Constant-current driving thermal type gas mass flow meter

Abstract

The invention provides a constant current driving thermal type gas mass flowmeter which is characterized in that a constant current is provided for an induction module through a constant current driving module, the induction module comprises a speed measuring resistor and a temperature measuring resistor, the speed measuring resistor is used for heating flowing gas, and the temperature measuring resistor is used for detecting the environment temperature of the gas; voltage sampling is conducted on the sensing module through the sampling module, sensing voltage and sampling voltage are obtained, the temperature difference between the speed measuring resistor and the temperature measuring resistor is determined through the signal processing module on the basis of the sensing voltage and the sampling voltage, and the mass flow of the gas is determined on the basis of the temperature difference and the preset temperature difference-mass flow relation. According to the mass flow meter provided by the invention, the constant current source is adopted to drive the sensing module, so that the heating current is still constant and the system is stable under the condition that the environment temperature fluctuates; meanwhile, complex feedback control is not needed, the circuit structure is simpler, and the system reliability is higher; flow change is reflected directly through the speed measuring resistor and the temperature measuring resistor, and the circuit is good in dynamic response characteristic and high in precision.

Description

Technical Field

[0001] This invention relates to the field of gas flow measurement technology, and in particular to a constant flow driven thermal gas mass flow meter. Background Technology

[0002] Thermal gas mass flow meters occupy a crucial strategic position in the flow measurement field, characterized by "high added value, solving specific pain points, and continuous growth." Based on King's Law, which states that there is a definite functional relationship between the heat carried away by a fluid and its mass flow rate, this technology is widely used in industrial process control, environmental monitoring, and energy metering due to its advantages such as direct measurement of mass flow rate and low pressure loss.

[0003] Currently, thermal flow meters mainly employ two operating modes: the constant temperature difference method and the constant power method. The constant temperature difference method, based on closed-loop feedback control, maintains a constant temperature difference between the speed-sensing resistor and the temperature-sensing resistor. It determines the mass flow rate by measuring the heating power required to maintain this constant temperature difference. While the constant temperature difference method has a fast response speed, its circuitry is complex, requiring real-time feedback adjustment, and its system stability is poor. The constant power method provides a constant power to the heating resistor and calculates the mass flow rate based on the temperature distribution changes caused by gas flow. The constant power method has a simple control method, but its sensor structure is complex and its manufacturing process requires high precision. Furthermore, the thermal isolation between the speed-sensing resistor and the heating zone can easily lead to temperature measurement deviations, and the temperature drift of the heating resistor itself can also cause changes in the actual heating power, further reducing measurement accuracy. Summary of the Invention

[0004] This invention provides a constant-flow driven thermal gas mass flow meter to solve the technical problems of thermal gas mass flow meters, such as complex design structure, poor stability, high manufacturing process and low measurement accuracy.

[0005] This invention provides a constant-flow driven thermal gas mass flow meter, comprising: The sensing module includes a speed-sensing resistor and a temperature-sensing resistor. The speed-sensing resistor heats the flowing gas, and the temperature-sensing resistor measures the ambient temperature of the gas. A constant current drive module is connected to the power supply terminal of the sensing module and is used to provide a constant current to the sensing module; A sampling module, connected to the sensing module, is used to acquire the sensing voltage and sampling voltage generated by the constant current in the sensing module. The signal processing module, connected to the sampling module, is used to determine the temperature difference between the speed measuring resistor and the temperature measuring resistor based on the sensing voltage and the sampling voltage, and to determine the mass flow rate of the gas based on a preset temperature difference-mass flow rate relationship.

[0006] In one embodiment of the present invention, the mass flow meter further includes a current limiting protection module, which is connected to a first power supply voltage and is used to limit the current of the first power supply voltage to obtain a second power supply voltage.

[0007] In one embodiment of the present invention, the current limiting protection module includes a first resistor, a second resistor, a third resistor, a first capacitor, a second capacitor, a first NPN transistor, and a first PMOS transistor. The first terminal of the first capacitor is connected to the first terminal of the first resistor, and the second terminal of the first capacitor is grounded. The second capacitor is connected in parallel with the first capacitor. The first terminal of the first resistor is also connected to the emitter of the first NPN transistor. The collector of the first NPN transistor is grounded via the second resistor. The collector of the first NPN transistor is also connected to the gate of the first PMOS transistor. The second terminal of the first resistor is connected to the base of the first NPN transistor. The second terminal of the first resistor is also connected to the source of the first PMOS transistor. The source of the first PMOS transistor is also connected to the first terminal of the third resistor. The second terminal of the third resistor is connected to the drain of the first PMOS transistor. The first terminal of the first resistor is connected to the first power supply voltage, and the drain of the first PMOS transistor outputs the second power supply voltage.

[0008] In one embodiment of the present invention, the constant current driving module includes a first constant current source driving unit and a second constant current source driving unit. The constant current includes the first constant current source and the second constant current source. The first constant current source driving unit generates the first constant current source based on a reference voltage and the second supply voltage, and the second constant current source driving unit generates the second constant current source based on the second supply voltage.

