A micro-wind speed sensor for fume hoods based on Kalman filter algorithm

Abstract

The present invention discloses a fume hood micro-wind speed sensor based on a Kalman filter algorithm, comprising a cover, a base, and a PCB circuit board installed between the cover and the base, the top of the cover is provided with fixing holes near both side edges, the top center of the cover is provided with an air through hole, the top of the cover is provided with a first screw through hole, a first connecting circular tube is fixed at the center of the inner top surface of the cover, and a square air inlet channel tube is fixed on the inner top surface of the cover and inside the first connecting circular tube. In the present invention, the adopted micro-wind speed sensor is less affected by the ambient temperature and humidity, and the error caused by temperature change can be further reduced by temperature calibration, and the collected voltage signal is filtered by using Kalman filtering in the single-chip microcomputer, which effectively suppresses and prevents the interference of noise in the circuit on the voltage signal, so that the output result is more accurate and the disturbance is very small.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro wind speed sensors, and in particular relates to a fume hood micro wind speed sensor based on a Kalman filter algorithm. Background Art

[0002] The micro wind speed sensor is used to measure the micro wind speed of 0-1.0m / s. The main application scenario is to measure the speed of air flow in the fume hood of a biological laboratory. The micro wind speed sensor adopts a multi-sensor fusion solution. Traditional micro wind speed sensors mostly use PT20 resistors to detect micro wind speed and NTC thermistors to detect ambient temperature; in addition, a single-chip microcomputer is used to receive voltage signals, which are processed and output as feedback voltages through the single-chip microcomputer program. The principle of the micro wind speed sensor: air with a certain wind speed flows through the micro wind speed sensor, taking away the heat of the PT20 in the speed measurement channel of the micro wind speed sensor. In order to keep the temperature constant, it is necessary to increase the heat, so the voltage change can be detected, and the voltage-wind speed relationship is used to measure the wind speed.

[0003] However, in the prior art, the existing micro wind speed sensors have the following disadvantages in use:

[0004] 1. When the ambient temperature changes, the measurement error increases; for example, when the ambient temperature rises by 4°C, the error is about 30% of the full scale.

[0005] Cause: The PT20 resistor relies on temperature to work normally. When the ambient temperature changes, it affects the normal output current of the PT20 resistor, resulting in errors in the measured value.

[0006] 2. Under the environmental conditions of constant wind speed and constant temperature, the voltage signal is disturbed and the deviation is about 5% of the full scale.

[0007] Cause: There is noise in the circuit, which makes the voltage signal received by the microcontroller inaccurate, thus causing wind speed measurement errors. Traditional products have simple filtering processing and cannot effectively handle the normally distributed random signal noise, resulting in unstable test results.

[0008] 3. The chip PT20 used to measure the micro-wind speed generates serious heat. Under normal working conditions, the chip temperature reaches above 70°C, which causes the NTC thermistor used to measure the ambient temperature to be placed far away from the speed measurement channel, resulting in a large gap between the measured temperature and the actual ambient temperature.

[0009] Cause: Problems arising from the principles of existing technical solutions. Summary of the invention

[0010] The purpose of the present invention is to measure the micro wind speed by adopting a multi-sensor fusion method. The micro wind speed sensor for measuring the wind speed adopts the SMD patch package type of the WIN series digital anemometer based on the MEMS semiconductor chip. The temperature scheme for measuring the ambient temperature adopts the NTC thermistor scheme. The STM32F072CBT6 single-chip microcomputer is used for signal processing. The Kalman filter is used for the filtering part after the voltage signal is converted from analog to digital to reduce the influence of noise.

