A control method of a digital hot-wire anemometer with a direct drive architecture

Abstract

This invention discloses a control method for a bridgeless direct-drive digital hot-wire anemometer, relating to the field of fluid measurement technology. The method employs a digital direct-drive closed-loop measurement circuit consisting of a main control unit, a power drive unit, a synchronous acquisition unit, and a hot-wire probe. By synchronously acquiring the voltage at both ends of the hot-wire probe and the voltage on the current sensing element, the real-time resistance and loop current of the hot-wire probe are accurately calculated. The main control unit dynamically sets the target working resistance based on the real-time ambient temperature and a preset superheat ratio, and adjusts the drive signal in real-time based on a digital PID control algorithm, enabling the hot-wire probe resistance to be quickly and accurately locked at the target value. Finally, based on steady-state data and the heat balance equation, the fluid velocity is deduced. This fundamentally eliminates the zero-point temperature drift and parasitic resistance of long wires inherent in traditional bridge circuits, achieving software-based setting of the superheat ratio and flexible optimization of control parameters, thus improving measurement accuracy, environmental adaptability, and the safety of the hot-wire probe.

Description

Technical Field

[0001] This invention relates to the field of fluid measurement technology, and in particular to a control method for a bridgeless direct-drive digital hot-wire anemometer. Background Technology

[0002] A hot-wire anemometer is a high-precision fluid measurement instrument based on the principle of convective heat transfer. It primarily determines fluid velocity by measuring changes in electrical parameters (such as resistance or voltage) caused by variations in the flow velocity through a tiny sensing element (hot wire) placed within the fluid. Due to its extremely high frequency response, high spatial resolution, and wide measurement range, the hot-wire anemometer can accurately capture the microstructure of turbulent flows, making it an indispensable key testing device in fields such as meteorological monitoring, wind tunnel experiments, aerospace, and automotive aerodynamics.

[0003] Existing constant-temperature hot-wire anemometers generally employ an analog Wheatstone bridge feedback structure, primarily composed of a Wheatstone bridge, operational amplifier circuit, and data acquisition circuit. The operational amplifier, along with the bridge containing the hot-wire probe (Rw) and three fixed bridge arm resistors (R1, R2, R3), forms a closed-loop feedback system. However, in high-precision applications and complex experimental environments, its inherent circuit structure suffers from the following technical drawbacks:

[0004] First, the Wheatstone bridge feedback structure is susceptible to ambient temperature fluctuations, exhibiting a "zero-point drift" problem. The balance of the Wheatstone bridge relies on the precise proportional relationship of the four bridge arm resistors; however, the three fixed bridge arm resistors each have an inherent temperature coefficient of resistance. In actual testing, fluctuations in ambient temperature cause slight drifts in the bridge arm resistance values. This thermal drift is misinterpreted by the feedback circuit as a flow rate signal, leading to a zero-point offset in the measurement. Although expensive, high-precision, low-temperature-drift resistors can be used to suppress it, it is difficult to fundamentally eliminate the systematic temperature drift error caused by the circuit structure.

[0005] Secondly, the parasitic resistance introduced by long lead wires significantly affects measurement accuracy and limits application scenarios: Wheatstone bridges typically use a two-wire connection for hot-wire probes, which results in the resistance of the transmission wires and the contact resistance of the connectors being directly connected in series in the measuring arm. For hot-wire probes with resistance values ​​typically only a few ohms, the parasitic resistance introduced by long lead wires cannot be ignored. Furthermore, changes in wire resistance (such as those caused by bending or ambient temperature) can be directly misinterpreted as changes in wind speed, severely impacting measurement accuracy. To mitigate this impact, existing equipment usually limits the probe lead length or requires the use of thick-diameter, low-resistance wires, which greatly restricts the deployment flexibility of hot-wire probes in large wind tunnels, high towers, or field experiments.

[0006] Third, the fixed hardware parameters make it unsuitable for environments with large temperature variations, and the overheat ratio is difficult to adjust: The Wheatstone bridge locks the working resistance of the hot-wire probe to a fixed value through a fixed bridge arm resistor structure. However, in actual applications such as radiosonde measurements, the ambient temperature often drops drastically with increasing altitude. Because traditional bridges cannot dynamically adjust the bridge arm resistance during operation, the overheat ratio of the hot wire drifts significantly with the ambient temperature. This not only severely alters the sensor's sensitivity coefficient, leading to measurement failure, but may also cause the hot-wire probe to experience excessive thermal stress and current surges due to the large temperature difference between the hot-wire probe and the ambient temperature in low-temperature environments, accelerating sensor aging or causing irreversible physical damage. Furthermore, existing methods of replacing resistors or adjusting potentiometers are insufficient to meet the dynamic measurement requirements of real-time temperature variations.

[0007] Fourth, analog feedback control relies on hardware components and cannot achieve real-time adaptive adjustment of control parameters: Traditional constant-temperature anemometers depend on analog circuits with fixed parameters, which can typically only be optimized for a specific steady-state flow field. When faced with large-span flow velocity changes, significant changes in fluid properties, or replacement of probes with different specifications, the fixed analog hardware cannot adjust the control strategy in real time. This makes the system prone to underdamped oscillations or overdamped hysteresis when deviating from the design conditions, making it difficult to maintain the accuracy of measurement data in full-range, multi-scenario applications. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, this invention proposes a control method for a bridgeless direct-drive architecture digital hot-wire anemometer.

