CN113406034A - Device with constant-temperature and constant-humidity carbon dioxide sensor and detection method thereof - Google Patents
Device with constant-temperature and constant-humidity carbon dioxide sensor and detection method thereof Download PDFInfo
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 title claims abstract description 110
- 229910002092 carbon dioxide Inorganic materials 0.000 title claims abstract description 55
- 239000001569 carbon dioxide Substances 0.000 title claims abstract description 54
- 238000001514 detection method Methods 0.000 title claims description 26
- 238000005070 sampling Methods 0.000 claims abstract description 51
- 238000000034 method Methods 0.000 claims abstract description 23
- 238000001035 drying Methods 0.000 claims abstract description 20
- 230000003287 optical effect Effects 0.000 claims abstract description 20
- 239000002808 molecular sieve Substances 0.000 claims abstract description 17
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 claims abstract description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 16
- 238000005485 electric heating Methods 0.000 claims abstract description 12
- 238000007789 sealing Methods 0.000 claims abstract description 8
- 238000001914 filtration Methods 0.000 claims abstract description 7
- 238000006243 chemical reaction Methods 0.000 claims abstract description 6
- 238000007605 air drying Methods 0.000 claims abstract description 5
- 238000007599 discharging Methods 0.000 claims description 27
- 238000010521 absorption reaction Methods 0.000 claims description 12
- 239000011148 porous material Substances 0.000 claims description 6
- 238000002835 absorbance Methods 0.000 claims description 5
- 238000005259 measurement Methods 0.000 claims description 5
- 230000008033 biological extinction Effects 0.000 claims description 2
- 238000012545 processing Methods 0.000 abstract description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 7
- 230000008569 process Effects 0.000 description 7
- 230000003321 amplification Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000003199 nucleic acid amplification method Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 230000001276 controlling effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 230000005855 radiation Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 230000003595 spectral effect Effects 0.000 description 2
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- -1 alkali metal aluminosilicate Chemical class 0.000 description 1
- 229910000323 aluminium silicate Inorganic materials 0.000 description 1
- 238000000149 argon plasma sintering Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000006012 detection of carbon dioxide Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000002848 electrochemical method Methods 0.000 description 1
- 230000005264 electron capture Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000005286 illumination Methods 0.000 description 1
- 238000000752 ionisation method Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 230000001105 regulatory effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
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Abstract
The invention discloses a device and a method with a constant temperature and humidity carbon dioxide sensor, which comprises a sampling air chamber, an infrared light source, a dual-channel thermopile detector, a temperature and humidity sensor, a motor, a driving circuit and a singlechip, wherein the sampling air chamber is provided with a sampling gas inlet; the device also comprises an air pump, a pressure reducing valve, a sealing cup for containing water and an air drying pipe; the sampling air chamber is internally of a reflection type flat cone structure, the air chamber is centrosymmetric, the PI electric heating piece and the refrigerating piece are wrapped on the periphery of the air chamber, and meanwhile, the air inlet and the air outlet are arranged on the periphery of the air chamber and connected with the gas drying pipe internally containing the molecular sieve; one end of the sampling air chamber is provided with an infrared light source, the other end of the sampling air chamber is packaged with a dual-channel thermopile detector, and the detector is provided with two paths of light intensity sensing windows which are respectively provided with a reference optical filter and a measuring optical filter; the detector outputs two paths of electric signals, the electric signals are transmitted to the single chip microcomputer after passing through the filtering and amplifying circuit and the A/D conversion circuit, and then are transmitted to a terminal through the upper computer; the invention has good stability and processing, good light reflection performance, reduced reflection and improved accuracy.
Description
Technical Field
The invention belongs to the technical field of gas sensors, and particularly relates to a carbon dioxide sensor device with a constant temperature and humidity and a detection method thereof.
Background
Carbon dioxide is an important component of gas and has a wide and important role in daily life and industry, and the control of carbon dioxide concentration is also an important index for applying carbon dioxide, so that the real-time, efficient and accurate detection of carbon dioxide is more important. At present, methods for detecting carbon dioxide mainly include an electrochemical method, an electron capture method, an ultraviolet ionization method, a non-dispersive infrared absorption method, and the like.
Among them, the non-dispersive infrared absorption method is favored in the field of carbon dioxide gas detection because of its advantages such as high sensitivity, wide detection range, and strong anti-interference. However, the application of the non-dispersive infrared absorption method is extremely susceptible to the environment in the practical measurement of the carbon dioxide, and particularly, the temperature and the humidity of the environment have great influence on the detection result.