[0011] The technical solution adopted by the present invention is as follows: a fume hood micro-wind speed sensor based on a Kalman filter algorithm, comprising a cover, a base, and a PCB circuit board installed between the cover and the inside of the base, the top of the cover is provided with fixing holes near the edges on both sides, the top center of the cover is provided with an air through hole, the top of the cover is provided with a first screw through hole, a first connecting circular tube is fixed at the center of the inner top surface of the cover, a square air inlet channel tube is fixed on the inner top surface of the cover and located inside the first connecting circular tube, and the top of the square air inlet channel tube is connected to the air through hole;

[0012] Support columns are fixed on the inner bottom surface of the base near the edges on both sides, and first threaded holes are opened inside the two support columns. Three debugging holes are opened at equal intervals on the outer surface of the base. A second connecting round tube is fixed at the center of the inner bottom surface of the base. A placement groove is opened on one side of the base, and an air inlet is opened at the center of the bottom of the base.

[0013] A circular through hole is opened at the center of the PCB circuit board, a micro wind speed sensor is fixed to one side of the bottom of the PCB circuit board close to the circular through hole, and a wiring terminal is fixed to the bottom of the PCB circuit board close to one side edge, and the wiring terminal is located inside the placement groove.

[0014] Wherein, two second threaded holes and one second screw through hole are respectively provided on the top of the PCB circuit board near the edge.

[0015] Wherein, a screw is threadedly connected between the inner surface wall of the second threaded hole and the first threaded hole.

[0016] A rectangular through hole is provided at the center of the micro wind speed sensor, and the inner diameter of the rectangular through hole is equal to the inner diameter of the square air intake channel tube.

[0017] Among them, a hexagonal groove is opened on one side of the bottom of the base close to the air inlet, and a long screw nail is threadedly connected between the inner surface walls of the first screw hole and the second screw hole, and the bottom end of the long screw nail extends to the inside of the hexagonal groove.

[0018] Wherein, a nut is provided on the threaded sleeve at the bottom end of the screw spike, and the nut is located inside the hexagonal groove.

[0019] The micro wind speed sensor adopts the SMD chip package of the WIN digital anemometer of the MEMS semiconductor chip, and the PCB circuit board includes an NTC thermistor and an STM32F072CBT6 single chip microcomputer.

[0020] A method for measuring a micro-wind speed sensor of a fume hood based on a Kalman filter algorithm comprises the following steps:

[0021] S1. Air with a certain wind speed flows through the speed measurement channel of the micro wind speed sensor, and the micro wind speed sensor receives the air and sends a signal in the form of a differential voltage signal;

[0022] S2, the voltage signal of the NTC thermistor is processed into a DC voltage signal in the range of 0 to 3.3V and then transmitted to the microcontroller;

[0023] S3. Measure the voltage-wind speed relationship in a self-built small wind tunnel, take multiple sets of data for polynomial fitting, and the goodness of fit R 2 =0.999, and the fitted polynomial is used as the mapping relationship between voltage and wind speed;

[0024] S4. By controlling the air temperature in a self-built small wind tunnel and performing multiple calibrations at different constant ambient temperatures, the voltage-wind speed relationship at different temperatures is obtained to reduce the error caused by temperature changes.

[0025] Among them, the operation steps of S2 also include the following steps:

[0026] S201, ambient temperature signal processing: converting the received DC voltage signal into actual temperature through the calculation formula of NTC thermistor;

[0027] S202, wind speed signal processing: calculating the received DC voltage signal through the voltage-wind speed relationship to obtain the corresponding wind speed;

[0028] S203, according to the calibrated relationship, select the voltage-wind speed relationship under the corresponding ambient temperature to map the voltage signal to the wind speed;

[0029] S204, collecting the micro-pressure difference signal of the ambient temperature and micro-wind speed sensor chip, establishing the state equation and observation equation of the Kalman filter under the nonlinear dynamic system, and establishing the Kalman filter model according to the state equation and observation equation of the Kalman filter;

[0030] S205, determining the initialization state of the nonlinear dynamic system, that is, confirming the initial values ​​of the state parameters of the initial epoch, the initial values ​​of the variance matrix, and the initial variance matrix of the dynamic noise;

