CN113075130A - Photoacoustics gas concentration detection device and control method thereof - Google Patents
Photoacoustics gas concentration detection device and control method thereof Download PDFInfo
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
- G01N2021/1704—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases
Abstract
The invention discloses a photoacoustics gas concentration detection device and a control method thereof, wherein the photoacoustics gas concentration detection device comprises a modulated light source module, a photoacoustics cavity module, a sound detection module and a signal processing module. According to the photoacoustics gas concentration detection device, infrared modulation light is periodically generated by the light source modulation module, the internal gas to be detected absorbs the infrared modulation light by the photoacoustic cavity module and is converted into a sound signal, the sound signal is detected by the sound detection module, the concentration of the gas to be detected is calculated by the signal processing module according to the sound signal, so that the gas concentration is measured by the photoacoustic effect, the whole device is small in size and wide in application field, gold plating in the absorption cavity is not needed for improving the reflection efficiency, the cost is reduced, meanwhile, all devices are integrally and firmly welded together, the stability is high, and the photoacoustics gas concentration detection device is suitable for being installed in mobile equipment, constant temperature controllers and other life intelligent household components.
Description
Technical Field
The invention belongs to the technical field of gas concentration measurement, and particularly relates to a photoacoustics gas concentration detection device and a control method thereof.
Background
Gas molecules sealed in the photoacoustic cell absorb incident light with specific frequency v and then are transited to an excited state E1 from a ground state E0, the energy difference between two energy levels is E1-E0 ═ h v, the excited molecules collide with surrounding gas molecules and return to the ground state from the excited state, and the absorbed light energy is converted into translational kinetic energy among the collision molecules through a non-radiative relaxation process, which is specifically represented as that the gas temperature is increased, namely heating. Energy required for energy level transition is different, so that electromagnetic radiation with different wavelengths is required for transition, namely, different absorption bands appear in different spectral regions. When the intensity of incident light is modulated by frequency omega, the heating process generates periodic variation, and according to the law of gas thermodynamics, the periodic temperature variation generates same-period pressure fluctuation, namely sound wave, which is detected by a microphone, a microphone or a piezoelectric ceramic microphone arranged on a photoacoustic cell and converted into an electric signal, namely a photoacoustic signal, the generation process of the signal is called photoacoustic effect, the magnitude of the photoacoustic signal is in direct proportion to the gas concentration, and the concentration of the gas to be detected can be obtained by detecting the signal value.
The working process of measuring the gas concentration by the non-dispersive infrared technology comprises the following steps: the infrared spectrum infrared light is radiated by an infrared light source, the infrared light passes through a gas to be detected in a specially designed high-reflection air chamber and then reaches an infrared thermopile chip in the sensor through a specific narrow band filter on the infrared thermopile sensor, the infrared thermopile chip generates corresponding voltage signals to be output according to the Seebeck effect after receiving infrared light signals, an operational amplifier with low noise and zero temperature drift is used for amplifying output signals of the infrared thermopile sensor, the amplified signals are converted into digital signals through an analog-to-digital conversion chip, algorithm calculation is carried out by using the beer Lambert law which accords with the gas absorption relation of NDIR, and finally the concentration of the gas to be detected is obtained.
However, when the gas concentration is measured by the non-dispersive infrared technology, an absorption chamber with a long optical path needs to be designed for achieving a good measurement resolution, the size is relatively large, and the cost is high; in order to improve the reflection efficiency of infrared radiation in the absorption cavity, gold plating treatment is usually performed in the absorption cavity made of plastic, so that the absorption cavity is poor in firmness and expensive, and micro deformation can occur after frequent high-temperature and low-temperature changes; the used light source is generally a small incandescent bulb, and the stability is poor; meanwhile, a signal processing and acquisition circuit is formed by a thermopile covered with a special optical filter, a low-temperature-drift high-precision operational amplifier and a high-precision analog-to-digital converter in a non-dispersive infrared technology (namely an NDIR technology), so that the cost is further increased, and meanwhile, the integration capability is low due to the large size of the circuit, the circuit can only be used in a limited field and is not suitable for being installed in mobile equipment, a constant temperature controller and other intelligent household components.
Disclosure of Invention
In order to solve the problems, the invention provides a photoacoustics gas concentration detection device which is small in size, wide in application field, low in cost, high in stability and suitable for being installed in mobile equipment, a constant temperature controller and other intelligent living household components.
Another object of the present invention is to provide a control method.
The technical scheme adopted by the invention is as follows:
the utility model provides a photoacoustics gas concentration detection device, is including the modulation light source module that is used for the periodic production infrared modulation light, be used for utilizing inside gas that awaits measuring to absorb the infrared light and change into the light and sound chamber module of sound signal, be used for detecting sound signal's sound detection module and be used for calculating the signal processing module of the gas concentration that awaits measuring according to the sound signal, modulation light source module and the equal electric signal processing module of sound detection module, light and sound chamber module is installed in modulation light source module and sound detection module top, sound detection module is analog microphone or digital microphone.
