A method and system for synchronous temperature and velocity measurement by TDLAS

Abstract

The application provides a TDLAS method and system for synchronously measuring temperature and speed, which comprises a laser, a laser temperature and current control module, a signal generator, a beam splitter, a collimating mirror, a photoelectric detector, a standard device and a data acquisition system. The wavelength output by the laser covers the water molecule absorption spectrum line through the control module, and the sawtooth wave modulation spectrum line is generated through the signal generator and is operated in a time division multiplexing mode. After the laser is emitted by the collimator, the collimating mirror and the photoelectric detector are arranged in a special manner, so that the temperature and speed can be synchronously measured. The laser passes through the measured area, the photoelectric detector receives the photoelectric information carried by the laser, converts the photoelectric information, acquires the data of the electric signal and transmits the data to a computer, and the temperature information and the speed information are synchronously measured by a processing module running in the computer. The installation module of the application is small and is suitable for harsh environments such as high temperature and high pressure. The application has the advantages of high precision, fast response speed, strong anti-noise capability and the capability of synchronously measuring the temperature and speed of the same flow field.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tunable diode laser absorption spectroscopy, and particularly relates to a TDLAS method for synchronous temperature and speed measurement and a system thereof. BACKGROUND

[0002] Temperature and speed are important parameters for describing many flow field environments, and strict requirements are imposed on temperature and speed in the industries of aerospace, automobile, railway transportation and the like, and accurate, real-time and simultaneous measurement of temperature and speed of a flow field is of great significance.

[0003] At present, common measurement methods are divided into two categories of contact type and non-contact type, the contact type measurement method has the disadvantages of high maintenance cost, low sensitivity, inconvenience for carrying and installation and the like, in addition, various probes for contact type measurement can damage the measured flow field and interfere with the flow, which is not conducive to the measurement of flow field parameters. The non-contact type measurement mainly refers to various optical measurement methods, and the non-contact type measurement has the advantages of meeting the requirements of non-invasion, real-time and long-term measurement, and being capable of obtaining rich measurement information. However, current non-contact type measurement technologies are mainly for single measurement of parameters such as temperature, concentration and speed, and cannot realize synchronous and accurate measurement of multiple physical parameters in the same flow field.

[0004] Tunable diode laser absorption spectroscopy (TDLAS) is a kind of absorption spectroscopy, which is a process of non-contact diagnosis of a flow field by using wavelength scanning and current adjustment characteristics of a diode laser, and has become one of important means for measurement. Compared with other optical methods, the TDLAS technology has the advantages of simple structure, simple principle, stable measurement and high measurement frequency. Optimization of spatial arrangement of a measurement mechanism, optimization of a post-processing program and algorithm to realize real-time and synchronous measurement of multiple parameters can greatly improve the application range of the TDLAS technology in an actual aero-engine, has a broad research prospect, and is a main development direction of the technology in the future.

[0005] Therefore, it is of great significance to propose a TDLAS method for synchronous temperature and speed measurement and a system thereof. SUMMARY

[0006] In view of the above problems, the application provides a TDLAS method for synchronous temperature and speed measurement and a system thereof, and the measurement system adopts a non-contact measurement method, and can synchronously, accurately and reliably monitor environment temperature and air flow speed of a flow field.

[0007] In a first aspect, the application provides a TDLAS method for synchronous temperature and speed measurement, which comprises the following steps:

[0008] The collimating mirror and the photodetector are built to ensure that the laser emitted by the collimating mirror can accurately enter the photodetector after entering the flow field to be measured; in the optical path adjustment, a red light test light source is used to access the optical fiber collimator, and the output red light is used to adjust the optical path, or an infrared display card is used to convert the invisible infrared band light beam into visible light, and the optical path is precisely adjusted after accessing the laser; the signal generator is turned on, the frequency and electrical signal parameters are set in the signal generator according to the selected spectrum line of the laser, the control module of the laser is turned on, and the temperature parameter is adjusted to match the working temperature of the laser; the NI control software is turned on, the acquisition card is self-calibrated and self-built to enter the working state, then the LabVIEW software is turned on, and the sampling number and sampling rate are set; the electrical signal is collected, a plurality of channels of data are measured and then averaged, the logarithmic diagram of the ratio of the incident laser intensity and the projected laser intensity is obtained by baseline fitting of the measured data, the ambient temperature is calculated, the wavelength center position is detected and the frequency shift diagram of the two light beams is calculated, and the gas flow rate is calculated.

