A thermal flow meter adaptive switching circuit and method

Abstract

The application provides a kind of thermal flowmeter adaptive switching circuit and method, the circuit includes acquisition amplification module, constant temperature difference module, constant power module and mass flow signal switching module, first raw data signal is amplified to first data signal by the acquisition amplification module, the first data signal is input into the constant power module and the constant temperature difference module for operation, the constant temperature difference module outputs second data signal and constant power data signal, the constant power module outputs third data signal and constant power data signal, the second data signal, the first threshold value of preset, the third data signal and the second threshold value of preset are logically processed, mode selection signal is obtained and one of constant power data signal and constant temperature difference data signal is controlled to output externally.The application realizes the automatic switching output of constant power principle circuit and constant temperature difference principle circuit in thermal flowmeter, widens the measurement range, and improves the reliability of thermal flowmeter.

Description

Technical Field

[0001] This invention relates to the field of process instrumentation, and more particularly to an adaptive switching circuit and method for a thermal flow meter. Background Technology

[0002] In practical industrial applications, thermal flow meters for measuring fluids fall into two categories: those based on the constant temperature difference principle and those based on the constant power principle. Currently, these two different principles of thermal flow meters differ. The constant temperature difference thermal flow meter has a fast response time, good stability, and is less affected by environmental conditions, making it suitable for both gases and liquids. However, it is only suitable for fluids with low flow rates and low temperatures. The constant power thermal flow meter is suitable for high-temperature, high-velocity fluids, but it has a slow response time, poor stability, is more affected by environmental conditions, and can only measure gases. In industrial applications, measurement accuracy is affected by various factors, and the requirements for response time also differ. Currently, the two separate principles of thermal flow meters cannot meet the demands of complex industrial production environments and cannot continuously output stable mass flow data.

[0003] Therefore, designing a thermal flow meter that can meet the requirements of use in complex industrial production environments is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the present invention provides a technical solution for adaptive switching of a thermal flow meter. This technical solution converts the fluid velocity using a speed-measuring resistor to obtain a first raw data signal. The first raw data signal is amplified to obtain a first data signal, which is the input signal of a constant power module and a constant temperature difference module. The constant temperature difference module performs voltage-to-current conversion on the first data signal to obtain a second data signal. The second signal is then divided, subtracted, and amplified to obtain a constant temperature difference data signal. The constant power module performs multiplication on the first data signal to obtain a third data signal. The third signal is then amplified, temperature-compensated, and subjected to multiple multiplications to obtain a constant power data signal. Logical processing of the second and third data signals yields a mode selection signal. Based on the mode selection signal, one of the constant temperature difference data signal and the constant power data signal is output, achieving adaptive switching between the constant power data signal and the constant temperature difference data signal. This can meet the requirements of use in complex industrial scenarios and ensure the accuracy of mass flow rate data output when measuring different temperatures and flow rates.

[0005] To achieve the above and other related objectives, the technical solution provided by this invention is as follows.

[0006] An adaptive switching circuit for a thermal flow meter includes:

[0007] The system comprises the following modules: a data acquisition and amplification module, which acquires a first raw data signal and amplifies it to obtain a first data signal, which is related to the fluid velocity; a constant temperature difference module, which receives the first data signal and converts it from voltage to current to obtain a second data signal, and also performs division, subtraction, and amplification operations on the second data signal to obtain a constant temperature difference data signal; a constant power module, which receives the first data signal and performs multiplication operations on it to obtain a third data signal, and also performs amplification, temperature compensation, and multiple product operations on the third data signal to obtain a constant power data signal; and a mass flow rate signal switching module, which receives the second data signal, the third data signal, the constant temperature difference data signal, and the constant power data signal, and performs logical processing on the second data signal with a preset first threshold and the third data signal with a preset second threshold to obtain a mode selection signal, which controls the output of one of the constant temperature difference data signal and the constant power data signal.

[0008] Optionally, the acquisition and amplification module includes a sensor speed measurement submodule and an amplification submodule. The sensor speed measurement submodule is used to acquire the first raw data signal, and the amplification submodule receives the first raw data signal and amplifies the first raw data signal to obtain the first data signal.