Preferably, still include temperature and humidity detection module and atmospheric pressure detection module, temperature and humidity detection module and atmospheric pressure detection module are all installed on signal processing module, temperature and humidity detection module and atmospheric pressure detection module all electricity connect signal processing module.
Preferably, the modulated light source module includes an infrared light source unit and a filter, and the filter is installed above the infrared light source unit to filter out the required narrow-band radiated infrared light.
Preferably, the optical-acoustic cavity module is a single-cavity optical-acoustic cavity module or a double-cavity optical-acoustic cavity module, the single-cavity optical-acoustic cavity module comprises an air chamber cover body unit, a first air hole and a dustproof sound insulation unit, the first air hole is formed in the upper portion of the air chamber cover body unit, and the dustproof sound insulation unit covers the first air hole.
Preferably, the dual-chamber photoacoustic cavity module further comprises a partition plate vertically arranged on the gas chamber cover unit to divide the gas chamber cover unit into two spaces, wherein the partition plate is made of a material which can transmit infrared rays and comprises but is not limited to silicon (coated or uncoated), germanium (coated or uncoated), fluoride glass, sulfide glass, sapphire glass and the like.
Preferably, the sound detection module includes a printed circuit board unit, a pressure detection unit, an amplification filtering unit, a cover plate unit and a second air hole, the pressure detection unit and the amplification filtering unit are both installed on the printed circuit board unit, the cover plate unit covers above the printed circuit board unit, and the second air hole is opened on the cover plate unit and is used for detecting the amplification filtering unit which is used for amplifying the filtering pressure signal and is electrically connected with the pressure detection unit of the pressure signal in the cover plate unit.
Preferably, the signal processing module comprises a signal conditioning unit and a signal processing unit, and the signal conditioning unit is electrically connected with the signal processing unit.
Preferably, the signal conditioning unit includes a first resistor R1, a first operational amplifier a1, a second operational amplifier a2, a third operational amplifier A3 and a fourth operational amplifier a4, one end of the first resistor R1 is connected in series with the sound signal and then grounded, the other end of the first resistor R3 is connected in parallel with one end of a third capacitor C1 and one end of a second capacitor C2, a positive input end of the first operational amplifier a1 is connected in parallel with the other end of the first capacitor C1 and one end of a second resistor R2, a negative input end of the first operational amplifier a1 is connected in parallel with one end of a fourth resistor R4 and one end of a fifth resistor R5, the other end of the fourth resistor R4 is electrically connected with the other end of the second capacitor C2, and a signal output end of the first operational amplifier a1 is connected in parallel with the other ends of the third resistor R3, the sixth resistor R6 and the fifth resistor R5;
the other end of the sixth resistor R6 is connected in parallel with one end of an eighth resistor R8, one end of a fourth capacitor C4 and one end of a third capacitor C3, the positive input end of the second operational amplifier a2 is connected in parallel with the other end of a fourth capacitor C4 and one end of a seventh resistor R7, the negative input end of the second operational amplifier a2 is connected in parallel with one end of a ninth resistor R9 and one end of a tenth resistor R10, the other end of the ninth resistor R9 is electrically connected with the other end of a third capacitor C3, and the signal output end of the second operational amplifier a2 is connected in parallel with the other end of an eighth resistor R8, one end of an eleventh resistor R11 and the other end of a tenth resistor R10;
the other end of the eleventh resistor R11 is connected in parallel with one end of a fifth capacitor C5, one end of a sixth capacitor C6 and one end of a twelfth resistor R12, the positive input end of the third operational amplifier A3 is connected in parallel with the other end of the sixth capacitor C6 and one end of a thirteenth resistor R13, the negative input end of the third operational amplifier A3 is connected in parallel with one end of a fourteenth resistor R14 and one end of a fifteenth resistor R15, the other end of the fourteenth resistor R14 is electrically connected with the other end of the fifth capacitor C5, and the signal output end of the third operational amplifier A3 is connected in parallel with the other end of a fifteenth resistor R15, one end of a sixteenth resistor R16 and the other end of a twelfth resistor R12;
the other end of the sixteenth resistor R16 is connected in parallel with one end of a seventh capacitor C7, one end of an eighth capacitor C8 and one end of a seventeenth resistor R17, the positive input end of the fourth operational amplifier a4 is connected in parallel with the other end of an eighth capacitor C8 and one end of an eighteenth resistor R18, the negative input end of the fourth operational amplifier a4 is connected in parallel with one end of a nineteenth resistor R19 and one end of a twentieth resistor R20, the other end of the nineteenth resistor R19 is electrically connected with the other end of a seventh capacitor C7, the signal output end of the fourth operational amplifier a4 is connected in parallel with the other end of a twentieth resistor R20 and the other end of a seventeenth resistor R17, and the other ends of the second resistor R2, the seventh resistor R7, the thirteenth resistor R13 and the eighteenth resistor R18 are all grounded.