[0031] S206, based on the state equation and observation equation of the initial epoch, the initial values ​​of the state parameters, the initial values ​​of the variance matrix and the dynamic noise variance matrix are filtered by the Kalman filter recursive equation to obtain new filtered values;

[0032] S207: Calculate the current optimal wind speed based on the current measured wind speed, the predicted wind speed at the previous moment, and the error, and then predict the wind speed at the next moment.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] 1. In the present invention, the micro wind speed sensor used is less affected by the ambient temperature and humidity, and the error caused by temperature change can be further reduced through temperature calibration. The collected voltage signal is filtered using Kalman filtering in the single-chip microcomputer, which effectively suppresses and prevents the interference of noise in the circuit on the voltage signal, making the output result more accurate and the disturbance very small.

[0035] 2. In the present invention, the micro wind speed sensor chip used generates less heat, and the impact on the ambient temperature is almost negligible under the conditions of background technology. Therefore, the NTC thermistor can be placed closer to the speed measurement channel of the micro wind speed sensor, making it more accurate in measuring the ambient temperature, with high precision, small error, good stability, and effectively solving the shortcoming that the ambient temperature has a great impact on traditional wind speed sensors.

[0036] 3. In the present invention, the speed measuring channel of the micro wind speed sensor is reduced in size to make it more sensitive to changes in micro wind speed, and a transition curved surface of the micro wind speed sensor facing the speed measuring channel is added to make the air flowing through the speed measuring channel more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 An exploded view of the present invention;

[0038] Figure 2 A perspective view of the present invention;

[0039] Figure 3 A perspective view of the present invention;

[0040] Figure 4 A perspective view of the present invention;

[0041] Figure 5 It is a three-dimensional diagram of the PCB circuit board of the present invention;

[0042] Figure 6A three-dimensional diagram of a lid of the present invention;

[0043] Figure 7 A three-dimensional diagram of a lid of the present invention;

[0044] Figure 8 A three-dimensional diagram of the base of the present invention;

[0045] Fig. 9 A three-dimensional diagram of the base of the present invention;

[0046] Markings in the figure: 1. Cover; 2. Fixing hole; 3. PCB circuit board; 301. Second threaded hole; 4. First threaded hole; 5. Second screw hole; 6. Base; 7. Nut; 8. Placement slot; 9. Circular through hole; 10. Screw nail; 11. First screw hole; 12. Air through hole; 13. Terminal block; 14. Support column; 15. Air inlet; 16. Micro wind speed sensor; 1601. Rectangular through hole; 17. Square air inlet channel tube; 18. First connecting round tube; 19. Second connecting round tube; 20. Debugging hole; 21. Hexagonal groove. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] Reference Figure 1-9 As shown: a fume hood micro-wind speed sensor based on Kalman filtering algorithm, comprising a cover 1, a base 6 and a PCB circuit board 3 installed between the cover 1 and the base 6, the top of the cover 1 is provided with fixing holes 2 near the edges on both sides, the fixing holes 2 are holes used for fixing in actual use, an air through hole 12 is provided at the center of the top of the cover 1, the air through hole 12 is a channel for air to pass through during measurement, a first screw through hole 11 is provided at the top of the cover 1, the first screw through hole 11 and the second screw through hole 5 are screw through holes used to fix the cover 1 and the base 6 up and down, a first connecting circular tube 18 is fixed at the center of the inner top surface of the cover 1, a square air inlet channel tube 17 is fixed on the inner top surface of the cover 1 and located inside the first connecting circular tube 18, and the top of the square air inlet channel tube 17 is connected to the air through hole 12, the square air inlet channel tube 17 is a channel for air to pass through during measurement;