[0009] Optionally, the sensor speed measurement submodule includes a first resistor, a second resistor, a first NPN transistor, and a first speed-measuring resistor. One end of the first resistor is connected to a first power supply voltage, and the other end of the first resistor is connected to the collector of the first NPN transistor. The emitter of the first NPN transistor is connected to one end of the first speed-measuring resistor, and the other end of the first speed-measuring resistor is connected to one end of the second resistor. The other end of the second resistor is grounded. The base of the first NPN transistor is the control terminal of the sensor speed measurement submodule, and the emitter of the first NPN transistor, the other end of the first speed-measuring resistor, and the other end of the third resistor are the output terminals of the sensor test submodule.

[0010] Optionally, the amplification submodule includes two amplification units. The first amplification unit includes a voltage divider subunit and an amplification subunit. The second amplification unit includes a current limiting subunit and the amplification subunit. Each amplification subunit includes a first capacitor, a second capacitor, a third capacitor, a third resistor, and a first operational amplifier. The other end of the first capacitor is connected to the inverting input terminal of the first operational amplifier. The other end of the first capacitor is connected to one end of the second capacitor. The other end of the first capacitor is also connected to the first output terminal of the voltage divider subunit or the current limiting subunit. One end of the first capacitor is grounded. The other end of the second capacitor is connected to one end of the third capacitor. The other end of the third capacitor is also connected to the first output terminal of the voltage divider subunit or the current limiting subunit. One end of the first capacitor is grounded. The non-inverting input terminal of an operational amplifier is connected to the third capacitor. One end of the third capacitor is also connected to the second output terminal of the voltage divider unit or the current limiting unit. The other end of the third capacitor is grounded. The third resistor is connected in series between the first gain resistor terminal and the second gain resistor terminal of the first operational amplifier. The negative power supply terminal of the first operational amplifier is connected to the first power supply voltage. The feedback terminal of the first operational amplifier is grounded. The positive power supply terminal of the first operational amplifier is also connected to the first power supply voltage. One end of the fourth capacitor is also connected to the positive power supply terminal. The other end of the fourth capacitor is grounded. The output terminal of the first operational amplifier is the output terminal of the amplification subunit.

[0011] Optionally, the mass flow rate signal switching module includes a mode selection submodule and a switch submodule. The mode selection submodule is connected to the second data signal and the third data signal, and performs logical conversion on the second data signal, a preset first threshold, the third data signal and the preset second threshold to obtain a mode selection signal. The switch submodule is connected to the mode selection signal, and under the control of the mode selection signal, the switch submodule selects one of the constant power data signal and the constant temperature difference data signal for external output.

[0012] Optionally, the mode selection submodule includes a first comparator, a second comparator, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, and a first RS flip-flop. The other end of the fifth resistor is connected to the inverting input of the first comparator, and the other end of the fifth resistor is also connected to one end of the sixth resistor. The other end of the sixth resistor is connected to the output of the first comparator, and the output of the first comparator is also connected to the set input of the first RS flip-flop. The other end of the seventh resistor is connected to the inverting input of the second comparator, and the other end of the seventh resistor is also connected to one end of the eighth resistor. The other end of the eighth resistor is connected to the output of the second comparator, and the output of the second comparator is also connected to the reset input of the first RS flip-flop. The non-inverting input of the first comparator, one end of the fifth resistor, the non-inverting input of the second comparator, and one end of the seventh resistor are the inputs of the mode selection submodule, and the output of the first RS flip-flop is the output of the mode selector submodule.

[0013] Optionally, the thermal flow meter adaptive switching circuit further includes a power over-limit protection module. The power over-limit protection module receives the third data signal and the preset power over-limit threshold, performs logical conversion on the third data signal and the preset power over-limit threshold to obtain a circuit protection signal. The circuit protection signal is used to perform over-power protection control on the thermal flow meter adaptive switching circuit. When the third data signal is greater than the preset power over-limit threshold, the output of the mass flow signal switching module is pulled down to ground.

[0014] An adaptive switching method for thermal flow meters includes:

[0015] Acquire the first data signal;

[0016] The first data signal is subjected to voltage-to-current conversion to obtain the second data signal. The second signal is then subjected to division, subtraction and amplification to obtain the constant temperature difference data signal.