[0009] In one embodiment of the present invention, the first constant current source driving unit includes a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a third capacitor, a first diode, a second diode, a first operational amplifier, a second operational amplifier, a first NMOS transistor, and a second PMOS transistor. The cathode of the first diode is connected to the inverting input terminal of the first operational amplifier via the fourth resistor, and the cathode of the first diode is also connected to the non-inverting input terminal of the first operational amplifier via the fifth resistor. The inverting input terminal of the first operational amplifier is connected to the cathode of the second diode. The output terminal of the first operational amplifier is connected to the gate of the second PMOS transistor via the sixth resistor. The anode of the second diode is connected to the gate of the second PMOS transistor, and the cathode of the second diode is also connected to the gate of the second PMOS transistor. The source of the MOS transistor, the positive power supply terminal of the second operational amplifier is connected to the first power supply voltage, the positive power supply terminal of the second operational amplifier is grounded through the third capacitor, the negative power supply terminal of the second operational amplifier is grounded, the inverting input terminal of the second operational amplifier is connected to the drain of the first NMOS transistor, the non-inverting input terminal of the second operational amplifier is connected to the reference voltage, the output terminal of the second operational amplifier is connected to the gate of the first NMOS transistor, the drain of the first NMOS transistor is grounded through the seventh resistor, and the source of the first NMOS transistor is connected to the non-inverting input terminal of the first operational amplifier. The anode of the first diode is the input terminal of the first constant current source driving unit, and the drain of the second PMOS transistor is the output terminal of the first constant current source driving unit.

[0010] In one embodiment of the present invention, the second constant current source driving unit includes a fourth capacitor, a first chip, and a third diode. The first current input terminal of the first chip is connected to the second current input terminal of the first chip. The first terminal of the fourth capacitor is connected to the first current input terminal of the first chip. The second terminal of the fourth capacitor is connected to the detection terminal of the first chip, which is grounded. The first current output terminal of the first chip is connected to the second current output terminal of the first chip. The first current output terminal of the first chip is connected to the anode of the third diode. The first current input terminal of the first chip is the input terminal of the second constant current source driving unit, and the cathode of the third diode is the output terminal of the second constant current source driving unit.

[0011] In one embodiment of the present invention, the sensing module further includes a first sampling resistor and a second sampling resistor. The first end of the speed measuring resistor is grounded after passing through the first sampling resistor, and the first end of the temperature measuring resistor is grounded after passing through the second sampling resistor. The second end of the temperature measuring resistor is the first power supply terminal of the sensing module, and the second end of the speed measuring resistor is the second power supply terminal of the sensing module. The speed measuring resistor and the temperature measuring resistor are platinum resistance thermometers.

[0012] In one embodiment of the present invention, the sampling module includes two first sampling units and two second sampling units. The sensing voltage includes a first sensing voltage and a second sensing voltage, and the sampling voltage includes a first sampling voltage and a second sampling voltage. The two first sampling units are respectively connected to the speed-sensing resistor and the temperature-sensing resistor, and the two first sampling units respectively sample the voltage of the speed-sensing resistor and the temperature-sensing resistor to obtain the first sensing voltage and the second sensing voltage. The two second sampling units are respectively connected to the first sampling resistor and the second sampling resistor, and the two second sampling units respectively sample the voltage of the first sampling resistor and the second sampling resistor to obtain the first sampling voltage and the second sampling voltage.

[0013] In one embodiment of the present invention, the first sampling unit includes an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, and a second chip. The first end of the eighth resistor is connected to the first end of the ninth resistor, the first end of the tenth resistor is connected to the first end of the ninth resistor, the second end of the tenth resistor is connected to the first end of the eleventh resistor, the second end of the ninth resistor is connected to the first differential input terminal of the second chip, the second end of the eleventh resistor is connected to the second differential input terminal of the second chip, the first differential input terminal of the second chip is grounded via the fifth capacitor, the second differential input terminal of the second chip is grounded via the seventh capacitor, the first end of the sixth capacitor is connected to the second end of the ninth resistor, the second end of the sixth capacitor is connected to the second end of the eleventh resistor, the positive power supply terminal of the second chip is connected to the first power supply voltage, the positive power supply terminal of the second chip is also grounded via the eighth capacitor, and the negative power supply terminal of the second chip is grounded. The second ends of the eighth resistor and the second ends of the tenth resistor are the input terminals of the first sampling unit, and the output terminal of the second chip is the output terminal of the first sampling unit.

[0014] In one embodiment of the present invention, the second sampling unit includes a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a ninth capacitor, a tenth capacitor, an eleventh capacitor, and a third chip. The first differential input terminal of the third chip is grounded after passing through the ninth capacitor. The first differential input terminal of the third chip is connected to the first end of the twelfth resistor. The second differential input terminal of the third chip is grounded after passing through the thirteenth resistor. The first differential input terminal of the third chip is also connected to the second differential input terminal of the third chip after passing through the tenth capacitor. The first gain terminal of the third chip is connected to the second gain terminal of the third chip after passing through the fourteenth resistor. The positive power supply terminal of the third chip is connected to the first power supply voltage. The positive power supply terminal of the third chip is grounded after passing through the eleventh capacitor. The negative power supply terminal of the third chip is grounded. The second end of the twelfth resistor is the input terminal of the second sampling unit, and the output terminal of the third chip is the output terminal of the second sampling unit.