[0009] To achieve the above objectives, the present invention adopts the following technical solution, including:

[0010] A control method for a bridgeless direct-drive architecture digital hot-wire anemometer, the bridgeless direct-drive architecture digital hot-wire anemometer includes: a main control unit, a power drive unit, a synchronous acquisition unit, a hot-wire probe interface, a current detection element, and a hot-wire probe connected to the hot-wire probe interface;

[0011] The main control unit is connected to the power drive unit and the synchronous acquisition unit respectively;

[0012] The power drive unit, hot wire probe interface, and current sensing element are connected in series. The hot wire probe interface and current sensing element are also connected to the synchronous acquisition unit, which is connected to the main control unit. The synchronous acquisition unit is used to acquire the voltages at both ends of the hot wire probe and the current sensing element, and simultaneously inputs the acquired voltages to the main control unit. The power drive unit, hot wire probe interface, hot wire probe, current sensing element, synchronous acquisition unit, and main control unit together form a closed direct-drive measurement loop.

[0013] The control method utilizes the power drive unit to receive the control signal from the main control unit, and drives the direct drive measurement circuit to adjust the working resistance of the hot wire probe, thereby accurately locking the working resistance of the hot wire probe to the target working resistance dynamically set based on the ambient temperature, and finally obtaining the actual fluid wind speed based on steady-state data; the steady-state data includes the actual resistance of the hot wire probe, the voltage across the hot wire probe, and the loop current in the direct drive measurement circuit.

[0014] Preferably, the bridgeless direct-drive architecture digital hot-wire anemometer also includes a power management unit, a communication interface unit, a data storage unit, and an environmental parameter monitoring unit; the main control unit is connected to the communication interface unit and the data storage unit respectively;

[0015] The power management unit supplies power to each unit; the environmental parameter monitoring unit acquires environmental parameters; the power drive unit includes a digital-to-analog converter circuit, an operational amplifier, and a power adjustment element connected in sequence; the digital-to-analog converter circuit converts digital signals into analog signals; the structure formed by the operational amplifier and the power adjustment element is used to adjust the loop current in the direct-drive measurement loop; the power adjustment element is connected to the power management unit and the hot-wire probe interface respectively; the digital-to-analog converter circuit is connected to the main control unit.

[0016] The power drive unit also includes a hardware current limiting protection circuit; one end of the hardware current limiting protection circuit is connected to the electrical connection line between the output terminal of the digital-to-analog converter circuit and the non-inverting input terminal of the operational amplifier, and the other end is grounded;

[0017] The synchronous acquisition unit includes a first voltage acquisition channel and a second voltage acquisition channel, which adopt a four-wire Kelvin connection. The two ends of the first voltage acquisition channel and the second voltage acquisition channel are respectively connected across the hot wire probe interface and the two ends of the current detection element.

[0018] Preferably, the control method includes:

[0019] S1: Initialize the hot-wire anemometer; the main control unit acquires system configuration parameters and the current real-time ambient temperature T. env ;

[0020] S2: The main control unit is based on the real-time ambient temperature T. env Obtain the target operating resistance of the hot wire probe;

[0021] S3: The main control unit obtains the initial drive voltage for digital-to-analog conversion based on the target operating resistance of the hot-wire probe. ;

[0022] S4: Initial drive voltage for digital-to-analog conversion The current is applied to the power drive unit, which adjusts the loop current in the direct drive measurement circuit to drive the actual resistance R of the hot wire probe.real Adjust to the target operating resistance of the hot wire probe nearby;

[0023] S5: The synchronous acquisition unit acquires the voltage of the hot-wire probe and current sensing element through a four-wire sampling method, and calculates the loop current in the direct-drive measurement circuit. Obtain the actual resistance R of the hot wire probe. real ;

[0024] S6: Based on the actual resistance R of the hot wire probe real and target working resistance The system employs PID control technology to correct the digital-to-analog converter voltage output value in real time. Based on this corrected output value, the power drive unit adjusts the loop current in the direct-drive measurement circuit, thereby ensuring the actual resistance R of the hot-wire probe is controlled. real Make the corresponding adjustments;

[0025] S7: Determine whether the absolute value of the resistance deviation at the current timing cycle is less than the resistance deviation threshold; if yes, mark the steady-state data; if no, jump to step S5; wherein, the steady-state data includes the actual resistance R of the hot wire probe at the current timing cycle. real Voltage at both ends of the hot wire probe and the loop current in the direct drive measurement circuit .

[0026] S8: Based on the steady-state data of the current time series, the main control unit calculates the actual fluid wind speed by back-calculating the heat balance equation. U .

[0027] Preferably, after obtaining the actual fluid wind speed, the main control unit continues to iterate steps S5-S8 at a set first frequency to obtain the real-time actual fluid flow rate; then, it obtains the real-time ambient temperature at a set second frequency, and executes steps S2 and S5-S8 based on the real-time ambient temperature to obtain the actual fluid wind speed that changes over time; wherein, the first frequency is greater than the second frequency.