Preferably, the signal processing unit comprises an analog-to-digital converter for converting an acoustic analog signal into an acoustic digital signal, a signal compensation component for measuring the temperature, humidity and atmospheric pressure in the photoacoustic cavity module, a pulse width modulation component for driving the modulated light source module to periodically change, and a central controller, and the analog-to-digital converter, the signal compensation component and the pulse width modulation component are all electrically connected with the central controller.
The other technical scheme of the invention is realized as follows:
a control method applying the photoacoustics gas concentration detection device specifically comprises the following steps:
s1, periodically generating infrared modulation light by a modulation light source module and transmitting the infrared modulation light to a photoacoustic cavity module, wherein the photoacoustic cavity module absorbs the infrared modulation light by using gas to be detected inside and converts the infrared modulation light into sound signals to be transmitted to a sound detection module;
and S2, detecting a sound signal through the sound detection module and transmitting the sound signal to the signal processing module, wherein the signal processing module calculates the concentration of the gas to be detected according to the sound signal.
Compared with the prior art, the photoacoustics gas concentration detection device provided by the invention periodically generates infrared modulation light by modulating the light source module, absorbs the infrared modulation light by utilizing the internal gas to be detected through the photoacoustics cavity module and converts the infrared modulation light into the sound signal, detects the sound signal through the sound detection module, and calculates the concentration of the gas to be detected through the signal processing module according to the sound signal, so that the gas concentration is measured through the photoacoustics effect.
Drawings
Fig. 1 is a schematic structural diagram of a photoacoustic gas concentration detection apparatus provided in embodiment 1 of the present invention;
fig. 2 is a schematic structural diagram of a modulated light source module of a photoacoustic gas concentration detection apparatus according to embodiment 1 of the present invention;
fig. 3 is a schematic structural diagram of a first photoacoustic cavity module of a photoacoustic gas concentration detection apparatus according to embodiment 1 of the present invention;
fig. 4 is a schematic structural diagram of a second photoacoustic cavity module of a photoacoustic gas concentration detection apparatus according to embodiment 1 of the present invention;
fig. 5 is a schematic structural diagram of a sound detection module of a photoacoustic gas concentration detection apparatus according to embodiment 1 of the present invention;
fig. 6 is a circuit diagram of a signal conditioning unit of a photoacoustic gas concentration detection apparatus according to embodiment 1 of the present invention;
fig. 7 is a schematic structural diagram of a signal processing unit of a photoacoustic gas concentration detection apparatus according to embodiment 1 of the present invention;
fig. 8 is a flowchart of a control method of a photoacoustic gas concentration detection apparatus according to embodiment 2 of the present invention.
Description of the reference numerals
The device comprises a 1-modulation light source module, a 11-infrared light source unit, a 12-optical filter, a 2-photoacoustic cavity module, a 21-photoacoustic cavity cover body unit, a 22-first air hole, a 23-dustproof sound insulation unit, a 24-partition plate, a 3-sound detection module, a 31-printed circuit board unit, a 32-pressure detection unit, a 33-amplification filtering unit, a 34-cover plate unit, a 35-second air hole, a 4-signal processing module, a 41-signal conditioning unit, a 42-signal processing unit, a 421-analog-to-digital converter, a 422-signal compensation assembly, a 423-pulse width modulation assembly, a 424-central controller, a 5-temperature and humidity detection module and a 6-atmospheric pressure detection module.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
An embodiment of the present invention provides a photoacoustics gas concentration detection apparatus, as shown in fig. 1-7, including a modulation light source module 1 for periodically generating infrared modulation light, a photoacoustic cavity module 2 for absorbing infrared light by using an internal gas to be detected and converting the infrared light into a sound signal, a sound detection module 3 for detecting the sound signal, and a signal processing module 4 for calculating a concentration of the gas to be detected according to the sound signal, where the modulation light source module 1 and the sound detection module 3 are both electrically connected to the signal processing module 4, the photoacoustic cavity module 2 is installed above the modulation light source module 1 and the sound detection module 3, and the sound detection module 3 is an analog microphone or a digital microphone.
Thus, by modulating the light source module 1 to periodically generate the narrow-band radiation infrared modulation light sensitive to the gas to be measured, the photoacoustic cavity module 2 absorbs infrared modulated light by using the gas to be measured in the photoacoustic cavity module to generate photoacoustic effect, converts absorbed light energy into heat energy, and periodically radiates to rapidly heat and cool the gas to be measured, thereby causing thermal expansion and contraction to generate an acoustic signal, detecting the acoustic signal through the acoustic detection module 3, calculating the concentration of the gas to be detected according to the acoustic signal through the signal processing module 4, thereby measuring the gas concentration by the photoacoustic effect, the whole device has small volume and wide application field, and does not need to plate gold in the absorption cavity in order to improve the reflection efficiency, thereby reducing the cost, simultaneously, all devices are integrally and firmly welded together, so that the device is high in stability and suitable for being installed in mobile equipment, a constant temperature controller and other life intelligent household components.
