CN109211825B - Underwater dissolved gas infrared detection device and method adopting acousto-optic effect collimation light path - Google Patents

Underwater dissolved gas infrared detection device and method adopting acousto-optic effect collimation light path Download PDF

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CN109211825B
CN109211825B CN201811175703.2A CN201811175703A CN109211825B CN 109211825 B CN109211825 B CN 109211825B CN 201811175703 A CN201811175703 A CN 201811175703A CN 109211825 B CN109211825 B CN 109211825B
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module
gas
air chamber
acousto
light source
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CN109211825A (en
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郑传涛
李亚飞
刘志伟
陈晨
谢洪涛
仁强
王一丁
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Jilin University
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Jilin University
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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
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis

Abstract

The invention provides an infrared detection device and method for dissolved gas in water by adopting an acousto-optic effect collimation light path, belonging to the field of infrared gas detection technology and application, and comprising optical, electrical, auxiliary and mechanical parts. The optical part comprises a light source module, an acoustic optical modulator, a closed air chamber and a photoelectric detection module, is in a linear light path structure, and utilizes the acoustic optical modulator to intelligently adjust the output light beam of the light source module, thereby realizing light path collimation; the electrical part comprises a power supply, a light source drive, an acousto-optic drive, an air chamber temperature control, an air chamber pressure control, data acquisition, phase-locked amplification, a DSP processor and an upper computer communication module; the auxiliary part is an air pump module; the mechanical part comprises a cylindrical sealing shell, an upper layer platform, a lower layer platform, a front panel, a rear panel, a 24V power supply input port, a communication cable outlet, a gas outlet and a gas inlet; the invention simplifies the complexity of the optical system of the sensor, improves the stability and portability of the instrument, and is more suitable for underwater working environment.

Description

Underwater dissolved gas infrared detection device and method adopting acousto-optic effect collimation light path
Technical Field
The invention belongs to the technical field of infrared gas detection technology and application, and particularly relates to an infrared detection device and method for dissolved gas in water by adopting an acousto-optic effect collimation light path.
Background
Natural gas hydrate is widely distributed in offshore bottom sediments around the world as a 21 st century new energy source expected to replace fossil fuels. Subsea exploration of gas hydrates and related materials has been the subject of intense research by scientists before a viable method of mining has been found. Dissolved carbon dioxide (CO) in seawater as one of the decomposition evolved gases of natural gas hydrate2) Methane (CH)4) Hydrogen sulfide (H)2S) concentration and its isotopic abundance are objects that one needs to measure heavily.
In the technical field of underwater gas detection, currently, common methods include a seismic reflection method and a chemical sensor detection method; the former is to utilize the propagation influence of bubbles escaping underwater to signals such as sound waves to carry out underwater imaging, and the disadvantage is that the quantitative analysis can not be carried out on the dissolved gas underwater, and the latter needs to carry out underwater sampling firstly and then carry out sample analysis on land, and the disadvantage is that the in-situ and real-time performance of gas detection can not be ensured.
The gas detection technology based on infrared absorption spectrum utilizes the absorption effect of different molecules on specific infrared spectrum to convert the concentration information of gas into optical signals, and then converts the optical signals into electric signals for analysis. The gas concentration is measured by adopting a Tunable Diode Laser Absorption Spectroscopy (TDLAS) combined with a Wavelength Modulation Spectroscopy (WMS) technology (TDLAS-WMS), and the basic principle is as follows: by utilizing the current tuning and temperature tuning characteristics of the laser wavelength, the output wavelength of the laser is enabled to scan a certain absorption peak of the gas to be detected by applying a sawtooth wave current scanning signal, the wavelength of the laser is subjected to sinusoidal modulation, and detection is carried out according to the correlation between the amplitude (relative to the modulation signal frequency) of a second harmonic signal and the gas concentration. Compared with the currently common underwater gas detection technology, the technology has the advantages of high sensitivity, good selectivity, real-time in-situ measurement, long-term stability and the like. However, the currently reported gas detection device based on the TDLAS-WMS technology has a complex and bulky structure of the optical path part, and needs a large volume space after the sensing system is integrated, so that a portable instrument cannot be formed; the optical path part generally adopts a mechanical collimation method which is extremely sensitive to vibration, and uncertain factors such as underwater vibration and the like easily cause optical path misalignment, so that the instrument cannot be used in an underwater environment, or the working performance of the instrument in the underwater environment is poor or even the instrument cannot work normally. Therefore, in order to adapt to the environments of high pressure, humidity, vibration and the like of an underwater closed space, the optical and electrical structures need to be optimized, and the size needs to be reduced, which puts higher requirements on the design of the gas sensor dissolved in water.
