CN116046721A - Correlation open-circuit laser gas detector and gas detection real-time calibration method - Google Patents
Correlation open-circuit laser gas detector and gas detection real-time calibration method Download PDFInfo
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Abstract
The utility model discloses a correlation open-circuit laser gas detector and a gas detection real-time calibration method in the field of gas sensors, wherein a transmitting device alternately transmits signal light and calibration light, wherein a part of laser signals emitted by a signal modulation wave control laser is transmitted to an open-circuit environment as the signal light, and the other part of the laser signals passes through a standard gas chamber and is converted into calibration modulation waves, and the laser is controlled to generate the calibration light; the receiving device receives the optical signal, and calculates and calibrates the product value of the concentration of the gas to be measured and the distance in the open-circuit environment in real time according to the voltage waveforms of the signal light and the calibration light and the product value of the concentration of the reference gas and the distance. The utility model overcomes the defect that the existing correlation open-circuit laser gas detector cannot automatically calibrate and calibrate in real time, and transmits signal light and calibration light in an optical communication mode, thereby realizing the calibration of the detection result of the concentration of the gas to be detected in an open-circuit environment, accurately eliminating the environmental interference in the detection process of the signal light and reducing the laying and maintenance cost of an electric power system.
Description
Technical Field
The utility model relates to the technical field of gas sensors, in particular to a correlation open-circuit laser gas detector and a gas detection real-time calibration method.
Background
The basic principle of the laser gas detector is based on tunable semiconductor absorption spectroscopy (TDLAS), and gas concentration detection is realized by utilizing infrared spectrum absorption effect of gas. The laser gas detector has two types of point-type laser gas detector and open-circuit type laser gas detector, wherein the open-circuit type laser gas detector belongs to the line type light beam type, can carry out gas detection to hundreds of meters open space, and compared with the point type laser gas detector, has the advantages of long optical path distance, high sensitivity, large detection range, good reliability, zero false alarm, no maintenance and the like, and can be widely applied to the fields of natural gas, coal mine, oil gas field, petrochemical industry, coal chemical industry, fine chemical industry, steel industry, pipeline transportation, gas storage facilities, electric power monitoring, environment monitoring and the like.
The open-circuit laser gas detector comprises an opposite-incidence open-circuit laser gas detector and a reflection open-circuit laser gas detector. The emission and the receiving of the reflective open-circuit laser gas detector are distributed on the same side (for example, the utility model of the application number CN201310291029.5 is shown), and the light emitted by the emission module is reflected by the reflecting plate and then enters the receiving module, but the light power received by the receiving distribution is weak due to the influence of factors such as light reflection efficiency, reflection distance, space environment and the like, the signal processing difficulty is high, the measuring error is large, and the anti-interference capability is weak. In order to solve the above-mentioned problem, an opposite-emission type open-circuit laser gas detector (for example, the utility model patent with patent application number CN 201220710383.8) is proposed, which is divided into two parts, namely a transmitting module and a receiving module, the transmitting module laser directly enters the receiving module after passing through the space to be measured, the received light power is strong, the signal processing is easy, and the reliability is good.
However, in an open light path environment to be detected, the laser signal is easily interfered by factors such as water mist, dust, rainwater, light source attenuation, noise light source and the like, so that the error of the measurement result of the open-circuit laser gas detector is large. The built-in calibration air chamber carries out real-time automatic calibration and calibration on the measurement result, thus being a reliable method for solving the problems.
In order to eliminate the influence of the open-circuit environment factors on the calibration result, the calibration air chamber is required to be arranged in the laser emission module, and the concentration measurement function in the open-circuit environment gas detection process is arranged in the laser receiving module. Therefore, how to quickly, real-time and reliably transmit the real-time calibration reference signal in the laser transmitting module to the laser receiving module through the open-circuit environment to realize the calibration and calibration of the measurement result, and avoid the influence of the open-circuit environment on the real-time calibration signal is an important technical problem facing the correlation type open-circuit laser gas detector.
The above drawbacks need to be addressed.
Disclosure of Invention
In order to overcome the defect that the existing correlation open-circuit laser gas detector cannot be automatically calibrated and calibrated in real time, the utility model provides a correlation open-circuit laser gas detector and a gas detection real-time calibration method.
The technical scheme of the utility model is as follows:
in one aspect, an open-ended laser gas detector comprises:
the transmitting device is used for alternately transmitting signal light with a signal modulation code and calibration light with a calibration modulation code, wherein the signal light is controlled by a signal modulation wave to emit from a laser, one part of the signal light is transmitted into an open-circuit environment, the other part of the signal light is converted into the calibration modulation wave after passing through a standard air chamber, and the calibration modulation wave is used for controlling the laser to generate the calibration light and emit into the open-circuit environment;
the receiving device is used for respectively receiving the signal light and the calibration light, and calculates and calibrates the product value of the concentration and the distance of the gas to be measured in the open-circuit environment in real time according to the received signal light voltage waveform, the calibration light voltage waveform and the product value of the concentration and the distance of the reference gas.