[0015] The beneficial effects of this invention are as follows: This invention provides a constant-current driven thermal gas mass flow meter, which includes: a constant-current driving module providing a constant current to a sensing module; the sensing module including a speed-measuring resistor and a temperature-measuring resistor; the speed-measuring resistor heating the flowing gas; and the temperature-measuring resistor detecting the ambient temperature of the gas; a sampling module sampling the voltage of the sensing module to obtain a sensing voltage and a sampling voltage; a signal processing module determining the temperature difference between the speed-measuring resistor and the temperature-measuring resistor based on the sensing voltage and the sampling voltage; and determining the mass flow rate of the gas based on the temperature difference and a preset temperature difference-mass flow rate relationship. The mass flow meter provided by this invention uses a constant-current source to drive the sensing module, ensuring a constant heating current and system stability even under fluctuating ambient temperature; it also eliminates the need for complex feedback control, resulting in a simpler circuit structure and higher system reliability; it directly reflects flow rate changes through the speed-measuring resistor and the temperature-measuring resistor, exhibiting good dynamic response characteristics; and it obtains the temperature difference between the two resistors through differential sampling, suppressing common-mode noise and improving the signal-to-noise ratio. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0017] In the attached diagram: Figure 1 This is a block diagram of a constant-flow driven thermal gas mass flow meter provided in one embodiment of the present invention. Figure 2This is a block diagram of a constant current driven thermal gas mass flow meter including a current limiting protection module, provided in one embodiment of the present invention. Figure 3 This is a detailed structural diagram of the current limiting protection module provided in one embodiment of the present invention; Figure 4 This is a detailed structural diagram of the first constant current source driving unit provided in one embodiment of the present invention; Figure 5 This is a detailed structural diagram of the second constant current source driving unit provided in one embodiment of the present invention; Figure 6 This is a detailed structural diagram of the sensing module provided in one embodiment of the present invention; Figure 7 This is a detailed structural diagram of the first sampling unit provided in one embodiment of the present invention; Figure 8 This is a structural diagram of the second sampling unit provided in one embodiment of the present invention.

[0018] The attached figures are labeled as follows: 110 - Constant current drive module; 120 - Sensing module; 130 - Sampling module; 140 - Signal processing module; 150 - Current limiting protection module; Ic - Constant current; Ic1 - First constant current source; Ic2 - Second constant current source; Vt - Sensing voltage; Vt1 - First sensing voltage; Vt2 - Second sensing voltage; Vs - Sampling voltage; Vs1 - First sampling voltage; Vs2 - Second sampling voltage; Qm - Mass flow rate; VCC1 - First power supply voltage; VCC2 - Second power supply voltage; VREF - Reference voltage. Detailed Implementation

[0019] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0020] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0021] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0022] Thermal gas mass flow meters occupy a crucial strategic position in the flow measurement field, characterized by "high added value, solving specific pain points, and continuous growth." Based on King's Law, which states that there is a definite functional relationship between the heat carried away by a fluid and its mass flow rate, thermal gas mass flow meters are widely used in industrial process control, environmental monitoring, and energy metering due to their advantages such as direct measurement of mass flow rate and low pressure loss. Currently, thermal flow meters mainly employ two operating modes: the constant temperature difference method and the constant power method.

[0023] The isothermal difference method: The sensor typically includes a speed-sensing resistor and a temperature-sensing resistor. A closed-loop feedback control circuit maintains a constant temperature difference between the two resistors. The heating power required to maintain this constant temperature difference is measured. The heating power has a specific functional relationship with the mass flow rate of the gas, thus determining the mass flow rate. While the isothermal difference method offers fast response, the real-time acquisition and continuous feedback adjustment of the temperature difference signal leads to a complex circuit system and poor system stability under high flow rate conditions.

[0024] The constant power method uses a sensor consisting of a heating resistor, a speed-sensing resistor, and a temperature-sensing resistor. A constant electrical power is applied to the heating resistor, and the mass flow rate is determined by measuring the temperature distribution changes caused by gas flow. While the control circuit of the constant power method is relatively simple, it has several inherent error sources: First, in the manufacturing process, the heating resistor and the speed-sensing resistor must be packaged together in the same measuring tube. Furthermore, to ensure electrical insulation, a certain distance must exist between the two resistors. This results in thermal isolation, preventing the temperature-sensing resistor from accurately sensing the true temperature of the heating zone. Second, over a wide range of ambient temperatures, the resistance of the heating resistor itself changes with temperature, causing the actual heating power to deviate from the set value and drift. These factors all introduce significant measurement errors, limiting its measurement accuracy.