[0009] Preferably, the electrical signal is collected, a plurality of channels of data are measured and then averaged, the logarithmic diagram of the ratio of the incident laser intensity and the projected laser intensity is obtained by baseline fitting of the measured data, the ambient temperature is calculated, including: the light intensity of the transmitted light and the incident light satisfies Beer-Lambert law:

[0010] ,

[0011] wherein, I 0 is the incident laser intensity; I t is the transmitted laser intensity; l is the length of the region to be measured; P is the total pressure; X is the concentration of the absorbing gas; T is the temperature; Ф is a linear function; S(T) is the line strength of the absorption spectrum; the above formula is transformed into the following formula, and A i is defined as the integral absorbance, then:

[0012] ,

[0013] is defined as the integral absorption coefficient at the path l , then:

[0014] ,

[0015] When the laser passes through a gas medium, the temperature, pressure and concentration are uniformly distributed, the integral absorption coefficient can be expressed as:

[0016] .

[0017] Further preferably, the temperature is measured by using the double-line ratio method, and the integral absorption areas of two spectral lines are used to calculate the temperature. The temperature formula is:

[0018] ,

[0019] In the formula, h is the Planck constant; c is the speed of light; k is the Boltzmann constant; are the low-energy level energies of the absorption transition of the two spectral lines, respectively; A 1 、A 2 are the integral absorbances of the two lasers, respectively; S 1 、S 2 are the line intensities of the two absorption spectral lines during the transition, respectively; T 0 is the reference temperature.

[0020] Further preferably, when the double-line ratio method is used to measure the temperature, two spectral lines of different wavebands are coupled during the system setup. The laser signals generated by two different lasers are collected by a beam splitter, and then the two signals are coupled in a time-division multiplexing manner. Subsequently, the coupled laser signals are divided into 8 beams of the same optical path and transmitted to the collimating mirror for measurement. The same measurement cycle is evenly divided into two time periods by triggering the opposite phases alternately, and only one of the lasers is turned on in the front and rear time periods, so that two spectral lines can be measured simultaneously in the same path.

[0021] Preferably, the wavelength center position is detected and the frequency shift diagram of the two light beams is calculated to obtain the gas flow rate. The method includes: using a double-path measurement method, two laser beams are generated by the same laser, and the two laser beams cross on the same plane after passing through the flow field to be measured. The flow field to be measured is regarded as a moving wave source, so the two laser beams will be compressed and stretched respectively due to the different flow directions of the flow field. The absorption spectral lines of the two laser beams will produce Doppler shifts respectively. The flow field velocity is calculated according to the following formula by combining the Doppler shift amounts of the two laser beams:

[0022] ,

[0023] In the formula, Δυ is the frequency;υ 0 is the centerline frequency; u represents the flow field velocity; c is the speed of light; represents the included angle between the laser beam and the gas flow direction.

[0024] Preferably, the laser is a distributed feedback ring-shaped vortex, the laser output range covers the water molecule absorption spectrum line, the signal generator is used to modulate the laser signal, the beams covering two water molecule spectrum lines respectively are coupled in a time division multiplexing manner by the beam splitter, and are divided into multiple beams, and are emitted by the collimating mirror; the signal generator generates a triangular wave. The signal generator generates a triangular wave, which is easy to couple in a time division multiplexing manner, and is also conducive to fitting of the absorption peak in data processing.

[0025] Preferably, the included angle between the collimating mirror and the photodetector is 60°-120°. The collimating mirror and the photodetector are installed and placed in a special included angle of 60°-120°. The arrangement of the light path and the velocity measurement signal are simultaneously optimized, and the temperature and the gas flow velocity of the flow field to be measured can be measured simultaneously.

[0026] In a second aspect, the embodiment of the present application provides a TDLAS system for synchronous temperature measurement and velocity measurement, comprising a laser, a laser temperature and current control module, a signal generator, a beam splitter, a collimating mirror, a photodetector, a standard device and a data acquisition system.

