CN114608523B - High-precision and high-stability barometric height measurement system - Google Patents
High-precision and high-stability barometric height measurement system Download PDFInfo
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- G—PHYSICS
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- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C5/00—Measuring height; Measuring distances transverse to line of sight; Levelling between separated points; Surveyors' levels
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C5/00—Measuring height; Measuring distances transverse to line of sight; Levelling between separated points; Surveyors' levels
- G01C5/06—Measuring height; Measuring distances transverse to line of sight; Levelling between separated points; Surveyors' levels by using barometric means
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Abstract
The application relates to the field of data processing, and provides a high-precision and high-stability barometric altimeter system, which is designed and subjected to experimental verification and performance analysis. The system mainly comprises a self-grinding function main control board, an MEMS resonant pressure sensor and upper computer software. The main control board adopts intensive four-layer platemaking to complete the functions of data acquisition, processing and receiving and dispatching. The pressure sensor outputs frequency and temperature data, and the master control module performs accurate acquisition and temperature compensation to obtain air pressure data. The air pressure data are converted into the height data through differential air pressure height measurement and are sent to the display module in a wireless or wired mode to be analyzed, displayed and stored, so that the requirements of the unmanned aerial vehicle on the high precision and stability of the height information during accurate operation are met.
Description
Technical Field
The application relates to the technical field of unmanned aerial vehicle detection, in particular to a high-precision and high-stability barometric height measurement system.
Background
Unmanned aerial vehicles (Unmanned Aerial Vehicle, UAVs) are widely applied in the fields of aviation, photography, rescue, security and the like in recent years, the functional requirements and application scenes are also more complex, and the reliability requirements on the height information are continuously increased. One of the important sources of the unmanned aerial vehicle height information is a pressure sensor, and the atmospheric pressure and the height change regularly, so that the height can be calculated indirectly by measuring the atmospheric pressure value according to the relation between the atmospheric pressure and the height. At present, a plurality of pressure sensors are widely applied to unmanned aerial vehicles (Unmanned Aerial Vehicle, UAVs) in the fields of aviation, photography, rescue, security protection and the like in recent years, the functional requirements and application scenes are more complex, and the reliability requirements on the height information are continuously increased. One of the important sources of the unmanned aerial vehicle height information is a pressure sensor, and the atmospheric pressure and the height change regularly, so that the height can be calculated indirectly by measuring the atmospheric pressure value according to the relation between the atmospheric pressure and the height. At present, more pressure sensors are used as piezoresistive pressure sensors, capacitive pressure sensors and resonant pressure sensors, wherein the resonant pressure sensors indirectly measure pressure by detecting natural frequencies of objects, and output frequency signals which are resonators. And with the development of Micro-Electro-Mechanical Systems (MEMS), the MEMS resonant pressure sensor has the characteristics of small volume, stable performance, low manufacturing cost, easy chip integration and the like.
Aiming at the requirements of the unmanned aerial vehicle on high accuracy and high stability of the height information, the application designs a set of barometric height measurement system by using the MEMS resonant pressure sensor.
Disclosure of Invention
The application aims to provide a high-precision and high-stability barometric height measurement system, which designs a high-precision acquisition module for a sensor frequency signal and a temperature signal respectively, integrates the high-precision acquisition module into a main control system, and adds a temperature compensation calibration barometric value. According to the barometric height measurement principle, the influence of the surrounding environment on the height conversion is eliminated in a differential height measurement mode, and accurate height information is obtained. The functions of data acquisition, processing and receiving and transmitting are completed.
In order to achieve the above purpose, the technical scheme adopted by the application is as follows: a high-precision and high-stability barometric height measurement system, which comprises a sensor module, a main control module and a display module,
the sensor module is used for acquiring simulation parameters of the unmanned aerial vehicle when the unmanned aerial vehicle is to be measured, wherein the simulation parameters are a frequency change value and a voltage output value of the sensor module when the unmanned aerial vehicle is to be measured, a preliminary air pressure value is determined through the frequency change value, and a preliminary temperature value is determined through the voltage output value;
the main control module is used for processing the simulation parameters, obtaining a standard air pressure value after temperature compensation, and calculating the height of the to-be-measured point by combining the relation sequence of the air pressure value and the temperature value of the measured reference point;
the main control module sends the height of the to-be-measured point to the display module through wireless communication.