[0025] like Figure 1 As shown, the present invention provides a constant-flow driven thermal gas mass flow meter, comprising: The sensing module 120 includes a speed measuring resistor RF1 and a temperature measuring resistor RT1. The speed measuring resistor RF1 heats the flowing gas, and the temperature measuring resistor RT1 is used to measure the ambient temperature of the gas. The constant current drive module 110 is connected to the power supply terminal of the sensing module 120 and is used to provide a constant current Ic to the sensing module 120. The sampling module 130 is connected to the sensing module 120 and is used to acquire the sensing voltage Vt and the sampling voltage Vs generated by the constant current Ic of the sensing module 120. The signal processing module 140, connected to the sampling module 130, is used to determine the temperature difference between the speed measuring resistor RF1 and the temperature measuring resistor RT1 based on the sensing voltage Vt and the sampling voltage Vs, and to determine the mass flow rate Qm of the gas based on the preset temperature difference-mass flow rate relationship.

[0026] In detail, such as Figure 2 As shown, the mass flow meter also includes a current limiting protection module 150. The current limiting protection module 150 is connected to the first power supply voltage VCC1 and is used to limit the current of the first power supply voltage VCC1 to obtain the second power supply voltage VCC2.

[0027] In detail, such as Figure 3 As shown, the current limiting protection module 150 includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, a first NPN transistor Q1, and a first PMOS transistor P1. The first terminal of the first capacitor C1 is connected to the first terminal of the first resistor R1, and the second terminal of the first capacitor C1 is grounded. The second capacitor C2 is connected in parallel with the first capacitor C1. The first terminal of the first resistor R1 is also connected to the emitter of the first NPN transistor Q1. The collector of the first NPN transistor Q1 is grounded via the second resistor R2. The collector of NPN transistor Q1 is also connected to the gate of first PMOS transistor P1. The second end of the first resistor R1 is connected to the base of first NPN transistor Q1. The second end of the first resistor R1 is also connected to the source of first PMOS transistor P1. The source of first PMOS transistor P1 is also connected to the first end of third resistor R3. The second end of third resistor R3 is connected to the drain of first PMOS transistor P1. The first end of the first resistor R1 is connected to the first supply voltage VCC1. The drain of first PMOS transistor P1 outputs the second supply voltage VCC2.

[0028] In detail, the constant current drive module 110 includes a first constant current source drive unit and a second constant current source drive unit. The constant current Ic includes a first constant current source Ic1 and a second constant current source Ic2. The first constant current source drive unit generates the first constant current source Ic1 based on the reference voltage VREF and the second supply voltage VCC2. The second constant current source drive unit generates the second constant current source Ic2 based on the second supply voltage VCC2.

[0029] More in detail, such as Figure 4As shown, the first constant current source driving unit includes a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a third capacitor C3, a first diode D1, a second diode D2, a first operational amplifier COMP1, a second operational amplifier COMP2, a first NMOS transistor M1, and a second PMOS transistor P2. The cathode of the first diode D1 is connected to the inverting input terminal of the first operational amplifier COMP1 via the fourth resistor R4. The cathode of the first diode D1 is also connected to the non-inverting input terminal of the first operational amplifier COMP1 via the fifth resistor R5. The inverting input terminal of the first operational amplifier COMP1 is connected to the cathode of the second diode D2. The output terminal of the first operational amplifier COMP1 is connected to the gate of the second PMOS transistor P2 via the sixth resistor R6. The anode of the second diode D2 is connected to the gate of the second PMOS transistor P2, and the cathode of the second diode D2 is also connected to the source of the second PMOS transistor P2. The second operational amplifier COMP2... The positive power supply terminal is connected to the first supply voltage VCC1. The positive power supply terminal of the second operational amplifier COMP2 is grounded after passing through the third capacitor C3. The negative power supply terminal of the second operational amplifier COMP2 is grounded. The inverting input terminal of the second operational amplifier COMP2 is connected to the drain of the first NMOS transistor M1. The non-inverting input terminal of the second operational amplifier COMP2 is connected to the reference voltage VREF. The output terminal of the second operational amplifier COMP2 is connected to the gate of the first NMOS transistor M1. The drain of the first NMOS transistor M1 is grounded after passing through the seventh resistor R7. The source of the first NMOS transistor M1 is connected to the non-inverting input terminal of the first operational amplifier COMP1. The anode of the first diode D1 is the input terminal of the first constant current source driving unit. The input terminal of the first constant current source driving unit is connected to the second supply voltage VCC2. The drain of the second PMOS transistor P2 is the output terminal of the first constant current source driving unit. The output terminal of the first constant current source driving unit outputs the first constant current source Ic1.

[0030] In detail, such as Figure 5 As shown, the second constant current source driving unit includes a fourth capacitor C4, a first chip U1, and a third diode D3. The first current input terminal of the first chip U1 is connected to the second current input terminal of the first chip U1. The first terminal of the fourth capacitor C4 is connected to the first current input terminal of the first chip U1, and the second terminal of the fourth capacitor C4 is connected to the detection terminal of the first chip U1. The detection terminal of the first chip U1 is grounded. The first current output terminal of the first chip U1 is connected to the second current output terminal of the first chip U1. The first current output terminal of the first chip U1 is connected to the anode of the third diode D3. The first current input terminal of the first chip U1 is the input terminal of the second constant current source driving unit, which is connected to the second power supply voltage VCC2. The cathode of the third diode D3 is the output terminal of the second constant current source driving unit, which outputs the second constant current source Ic2. The first chip U1 can be a REF200 chip.