[0027] The laser is used to provide a stable light source output, and is arranged as a distributed feedback ring-shaped vortex. The laser temperature and current control module comprises a laser temperature controller and a circuit controller, and is used to control the temperature control voltage and the injected current of the laser. The laser output wavelength is controlled to be a water molecule absorption spectrum line, the sawtooth wave generated by the signal generator is used to control the spectrum line, the laser signal is modulated, and the signal acquisition is facilitated. The signal generator is used to generate specific triangular wave and sine wave signals, and the laser signal is modulated. The beam splitter is used to connect the adjusted light. Two laser signals generated by different lasers are collected, coupled in a time division multiplexing manner, and then divided into multiple light paths. The collimating mirror is used to emit the laser in the measurement area, and carries the flow field related information after passing through the measurement area. The photodetector is used to receive the laser in the measurement area, convert the photoelectric information, and receive the information carried by the laser. The standard device is used to establish a one-to-one correspondence between time and frequency through the principle of multi-beam interference. The data acquisition system is used to collect the photoelectric signals received by the photodetector, average process the two data measured respectively, and obtain the logarithmic graph of the laser intensity ratio before and after the baseline fitting. The frequency shift graph of the two beams is calculated, and then the temperature and velocity information of the flow field are synchronously obtained.

[0028] Preferably, the beam splitter collects laser signals generated by two different lasers, couples the two in a time-division multiplexing manner, and then divides the coupled laser signals into 8 beams in the same optical path for transmission to the collimating mirror for measurement.

[0029] Preferably, the angle between the collimating mirror and the photodetector is 60°-120°.

[0030] Compared with the prior art, the present application has the following advantages:

[0031] (1) The measurement method of the collection system of the present application is non-contact measurement, which overcomes the problems of other contact measurement instruments, such as easy disturbance of flow field, low noise resistance, and short service life.

[0032] (2) After adjusting the laser wavelength of the laser system part of the present application, the water molecule absorption spectrum can be perfectly covered, and the receiving laser and data collection system are designed reasonably, having good stability.

[0033] (3) The practical installation part of the present application is small and flexible, and can be used in harsh environments such as high temperature and high pressure, so the application scenarios are very broad. The present application uses various methods to reduce measurement error, including averaging data collected in multiple cycles, discarding the first and tail parts of data, and using high-frequency collection frequency to increase noise resistance.

[0034] (4) The present application has a special data processing part, which can obtain the temperature information and speed information of the flow field to be measured in real time after the collection system is arranged, the data is obtained in time, has good dynamic performance, and can realize real-time detection of the flow field. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain the principles of the present application. Other embodiments and many of the intended advantages of the embodiments will be readily appreciated as the same becomes better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

[0036] Figure 1 is a flowchart of the TDLAS method of the present application for simultaneous temperature measurement and speed measurement;

[0037] Figure 2 is a schematic diagram of a typical measurement system in the TDLAS method of the present application for simultaneous temperature measurement and speed measurement;

[0038] Figure 3A flowchart of a process for post-processing collected data, obtaining a gas flow rate and an ambient temperature in a synchronous temperature and velocity measuring TDLAS method of an embodiment of the present application is shown in Figure 1.

[0039] Figure 4 A schematic diagram of an architecture of a synchronous temperature and velocity measuring TDLAS system of an embodiment of the present application is shown in Figure 2.

[0040] Figure 5 A schematic diagram of a structure and a mounting method of a synchronous temperature and velocity measuring TDLAS system of an embodiment of the present application is shown in Figure 3. DETAILED DESCRIPTION

[0041] The present application will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely intended for the purpose of illustration of the related application and are not intended to limit the application. In addition, it should be noted that only parts related to the application are shown in the accompanying drawings for the purpose of description.

[0042] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and embodiments.

[0043] Figure 1 An embodiment of the present application discloses a synchronous temperature and velocity measuring TDLAS method, as shown in Figure 1, which comprises the following steps: Figure 1

[0044] S1, a collimating mirror 5 and a photodetector 6 are set up to ensure that the laser emitted by the collimating mirror 5 can accurately enter the photodetector 6 after entering the flow field to be measured;

[0045] S2, in the light path adjustment, a red light test light source is used to access the optical fiber collimator, and red light is output to adjust the light path, or an infrared display card is used to convert the invisible infrared band light beam into visible light, and the light path is precisely adjusted after accessing the laser 1;

[0046] S3, the signal generator 3 is turned on, the frequency and electrical signal parameters are set in the signal generator 3 according to the selected spectrum line of the laser 1, the control module of the laser 1 is turned on, and the temperature parameter is adjusted to match the working temperature of the laser 1;

[0047] S4, the NI control software is turned on, the collection card is self-calibrated and self-built to enter the working state, then the LabVIEW software is turned on, and the sampling number and sampling rate are set; and

[0048] ​S5, data acquisition of the electrical signal, a number of data are measured and then averaged, by measuring data baseline fitting to obtain the incident laser intensity and the projection of the light intensity ratio of the logarithmic graph, the ambient temperature, the detection wavelength center position and the calculation of the two beams of frequency shift map, the calculation of the gas flow rate.