Disclosure of Invention
The invention provides an infrared detection device and method for dissolved gas in water by adopting an acousto-optic effect collimation light path, aiming at the technical requirements of detection of the dissolved gas in water and the defects of the existing TDLAS-WMS infrared gas detection device in optical design.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
an infrared detection device for dissolved gas in water by adopting an acousto-optic effect collimation light path comprises an optical part, an electrical part, an auxiliary part and a mechanical part; the optical part comprises a light source module, an acousto-optic modulator, a closed air chamber and a photoelectric detection module, wherein the light source module, the acousto-optic modulator, the closed air chamber and the photoelectric detection module are arranged on the same straight line to form a straight line type light path structure; the electrical part comprises a power supply module, a light source driving module, an acousto-optic driving module, an air chamber temperature control module, an air chamber pressure control module, a data acquisition module, a phase-locked amplification module, a DSP processor module and an upper computer communication module; the air chamber temperature control module comprises a heating sheet, a temperature sensor and a temperature control circuit, and the output end of the temperature control circuit is electrically connected with the input ends of the heating sheet and the temperature sensor respectively; the air chamber pressure control module comprises a pressure sensor, a flow control valve and a pressure control circuit, wherein the output end of the pressure control circuit is respectively and electrically connected with the input ends of the pressure sensor and the flow control valve; the auxiliary part comprises an air pump module; the mechanical part comprises a cylindrical sealing shell, an upper layer platform, a lower layer platform, a front panel, a rear panel, a 24V power supply input port, a communication cable outlet, a gas outlet and a gas inlet;
wherein the input end of the light source module is electrically connected with the output end of the light source driving module in the electrical part; the output end of the light source module is connected with the optical input end of the acousto-optic modulator; the electrical input end of the acousto-optic modulator is electrically connected with the output end of the acousto-optic driving module; the optical output end of the acousto-optic modulator is connected with the optical input end of the closed air chamber; the optical output end of the closed air chamber is connected with the input end of the photoelectric detection module; the gas output end, namely the gas outlet, of the closed gas chamber is connected with the input end of the gas pump module through a gas pipeline; the output end of the photoelectric detection module is electrically connected with the input end of the phase-locked amplification module;
the DSP processor module in the electrical part is respectively and electrically connected with the input end of the upper computer communication module, the input end of the light source driving module, the input end of the acousto-optic driving module, the input end of the pressure control circuit in the air chamber pressure control module, the input end of the temperature control circuit in the air chamber temperature control module and the air pump module in the auxiliary part; the output end of the upper computer communication module is connected with the communication cable outlet; the output end of a pressure control circuit in the air chamber pressure control module is respectively and electrically connected with the input ends of the pressure sensor and the flow control valve; the output end of the flow control valve is connected with the gas input end, namely the gas inlet, of the closed gas chamber; the gas input end of the flow control valve is connected with the gas inlet; the pressure sensor is communicated with the internal gas of the closed gas chamber through a flow control valve, and the output end of the pressure sensor is connected with the input end of the data acquisition module; the heating sheet of the air chamber temperature control module is wrapped outside the closed air chamber; the temperature sensor is sealed in the closed air chamber, and the output end of the temperature sensor is connected with the input end of the data acquisition module; the output end of the temperature control circuit is respectively and electrically connected with the input ends of the heating sheet and the temperature sensor; the output end of the phase-locked amplification module is electrically connected with the input end of the data acquisition module; the output end of the data acquisition module is electrically connected with the input end of the DSP processor module; the output end of the power supply module is connected with each module in the electrical part;
the input end of the air pump module in the auxiliary part is connected with the air output end, namely an air outlet, of the closed air chamber, the output end of the air pump module is connected with the air outlet, and meanwhile, the air pump module is also electrically connected with the DSP processor module;
the upper platform and the lower platform in the mechanical part are fixed in a cylindrical sealed shell, the front panel and the rear panel are respectively arranged on two side surfaces of the cylindrical sealed shell, the upper platform is used for installing a temperature sensor and a heating sheet in an air chamber temperature control module in the optical part, the auxiliary part and the electrical part, and the lower platform is used for installing the electrical part, wherein only a temperature control circuit in the air chamber temperature control module in the electrical part is arranged on the lower platform; the 24V power supply input port and the communication cable outlet are arranged on the front panel; the gas inlet and the gas outlet are arranged on the back panel; the 24V power supply input port is connected with the input end of the power supply module; the outlet of the communication cable is connected with the output end of the upper computer communication module; the gas inlet is connected with the input end of the flow control valve; the gas outlet is connected with the output end of the gas pump module through a gas pipeline.
The use method of the underwater dissolved gas infrared detection device adopting the acousto-optic effect collimation light path has three working modes of collimation, calibration and measurement, and specifically comprises the following steps:
1 in collimation mode, the device is placed in a laboratory application environment, bottled target gas is used as an auxiliary collimation material, and the method comprises the following specific steps:
(a) voltage is supplied to the power supply module through the 24V power supply input port, so that the power supply module generates working voltage required by the electric part and the air pump module; the DSP module collects the working voltage of each module through the data collection module, and if the working voltage is abnormal, the collimation process is interrupted; if the voltage is normal, entering the step (b);
(b) connecting a gas inlet to a steel cylinder for bottling target gas by using a gas pipeline, and adjusting the pressure of a pressure reducing valve of the steel cylinder to meet the inlet pressure requirement of a flow control valve; opening the air pump module, and pumping bottled target gas into the closed air chamber; the DSP processor module adjusts the gas flow rate of the flow control valve, reads the pressure in the closed gas chamber through the pressure sensor, and enables the pressure in the closed gas chamber to reach a set value through feedback control;
(c) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(d) the DSP processor module starts the light source driving module and adjusts the working temperature of the light source module to be a set value;
(e) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(f) the light source module, the acousto-optic modulator, the closed air chamber and the photoelectric detection module are manually adjusted, so that infrared light emitted by the light source module is incident on the photoelectric detection module after passing through the acousto-optic modulator and the closed air chamber; the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(g) according to the set initial value of the acousto-optic driving signal, the DSP processor module sends a driving signal to the acousto-optic driving module, the acousto-optic driving module generates an electric signal with a specific carrier frequency to drive the acousto-optic modulator, after ultrasonic waves enter the acousto-optic modulator, the refractive index of an acousto-optic medium changes and forms a grating, and an incident infrared light signal is diffracted when passing through the acousto-optic medium at a certain angle, so that the propagation direction of the infrared light is changed;