The utility model according to the above scheme is characterized in that the emitting device comprises a laser, an optical fiber coupler, a standard gas chamber, a first photoelectric detector, a first micro-processing unit and a circuit component,
the laser is used for generating and emitting corresponding laser according to the signal modulation wave and the calibration modulation wave;
the optical fiber coupler is used for splitting the laser signals generated by the laser, so that one part of the laser signals are directly emitted to an open-circuit environment, and the other part of the laser signals are emitted to the standard air chamber;
the standard gas chamber is filled with reference gas with known concentration;
the first photoelectric detector is used for receiving the laser signal passing through the standard air chamber and converting the laser signal into a voltage signal;
the first micro-processing unit and the circuit component are used for generating the signal modulation wave or generating a calibration modulation wave according to the voltage signal emitted by the first photoelectric detector.
Further, the first micro-processing unit and the circuit assembly comprise a first amplifying and filtering circuit, a first data processing circuit, a singlechip control circuit and a signal generating circuit:
the first amplifying filter circuit is used for receiving and amplifying the voltage signal converted by the first photoelectric detector;
the first data processing circuit is used for receiving the voltage signal of the first amplifying and filtering circuit and performing data analysis;
the single chip microcomputer control circuit is used for directly generating a signal voltage modulation waveform with a signal modulation wave or generating a calibration voltage modulation waveform with a calibration modulation wave according to the processing result of the first data processing circuit;
the signal generation circuit is used for converting the signal voltage modulation waveform and the calibration voltage modulation waveform into corresponding current modulation waveforms.
Further, the transmitting device further comprises a wavelength division multiplexer, one input end of the wavelength division multiplexer is connected with the optical fiber coupler, the other input end of the wavelength division multiplexer is connected with the visible light laser, and the wavelength division multiplexer is used for combining laser emitted by the optical fiber coupler and laser emitted by the visible light laser and outputting the combined laser and the optical fiber.
The utility model according to the above scheme is characterized in that the receiving device comprises a second photodetector, a second micro-processing unit and a circuit assembly:
the second photoelectric detector is used for receiving the signal light and the calibration light which pass through an open circuit environment and converting the signal light and the calibration light into corresponding electric signals;
the second micro-processing unit and the circuit component are used for receiving the electric signals sent by the second photoelectric detector, and calculating to obtain the product value of the concentration and the distance of the gas to be detected in the open-circuit environment according to the electric signals corresponding to the signal light and the electric signals corresponding to the calibration light.
Further, the second micro-processing unit includes a second amplification filter circuit, a second data processing circuit, and a signal output circuit:
the second amplifying and filtering circuit is used for receiving and amplifying the voltage signal formed by the conversion of the second photoelectric detector;
the second data processing circuit and the signal output circuit are used for calculating and calibrating the product value of the concentration and the distance of the gas to be measured in the open-circuit environment in real time according to the calibration photovoltage waveform, the signal photovoltage waveform and the product value of the concentration and the distance of the reference gas;
the signal output circuit is used for outputting target information.
On the other hand, a real-time calibration method for correlation open-circuit laser gas detection is characterized in that,
at the signal transmitting end, the signal modulating wave controls the laser to emit signal light, one part of the signal light is directly emitted to an open-circuit environment to detect the concentration information of the gas to be detected, the other part of the signal light is emitted to a standard air chamber to detect the concentration information of the gas to be detected, the signal light passes through the standard air chamber and is converted into calibration modulating wave, the calibration modulating wave controls the laser to emit calibration light, and the signal modulating wave and the calibration modulating wave alternately control the laser to emit corresponding laser signals;
and the signal receiving end receives the signal light and the calibration light which pass through the open-circuit environment, and calculates and calibrates the product value of the concentration and the distance of the gas to be measured in the open-circuit environment in real time according to the signal light voltage waveform, the calibration light voltage waveform and the product value of the concentration and the distance of the reference gas.
According to the above scheme, the temperature when the laser emits the laser signal as the signal light is different from the temperature when the laser signal as the calibration light is emitted, the center wavelength when the laser emits the laser signal as the signal light is overlapped with the absorption spectrum center of the gas to be measured in the open-circuit environment by adjusting the internal temperature of the laser, and the center wavelength when the laser emits the laser signal as the calibration light is offset by a distance from the absorption spectrum center of the gas to be measured in the open-circuit environment.
The utility model according to the scheme is characterized in that a signal modulation code is added before a laser signal is emitted by a signal modulation wave control laser; before the laser emits calibration light, a calibration modulation code is added before the calibration light is controlled by the calibration modulation wave; the calibration modulation code is different from the signal modulation code.
Further, after the signal receiving end receives the optical signal, the type of the subsequent optical signal is determined by distinguishing the signal modulation code from the calibration modulation code: when the optical modulation bit is a calibration modulation code, determining a received calibration photovoltage waveform; when the light modulation bit is a signal modulation code, determining the product value of the concentration and the distance of the gas to be measured in the open-circuit environment according to the received signal photovoltage waveform, the calibration photovoltage waveform and the product value of the concentration and the distance of the reference gas in the standard gas chamber.