[0028] Preferably, the system configuration parameters include a preset superheat ratio coefficient. The calibrated resistance of the hot wire probe Temperature coefficient of resistance The resistance of the current sensing element First, second, and third calibration constants; proportional coefficient K of the PID controller. p Integral coefficient K i and differential coefficient K d .

[0029] Preferably, step S2 includes:

[0030] S21: The main control unit calculates the cold resistance of the hot wire probe under the current real-time ambient temperature. The calculation formula is:

[0031]

[0032] in, For reference temperature; This is the calibration resistance value for the hot wire probe; It is the temperature coefficient of resistance;

[0033] S22: Calculate and maintain the preset superheat ratio coefficient Target operating resistance of the required hot wire probe The calculation formula is:

[0034]

[0035] in, This is the preset superheat ratio coefficient;

[0036] Step S3 includes:

[0037] The main control unit acquires the target operating resistance of the hot wire probe. Required start-up current The calculation formula is:

[0038]

[0039] in, This is the first calibration constant;

[0040] Then, the initial drive voltage for digital-to-analog conversion is calculated based on the startup current. The calculation formula is:

[0041]

[0042] in, This is the resistance value of the current sensing element.

[0043] Preferably, step S5 includes:

[0044] S51: The synchronous acquisition unit measures and acquires the voltage across the hot wire probe. ;

[0045] S52: Synchronous acquisition unit measures the voltage across the current sensing element. The main control unit is based on Ohm's law. Calculate the loop current in the direct drive measurement circuit. ;in, The resistance value of the current sensing element;

[0046] S53: Based on the voltage across the hot wire probe and the loop current in the direct drive measurement circuit The actual resistance of the hot wire probe is obtained according to Ohm's law. The calculation formula is:

[0047]

[0048] Preferably, step S6 includes:

[0049] S61: The main control unit calculates the resistance deviation at the current sampling time period k based on the actual resistance and target operating resistance of the hot-wire probe. The calculation formula is:

[0050]

[0051] S62: Resistance deviation based on the current timing period k Resistance deviations from historical time series periods k-1 and k-2 , Obtain the voltage correction amount at the current timing period k. The calculation formula is:

[0052]

[0053] When k=1, historical time deviation and Set all to 0;

[0054] S63: Voltage correction amount based on the current timing period k The digital-to-analog conversion voltage output value at the previous timing cycle The correction is performed to obtain the corrected digital-to-analog converter voltage output value at the current timing period k, i.e. ;

[0055] When k=1, the digital-to-analog conversion voltage output value at the previous timing cycle This is the initial drive voltage for digital-to-analog conversion. .

[0056] S64: Apply the corrected digital-to-analog converter voltage output value at the current timing period k to the power drive unit for drive adjustment, thereby adjusting the actual resistance R of the hot wire probe. real Make the corresponding adjustments.

[0057] Preferably, in step S8, the heat balance equation is:

[0058]

[0059] in, This refers to the voltage across the two ends of the hot wire probe; For direct drive measurement of loop current; The cold resistance of the hot-wire probe at the current ambient temperature; It is the temperature coefficient of resistance; These are the first, second, and third calibration constants, respectively.

[0060] Preferably, the control method employs a dual protection system combining hardware and software, which limits the maximum input voltage of the operational amplifier through a Zener diode throughout the entire system operation process;

[0061] The main control unit monitors the loop current in step S4 in real time. When the loop current is detected continuous The current safety threshold was exceeded for one timing cycle. When the system experiences an overcurrent fault, the main control unit determines that an overcurrent fault has occurred, issues an alarm, and immediately forces the digital-to-analog converter voltage output value to zero.

[0062] The advantages of this invention are:

[0063] (1) This invention abandons the traditional Wheatstone bridge structure that relies on three fixed bridge arm resistors and adopts a purely digital bridgeless direct-drive architecture. The main control unit calculates and dynamically adjusts the drive voltage in real time to lock the hot wire probe resistance to the target value. This process completely avoids the direct impact of fixed bridge arm resistor temperature drift on the measurement zero point. At the same time, combined with real-time monitoring of ambient temperature, the software algorithm dynamically compensates for the change of cold resistance of the hot wire probe with temperature online. It does not rely on expensive low-temperature drift hardware, eliminates the main error source of bridge resistance temperature drift, and improves the measurement stability of the equipment in long-term operation and variable temperature environments.

[0064] (2) The control method of this invention effectively eliminates the interference of transmission wires and connector contact resistance on voltage measurement based on a four-wire (Kelvin) synchronous acquisition method. The first voltage acquisition channel is directly connected across the two ends of the hot wire probe for sampling, and the measured voltage signal does not include the voltage drop across the leads and contact resistance. The current is accurately measured through an independent current detection element (connected in series with the probe). Therefore, the parasitic resistance voltage drop generated by the loop current flowing through the long wire will not interfere with the accurate measurement of the voltage across the hot wire probe, and the probe resistance value calculated by the main control unit is independent of the wire resistance. This allows the probe to be connected to wires that are tens or even hundreds of meters long without worrying about accuracy loss, fully meeting the complex experimental requirements of large wind tunnels, high-rise buildings, and field atmospheric observations that require long-distance probe deployment.