(h) the DSP module collects the second harmonic signal output by the phase-locked amplifying module through the data collecting module, compares the second harmonic signal with the standard second harmonic signal calculated from the database, calculates the similarity of the harmonic signals and stores the similarity in the internal memory;
(i) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, returning to the step (a); if the driving signal is normal, adjusting the wavelength according to the set driving signal of the acousto-optic driving module, modifying the acousto-optic driving signal, and repeating the steps (g) to (i) until the circulation is finished;
(j) finding out the maximum similarity from the similarity result obtained by calculation, determining a driving signal, namely a driving voltage value, of the acousto-optic driving module corresponding to the maximum similarity, and taking the driving signal as the optimal driving signal of the acousto-optic driving module;
(k) the DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(l) Manually closing the DSP processor module and the power supply module, and ending the collimation adjustment process;
2 under the calibration mode, the device is placed in a laboratory application environment, and a gas distribution system, bottled nitrogen and bottled target gas are adopted as auxiliary calibration equipment or materials of the device, and the method comprises the following specific steps:
(a) supplying voltage to the power supply module through the 24V power supply input port so as to generate working voltage required by the electric part and the air pump module; the DSP module collects the working voltage of each module through the data collection module, and if the working voltage is abnormal, the calibration process is interrupted; if the result is normal, entering the step (b);
(b) determining the concentration of the bottled target gas according to the concentration range of the target gas to be calibrated and the flow regulation range of the gas distribution system, using the bottled nitrogen and the bottled target gas as input gases of the gas distribution system, and connecting a gas inlet to an output port of the gas distribution system by using a gas pipeline;
(c) setting the flow rates of bottled nitrogen and bottled target gas of a gas distribution system according to the concentration of the target gas to be calibrated to generate the target gas with the required concentration;
(d) opening the air pump module, and pumping target gas with the concentration to be calibrated into the air chamber; the gas flow rate of the flow control valve is adjusted through the DSP module, the pressure in the closed gas chamber is read through the pressure sensor, and the pressure in the closed gas chamber reaches a set value through feedback control;
(e) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(f) the DSP processor module starts the light source driving module and adjusts the working temperature of the light source module to be a set value;
(g) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(h) according to the optimization result of the collimation mode, the DSP processor module sends an optimal driving voltage value to the acousto-optic driving module; infrared light emitted by the light source module is made to pass through the acousto-optic modulator and the closed air chamber and then is incident on the photoelectric detection module; the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(i) according to the acquisition time of each gas sample with the calibrated concentration, the DSP module circularly acquires a second harmonic signal obtained by the phase-locked amplification module in the sampling period through the data acquisition module, acquires the amplitude of the second harmonic signal and stores the amplitude into the internal memory; after the acquisition time is up, calculating the average value of the amplitude of the acquired second harmonic signal, and storing the average value and the concentration of the calibration gas into an internal memory;
(j) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, returning to the step (a); if the concentration is normal, adjusting the flow of the gas in two input steel cylinders of the gas distribution system according to the set next calibration concentration, and repeating the steps (c) to (j) until the calibration of all the concentrations is finished;
(k) fitting a linear relation between the amplitude of the second harmonic signal and the concentration of the calibrated gas according to the result of the cyclic calibration, and storing a fitting coefficient into an internal memory of the DSP module;
(l) The DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(m) manually closing the DSP processor module and the power supply module, and ending the calibration process;
3 under the measuring mode, the device is arranged in an underwater application environment, and an underwater gas-liquid separation device, an overwater hull deck monitoring computer and an overwater hull deck 24V power supply are adopted as auxiliary application devices of the device, and the method specifically comprises the following steps:
(a) on the deck, a gas pipeline is utilized to connect a gas inlet to a gas outlet of the underwater gas-liquid separation equipment; a 24V power supply of a deck of the water ship body is used for supplying working voltage to a power supply module through a 24V power supply input port through a cable, so that working voltage required by an electrical part and an air pump module is generated; the overwater ship body deck monitoring computer is connected with an upper computer communication module through a cable conductor and a communication cable outlet, and the DSP processor module is used for collecting working voltage of each module through the data collection module and transmitting the working voltage to the overwater ship body deck monitoring computer until the overwater ship body deck monitoring computer works normally; placing underwater gas-liquid separation equipment and the device of the invention in a pressure-resistant cabin, and placing the equipment in water through a towing body;
(b) the overwater hull deck monitoring computer sends a measurement starting command to the DSP processor module;
(c) the DSP processor module opens the air pump module and pumps air output by the gas-liquid separation equipment into the closed air chamber; the DSP processor module adjusts the gas flow rate of the flow control valve, reads the pressure in the closed gas chamber through the pressure sensor and transmits the pressure to the overwater ship deck monitoring computer; the pressure in the closed air chamber reaches a set value through feedback control;
(d) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(e) the DSP processor module starts the light source driving module, and adjusts the working temperature of the light source module to be a set value;
(f) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(g) according to the collimation result, the DSP processor module sets the voltage of the acousto-optic driving module as an optimal driving voltage value; infrared light emitted by the light source module is made to pass through the acousto-optic modulator and the closed air chamber and then is incident on the photoelectric detection module;
(h) the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(i) the DSP module calculates the concentration of the gas to be detected according to the second harmonic signal amplitude obtained by sampling and the linear relation between the calibrated target gas concentration and the second harmonic signal amplitude, and transmits the concentration to the monitoring computer on the deck of the ship body through a cable;
(j) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, an alarm instruction is sent to a deck monitoring computer; if the command is normal, inquiring whether a measurement stopping command sent by the monitoring computer is received; if a measurement stopping command is received, turning to the step (k); if the measurement stopping command is not received, repeating the steps (h) to (j);
(k) the DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(l) And manually cutting off the 24V power supply of the water ship body deck on the deck, and finishing the measurement process.
The concentration range of the target gas to be calibrated in the step (b) in the step 2 is consistent with the concentration range of the target gas dissolved in water at different depths, and the concentration of the bottled target gas is greater than the range, so that the target gas with different concentrations can be configured through the gas distribution system.
The linear relation between the amplitude of the second harmonic signal and the concentration of the calibrated gas is fitted by Origin software according to the result of the cyclic calibration in the step (k) in the step 2, and the average amplitude of the second harmonic signal and the concentration of the calibrated gas can be fitted by introducing the average amplitude of the second harmonic signal and the concentration of the calibrated gas into the software to obtain a fitting coefficient.