First, when the ambient temperature changes, the spectral characteristics of the carbon dioxide gas itself change, which causes the absorption efficiency of infrared light to decrease and the center wavelength of the filter to shift, and a large error occurs in the detection result of the carbon dioxide concentration.
Second, changes in humidity affect the infrared absorption frequency of carbon dioxide. A large amount of water vapor is generally attached to untreated carbon dioxide gas, when infrared light passes through the carbon dioxide gas, a scattering phenomenon occurs due to water molecules, loss occurs due to secondary radiation diffusion of an infrared light source, and a large error also occurs in a carbon dioxide concentration detection result.
Third, the humidity factor also indirectly causes the temperature to change, so that the spectral characteristics of the carbon dioxide itself are changed. In order to solve the detection error caused by the ambient temperature and humidity, most of the methods usually adopt a software compensation method to correct the temperature error and use dry gas as much as possible, so that the influence of the temperature and the humidity on the detection result of the carbon dioxide gas concentration is reduced.
Disclosure of Invention
The purpose of the invention is as follows: the method aims to solve the problem that the influence of the environmental temperature and humidity on the detection result of the concentration of the carbon dioxide meets the requirement of high-sensitivity and high-accuracy detection of the carbon dioxide sensor in the actual production process. The invention provides a constant-temperature and constant-humidity carbon dioxide gas sensor system based on non-dispersive infrared absorption.
The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows:
a device with a constant temperature and humidity carbon dioxide sensor comprises a sampling air chamber, an infrared light source, a dual-channel thermopile detector, a temperature and humidity sensor, a motor, a driving circuit and a singlechip; the device also comprises an air pump, a pressure reducing valve, a sealing cup filled with water, an air drying pipe, a feeding funnel and a discharging funnel;
the air pump outputs carbon dioxide gas with different concentrations through the pressure reducing valve, and the gas enters the gas drying pipe after passing through the water-containing sealing cup;
the sampling air chamber is internally of a reflection type flat cone structure, the air chamber is centrosymmetric, the periphery of the sampling air chamber is wrapped with PI electric heating sheets and refrigerating sheets, meanwhile, the periphery of the air chamber is provided with an air inlet and an air outlet, the air inlet is connected with the gas drying pipe, the drying pipe contains a molecular sieve, a feeding funnel is arranged above the drying pipe, a discharging funnel is arranged below the drying pipe, and a funnel opening is sealed;
the infrared light source is arranged at one end of the sampling air chamber with the large section diameter, the dual-channel thermopile detector is packaged at the other end of the sampling air chamber, and the detector is provided with two paths of light intensity sensing windows which are respectively provided with the reference optical filter and the measuring optical filter;
infrared rays emitted by the infrared light source pass through the carbon dioxide gas to be detected in the sampling gas chamber, respectively pass through the reference optical filter and the measurement optical filter, and are received by the dual-channel thermopile detector;
the detector outputs two paths of electric signals, the electric signals are transmitted to the single chip microcomputer after passing through the filtering and amplifying circuit and the A/D conversion circuit, and then are transmitted to a terminal through the upper computer;
the temperature and humidity sensor is connected with the gas outlet of the sampling gas chamber and used for acquiring the actual temperature/humidity of the gas in the sampling gas chamber in real time and transmitting the temperature/humidity information to the single chip microcomputer;
the single chip microcomputer is used for setting target temperature/humidity, comparing the received actual humidity/temperature with the set target humidity/temperature respectively, and sending a signal to the driving circuit to drive the motor to rotate forwards or backwards so as to open the feeding/discharging hopper or drive the PI electric heating piece/refrigerating piece to heat or radiate.
Furthermore, the interface of the feeding funnel is designed into two layers, a quarter of sieve holes are reserved in the inner layer, the outer layer is hollowed out in the quarter of sieve holes, the other parts are sealed, and the outer layer of the funnel interface is connected with a motor by a pull rope;
and a quarter of sieve pores are reserved in the inner layer of the interface of the discharging funnel at the quarter of the diagonal angle of the inner layer of the interface of the feeding funnel, namely the sieve pores of the discharging funnel and the sieve pores of the feeding funnel have a 180-degree difference, and the outer layer of the interface of the discharging funnel is designed to be consistent with the outer layer of the interface of the feeding funnel.
Furthermore, the axis of the sampling air chamber is parallel to the infrared rays emitted by the infrared light source.
