, thereby achieving accurate measurement of the current signal.

[0092] The gain adjustment circuit 43 realizes the difference operation of the two signals and the signal amplification function, and can use corresponding comparison circuits and amplifier circuits. In an optional embodiment, as shown in FIG. Figure 6 As shown, the gain adjustment circuit 43 includes:

[0093] A subtractor circuit 431, wherein a first input terminal of the subtractor circuit 431 is connected to an output terminal of the main control circuit 60, and a second input terminal of the subtractor circuit 431 is connected to an output terminal of the current detection circuit 42, and the subtractor circuit 431 is used to calculate a voltage difference between the adjustment signal and the current detection signal, and output a voltage difference signal;

[0094] The signal amplifier circuit 432 is connected to the subtractor circuit 431, and the signal amplifier circuit 432 is used to amplify the pressure difference signal and output the amplified pressure difference signal;

[0095] The filter circuit 433 is connected to the signal amplifying circuit 432 and the output circuit 41 respectively. The filter circuit 433 is used to filter the amplified voltage difference signal and output a voltage regulation signal.

[0096] In this embodiment, the subtractor circuit 431 has two input signals, which are the output voltage signals of the main control circuit 60 and the current detection circuit 42 respectively. The subtractor circuit 431 performs a subtraction operation on the two input signals. The output signal of the subtractor circuit 431 is the difference between the adjustment signal output by the main control circuit 60 and the current detection signal output by the current detection circuit 42. When the adjustment signal increases or decreases and the current detection signal remains unchanged, the output of the subtractor circuit 431 increases or decreases. When the adjustment signal remains unchanged and the current detection signal becomes larger or smaller, the output of the subtractor circuit 431 decreases or increases. The output signal of the subtractor circuit 431 is amplified by the signal amplification circuit 432. The amplified voltage signal is converted into a voltage regulation signal by the filter circuit 433 and output to the output circuit 41 to be converted into a current signal.

[0097] The signal amplifier circuit 432 is used to amplify the signal to improve the circuit load capacity, and the filter circuit 433 is used to modulate the frequency of the output signal to avoid high-frequency oscillation of the circuit.

[0098] The subtractor circuit 431 can be a comparator, a subtractor, etc., the signal amplifier circuit 432 can be a transistor amplifier circuit, an operational amplifier, etc., and the filter circuit 433 can be a low-pass filter circuit 433. In an optional embodiment, as Figure 7 As shown, the subtractor circuit 431 includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9 and a second operational amplifier U2;

[0099] The first end of the sixth resistor R6 constitutes the first input end of the subtractor circuit 431, the second end of the sixth resistor R6, the first end of the seventh resistor R7 and the non-inverting input end of the second operational amplifier U2 are connected, the second end of the seventh resistor R7 is grounded, the first end of the eighth resistor R8 constitutes the second input end of the subtractor circuit 431, the second end of the eighth resistor R8, the first end of the ninth resistor R9 and the inverting input end of the operational amplifier are connected, and the output end of the operational amplifier and the second end of the ninth resistor R9 are connected to constitute the output end of the subtractor circuit 431.

[0100] Optionally, the signal amplification circuit 432 includes a third operational amplifier U3;

[0101] The non-inverting input terminal of the third operational amplifier U3 constitutes the input terminal of the signal amplifying circuit 432 , and the inverting input terminal of the third operational amplifier U3 and the output terminal of the third operational amplifier U3 are connected to constitute the output terminal of the signal amplifying circuit 432 .

[0102] Optionally, the filter circuit 433 includes a tenth resistor R10 and a capacitor C1;

[0103] The first end of the tenth resistor R10 constitutes the input end of the filter circuit 433 , the second end of the tenth resistor R10 and the first end of the capacitor C1 are connected to constitute the output end of the filter circuit 433 , and the second end of the capacitor C1 is grounded.

[0104] In this embodiment, the adjustment signal and the current detection signal of the main control circuit 60 are subtracted in the second operational amplifier U2, and a voltage difference signal is output. The third operational amplifier U3 constitutes a voltage follower and amplifies the voltage difference signal. The tenth resistor R10 and the capacitor C1 constitute a low-pass filter circuit 433. The amplified voltage difference signal is low-pass filtered by the low-pass filter circuit 433 to eliminate high-frequency noise.

[0105] Compared with the prior art, the beneficial effects of the embodiment of the utility model are as follows: the above-mentioned mass flowmeter 1 includes a flow sensor 10, a temperature detection circuit 20, a flow detection circuit 30, a temperature sensor 50, a main control circuit 60 and an adjustment circuit 40. The main control circuit 60 determines the temperature and flow of the fluid 2 through the temperature detection circuit 20 and the flow detection circuit 30, and outputs an adjustment signal of corresponding size according to the ambient temperature detected by the temperature sensor 50. The adjustment circuit 40 adjusts the two heating resistors inside the flow sensor 10 according to the adjustment signal, so that the current signal of the heating resistor changes in a positive correlation with the ambient temperature, so that the difference between the temperature of the heating resistor and the ambient temperature is within a preset temperature range, thereby realizing adaptive adjustment of the temperature of the heating resistor and improving the sensitivity and response speed of the mass flowmeter 1.