The invention has the beneficial effects that:
(1) the invention adopts a full-automatic light beam collimation method, utilizes the acousto-optic modulator to carry out electric control adjustment on the incident angle of the light beam output by the laser, automatically judges whether the shape and the amplitude of the acquired second harmonic signal meet the requirements or not through a program under the condition of introducing collimation gas into the gas chamber, feeds back and adjusts a driving signal of the acousto-optic modulator until the light path meets the collimation requirements, and reduces the collimation process of the optical system of the sensor.
(2) The invention provides a linear light path structure based on an acousto-optic modulator, which simplifies the optical complexity of a sensor system, improves the stability, reliability and portability of an instrument and is more suitable for an underwater working environment.
(3) Compared with an optical system and a sensor which are manually aligned, the method can judge the alignment performance of the light path by using the alignment gas on line, thereby improving the sensing performance of the underwater mobile measurement environment.
Drawings
FIG. 1 is a block diagram of the present invention;
FIG. 2 is a schematic view of the cylindrical seal housing of the present invention;
FIG. 3 is a schematic block diagram of the internal structure of the cylindrical hermetic enclosure of the present invention;
FIG. 4 is a detail view of the front panel of the cylindrical seal housing of the present invention;
FIG. 5 is a detail view of the rear panel of the cylindrical seal housing of the present invention;
FIG. 6 is a diagram of the operational configuration of the present invention in the collimation mode;
FIG. 7 is a diagram of the operating configuration of the present invention in the calibration mode;
FIG. 8 is a diagram of the operating configuration of the present invention in a measurement mode;
FIG. 9 is a flow chart of the operation of the present invention in the collimation mode;
FIG. 10 is a flow chart of the operation of the present invention in the calibration mode;
FIG. 11 is a flow chart of the operation of the present invention in a measurement mode;
fig. 12 is a waveform of a second harmonic signal extracted with carbon dioxide as a target gas according to the present invention.
Detailed Description
As shown in fig. 1, 2, 3, 4 and 5, an infrared detection device for dissolved gas in water using an acousto-optic effect collimation light path comprises an optical part, an electrical part, an auxiliary part and a mechanical part; the optical part comprises a light source module, an acousto-optic modulator, a closed air chamber and a photoelectric detection module, wherein the light source module, the acousto-optic modulator, the closed air chamber and the photoelectric detection module are arranged on the same straight line to form a straight line type light path structure; the electrical part comprises a power supply module, a light source driving module, an acousto-optic driving module, an air chamber temperature control module, an air chamber pressure control module, a data acquisition module, a phase-locked amplification module, a DSP processor module and an upper computer communication module; the air chamber temperature control module comprises a heating sheet, a temperature sensor and a temperature control circuit, and the output end of the temperature control circuit is electrically connected with the input ends of the heating sheet and the temperature sensor respectively; the air chamber pressure control module comprises a pressure sensor, a flow control valve and a pressure control circuit, wherein the output end of the pressure control circuit is respectively and electrically connected with the input ends of the pressure sensor and the flow control valve; the auxiliary part comprises an air pump module; the mechanical part comprises a cylindrical sealing shell, an upper layer platform, a lower layer platform, a front panel, a rear panel, a 24V power supply input port, a communication cable outlet, a gas outlet and a gas inlet;
wherein the input end of the light source module is electrically connected with the output end of the light source driving module in the electrical part; the output end of the light source module is connected with the optical input end of the acousto-optic modulator; the electrical input end of the acousto-optic modulator is electrically connected with the output end of the acousto-optic driving module; the optical output end of the acousto-optic modulator is connected with the optical input end of the closed air chamber; the optical output end of the closed air chamber is connected with the input end of the photoelectric detection module; the gas output end, namely the gas outlet, of the closed gas chamber is connected with the input end of the gas pump module through a gas pipeline; the output end of the photoelectric detection module is electrically connected with the input end of the phase-locked amplification module;
the DSP processor module in the electrical part is respectively and electrically connected with the input end of the upper computer communication module, the input end of the light source driving module, the input end of the acousto-optic driving module, the input end of the pressure control circuit in the air chamber pressure control module, the input end of the temperature control circuit in the air chamber temperature control module and the air pump module in the auxiliary part; the output end of the upper computer communication module is connected with the communication cable outlet; the output end of a pressure control circuit in the air chamber pressure control module is respectively and electrically connected with the input ends of the pressure sensor and the flow control valve; the output end of the flow control valve is connected with the gas input end, namely the gas inlet, of the closed gas chamber; the gas input end of the flow control valve is connected with the gas inlet; the pressure sensor is communicated with the internal gas of the closed gas chamber through a flow control valve, and the output end of the pressure sensor is connected with the input end of the data acquisition module; the heating sheet of the air chamber temperature control module is wrapped outside the closed air chamber; the temperature sensor is sealed in the metal shell of the closed air chamber, and the output end of the temperature sensor is connected with the input end of the data acquisition module; the output end of the temperature control circuit is respectively and electrically connected with the input ends of the heating sheet and the temperature sensor; the output end of the power supply module is electrically connected with the input end of the data acquisition module; the output end of the phase-locked amplification module is electrically connected with the input end of the data acquisition module; the output end of the data acquisition module is electrically connected with the input end of the DSP processor module; the output end of the power supply module is connected with each module in the electrical part;
the input end of the air pump module in the auxiliary part is connected with the air output end, namely an air outlet, of the closed air chamber, the output end of the air pump module is connected with the air outlet, and meanwhile, the air pump module is also electrically connected with the DSP processor module;
the upper platform and the lower platform in the mechanical part are fixed in a cylindrical sealed shell, the front panel and the rear panel are respectively arranged on two side surfaces of the cylindrical sealed shell, the upper platform is used for installing a temperature sensor and a heating sheet in an air chamber temperature control module in the optical part, the auxiliary part and the electrical part, and the lower platform is used for installing the electrical part, wherein only a temperature control circuit in the air chamber temperature control module in the electrical part is arranged on the lower platform; the 24V power supply input port and the communication cable outlet are arranged on the front panel; the gas inlet and the gas outlet are arranged on the back panel; the 24V power supply input port is connected with the input end of the power supply module; the outlet of the communication cable is connected with the output end of the upper computer communication module; the gas inlet is connected with the input end of the flow control valve; the gas outlet is connected with the output end of the gas pump module through a gas pipeline.