[0017] The first data signal is multiplied to obtain the third data signal. The third signal is then amplified, temperature compensated, and multiplied multiple times to obtain the constant power data signal.

[0018] The second data signal, the preset first threshold, the third data signal, and the preset second threshold are logically processed to obtain the mode selection signal. One of the constant temperature difference data signal and the constant power data signal is output according to the mode selection signal.

[0019] Optionally, the step of acquiring the first data signal includes: converting the fluid velocity into the first raw data signal through a speed measuring resistor; and amplifying the first raw data signal to obtain the first data signal.

[0020] Optionally, the step of outputting one of the constant temperature difference data signal and the constant power data signal from the mode selection signal includes: when the mode selection signal is high, the thermal flow meter adaptive switching circuit outputs the constant power data signal; when the mode selection signal is low, the thermal flow meter adaptive switching circuit outputs the constant temperature difference data signal.

[0021] This invention provides a technical solution for adaptive switching of a thermal flow meter, comprising a data acquisition and amplification module, a constant power module, a constant temperature difference module, and a mass flow signal switching module. This solution converts and amplifies the fluid velocity to obtain a first data signal. The constant temperature difference module and the constant power module process the first data signal to obtain a second data signal, a third data signal, a constant power data signal, and a constant temperature difference data signal. Logical processing is performed on the second data signal, the preset first threshold, the third data signal, and the preset second threshold to obtain an analog selection signal. Based on the analog selection signal, one of the constant power data signal and the constant temperature difference data signal is output. When measuring fluids at different temperatures and velocities, the thermal flow meter designed in this invention can adaptively switch between constant temperature difference and constant power principles for detection, ensuring accurate measurement. When measuring low-velocity and low-temperature fluids, the mode selection signal outputs a low level, and the thermal flow meter outputs a constant temperature difference data signal. When measuring high-temperature and high-velocity gases, the thermal flow meter outputs a constant power data signal. Attached Figure Description

[0022] Figure 1 This is a block diagram of the adaptive switching current of the thermal flow meter in an embodiment of the present invention;

[0023] Figure 2 This is a circuit diagram of the sensor speed measurement submodule in an embodiment of the present invention;

[0024] Figure 3 This is a circuit diagram of the first amplification unit in an embodiment of the present invention;

[0025] Figure 4 This is a circuit diagram of the second amplification unit in an embodiment of the present invention;

[0026] Figure 5 This is a circuit diagram of the mode selection submodule in an embodiment of the present invention;

[0027] Figure 6This is a circuit diagram of the switch submodule in an embodiment of the present invention;

[0028] Figure 7 This is a circuit diagram of the power over-limit protection module and the output module in an embodiment of the present invention. Detailed Implementation

[0029] 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, and 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. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0030] Common thermal flow meters contain two platinum resistance thermometers. One is heated as an active element and is called a velocity probe, whose main function is to measure the velocity of the fluid. The other is not heated and serves as a reference element and is called a temperature probe, whose main function is to measure the temperature of the fluid.

[0031] The formula for calculating the mass flow rate of a fluid is shown below:

[0032]

[0033] Where Qm is the mass flow rate, K is the ratio of dynamic viscosity to the diameter of the transfer head, S is the cross-sectional area, f is the thermal conductivity, and I... w R is the converted current. w Tw is the resistance value of the speed measuring resistor; Ta is the temperature of the hot wire; and Ta is the temperature of the fluid.

[0034] From formula (1), it can be seen that when the composition of the measured stream remains unchanged (i.e., the physical property parameters remain unchanged), if the ratio of (Tw–Ta) / Rw remains unchanged, a single-valued function can be established between the current Iw flowing through the heating probe and the mass flow rate Qm to be determined. This is the principle of constant temperature difference measurement. If the heating power is kept constant... If the temperature remains constant, the temperature difference ΔT = T between the two probes can be established. w -T a and the mass flow rate Q to be determined m This is a single-valued function between the two, which is the principle of constant power measurement.