[0049] Specifically, the basic law of light absorption by matter is called Beer-Lambert law, Beer-Lambert law is applicable to all electromagnetic radiation and light-absorbing substances including gas, liquid, molecule and ion. When a beam of light with a central frequency of υ Laser through the measured medium, the measured medium absorbs laser, different molecules in the measured medium will produce transition and other reactions, so the light intensity before and after the incident will change accordingly. The light intensity of the transmitted light and the incident light satisfies Beer-Lambert law:

[0050] ,

[0051] In the formula, I 0 is the incident laser intensity; I t is the transmitted laser intensity; l is the length of the measured area; P is the total pressure; X is the concentration of the absorbing gas; T is the temperature; Ф is a linear function; S(T) is the line intensity of the absorption spectrum; the above formula is transformed into the following formula, and A i defined as the integral absorbance, then:

[0052] ,

[0053] defined as the integral absorption coefficient at the path l , then:

[0054] ,

[0055] When the laser passes through a gas medium, the temperature, pressure and concentration of which are uniformly distributed, the integral absorption coefficient can be expressed as:

[0056] .

[0057] In this embodiment, the double-line ratio method is used when measuring the temperature. The double-line ratio method is to use two spectral lines with the same path to obtain the temperature by comparing the integral absorption area of the two spectral lines. The temperature formula is:

[0058] ,

[0059] wherein, h is the Planck constant; c is the speed of light; k is the Boltzmann constant; are the low energy level energies of the absorption transition of the two spectral lines, respectively; A 1 、A 2 are the integrated absorbances of the two lasers, respectively; S 1 、S 2 are the line strengths of the two absorption spectral lines at the transition, respectively; T 0 is the reference temperature, usually set to 296 K.

[0060] Further, the method of calculating temperature directly using incident light intensity and outgoing light intensity based on Beer-Lambert law and double-line ratio method is called direct absorption method, and a typical measurement system is shown in FIG. 1. The function of the signal generator 3 is to generate a sawtooth wave to load on the laser signal to generate an absorption line type for the convenience of data collection and signal visualization adjustment; a single laser beam is dispersed into multiple laser beams by the optical fiber beam splitter 4, and then enters the etalon and the flow field to be measured; the post-processing system 71 processes the signals of the signal acquisition system, and then obtains the final measurement result. Figure 2

[0061] When TDLAS technology is used for measurement, the double-line ratio method is selected, so it is necessary to couple two spectral lines of different wave bands when the system is built. The time division multiplexing scheme is simple in equipment, the beam splitter 4 combines different lasers into the same path, and different lasers have the same receiving source, i.e. are received by the same photodetector 6, which can eliminate the error caused by different receiving sources, so the time division multiplexing scheme can effectively match the direct absorption method using the double-line temperature measurement method. For the double-line temperature measurement time division multiplexing scheme used in this embodiment, two spectral lines of different wavelengths are coupled into the same optical path, and are alternated in time by opposite-phase triggering, so that the same measurement period is evenly divided into two time periods, and only one laser 1 is turned on in the front and rear time periods, so that two spectral lines can be measured simultaneously in the same path.

[0062] ​Specifically, in this embodiment, when using the dual-line ratio method for temperature measurement, it is necessary to couple two spectral lines of different wavelengths during system setup. A beam splitter 4 is used to collect the laser signals generated by two different lasers 1, and then the two are coupled using time-division multiplexing. Subsequently, the coupled laser signals are divided into eight identical optical paths and transmitted to the collimating lens 5 for measurement. By triggering with opposite phases, the measurement cycle is evenly divided into two time periods, with only one laser 1 turned on in each time period, so as to achieve simultaneous measurement of two spectral lines on the same path.