[0031] In detail, such as Figure 6 As shown, the sensing module 120 also includes a first sampling resistor RS1 and a second sampling resistor RS2. The first end of the speed measuring resistor RF1 is grounded through the first sampling resistor RS1, and the first end of the temperature measuring resistor RT1 is grounded through the second sampling resistor RS2. The second end of the speed measuring resistor RF1 is the first power supply terminal of the sensing module 120, which is connected to the first constant current source Ic1. The second end of the temperature measuring resistor RT1 is the second power supply terminal of the sensing module 120, which is connected to the second constant current source Ic2. The speed measuring resistor RF1 and the temperature measuring resistor RT1 are platinum resistance thermometers.

[0032] In detail, the sampling module 130 includes two first sampling units and two second sampling units. The sensing voltage Vt includes a first sensing voltage Vt1 and a second sensing voltage Vt2, and the sampling voltage Vs includes a first sampling voltage Vs1 and a second sampling voltage Vs2. The two first sampling units are respectively connected to a speed measuring resistor RF1 and a temperature measuring resistor RT1. The two first sampling units sample the voltage of the speed measuring resistor RF1 and the temperature measuring resistor RT1 to obtain the first sensing voltage Vt1 and the second sensing voltage Vt2. The two second sampling units are respectively connected to a first sampling resistor RS1 and a second sampling resistor RS2. The two second sampling units sample the voltage of the first sampling resistor RS1 and the second sampling resistor RS2 to obtain the first sampling voltage Vs1 and the second sampling voltage Vs2.

[0033] More in detail, such as Figure 7 As shown, the first sampling unit includes an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, and a second chip U2. The first terminal of the eighth resistor R8 is connected to the first terminal of the ninth resistor R9, the first terminal of the tenth resistor R10 is connected to the first terminal of the ninth resistor R9, the second terminal of the tenth resistor R10 is connected to the first terminal of the eleventh resistor R11, the second terminal of the ninth resistor R9 is connected to the first differential input terminal of the second chip U2, and the second terminal of the eleventh resistor R11 is connected to the second differential input terminal of the second chip U2. One differential input terminal is grounded after passing through the fifth capacitor C5. The second differential input terminal of the second chip U2 is grounded after passing through the seventh capacitor C7. The first end of the sixth capacitor C6 is connected to the second end of the ninth resistor R9. The second end of the sixth capacitor C6 is connected to the second end of the eleventh resistor R11. The positive power supply terminal of the second chip U2 is connected to the first supply voltage VCC1. The positive power supply terminal of the second chip U2 is also grounded after passing through the eighth capacitor C8. The negative power supply terminal of the second chip U2 is grounded. The second ends of the eighth resistor R8 and the tenth resistor R10 are the input terminals of the first sampling unit. The output terminal of the second chip U2 is the output terminal of the first sampling unit.

[0034] It should be noted that, as Figure 7 As shown, the input terminal of the first sampling unit is connected to both ends (V1+, V1-) of the speed measuring resistor RF1, the second end of the eighth resistor R8 is connected to the second end of the speed measuring resistor RF1, and the second end of the tenth resistor R10 is connected to the first end of the speed measuring resistor RF1. The output terminal of the first sampling unit outputs the first sensing voltage Vt1. The input terminal of the second sampling unit is connected to both ends (V2+, V2-) of the temperature measuring resistor RT1, the second end of the eighth resistor R8 is connected to the second end of the temperature measuring resistor RT1, and the second end of the tenth resistor R10 is connected to the first end of the temperature measuring resistor RT1. The output terminal of the second sampling unit outputs the second sensing voltage Vt2. The first sensing voltage Vt1 and the second sensing voltage Vt2 are input to the signal processing module 140.

[0035] In detail, such as Figure 8 As shown, the second sampling unit includes a twelfth resistor R12, a thirteenth resistor R13, a fourteenth resistor R14, a ninth capacitor C9, a tenth capacitor C10, an eleventh capacitor C11, and a third chip U3. The first differential input terminal of the third chip U3 is grounded after passing through the ninth capacitor C9. The first differential input terminal of the third chip U3 is connected to the first end of the twelfth resistor R12. The second differential input terminal of the third chip U3 is grounded after passing through the thirteenth resistor R13. The first differential input terminal of the third chip U3 is also connected to the second differential input terminal of the third chip U3 after passing through the tenth capacitor C10. The first gain terminal of the third chip U3 is connected to the second gain terminal of the third chip U3 after passing through the fourteenth resistor R14. The positive power supply terminal of the third chip U3 is connected to the first supply voltage VCC1. The positive power supply terminal of the third chip U3 is grounded after passing through the eleventh capacitor C11. The negative power supply terminal of the third chip U3 is grounded. The second end of the twelfth resistor R12 is the input terminal of the second sampling unit, and the output terminal of the second chip U2 is the output terminal of the second sampling unit.