Preferably, the sensor module is a silicon resonant pressure sensor, and the output end of the silicon resonant pressure sensor is respectively connected with the frequency acquisition module and the voltage acquisition module on the main control module.
Preferably, the output ends of the frequency acquisition module and the voltage acquisition module are respectively connected with a data processing module on the main control module, the converted simulation parameters are processed through the data processing module, and the data processing module is pre-stored with the air pressure value and the temperature value of the measured reference point.
Preferably, the calculation formula of the height h of the point to be measured is as follows,
wherein T is m Can be obtained by averaging the temperature value of the point to be measured and the temperature value of the reference point, wherein the unit is DEG C, R d Constant 287.05J/(kg.K), g constant 9.8m/s 2 P is the atmospheric pressure of the point to be measured, and the unit is Pa; p (P) 0 The barometric pressure is the reference point in Pa; h is the altitude value of the to-be-measured point, and the unit is m; h is a 0 The altitude value of the reference point is given in m.
Preferably, the compensated barometric pressure calculation process includes the following:
step S1: measuring frequency output and voltage output of experimental points with different heights through a silicon resonant pressure sensor, wherein a temperature sensor is arranged on the silicon resonant pressure sensor;
step S2: the air pressure value is calculated by a plurality of groups of data,
Pressure＝∑ i ∑ j K ij ·x i ·y i
wherein Pressure is a Pressure value at absolute Pressure, and the unit is kPa; k (K) ij A coefficient compensation table corresponding to each sensor; i is 0 to 4,j is 0 to 3; x=sensor frequency output-x ', y=sensor voltage output-y', step S3: a silicon resonant pressure sensor coefficient compensation table is established through calibration, and a compensation air pressure value P of a to-be-measured point is obtained,
P＝∑ i ∑ j K ij ·x i ·y i
p is the atmospheric pressure of the to-be-measured point, the unit is Pa, the compensation coefficients are x 'and y', and the compensation coefficients are constants.
Preferably, the frequency acquisition module is formed by FPGA Spartan6 xc6slx and 74LVC245, and the 74LVC245 is an 8-bit bus transceiver.
Preferably, the data processing module employs STM32F407ZET6.
Preferably, the temperature acquisition module selects an ADC (analog to digital converter) built in the AD7606 module for voltage acquisition.
In summary, the beneficial effects of the application are as follows:
1. the application is based on a self-developed MEMS resonant pressure sensor, and the barometric altimeter system is continuously researched and developed. The beneficial effects are as follows: the relative standard deviation in the middle-long distance measuring range is less than 1%, the precision reaches centimeter level, and the method is superior to decimeter-level main stream products with the same functions on the current market, and has the obvious advantages of high precision, stability, reliability and the like.
Drawings
FIG. 1 is a schematic diagram of a high accuracy and high stability barometric altimeter system of the present application;
FIG. 2 is a schematic diagram of an equal-precision frequency measurement method in an embodiment of the application;
FIG. 3 is a schematic diagram of a frequency acquisition module according to an embodiment of the present application;
FIG. 4 is a schematic diagram of a temperature acquisition module according to an embodiment of the present application;
FIG. 5 is an experimental platform in an embodiment of the application;
FIG. 6 is a fixed 25cm height difference measurement in an embodiment of the application;
FIG. 7 fixed 50cm height differential measurement;
FIG. 8 fixed 75cm height differential measurement;
FIG. 9 fixed 100cm height differential measurement;
fig. 10 east 7A floor 1-8 level height difference measurement.