[0063] The theoretical basis of TDLAS velocity measurement is the Doppler effect of light. Its main principle is that the wavelength of light emitted by an object changes due to the relative motion between the wave source and the observer. Objects in front of and behind a moving wave source will have their radiated waves compressed and stretched, respectively, resulting in opposite frequency changes. Based on the degree of frequency shift in front of and behind the moving wave source, the velocity of the wave source along the observation direction can be calculated.

[0064] Based on the Doppler effect, velocity measurement using TDLAS technology is a dual-optical-path measurement method, such as... Figure 2 As shown. Two laser beams are generated by the same laser 1. Both beams pass through the flow field under test and intersect on the same plane. Considering the flow field as a moving wave source, the two laser beams will be compressed and stretched respectively due to their different directions relative to the flow field. The absorption spectra of the two laser beams will generate Doppler frequency shifts. Combining the Doppler frequency shift ∆v of the two laser beams, the flow field velocity is calculated using the following formula:

[0065] ,

[0066] In the formula, Δυ For frequency; υ 0 The centerline frequency; u Represents the flow velocity; c is the speed of light; This represents the angle between the laser beam and the airflow direction.

[0067] Furthermore, Figure 3 This is a schematic diagram illustrating the process of post-processing acquired data to obtain gas flow rate and ambient temperature using a TDLAS system according to an embodiment of this application. The software portion of the TDLAS system built in this embodiment consists of two parts: a LabVIEW-based data acquisition system and a Python-based post-processing program. The data acquisition system controls the opening and closing of the entire system and the setting of acquisition parameters, while the Python post-processing program processes and analyzes the acquired data.

[0068] The collected data is loaded into the Python program prepared in advance, and the start and end sampling points are selected according to the position of the absorption peak in the directly absorbed signal. The start and end sampling points are used to perform baseline fitting of the two ends, so as to obtain the fitting formula and related coefficient of the incident light intensity I0. After observing and selecting the appropriate first and last baseline data, the logarithmic processing is performed on the baseline data and the actual collected data of the double-channel laser, and the -ln(It / I0) relationship conversion graph is obtained. At this time, the ambient temperature information can be obtained.

[0069] In order to further obtain the speed information, it is necessary to establish a one-to-one correspondence between frequency and time through the etalon signal. The frequency of the first absorption peak is identified as 0, as the starting point of time and frequency, and the frequency difference between adjacent peaks of the etalon is 0.05 cm -1 By calculation, the frequency of each absorption peak and its corresponding time can be obtained. By using the least square method, the corresponding curve of time and frequency in each period can be fitted. The least square fitting of the etalon signal of the two-channel laser signal is performed, and the obtained curve is the corresponding change of time and frequency. The red curve is the fitted curve. When using TDLAS to measure the speed, it is necessary to obtain the frequency shift of the optical path due to the Doppler effect, so it is necessary to convert the time into frequency. After substituting time and frequency, the center frequency corresponding to the peak value is found by using the maximum value extraction algorithm, and then the frequency shift of the two-channel signal is obtained, and the gas flow speed is calculated.

[0070] Specifically, the process of measuring the temperature and airflow speed of the environment by using the application is as follows: first, the collimating mirror 1 and the photodetector 6 are set up to ensure that the laser emitted by the collimating mirror 1 can accurately enter the photodetector 6 after entering the flow field to be measured. At this time, a red light test light source is needed to be connected to the optical fiber collimator in the light path adjustment, and the red light is used to adjust the light path or an infrared display card is used to convert the invisible infrared waveband light beam into visible light, and the light path is precisely adjusted after being connected to the semiconductor laser 1. Then the signal generator 3 is turned on, and the frequency and electrical signal parameters are set in the signal generator 3 according to the selected DFB laser 1 spectrum line, that is, two selected H2O absorption spectrum lines with wavelengths of 1388.1 nm and 1344.9 nm. Then the laser 1 control module is turned on, and the temperature parameter is adjusted to match the working temperature of the DFB laser 1. The NI control software is turned on to calibrate and build the acquisition card, so that it enters the working state. Then the LabVIEW software is turned on, and the sampling number and sampling rate are set. The sampling number / sampling rate is the frequency, which needs to be consistent with the frequency set in the signal generator 3. The sampling number represents the number of sampling points per cycle, and in this embodiment, the sampling number is set to 2000 per cycle. The phase-locked amplifier is adjusted to stabilize the signal waveform, and then the data collection is started. After the data is collected, it is entered into the computer. In the computer, the collected data is measured and averaged, and the baseline is fitted to obtain the logarithmic graph of the intensity ratio of the laser before and after the laser, and the environmental temperature information is calculated. Then the frequency shift graph of the two light beams is calculated, and the gas speed information is obtained synchronously.