Further, the single chip microcomputer specifically executes the following operations:
setting a desired target temperature/humidity; comparing the actual humidity/temperature of the gas in the sampling gas chamber acquired by the temperature and humidity sensor in real time with the set target humidity/temperature respectively;
when the actual humidity is higher than the target humidity, the single chip outputs a PWM signal with variable duty ratio to a driving circuit to drive a motor to rotate forwards so as to open a feeding hopper and increase the number of molecular sieves;
when the actual humidity is lower than the target humidity, the single chip outputs a PWM signal with variable duty ratio to the driving circuit to drive the motor to rotate reversely, so that the discharging hopper is opened to reduce the number of the molecular sieves;
when the actual temperature is lower than the target temperature, the single chip outputs a PWM signal with a variable duty ratio to a driving circuit to drive a PI electric heating piece to be heated;
when the actual temperature is higher than the target temperature, the single chip outputs a PWM signal with a variable duty ratio to the driving circuit to drive the refrigerating sheet to dissipate heat.
Furthermore, the single chip microcomputer adopts an incremental PID algorithm to regulate and control the temperature/humidity of the sampling air chamber;
and inputting the set target temperature/humidity and the current temperature/humidity as inlet parameters into an incremental PID algorithm, and calculating the PWM increment output by the current singlechip by the algorithm.
The invention provides a carbon dioxide gas concentration detection method based on the sensor device, which specifically comprises the following steps:
firstly, Lambert-beer's law is corrected to calculate the light intensity of the emitted light, and the corrected Lambert-beer's law is expressed as
I is the light intensity of the emergent light, I0Is the light intensity of incident light, S is the proportionality coefficient of non-absorption wave band in the incident light range of detection channel, C is the concentration of gas, L is the effective path of infrared light passing through gas, beta1Is the extinction coefficient of the gas;
then correcting the Lambert-beer law integral formula to calculate the infrared light absorbance, and expressing the corrected formula as
A is infrared light absorbance, beta2Response coefficient of carbon dioxide gas on the measuring channel;
finally, the carbon dioxide gas concentration is calculated and expressed as
Has the advantages that: compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
the structure of the sampling air chamber selects a novel reflection type flat cone cavity air chamber, the air chamber is centrosymmetric, stable and easy to process, and the interior of the air chamber is polished and plated with gold, so that the light reflection performance is good. Meanwhile, the axis of the sampling air chamber is designed to be parallel to the infrared rays emitted by the infrared light source, so that reflection can be reduced, and the accuracy of the system is improved.
The invention adopts an incremental PID algorithm to adjust and control the temperature/humidity of the sampling air chamber. In the actual temperature and humidity control process, the set target temperature/humidity and the current temperature/humidity are only needed to be used as inlet parameters to be sent to an incremental PID algorithm, and the PWM duty ratio variable quantity output by the current single chip microcomputer is calculated by the algorithm, so that the temperature and humidity are controlled.
The invention adopts a dual-channel detection method to avoid the influence of factors such as unstable power of a light source, noise of the light source and the like on a detection mode. The dual-channel detection method is adopted to measure the concentration of the carbon dioxide, so that the detection influence can be ignored, the detection precision of the gas concentration is improved, and the measurement process of the system is not complicated.
Drawings
FIG. 1 is a diagram of the effect of the apparatus of the present invention;
FIG. 2 is a cross-sectional view of a sampling gas cell of the present invention;
FIG. 3 is a diagram of a funnel interface of the present invention;
FIG. 4 is a cross-sectional view of a thermopile detector of the present invention;
FIG. 5 is a system block diagram of the present invention;
FIG. 6 is a schematic block diagram of PID constant temperature and humidity control of the present invention;
FIG. 7 is a flow chart of the PID algorithm control of the present invention;
FIG. 8 is a flow chart of concentration calculation according to the present invention;
reference numerals: 1. the device comprises an infrared light source, 2 parts of PI electric heating sheets, 3 parts of a dual-channel thermopile detector, 4 parts of a measuring optical filter, 5 parts of a reference optical filter, 6 parts of an air outlet, 7 parts of an air inlet, 8 parts of a refrigerating sheet, 9 parts of an air pump, 10 parts of a pressure reducing valve, 11 parts of a sealing cup for containing water, 12 parts of an air drying pipe, 13 parts of a molecular sieve, 14 parts of a feeding funnel, 15 parts of a discharging funnel, 16 parts of a feeding funnel connector, 16-a parts of a feeding funnel connector inner layer, 16-b parts of a sieve mesh, 16-c parts of a funnel connector outer layer, 17 parts of a discharging funnel connector, 17-a parts of a discharging funnel connector inner layer, 18 parts of a pull rope, 19 parts of a motor and a driving circuit, 20 parts of a sampling air chamber and 21 parts of a temperature and humidity sensor.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
The carbon dioxide sensor device with constant temperature and humidity provided by the invention is characterized in that a single-air-chamber dual-wavelength sampling air chamber 20 is designed on the basis of PID constant temperature control, as shown in figures 1 and 5, the structure of the sensor device comprises an optical system and a peripheral circuit, wherein the optical system comprises the sampling air chamber 20, an infrared light source 1 and a dual-channel thermopile detector 3; the peripheral circuit comprises a singlechip, a motor and drive circuit 19, a light source drive circuit, a power supply circuit, a heating module, a filtering amplification circuit, a temperature acquisition circuit (temperature and humidity sensor 21), an A/D conversion circuit, a wireless Bluetooth module and an upper computer; the system can realize the control of the temperature in the sampling air chamber 20 and can also collect and process the carbon dioxide gas concentration signal to be detected.