[0035] The inventors discovered that products made using the constant temperature difference principle and the constant power principle each have different advantages and disadvantages. The constant temperature difference thermal flow meter has a faster response speed than the constant power thermal flow meter. The constant temperature difference thermal flow meter has better stability and is less affected by ambient temperature. The constant power thermal flow meter can measure gases with higher temperatures and higher flow rates, but it has poor stability and is greatly affected by the environment. The two types of thermal flow meters differ in the velocity of the fluid they measure, the temperature of the sensing element, and the substances they measure.

[0036] In view of the above, the present invention provides a technical solution for adaptive switching of a thermal flow meter. This solution converts the fluid velocity into a first data signal, and performs calculations on the first data signal through a constant temperature difference module and a constant power module to obtain a second data signal, a third data signal, a constant temperature difference data signal, and a constant power data signal. The second data signal, a preset first threshold, the third data signal, and a preset second threshold are logically processed to obtain a mode selection signal. Based on the mode selection signal, one of the constant temperature difference data signal and the constant power data signal is selected for external output.

[0037] like Figure 1 As shown, an embodiment of the present invention provides an adaptive switching circuit for a thermal flow meter, which includes:

[0038] The acquisition and amplification module acquires and amplifies a first raw data signal to obtain a first data signal, which is related to the fluid velocity. The constant temperature difference module receives the first data signal and performs voltage-to-current conversion to obtain a second data signal. It also performs division, subtraction, and amplification on the second data signal to obtain a constant temperature difference data signal. The constant power module receives the first data signal and performs multiplication on it to obtain a third data signal. It also performs amplification, temperature compensation, and multiple product operations on the third data signal to obtain a constant power data signal. The mass flow rate signal switching module receives the second, third, constant temperature difference, and constant power data signals. It performs logical processing on the second data signal with a preset first threshold and the third data signal with a preset second threshold to obtain a mode selection signal. The mode selection signal controls the output of either the constant temperature difference data signal or the constant power data signal.

[0039] In detail, the acquisition and amplification module includes a sensor speed measurement submodule and an amplification submodule. The sensor speed measurement submodule is used to acquire the first raw data signal, and the amplification submodule receives the first raw data signal and amplifies the first raw data signal to obtain the first data signal.

[0040] More in detail, such as Figure 2As shown, the sensor speed measurement submodule includes a first resistor R1, a second resistor R2, a first NPN transistor Q1, and a first speed-measuring resistor RT1. One end of the first resistor R1 is connected to a first power supply voltage, and the other end of the first resistor R1 is connected to the collector of the first NPN transistor Q1. The emitter of the first NPN transistor Q1 is connected to one end of the first speed-measuring resistor RT1, and the other end of the first speed-measuring resistor RT1 is connected to one end of the second resistor R2. The other end of the second resistor R2 is grounded. The base of the first NPN transistor Q1 is the control terminal of the sensor speed measurement submodule, and its control terminal is connected to the feedback signal of the thermal flow meter adaptive switching circuit. The emitter of the first NPN transistor Q1, the other end of the first speed-measuring resistor RT1, and the other end of the second resistor are the output terminals of the sensor test submodule, which output a first data signal to the amplification submodule.