[0071] In a second aspect, the embodiment of the application provides a TDLAS system for synchronous temperature measurement and speed measurement, as shown in Figure 4 and Figure 5 , which comprises a laser 1, a laser temperature and current control module 2, a signal generator 3, a beam splitter 4, a collimating mirror 5, a photodetector 6, a standard device and a data acquisition system 7.

[0072] In one embodiment, the laser 1 is used to provide a stable light source output, configured as a distributed feedback ring vortex; the laser temperature and current control module 2 includes a laser temperature controller 21 and a circuit controller for controlling the temperature control voltage and injection current of the laser 1, controlling the output wavelength of the laser 1 to be the water molecule absorption spectrum line, and generating a sawtooth wave control spectrum line through the signal generator 3 to modulate the laser 1 signal, facilitating signal acquisition; the signal generator 3 is used to generate specific triangular wave and sine wave signals, which act on the laser 1 to modulate the laser signal; the beam splitter 4 is used to connect the adjusted light, first collecting two different laser signals generated by the laser 1, coupling in a time division multiplexing manner, and then splitting into multiple optical paths; the collimating mirror 5 is responsible for the emission of the laser in the measurement area, which carries the flow field related information after passing through the measurement area; the photodetector 6 is used to receive the laser in the measurement area, accept the information carried by the laser, and convert the photoelectric information; the etalon is used to establish a one-to-one correspondence between time and frequency through the principle of multi-beam interference; the data acquisition system 7 is used to collect the photoelectric signal received by the photodetector 6, measure two-way data respectively, and average process after measurement, and obtain the logarithmic graph of the laser intensity ratio after baseline fitting, calculate the frequency shift graph of the two beams, and then the temperature and velocity information of the flow field can be obtained synchronously.

[0073] Reference Figure 5 In this embodiment, the laser 1 is a distributed feedback laser (DFB). The DFB laser has a wide wavelength range, high temperature resistance, narrow line width, high tuning accuracy and high cost performance, so the DFB laser 1 is selected for the experimental system. The working temperature is controlled by the temperature control module 2, and stable working temperature output can ensure stable output in the waveband.

[0074] The laser 1 is fixed on a butterfly clamp, which is provided with a signal input port to receive the signal output by the laser temperature and current control module 2 to excite the laser 1. In this embodiment, the model is a Japanese NTT / NEL infrared semiconductor laser 1. The wavelength of the laser 1 covers the water vapor and carbon dioxide characteristic absorption peaks, and the wavelength range is specifically 1290-1360 nm, the fiber output power is 10 mW, and the output line width is 2 MHz. The butterfly packaged DFB semiconductor laser 1 fixed seat is used to fix the semiconductor laser 1, which has a DB9 interface to facilitate connection with test instruments, and a Y-shaped groove is designed at the front end of the clamp to facilitate fixation with an optical platform. The laser temperature and current control module 2 is a North Space The company self-made product can realize the control of the temperature control voltage and the injection current of the DFB laser 1, so that the output laser center wavelength scans the characteristic absorption peak of the gas to be measured. After the absorption of the gas to be measured, the light signal carrying the change is converted into an electrical signal, which is input into the host computer for signal processing.

[0075] The signal generator 3 mainly functions to generate specific triangular wave and sine wave signals, which are applied to the DFB laser 1 to modulate the laser signals. The selected signal generator 3 is a model AFG1062 of Tektronix, with double-channel output, and the output voltage is manually adjusted. The parameters meet the requirements. The function of the beam splitter 4 is to collect the laser signals generated by the two different lasers 1, and then couple them in a time division multiplexing manner. Subsequently, the coupled laser signals are divided into 8 beams of the same light path and transmitted to the collimator 5 for measurement. The collimator is used to convert the divergent light emitted from the tail fiber of the laser 1 into parallel light, so as to ensure that the spot size is basically consistent within the test distance, reduce the light power loss, and ensure the accuracy of the test. The working distance is greater than or equal to 30 cm, and it is coated with an anti-reflection film, which can meet the requirements of 1050 nm-2700 nm laser transmission.