[0065] (3) The control method of this invention fully software-izes core parameters such as superheat ratio setting, cold resistance calculation, and target working resistance determination. The main control unit dynamically calculates the cold resistance of the hot wire probe at the current temperature based on the real-time collected ambient temperature, and calculates the target working resistance in combination with the preset superheat ratio coefficient. Then, the hot wire resistance is driven to be accurately stabilized at the target value through a closed-loop control algorithm. This mechanism enables the hot wire anemometer to automatically adapt to drastic changes in ambient temperature from low temperature at high altitudes to high temperature near the ground, always maintaining a constant superheat ratio, thereby ensuring the stability of measurement sensitivity and effectively preventing the hot wire probe from being subjected to excessive thermal stress and current impact due to the large temperature difference between the hot wire probe and the ambient temperature at low temperatures, greatly improving the reliability, accuracy and measurement range of the equipment.

[0066] (4) This invention uses a main control unit as its core and employs a digital PID algorithm to perform real-time closed-loop adjustment of the hot-wire resistance, replacing the traditional analog feedback control loop based on bridge self-balancing. Control parameters (such as Kp, Ki, Kd) can be entirely defined by software and can be adaptively adjusted or switched in real-time and online according to the flow rate range, fluid medium, or the dynamic response characteristics of different probe models. This enables the system to optimize response speed and stability for dynamic processes such as transient flow and turbulence, avoiding underdamped oscillations or overdamped hysteresis, and ensuring high-precision measurement results across the entire range and under multi-fluid conditions. Furthermore, system upgrades and maintenance only require software updates, without hardware changes, offering exceptional flexibility and scalability.

[0067] (5) At the hardware level, this invention incorporates a hardware current-limiting protection circuit composed of Zener diodes, which clamps the input voltage of the operational amplifier, thereby limiting the output current amplitude and preventing accidental overshoot. At the software level, the main control unit monitors the loop current in real time, uses intelligent algorithms to determine overcurrent faults, and executes protective actions such as forced zero-output. This dual protection strategy combining hardware and software provides more comprehensive and faster overload protection for delicate and fragile metal film hot wire or hot film probes, effectively reducing the risk of probe damage under complex operating conditions or misoperation, and extending the service life of the core sensor. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of the structure of a digital hot-wire anemometer with a bridgeless direct-drive architecture according to the present invention.

[0069] Figure 2 This is a schematic diagram of the circuit principle of the direct-drive measurement circuit in an embodiment of the present invention;

[0070] Figure 3 This is a flowchart of the control method of the present invention. Detailed Implementation

[0071] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0072] Example 1

[0073] like Figures 1-3 As shown, this invention proposes a control method for a bridgeless direct-drive digital hot-wire anemometer, implemented using a bridgeless direct-drive digital hot-wire anemometer. The bridgeless direct-drive digital hot-wire anemometer includes a main control unit 1, a power management unit 2, a power drive unit 3, a synchronous acquisition unit 4, a hot-wire probe interface 5, a current detection element 6, a communication interface unit 7, a data storage unit 8, and an environmental parameter monitoring unit 9. When the digital hot-wire anemometer is working, it also includes a hot-wire probe 10 connected to the hot-wire probe interface 5.

[0074] The power management unit 2 is electrically connected to the power drive unit 3, the synchronous acquisition unit 4, the main control unit 1, and the environmental monitoring unit 9, respectively, to provide power to each unit and supply the required DC operating voltage. In this embodiment, the power management unit 2 provides a +3.3V digital voltage to the main control unit 1 and the environmental parameter monitoring unit 9, and provides a +24V drive power to the power drive unit 3.

[0075] The main control unit 1 is used for timing and periodic control and data processing of the hot-wire anemometer, and is electrically connected to the power drive unit 3, the synchronous acquisition unit 4, the communication interface unit 7, and the data storage unit 8. In this embodiment, the main control unit 1 is an STM32H7 series high-performance microcontroller.

[0076] The power drive unit 3, hot wire probe interface 5, and current sensing element 6 are connected in series. Simultaneously, the hot wire probe interface 5 and current sensing element 6 are connected to the synchronous acquisition unit 4, which is connected to the main control unit 1. The synchronous acquisition unit 4 is used to acquire the voltages across the hot wire probe 10 and the current sensing element 6, and simultaneously inputs the acquired voltages to the main control unit 1. The power drive unit 3, hot wire probe interface 5, hot wire probe 10, current sensing element 6, synchronous acquisition unit 4, and main control unit 1 together form a closed direct-drive measurement loop. The power drive unit 3 receives the control signal from the main control unit 1 and drives the direct-drive measurement loop to operate in a constant overheat ratio mode. The hot wire probe interface 5 is used for detachable connection of the hot wire probe 10. In this embodiment, the current sensing element 6 is a low-temperature drift alloy resistor.

[0077] like Figure 2As shown, the power drive unit 3 includes a digital-to-analog converter circuit 31, an operational amplifier 32, and a power adjustment element 33 connected in sequence; the power adjustment element 33 is also connected to the power management unit 2 and the hot wire probe interface 5 respectively; the digital-to-analog converter circuit 31 is connected to the main control unit 1.