Detailed Description
The following description of the embodiments of the present application will be made clearly and fully with reference to fig. 1 of the drawings, it being apparent that the embodiments described are only some, but not all, embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
Example 1:
a high-precision and high-stability barometric altimeter system has the general scheme shown in figure 1, and a sensor outputs a voltage signal representing temperature for compensation in addition to a frequency signal representing barometric pressure. The sensor outputs two paths of signals which respectively enter a frequency acquisition module and a temperature acquisition module, and the frequency acquisition module mainly comprises an FPGA Spartan6 xc6slx and a 74LVC 245: the FPGA has unique programmable characteristics, so that the FPGA can realize a specific digital circuit aiming at a specific task, and is optimally designed from the bottom layer, thereby having the characteristics of high efficiency, high speed and high reliability. The method has the characteristic of executing a plurality of instructions in parallel, and can reduce errors when measuring frequency signals, thereby meeting the requirement of high precision. The 74LVC245 is an 8-bit bus transceiver with a non-inverting 3-state bus compatible output in both transmit and receive directions, which effectively isolates the bus. The function of the method is that the frequency signal voltage is reduced to the tolerance range of the FPGA pin, and the requirement of counting is met by the rising edge of the auxiliary detection frequency; the temperature compensation acquisition module uses AD7606 as a 16-bit and 8-channel synchronous sampling analog-digital data acquisition system, is internally provided with analog input clamping protection, a second-order anti-aliasing filter, a track-and-hold amplifier and the like, can process + -5V bipolar input signals, and has a highest throughput rate of 200Ksps. The device adopts a single power supply working mode, has on-chip filtering and high input impedance, does not need to drive an operational amplifier and an external bipolar power supply, and occupies a small space while meeting the requirement of accurate acquisition. After the two paths of signals are collected, the signals enter a data processing module for compensation, and the data processing module adopts STM32F407ZET6, so that the data processing module has the characteristics of high performance, low power consumption and multiple peripherals, has good expansibility and rich firmware libraries, can mount multiple paths of equipment, can complete complex functions, and is suitable for data exchange among multiple equipment and calculation processing of multiple types of data. The display module is designed by using Labview software, and Labview has good exhibition and compatibility, supports multiple languages and platforms, has rich tool kits and drivers, is suitable for controlling and testing the embedded platform, and achieves the functions of receiving data, displaying the data, storing logs and the like in real time. The whole system is characterized in that frequency data are collected by a frequency collection module, temperature data are collected by a temperature collection module, temperature compensated information such as air pressure and height difference is calculated by a data processing module, and finally the temperature compensated information is sent to a display module in a serial UART or wireless wifi mode, and the display module displays and stores the data in real time after analyzing the data.
The common frequency measurement methods include a direct frequency measurement method, a direct period frequency measurement method, an equal-precision frequency measurement method and the like. The direct frequency measurement method is to count the pulse number of the measured signal in unit time, namely the frequency of the measured signal; the direct period frequency measurement method is to measure the period of the measured signal first, and the frequency is the reciprocal of the period. Both methods can generate error of + -1 pulse to be measured, and the requirement of high precision can not be met. The gate time of the equal-precision frequency measurement method is not a fixed value, but is the whole time period of the measured signal, and is synchronous with the measured signal. And in the counting allowable time, synchronously counting the standard signal and the measured signal, and deducing the frequency of the measured signal by using a formula. Since the standard signal period is an integer multiple of the measured signal period, errors of + -1 pulse generated by the measured signal are eliminated. Compared with the former two methods, the equal-precision frequency measurement method has higher precision and smaller error, so the equal-precision frequency measurement method is selected to measure the frequency, the specific principle is as shown in figure 2,
the equal-precision frequency measurement needs to use a larger clock source to measure the frequency to be measured, and an FPGA system clock is selected. When the rising edge of the frequency to be measured is detected, the system clock and the frequency to be measured start to be counted simultaneously, when the frequency to be measured passes through N periods, the system clock correspondingly passes through N periods, and as the frequency of the system clock is known, the period of the frequency to be measured can be calculated, as shown by the formula (1),
wherein T is the period of the frequency to be measured, N is the count number of the frequency to be measured, S is the system clock frequency (Hz), and N is the count number of the system clock. From (1), the frequency F (Hz) to be measured can be calculated as
The FPGA system clock is 50MHz, the frequency to be measured of the MEMS resonant pressure sensor is limited in the range of 25kHz-35kHz, in order to make the system approach to twice data measurement in one second, the 25kHz and 35kHz are respectively brought into the frequency F to be measured in the formula (2), and n is 5 multiplied by 10 7 Half of 2.5X10) 7 The obtained result N is in the interval of 12500-17500, wherein the value of N is 16000, the final calculation formula is formula (3), and the frequency detection precision reaches 1/50MHz.
