Laser gas detection method, device and system

Abstract

The invention discloses a laser gas detection method, a detection device and a system, which are suitable for the occasion that a laser has no semiconductor cooler, and the method comprises the following steps: acquiring the current temperature T and the current driving current I of the laser, and the initial wavelength lambda0, the wavelength current coefficient kI and the wavelength temperature coefficient kT under the preset temperature and the preset driving current; obtaining the current wavelength according to the current temperature T, the current driving current I, the initial wavelength lambda0, the wavelength current coefficient kI and the wavelength temperature coefficient kT; determining an absorption peak to be locked according to the wavelength interval position of the current wavelength; and comparing the current wavelength with the absorption peak wavelength to obtain the distance between the two wavelengths, and adjusting the driving current of the laser according to the distance between the two wavelengths to lock the absorption peak so as to realize gas detection. The method has the advantages that gas detection is accurate, and meanwhile system power consumption and cost are remarkably reduced.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of gas detection, and in particular to a laser gas detection method, a detection device and a system. Background Art

[0002] Tunable semiconductor laser absorption spectroscopy (TDLAS) technology is a detection technology based on laser absorption spectroscopy (LAS). It uses the narrow line width and wavelength of tunable semiconductor lasers that change with the injected current. By modulating the wavelength of the laser, the wavelength of the laser scans across the absorption peak of the gas molecules being measured, and the concentration of gas molecules is measured based on Beer-Lambert's law:

[0003]

[0004] Where I0 is the reference laser intensity when there is no gas absorption; I t is the laser intensity after being absorbed by the gas when passing through the gas medium; α(v) represents the gas absorption coefficient; L[cm] is the distance the laser propagates in the gas; and C is the volume concentration of the gas.

[0005] Among them, the gas absorption coefficient α(v) can be expressed as:

[0006]

[0007] Where α0 is the absorption cross section of pure gas at the center of the absorption line, v is the center frequency of the laser, and v is c is the center frequency of the absorption peak, Δv is the half-height width of the absorption spectrum; by obtaining α(v), the gas concentration can be calculated.

[0008] According to the different laser driving methods, TDLAS technology is divided into direct absorption method, wavelength modulation spectroscopy (WMS) and frequency modulation spectroscopy (FMS). The direct absorption method has a simple structure and low cost, but it is easily interfered with and has relatively low sensitivity; both wavelength modulation spectroscopy and frequency modulation spectroscopy can effectively suppress background noise, the circuit structure is relatively complex, and the sensitivity is high, but the modulation frequency of frequency modulation spectroscopy is high (MHz level), the technology is complex, and the circuit is difficult to miniaturize. The modulation frequency of wavelength modulation spectroscopy is low (kHz level) and the circuit is relatively simple, so gas sensors generally use wavelength modulation spectroscopy to measure gas concentration.

[0009] The wavelength modulation spectroscopy technology modulates the laser current through a low-frequency triangular wave so that the laser emission wavelength scans the absorption spectrum of the gas. The laser wavelength is modulated at high frequency by a high-frequency sine wave with an amplitude lower than the triangular wave (the sine wave is for harmonic detection and noise suppression). The synchronous detection technology is used at the back end of the detector to extract the second harmonic signal, and then the correlation between the second harmonic signal peak and the gas concentration is used to measure the gas.

[0010] Laser gas sensor developed based on tunable semiconductor laser absorption spectroscopy (TDLAS) technology. The principle block diagram of a typical laser gas sensor is as follows: Figure 1 As shown. The sensor consists of a microprocessor, a driving circuit, a laser, an optical path, a detector, a transimpedance amplifier circuit (IV conversion circuit), a signal detection circuit, etc. Although the laser gas sensor has high sensitivity, good selectivity, and fast response speed, it is not suitable for battery-powered scenarios due to its large operating current and high power consumption.

[0011] The main reason for the high power consumption and large working current of laser gas sensors is that the core component, the laser, has a large working current and high power consumption. A typical laser is composed of a thermistor (NTC), a laser chip (LD) and a semiconductor cooler (TEC). The stability of the laser wavelength is affected by temperature and current (generally expressed by the temperature wavelength coefficient and the current wavelength coefficient). In the application process, in order to maintain the stability of the wavelength, a semiconductor cooler is generally used to control the laser at a constant temperature. However, this temperature control strategy will inevitably increase the power consumption of the sensor, especially when there is a large difference between the external ambient temperature and the set operating temperature of the laser, the increase in power consumption is particularly obvious. Therefore, finding a method that can effectively reduce the power consumption of the sensor and accurately measure and realize gas detection is of great significance for the use of laser gas sensors in low-power occasions.