According to the scheme, the utility model has the beneficial effects that,
the standard air chamber is arranged in the transmitting device, so that the calibration of the detector to the detection result of the concentration of the gas to be detected in the open-circuit environment can be realized, and the product value of the concentration of the gas to be detected and the distance in the open-circuit environment measured by the detector can be calibrated in real time.
In the correlation type open-circuit environment, the signal light and the calibration light signal are transmitted simultaneously, so that the signal light and the calibration light can both pass through the open-circuit environment and are influenced by environmental factors to be consistent, and the environmental interference in the signal light detection process can be accurately eliminated through calibration of the calibration light.
The utility model transmits the signal light and the calibration light in an optical communication mode, replaces the transmission process of cable communication or wireless communication mode, increases the stability and consistency of signal transmission, greatly reduces the cost of manpower and material resources, reduces the signal certainty possibly caused by the electric signal transmission process, and simultaneously reduces the maintenance time and cost.
Drawings
FIG. 1 is a system block diagram of the present utility model;
FIG. 2 is a waveform diagram of the open circuit environment without the gas to be measured in the detection process of the present utility model;
FIG. 3 is a waveform diagram of the open circuit environment with the gas to be measured in the detection process of the present utility model;
FIG. 4 is a flow chart of the present utility model for implementing measured signal correction;
FIG. 5 is a waveform diagram of the modulation of signal light according to the present utility model;
FIG. 6 is a graph of a modulated waveform of the calibration light in the present utility model;
FIG. 7 is a graph showing methane gas concentration versus concentration for an embodiment of the present utility model.
Detailed Description
The utility model is further described below with reference to the drawings and embodiments:
as shown in fig. 1 to 6, in order to overcome the defect that the existing correlation open-circuit laser gas detector cannot automatically calibrate and calibrate in real time, the utility model provides a correlation open-circuit laser gas detector and a gas detection real-time calibration method.
The opposite-emission type open-circuit laser gas detector comprises a transmitting device and a receiving device, wherein the transmitting device and the receiving device are respectively positioned at two ends of an open-circuit environment to be detected, the transmitting device generates optical signals and transmits the optical signals to the open-circuit environment, the receiving device receives the optical signals in the open-circuit environment, and a result of whether gas to be detected exists in the open-circuit environment or not and the concentration information of the gas to be detected is obtained after data processing.
Referring to fig. 2 and 3, the basic principle of the present utility model for detecting the concentration of a gas is to use the infrared spectrum absorption effect of the gas to detect the concentration and the length of the gas based on tunable semiconductor laser absorption spectroscopy (TDLAS).
Specifically, at the transmitting end, the tunable semiconductor laser is adopted as a light source, the sawtooth wave voltage modulation circuit is generated by the microprocessor, and is input into the constant current source circuit to generate a current modulation signal to drive the tunable semiconductor laser, so that the frequency sweep of signal laser is realized, and meanwhile, the central wavelength of the frequency sweep of the laser is enabled to coincide with the absorption peak spectral line of the gas to be detected by setting a proper target temperature. In a specific frequency sweeping process, a spectral line which is most suitable for gas detection is determined according to an absorption spectral line of a gas to be detected (the absorption intensity is required to be as strong as possible, no other gas absorption spectral line exists nearby the spectral line, and cross interference of the gas is avoided), the wavelength of the laser is swept by controlling the current of the tunable semiconductor laser, and meanwhile, the frequency sweeping center wavelength of the tunable semiconductor laser is overlapped with the absorption spectral line of the gas to be detected by controlling the internal temperature of the tunable semiconductor laser.
Specifically, at the receiving end, a photoelectric detector is used for receiving the optical signal, and whether the gas to be detected exists in the open-circuit environment is judged by judging whether an absorption peak exists in the received optical signal. In a specific detection process, if no gas to be detected exists in an open-circuit environment, no absorption peak exists in a signal detected by the photoelectric detector; if the gas to be detected exists in the open-circuit environment, the signal detected by the photoelectric detector has an absorption peak, and the higher the concentration of the gas to be detected is, the stronger the intensity of the absorption peak is, and the concentration of the gas to be detected in the open-circuit environment is calculated according to the intensity of the absorption peak of the detected signal.
In order to realize automatic calibration of detection signals of a receiving end, a calibration branch exists in the correlation open-circuit laser gas detector. The utility model realizes the real-time calibration and demarcation of the correlation open-circuit laser gas detector in the measuring process by the mutual coordination of the signal light and the calibration light, so that the whole laser detector has better reliability, stability and anti-interference performance.
1. Transmitting device
The transmitting device is used for alternately transmitting signal light and calibration light, wherein the signal light is provided with a signal modulation code, the calibration light is provided with a calibration modulation code, and the receiving device can conveniently recognize whether the received light signal is the signal light or the calibration light through the signal modulation code and the calibration modulation code. In a specific embodiment, two optical modulation bits are added before the signal light and the calibration light, for example, the signal modulation code before the signal light is low level-low level (i.e. 00), and the calibration modulation code before the calibration light is low level-high level (i.e. 01), so as to realize the distinction between the signal light and the calibration light.