Still include temperature and humidity detection module 5 and atmospheric pressure detection module 6, temperature and humidity detection module 5 and atmospheric pressure detection module 6 all electricity are connected on signal processing module 4.
Like this, detect the humiture in the optoacoustic chamber module 2 through temperature and humidity detection module 5 to be used for the atmospheric pressure value in the optoacoustic chamber module 2 through atmospheric pressure detection module 6, with the atmospheric pressure degree compensation that is used for gas concentration.
The modulation light source module 1 comprises an infrared light source unit 11 and an optical filter 12, wherein the optical filter 12 is installed above the infrared light source unit 11 to filter out required narrow-band radiation infrared light.
Therefore, the MEMS light source is used as the infrared light source unit 11, the infrared filter 12 with specific wavelength is arranged above the infrared light source unit 11 and used for filtering out required narrow-band radiation, the purpose of modulating the light source is achieved by controlling the power supply, the cost is low, the size is small, periodic radiation can be generated without a mechanical chopper, and the MEMS light source is suitable for application of miniaturized products.
The infrared filter 12 can filter out the required narrow-band radiation, eliminate the influence of other components in the atmosphere on the measurement result, and the water vapor and the like in the atmosphere have strong absorption effect on the infrared light with specific wavelength, if the radiation in the whole wavelength range emitted by the MEMS light source reaches the photoacoustic cavity module 2, other gases can also absorb the radiation to generate a photoacoustic effect, and interfere the measurement result of the gas to be measured, thereby influencing the output result. The silicon-based infrared filter loaded on the MEMS light source window can selectively transmit radiation in a specific wavelength range, and by designing the transmission-cut-off wavelength parameter of the infrared filter, an atmospheric absorption waveband causing interference can be shielded outside, so that the radiation reaching the photoacoustic cavity module 2 is ensured to be narrow-band radiation sensitive to the gas to be detected. In addition, the filter 12 can be replaced to filter out narrow-band radiation of specific wavelength for the purpose of measuring other gases. In addition, the infrared light source unit 11 may also use a small incandescent bulb with low price, but because the incandescent bulb is turned on slowly, in order to reach a certain modulation frequency, the bulb needs to be operated to a certain current (40mA to 90mA), and then the bulb generates relatively high-frequency radiation excitation by a method of recovering voltage by applying voltage instantaneously.
The optical-acoustic cavity module 2 is a single-cavity optical-acoustic cavity module or a double-cavity optical-acoustic cavity module, the single-cavity optical-acoustic cavity module comprises an air chamber cover body unit 21, a first air hole 22 and a dustproof sound insulation unit 23, the first air hole 22 is arranged above the air chamber cover body unit 21, and the dustproof sound insulation unit 23 covers the first air hole 22.
In this way, the narrow-band radiation emitted by the MEMS light source is absorbed by the gas to be measured in the gas chamber cover unit 21, the absorbed light energy is converted into heat energy, and the periodic radiation causes rapid heating and cooling of the gas to be measured, which in turn causes thermal expansion and contraction, thereby generating sound waves. A first air hole 22 is reserved above the air chamber cover body unit 21 and used for introducing the gas to be detected; a layer of dustproof and sound-proof unit 23, namely a waterproof and breathable film, is attached above the first air hole 22 and used for preventing dust and liquid water from entering the pollution and blocking the sound detection module 3 and the modulated light source module 1, and meanwhile, the dustproof and sound-proof unit plays a certain sound-proof role and reduces the influence of environmental noise on the sound detection module 3.
The dual-chamber photoacoustic cavity module further comprises a partition plate 24, wherein the partition plate 24 is vertically arranged on the gas chamber cover unit 21 so as to divide the gas chamber cover unit 21 into two spaces, namely an absorption photoacoustic cell and a reference photoacoustic cell.