[0012] In the scheme with TEC, a spectral line with strong absorption is generally selected as the fixed spectral line, and the absorption coefficient of the spectral line at different temperatures, concentrations, and pressures is determined through calibration. In the scheme without TEC, the conventional practice is to first determine the wavelength according to the ambient temperature, and then adjust the driving current to lock the wavelength to a certain absorption spectral line. By calibrating all absorption spectral lines within a certain wavelength range, the absorption coefficient of each spectral line at different temperatures, concentrations, and pressures is determined, thereby realizing gas concentration measurement.

[0013] The wavelength of the laser is affected by temperature and current. There are two wavelength modulation methods for laser gas sensors: wavelength current modulation and wavelength temperature modulation. Wavelength current modulation changes the wavelength of the light by changing the size of the injected current; wavelength temperature modulation changes the wavelength of the light by changing the operating temperature of the laser. Due to the thermal inertia of the laser, it is extremely difficult to accurately control the temperature. The current control circuit is simple and the control current is highly accurate. Therefore, in practical applications, the laser is often subjected to constant temperature control and wavelength current modulation technology is used.

[0014] In order to reduce the impact of temperature on wavelength, a semiconductor cooler (TEC) + PID control circuit is usually used to control the laser's constant temperature. Although this method reduces the impact of temperature on wavelength and improves product stability, it increases system power consumption, circuit complexity, and hardware costs. The increase in power consumption makes it unsuitable for battery-powered applications and explosion-proof applications. Summary of the invention

[0015] In view of the technical problems existing in the prior art, the present invention provides a laser gas detection method, a detection device and a system which ensure the accuracy of gas detection while significantly reducing the power consumption and cost of the system.

[0016] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0017] A laser gas detection method, applicable to the occasion where the laser has no semiconductor refrigerator, comprises the steps of:

[0018] Get the current temperature T, current drive current I, initial wavelength λ0 and wavelength current coefficient k of the laser at the preset temperature and preset drive current I and wavelength temperature coefficient k T ;

[0019] According to the current temperature T, the current driving current I, the initial wavelength λ0, the wavelength current coefficient k I and wavelength temperature coefficient k T , get the current wavelength;

[0020] Determine the absorption peak to be locked according to the wavelength interval position of the current wavelength; wherein the wavelength is divided into a plurality of wavelength interval positions, and each wavelength interval position corresponds to a locked absorption peak;

[0021] The current wavelength is compared with the absorption peak wavelength to obtain the distance between the two, and then the laser drive current is adjusted according to the distance between the two to lock the absorption peak, thereby realizing gas detection.

[0022] Preferably, according to the current temperature T, the current driving current I, the initial wavelength λ0, the wavelength current coefficient k I and wavelength temperature coefficient k T, the specific formula for obtaining the current wavelength λ is:

[0023] λ=λ0+k T ΔT+k I ΔI;

[0024] ΔT is the change of the current temperature relative to the preset temperature, and ΔI is the change of the current driving current relative to the preset driving current.

[0025] Preferably, the wavelength is divided into a plurality of wavelength interval positions, and the specific process of each wavelength interval position corresponding to a locked absorption peak is:

[0026] In the absence of a semiconductor cooler, assuming that the laser current is constant, the wavelength is modulated by the ambient temperature and fluctuates within the range of 1634nm to 1659nm;

[0027] There are 9 absorption peaks of methane gas in the range of 1634nm to 1659nm; in the spectral line cluster, one spectral line is selected as the absorption line every other spectral line, that is, 1653.55nm, 1650.96nm, 1645.54nm, 1640.27nm, and 1635.42nm are selected as the absorption lines, and four absorption lines at 1656.74nm, 1648.23nm, 1642.91nm, and 1637.73nm are used as dividing lines to divide the spectral lines into five intervals.

[0028] Preferably, after locking the absorption peak, the gain of the signal detection circuit is adjusted according to the selected locked absorption peak to increase the signal amplitude and improve the signal-to-noise ratio.

[0029] Preferably, when performing gas detection, the measured signal is collected, and phase locking and second harmonic extraction are performed; and the gas concentration is inverted according to the second harmonic peak value.