[0041] More in detail, such as Figure 3 and Figure 4 As shown, the amplification submodule includes two amplification units. The first amplification unit includes a voltage divider subunit and an amplification subunit, and the second amplification unit includes a current limiting subunit and an amplification subunit. The two amplification subunits have the same structure. Figure 3 As shown, the amplification subunit in the first amplification unit includes a first capacitor C1, a second capacitor C2, a third capacitor C3, a third resistor R7, and a first operational amplifier U1. The other end of the first capacitor C1 is connected to the inverting input terminal of the first operational amplifier U1. The other end of the first capacitor C1 is connected to one end of the second capacitor C2. The other end of the first capacitor C1 is also connected to the first output terminal of the voltage divider subunit. One end of the first capacitor C1 is grounded. The other end of the second capacitor C2 is connected to one end of the third capacitor C3. One end of the third capacitor C3 is also connected to the non-inverting input terminal of the first operational amplifier U1. The voltage divider unit's output is connected to the second output terminal of the voltage divider unit. The other end of the third capacitor C3 is grounded. A third resistor R7 is connected in series between the first gain resistor terminal and the second gain resistor terminal of the first operational amplifier U1. The negative power supply terminal of the first operational amplifier U1 is connected to the first power supply voltage. The feedback terminal of the first operational amplifier U1 is grounded. The positive power supply terminal of the first operational amplifier U1 is connected to the first power supply voltage. The positive power supply terminal of the first operational amplifier U1 is also connected to one end of the fourth capacitor C4. The other end of the fourth capacitor C4 is grounded. The output terminal of the first operational amplifier U1 is the output terminal of the amplification unit. The voltage divider unit includes four resistors. One end of resistor R3 is grounded. The other end of resistor R3 is connected to one end of resistor R4. The other end of resistor R3 is also connected to the other end of the first capacitor C1 in the amplification unit. The other end of resistor R4 is connected to the positive-phase first data signal. The other end of resistor R6 is grounded. One end of resistor R6 is connected to one end of resistor R5. One end of resistor R6 is also connected to one end of the third capacitor C3 in the amplification unit. The other end of resistor R5 is connected to the negative-phase first data signal. Figure 4As shown, the current limiting sub-unit includes two resistors. One end of resistor R8 is connected to the negative phase first data signal, and the other end of resistor R8 is connected to the other end of the first capacitor C5 in the amplification sub-module. One end of resistor R9 is connected to the negative phase first data signal, and the other end of resistor R9 is connected to one end of the third capacitor C7 in the amplification sub-module.

[0042] In detail, the mass flow signal switching module includes a mode selection submodule and a switch submodule. The mode selection submodule is connected to a second data signal and a third data signal. It performs logical conversion on the second data signal, a preset first threshold, the third data signal and the preset second threshold to obtain a mode selection signal. The switch submodule is connected to the mode selection signal. Under the control of the mode selection signal, the switch submodule selects one of the constant power data signal and the constant temperature difference data signal for external output.

[0043] More in detail, such as Figure 5 As shown, the mode selection submodule includes a first comparator U1B, a second comparator U2B, a fifth resistor R11, a sixth resistor R12, a seventh resistor R13, an eighth resistor R14, and a first RS flip-flop. The other end of the fifth resistor R11 is connected to the inverting input of the first comparator U1B. The other end of the fifth resistor R11 is also connected to one end of the sixth resistor R12. The other end of the sixth resistor R12 is connected to the output of the first comparator U1B. The output of the first comparator U1B is also connected to the set input of the first RS flip-flop. The other end of the seventh resistor R13 is connected to the inverting input of the second comparator U2B. The other end of the seventh resistor R13 is also connected to one end of the eighth resistor R14. The other end of the eighth resistor R14... The output of the second comparator U2B is connected to the reset terminal of the first RS flip-flop. The non-inverting input of the first comparator U1B is connected to the third data signal. One end of the fifth resistor R11 is connected to the preset second threshold. The non-inverting input of the second comparator U2B is connected to the second data signal. One end of the seventh resistor R13 is connected to the preset first threshold. The third pin of the first RS flip-flop is the output terminal, which outputs the mode selection signal. The second data signal is the current signal output by the constant temperature difference module. The preset first threshold is the threshold set in the constant temperature difference module. The third data signal is the actual power signal output by the constant power module. The preset second threshold is the threshold set in the constant power module.

[0044] More in detail, such as Figure 6As shown, the switch submodule protects the second chip U3. The positive power supply terminal of the second chip U3 is connected to the first power supply voltage. The first input terminal of the second chip U3 is connected to the constant temperature difference data signal. The second input terminal of the second chip U3 is connected to the mode selection signal. The third input terminal of the second chip U3 is connected to the constant power data signal. The third pin of the second chip U3 is the output terminal of the switch submodule. When the mode selection signal input is high, the switch submodule outputs the constant power data signal. When the mode selection signal input is low, the switch submodule outputs the constant temperature difference data signal.

[0045] In detail, the adaptive switching circuit of the thermal flow meter also includes a power over-limit protection module. The power over-limit protection module is connected to a third data signal and a preset power over-limit threshold. The third data signal and the preset power over-limit threshold are logically converted to obtain a circuit protection signal. The circuit protection signal is used to perform over-power protection control on the adaptive switching circuit of the thermal flow meter. When the third data signal is greater than the preset power over-limit threshold, the output of the mass flow signal switching module is pulled down to ground.