The sensor device also comprises an air pump 9, a pressure reducing valve 10, a sealing cup 11 for containing water, an air drying pipe 12, a feeding funnel 14 and a discharging funnel 15; the air pump 9 outputs carbon dioxide gas with different concentrations through the pressure reducing valve 10, and the gas enters the gas drying pipe 12 after passing through the water-containing sealing cup 11;
as shown in fig. 2, the sampling air chamber 20 has a reflective flat cone structure inside, is centrosymmetric, is wrapped by a PI electric heating sheet 2 and a refrigerating sheet 8 at the periphery, is provided with an air inlet 7 and an air outlet 6 at the periphery, the air inlet 7 is connected with the gas drying pipe 12, the drying pipe contains a molecular sieve 13, a feeding funnel 14 is arranged above the drying pipe, a discharging funnel 15 is arranged below the drying pipe, and the funnel opening is sealed; before the experiment, a proper amount of molecular sieve 13 is put into a feeding funnel 14;
the infrared light source 1 is arranged at one end of the sampling air chamber 20 with the large section diameter, the dual-channel thermopile detector 3 is packaged at the other end of the sampling air chamber, and the detector is provided with two paths of light intensity sensing windows which are respectively provided with a reference optical filter 5 and a measuring optical filter 4; preferably, the axis of the sampling air chamber 20 is parallel to the infrared rays emitted by the infrared light source 1, so that reflection is reduced, and the system accuracy is improved;
infrared rays emitted by the infrared light source 1 pass through carbon dioxide gas to be detected in the sampling gas chamber 20, respectively pass through the reference optical filter 5 and the measurement optical filter 4, and are received by the dual-channel thermopile detector 3;
the detector outputs two paths of electric signals, the electric signals are transmitted to the single chip microcomputer after passing through the filtering and amplifying circuit and the A/D conversion circuit, and then are transmitted to a terminal through the upper computer;
the temperature and humidity sensor 21 is connected with the gas outlet 6 of the sampling gas chamber 20 and is used for acquiring the actual temperature/humidity of the gas in the sampling gas chamber 20 in real time and transmitting the temperature/humidity information to the single chip microcomputer;
the single chip microcomputer is used for setting target temperature/humidity, comparing the received actual humidity/temperature with the set target humidity/temperature respectively, sending a signal to the driving circuit to drive the motor to rotate forwards or backwards so as to open the feeding/discharging hopper 15, or driving the PI electric heating piece 2/the refrigerating piece 8 to heat or radiate.
As shown in fig. 3, the feeding funnel interface 16 is designed in two layers, a quarter of sieve holes are reserved in the inner layer, the outer layer is hollowed out at the quarter, the other parts are sealed, and the outer layer of the funnel interface is connected with a motor by a pull rope 18;
a quarter of sieve holes are reserved in the inner layer 17-a of the discharging funnel connector at the diagonal quarter of the inner layer 16-a of the feeding funnel connector, namely the sieve holes of the discharging funnel 15 are 180 degrees different from the sieve holes of the feeding funnel 14, and the outer layer of the discharging funnel connector 17 is designed to be consistent with the outer layer of the inlet funnel 16 connector.