Thus, the air chamber cover body unit 21 is divided into two spaces by the partition plate 24, the modulated light source module 1 emits infrared radiation with a certain frequency, the infrared radiation is incident to the reference acousto-optic cell through the absorption acousto-optic cell, and high-concentration gas to be detected in the reference acousto-optic cell is excited to generate sound waves with the same frequency; the microphone receives sound wave excitation to generate an electric signal, if no gas to be detected exists in the absorption acousto-optic pool, the periodic infrared radiation generated by the light source is incident to the reference acousto-optic pool through the absorption acousto-optic pool without loss, the periodic infrared radiation is absorbed by the high-concentration gas to be detected in the reference acousto-optic pool, the gas generates periodic sound waves, the microphone is excited to generate the electric signal, and at the moment, the intensity of the incident infrared radiation is the highest, so that the signal generated by the microphone is the strongest;
when the absorption sound-light pool contains the measured gas with a certain concentration, infrared radiation generated by the light source passes through the absorption sound-light pool and can be partially lost, at the moment, the infrared radiation incident into the reference absorption pool can be reduced, the infrared radiation is absorbed by the high-concentration measured gas in the reference sound-light pool again, the gas generates periodic sound waves, at the moment, the intensity of the sound waves can be reduced, then, electric signals generated by the microphone can be weakened, and the concentration of the measured gas can be calculated according to the weakening degree of the electric signals output by the microphone.
The absorption photoacoustic cell internally comprises an MEMS light source, the reference photoacoustic cell is a cavity filled with high-concentration gas to be detected, the concentration of the reference photoacoustic cell is up to 100%, and an MEMS microphone, a temperature and humidity sensor and an atmospheric pressure sensor are packaged in the reference photoacoustic cell. The MEMS light source window and the reference photoacoustic cell window are covered by sapphire glass with wider and higher infrared transmittance or silicon, germanium and other materials plated with antireflection films.
The sound detection module 3 comprises a printed circuit board unit 31, a pressure detection unit 32, an amplification filtering unit 33, a cover plate unit 34 and a second air hole 35, wherein the pressure detection unit 32 and the amplification filtering unit 33 are both installed on the printed circuit board unit 31, the cover plate unit 34 covers the printed circuit board unit 31, and the second air hole 35 is formed in the cover plate unit 34 and used for detecting the amplification filtering unit 33 used for amplifying the filtering pressure signal and electrically connected with the pressure detection unit 32 of the pressure signal in the cover plate unit 34.
In this way, the sound detection module 3 is an MEMS analog microphone or an MEMS digital microphone, wherein the MEMS analog microphone senses sound pressure through the pressure detection unit 32 and converts the sound pressure into a weak electrical signal, and the weak electrical signal is amplified and filtered by the amplification and filtering unit 33 and then output to the signal processing module 4; the MEMS digital microphone senses the sound pressure by the pressure detection unit 32 and converts the sound pressure into a weak electrical signal, and outputs a digital signal in a PDM protocol format or a standard IIS protocol format to the signal processing module 4 after the weak electrical signal is amplified and filtered by the amplification and filtering unit 33 and then is subjected to analog-to-digital conversion; the conduction of the acoustic wave is performed through the second air holes 35.
The signal processing module 4 includes a signal conditioning unit 41 and a signal processing unit 42, and the signal conditioning unit 41 is electrically connected to the signal processing unit 42.
In this way, for the extraction of the specific frequency signal, the signal conditioning unit 41 may adopt a lock-in amplifier or a band-pass filter, and after the signal conditioning unit 41 performs filtering amplification and ADC sampling on the weak voltage output by the sound detection module 3, the signal processing unit 42 performs digital filtering algorithm processing.
The signal conditioning unit 41 includes a first resistor R1, a first operational amplifier a1, a second operational amplifier a2, a third operational amplifier A3 and a fourth operational amplifier a4, one end of the first resistor R1 is connected in series with an audio signal and then grounded, the other end of the first resistor R8538 is connected in parallel with one end of a third resistor R3, one end of a first capacitor C1 and one end of a second capacitor C2, a positive input end of the first operational amplifier a1 is connected in parallel with the other end of the first capacitor C1 and one end of a second resistor R2, a negative input end of the first operational amplifier a1 is connected in parallel with one end of a fourth resistor R4 and one end of a fifth resistor R5, the other end of the fourth resistor R4 is electrically connected with the other end of the second capacitor C2, and a signal output end of the first operational amplifier a1 is connected in parallel with the other ends of the third resistor R3, the sixth resistor 539r 6 and the fifth resistor R5;
the other end of the sixth resistor R6 is connected in parallel with one end of an eighth resistor R8, one end of a fourth capacitor C4 and one end of a third capacitor C3, the positive input end of the second operational amplifier a2 is connected in parallel with the other end of a fourth capacitor C4 and one end of a seventh resistor R7, the negative input end of the second operational amplifier a2 is connected in parallel with one end of a ninth resistor R9 and one end of a tenth resistor R10, the other end of the ninth resistor R9 is electrically connected with the other end of a third capacitor C3, and the signal output end of the second operational amplifier a2 is connected in parallel with the other end of an eighth resistor R8, one end of an eleventh resistor R11 and the other end of a tenth resistor R10;
the other end of the eleventh resistor R11 is connected in parallel with one end of a fifth capacitor C5, one end of a sixth capacitor C6 and one end of a twelfth resistor R12, the positive input end of the third operational amplifier A3 is connected in parallel with the other end of the sixth capacitor C6 and one end of a thirteenth resistor R13, the negative input end of the third operational amplifier A3 is connected in parallel with one end of a fourteenth resistor R14 and one end of a fifteenth resistor R15, the other end of the fourteenth resistor R14 is electrically connected with the other end of the fifth capacitor C5, and the signal output end of the third operational amplifier A3 is connected in parallel with the other end of a fifteenth resistor R15, one end of a sixteenth resistor R16 and the other end of a twelfth resistor R12;
the other end of the sixteenth resistor R16 is connected in parallel with one end of a seventh capacitor C7, one end of an eighth capacitor C8 and one end of a seventeenth resistor R17, the positive input end of the fourth operational amplifier a4 is connected in parallel with the other end of an eighth capacitor C8 and one end of an eighteenth resistor R18, the negative input end of the fourth operational amplifier a4 is connected in parallel with one end of a nineteenth resistor R19 and one end of a twentieth resistor R20, the other end of the nineteenth resistor R19 is electrically connected with the other end of a seventh capacitor C7, the signal output end of the fourth operational amplifier a4 is connected in parallel with the other end of a twentieth resistor R20 and the other end of a seventeenth resistor R17, and the other ends of the second resistor R2, the seventh resistor R7, the thirteenth resistor R13 and the eighteenth resistor R18 are all grounded.