[0030] The present invention also discloses a laser gas detection device, comprising a microcontroller, a laser driving circuit, a laser, a transimpedance amplifier circuit and a signal detection circuit; the microcontroller is connected to the laser through the laser driving circuit; the laser is connected to the microcontroller through the transimpedance amplifier circuit and the signal detection circuit in turn; the microcontroller is connected to the laser driving circuit through a current detection circuit.

[0031] Preferably, the signal detection circuit is provided with a programmable signal amplifier for automatically adjusting the gain according to the signal size.

[0032] The present invention further discloses a computer program product, comprising a computer program, wherein the computer program executes the steps of the method described above when executed by a processor.

[0033] The present invention also discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described above are executed.

[0034] The present invention further discloses a laser gas detection system, comprising a memory and a processor connected to each other, wherein a computer program is stored in the memory, and when the computer program is run by the processor, the steps of the method described above are executed.

[0035] Compared with the prior art, the advantages of the present invention are:

[0036] The gas detection scheme of the present invention does not require the use of a semiconductor refrigerator. By real-time monitoring of the temperature inside the laser, combined with the current regulation mechanism of the laser wavelength and the "wave-hopping" regulation technology, dynamic adjustment of the laser wavelength is achieved. This design can maintain the stability of the laser wavelength under different ambient temperatures, thereby ensuring the accuracy of gas detection, while significantly reducing the power consumption and cost of the system and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the structure of a laser gas detection device in the prior art.

[0038] Figure 2 It is a schematic structural diagram of the laser gas detection device of the present invention.

[0039] Figure 3 The figure is a flow chart of a gas detection method according to an embodiment of the present invention.

[0040] Figure 4 This is the absorption spectrum of methane in the range of 1634nm to 1659nm in the present invention.

[0041] Figure 5 This is a schematic diagram of the “wave-hopping” methane absorption spectrum in the present invention.

[0042] Figure 6 This is a flow chart of the absorption peak locking method in the present invention. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0044] like Figure 3 As shown, the low-power gas detection method provided by the embodiment of the present invention has the core idea of ​​utilizing the laser wavelength-temperature characteristics, wavelength-current characteristics, gas absorption spectrum information and "wave hopping" to achieve the concentration measurement of the gas to be measured.

[0045] Taking methane as an example, the absorption lines in the range of 1634nm to 1659nm are as follows Figure 4As shown, its spectral lines have the following characteristics:

[0046] In the non-TEC state, assuming that the laser current is constant and the wavelength is modulated by the ambient temperature, theoretically its output wavelength will fluctuate within the range of 1634nm to 1659nm. Therefore, it is necessary to dynamically adjust the laser operating temperature or current to lock the absorption peak in real time.

[0047] There are 9 absorption peaks of methane gas in the range of 1634nm to 1659nm. To simplify the calibration process, a spectrum line is selected as the absorption spectrum line every other spectrum line in the spectrum line cluster, that is, 1653.55nm, 1650.96nm, 1645.54nm, 1640.27nm, and 1635.42nm are selected as absorption spectrum lines, and 1656.74nm, 1648.23nm, 1642.91nm, and 1637.73nm are used as dividing lines to divide the spectrum lines into λ L0 ~λ L4 There are 5 intervals in total, see Figure 5 .

[0048] When the laser has no TEC, the laser is affected by temperature and may theoretically fall into Figure 5 Lambda L0 ~λ L4 Any position in the interval. Assume that the initial wavelength λ0 of a laser at a certain temperature and driving current, and the current wavelength current coefficient k I , wavelength temperature coefficient k T , current laser temperature T, current drive current I, then the current output wavelength λ:

[0049] λ=λ0+k T ΔT+k I ΔI;

[0050] Where ΔT is the change in temperature relative to a known temperature, and ΔI is the change in current relative to a known current;

[0051] Then according to λ in λ L0 ~λ L4 Interval position, determine and adjust the drive current to lock the nearest absorption peak;

[0052] Then, the gain of the signal detection circuit is adjusted according to the selected absorption peak to increase the signal amplitude;

[0053] Finally, the measured signal is collected, phase-locked and second harmonic extracted, and the gas concentration is inverted based on the second harmonic peak.

[0054] The present invention adopts a low-power laser gas detection method without a semiconductor cooler (TEC), which can reduce the power consumption and cost of the product to a certain extent, while expanding the product application scenarios; the "wave-hopping" wavelength locking method is adopted to reduce the calibration time and improve production efficiency. The present invention is not limited to the application of laser methane sensors, but can also be used for other gas sensors such as laser oxygen.