In the embodiment, the inner layer 16-a of the interface of the feeding funnel is reserved with sieve holes 16-b at the position of-90 to 0 degrees, the outer layer is hollowed at the position of 0 to 90 degrees, other parts are sealed, and the outer layer 16-c of the interface of the feeding funnel is connected with a motor by a pull rope 18; sieve holes are reserved in the inner layer 17-a of the discharging funnel connector at 90-180 degrees, the outer layer is hollowed at 0-90 degrees, other parts are sealed, and the outer layer 16-c of the funnel connector is connected with a motor by a pull rope 18; the design can realize the control of two interfaces simultaneously by one motor.
When the motor corotation, pulling stay cord 18 makes interface clockwise rotation 90, and feed hopper 14 is opened, increases 3A molecular sieve quantity in the drying tube, and after the feeding, motor reversal pulling stay cord 18 makes interface anticlockwise rotation 90 get back to the sealed feed inlet of initial position, because discharge hopper 15's sieve mesh and feed hopper 14 sieve mesh differ 180 at this in-process, so discharge hopper interface 17 department is sealed all the time. When the motor reverses, the pulling stay cord 18 makes the interface rotate 90 degrees anticlockwise, the discharging hopper 15 is opened, the number of the 3A molecular sieves in the drying tube is reduced, after feeding is finished, the motor reverses to pull the stay cord 18 to make the interface rotate 90 degrees clockwise to return to the initial position to seal the feeding hole, and the feeding hopper interface 16 is always sealed in the process.
The single chip microcomputer specifically executes the following operations:
setting a desired target temperature/humidity; comparing the actual humidity/temperature of the gas in the sampling gas chamber 20 acquired by the temperature and humidity sensor 21 in real time with the set target humidity/temperature respectively;
when the actual humidity is higher than the target humidity, the single chip outputs a PWM signal with a variable duty ratio to a driving circuit to drive a motor to rotate forward so as to open a feeding hopper 14 and increase the number of molecular sieves;
when the actual humidity is lower than the target humidity, the single chip outputs a PWM signal with variable duty ratio to the driving circuit to drive the motor to rotate reversely, so that the discharging hopper 15 is opened to reduce the number of the molecular sieves;
when the actual temperature is lower than the target temperature, the single chip outputs a PWM signal with a variable duty ratio to the driving circuit to drive the PI electric heating piece 2 to heat;
when the actual temperature is higher than the target temperature, the single chip outputs a PWM signal with a variable duty ratio to the driving circuit to drive the refrigerating sheet 8 to dissipate heat.
In the embodiment, the single chip microcomputer is an STM32 single chip microcomputer; the drive circuit selects a TB6612FNG chip as a power amplification chip; the model of the dual-channel thermopile detector 3 is TPS 2534; the central wavelength of the measuring filter is 4.26 mu m; the center wavelength of the reference filter 5 is 4 μm; the temperature and humidity sensor 21 is SHT 11.
The molecular sieve 13 is preferably a 3A molecular sieve; the 3A molecular sieve is an alkali metal aluminosilicate, has obvious effect of adsorbing water molecules, and is often applied to the work of drying gas; the 3A molecular sieve is provided with a plurality of small holes with the effective aperture of 0.3nm, the diameter of water molecules is about 0.27-0.29nm, the diameter of carbon dioxide molecules is about 0.33nm, and the diameter of the small holes of the molecular sieve is larger than that of the water molecules, so that the water molecules passing through can be adsorbed but the carbon dioxide molecules can not be absorbed, and the 3A molecular sieve can effectively filter the water in the carbon dioxide gas, reduce the humidity of the carbon dioxide gas and achieve the aim of controlling the humidity as required.
The diameter of the detection surface (the plane corresponding to the detector) of the sampling air chamber 20 is 10mm, the cone angle is set to be 5 degrees, and the length is about 80 mm; in order to reduce the interference of infrared light scattering on the detection result, the inner wall of the sampling gas chamber 20 is polished and plated with gold.
The infrared light source 1 can be an incandescent lamp HSL-115-S with the diameter of 3mm, the radiation wavelength coverage range of the infrared light source is from visible light to 5 mu m, and the infrared light source comprises a CO2 gas characteristic absorption peak; an IR715EN infrared light source, a filament type C-2R 5V power supply, 115mA current, a wavelength range of 0-5 um, a stable output light source, a long service life and a control voltage of 5V can also be selected.
The filtering amplification circuit is an instrument amplifier, has ultrahigh input impedance, extremely good CMRR, low input offset and low output impedance, and can amplify signals under common-mode voltage. The light source driving circuit adopts LM 538. The A/D converter adopts AD 7195.