[0046] More in detail, such as Figure 6 As shown, the power over-limit protection module includes resistors R15 and R16, and a third comparator U3B. The other end of resistor R15 is connected to the inverting input of the third comparator U3B, and the other end of resistor R15 is also connected to one end of resistor R16. The other end of resistor R16 is connected to the output of the third comparator U3B. The non-inverting input of the third comparator U3B is connected to the third data signal. The other end of resistor R15 is connected to the power over-limit setting signal. The output of the third comparator U3B is a circuit protection signal. The output module includes an electrical... Resistors R17 and R18, and a second NPN transistor Q2 are connected. One end of resistor R17 is connected to the output of the third comparator U3B, and the other end of resistor R17 is connected to ground. The collector of the second NPN transistor Q2 is connected to the other end of resistor R18, and the collector of the second NPN transistor Q2 outputs a feedback signal. The emitter of the second NPN transistor Q2 is grounded. One end of resistor R18 is connected to the mass flow rate signal output by the switching submodule. When the third data signal is greater than the preset power over-limit threshold, the third comparator outputs a high-level circuit protection signal, the second NPN transistor Q2 is turned on and grounded, pulling the mass flow rate signal to ground. The first NPN transistor in the sensor speed measurement submodule is turned off, and the sensor speed measurement submodule stops working. When the third data signal is less than or equal to the preset power over-limit threshold, the third comparator outputs a low-level circuit protection signal, the second NPN transistor Q2 is turned off, and the mass flow rate signal is output normally.

[0047] In detail, such as Figure 1-6 As shown, the working principle of an adaptive switching circuit for a thermal flow meter is as follows:

[0048] The acquisition and amplification module acquires the first raw data signal and amplifies it into a first data signal. The first data signal serves as the input signal for the constant power module and the constant temperature difference module. Through the operation of the first data signal, the constant temperature difference module outputs a second data signal and a constant temperature difference data signal, and the constant power module outputs a third data signal and a constant power data signal.

[0049] More specifically, there are four possible combinations of the second and third data signals. The principle behind the automatic switching between constant power and constant temperature difference data signals via the mass flow signal switching module is as follows:

[0050] 1) When the second data signal is less than the preset first threshold and the third data signal is greater than or equal to the preset second threshold, the first comparator outputs a high level, the second comparator outputs a low level, the first RS flip-flop outputs a high level, and the mode selection submodule outputs a constant power data signal.

[0051] 2) When the second data signal is greater than or equal to the preset first threshold and the third data signal is less than the preset second threshold, the first comparator outputs a low level, the second comparator outputs a high level, the first RS flip-flop outputs a low level, and the mode selection submodule outputs a constant temperature difference data signal.

[0052] 3) When the second data signal is greater than or equal to the preset first threshold and the third data signal is greater than or equal to the preset second threshold, the first comparator outputs a high level, the second comparator outputs a high level, the first RS flip-flop outputs the same level as before, and the output signal of the mode selection submodule remains unchanged.

[0053] 4) When the second data signal is less than the preset first threshold and the third data signal is less than the preset second threshold, the first comparator outputs a low level, the second comparator outputs a low level, and the output level of the first RS flip-flop is uncertain. This situation is not allowed.

[0054] This invention also provides an adaptive switching method for thermal flow meters, comprising:

[0055] S1. Provide the above-mentioned adaptive switching circuit for thermal flow meters.

[0056] S2. Obtain the first data signal;

[0057] In step S2, the fluid velocity is converted into a first raw data signal by a speed measuring resistor, and the first raw data signal is amplified to obtain the first data signal.

[0058] S3. Perform voltage-to-current conversion on the first data signal to obtain the second data signal. Also perform division, subtraction and amplification on the second signal to obtain the constant temperature difference data signal.

[0059] S4. Perform a multiplication operation on the first data signal to obtain the third data signal. Then, perform operational amplification, temperature compensation, and multiple multiplication operations on the third signal to obtain a constant power data signal.