[0049] Support columns 14 are fixed to the inner bottom surface of the base 6 near the edges on both sides. The two support columns 14 are used to support and install the position of the PCB circuit board 3. The inside of the two support columns 14 is provided with a first threaded hole 4. The outer surface of the base 6 is provided with three debugging holes 20 at equal intervals. Through the debugging holes 20, it can be connected to the inside after the whole is assembled. A second connecting round tube 19 is fixed at the center of the inner bottom surface of the base 6. There is a convex block (such as Figure 5 As shown), the second connecting round tube 19 has a snap-fit ​​opening (as shown Figure 8 As shown), when the cover 1 and the base 6 are docked and installed, the protruding block on the first connecting round tube 18 will be snap-connected with the snap-in opening of the second connecting round tube 19, which is convenient for installation. A placement groove 8 is provided on one side of the base 6, and the placement groove 8 is used to install and place the position of the wiring terminal 13. An air inlet 15 is provided at the bottom center of the base 6. The air inlet 15 is a channel for air to pass through during measurement, and is treated as a guide surface;

[0050] A circular through hole 9 is opened at the center of the PCB circuit board 3, and the first connecting circular tube 18 and the second connecting circular tube 19 are connected through the circular through hole 9. A micro wind speed sensor 16 is fixed to the bottom of the PCB circuit board 3 near the circular through hole 9, and a wiring terminal 13 is fixed to the bottom of the PCB circuit board 3 near the edge of one side, and the wiring terminal 13 is located inside the placement groove 8.

[0051] Two second threaded holes 301 and one second screw through hole 5 are respectively provided on the top of the PCB circuit board 3 near the edge.

[0052] A screw is threadedly connected between the second threaded hole 301 and the inner surface wall of the first threaded hole 4 , and the position of the PCB circuit board 3 can be installed and fixed by passing the screw between the first threaded hole 4 and the second threaded hole 301 .

[0053] A rectangular through hole 1601 is provided at the center of the micro wind speed sensor 16, and the inner diameter of the rectangular through hole 1601 is equal to the inner diameter of the square air inlet channel tube 17, so that micro wind can pass through.

[0054] A hexagonal groove 21 is provided on one side of the bottom of the base 6 near the air inlet 15, and a screw spike 10 is threadedly connected between the inner wall of the first screw hole 11 and the second screw hole 5, and the bottom end of the screw spike 10 extends to the inside of the hexagonal groove 21. The screw spike 10 is threaded through the first screw hole 11 and the second screw hole 5, so that the cover 1 and the base 6 can be installed.

[0055] The bottom end of the screw spike 10 is threadedly sleeved with a nut 7 , and the nut 7 is located inside the hexagonal groove 21 , and the screw spike 10 can be tightened by the nut 7 .

[0056] The micro wind speed sensor 16 adopts the SMD patch package type of the WIN series digital anemometer of the MEMS semiconductor chip. The PCB circuit board 3 includes an NTC thermistor and an STM32F072CBT6 microcontroller. The temperature scheme for measuring the ambient temperature uses the NTC thermistor scheme, and the STM32F072CBT6 microcontroller is used for signal processing. The Kalman filter is used for the filtering part of the voltage signal to reduce the impact of noise.

[0057] A method for measuring a micro-wind speed sensor of a fume hood based on a Kalman filter algorithm comprises the following steps:

[0058] Step 1: Air with a certain wind speed flows through the speed measurement channel of the micro wind speed sensor 16. The micro wind speed sensor 16 receives the air and sends a signal in the form of a differential voltage signal. After being processed by the circuit, the differential signal is converted into a 0-3.3V DC voltage signal and transmitted to the single chip microcomputer.

[0059] Step 2: The voltage signal of the NTC thermistor is processed into a DC voltage signal in the range of 0 to 3.3V and then transmitted to the microcontroller;

[0060] Step 3: Measure the voltage-wind speed relationship in a self-built small wind tunnel, take multiple sets of data for polynomial fitting, and the goodness of fit R 2 =0.999, and the fitted polynomial is used as the mapping relationship between voltage and wind speed;

[0061] Step 4: By controlling the air temperature in the self-built small wind tunnel, multiple calibrations are performed at different constant ambient temperatures to obtain the voltage-wind speed relationship at different temperatures to reduce the error caused by temperature changes.