The laser emits signal light under the control of signal modulation wave (sawtooth wave modulation is adopted in the utility model), one part of the signal light is emitted into an open-circuit environment, the other part of the signal light passes through a standard air chamber and is converted into calibration modulation wave, and the calibration modulation wave controls the laser to generate calibration light and emit the calibration light into the open-circuit environment.
The transmitting device comprises a laser, an optical fiber coupler, a standard air chamber, a first photoelectric detector, a first micro-processing unit and a circuit component, and can also comprise a wavelength division multiplexer and a parabolic reflector. Wherein,,
the laser is used for modulating the wave according to the signals, calibrating the modulated wave, and generating and emitting corresponding laser light.
The optical fiber coupler is used for carrying out light splitting on laser signals generated by the laser (the light splitting ratio is 9:1, wherein 90% of the laser signals are emitted to a branch where the open-circuit environment is located, and 10% of the laser signals are emitted to a branch where the standard air chamber is located), so that one part of the laser signals (the majority of light (90%) are directly emitted to the open-circuit environment, and the other part of the laser signals (the minority of light (10%)) are emitted to the standard air chamber for calibration.
The standard gas chamber is filled with reference gas with known concentration, and the length of the standard gas chamber is known, so that the product value of the concentration and the distance of the reference gas can be calculated in the detection result obtained by the optical signal of the standard gas chamber. The reference gas in the standard gas chamber (consistent with the gas to be measured in the open-circuit environment) can be pure reference gas or mixed gas of the reference gas and inert gas (such as nitrogen), and the content of the reference gas and the inert gas in the mixed gas is known. The light-transmitting sheets of the windows on the two sides of the standard air chamber are high in transmittance to laser of a wave band to be detected, so that energy loss is reduced.
The first photodetector is configured to receive the laser signal passing through the standard gas cell and convert the laser signal to a voltage signal.
The first micro-processing unit and the circuit component are used for generating signal modulation waves or generating calibration modulation waves according to voltage signals emitted by the first photoelectric detector. The signal laser generated by the laser in the same period comprises signal light generated by signal modulation wave modulation and calibration light generated by calibration modulation wave modulation obtained by processing the signal light through the standard air chamber, wherein the signal light is provided with a signal modulation code, and the calibration light is provided with a calibration modulation code, so that the first micro-processing unit and the circuit component determine the processing mode of the voltage signal according to different modulation codes: the voltage signal with the signal modulation code is determined as the voltage signal of the signal light, and a calibration modulation wave with the calibration modulation code is generated after the partial voltage signal is subjected to data processing; the voltage signal with the calibration modulation code is determined as a "secondary signal" (i.e., a portion of the calibration light that is split into unwanted signals), and this portion of the voltage signal is directly discarded.
Specifically, the first micro-processing unit and the circuit assembly comprise a first amplifying and filtering circuit, a first data processing circuit, a singlechip control circuit and a signal generating circuit:
the first amplifying filter circuit is used for receiving the voltage signal converted by the first photoelectric detector and amplifying the voltage signal;
the first data processing circuit is used for receiving the voltage signal of the first amplifying and filtering circuit and performing data analysis, and comprises determining the type of the voltage signal (the voltage signal corresponding to the signal light generated by the signal modulation wave modulation laser and the voltage signal corresponding to the calibration light generated by the calibration modulation wave modulation laser) according to the modulation code in the amplified voltage signal, judging the processing mode of the voltage signal (if the voltage signal corresponding to the signal light generated by the signal modulation wave modulation laser is fed back to the singlechip control circuit for calibration and light modulation, and if the voltage signal corresponding to the calibration light generated by the calibration modulation wave modulation laser is directly abandoned);
the single chip microcomputer control circuit is used for generating a voltage modulation waveform, which can directly generate a signal voltage modulation waveform with a signal modulation wave (used for modulating and generating signal light), or generates a calibration voltage modulation waveform with a calibration modulation wave (used for modulating and generating calibration light) according to the processing result of the first data processing circuit;
the signal generating circuit (constant current source circuit) is used for converting the signal voltage modulation waveform and the calibration voltage modulation waveform into corresponding current modulation waveforms and controlling the laser to emit laser signals with corresponding waveforms.
One input end of the wavelength division multiplexer is connected with the optical fiber coupler, the other input end of the wavelength division multiplexer is connected with the visible light laser, and the wavelength division multiplexer is used for combining laser emitted by the optical fiber coupler and laser emitted by the visible light laser and outputting the combined laser and the optical fiber. In the utility model, a green laser is selected as a visible light laser, and in other embodiments, other visible light lasers with other colors are selected for output. Compared with other visible light with other colors, the utility model adopts the green laser, so that the laser signals with the same power are more clear and high in brightness.
The parabolic mirror is used for collimating the laser: the signal light and the calibration light are incident to the parabolic reflector, and are collimated by the parabolic reflector and then are incident to the open-circuit environment. The reflecting surface of the parabolic reflector is plated with gold, so that the optical loss is reduced, the optical power incident into an open-circuit environment is increased, and the parabolic reflector is stable and has no optical dispersion effect, so that the laser emitted by the tunable semiconductor laser and the laser light path emitted by the green laser can be kept consistent by adopting the collimation of the parabolic reflector.