[0055] like Figure 2 As shown, the embodiment of the present invention further discloses a laser gas detection device, including a microcontroller, a laser driving circuit, a laser, a transimpedance amplifier circuit and a signal detection circuit; the microcontroller is connected to the laser through the laser driving circuit; the laser is connected to the microcontroller through the transimpedance amplifier circuit and the signal detection circuit in turn; the microcontroller is connected to the laser driving circuit through the current detection circuit. Figure 1 On the basis of the conventional circuit, a current detection circuit is added to monitor the driving current of the laser in real time; at the same time, a programmable signal amplifier is provided inside the signal detection circuit, that is, the fixed gain is changed to a programmable gain, and the signal-to-noise ratio is improved by increasing the signal amplitude.

[0056] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0057] Methane gas detection method implementation process:

[0058] 1) Laser screening. The screening wavelength range is 1635-1658nm, the current tuning coefficient is 0.8-1nm / mA, the temperature tuning is less than 0.08nm / ℃, and the threshold current is less than 1mA.

[0059] 2) Determine the initial wavelength λ0 of the laser at a certain current and temperature; for example, the wavelength of a sensor is 1654nm@2mA, 20℃;

[0060] 3) Determine the laser wavelength current coefficient k I and wavelength temperature coefficient k T ;

[0061] 4) Select the absorption line.

[0062] Select the absorption line by "wave hopping" mode, and select 1656.55nm, 1650.96nm, 1645.54nm, 1640.27nm, and 1635.42nm as the absorption line;

[0063] Division interval: Select 1653.74nm, 1648.23nm, 1642.91nm, 1637.73nm as the dividing lines;

[0064] 5) Use the laser internal temperature sensor to measure the laser temperature T in the current environment, collect the laser current drive current I, and calculate the current wavelength λ=λ0+k T ΔT+k I ΔI, ΔT are the temperature changes relative to the known temperature, in this case, relative to 25°C; ΔI is the current change relative to the known current, in this case, relative to 2mA, and the initial wavelength λ0 of the laser is 1654nm;

[0065] 6) If Figure 6 As shown, the absorption peak locking program is used to determine the range of the current wavelength and determine the absorption peak wavelength λ to be locked. c Assume that the laser temperature T in the current environment is 60°C, the current drive current I of the acquisition laser is 2mA, and the wavelength current coefficient k I is 0.8nm / mA, wavelength temperature coefficient k T is 0.08nm / ℃, λ0 is 1654nm@2mA, 20℃, then λ=1657.2nm, the current wavelength range is λ L0 , then the absorption peak wavelength λ to be locked c =1656.55nm; when the wavelength λ0 falls on the dividing line, the absorption peak in the area to the right of the dividing line is preferred.

[0066] 7) The distance between the current wavelength and the absorption peak wavelength to be locked is Δλ=λ-λ c , using the laser wavelength current characteristics, Δλ=k I ΔI, i.e. ΔI = Δλ / k I Assuming λ is 1657.2nm, λ c is 1656.55nm, Δλ is 0.65nm, then ΔI is -0.8125mA, that is, the drive current I is adjusted to 1.1875mA;

[0067] 8) adjusting the gain of the programmable signal amplifier according to the selected absorption peak; if the signal is greater than the threshold, adjusting the gain; wherein the signal of the programmable signal amplifier is a triangular wave and a sine wave superimposed voltage signal output by the transimpedance amplifier circuit and high-pass filtered, wherein the distorted part of the sine wave corresponds to the gas absorption peak;

[0068] 9) Collect the measured signal and perform phase locking and second harmonic extraction;

[0069] 10) Invert the gas concentration based on the second harmonic peak.

[0070] The gas detection scheme of the present invention does not require the use of a semiconductor refrigerator. By real-time monitoring of the temperature inside the laser, combined with the current regulation mechanism of the laser wavelength and the "wave-hopping" regulation technology, dynamic adjustment of the laser wavelength is achieved. This design can maintain the stability of the laser wavelength under different ambient temperatures, thereby ensuring the accuracy of gas detection, while significantly reducing the power consumption and cost of the system and improving production efficiency.

[0071] The present invention utilizes the laser current modulation characteristics and the "wave-hopping" wavelength locking and gas detection method on a laser without a semiconductor refrigerator. The method can be used for a laser without a TEC, which can not only reduce the power consumption of the laser (the greater the temperature difference, the more significant the effect), but also improve the batch production efficiency of the product.