[0062] The operation steps of step 2 also include the following steps:

[0063] 1) Signal processing of ambient temperature: The received DC voltage signal is converted into actual temperature (unit: °C) through the calculation formula of NTC thermistor;

[0064] 2) Wind speed signal processing: The received DC voltage signal is calculated through the voltage-wind speed relationship to obtain the corresponding wind speed;

[0065] 3) According to the calibrated relationship, the voltage-wind speed relationship at the corresponding ambient temperature is selected to map the voltage signal to the wind speed;

[0066] 4) Collect the micro-pressure difference signal (T, V) of the ambient temperature and micro-wind speed sensor 16 chips, establish the state equation and observation equation of the Kalman filter under the nonlinear dynamic system, and establish the Kalman filter model based on the state equation and observation equation of the Kalman filter;

[0067] 5) Determine the initial state of the nonlinear dynamic system, that is, confirm the initial values ​​of the state parameters of the initial epoch, the initial values ​​of the variance matrix, and the initial variance matrix of the dynamic noise;

[0068] 6) Based on the state equation and observation equation of the initial epoch, the initial values ​​of the state parameters, the initial values ​​of the variance matrix and the dynamic noise variance matrix are filtered by the Kalman filter recursive equation to obtain new filtered values;

[0069] 7) According to the current measured wind speed and the predicted wind speed and error at the previous moment, the current optimal wind speed is calculated, and then the wind speed at the next moment is predicted.