[0036] It needs to be emphasized that, such as Figure 8 As shown, the input terminal of the first second sampling unit is connected to the common terminal (V1-) of the speed measuring resistor RF1 and the first sampling resistor RS1, and the output terminal of the first second sampling unit outputs the first sampling voltage Vs1; the input terminal of the second second sampling unit is connected to the common terminal (V2-) of the temperature measuring resistor RT1 and the second sampling resistor RS2, and the output terminal of the second second sampling unit outputs the second sampling voltage Vs2.

[0037] Among them, the second chip U2 and the third chip U3 are instrumentation amplifiers, and the model of the second chip U2 and the third chip U3 can be INAI88IDR.

[0038] Please see Figures 1 to 8The working principle of the constant current driven thermal gas mass flow meter provided by this invention is as follows: like Figure 1-2 As shown, the input terminal of the current limiting protection module 150 is connected to the first supply voltage VCC1. The current limiting protection module 150 limits the current of the first supply voltage VCC1 to obtain the second supply voltage VCC2. The constant current drive module 110 is connected to the output terminal of the current limiting protection module 150 and generates a constant current Ic based on the second supply voltage VCC2. The sensing module 120 includes a speed measuring resistor RF1 and a temperature measuring resistor RT1. The speed measuring resistor RF1 and the temperature measuring resistor RT1 are respectively installed in two measuring tubes. The speed measuring resistor RF1 measures the gas in the measuring tube. The system drives heating to achieve heat exchange, and the temperature measuring resistor RT1 detects the ambient temperature of the gas being measured. The sampling module 130 is connected to the sensing module 120, and the voltage of the sensing module 120 is sampled to obtain the sensing voltage Vt and the sampling voltage Vs. The signal processing module 140 is connected to the output terminal of the sampling module 130. The signal processing module 140 calculates the temperature difference between the speed measuring resistor RF1 and the temperature measuring resistor RT1 based on the sensing voltage Vt and the sampling voltage Vs, and obtains the mass flow rate Qm of the gas according to the preset temperature difference-mass flow rate relationship.

[0039] like Figure 3 As shown, when the current limiting protection module 150 receives a wide range of first supply voltage VCC1, the first NPN transistor Q1 is turned on and the first PMOS transistor P1 is also turned on. Part of the current flows into the ground terminal through the second resistor R2, and the other part of the current flows through the first resistor R1 and the third resistor R3 in sequence before outputting the second supply voltage VCC2.

[0040] like Figure 4 As shown, in the first constant current source drive unit, after the reference voltage VREF passes through the second operational amplifier COMP2, the voltage across the seventh resistor R7 is the reference voltage VREF, and the current flowing through the seventh resistor R7 is as shown in expression (1): (1) Among them, I R7 The current flowing through the seventh resistor R7 is denoted as VREF, where VREF is the reference voltage and R7 is the seventh resistor.

[0041] Since the current flowing through the fifth resistor R5 is equal to the current flowing through the seventh resistor R7, the voltage across the fifth resistor R5 is as shown in expression (2): VR5 (2) Where VR5 is the voltage across the fifth resistor R5, I R7 R5 is the current flowing through the seventh resistor R7, and R5 is the fifth resistor.

[0042] According to the virtual short principle of the first operational amplifier COMP1, the voltage across the fourth resistor R4 is equal to the voltage across the fifth resistor R5, and the current flowing through the fourth resistor R4 is as shown in expression (3): (3) Among them, I R4 VR5 is the current flowing through the fourth resistor R4, and R4 is the voltage across the fifth resistor R5.

[0043] Combination Figure 4 and Figure 6 It can be seen that the current flowing through the speed measuring resistor RF1 is equal to the current flowing through the fourth resistor R4, and the voltage of the speed measuring resistor RF1 is as shown in expression (4): VRF1 (4) in, I is the voltage across the speed measuring resistor RF1. R4 RF1 is the current flowing through the fourth resistor R4, and RF1 is the speed measuring resistor.

[0044] The current flowing through the first sampling resistor RS1 is equal to the current flowing through the fourth resistor R4. The voltage across the first sampling resistor RS1 is shown in expression (5): VRS1 (5) in, I is the voltage across the first sampling resistor RS1. R4 The current flowing through the fourth resistor R4 is denoted as RS1, and RS1 is the first sampling resistor RS1.

[0045] The voltage across the speed measuring resistor RF1 is sampled by the first sampling unit to obtain the first sensing voltage Vt1, which is shown in expression (6): (6) Wherein, Vt1 is the first sensing voltage. R1 is the voltage across the speed measuring resistor RF1, R8 is the eighth resistor, and R10 is the tenth resistor.

[0046] The first sampling voltage Vs1 is obtained by sampling the two ends of the first sampling resistor RS1 through the first second sampling unit. The first sampling voltage Vs1 is as shown in expression (7): (7) Where Vs1 is the first sampling voltage, R14 is the voltage across the first sampling resistor RS1, R14 is the fourteenth resistor, and 50KΩ is the built-in resistance value of the third chip U3.

[0047] like Figure 5-6 As shown, the second power supply voltage VCC2 is converted into a second constant current source Ic2 by the second constant current source driving unit. The second constant current source Ic2 flows through the temperature measuring resistor RT1 and the second sampling resistor RS2 and then flows into the ground. The voltage across the temperature measuring resistor RT1 is sampled by the second first sampling unit to obtain the second sensing voltage Vt2. The second sampling resistor RS2 is sampled by the second second sampling unit to obtain the second sampling voltage VS2.