[0078] In this embodiment, the power management unit 2 includes a drive power supply; the power regulation element 33 is an N-channel enhancement-mode field-effect transistor (N-type MOSFET), the gate of the N-channel enhancement-mode field-effect transistor is connected to the output terminal of the operational amplifier 32, the source of the N-channel enhancement-mode field-effect transistor is connected to the hot wire probe interface 5, and the drain of the N-channel enhancement-mode field-effect transistor is connected to the drive power supply of the power management unit 2. In this embodiment, the voltage of the drive power supply is +24V to ensure that the N-type MOSFET has sufficient dynamic drive range; at the same time, the power management unit 2 also includes a capacitor C1, one end of which is connected to the line between the N-channel enhancement-mode field-effect transistor and the drive power supply, and the other end is grounded to filter out power ripple.

[0079] The power drive unit 3 also includes a hardware current limiting protection circuit 34. In this embodiment, a Zener diode or a TVS diode is selected. The negative terminal of the Zener diode 34 is connected to the electrical connection line between the output terminal of the digital-to-analog converter circuit 31 and the non-inverting input terminal of the operational amplifier 32, and the positive terminal is grounded. The hardware current limiting protection circuit 34 is used to force the analog control voltage input to the operational amplifier 32 to be clamped within a preset voltage safety threshold. This utilizes the closed-loop negative feedback mechanism formed by the operational amplifier and the N-channel MOSFET to limit the maximum current flowing through the hot wire probe 10 to within the safety threshold range, preventing the hot wire probe 10 from burning out.

[0080] The synchronous acquisition unit 4 includes a first voltage acquisition channel and a second voltage acquisition channel, which adopt a four-wire Kelvin connection. The two ends of the first voltage acquisition channel and the second voltage acquisition channel are respectively connected across the hot wire probe interface 5 and the current detection element 6. Since the bridging points across the two ends of the hot wire probe interface 5 extend directly to the root of the hot wire probe 10, the synchronous acquisition unit 4 can directly acquire the actual voltage across the two ends of the hot wire probe 10, thereby eliminating the interference caused by the contact resistance of the hot wire probe interface and the lead resistance of the hot wire probe 10.

[0081] The environmental parameter monitoring unit 9 preferentially adopts a high-precision temperature sensor. In this embodiment, the SHT4x series sensor is selected to collect the ambient temperature of the fluid to be measured in real time and then send it to the main control unit 1. The main control unit 1 uses the ambient temperature data to adjust the cold resistance of the hot wire probe 10 in real time in the fluid wind speed calculation to correct the thermal convection calculation error caused by the change of ambient temperature.

[0082] The communication interface unit 7, such as a USB, Ethernet or RS485 interface, is connected to the main control unit 1 to realize data interaction between the main control unit 1 and an external terminal (PC);

[0083] Data storage unit 8 is a non-volatile solid-state memory, such as an SD card or a high-capacity Flash chip, connected to the main control unit 1, used to store system configuration and measurement data to prevent data loss in case of power failure.

[0084] The control method utilizes the power drive unit 3 to receive control signals from the main control unit 1, driving the direct drive measurement circuit to adjust the working resistance of the hot wire probe 10, thereby precisely locking the working resistance of the hot wire probe 10 to the target working resistance dynamically set based on the ambient temperature, and finally obtaining the actual fluid wind speed based on steady-state data. Specifically, it includes:

[0085] S1: Initialize the hot-wire anemometer. Simultaneously, the main control unit 1 reads the system configuration parameters stored in the data storage unit 8 and sends an environmental temperature acquisition command to the environmental parameter monitoring unit 9 to obtain the current real-time environmental temperature T. env The system configuration parameters include the preset superheat ratio coefficient. (In this embodiment, the resistance is preferably set to 0.6), the calibrated resistance value of the hot wire probe 10. That is, the rated resistance of the hot wire probe at 20°C (in this embodiment, it is...). Temperature coefficient of resistance (In this embodiment, the resistance value is set to 0.0036), the resistance value of the current sensing element 6. (In this embodiment, it is preferably set to) The first calibration constant A, the second calibration constant B, the third calibration constant n, and the initial gain parameter of the PID controller (proportional coefficient K) p Integral coefficient K i Differential coefficient K d In this embodiment, to ensure the system responds quickly to wind speed changes without overshoot oscillation, the initial gain parameter is configured as: proportional coefficient. Integral coefficient Differential coefficients .

[0086] S2: Main control unit 1 is based on real-time ambient temperature T env To obtain the target operating resistance of the hot wire probe, including:

[0087] S21: The main control unit 1 calculates the cold resistance of the hot wire probe 10 under the current ambient temperature based on the resistance-temperature characteristic model of the hot wire probe material. The calculation formula is:

[0088]

[0089] in, The reference temperature is (preferably set to 20°C in this embodiment). This is the calibration resistance value of the hot wire probe 10 (i.e., the calibration resistance value at 20℃). is the temperature coefficient of resistance.

[0090] S22: Calculate and maintain the preset superheat ratio coefficient Target operating resistance of the required hot wire probe The calculation formula is:

[0091]

[0092] in, This is the preset superheat ratio coefficient; The physical quantity of the hot-wire probe 10 that the system needs to lock at the current moment is the thermal target.