[0060] S5. Perform logical processing on the second data signal, the preset first threshold, the third data signal, and the preset second threshold to obtain a mode selection signal. Output one of the constant temperature difference data signal and the constant power data signal according to the mode selection signal.

[0061] In step S5, the step of outputting one of the constant temperature difference data signal and the constant power data signal from the mode selection signal includes: when the mode selection signal is high, the thermal flow meter adaptive switching circuit outputs the constant power data signal; when the mode selection signal is low, the thermal flow meter adaptive switching circuit outputs the constant temperature difference data signal.

[0062] The embodiments of this invention clearly demonstrate that the adaptive switching circuit of the thermal flow meter, designed with an amplification module, a constant temperature difference module, a constant power module, and a mass flow signal switching module, acquires a first data signal. The constant temperature difference module and the constant power module process the first data signal to obtain a second data signal, a third data signal, a constant temperature difference data signal, and a constant power data signal. Logical processing is performed on the second data signal, a preset first threshold, and a preset second threshold for the third data signal to obtain a mode selection signal. Based on the mode selection signal, the circuit adaptively switches between the constant temperature difference data signal and the constant power data signal. This invention enables the thermal flow meter to simultaneously measure liquids and gases, ensuring optimal measurement accuracy at different temperatures and speeds. It overcomes the shortcomings of thermal flow meters designed with a single detection principle. When the thermal flow meter measures low-speed, low-temperature fluids, the mode selection signal outputs a low level, and the thermal flow meter outputs a constant temperature difference data signal. When the thermal flow meter measures high-temperature, high-speed gases, the thermal flow meter outputs a constant power data signal.

[0063] 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. An adaptive switching circuit for a thermal flow meter, characterized in that, include: The acquisition and amplification module acquires a first raw data signal and amplifies the first raw data signal to obtain a first data signal, wherein the first raw data signal is related to the fluid velocity; The constant temperature difference module receives the first data signal and performs voltage-to-current conversion on the first data signal to obtain the second data signal. It also performs division, subtraction and amplification operations on the second data signal to obtain the constant temperature difference data signal. The constant power module receives the first data signal and performs a multiplication operation on the first data signal to obtain a third data signal. It also performs operational amplification, temperature compensation, and multiple product operations on the third data signal to obtain a constant power data signal. The third data signal is the actual power signal output by the constant power module. The mass flow rate signal switching module receives the second data signal, the third data signal, the constant temperature difference data signal, and the constant power data signal. It performs logical processing on the second data signal and a preset first threshold, and on the third data signal and a preset second threshold, to obtain a mode selection signal. The mode selection signal controls one of the constant temperature difference data signal and the constant power data signal to be output externally.

2. The adaptive switching circuit for the thermal flow meter according to claim 1, characterized in that, The acquisition and amplification module includes a sensor speed measurement submodule and an amplification submodule. The sensor speed measurement submodule is used to acquire the first raw data signal, and the amplification submodule receives the first raw data signal and amplifies the first raw data signal to obtain the first data signal.

3. The adaptive switching circuit for the thermal flow meter according to claim 2, characterized in that, The sensor speed measurement submodule includes a first resistor, a second resistor, a first NPN transistor, and a first speed-measuring resistor. One end of the first resistor is connected to a first power supply voltage, and the other end of the first resistor is connected to the collector of the first NPN transistor. The emitter of the first NPN transistor is connected to one end of the first speed-measuring resistor, and the other end of the first speed-measuring resistor is connected to one end of the second resistor. The other end of the second resistor is grounded. The base of the first NPN transistor is the control terminal of the sensor speed measurement submodule, and the emitter of the first NPN transistor, the other end of the first speed-measuring resistor, and the other end of the second resistor are the output terminals of the sensor speed measurement submodule.