Fre input is the frequency signal that the sensor output, and 74LVC245 level conversion chip is passed through and is fallen the level of frequency signal to the pin withstand voltage scope of FPGA chip. And the FPGA outputs the number of the system clocks to the internal serial port module according to the rising edge of the threshold detection signal and counts, and the sign signal is turned over once when the count reaches 16000. After the internal serial port module detects that the flag signal is turned over, the number of output clocks is sent to the STM32F407 in an ASCII code format. The FPGA chip uses a 50Mhz active crystal oscillator to provide a system clock, and the W25Q128 jhfiq chip serves as a FLASH chip curing program and has a JTAG port for downloading a debugging program.
The temperature measurement is actually voltage measurement, the AD7606 module is used for acquisition by using an built-in ADC, the bit number is 16, 8 channels can be sampled simultaneously, the sampling rate is 200kSPS at the highest, 2.5V reference voltage is built in, the voltage of-5V to 5V can be accurately measured, and the voltage calculation formula is that
Wherein V is a voltage value (V), and AD is an AD value measured by the temperature acquisition module. According to the formula (4), AD is set to 1 unit, and the resolution can be calculated to be 0.15mV, so that the accuracy requirement is met.
The main design part of the temperature acquisition module is shown in fig. 4, the Value input is the temperature signal output by the sensor, the AD7606 and the STM32F407 perform data interaction through the FSMC in a parallel interface mode, the clock is generated by MCU hardware in the mode, the stability of the acquisition clock can be ensured, and finally, the acquisition clock is divided into digital and analog modes to reduce interference. Acquisition procedure configurationThe SER/BYTE SEL interface is a parallel interface input mode; the CONVST A and CONVST B interfaces are used for simultaneously sampling the full-channel ADC; the interfaces of OS0, OS1 and OS2 are non-oversampling multiplying power; REF SELECT interface connects high level to use internal reference voltage; the RANGE interface sets a voltage RANGE of-5V to 5V. Monitoring the states of ADC start and finish by BUSY signal level state to set interrupt trigger, when interrupt is generated, the control signal is selected by the chip select signal>And->And (3) outputting a sampling result by the SCLK signal, converting the result into voltage data, and clearing the interrupt to perform the next sampling after the data is obtained, thereby completing the process of circularly collecting the temperature.
The semiconductor material is very sensitive to the temperature of the sensor, so that the output of the silicon resonant pressure sensor is influenced by pressure and working temperature, temperature drift is generated, and the measurement accuracy of the sensor is greatly reduced due to the nonlinearity problem existing in the sensor, and measures are needed to be taken for temperature drift compensation and nonlinearity correction. The MEMS resonant pressure sensor chip used in the method is provided with a temperature sensor for temperature compensation, a relation model of air pressure and temperature change is established through calibration, a corresponding coefficient compensation table of each sensor is shown in table 1, and the following polynomial fitting is adopted for temperature compensation.
Pressure＝∑ i ∑ j K ij ·x i ·y i (5)
Wherein Pressure is a barometric Pressure value (absolute Pressure, in kPa); k (K) ij A coefficient compensation table corresponding to each sensor; i is 0 to 4,j is 0 to 3; x=sensor frequency output (Hz) -x ', y=sensor voltage output (mV) -y'. The collected data is subjected to polynomial operation to obtain a compensated air pressure value.
Table 1 resonant sensor coefficient compensation table
In the earth gravitational field, the atmospheric pressure and the altitude change regularly, so the altitude can be calculated indirectly according to the relation between the air pressure and the altitude. However, barometric pressure can be affected by a variety of factors such as atmospheric temperature, latitude, season, etc., and this physical characteristic results in a relatively large direct calculated altitude error. The differential barometric altimetry mode can effectively solve the problem: the physical characteristics such as the atmospheric motion and the change rule in a certain area are relatively close, so that the difference correction can be carried out by utilizing the measured and calibrated air pressure and temperature values of the datum point in the area and the air pressure and temperature values of the to-be-measured point, thereby obtaining the accurate height difference between the datum point and the to-be-measured point.