2. Receiving device
The receiving device is used for respectively receiving the signal light and the calibration light and performing signal processing to realize detection of the concentration of the gas to be detected in the open-circuit environment, and the detection result is calibrated through the reference gas of the standard gas chamber. In the calibration process, the receiving device calculates and calibrates the product value of the concentration of the gas to be measured and the distance in the open-circuit environment in real time according to the received signal photovoltage waveform, the calibration photovoltage waveform and the product value of the concentration of the reference gas and the distance.
The receiving device comprises a second photoelectric detector, a second micro-processing unit and a circuit component, and further comprises a convex lens and an optical filter:
the convex lens is used for realizing focusing of optical signals, the second photoelectric detector is positioned at the focus of the convex lens, and the convex lens can enable signal light and calibration light in an open-circuit environment to be focused to the second photoelectric detector.
The optical filter is positioned between the convex lens and the second photoelectric detector and is used for filtering out optical signals of other wave bands except signal light and calibration light.
The second photoelectric detector is used for receiving the signal light and the calibration light which pass through the open-circuit environment and converting the signal light and the calibration light into corresponding electric signals;
the second micro-processing unit and the circuit component are used for receiving the electric signals sent by the second photoelectric detector, and calculating to obtain the product value of the concentration and the distance of the gas to be detected in the open-circuit environment according to the electric signals corresponding to the signal light and the electric signals corresponding to the calibration light. Specifically, the second micro-processing unit includes a second amplification filter circuit, a second data processing circuit, and a signal output circuit:
the second amplifying filter circuit is used for receiving the voltage signal converted by the second photoelectric detector and amplifying the voltage signal;
the second data processing circuit and the signal output circuit are used for calculating and calibrating the product value of the concentration and the distance of the gas to be measured in the open-circuit environment in real time according to the calibrated photovoltage waveform, the signal photovoltage waveform and the product value of the concentration and the distance of the reference gas;
the signal output circuit is used for realizing the output of the target information.
Because the open-circuit environment to be detected is interfered by factors such as water mist, dust, rainwater, light source attenuation, noise light source and the like, the error of the measurement result of the laser gas detector is easy to cause, and the measurement result of the standard gas chamber is required to be used for calibrating and calibrating the measurement record of the laser gas detector. However, in the correlation type open-circuit laser gas detector, the standard gas chamber and the open-circuit environment detection sensor are respectively positioned in the transmitting device and the receiving device, the common distance between the transmitting device and the receiving device is far (more than 100 m), and the communication of electric signals is difficult (the cable communication mode has high cost and difficult maintenance, the wireless communication mode has easy data loss and low detection result accuracy).
Therefore, the utility model realizes the communication of real-time signals between the transmitting device and the receiving device in an optical communication mode, realizes the automatic calibration and calibration of the correlation type open-circuit laser gas detector, can solve the problem of difficult communication between the transmitting device and the receiving device, and can also enable the reference optical signal passing through the standard air chamber to pass through an open-circuit environment so as to eliminate the interference of various interference factors in the open-circuit environment on the signal light.
As shown in fig. 4, the present utility model further provides a real-time calibration method for correlation open-circuit laser gas detection, which is implemented based on the correlation open-circuit laser gas detector, and sends the calibration signal light of the calibration branch in the transmitting device to the receiving device in an optical communication manner, so that the automatic calibration and calibration of the correlation open-circuit laser gas detector are implemented in the receiving device to eliminate the influence of the open-circuit environmental factors on the error detection result; secondly, the real-time calibration reference signal can be quickly, reliably transmitted to the receiving device in real time through an open-circuit environment and the calibration and calibration of the measurement result are realized, thirdly, the defects of large detection result deviation, data missing and the like caused by factors such as unstable signals, long distance and the like when the calibration signal of the calibration branch is directly transmitted to the receiving device through an electric signal can be avoided.
The correlation type open-circuit laser gas detection real-time calibration method comprises the processing procedures of optical signals and electric signals of a signal transmitting end and the processing procedures of the optical signals and the electric signals of a signal receiving end.
At the signal transmitting end, the laser is controlled to emit laser signals through the signal modulation wave, one part of the laser signals is used as signal light for directly detecting concentration information of gas to be detected in an open-circuit environment, the other part of the laser signals is used for detecting concentration information of the gas to be detected in the standard gas chamber, the laser signals pass through the standard gas chamber and then are converted into calibration modulation waves, the laser is controlled to emit calibration light through the calibration modulation waves, and the signal light and the calibration light are alternately incident into the open-circuit environment. Before the laser device emits laser signals, signal modulation codes are added in front of the laser signals; before the laser emits calibration light, a calibration modulation code is added before the calibration light is controlled by the calibration modulation wave; the calibration modulation code is different from the signal modulation code.