Thus, the signal conditioning unit 41 forms an 8-order bandpass filter by 4 paths of operational amplifiers, and it should be noted that the bandpass filter with a very low center wavelength inevitably uses a filter capacitor with a large capacity and a resistor with a large resistance value, so that it is inevitable that the gain of the filter circuit generates a large deviation in a high and low temperature range due to temperature drift of components, and therefore, the center frequency and the bandwidth of the bandpass filter circuit need to be designed reasonably to avoid the deviation caused by temperature drift of the components, so the center frequency of the filter circuit of the present invention is 40Hz, and the bandwidth is 100 Hz.
The signal processing unit 42 includes an analog-to-digital converter 421 for converting an acoustic analog signal into an acoustic digital signal, a signal compensation component 422 for measuring the temperature, humidity and atmospheric pressure in the photoacoustic cavity module 2, a pulse width modulation component 423 for driving the modulated light source module 1 to periodically change, and a central controller 424, and the analog-to-digital converter 421, the signal compensation component 422, and the pulse width modulation component 423 are all electrically connected to the central controller 424.
In this way, the signal processing unit 42 selects an inner core Cortex-M4 with strong functions and operation processing capabilities, the analog voltage output by the analog microphone is digitally processed by the analog-to-digital converter 421, the temperature, humidity and atmospheric pressure values inside the photoacoustic cavity module 2 are measured by the signal compensation component 422 (i.e., IIC module) for system compensation, and the central controller 424 (i.e., MCU) generates a PWM signal by using an internal advanced timer (i.e., the pulse width modulation component 423) for driving the modulation light source module 1 to generate periodically-varying infrared radiation.
Data processing algorithm
Since there is noise with complex frequency composition in the environment and the sound detection module 3 itself also has noise floor, even the signal filtered by the analog filter (the digital microphone scheme does not have the analog filter design) also contains a lot of noise, and further processing is needed to extract the most important signal. The invention uses a data processing mode combining FIR filtering algorithm and Kalman filtering algorithm to process the original ADC data to filter noise and extract the signal related to the concentration of the measured gas.
Conversion of concentration
According to the photoacoustic spectrometry principle of the application, the signal amplitude extracted by the central controller 424 has a certain relation with the concentration of the gas to be measured, and the signal amplitude and the concentration are measured to be approximately linear but not completely linear through experiments. Therefore, the present application uses a fitting algorithm, first, a gas divider (mixer) is used to generate the measured gas with different concentrations from low to high, the computer continuously reads the signal amplitudes corresponding to the gas with different concentrations from the central controller 424 (i.e. MCU) to obtain a concentration-signal amplitude list, and a curve fitting algorithm is used to obtain the fitting coefficient of the signal amplitude-concentration.