[0093] S3: To improve the dynamic response speed of the system, the main control unit 1 is based on the target working resistance of the hot wire probe. and the resistance value of current sensing element 6 Calculate the initial drive voltage for digital-to-analog conversion. As a feedforward for PID control; including:

[0094] Main control unit 1 calculates the target operating resistance of the hot wire probe based on a thermal balance model under zero wind speed conditions. Required start-up current The calculation formula is:

[0095]

[0096] in, This is the first calibration constant; This is the preset superheat ratio coefficient;

[0097] Then, the initial drive voltage for digital-to-analog conversion is calculated based on the startup current. The calculation formula is:

[0098]

[0099] in, The resistance value of the current sensing element 6.

[0100] S4: The main control unit 1 converts the initial drive voltage for digital-to-analog conversion. The signal is sent to the digital-to-analog converter (DAC) 31; the DAC 31 then uses the initial drive voltage for the digital-to-analog conversion. The corresponding analog voltage value is output to the non-inverting input of operational amplifier 32; operational amplifier 32 and power adjustment element 33 constitute a voltage-controlled constant current drive circuit to adjust the loop current in the direct drive measurement circuit and drive the actual resistance R of hot wire probe 10. real Quickly adjust to the target operating resistance of the hot wire probe. nearby.

[0101] The actual resistance of the hot wire probe 10 is the actual working resistance (hot resistance).

[0102] S5: Synchronous acquisition unit 4 acquires voltage using a four-wire sampling method and calculates the loop current in the direct drive measurement circuit. Obtain the actual resistance R of the hot wire probe 10. real ,include:

[0103] S51: The first voltage acquisition channel directly measures and acquires the voltage across the hot wire probe 10. Because of the use of an independent sensing line, the voltage value directly reflects the voltage of the hot wire probe body, effectively eliminating the parasitic voltage drop generated on the transmission wire and interface contact resistance.

[0104] S52: The second voltage acquisition channel measures the voltage across the current detection element 6. Main control unit 1, according to Ohm's law Calculate the loop current in the direct drive measurement circuit. ,in, The resistance value of the current sensing element 6.

[0105] S53: Based on the voltage across the hot wire probe 10 and the loop current in the direct drive measurement circuit The actual resistance of the hot wire probe 10 is obtained according to Ohm's law. This eliminates resistance interference in all transmission lines at the probe interface front end. The calculation formula is:

[0106]

[0107] S6: Actual resistance based on hot wire probe 10 and target working resistance The PID control technology is used to correct the digital-to-analog converter voltage output value V in real time. The corrected digital-to-analog converter voltage output value is then used to drive and adjust the power drive unit 3, thereby adjusting the actual resistance R of the hot wire probe 10. real Make the following adjustments:

[0108] S61: The main control unit 1 calculates the resistance deviation at the current sampling time period k based on the actual resistance and target working resistance of the hot wire probe 10. The calculation formula is:

[0109]

[0110] S62: Based on the resistance deviation between the current time period k and the historical time periods, substitute it into the incremental PID control algorithm model to obtain the voltage correction at the current time period k. The calculation formula is:

[0111]

[0112] During the initial cycle of system startup, the missing historical deviations are initialized to zero by default; that is, when k=1, the historical time deviations are zero. and Set all values ​​to 0.

[0113] S63: Voltage correction amount based on the current timing period k The digital-to-analog conversion voltage output value at the previous timing cycle The correction is performed to obtain the corrected digital-to-analog converter voltage output value at the current timing period k, i.e. .

[0114] Wherein, when k=1, the digital-to-analog conversion voltage output value at the previous timing cycle This is the initial drive voltage for digital-to-analog conversion. .

[0115] S64: Apply the corrected digital-to-analog conversion voltage output value at the current timing period k to the power drive unit 3 to drive and adjust the loop current in the direct drive measurement circuit, thereby making the actual resistance R of the hot wire probe 10... real Adjustments were made accordingly. Steady-state errors were eliminated by dynamically refreshing the output voltage of the power drive unit 3, ultimately precisely locking the resistance value of the hot-wire probe 10 to the target operating resistance. .

[0116] S7: Determine the resistance deviation at the current timing cycle. Whether the absolute value is less than the resistance deviation threshold, i.e., whether the system is in a steady state (in this embodiment, the resistance deviation threshold is set to 0.01Ω); if yes, the actual resistance R of the hot wire probe 10 at the current timing cycle is... real Voltage at both ends of the hot wire probe and the loop current in the direct drive measurement circuit Mark as steady-state data; otherwise, continue to step S5.

[0117] S8: Based on steady-state data, main control unit 1 calculates the actual fluid wind speed by back-calculating the heat balance equation. U The heat balance equation is:

[0118]

[0119] in, The voltage across the hot wire probe 10; For direct drive measurement of loop current; The cold resistance of the hot wire probe 10 at the current ambient temperature; It is the temperature coefficient of resistance; These are the first, second, and third calibration constants, respectively. The actual Joule thermal power of the hot wire probe 10 is represented by the heat dissipation power term on the right side of the equation. It directly replaces the temperature difference term in the traditional King's formula by utilizing the rate of change of resistance. This formula directly calls the real-time voltage, current and resistance variables already in memory, ensuring the rigor of the physical equations while avoiding the tedious temperature back-calculation process and improving the computational efficiency of the digital system.

[0120] In obtaining actual fluid wind speed U Then, the main control unit 1 continues to iterate steps S5-S8 at a set first frequency to obtain the real-time actual fluid flow rate; then, it obtains the real-time ambient temperature at a set second frequency, and executes steps S2 and S5-S8 based on the real-time ambient temperature to obtain the actual fluid wind speed changing over time. The first frequency is greater than the second frequency.