The use method of the underwater dissolved gas infrared detection device adopting the acousto-optic effect collimation light path has three working modes of collimation, calibration and measurement, and specifically comprises the following steps:
1 in the collimation mode, the device is placed in a laboratory application environment, and bottled target gas is used as an auxiliary collimation material of the device, as shown in fig. 6 and 9, the specific steps are as follows:
(a) voltage is supplied to the power supply module through the 24V power supply input port, so that the power supply module generates working voltage required by the electric part and the air pump module; the DSP module collects the working voltage of each module through the data collection module, and if the working voltage is abnormal, the collimation process is interrupted; if the voltage is normal, entering the step (b);
(b) connecting a gas inlet to a steel cylinder for bottling target gas by using a gas pipeline, and adjusting the pressure of a pressure reducing valve of the steel cylinder to meet the inlet pressure requirement of a flow control valve; opening the air pump module, and pumping bottled target gas into the closed air chamber; the DSP processor module adjusts the gas flow rate of the flow control valve, reads the pressure in the closed gas chamber through the pressure sensor, and enables the pressure in the closed gas chamber to reach a set value through feedback control;
(c) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(d) the DSP processor module starts the light source driving module and adjusts the working temperature of the light source module to be a set value;
(e) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(f) the light source module, the acousto-optic modulator, the closed air chamber and the photoelectric detection module are manually adjusted, so that infrared light emitted by the light source module is incident on the photoelectric detection module after passing through the acousto-optic modulator and the closed air chamber; the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(g) according to the set initial value of the acousto-optic driving signal, the DSP processor module sends a driving signal to the acousto-optic driving module, the acousto-optic driving module generates an electric signal with a specific carrier frequency to drive the acousto-optic modulator, after ultrasonic waves enter the acousto-optic modulator, the refractive index of an acousto-optic medium changes and forms a grating, and an incident infrared light signal is diffracted when passing through the acousto-optic medium at a certain angle, so that the propagation direction of the infrared light is changed;
(h) the DSP module collects the second harmonic signal output by the phase-locked amplifying module through the data collecting module, compares the second harmonic signal with the standard second harmonic signal calculated from the database, calculates the similarity of the harmonic signals and stores the similarity in the internal memory;
(i) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, returning to the step (a); if the driving signal is normal, adjusting the wavelength according to the set driving signal of the acousto-optic driving module, modifying the acousto-optic driving signal, and repeating the steps (g) to (i) until the circulation is finished;
(j) finding out the maximum similarity from the similarity result obtained by calculation, determining a driving signal, namely a driving voltage value, of the acousto-optic driving module corresponding to the maximum similarity, and taking the driving signal as the optimal driving signal of the acousto-optic driving module;
(k) the DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(l) Manually closing the DSP processor module and the power supply module, and ending the collimation adjustment process;
2 in the calibration mode, the device is placed in a laboratory application environment, and a gas distribution system, bottled nitrogen and bottled target gas are used as auxiliary calibration equipment or materials of the device, as shown in fig. 7 and 10, the specific steps are as follows:
(a) supplying voltage to the power supply module through the 24V power supply input port so as to generate working voltage required by the electric part and the air pump module; the DSP module collects the working voltage of each module through the data collection module, and if the working voltage is abnormal, the calibration process is interrupted; if the result is normal, entering the step (b);
(b) determining the concentration of the bottled target gas according to the concentration range of the target gas to be calibrated and the flow regulation range of the gas distribution system, using the bottled nitrogen and the bottled target gas as input gases of the gas distribution system, and connecting a gas inlet to an output port of the gas distribution system by using a gas pipeline;
(c) setting the flow rates of bottled nitrogen and bottled target gas of a gas distribution system according to the concentration of the target gas to be calibrated to generate the target gas with the required concentration;
(d) opening the air pump module, and pumping target gas with the concentration to be calibrated into the air chamber; the gas flow rate of the flow control valve is adjusted through the DSP module, the pressure in the closed gas chamber is read through the pressure sensor, and the pressure in the closed gas chamber reaches a set value through feedback control;
(e) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(f) the DSP processor module starts the light source driving module and adjusts the working temperature of the light source module to be a set value;
(g) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(h) according to the optimization result of the collimation mode, the DSP processor module sends an optimal driving voltage value to the acousto-optic driving module; infrared light emitted by the light source module is made to pass through the acousto-optic modulator and the closed air chamber and then is incident on the photoelectric detection module; the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(i) according to the acquisition time of each gas sample with the calibrated concentration, the DSP module circularly acquires a second harmonic signal obtained by the phase-locked amplification module in the sampling period through the data acquisition module, acquires the amplitude of the second harmonic signal and stores the amplitude into the internal memory; after the acquisition time is up, calculating the average value of the amplitude of the acquired second harmonic signal, and storing the average value and the concentration of the calibration gas into an internal memory;
(j) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, returning to the step (a); if the concentration is normal, adjusting the flow of the gas in two input steel cylinders of the gas distribution system according to the set next calibration concentration, and repeating the steps (c) to (j) until the calibration of all the concentrations is finished;
(k) fitting a linear relation between the amplitude of the second harmonic signal and the concentration of the calibrated gas according to the result of the cyclic calibration, and storing a fitting coefficient into an internal memory of the DSP module;
(l) The DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(m) manually closing the DSP processor module and the power supply module, and ending the calibration process;
3 under the measurement mode, the device is placed in an underwater application environment, an underwater gas-liquid separation device, an overwater hull deck monitoring computer and an overwater hull deck 24V power supply are adopted as auxiliary application devices of the device, and as shown in fig. 8 and fig. 11, the specific steps are as follows:
(a) on the deck, a gas pipeline is utilized to connect a gas inlet to a gas outlet of the underwater gas-liquid separation equipment; a 24V power supply of a deck of the water ship body is used for supplying working voltage to a power supply module through a 24V power supply input port through a cable, so that working voltage required by an electrical part and an air pump module is generated; the overwater ship body deck monitoring computer is connected with an upper computer communication module through a cable conductor and a communication cable outlet, and the DSP processor module is used for collecting working voltage of each module through the data collection module and transmitting the working voltage to the overwater ship body deck monitoring computer until the overwater ship body deck monitoring computer works normally; placing underwater gas-liquid separation equipment and the device of the invention in a pressure-resistant cabin, and placing the equipment in water through a towing body;
(b) the overwater hull deck monitoring computer sends a measurement starting command to the DSP processor module;
(c) the DSP processor module opens the air pump module and pumps air output by the gas-liquid separation equipment into the closed air chamber; the DSP processor module adjusts the gas flow rate of the flow control valve, reads the pressure in the closed gas chamber through the pressure sensor and transmits the pressure to the overwater ship deck monitoring computer; the pressure in the closed air chamber reaches a set value through feedback control;
(d) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(e) the DSP processor module starts the light source driving module, and adjusts the working temperature of the light source module to be a set value;
(f) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(g) according to the collimation result, the DSP processor module sets the voltage of the acousto-optic driving module as an optimal driving voltage value; infrared light emitted by the light source module is made to pass through the acousto-optic modulator and the closed air chamber and then is incident on the photoelectric detection module;
(h) the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(i) the DSP module can calculate the concentration of the gas to be measured in an inversion mode according to the second harmonic signal amplitude obtained by sampling and the linear relation between the calibrated target gas concentration and the second harmonic signal amplitude, and transmits the concentration to the monitoring computer on the deck of the ship body through a cable;
(j) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, an alarm instruction is sent to a deck monitoring computer; if the command is normal, inquiring whether a measurement stopping command sent by the monitoring computer is received; if a measurement stopping command is received, turning to the step (k); if the measurement stopping command is not received, repeating the steps (h) to (j);
(k) the DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(l) And manually cutting off the 24V power supply of the water ship body deck on the deck, and finishing the measurement process.
The concentration range of the target gas to be calibrated in the step (b) in the step 2 is consistent with the concentration range of the target gas dissolved in water at different depths, and the concentration of the bottled target gas is greater than the range, so that the target gas with different concentrations can be configured through the gas distribution system.
The linear relation between the amplitude of the second harmonic signal and the concentration of the calibrated gas is fitted by Origin software according to the result of the cyclic calibration in the step (k) in the step 2, and the average amplitude of the second harmonic signal and the concentration of the calibrated gas can be fitted by introducing the average amplitude of the second harmonic signal and the concentration of the calibrated gas into the software to obtain a fitting coefficient.
The light source module adopted in the embodiment is a band-to-band cascade laser with the wavelength of 4319nm, which is manufactured by Nanoplus Germany; the acousto-optic modulator is I-M0XX-XC11B76-P5-GH105 of Gooch & Housego; the adopted closed air chamber is a dense light spot type multi-pass pool with an optical path of 26 m; the photoelectric detection module is a mid-infrared mercury cadmium telluride detector.
Referring to FIG. 12, the signal waveform obtained by performing the experiment using a standard carbon dioxide gas sample having a concentration of 5ppm at a pressure of 40Torr and a temperature of 20 ℃. In the figure, the upper branch curve is an output signal of the photoelectric detection module, and the lower branch curve is a secondary waveform signal output by the phase-locked amplification module. It can be seen that there are two distinct absorption peaks of carbon dioxide gas (upper branch) and corresponding second harmonics (lower branch) in the graph.

Claims (3)

1. The using method of the infrared detection device for the dissolved gas in the water by adopting the acousto-optic effect collimation light path is characterized in that the infrared detection device for the dissolved gas in the water by adopting the acousto-optic effect collimation light path comprises an optical part, an electrical part, an auxiliary part and a mechanical part; the optical part comprises a light source module, an acousto-optic modulator, a closed air chamber and a photoelectric detection module, wherein the light source module, the acousto-optic modulator, the closed air chamber and the photoelectric detection module are arranged on the same straight line to form a straight line type light path structure; the electrical part comprises a power supply module, a light source driving module, an acousto-optic driving module, an air chamber temperature control module, an air chamber pressure control module, a data acquisition module, a phase-locked amplification module, a DSP processor module and an upper computer communication module; the air chamber temperature control module comprises a heating sheet, a temperature sensor and a temperature control circuit, and the output end of the temperature control circuit is electrically connected with the input ends of the heating sheet and the temperature sensor respectively; the air chamber pressure control module comprises a pressure sensor, a flow control valve and a pressure control circuit, wherein the output end of the pressure control circuit is respectively and electrically connected with the input ends of the pressure sensor and the flow control valve; the auxiliary part comprises an air pump module; the mechanical part comprises a cylindrical sealing shell, an upper layer platform, a lower layer platform, a front panel, a rear panel, a 24V power supply input port, a communication cable outlet, a gas outlet and a gas inlet;
wherein the input end of the light source module is electrically connected with the output end of the light source driving module in the electrical part; the output end of the light source module is connected with the optical input end of the acousto-optic modulator; the electrical input end of the acousto-optic modulator is electrically connected with the output end of the acousto-optic driving module; the optical output end of the acousto-optic modulator is connected with the optical input end of the closed air chamber; the optical output end of the closed air chamber is connected with the input end of the photoelectric detection module; the gas output end, namely the gas outlet, of the closed gas chamber is connected with the input end of the gas pump module through a gas pipeline; the output end of the photoelectric detection module is electrically connected with the input end of the phase-locked amplification module;