[0048] The signal processing module 140 calculates the first sampling current flowing through the first sampling resistor RS1 based on the first sampling voltage Vs1 and the first sampling resistor RS1. Based on the first sampling current and the first sensing voltage Vt1, it calculates the resistance value of the speed measuring resistor RF1. The signal processing module 140 calculates the second sampling current flowing through the second sampling resistor RS2 based on the second sampling voltage Vs2 and the second sampling resistor RS2. Based on the second sampling current and the second sensing voltage Vt2, it calculates the resistance value of the temperature measuring resistor RT1. Since both the speed measuring resistor RF1 and the temperature measuring resistor RT1 are platinum resistance resistors, the temperature of the speed measuring resistor RF1 and the temperature measuring resistor RT1 are determined according to the resistance characteristics of the two resistors. The temperature difference between the speed measuring resistor RF1 and the temperature measuring resistor RT1 is calculated. Based on the temperature difference and the preset temperature difference-mass flow rate relationship, the mass flow rate of the gas flowing through the measuring tube is calculated.

[0049] This invention provides a constant-current driven thermal gas mass flow meter, comprising: a constant-current driving module providing a constant current to a sensing module; the sensing module including a speed-sensing resistor and a temperature-sensing resistor; the speed-sensing resistor heating the flowing gas; and the temperature-sensing resistor detecting the ambient temperature of the gas; a sampling module sampling the voltage of the sensing module to obtain a sensing voltage and a sampling voltage; a signal processing module determining the temperature difference between the speed-sensing resistor and the temperature-sensing resistor based on the sensing voltage and the sampling voltage; and determining the mass flow rate of the gas based on the temperature difference and a preset temperature difference-mass flow rate relationship. The mass flow meter provided by this invention uses a constant-current source to drive the sensing module, ensuring a constant heating current even under fluctuating ambient temperature; it also eliminates the need for complex feedback control, resulting in a simpler circuit structure and higher system reliability; it directly reflects flow rate changes through the speed-sensing resistor and the temperature-sensing resistor, exhibiting good dynamic response characteristics; and it obtains the temperature difference between the two resistors through differential sampling, suppressing common-mode noise and improving the signal-to-noise ratio.

[0050] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A constant-flow driven thermal gas mass flow meter, characterized in that, include: The sensing module includes a speed-sensing resistor and a temperature-sensing resistor. The speed-sensing resistor heats the flowing gas, and the temperature-sensing resistor measures the ambient temperature of the gas. A constant current drive module is connected to the power supply terminal of the sensing module and is used to provide a constant current to the sensing module; A sampling module, connected to the sensing module, is used to acquire the sensing voltage and sampling voltage generated by the constant current in the sensing module. The signal processing module, connected to the sampling module, is used to determine the temperature difference between the speed measuring resistor and the temperature measuring resistor based on the sensing voltage and the sampling voltage, and to determine the mass flow rate of the gas based on a preset temperature difference-mass flow rate relationship.

2. The constant-flow driven thermal gas mass flow meter according to claim 1, characterized in that, The mass flow meter also includes a current limiting protection module, which is connected to a first power supply voltage and is used to limit the current of the first power supply voltage to obtain a second power supply voltage.

3. The constant-flow driven thermal gas mass flow meter according to claim 2, characterized in that, The current limiting protection module includes a first resistor, a second resistor, a third resistor, a first capacitor, a second capacitor, a first NPN transistor, and a first PMOS transistor. The first terminal of the first capacitor is connected to the first terminal of the first resistor, and the second terminal of the first capacitor is grounded. The second capacitor is connected in parallel with the first capacitor. The first terminal of the first resistor is also connected to the emitter of the first NPN transistor. The collector of the first NPN transistor is grounded via the second resistor. The collector of the first NPN transistor is also connected to the gate of the first PMOS transistor. The second terminal of the first resistor is connected to the base of the first NPN transistor and the source of the first PMOS transistor. The source of the first PMOS transistor is also connected to the first terminal of the third resistor. The second terminal of the third resistor is connected to the drain of the first PMOS transistor. The first terminal of the first resistor is connected to the first power supply voltage, and the drain of the first PMOS transistor outputs the second power supply voltage.

4. The constant-flow driven thermal gas mass flow meter according to claim 2, characterized in that, The constant current driving module includes a first constant current source driving unit and a second constant current source driving unit. The constant current includes the first constant current source and the second constant current source. The first constant current source driving unit generates the first constant current source based on the reference voltage and the second supply voltage, and the second constant current source driving unit generates the second constant current source based on the second supply voltage.