The fitting coefficient of the amplitude-concentration of the lower signal is a multi-order coefficient, generally 2-5 orders, and the specific formula for calculating the concentration is as follows:
C＝Yn*Bn+Yn-1*Bn-1+Yn-2*Bn-2+…Y1*B1+B0
wherein C represents concentration, Y represents standard signal amplitude, and Bn-B0For the purpose of the multi-order coefficients,
calibration method
Because of the assembly difference and the electronic element difference of each sensor, finally each sensor can reach the identification precision only by calibration, the method adopts a two-point or multi-point fitting algorithm, the number of calibration points is determined by the linearity analysis of a signal amplitude-concentration curve, after the number and the concentration of the calibration points are determined, standard gas with corresponding concentration is sequentially supplied to the sensors, the computer reads the amplitude from the sensors, meanwhile, the computer reversely converts the standard signal amplitude according to the concentration of the current gas to be supplied, and after the signals of a plurality of concentration points are acquired, the original amplitude X of the sensors is obtained0，X1…XnMeanwhile, the computer obtains a standard amplitude Y through inverse conversion, and a group of fitting coefficients can be obtained through an n-1 order fitting algorithm: a. then，An-1…A1，A0。
Y＝Xn*An+Xn-1*An-1+Xn-2*An-2+…X1*A1+A0
The measured amplitude of each sensor can be converted into a standard amplitude through the formula, and then the concentration is obtained through a concentration conversion formula.
According to the photoacoustics gas concentration detection device, infrared modulation light is periodically generated by modulating the light source module, the internal gas to be detected is used for absorbing the infrared modulation light by the photoacoustic cavity module and converting the infrared modulation light into a sound signal, the sound signal is detected by the sound detection module, the concentration of the gas to be detected is calculated by the signal processing module according to the sound signal, so that the gas concentration is measured by the photoacoustic effect, the whole device is small in size and wide in application field, gold plating in the absorption cavity is not needed for improving the reflection efficiency, the cost is reduced, meanwhile, all devices are integrally and firmly welded together, the stability is high, and the photoacoustics gas concentration detection device is suitable for being installed in mobile equipment, constant temperature controllers and other life intelligent.
Example 2
As shown in fig. 8, embodiment 2 of the present invention provides a control method using the photoacoustic gas concentration detection apparatus, which specifically includes the following steps:
s1, periodically generating infrared modulation light by a modulation light source module and transmitting the infrared modulation light to a photoacoustic cavity module, wherein the photoacoustic cavity module absorbs the infrared modulation light by using gas to be detected inside and converts the infrared modulation light into sound signals to be transmitted to a sound detection module;
and S2, detecting a sound signal through the sound detection module and transmitting the sound signal to the signal processing module, wherein the signal processing module calculates the concentration of the gas to be detected according to the sound signal.
Thus, according to the control method of the photoacoustics gas concentration detection device, the light source modulation module periodically generates infrared modulation light, the photoacoustic cavity module absorbs the infrared modulation light by using the gas to be detected inside and converts the infrared modulation light into a sound signal, the sound detection module detects the sound signal, and the signal processing module calculates the concentration of the gas to be detected according to the sound signal, so that the gas concentration is measured through the photoacoustic effect.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. The utility model provides a photoacoustics gas concentration detection device, its characterized in that, including modulation light source module (1) that is used for periodic production infrared modulation light, be used for utilizing inside gas that awaits measuring to absorb infrared light and change photoacoustic cavity module (2) into sound signal, be used for detecting sound signal's sound detection module (3) and be used for calculating the signal processing module (4) of the gas concentration that awaits measuring according to sound signal, modulation light source module (1) and sound detection module (3) all electricity connect signal processing module (4), install in modulation light source module (1) and sound detection module (3) top photoacoustic cavity module (2), sound detection module (3) are analog microphone or digital microphone.
2. The photoacoustic gas concentration detection apparatus according to claim 1, further comprising a temperature and humidity detection module (5) and an atmospheric pressure detection module (6), wherein the temperature and humidity detection module (5) and the atmospheric pressure detection module (6) are both electrically connected to the signal processing module (4).
3. Photoacoustics gas concentration detection apparatus according to claim 2, characterized in that the modulated light source module (1) comprises an infrared light source unit (11) and a filter (12), said filter (12) being mounted above the infrared light source unit (11) for filtering out the required narrow-band radiated infrared light.
4. The photoacoustics gas concentration detection apparatus according to claim 3, wherein the photoacoustics cavity module (2) is a single-chamber photoacoustics cavity module or a dual-chamber photoacoustics cavity module, the single-chamber photoacoustics cavity module comprises an air chamber cover unit (21), a first air hole (22), and a dust-proof and sound-proof unit (23), the first air hole (22) is opened above the air chamber cover unit (21), and the dust-proof and sound-proof unit (23) covers the first air hole (22).
5. The photoacoustic gas concentration detecting device according to claim 4, wherein the dual-chamber photoacoustic cavity module further comprises a partition plate (24), the partition plate (24) being vertically provided at the gas chamber cover unit (21) for dividing the gas chamber cover unit (21) into two spaces.
6. The photoacoustics gas concentration detection apparatus according to claim 4 or 5, wherein the sound detection module (3) comprises a printed circuit board unit (31), a pressure detection unit (32), an amplification filter unit (33), a cover plate unit (34), and a second air hole (35), wherein the pressure detection unit (32) and the amplification filter unit (33) are both mounted on the printed circuit board unit (31), the cover plate unit (34) covers the printed circuit board unit (31), the second air hole (35) is opened on the cover plate unit (34), and the pressure detection unit (32) for detecting the pressure signal in the cover plate unit (34) is electrically connected to the amplification filter unit (33) for amplifying the filtered pressure signal.