the DSP processor module in the electrical part is respectively and electrically connected with the input end of the upper computer communication module, the input end of the light source driving module, the input end of the acousto-optic driving module, the input end of the pressure control circuit in the air chamber pressure control module, the input end of the temperature control circuit in the air chamber temperature control module and the air pump module in the auxiliary part; the output end of the upper computer communication module is connected with the communication cable outlet; the output end of a pressure control circuit in the air chamber pressure control module is respectively and electrically connected with the input ends of the pressure sensor and the flow control valve; the output end of the flow control valve is connected with the gas input end, namely the gas inlet, of the closed gas chamber; the gas input end of the flow control valve is connected with the gas inlet; the pressure sensor is communicated with the internal gas of the closed gas chamber through a flow control valve, and the output end of the pressure sensor is connected with the input end of the data acquisition module; the heating sheet of the air chamber temperature control module is wrapped outside the closed air chamber; the temperature sensor is sealed in the closed air chamber, and the output end of the temperature sensor is connected with the input end of the data acquisition module; the output end of the temperature control circuit is respectively and electrically connected with the input ends of the heating sheet and the temperature sensor; the output end of the phase-locked amplification module is electrically connected with the input end of the data acquisition module; the output end of the data acquisition module is electrically connected with the input end of the DSP processor module; the output end of the power supply module is connected with each module in the electrical part;
the input end of the air pump module in the auxiliary part is connected with the air output end, namely an air outlet, of the closed air chamber, the output end of the air pump module is connected with the air outlet, and meanwhile, the air pump module is also electrically connected with the DSP processor module;
the upper platform and the lower platform in the mechanical part are fixed in a cylindrical sealed shell, the front panel and the rear panel are respectively arranged on two side surfaces of the cylindrical sealed shell, the upper platform is used for installing a temperature sensor and a heating sheet in an air chamber temperature control module in the optical part, the auxiliary part and the electrical part, and the lower platform is used for installing the electrical part, wherein only a temperature control circuit in the air chamber temperature control module in the electrical part is arranged on the lower platform; the 24V power supply input port and the communication cable outlet are arranged on the front panel; the gas inlet and the gas outlet are arranged on the back panel; the 24V power supply input port is connected with the input end of the power supply module; the outlet of the communication cable is connected with the output end of the upper computer communication module; the gas inlet is connected with the input end of the flow control valve; the gas outlet is connected with the output end of the gas pump module through a gas pipeline;
the using method has three working modes of collimation, calibration and measurement, and specifically comprises the following steps:
firstly, under the collimation mode, the device is placed in a laboratory application environment, bottled target gas is used as an auxiliary collimation material, and the method comprises the following specific steps:
(a) voltage is supplied to the power supply module through the 24V power supply input port, so that the power supply module generates working voltage required by the electric part and the air pump module; the DSP module collects the working voltage of each module through the data collection module, and if the working voltage is abnormal, the collimation process is interrupted; if the voltage is normal, entering the step (b);
(b) connecting a gas inlet to a steel cylinder for bottling target gas by using a gas pipeline, and adjusting the pressure of a pressure reducing valve of the steel cylinder to meet the inlet pressure requirement of a flow control valve; opening the air pump module, and pumping bottled target gas into the closed air chamber; the DSP processor module adjusts the gas flow rate of the flow control valve, reads the pressure in the closed gas chamber through the pressure sensor, and enables the pressure in the closed gas chamber to reach a set value through feedback control;
(c) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(d) the DSP processor module starts the light source driving module and adjusts the working temperature of the light source module to be a set value;
(e) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(f) the light source module, the acousto-optic modulator, the closed air chamber and the photoelectric detection module are manually adjusted, so that infrared light emitted by the light source module is incident on the photoelectric detection module after passing through the acousto-optic modulator and the closed air chamber; the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(g) according to the set initial value of the acousto-optic driving signal, the DSP processor module sends a driving signal to the acousto-optic driving module, the acousto-optic driving module generates an electric signal with a specific carrier frequency to drive the acousto-optic modulator, after ultrasonic waves enter the acousto-optic modulator, the refractive index of an acousto-optic medium changes and forms a grating, and an incident infrared light signal is diffracted when passing through the acousto-optic medium at a certain angle, so that the propagation direction of the infrared light is changed;
(h) the DSP module collects the second harmonic signal output by the phase-locked amplifying module through the data collecting module, compares the second harmonic signal with the standard second harmonic signal calculated from the database, calculates the similarity of the harmonic signals and stores the similarity in the internal memory;
(i) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, returning to the step (a); if the driving signal is normal, adjusting the wavelength according to the set driving signal of the acousto-optic driving module, modifying the acousto-optic driving signal, and repeating the steps (g) - (i) until the cycle is finished;
(j) finding out the maximum similarity from the similarity result obtained by calculation, determining a driving signal, namely a driving voltage value, of the acousto-optic driving module corresponding to the maximum similarity, and taking the driving signal as the optimal driving signal of the acousto-optic driving module;
(k) the DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(l) Manually closing the DSP processor module and the power supply module, and ending the collimation adjustment process;
secondly, under the calibration mode, the device is placed in a laboratory application environment, a gas distribution system, bottled nitrogen and bottled target gas are adopted as auxiliary calibration equipment or materials, and the method comprises the following specific steps:
(a) supplying voltage to the power supply module through the 24V power supply input port so as to generate working voltage required by the electric part and the air pump module; the DSP module collects the working voltage of each module through the data collection module, and if the working voltage is abnormal, the calibration process is interrupted; if the result is normal, entering the step (b);
(b) determining the concentration of the bottled target gas according to the concentration range of the target gas to be calibrated and the flow regulation range of the gas distribution system, using the bottled nitrogen and the bottled target gas as input gases of the gas distribution system, and connecting a gas inlet to an output port of the gas distribution system by using a gas pipeline;