[0121] Note: The PID control loop is not paused during the actual fluid wind speed calculation process.

[0122] The system employs a task-level processing strategy: For the closed-loop control tasks in steps S5-S8, the main control unit 1 executes subsequent sampling and PID control steps at a high frequency (20kHz in this embodiment). Regardless of the state of the parameter update task, the closed-loop control task is always based on the latest data in memory. The value is continuously calculated.

[0123] Meanwhile, the main control unit 1 periodically reads the data from the environmental parameter monitoring unit 9 at a lower update frequency (i.e., 1Hz in this embodiment) and recalculates the target operating resistance. Because ambient temperature has a large thermal inertia, this low-frequency update is sufficient to meet real-time requirements.

[0124] The calculated actual fluid wind speed and original electrical parameters are uploaded to the external terminal through the communication interface unit 7 and simultaneously written to the data storage unit 8.

[0125] This method employs a dual protection system combining hardware and software, executing the following dual protection logic throughout the entire system operation:

[0126] Hardware transient protection: The maximum input voltage of the operational amplifier 32 is physically limited by the Zener diode 34 to prevent the hot wire probe from melting due to excessive current.

[0127] Software steady-state protection: The main control unit 1 monitors the loop current in the direct drive measurement circuit in step S4 in real time. The system is set with a current safety threshold. (In this embodiment, the current is preferably set to 300mA). When the loop current is monitored... continuous One time period (preferably set to one time period in this embodiment) Exceeding the current safety threshold When the main control unit 1 determines that the system has an overcurrent fault (which may be due to a short circuit in the probe or a sudden change in wind speed), it immediately forces the digital-to-analog converter voltage output value to zero and disconnects the power drive unit 3, causing the system to stop for processing. At the same time, it issues an alarm until the system is reset.

[0128] Throughout the entire control process, the system performs cyclic control according to a preset time period (preferably set to a frequency of 20kHz in this embodiment). High-frequency sampling and control ensure that the hot wire probe 10 can always be accurately locked in a constant superheat ratio state in the transient flow field, thereby ensuring high-frequency response and high-precision wind speed measurement across the entire range.

[0129] Of course, those skilled in the art will recognize that the present invention is not limited to the details of the exemplary embodiments described above, but also includes the same or similar structures that can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0130] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0131] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A control method for a bridgeless direct-drive digital hot-wire anemometer, characterized in that, The bridgeless direct-drive architecture digital hot-wire anemometer includes: a main control unit, a power drive unit, a synchronous acquisition unit, a hot-wire probe interface, a current detection element, and a hot-wire probe connected to the hot-wire probe interface; The main control unit is connected to the power drive unit and the synchronous acquisition unit respectively; The power drive unit, hot wire probe interface, and current sensing element are connected in series. The hot wire probe interface and current sensing element are also connected to the synchronous acquisition unit, which is connected to the main control unit. The synchronous acquisition unit is used to acquire the voltages at both ends of the hot wire probe and the current sensing element, and simultaneously inputs the acquired voltages to the main control unit. The power drive unit, hot wire probe interface, hot wire probe, current sensing element, synchronous acquisition unit, and main control unit together form a closed direct-drive measurement loop. The control method utilizes the power drive unit to receive the control signal from the main control unit, and drives the direct drive measurement circuit to adjust the working resistance of the hot wire probe, thereby accurately locking the working resistance of the hot wire probe to the target working resistance dynamically set based on the ambient temperature, and finally obtaining the actual fluid wind speed based on steady-state data; the steady-state data includes the actual resistance of the hot wire probe, the voltage across the hot wire probe, and the loop current in the direct drive measurement circuit.

2. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 1, characterized in that, The bridgeless direct-drive architecture digital hot-wire anemometer also includes a power management unit, a communication interface unit, a data storage unit, and an environmental parameter monitoring unit; the main control unit is connected to both the communication interface unit and the data storage unit. The power management unit supplies power to each unit; the environmental parameter monitoring unit acquires environmental parameters; the power drive unit includes a digital-to-analog converter circuit, an operational amplifier, and a power adjustment element connected in sequence; the digital-to-analog converter circuit converts digital signals into analog signals; the structure formed by the operational amplifier and the power adjustment element is used to adjust the loop current in the direct-drive measurement loop; the power adjustment element is connected to the power management unit and the hot-wire probe interface respectively; the digital-to-analog converter circuit is connected to the main control unit. The power drive unit also includes a hardware current limiting protection circuit; One end of the hardware current limiting protection circuit is connected to the electrical connection line between the output terminal of the digital-to-analog converter circuit and the non-inverting input terminal of the operational amplifier, and the other end is grounded; The synchronous acquisition unit includes a first voltage acquisition channel and a second voltage acquisition channel, which adopt a four-wire Kelvin connection. The two ends of the first voltage acquisition channel and the second voltage acquisition channel are respectively connected across the hot wire probe interface and the two ends of the current detection element.

3. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 1 or 2, characterized in that, The control method includes: S1: Initialize the hot-wire anemometer; the main control unit acquires system configuration parameters and the current real-time ambient temperature T. env ; S2: The main control unit is based on the real-time ambient temperature T. env Obtain the target operating resistance of the hot wire probe; S3: The main control unit obtains the initial drive voltage for digital-to-analog conversion based on the target operating resistance of the hot-wire probe. ; S4: Initial drive voltage for digital-to-analog conversion The current is applied to the power drive unit, which adjusts the loop current in the direct drive measurement circuit to drive the actual resistance R of the hot wire probe. real Adjust to the target operating resistance of the hot wire probe nearby; S5: The synchronous acquisition unit acquires the voltage of the hot-wire probe and current sensing element through a four-wire sampling method, and calculates the loop current in the direct-drive measurement circuit. Obtain the actual resistance R of the hot wire probe. real ; S6: Based on the actual resistance R of the hot wire probe real and target working resistance The system employs PID control technology to correct the digital-to-analog converter voltage output value in real time. Based on this corrected output value, the power drive unit adjusts the loop current in the direct-drive measurement circuit, thereby ensuring the actual resistance R of the hot-wire probe is controlled. real Make the corresponding adjustments; S7: Determine whether the absolute value of the resistance deviation at the current timing cycle is less than the resistance deviation threshold; if yes, mark the steady-state data; if no, jump to step S5; wherein, the steady-state data includes the actual resistance R of the hot wire probe at the current timing cycle. real Voltage at both ends of the hot wire probe and the loop current in the direct drive measurement circuit ; S8: Based on the steady-state data of the current time series, the main control unit calculates the actual fluid wind speed by back-calculating the heat balance equation. U .

4. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 3, characterized in that, After obtaining the actual fluid wind speed, the main control unit continues to iterate steps S5-S8 at a set first frequency to obtain the real-time actual fluid flow rate; then, it obtains the real-time ambient temperature at a set second frequency, and executes steps S2 and S5-S8 based on the real-time ambient temperature to obtain the actual fluid wind speed that changes over time; wherein, the first frequency is greater than the second frequency.

5. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 3, characterized in that, System configuration parameters include preset superheat ratio coefficients. The calibrated resistance of the hot wire probe Temperature coefficient of resistance The resistance of the current sensing element First, second, and third calibration constants; proportional coefficient K of the PID controller. p Integral coefficient K i and differential coefficient K d .

6. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 5, characterized in that, Step S2 includes: S21: The main control unit calculates the cold resistance of the hot wire probe under the current real-time ambient temperature. The calculation formula is: in, For reference temperature; This is the calibration resistance value for the hot wire probe; It is the temperature coefficient of resistance; S22: Calculate and maintain the preset superheat ratio coefficient Target operating resistance of the required hot wire probe The calculation formula is: in, This is the preset superheat ratio coefficient; Step S3 includes: The main control unit acquires the target operating resistance of the hot wire probe. Required start-up current The calculation formula is: in, This is the first calibration constant; Then, the initial drive voltage for digital-to-analog conversion is calculated based on the startup current. The calculation formula is: in, This is the resistance value of the current sensing element.

7. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 3, characterized in that, Step S5 includes: S51: The synchronous acquisition unit measures and acquires the voltage across the hot wire probe. ; S52: Synchronous acquisition unit measures the voltage across the current sensing element. The main control unit is based on Ohm's law. Calculate the loop current in the direct drive measurement circuit. ;in, The resistance value of the current sensing element; S53: Based on the voltage across the hot wire probe and the loop current in the direct drive measurement circuit The actual resistance of the hot wire probe is obtained according to Ohm's law. The calculation formula is:

8. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 5, characterized in that, Step S6 includes: S61: The main control unit calculates the resistance deviation at the current sampling time period k based on the actual resistance and target operating resistance of the hot-wire probe. The calculation formula is: S62: Resistance deviation based on the current timing period k Resistance deviations from historical time series periods k-1 and k-2 , Obtain the voltage correction amount at the current timing period k. The calculation formula is: When k=1, historical time deviation and Set all to 0; S63: Voltage correction amount based on the current timing period k The digital-to-analog conversion voltage output value at the previous timing cycle The correction is performed to obtain the corrected digital-to-analog converter voltage output value at the current timing period k, i.e. ; When k=1, the digital-to-analog conversion voltage output value at the previous timing cycle This is the initial drive voltage for digital-to-analog conversion. ; S64: Apply the corrected digital-to-analog converter voltage output value at the current timing period k to the power drive unit for drive adjustment, thereby adjusting the actual resistance R of the hot wire probe. real Make the corresponding adjustments.

9. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 3, characterized in that, In step S8, the heat balance equation is: in, This refers to the voltage across the two ends of the hot wire probe; For direct drive measurement of loop current; The cold resistance of the hot-wire probe at the current ambient temperature; It is the temperature coefficient of resistance; These are the first, second, and third calibration constants, respectively.

10. The control method for a bridgeless direct-drive digital hot-wire anemometer as described in claim 3, characterized in that, The control method employs a dual protection system combining hardware and software, which limits the maximum input voltage of the operational amplifier through a Zener diode throughout the entire system operation process. The main control unit monitors the loop current in step S4 in real time. When the loop current is detected continuous The current safety threshold was exceeded for one timing cycle. When the system experiences an overcurrent fault, the main control unit determines that an overcurrent fault has occurred, issues an alarm, and immediately forces the digital-to-analog converter voltage output value to zero.

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