When an air block is in static equilibrium state, under the condition of that all the forces on horizontal direction are mutually counteracted, its upward net pressure (upper and lower pressure difference) must be balanced by gravity, i.e. it is static equilibrium equation
Wherein P is the current atmospheric pressure (Pa); z is altitude (m); ρ is the atmospheric air density (kg/m) 3 ) The method comprises the steps of carrying out a first treatment on the surface of the g is gravity acceleration (m/s) 2 ). If the influence of humidity on the local air pressure is not considered, the air state equation of absolute dry air without any water vapor is as follows under the premise of only considering the influence of temperature on the air pressure:
P＝ρR d T (7)
wherein P is the current atmospheric pressure (Pa); ρ is the atmospheric air density (kg/m) 3 ) The method comprises the steps of carrying out a first treatment on the surface of the T is the thermodynamic temperature (K) of the air to be measured; r is R d 287.05J/(kg.K) was taken as the gas constant of the dry air. Bringing formula (6) into formula (5) for a height of from h 0 By h integration, the relationship between air pressure and height can be obtained:
wherein P is the atmospheric pressure (Pa) of the point to be measured; p (P) 0 Atmospheric pressure (Pa) being a reference point; h is the altitude value (m) of the point to be measured; h is a 0 Is the altitude value (m) of the reference point. The above is transformed to obtain:
since the relationship between the altitude and the atmospheric temperature is complex, a simple functional relationship is difficult to express, and it is difficult to integrate equation (8). Therefore, assuming that the atmospheric pressure value is the same, the temperature is the same, let T m The average temperature of the atmosphere between the to-be-measured point and the reference point is obtained by carrying out integration:
converting the Fahrenheit temperature into the Centigrade temperature, and converting by using a bottom-changing formula to obtain the following formula:
wherein T is m The temperature (DEG C) can be obtained by averaging the temperature value of the reference point and the temperature value of the point to be measured. R is R d Constant 287.05J/(kg.K), g constant 9.8m/s 2 The final height difference can be obtained by only obtaining the temperature and air pressure data of the reference point and the temperature and air pressure data of the to-be-measured point.
The display module is used for receiving the data transmitted by the main control module and displaying the real-time change of the data in the interface. The module is completed by Labview, after software is operated, all data areas are initialized, data transmitted by a lower computer are read, the number of data bits and frame heads are judged after the data are read, and if no error exists, the data are analyzed to obtain the data such as frequency, voltage and air pressure. The height is calculated according to the air pressure data, the data is displayed in a chart mode and the like, and finally the data is stored in a log file, so that later statistics and viewing are facilitated.
According to the design of the software and the hardware, a set of experimental platform is developed and built as shown in fig. 5. In addition to the MEMS resonant pressure sensor used in the present design, an MS5611 pressure sensor was added for use as a control experiment. MS5611 is MEMS piezoresistive sensor, and inside possess temperature sensor can carry out temperature compensation function, and the resolution can reach 10cm, and the wide application is in flight control system at present. Temperature and humidity sensor DHT11 is arranged in the platform and is used for detecting ambient temperature and assisting differential barometric height measurement, the mode of EPS8266 wireless wifi is used for communication with the upper computer, the whole system is used for collecting signals of the MEMS resonant pressure sensor and the MS5611 pressure sensor through the main control board, converting the signals into barometric data and compensating the barometric data, and finally converting barometric into altitude information and sending the altitude information to the upper computer to be displayed in real time in a wireless mode.
In order to test the accuracy and stability of the system, a platform with fixed heights of 25cm, 50cm, 75cm and 100cm is built in an indoor environment within one day, 1 layer and 8 layers of east 7A building in southwest science, and multiple height difference measurements are performed at the same position and the same height. Firstly, placing equipment at the bottom layer of a platform for standing for half a minute, then moving the equipment to the top layer of the platform for standing for half a minute, and recording the time, temperature, air pressure and the like during standing. And carrying out multiple groups of experiments at different times in one day, and keeping the placement position of each equipment consistent with the previous position to obtain complete experimental data. After the data collection is completed, 20/12 groups of the data are extracted, the height difference is obtained by using a differential barometric altimetry mode, the time of each building test is counted as an abscissa according to a time sequence, the height difference measured each time is an ordinate, and all the data are drawn, wherein the conditions are shown in fig. 6, 7, 8, 9 and 10. From each set of test results, the height differences were averaged, standard deviation (Standard Deviation, SD), relative standard deviation (Relative Standard Deviation, RSD), and the results are summarized in table 2.