(c) setting the flow rates of bottled nitrogen and bottled target gas of a gas distribution system according to the concentration of the target gas to be calibrated to generate the target gas with the required concentration;
(d) opening the air pump module, and pumping target gas with the concentration to be calibrated into the air chamber; the gas flow rate of the flow control valve is adjusted through the DSP module, the pressure in the closed gas chamber is read through the pressure sensor, and the pressure in the closed gas chamber reaches a set value through feedback control;
(e) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(f) the DSP processor module starts the light source driving module and adjusts the working temperature of the light source module to be a set value;
(g) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(h) according to the optimization result of the collimation mode, the DSP processor module sends an optimal driving voltage value to the acousto-optic driving module; infrared light emitted by the light source module is made to pass through the acousto-optic modulator and the closed air chamber and then is incident on the photoelectric detection module; the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(i) according to the acquisition time of each gas sample with the calibrated concentration, the DSP module circularly acquires a second harmonic signal obtained by the phase-locked amplification module in the sampling period through the data acquisition module, acquires the amplitude of the second harmonic signal and stores the amplitude into the internal memory; after the acquisition time is up, calculating the average value of the amplitude of the acquired second harmonic signal, and storing the average value and the concentration of the calibration gas into an internal memory;
(j) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, returning to the step (a); if the concentration is normal, adjusting the flow rates of the two input steel cylinder gases of the gas distribution system according to the set next calibration concentration, and repeating the steps (c) - (j) until the calibration of all the concentrations is finished;
(k) fitting a linear relation between the amplitude of the second harmonic signal and the concentration of the calibrated gas according to the result of the cyclic calibration, and storing a fitting coefficient into an internal memory of the DSP module;
(l) The DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(m) manually closing the DSP processor module and the power supply module, and ending the calibration process;
thirdly, under the measuring mode, the device is arranged in an underwater application environment, and an underwater gas-liquid separation device, an overwater ship deck monitoring computer and an overwater ship deck 24V power supply are adopted as auxiliary application devices, and the method specifically comprises the following steps:
(a) on the deck, a gas pipeline is utilized to connect a gas inlet to a gas outlet of the underwater gas-liquid separation equipment; a 24V power supply of a deck of the water ship body is used for supplying working voltage to a power supply module through a 24V power supply input port through a cable, so that working voltage required by an electrical part and an air pump module is generated; the overwater ship body deck monitoring computer is connected with an upper computer communication module through a cable conductor and a communication cable outlet, and the DSP processor module is used for collecting working voltage of each module through the data collection module and transmitting the working voltage to the overwater ship body deck monitoring computer until the overwater ship body deck monitoring computer works normally; placing underwater gas-liquid separation equipment and the device in a pressure-resistant cabin and placing the pressure-resistant cabin in water through a towing body;
(b) the overwater hull deck monitoring computer sends a measurement starting command to the DSP processor module;
(c) the DSP processor module opens the air pump module and pumps air output by the gas-liquid separation equipment into the closed air chamber; the DSP processor module adjusts the gas flow rate of the flow control valve, reads the pressure in the closed gas chamber through the pressure sensor and transmits the pressure to the overwater ship deck monitoring computer; the pressure in the closed air chamber reaches a set value through feedback control;
(d) the DSP processor module adjusts the working voltage of the heating sheet, reads the temperature of the closed air chamber through the temperature sensor, and enables the temperature of the closed air chamber to reach a set value through feedback control;
(e) the DSP processor module starts the light source driving module, and adjusts the working temperature of the light source module to be a set value;
(f) the DSP processor module applies a triangular wave signal and a sine wave signal to the light source driving module to enable the light source module to emit an infrared light signal with the wavelength being scanned and modulated;
(g) according to the collimation result, the DSP processor module sets the voltage of the acousto-optic driving module as an optimal driving voltage value; infrared light emitted by the light source module is made to pass through the acousto-optic modulator and the closed air chamber and then is incident on the photoelectric detection module;
(h) the phase-locked amplification module extracts a second harmonic signal from the signal output by the photoelectric detection module and transmits the second harmonic signal to the DSP processor module through the data acquisition module;
(i) the DSP module calculates the concentration of the gas to be detected according to the second harmonic signal amplitude obtained by sampling and the linear relation between the calibrated target gas concentration and the second harmonic signal amplitude, and transmits the concentration to the monitoring computer on the deck of the ship body through a cable;
(j) the DSP module circularly monitors the output voltage of the power supply module, the pressure of the closed air chamber and the temperature of the closed air chamber and observes whether the output voltage, the pressure of the closed air chamber and the temperature of the closed air chamber are normal or not; if not, an alarm instruction is sent to a deck monitoring computer; if the command is normal, inquiring whether a measurement stopping command sent by the monitoring computer is received; if a measurement stopping command is received, turning to the step (k); if the measurement stopping command is not received, repeating the steps (h) to (j);
(k) the DSP processor module sequentially turns off the light source driving module, the acousto-optic driving module, the air pump module, the pressure control module, the temperature control module, the photoelectric detection module and the data acquisition module;
(l) And manually cutting off the 24V power supply of the water ship body deck on the deck, and finishing the measurement process.
2. The method according to claim 1, wherein the concentration range of the target gas to be calibrated in step (b) in the calibration mode is consistent with the concentration range of the target gas dissolved in water at different depths, and the concentration of the bottled target gas is greater than the range, so that the target gas with different concentrations can be configured through the gas distribution system.
3. The method of claim 2, wherein the step (k) of fitting the linear relationship between the second harmonic signal amplitude and the concentration of the calibrated gas is performed by using Origin software, and the average amplitude of the second harmonic signal and the concentration of the calibrated gas are introduced into the software for fitting and obtaining the fitting coefficient.
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