[0076] The angle between the collimator 5 and the photodetector 6 is 60°-120°. The collimator 5 and the photodetector 6 are installed and placed at a special angle of 60°-120°. This arrangement can optimize the light path and the measurement trace, and can also achieve the goal of simultaneously measuring the temperature and gas flow rate of the flow field to be measured.

[0077] Then is the system part after the measured area. The photodetector 6 converts the received light signal into an electrical signal, with a detection range of 1.2-2.0 μm, a bandwidth of 15 MHz, and a light-sensitive surface of 2.5 mm. It is responsible for receiving laser in the measurement area, and is fixed by an optical fixing and adjusting device. The fine adjustment screw on the fixing device is used for light path fine adjustment and alignment. The purpose of the etalon is to establish a one-to-one correspondence between time and frequency through the principle of multi-beam interference. The present application adopts a Fabry-Perot etalon, i.e. a F-P interferometer, which is a scanning type SA200-12B of Thorlabs company, suitable for a wavelength range of 1275-2000 nm. The data acquisition system 7 can collect the photoelectric signal received by the photodetector 6, and perform the next step of analysis and processing under the control of the application program in the computer. The data acquisition card is integrated with the computer. The NI PCI-1633 type acquisition card of NI company is selected in the experimental system, with a maximum sampling rate of 2.5 MS / s, i.e. 25 million data points per second. The signal acquisition card can realize 8-way data acquisition at the same time, which meets the requirements of the experimental embodiment of the present application.

[0078] In summary, the application uses TDLAS technology, non-contact measurement and small and convenient installation part, so that the application can complete synchronous, real-time and accurate reliable monitoring of environment temperature and gas speed in harsh environment such as high temperature and high pressure. Various data processing methods are adopted to make the application have good data precision; special collimating mirror and installation scheme of photoelectric detector are adopted, and temperature and speed of target flow field are synchronously measured, so that the application has good noise resistance, high measurement precision, fast time response and can synchronously measure multiple physical parameters of the same physical flow field.

[0079] The above description is merely preferred embodiments of the application and a description of the principles of the technology used. Those skilled in the art should understand that the scope of the application involved in the application is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or equivalent features without departing from the above inventive concept. For example, the above features are replaced with the technical features disclosed in the application (but not limited to) having similar functions to form a technical solution.