TABLE 2 relative standard deviation of height test results
As can be seen from the graph, in the measurement with shorter distance, the average value of the system is closer to the true value, the height difference measured at each time point is basically equal, the standard deviation and the relative standard deviation are obviously better than those of MS5611, the accuracy, the stability and the repeatability are better, and the error is in the centimeter range. In the measurement with relatively long distance, the average value of the two is not greatly different, no abnormal data exists, the relative standard deviation is smaller than 1%, and the standard deviation of the system is smaller than the relative standard deviation, so that the repeatability and the stability are more excellent.
The altimeter requirement under the current unmanned aerial vehicle application background is deeply analyzed, and the stable, accurate and reliable important index is pointed out. Therefore, a set of barometric height measurement system is designed by using an autonomously designed small functional main control board and an MEMS resonant pressure sensor, frequency measurement and temperature compensation calculation are integrated into a whole, the functions of data acquisition, calculation, compensation, transmission and the like are realized, and real-time barometric detection and height conversion are completed. Meanwhile, the remote upper computer program can monitor the data change in real time and visually display and analyze the data. A large number of experimental analysis shows that the system has accurate, stable and reliable height measurement data and can adapt to different external environments. The method has good application value in occasions such as unmanned aerial vehicle emergency rescue, fire fighting and disaster relief, environment monitoring and the like.
In summary, in order to meet the requirements of the unmanned aerial vehicle on the high precision and stability of the height information during the accurate operation, a set of barometric altimetry system is designed and subjected to experimental verification and performance analysis. The system mainly comprises a self-grinding function main control board, an MEMS resonant pressure sensor and upper computer software. The main control board adopts intensive four-layer platemaking to complete the functions of data acquisition, processing and receiving and dispatching. The pressure sensor outputs frequency and temperature data, and the master control module performs accurate acquisition and temperature compensation to obtain air pressure data. The air pressure data are converted into height data through differential air pressure height measurement and sent to a display module in a wireless or wired mode for analysis, display and storage. In order to verify the performance index and the working advantage of the height measurement system, a high repeatability experiment and a comparison experiment are carried out on the height measurement system. The result shows that the relative standard deviation of the system in a short-distance measurement range is less than 6%; the relative standard deviation in the relative long-distance measuring range is less than 1%, the precision reaches centimeter level, and the method is superior to decimeter-level main stream products with the same functions on the current market, and has the obvious advantages of high precision, stability, reliability and the like.
In the description of the present application, it should be understood that the terms "counterclockwise," "clockwise," "longitudinal," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, are merely for convenience in describing the present application, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present application.
Claims (8)
1. A high-precision and high-stability barometric altimeter system is characterized by comprising a sensor module, a main control module and a display module,
the sensor module is used for acquiring simulation parameters of the unmanned aerial vehicle when the unmanned aerial vehicle is to be measured, wherein the simulation parameters are a frequency change value and a voltage output value of the sensor module when the unmanned aerial vehicle is to be measured, a preliminary air pressure value is determined through the frequency change value, and a preliminary temperature value is determined through the voltage output value;
the main control module is used for processing the simulation parameters, obtaining a standard air pressure value after temperature compensation, and calculating the height of the to-be-measured point by combining the relation sequence of the air pressure value and the temperature value of the measured reference point;
the main control module sends the height of the to-be-measured point to the display module through wireless communication;
wherein, the frequency variation value is measured by an equal precision frequency measurement method: selecting an FPGA system clock, when detecting the rising edge of the frequency to be detected, starting counting the system clock and the frequency to be detected at the same time, when the frequency to be detected passes N periods, the system clock correspondingly passes N periods, and the period of the frequency to be detected is calculated as shown in a formula (1) because the frequency of the system clock is known:
the frequency to be measured F (Hz) is calculated from equation (1) as:
wherein T is the period of the frequency to be measured, N is the count number of the frequency to be measured, S is the system clock frequency (Hz), and N is the count number of the system clock;
the sensor module is a silicon resonance type pressure sensor, and the output end of the silicon resonance type pressure sensor is respectively connected with the frequency acquisition module and the voltage acquisition module on the main control module; in order to make the system approach to measuring data twice in one second as much as possible, the frequency range to be measured of the silicon resonant pressure sensor is respectively brought into the frequency F to be measured of the formula (2), and the final calculation formula is the formula (3):
the FPGA system clock is 50MHz, the frequency range to be detected of the silicon resonant pressure sensor is limited to be within the range of 25kHz-35kHz, and the frequency detection precision reaches 1/50MHz.