[0106] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A mass flow meter, characterized in that: include: A flow sensor, wherein the flow sensor comprises two heating resistors, the two heating resistors are arranged at intervals along the flow direction of the fluid, and the flow sensor is used to detect the temperature or power of the two heating resistors and output a detection signal; A temperature detection circuit connected to the flow sensor, the temperature detection circuit being used to determine the temperature of the fluid according to the detection signal and output a first temperature detection signal; A flow detection circuit connected to the flow sensor, the flow detection circuit being used to determine the flow rate of the fluid according to the detection signal and output a flow detection signal; The temperature sensor is used to detect the ambient temperature and output a second temperature detection signal; a main control circuit, connected to the temperature detection circuit, the flow detection circuit and the temperature sensor respectively, the main control circuit being used to determine the temperature and flow of the fluid according to the first temperature detection signal and the flow detection signal, and to output an adjustment signal triggered by the second temperature detection signal; The adjustment circuit is connected to the flow sensor and the main control circuit respectively. The adjustment circuit is triggered by the adjustment signal to output a current signal of corresponding magnitude to the flow sensor to adjust the difference between the temperature of the two heating resistors and the ambient temperature within a preset temperature range. The current signal changes in a positive correlation with the ambient temperature.

2. The mass flow meter according to claim 1, characterized in that The adjustment circuit comprises: an output circuit, connected to the flow sensor, for converting the received voltage regulation signal into the current signal, wherein the current signal changes in a positive correlation with the voltage regulation signal; A current detection circuit, connected to the output circuit, for detecting the current magnitude and outputting a current detection signal; The gain adjustment circuit is connected to the main control circuit, the current detection circuit and the output circuit respectively. The gain adjustment circuit is used to amplify the voltage difference between the adjustment signal and the current detection signal, and output the voltage regulation signal.

3. The mass flow meter according to claim 2, characterized in that The output circuit includes a voltage-controlled current source.

4. The mass flow meter according to claim 2, characterized in that The current detection circuit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor and a first operational amplifier; The first end of the first resistor and the first end of the second resistor are connected to the output end of the output circuit, the second end of the first resistor and the first end of the third resistor are connected to the input end of the flow sensor, the second end of the second resistor and the first end of the fourth resistor are connected to the non-inverting input end of the first operational amplifier, the second end of the third resistor and the first end of the fifth resistor are connected to the inverting input end of the first operational amplifier, the second end of the fourth resistor is grounded, and the output end of the first operational amplifier and the second end of the fifth resistor are connected to form the output end of the current detection circuit.

5. The mass flow meter according to claim 2, characterized in that: The gain adjustment circuit comprises: a subtractor circuit, wherein a first input end of the subtractor circuit is connected to an output end of the main control circuit, a second input end of the subtractor circuit is connected to an output end of the current detection circuit, and the subtractor circuit is used to calculate a voltage difference between the adjustment signal and the current detection signal, and output a voltage difference signal; a signal amplifying circuit connected to the subtractor circuit, the signal amplifying circuit being used to amplify the pressure difference signal and output the amplified pressure difference signal; The filter circuit is connected to the signal amplifying circuit and the output circuit respectively, and the filter circuit is used to filter the amplified pressure difference signal and output the voltage regulation signal.

6. The mass flow meter according to claim 5, characterized in that The subtractor circuit includes a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor and a second operational amplifier; The first end of the sixth resistor constitutes the first input end of the subtractor circuit, the second end of the sixth resistor, the first end of the seventh resistor and the non-inverting input end of the second operational amplifier are connected, the second end of the seventh resistor is grounded, the first end of the eighth resistor constitutes the second input end of the subtractor circuit, the second end of the eighth resistor, the first end of the ninth resistor and the inverting input end of the operational amplifier are connected, and the output end of the operational amplifier and the second end of the ninth resistor are connected to constitute the output end of the subtractor circuit.

7. The mass flow meter according to claim 5, characterized in that The signal amplification circuit comprises a third operational amplifier; The non-inverting input terminal of the third operational amplifier constitutes the input terminal of the signal amplifying circuit, and the inverting input terminal of the third operational amplifier and the output terminal of the third operational amplifier are connected to constitute the output terminal of the signal amplifying circuit.

8. The mass flow meter according to claim 5, characterized in that The filtering circuit includes a tenth resistor and a capacitor; The first end of the tenth resistor constitutes the input end of the filter circuit, the second end of the tenth resistor and the first end of the capacitor are connected to constitute the output end of the filter circuit, and the second end of the capacitor is grounded.

9. The mass flow meter according to claim 1, characterized in that The main control circuit comprises: an analog-to-digital conversion circuit, wherein the input end of the analog-to-digital conversion circuit is respectively connected to the temperature detection circuit, the flow detection circuit and the ambient temperature sensor, the output end of the analog-to-digital conversion circuit is connected to the main control circuit, and the analog-to-digital conversion circuit is used to perform analog-to-digital conversion on the first temperature detection signal, the flow detection signal and the second temperature detection signal and output the analog-to-digital conversion; A main controller is connected to the analog-to-digital conversion circuit and the adjustment circuit. The main controller is used to determine the temperature and flow rate of the fluid based on the first temperature detection signal and the flow detection signal of the digital signal, and to output an adjustment signal triggered by the second temperature detection signal of the digital signal.

10. The mass flow meter according to claim 2, characterized in that: The adjustment circuit further includes: The digital-to-analog conversion circuit is connected between the gain adjustment circuit and the output circuit. The digital-to-analog conversion circuit is used to perform digital-to-analog conversion on the voltage adjustment signal output by the gain adjustment circuit, and output the voltage adjustment signal as an analog signal to the output circuit.

Images