The specific optical signal and electric signal processing process is as follows:
firstly, a single chip microcomputer control circuit controls a signal generation circuit to generate a sawtooth wave modulation signal, a modulation laser generates signal light, and a signal modulation code (00) is arranged in front of the signal light;
and secondly, the signal light is split by an optical fiber coupler, wherein 90% of the signal light is combined with green light generated by a green laser by a wavelength division multiplexer and is transmitted to an open-circuit environment by a parabolic reflector, and the other 10% of the signal light is received and converted by a first photoelectric detector to form an electric signal after passing through a standard air chamber, the electric signal is amplified and filtered by a first amplifying and filtering circuit and is subjected to data processing by a first data processing circuit, then a singlechip control circuit is used for controlling a signal generator to generate a modulating signal of calibration light, the modulating laser is modulated to generate the calibration light, the calibration light is provided with a calibration modulating code (01) before the calibration light, and the calibration light is transmitted to the open-circuit environment after passing through the optical fiber coupler and the wavelength division multiplexer.
The temperature of the laser device when emitting the laser signal as the signal light is different from the temperature of the laser device when emitting the laser signal as the calibration light, and the central wavelength of the laser device when emitting the laser signal as the signal light is overlapped with the absorption spectrum center of the gas to be measured in the open circuit environment by adjusting the internal temperature of the laser device, and the central wavelength of the laser device when emitting the laser signal as the calibration light is offset by a distance from the absorption spectrum center of the gas to be measured in the open circuit environment. In the specific implementation process, the center wavelength of the signal light is ensured to coincide with the center of the absorption spectrum of the gas to be detected in the open-circuit environment, the absorption spectrum of the gas to be detected in the open-circuit environment is not in the range of the calibrated light modulation waveform, and the offset distance can be generally selected to be 1 nm-2 nm.
Based on the characteristics of the tunable semiconductor laser, the temperature of the laser can be changed to change the central wavelength of the laser, so that the scanning wavelength range of the calibration light cannot cover the absorption spectrum of the gas to be measured, the calibration light cannot be absorbed by the gas to be measured when passing through an open-circuit environment, the scanning central wavelength of the laser is different when the calibration light is emitted from the signal light, and the temperature of the laser is different when the calibration light is emitted from the signal light.
And the signal receiving end receives the signal light and the calibration light which pass through the open-circuit environment, and calculates and calibrates the product value of the concentration and the distance of the gas to be measured in the open-circuit environment in real time according to the signal light voltage waveform, the calibration light voltage waveform and the product value of the concentration and the distance of the reference gas.
Since the signal modulation code is different from the calibration modulation code, after the signal receiving end receives the optical signal, the type of the subsequent optical signal is determined by distinguishing the signal modulation code from the calibration modulation code: when the light modulation bit is a calibration modulation code, determining a received calibration light voltage waveform, and detecting a product value of the concentration and the distance of reference gas of a standard gas chamber in the transmitting device; when the light modulation bit is a signal modulation code, the received signal light voltage waveform is determined, the product value of the concentration and the distance of the gas to be detected in the open-circuit environment is detected, and the product value of the concentration and the distance of the gas to be detected in the open-circuit environment is determined according to the received signal light voltage waveform, the calibration light voltage waveform and the product value of the concentration and the distance of the reference gas in the standard gas chamber.
As shown in fig. 4 to 6, in one embodiment, in the process of emitting the signal light and the calibration light, the signal period is 1s, where the first 0.5s is the signal light and the second 0.5s is the calibration light:
(1) Signal light: referring to fig. 5, a sawtooth voltage scanning signal is first added with a modulation code (00), and is converted into a current modulation signal through a constant current source current, so as to control a laser to generate laser. The 90% laser is output to the open-circuit environment and received by the receiving device, and the 90% laser is used for detecting the product value of the concentration and the distance of the gas to be detected in the open-circuit environment; 10% of the laser light is incident on a standard gas cell, which contains a reference gas, which is received by a first photodetector inside the emitting device and converts the optical signal into an electrical signal.
In the first half period, the temperature of the laser is controlled to be the target temperature T1, so that the central wavelength of the output of the laser coincides with the absorption spectrum of the gas to be detected, and the purpose is to enable the signal light to interact with the gas to be detected in an open circuit environment.
(2) Calibration light: referring to fig. 6, in the first 0.5s, 10% of the signal light is incident on the standard gas cell and is received and converted by the first photodetector to form an electrical signal, and the electrical signal is amplified and encoded (01) (i.e. the original modulation code 00 is changed to 01).
In the last 0.5s, the amplified and coded voltage signal is converted into a current modulation signal through a constant current source current, the laser is controlled to generate calibration light, 90% of the calibration light is output to an open circuit environment and is received by a receiving device for calibrating a signal detected by the signal light, 10% of the calibration light is also incident to a standard air chamber, and the signal detected by the calibration light is discarded (whether the signal light or the calibration light is distinguished according to a modulation code). Meanwhile, the temperature of the laser is controlled to enable the target temperature to be T2, so that the wavelength output by the laser cannot cover the absorption spectrum of the gas to be measured, and the interaction between the calibration light and the gas to be measured in the open-circuit environment is avoided.