7. The photoacoustics gas concentration detection apparatus according to claim 6, wherein the signal processing module (4) comprises a signal conditioning unit (41) and a signal processing unit (42), and the signal conditioning unit (41) is electrically connected to the signal processing unit (42).
8. The photoacoustic gas concentration detecting device according to claim 7, wherein the signal conditioning unit (41) comprises a first resistor R1, a first operational amplifier A1, a second operational amplifier A2, a third operational amplifier A3 and a fourth operational amplifier A4, one end of the first resistor R1 is connected in series with the sound signal and then grounded, the other end is connected in parallel with one end of a third resistor R3, one end of a first capacitor C1 and one end of a second capacitor C2, the positive input end of the first operational amplifier A1 is connected in parallel with the other end of the first capacitor C1 and one end of a second resistor R2, the negative input end of the first operational amplifier A1 is connected in parallel with one end of a fourth resistor R4 and one end of a fifth resistor R5, the other end of the fourth resistor R4 is electrically connected to the other end of the second capacitor C2, the signal output end of the first operational amplifier A1 is connected in parallel with the other end of the third resistor R3, One end of a sixth resistor R6 and the other end of a fifth resistor R5;
the other end of the sixth resistor R6 is connected in parallel with one end of an eighth resistor R8, one end of a fourth capacitor C4 and one end of a third capacitor C3, the positive input end of the second operational amplifier a2 is connected in parallel with the other end of a fourth capacitor C4 and one end of a seventh resistor R7, the negative input end of the second operational amplifier a2 is connected in parallel with one end of a ninth resistor R9 and one end of a tenth resistor R10, the other end of the ninth resistor R9 is electrically connected with the other end of a third capacitor C3, and the signal output end of the second operational amplifier a2 is connected in parallel with the other end of an eighth resistor R8, one end of an eleventh resistor R11 and the other end of a tenth resistor R10;
the other end of the eleventh resistor R11 is connected in parallel with one end of a fifth capacitor C5, one end of a sixth capacitor C6 and one end of a twelfth resistor R12, the positive input end of the third operational amplifier A3 is connected in parallel with the other end of the sixth capacitor C6 and one end of a thirteenth resistor R13, the negative input end of the third operational amplifier A3 is connected in parallel with one end of a fourteenth resistor R14 and one end of a fifteenth resistor R15, the other end of the fourteenth resistor R14 is electrically connected with the other end of the fifth capacitor C5, and the signal output end of the third operational amplifier A3 is connected in parallel with the other end of a fifteenth resistor R15, one end of a sixteenth resistor R16 and the other end of a twelfth resistor R12;
the other end of the sixteenth resistor R16 is connected in parallel with one end of a seventh capacitor C7, one end of an eighth capacitor C8 and one end of a seventeenth resistor R17, the positive input end of the fourth operational amplifier a4 is connected in parallel with the other end of an eighth capacitor C8 and one end of an eighteenth resistor R18, the negative input end of the fourth operational amplifier a4 is connected in parallel with one end of a nineteenth resistor R19 and one end of a twentieth resistor R20, the other end of the nineteenth resistor R19 is electrically connected with the other end of a seventh capacitor C7, the signal output end of the fourth operational amplifier a4 is connected in parallel with the other end of a twentieth resistor R20 and the other end of a seventeenth resistor R17, and the other ends of the second resistor R2, the seventh resistor R7, the thirteenth resistor R13 and the eighteenth resistor R18 are all grounded.
9. The photoacoustic gas concentration detection apparatus according to claim 8, wherein the signal processing unit (42) comprises an analog-to-digital converter (421) for converting an acoustic analog signal into an acoustic digital signal, a signal compensation component (422) for measuring the temperature, humidity and atmospheric pressure in the photoacoustic cavity module (2), a pulse width modulation component (423) for driving the modulated light source module (1) to periodically change, and a central controller (424), and the analog-to-digital converter (421), the signal compensation component (422) and the pulse width modulation component (423) are all electrically connected to the central controller (424).
10. A control method using the photoacoustic gas concentration detection apparatus according to any one of claims 1 to 9, comprising the following steps:
s1, periodically generating infrared modulation light by a modulation light source module and transmitting the infrared modulation light to a photoacoustic cavity module, wherein the photoacoustic cavity module absorbs the infrared modulation light by using gas to be detected inside and converts the infrared modulation light into sound signals to be transmitted to a sound detection module;
and S2, detecting a sound signal through the sound detection module and transmitting the sound signal to the signal processing module, wherein the signal processing module calculates the concentration of the gas to be detected according to the sound signal.
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