[0072] The gas detection method of the present invention does not need to divide the temperature interval, and the wavelength scanning range only needs to cover one absorption peak; the "wave hopping" wavelength locking method of the present invention does not need to calibrate all absorption peaks in the range of 1640nm to 1660nm, and is highly efficient.

[0073] The present invention further discloses a computer program product, including a computer program, which executes the steps of the above method when executed by a processor. The present invention also discloses a computer-readable storage medium, which stores a computer program, which executes the steps of the above method when executed by a processor. The present invention further discloses a laser gas detection system, including a memory and a processor connected to each other, the memory storing a computer program, which executes the steps of the above method when executed by the processor. The product, medium and system of the present invention correspond to the above method and also have the advantages described in the above method.

[0074] The present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by hardware related to computer program instructions. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned method embodiment when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. Computer-readable storage media include: any entity or device that can carry computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. The memory is used to store computer programs and / or modules, and the processor implements various functions by running or executing computer programs and / or modules stored in the memory, and calling data stored in the memory. The memory may include high-speed random access memory and may also include non-volatile memory, such as a hard disk, an internal memory, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0075] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A laser gas detection method, suitable for the occasion where the laser has no semiconductor refrigerator, characterized in that: Includes steps: Get the current temperature T, current drive current I, initial wavelength λ0 and wavelength current coefficient k of the laser at the preset temperature and preset drive current I and wavelength temperature coefficient k T ; According to the current temperature T, the current driving current I, the initial wavelength λ0, the wavelength current coefficient k I and wavelength temperature coefficient k T , get the current wavelength; According to the wavelength interval position of the current wavelength, determine the absorption peak to be locked; The wavelength is divided into a plurality of wavelength interval positions, and each wavelength interval position corresponds to a locked absorption peak; The current wavelength is compared with the absorption peak wavelength to obtain the distance between the two, and then the laser drive current is adjusted according to the distance between the two to lock the absorption peak, thereby realizing gas detection.

2. The laser gas detection method according to claim 1, characterized in that: According to the current temperature T, the current driving current I, the initial wavelength λ0, the wavelength current coefficient k I and wavelength temperature coefficient k T , the specific formula for obtaining the current wavelength λ is: λ=λ0+k T ·ΔT+k I ·ΔI; ΔT is the change of the current temperature relative to the preset temperature, and ΔI is the change of the current driving current relative to the preset driving current.

3. The laser gas detection method according to claim 1 or 2, characterized in that: The wavelength is divided into multiple wavelength intervals, and the specific process of each wavelength interval corresponding to a locked absorption peak is as follows: In the absence of a semiconductor cooler, assuming that the laser current is constant, the wavelength is modulated by the ambient temperature and fluctuates within the range of 1634nm to 1659nm; There are 9 absorption peaks of methane gas in the range of 1634nm to 1659nm; in the spectral line cluster, one spectral line is selected as the absorption line every other spectral line, that is, 1653.55nm, 1650.96nm, 1645.54nm, 1640.27nm, and 1635.42nm are selected as the absorption lines, and four absorption lines at 1656.74nm, 1648.23nm, 1642.91nm, and 1637.73nm are used as dividing lines to divide the spectral lines into five intervals.

4. The laser gas detection method according to claim 1 or 2, characterized in that: After the absorption peak is locked, the gain of the signal detection circuit is adjusted according to the selected locked absorption peak to increase the signal amplitude.

5. The laser gas detection method according to claim 1 or 2, characterized in that: When performing gas detection, the measured signal is collected, and phase locking and second harmonic extraction are performed; the gas concentration is inverted based on the second harmonic peak value.

6. A laser gas detection device, characterized in that: The invention comprises a microcontroller, a laser driving circuit, a laser, a transimpedance amplifier circuit and a signal detection circuit; the microcontroller is connected to the laser through the laser driving circuit; the laser is connected to the microcontroller through the transimpedance amplifier circuit and the signal detection circuit in turn; the microcontroller is connected to the laser driving circuit through a current detection circuit.

7. The laser gas detection device according to claim 6, characterized in that: The signal detection circuit is provided with a programmable signal amplifier for automatically adjusting the gain according to the signal size.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are performed.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 5.

10. A laser gas detection system, comprising a memory and a processor connected to each other, wherein a computer program is stored in the memory, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 5.

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