In this embodiment, in the process of receiving the signal light and the calibration light:
first, the second photodetector in the receiving device discriminates the waveform by discriminating the modulation code: when the second photoelectric detector receives the laser with the front modulation code of 00, representing the subsequent optical signal as signal light, detecting the product value of the concentration and the distance of the gas to be detected in the open-circuit environment; when the second photoelectric detector receives the laser with the front modulation code of 01, the subsequent optical signal is represented as calibration light, and the product value of the concentration and the distance of the gas to be detected of the standard gas chamber in the detected transmitting device.
And secondly, calculating the product value of the concentration of the gas to be measured and the distance in the calibration open-circuit environment in real time according to the calibration photovoltage waveform, the signal photovoltage waveform and the product value of the concentration of the reference gas and the distance which are received by the receiving device.
From lambert beer's law, gas absorption satisfies: i=i 0 ·e -α(ν)CL Wherein:
i is the light intensity of the laser after gas absorption,
I 0 for the intensity of the light before the absorption of the gas,
alpha (v) is the absorption coefficient of the gas when the laser frequency is v,
c is the concentration of the gas, and the concentration of the gas is the same as the concentration of the gas,
l is the effective absorption length of the laser.
Fig. 7 is a methane gas response curve for a test using a correlation open-loop laser gas detector. Fitting a gas absorption curve to be measured using a logarithmic function f (x) =ain (x) +b, wherein:
x is the change in the intensity of the absorbed optical signal compared to the initial optical signal,
f (x) is the calculated product of the concentration of the gas to be measured and the distance,
A. b is two constant terms.
Since the product value of the reference gas concentration and the distance in the standard gas chamber is known, the change of the intensity of the absorbed optical signal compared with the intensity of the initial optical signal can be calculated by the waveform of the calibration light received by the receiving device; the product value of the concentration and the distance of the gas to be detected in the open-circuit environment is unknown, and the change of the intensity of the absorbed optical signal compared with the intensity of the initial optical signal can be calculated by the waveform of the signal light received by the receiving device. Specifically, the receiving device determines the above-described "change in intensity" according to the light intensity at the position where the absorption peak of the received light signal is located, that is, change in intensity=the light intensity of the absorption peak/the initial light intensity.
Assuming that the change of the light signal intensity after absorption of the signal light after passing through the open circuit environment is X 1 The change of the absorbed optical signal intensity of the calibration optical waveform compared with the initial optical signal intensity is X 0 The product value of the gas concentration and the distance in the standard gas chamber is C 0 L 0 The product value of the concentration and the distance of the gas to be measured in the actual open-circuit environment is C 1 L 1 ＝f(X 1 )/f(X 0 )×C 0 L 0 。
As shown in fig. 7, in an embodiment for detecting methane gas concentration information in an open circuit environment, a curve is obtained by fitting the variation of the optical signal intensities corresponding to the different gas concentrations from the initial optical signal intensity, and the constant coefficient of the fitting function f is calculated therefrom.
In practical application, the constant coefficient A, B of the fitting function can be obtained by fitting, and the change X of the light signal intensity after the signal light passes through the open-circuit environment compared with the initial light signal intensity 1 Variation X of the absorbed optical signal intensity compared to the initial optical signal intensity compared to the calibration optical waveform 0 All can be measured and calculated by a photoelectric detector, and the product value C of the concentration and the distance of the gas in the standard gas chamber 0 L 0 It is known that the product value of the concentration of the gas to be measured and the distance in the actual open-circuit environment can be calculated therefrom by a formula.
It will be understood that modifications and variations will be apparent to those skilled in the art from the foregoing description, and it is intended that all such modifications and variations be included within the scope of the following claims.
While the utility model has been described above with reference to the accompanying drawings, it will be apparent that the implementation of the utility model is not limited by the above manner, and it is within the scope of the utility model to apply the inventive concept and technical solution to other situations as long as various improvements made by the inventive concept and technical solution are adopted, or without any improvement.
Claims (10)
1. A correlation open-circuit laser gas detector, comprising:
the transmitting device is used for alternately transmitting signal light with a signal modulation code and calibration light with a calibration modulation code, wherein the signal light is controlled by a signal modulation wave to emit from a laser, one part of the signal light is transmitted into an open-circuit environment, the other part of the signal light is converted into the calibration modulation wave after passing through a standard air chamber, and the calibration modulation wave is used for controlling the laser to generate the calibration light and emit into the open-circuit environment;
the receiving device is used for respectively receiving the signal light and the calibration light, and calculates and calibrates the product value of the concentration and the distance of the gas to be measured in the open-circuit environment in real time according to the received signal light voltage waveform, the calibration light voltage waveform and the product value of the concentration and the distance of the reference gas.
2. The correlation open-loop laser gas detector according to claim 1, wherein the emitting device comprises a laser, a fiber coupler, a standard gas cell, a first photodetector, a first micro-processing unit, and a circuit assembly,
the laser is used for generating and emitting corresponding laser according to the signal modulation wave and the calibration modulation wave;
the optical fiber coupler is used for splitting the laser signals generated by the laser, so that one part of the laser signals are directly emitted to an open-circuit environment, and the other part of the laser signals are emitted to the standard air chamber;
the standard gas chamber is filled with reference gas with known concentration;
the first photoelectric detector is used for receiving the laser signal passing through the standard air chamber and converting the laser signal into a voltage signal;
the first micro-processing unit and the circuit component are used for generating the signal modulation wave or generating a calibration modulation wave according to the voltage signal emitted by the first photoelectric detector.