2. The high-precision and high-stability barometric altimeter system according to claim 1, wherein the output ends of the frequency acquisition module and the voltage acquisition module are respectively connected with a data processing module on the main control module, the converted simulation parameters are processed through the data processing module, and a relationship sequence of barometric pressure values and temperature values of the measured reference points is prestored in the data processing module.
3. The barometric altimeter system of claim 2, wherein the calculation formula of the height h of the point to be measured is,
wherein T is m Can be obtained by averaging the temperature value of the point to be measured and the temperature value of the reference point, wherein the unit is DEG C, R d Constant 287.05J/(kg.K), g constant 9.8m/s 2 P is the atmospheric pressure of the point to be measured, and the unit is Pa; p (P) 0 The barometric pressure is the reference point in Pa; h is the altitude value of the to-be-measured point, and the unit is m; h is a 0 The altitude value of the reference point is given in m.
4. The high-precision and high-stability barometric altimeter system of claim 1, wherein the compensated barometric pressure calculation process comprises the following steps:
step S1: measuring frequency output and voltage output of experimental points with different heights through a silicon resonant pressure sensor, wherein a temperature sensor is arranged on the silicon resonant pressure sensor;
step S2: the air pressure value is calculated by a plurality of groups of data,
Pressure＝∑ i ∑ j K ij ·x i ·y i
wherein Pressure is a Pressure value at absolute Pressure, and the unit is kPa; k (K) ij A coefficient compensation table corresponding to each sensor; i is 0 to 4,j is 0 to 3; x=sensor frequency output-x ', y=sensor voltage output-y',
step S3: a silicon resonant pressure sensor coefficient compensation table is established through calibration, and a compensation air pressure value P of a to-be-measured point is obtained,
P＝∑ i ∑ j K ij ·x i ·y i
p is the atmospheric pressure of the to-be-measured point, the unit is Pa, x 'and y' are compensation coefficient values of the silicon resonant pressure sensor, and x 'and y' are constants.
5. The high-precision and high-stability barometric altimeter system of claim 2, wherein the frequency acquisition module is formed by FPGA Spartan6 xc6slx and 74LVC245, and the 74LVC245 is an 8-bit bus transceiver.
6. The high-precision and high-stability barometric altimeter system of claim 5 wherein said data processing module is STM32F407ZET6.
7. The high-precision and high-stability barometric altimeter system of claim 6, wherein the temperature acquisition module is an AD7606 module built-in ADC for voltage acquisition.
8. The high-precision and high-stability barometric altimeter system of claim 7, wherein the Fre input is a frequency signal output by the sensor, and the level of the frequency signal is reduced to be within the pin withstand voltage range of the FPGA chip through a 74LVC245 level conversion chip; the FPGA detects the rising edge of the signal and counts according to the threshold value, when the count reaches 16000, the number of system clocks is output to the internal serial port module, and the sign signal is turned over once;
after the internal serial port module detects that the sign signal is overturned, the number of output clocks is sent to STM32F407 in an ASCII code format; the FPGA chip uses a 50Mhz active crystal oscillator to provide a system clock, and the W25Q128 jhfiq chip serves as a FLASH chip curing program and has a JTAG port for downloading a debugging program.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111651966.8A CN114608523B (en) | 2021-12-30 | 2021-12-30 | High-precision and high-stability barometric height measurement system |
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