5. The constant-flow driven thermal gas mass flow meter according to claim 4, characterized in that, The first constant current source driving unit includes a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a third capacitor, a first diode, a second diode, a first operational amplifier, a second operational amplifier, a first NMOS transistor, and a second PMOS transistor. The cathode of the first diode is connected to the inverting input terminal of the first operational amplifier via the fourth resistor. The cathode of the first diode is also connected to the non-inverting input terminal of the first operational amplifier via the fifth resistor. The inverting input terminal of the first operational amplifier is connected to the cathode of the second diode. The output terminal of the first operational amplifier is connected to the gate of the second PMOS transistor via the sixth resistor. The anode of the second diode is connected to the gate of the second PMOS transistor. The cathode of the second diode is also connected to the gate of the second PMOS transistor. The source of the second operational amplifier is connected to the first supply voltage. The positive power supply terminal of the second operational amplifier is grounded through the third capacitor. The negative power supply terminal of the second operational amplifier is grounded. The inverting input terminal of the second operational amplifier is connected to the drain of the first NMOS transistor. The non-inverting input terminal of the second operational amplifier is connected to the reference voltage. The output terminal of the second operational amplifier is connected to the gate of the first NMOS transistor. The drain of the first NMOS transistor is grounded through the seventh resistor. The source of the first NMOS transistor is connected to the non-inverting input terminal of the first operational amplifier. The anode of the first diode is the input terminal of the first constant current source driving unit, and the drain of the second PMOS transistor is the output terminal of the first constant current source driving unit.

6. The constant-flow driven thermal gas mass flow meter according to claim 4, characterized in that, The second constant current source driving unit includes a fourth capacitor, a first chip, and a third diode. The first current input terminal of the first chip is connected to the second current input terminal of the first chip. The first terminal of the fourth capacitor is connected to the first current input terminal of the first chip. The second terminal of the fourth capacitor is connected to the detection terminal of the first chip, which is grounded. The first current output terminal of the first chip is connected to the second current output terminal of the first chip. The first current output terminal of the first chip is connected to the anode of the third diode. The first current input terminal of the first chip is the input terminal of the second constant current source driving unit, and the cathode of the third diode is the output terminal of the second constant current source driving unit.

7. The constant-flow driven thermal gas mass flow meter according to claim 1, characterized in that, The sensing module further includes a first sampling resistor and a second sampling resistor. The first end of the speed measuring resistor is grounded after passing through the first sampling resistor, and the first end of the temperature measuring resistor is grounded after passing through the second sampling resistor. The second end of the speed measuring resistor is the first power supply terminal of the sensing module, and the second end of the speed measuring resistor is the second power supply terminal of the sensing module. The temperature measuring resistor and the temperature measuring resistor are platinum resistance thermometers.

8. The constant-flow driven thermal gas mass flow meter according to claim 7, characterized in that, The sampling module includes two first sampling units and two second sampling units. The sensing voltage includes a first sensing voltage and a second sensing voltage. The sampling voltage includes a first sampling voltage and a second sampling voltage. The two first sampling units are respectively connected to the speed measuring resistor and the temperature measuring resistor. The two first sampling units respectively sample the voltage of the speed measuring resistor and the temperature measuring resistor to obtain the first sensing voltage and the second sensing voltage. The two second sampling units are respectively connected to the first sampling resistor and the second sampling resistor, and the two second sampling units respectively sample the voltage of the first sampling resistor and the second sampling resistor to obtain the first sampling voltage and the second sampling voltage.

9. The constant-flow driven thermal gas mass flow meter according to claim 8, characterized in that, The first sampling unit includes an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, and a second chip. The first end of the eighth resistor is connected to the first end of the ninth resistor, the first end of the tenth resistor is connected to the first end of the ninth resistor, the second end of the tenth resistor is connected to the first end of the eleventh resistor, the second end of the ninth resistor is connected to the first differential input terminal of the second chip, the second end of the eleventh resistor is connected to the second differential input terminal of the second chip, the first differential input terminal of the second chip is grounded through the fifth capacitor, the second differential input terminal of the second chip is grounded through the seventh capacitor, the first end of the sixth capacitor is connected to the second end of the ninth resistor, the second end of the sixth capacitor is connected to the second end of the eleventh resistor, the positive power supply terminal of the second chip is connected to the first power supply voltage, the positive power supply terminal of the second chip is also grounded through the eighth capacitor, and the negative power supply terminal of the second chip is grounded. The second ends of the eighth resistor and the second ends of the tenth resistor are the input terminals of the first sampling unit, and the output terminal of the second chip is the output terminal of the first sampling unit.

10. The constant-flow driven thermal gas mass flow meter according to claim 8, characterized in that, The second sampling unit includes a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a ninth capacitor, a tenth capacitor, an eleventh capacitor, and a third chip. The first differential input terminal of the third chip is grounded after passing through the ninth capacitor. The first differential input terminal of the third chip is connected to the first end of the twelfth resistor. The second differential input terminal of the third chip is grounded after passing through the thirteenth resistor. The first differential input terminal of the third chip is also connected to the second differential input terminal of the third chip after passing through the tenth capacitor. The first gain terminal of the third chip is connected to the second gain terminal of the third chip after passing through the fourteenth resistor. The positive power supply terminal of the third chip is connected to the first power supply voltage. The positive power supply terminal of the third chip is grounded after passing through the eleventh capacitor. The negative power supply terminal of the third chip is grounded. The second end of the twelfth resistor is the input terminal of the second sampling unit, and the output terminal of the third chip is the output terminal of the second sampling unit.

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