3. The correlation open-loop laser gas detector according to claim 2, wherein the first micro-processing unit and circuit assembly comprises a first amplification filter circuit, a first data processing circuit, a single-chip microcomputer control circuit and a signal generation circuit:
the first amplifying filter circuit is used for receiving and amplifying the voltage signal converted by the first photoelectric detector;
the first data processing circuit is used for receiving the voltage signal of the first amplifying and filtering circuit and performing data analysis;
the single chip microcomputer control circuit is used for directly generating a signal voltage modulation waveform with a signal modulation wave or generating a calibration voltage modulation waveform with a calibration modulation wave according to the processing result of the first data processing circuit;
the signal generation circuit is used for converting the signal voltage modulation waveform and the calibration voltage modulation waveform into corresponding current modulation waveforms.
4. The correlation open-loop laser gas detector according to claim 2, wherein the emitting device further comprises a wavelength division multiplexer, one input end of the wavelength division multiplexer is connected to the optical fiber coupler, the other input end of the wavelength division multiplexer is connected to a visible light laser, and the wavelength division multiplexer is used for combining laser light emitted by the optical fiber coupler and laser light emitted by the visible light laser and outputting the combined laser light and the visible light laser to an optical fiber.
5. The correlation open-loop laser gas detector of claim 1, wherein the receiving means comprises a second photodetector, a second microprocessor unit, and a circuit assembly:
the second photoelectric detector is used for receiving the signal light and the calibration light which pass through an open circuit environment and converting the signal light and the calibration light into corresponding electric signals;
the second micro-processing unit and the circuit component are used for receiving the electric signals sent by the second photoelectric detector, and calculating to obtain the product value of the concentration and the distance of the gas to be detected in the open-circuit environment according to the electric signals corresponding to the signal light and the electric signals corresponding to the calibration light.
6. The correlation open-loop laser gas detector of claim 5, wherein the second micro-processing unit comprises a second amplification filter circuit, a second data processing circuit, and a signal output circuit:
the second amplifying and filtering circuit is used for receiving the voltage signal converted by the second photoelectric detector and filtering and amplifying the voltage signal;
the second data processing circuit and the signal output circuit are used for calculating and calibrating the product value of the concentration and the distance of the gas to be measured in the open-circuit environment in real time according to the calibration photovoltage waveform, the signal photovoltage waveform and the product value of the concentration and the distance of the reference gas;
the signal output circuit is used for outputting target information.
7. A real-time calibration method for correlation open-circuit laser gas detection is characterized in that,
at the signal transmitting end, the signal modulating wave controls the laser to emit signal light, one part of the signal light is directly emitted to an open-circuit environment to detect the concentration information of the gas to be detected, the other part of the signal light is emitted to a standard air chamber to detect the concentration information of the gas to be detected, the signal light passes through the standard air chamber and is converted into calibration modulating wave, the calibration modulating wave controls the laser to emit calibration light, and the signal modulating wave and the calibration modulating wave alternately control the laser to emit corresponding laser signals;
and the signal receiving end receives the signal light and the calibration light which pass through the open-circuit environment, and calculates and calibrates the product value of the concentration and the distance of the gas to be measured in the open-circuit environment in real time according to the signal light voltage waveform, the calibration light voltage waveform and the product value of the concentration and the distance of the reference gas.
8. The correlation type open-circuit laser gas detection real-time calibration method according to claim 7, wherein the temperature when the laser emits the laser signal as the signal light is different from the temperature when the laser signal as the calibration light is emitted, the center wavelength when the laser emits the laser signal as the signal light coincides with the absorption spectrum center of the gas to be detected in the open-circuit environment by adjusting the internal temperature of the laser, and the center wavelength when the laser emits the laser signal as the calibration light is offset by a distance from the absorption spectrum center of the gas to be detected in the open-circuit environment.
9. The method for calibrating correlation open-loop laser gas detection in real time according to claim 7, wherein a signal modulation code is added before a laser signal is emitted by a signal modulation wave control laser; before the laser emits calibration light, a calibration modulation code is added before the calibration light is controlled by the calibration modulation wave; the calibration modulation code is different from the signal modulation code.
10. The method for calibrating correlation open-loop laser gas detection in real time according to claim 9, wherein after the signal receiving end receives the optical signal, the type of the subsequent optical signal is determined by distinguishing a signal modulation code from a calibration modulation code: when the optical modulation bit is a calibration modulation code, determining a received calibration photovoltage waveform; when the light modulation bit is a signal modulation code, determining the product value of the concentration and the distance of the gas to be measured in the open-circuit environment according to the received signal photovoltage waveform, the calibration photovoltage waveform and the product value of the concentration and the distance of the reference gas in the standard gas chamber.
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