[0070] In the present invention, the adopted micro wind speed sensor 16 is less affected by the ambient temperature and humidity, and the error caused by temperature change can be further reduced by temperature calibration. The collected voltage signal is filtered by using Kalman filtering in the single chip microcomputer, which effectively suppresses and prevents the interference of noise in the circuit on the voltage signal, making the output result more accurate and the disturbance very small. The adopted micro wind speed sensor 16 chip generates less heat, and the impact on the ambient temperature is almost negligible under the background technical conditions. Therefore, the NTC thermistor can be placed closer to the speed measurement channel of the micro wind speed sensor 16, so that it can measure the ambient temperature more accurately, and the speed measurement channel of the micro wind speed sensor 16 is reduced to make it more sensitive to the change of micro wind speed. The transition surface of the micro wind speed sensor 16 facing the speed measurement channel is added, so that the air flowing through the speed measurement channel is more stable. The present invention has high precision, small error, good stability, and effectively solves the shortcomings of the large influence of ambient temperature on traditional wind speed sensors.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring a micro wind speed sensor in a fume hood based on a Kalman filter algorithm, characterized in that: The micro wind speed sensor comprises a cover (1), a base (6), and a PCB circuit board (3) installed between the cover (1) and the base (6); the top of the cover (1) is provided with fixing holes (2) near the edges on both sides; the top center of the cover (1) is provided with an air through hole (12); the top of the cover (1) is provided with a first screw through hole (11); a first connecting circular tube (18) is fixed at the center of the inner top surface of the cover (1); a square air inlet channel tube (17) is fixed on the inner top surface of the cover (1) and located inside the first connecting circular tube (18); and the top of the square air inlet channel tube (17) is connected to the air through hole (12); Support columns (14) are fixed to the inner bottom surface of the base (6) near the two side edges, and first threaded holes (4) are provided inside the two support columns (14). Three debugging holes (20) are provided at equal intervals on the outer surface of the base (6). A second connecting circular tube (19) is fixed at the center of the inner bottom surface of the base (6). A placement groove (8) is provided on one side of the base (6), and an air inlet (15) is provided at the center of the bottom of the base (6); A circular through hole (9) is provided at the center of the PCB circuit board (3); a micro wind speed sensor (16) is fixed to a side of the bottom of the PCB circuit board (3) close to the circular through hole (9); a wiring terminal (13) is fixed to a side edge of the bottom of the PCB circuit board (3); and the wiring terminal (13) is located inside the placement groove (8); A rectangular through hole (1601) is provided at the center of the micro wind speed sensor (16), and the inner diameter of the rectangular through hole (1601) is equal to the inner diameter of the square air intake channel tube (17); The micro wind speed sensor (16) adopts the SMD chip package of the WIN digital anemometer of the MEMS semiconductor chip, and the PCB circuit board (3) includes an NTC thermistor and an STM32F072CBT6 single chip microcomputer; The measuring method comprises the following steps: S1, air with a certain wind speed flows through the speed measurement channel of the micro wind speed sensor (16), and the micro wind speed sensor (16) sends a signal in the form of a differential voltage signal after receiving the air; S2, the voltage signal of the NTC thermistor is processed into a DC voltage signal in the range of 0 to 3.3V and then transmitted to the microcontroller; S3. Measure the voltage-wind speed relationship in a self-built small wind tunnel, take multiple sets of data for polynomial fitting, and the goodness of fit R 2 =0.999, and the fitted polynomial is used as the mapping relationship between voltage and wind speed; S4. By controlling the air temperature in the self-built small wind tunnel, multiple calibrations are performed at different constant ambient temperatures to obtain the voltage-wind speed relationship at different temperatures to reduce the error caused by temperature changes; The operation steps of S2 also include the following steps: S201, ambient temperature signal processing: converting the received DC voltage signal into actual temperature through the calculation formula of NTC thermistor; S202, wind speed signal processing: calculating the received DC voltage signal through the voltage-wind speed relationship to obtain the corresponding wind speed; S203, according to the calibrated relationship, select the voltage-wind speed relationship under the corresponding ambient temperature to map the voltage signal to the wind speed; S204, collecting the micro-pressure difference signal of the ambient temperature and micro-wind speed sensor (16) chip, establishing the state equation and observation equation of Kalman filtering under the nonlinear dynamic system, and establishing a Kalman filtering model according to the state equation and observation equation of Kalman filtering; S205, determining the initialization state of the nonlinear dynamic system, that is, confirming the initial values ​​of the state parameters of the initial epoch, the initial values ​​of the variance matrix, and the initial variance matrix of the dynamic noise; S206, based on the state equation and observation equation of the initial epoch, the initial values ​​of the state parameters, the initial values ​​of the variance matrix and the dynamic noise variance matrix are filtered by the Kalman filter recursive equation to obtain new filtered values; S207: Calculate the current optimal wind speed based on the current measured wind speed, the predicted wind speed at the previous moment, and the error, and then predict the wind speed at the next moment.

2. The method for measuring a micro wind speed sensor of a fume hood based on a Kalman filter algorithm as claimed in claim 1, characterized in that: Two second threaded holes (301) and a second screw through hole (5) are respectively provided on the top of the PCB circuit board (3) near the edge.

3. The method for measuring a micro wind speed sensor of a fume hood based on a Kalman filter algorithm as claimed in claim 2, characterized in that: A screw is threadedly connected between the second threaded hole (301) and the inner surface wall of the first threaded hole (4).

4. The method for measuring a micro wind speed sensor of a fume hood based on a Kalman filter algorithm as claimed in claim 2, characterized in that: A hexagonal groove (21) is provided on one side of the bottom of the base (6) close to the air inlet (15), and a long screw spike (10) is threadedly connected between the inner surface wall of the first screw through hole (11) and the second screw through hole (5), and the bottom end of the long screw spike (10) extends to the inside of the hexagonal groove (21).

5. The method for measuring a micro wind speed sensor of a fume hood based on a Kalman filter algorithm as claimed in claim 4, characterized in that: A nut (7) is threadedly sleeved on the bottom end of the screw spike (10), and the nut (7) is located inside the hexagonal groove (21).

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