As shown in fig. 4, the measuring filter 4 on the detector allows light of a wavelength of 4.26 μm, which can be absorbed only by carbon dioxide gas molecules, to pass through, and other gas molecules do not absorb light of this wavelength.
As shown in fig. 1 and 5, set up required target temperature of input and target humidity on singlechip MCU button, open air pump 9 after the carbon dioxide gas of different concentrations of relief pressure valve 10 output, gaseous through being equipped with the sealed cup of suitable amount of water and improving the humidity after gaseous through gaseous drying tube 12, 3A molecular sieve in the pipe absorbs unnecessary moisture, the humidity information of gaseous indoor gas is gathered in real time to SHT11 temperature and humidity sensor simultaneously, transmit to the cell-phone end through wireless bluetooth module and carry out real-time display, and transmit for the singlechip, compare actual humidity and the target humidity of settlement.
When the actual humidity is higher than the target humidity, the STM32 singlechip outputs a PWM signal with variable duty ratio to the driving circuit to drive the motor to rotate forwards, so that the feeding hopper 14 is opened to increase the number of the 3A molecular sieves; when the actual humidity is lower than the target humidity, the STM32 singlechip outputs a PWM signal with variable duty ratio to the driving circuit to drive the motor to rotate reversely, so that the discharging hopper 15 is opened to reduce the number of the 3A molecular sieves; when the actual humidity is equal to the target humidity, the duty cycle is maintained while maintaining the 3A molecular sieve quantity.
Then the gas enters the sampling air chamber 20 through the air inlet 7, the SHT11 temperature and humidity sensor also collects the temperature information of the sampling air chamber 20 in real time and transmits the temperature information to the single chip microcomputer, and the actual temperature is compared with the set target temperature; when the actual temperature is lower than the target temperature, the STM32 singlechip outputs a PWM signal with variable duty ratio to the driving circuit to drive the PI electric heating sheet 2 to heat; when the actual temperature is higher than the target temperature, the STM32 singlechip outputs a PWM signal with variable duty ratio to the driving circuit to drive the refrigerating sheet 8 to dissipate heat; when the actual temperature is equal to the target temperature, the duty cycle is kept constant while the temperature of the gas chamber is kept constant.
Meanwhile, the TPS2534 dual-channel thermopile detector 3 packaged on the right side of the sampling air chamber 20 is provided with two light intensity sensing windows which are respectively packaged with corresponding narrow-band filters. After infrared light emitted by the infrared light source 1 passes through carbon dioxide gas to be detected in the sampling air chamber 20, the infrared light passes through the reference optical filter 5 with the central wavelength of 4 microns and the measuring optical filter 4 with the central wavelength of 4.26 microns respectively, the two-channel thermopile detector 3 receives and analyzes the infrared light to obtain two paths of electric signals, and the electric signals are transmitted to the inside of the single chip microcomputer after being subjected to filtering amplification and A/D conversion and are transmitted to a terminal through an upper computer to be analyzed to obtain the concentration of the carbon dioxide.
Because the TPS2534 dual-channel thermopile detector 3 is sensitive to the infrared light intensity change, the infrared light source 1 needs to be subjected to low-frequency pulse modulation in the detection process. Therefore, the LM358 driving circuit modulates the infrared light signal in real time, so that the influence of the illumination of the external environment is reduced, and the purpose of prolonging the service life of the infrared light source 1 is achieved.
The single chip microcomputer adjusts and controls the temperature/humidity of the sampling air chamber 20 by adopting an incremental PID algorithm; and inputting the set target temperature/humidity and the current temperature/humidity as inlet parameters into an incremental PID algorithm, and calculating the PWM increment output by the current singlechip by the algorithm.
The PID algorithm is a control algorithm which is the most mature in technology and the most widely applied in the continuous system at present and has been widely applied in real life. The principle of the PID algorithm is that a controller controls through deviation of a set value and an actual value, the deviation is used as an input value, and then output of the controller is obtained after proportional, integral and differential linear combination. When the output and the set value still have deviation, the detection to the signal is continuously transmitted back to the control system, thereby the actual value is closer and closer to the set value to achieve the purpose of stable output.