Claims

1. A TDLAS method for synchronous temperature and velocity measurement, characterized in that, The method comprises the following steps: The collimating mirror and the photodetector are set up to ensure that the laser emitted by the collimating mirror can accurately enter the photodetector after passing through the flow field to be measured; In the optical path adjustment, a red light test light source is used to access the optical fiber collimator, and red light is output to adjust the optical path, or an infrared display card is used to convert the invisible infrared band light beam into visible light, and the optical path is precisely adjusted after accessing the laser; The signal generator is turned on, the frequency and electrical signal parameters are set in the signal generator according to the selected laser spectral line, the control module of the laser is turned on, and the temperature parameter is adjusted to match the working temperature of the laser; The NI control software is turned on, the acquisition card is self-calibrated and self-built to make it enter the working state, then the LabVIEW software is turned on, and the sampling number and sampling rate are set; and The electrical signals are collected, a plurality of channels of data are measured and then averaged, the logarithmic graph of the ratio of the incident laser intensity to the projected laser intensity is obtained by baseline fitting of the measured data, the environmental temperature is calculated, the wavelength center position is detected and the frequency shift graph of the two light beams is calculated, and the gas flow rate is calculated; Specifically includes: the light intensity of the transmitted light and the incident light satisfies Beer-Lambert law: , wherein, is the incident laser intensity; I t is the transmitted laser intensity; l is the length of the region to be measured; P is the total pressure; X is the concentration of the absorbing gas; T is the temperature; is a linear function; S(T) is the line intensity of the absorption line; the above equation is transformed to the following equation, and A i is defined as the integral absorbance, then: ， defined as the integral absorption coefficient at the path l then: ; When the laser passes through a gas medium, whose temperature, pressure and concentration are in uniform distribution, the integral absorption coefficient can be expressed as: ; The double optical path measurement method is used, two laser beams are generated by the same laser, the two laser beams are crossed on the same plane through the flow field to be measured, the flow field to be measured is regarded as a moving wave source, the two laser beams are compressed and elongated respectively due to the different flow directions of the flow field, the absorption spectral lines of the two laser beams are respectively subjected to Doppler frequency shift, the Doppler frequency shift amounts of the two laser beams are combined , and the flow field velocity is calculated according to the following formula: , wherein, υ 0 is the center line frequency; u represents the flow field velocity; c is the speed of light; represents the included angle between the laser beam and the air flow direction. 2.The synchronous temperature and velocity measurement TDLAS method according to claim 1, wherein, Further comprising: The temperature is measured by using the double-line ratio method, the integral absorption areas of two spectral lines are taken to obtain the temperature, and the temperature formula is: ， wherein h is the Planck constant; c is the speed of light; k is the Boltzmann constant; are the low energy level energies of the two absorption transitions, respectively; A 1 、A 2 are the integrated absorbances of the two lasers, respectively; S 1 、S 2 are the light intensities of the two absorption lines at the transition, respectively; T 0 is the reference temperature. 3.The synchronous temperature and velocity measurement TDLAS method according to claim 2, wherein, Further comprising: When the double-line ratio method is used to measure the temperature, two spectral lines of different wave bands are coupled when the system is set up, the laser signals generated by the two different lasers are collected by using a beam splitter, then the two are coupled in a time division multiplexing manner, and then the coupled laser signals are divided into 8 beams of the same optical path and transmitted to the collimating mirror for measurement; the same measurement cycle is evenly divided into two time periods by triggering in opposite phases, and only one of the lasers is turned on in the front and rear time periods, so that two spectral lines can be measured simultaneously on the same path. 4.The synchronous temperature and velocity measurement TDLAS method according to claim 3, wherein, The laser is a distributed feedback ring-shaped vortex, the output range of the laser covers the water molecule absorption spectral line, the signal generator is used to modulate the laser signal, the beam splitter is used to couple the light beams covering two water molecule spectral lines in a time division multiplexing manner, and the light beams are divided into a plurality of beams and emitted by the collimating mirror; the signal generator generates a triangular wave. 5.The synchronous thermometric and velocimetric TDLAS method of claim 1, wherein, The included angle between the collimating mirror and the photodetector is 60°-120°.

6. A TDLAS system for simultaneous temperature and velocity measurement, characterized in that The method for realizing any one of claims 1-5 further comprises a laser, a laser temperature and current control module, a signal generator, a beam splitter, a collimating mirror, a photodetector, a etalon and a data acquisition system; The laser is used to provide stable light source output and is set as a distributed feedback ring-shaped vortex; The laser temperature and current control module comprises a laser temperature controller and a circuit controller, which are used to control the temperature control voltage and the injected current of the laser, control the output wavelength of the laser to be the water molecule absorption spectral line, control the spectral line by the sawtooth wave generated by the signal generator, modulate the laser signal, and facilitate signal acquisition. The signal generator is used for generating specific triangular wave and sine wave signals, and the signals are used for modulating laser signals of the lasers; The beam splitter is used for connecting the adjusted light rays, collecting the laser signals generated by the two different lasers, coupling in a time division multiplexing mode, and then splitting into multiple light paths; The collimating mirror is used for emitting the laser of the measurement area, passing through the measurement area, and carrying the flow field related information; The photodetector is used for receiving the laser of the measurement area, receiving the information carried by the laser, and converting the photoelectric information; The etalon is used for establishing the one-to-one correspondence between time and frequency through the principle of interference of multiple beams; The data acquisition system is used for collecting the photoelectric signals received by the photodetector, averaging the two data after measurement, fitting the baseline, obtaining the logarithmic diagram of the intensity ratio of the laser before and after, calculating the frequency shift diagram of the two beams, and then synchronously obtaining the temperature and speed information of the flow field.

7. The synchronous thermometric and velocimetric TDLAS system of claim 6, wherein, The beam splitter collects the laser signals generated by the two different lasers, couples the two laser signals in a time division multiplexing mode, and then splits the coupled laser signals into 8 beams of the same light path and transmits them to the collimating mirror for measurement.

8. The synchronous thermometric and velocimetric TDLAS system of claim 6, wherein, The included angle between the collimating mirror and the photodetector is 60°-120°.

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