4. The adaptive switching circuit for the thermal flow meter according to claim 3, characterized in that, The amplification submodule includes two amplification units. The first amplification unit includes a voltage divider subunit and an amplification subunit. The second amplification unit includes a current limiting subunit and the amplification subunit. Each amplification subunit includes a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a third resistor, and a first operational amplifier. The other end of the first capacitor is connected to the inverting input terminal of the first operational amplifier. The other end of the first capacitor is also connected to one end of the second capacitor. The other end of the first capacitor is also connected to the first output terminal of either the voltage divider subunit or the current limiting subunit. One end of the first capacitor is grounded. The other end of the second capacitor is connected to one end of the third capacitor. The other end of the third capacitor is also connected to the first output terminal of the voltage divider subunit or the current limiting subunit. The first operational amplifier has a non-inverting input terminal. One end of the third capacitor is also connected to the second output terminal of the voltage divider unit or the current limiting unit. The other end of the third capacitor is grounded. The third resistor is connected in series between the first gain resistor terminal and the second gain resistor terminal of the first operational amplifier. The negative power supply terminal of the first operational amplifier is connected to the first power supply voltage. The feedback terminal of the first operational amplifier is grounded. The positive power supply terminal of the first operational amplifier is also connected to the first power supply voltage. One end of the fourth capacitor is also connected to the positive power supply terminal of the first operational amplifier. The other end of the fourth capacitor is grounded. The output terminal of the first operational amplifier is the output terminal of the amplification subunit.

5. The adaptive switching circuit for the thermal flow meter according to claim 1, characterized in that, The mass flow rate signal switching module includes a mode selection submodule and a switch submodule. The mode selection submodule is connected to the second data signal and the third data signal, and performs logical conversion on the second data signal, the preset first threshold, the third data signal and the preset second threshold to obtain a mode selection signal. The switch submodule is connected to the mode selection signal, and under the control of the mode selection signal, the switch submodule selects one of the constant power data signal and the constant temperature difference data signal for external output.

6. The adaptive switching circuit for the thermal flow meter according to claim 5, characterized in that, The mode selection submodule includes a first comparator, a second comparator, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, and a first RS flip-flop. One end of the fifth resistor is connected to the inverting input of the first comparator, and another end of the fifth resistor is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to the output of the first comparator, and the output of the first comparator is also connected to the set input of the first RS flip-flop. One end of the seventh resistor is connected to the inverting input of the second comparator, and another end of the seventh resistor is connected to one end of the eighth resistor. The other end of the eighth resistor is connected to the output of the second comparator, and the output of the second comparator is also connected to the reset input of the first RS flip-flop. The non-inverting input of the first comparator, one end of the fifth resistor, the non-inverting input of the second comparator, and one end of the seventh resistor are the inputs of the mode selection submodule, and the output of the first RS flip-flop is the output of the mode selection submodule.

7. The adaptive switching circuit for the thermal flow meter according to claim 1, characterized in that, The adaptive switching circuit of the thermal flow meter also includes a power over-limit protection module. The power over-limit protection module receives the third data signal and the preset power over-limit threshold, performs logical conversion on the third data signal and the preset power over-limit threshold to obtain a circuit protection signal. The circuit protection signal is used to perform over-power protection control on the adaptive switching circuit of the thermal flow meter. When the third data signal is greater than the preset power over-limit threshold, the output of the mass flow signal switching module is pulled down to ground.

8. An adaptive switching method for a thermal flow meter, characterized in that, Provide an adaptive switching circuit for a thermal flow meter as described in any one of claims 1-7; Acquire the first data signal; The first data signal is converted from voltage to current to obtain the second data signal. The second data signal is then divided, subtracted, and amplified to obtain the constant temperature difference data signal. The first data signal is multiplied to obtain the third data signal. The third data signal is then amplified, temperature compensated, and multiplied multiple times to obtain the constant power data signal. The second data signal, the preset first threshold, the third data signal, and the preset second threshold are logically processed to obtain the mode selection signal. One of the constant temperature difference data signal and the constant power data signal is output according to the mode selection signal.

9. The adaptive switching method for thermal flow meters according to claim 8, characterized in that, The step of acquiring the first data signal includes: The fluid velocity is converted into the first raw data signal by a speed-measuring resistor; The first original data signal is amplified to obtain the first data signal.

10. The adaptive switching method for thermal flow meters according to claim 8, characterized in that, The step of outputting one of the constant temperature difference data signal and the constant power data signal from the mode selection signal includes: When the mode selection signal is high, the thermal flow meter adaptive switching circuit outputs the constant power data signal; When the mode selection signal is low, the thermal flow meter adaptive switching circuit outputs the constant temperature difference data signal.

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