And u (t) represents the output of the system, e (t) represents the difference value of the temperature/humidity control, and the formula of the intelligent temperature/humidity control system based on the PID algorithm is as follows:
u(t)＝kp[e(t)-e(t-1)]+kie(t)+
kd[e(t)-2e(t-1)+e(t-2)]
wherein kp represents a proportionality coefficient, ki represents an integral coefficient, and kd represents a differential coefficient; adjusting kp can accelerate the response speed of the system, adjusting ki can eliminate static errors and accelerate the response speed, and adjusting kd can control the overshoot of the system.
In practical application, PID algorithm control can be realized by only taking the target temperature/humidity and the current temperature/humidity as inlet parameters and then obtaining the error e (t) between the target temperature/humidity and the current temperature/humidity and the errors e (t-1) and e (t-2) of the previous two moments.
The PID constant temperature control principle of the invention is shown in figure 6, in the process of intelligently controlling the temperature/humidity by the PID algorithm, the target temperature/humidity is set firstly, then kp, ki and kd are set, the set value is compared with the actual value, the difference value is obtained, the increment e (t) (which can be positive or negative) is calculated by the PID algorithm, the duty ratio is modified according to the increment, and the temperature difference is continuously obtained by changing kp, ki and kd, so that the temperature and the humidity can be stabilized in a certain range of the set value.
The PID algorithm control flow is initialized and carries out screen clearing processing, temperature acquisition program initialization, a PID algorithm program module also initializes and sets target temperature and values of kp, ki and kd, and a function of reading a temperature sensor is always executed through a while function, as shown in FIG. 7. The controller judges whether the actual temperature/humidity is equal to the target temperature/humidity or not, if the actual temperature/humidity is different from the target temperature/humidity, the actual temperature/humidity is continuously returned to the algorithm until the actual temperature/humidity is equal to the target temperature/humidity, and the duty ratio is kept unchanged after the actual temperature/humidity is equal to the target temperature/humidity. And then judging whether the temperature/humidity error is within the error range, and if not, continuously regulating and controlling values of kp, ki and kd to enable the temperature/humidity error to be within a certain range.
The invention provides a carbon dioxide gas concentration detection method based on the sensor device, and the flow is shown in fig. 8, and the method specifically comprises the following steps:
firstly, Lambert-beer's law is corrected to calculate the light intensity of the emitted light, and the corrected Lambert-beer's law is expressed as
Wherein I is the light intensity of the emergent light, I0Is the light intensity of incident light, S is the proportionality coefficient of non-absorption wave band in the incident light range of detection channel, C is the concentration of gas, L is the effective path of infrared light passing through gas, beta1The absorption coefficient of the gas is determined by the properties of the gas, and is generally constant;
then correcting the Lambert-beer law integral formula to calculate the infrared light absorbance, and expressing the corrected formula as
Wherein A is the infrared light absorbance, beta2Response coefficient of carbon dioxide gas on the measuring channel; finally, the carbon dioxide gas concentration is calculated and expressed as
The invention provides a device and a method with a constant temperature and humidity carbon dioxide sensor, and the device and the method are not limited to the embodiments. Variations and modifications of the principles, constructions and methods described herein are intended to be included within the scope of the invention.
Claims (6)
1. The utility model provides a take constant temperature and humidity carbon dioxide sensor device which characterized in that: the device comprises a sampling air chamber, an infrared light source, a dual-channel thermopile detector, a temperature and humidity sensor, a motor, a driving circuit and a singlechip; the device also comprises an air pump, a pressure reducing valve, a sealing cup filled with water, an air drying pipe, a feeding funnel and a discharging funnel;
the air pump outputs carbon dioxide gas with different concentrations through the pressure reducing valve, and the gas enters the gas drying pipe after passing through the water-containing sealing cup;
the sampling air chamber is internally of a reflection type flat cone structure, the air chamber is centrosymmetric, the periphery of the sampling air chamber is wrapped with PI electric heating sheets and refrigerating sheets, meanwhile, the periphery of the air chamber is provided with an air inlet and an air outlet, the air inlet is connected with the gas drying pipe, the drying pipe contains a molecular sieve, a feeding funnel is arranged above the drying pipe, a discharging funnel is arranged below the drying pipe, and a funnel opening is sealed;
the infrared light source is arranged at one end of the sampling air chamber with the large section diameter, the dual-channel thermopile detector is packaged at the other end of the sampling air chamber, and the detector is provided with two paths of light intensity sensing windows which are respectively provided with the reference optical filter and the measuring optical filter;
infrared rays emitted by the infrared light source pass through the carbon dioxide gas to be detected in the sampling gas chamber, respectively pass through the reference optical filter and the measurement optical filter, and are received by the dual-channel thermopile detector;
the detector outputs two paths of electric signals, the electric signals are transmitted to the single chip microcomputer after passing through the filtering and amplifying circuit and the A/D conversion circuit, and then are transmitted to a terminal through the upper computer;
the temperature and humidity sensor is connected with the gas outlet of the sampling gas chamber and used for acquiring the actual temperature/humidity of the gas in the sampling gas chamber in real time and transmitting the temperature/humidity information to the single chip microcomputer;
the single chip microcomputer is used for setting target temperature/humidity, comparing the received actual humidity/temperature with the set target humidity/temperature respectively, and sending a signal to the driving circuit to drive the motor to rotate forwards or backwards so as to open the feeding/discharging hopper or drive the PI electric heating piece/refrigerating piece to heat or radiate.
2. The device with constant temperature and humidity carbon dioxide sensor according to claim 1, characterized in that: the interface of the feeding funnel is designed into two layers, a quarter of sieve holes are reserved in the inner layer, the outer layer is hollowed out in the quarter of sieve holes, the other parts are sealed, and the outer layer of the funnel interface is connected with a motor by a pull rope;
and a quarter of sieve pores are reserved in the inner layer of the interface of the discharging funnel at the quarter of the diagonal angle of the inner layer of the interface of the feeding funnel, namely the sieve pores of the discharging funnel and the sieve pores of the feeding funnel have a 180-degree difference, and the outer layer of the interface of the discharging funnel is designed to be consistent with the outer layer of the interface of the feeding funnel.
3. The device with constant temperature and humidity carbon dioxide sensor according to claim 1, characterized in that: the axis of the sampling air chamber is parallel to the infrared rays emitted by the infrared light source.
4. The device with a constant temperature and humidity carbon dioxide sensor according to any one of claims 1 to 3, characterized in that: the single chip microcomputer specifically executes the following operations:
setting a desired target temperature/humidity; comparing the actual humidity/temperature of the gas in the sampling gas chamber acquired by the temperature and humidity sensor in real time with the set target humidity/temperature respectively;
when the actual humidity is higher than the target humidity, the single chip outputs a PWM signal with variable duty ratio to a driving circuit to drive a motor to rotate forwards so as to open a feeding hopper and increase the number of molecular sieves;
when the actual humidity is lower than the target humidity, the single chip outputs a PWM signal with variable duty ratio to the driving circuit to drive the motor to rotate reversely, so that the discharging hopper is opened to reduce the number of the molecular sieves;
when the actual temperature is lower than the target temperature, the single chip outputs a PWM signal with a variable duty ratio to a driving circuit to drive a PI electric heating piece to be heated;
when the actual temperature is higher than the target temperature, the single chip outputs a PWM signal with a variable duty ratio to the driving circuit to drive the refrigerating sheet to dissipate heat.
5. The device with constant temperature and humidity carbon dioxide sensor according to claim 4, characterized in that: the single chip microcomputer adjusts and controls the temperature/humidity of the sampling air chamber by adopting an incremental PID algorithm;
and inputting the set target temperature/humidity and the current temperature/humidity as inlet parameters into an incremental PID algorithm, and calculating the PWM increment output by the current singlechip by the algorithm.
6. A method for detecting the concentration of carbon dioxide gas, which is implemented based on the device of claim 1, characterized in that: the method specifically comprises the following steps:
firstly, Lambert-beer's law is corrected to calculate the light intensity of the emitted light, and the corrected Lambert-beer's law is expressed as
I is the light intensity of the emergent light, I0Is the light intensity of incident light, S is the proportionality coefficient of non-absorption wave band in the incident light range of detection channel, C is the concentration of gas, L is the effective path of infrared light passing through gas, beta1Is the extinction coefficient of the gas;
then correcting the Lambert-beer law integral formula to calculate the infrared light absorbance, and expressing the corrected formula as
A is infrared lightDegree of absorption, beta2Response coefficient of carbon dioxide gas on the measuring channel;
finally, the carbon dioxide gas concentration is calculated and expressed as
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Application publication date: 20210917 Assignee: Guangdong Kaide Intelligent Technology Co.,Ltd. Assignor: Nanjing University of Information Science and Technology Contract record no.: X2023980047631 Denomination of invention: A device with a constant temperature and humidity carbon dioxide sensor and its detection method Granted publication date: 20230530 License type: Common License Record date: 20231121 |