TDLAS (Tunable Diode Laser Absorption Spectroscopy)-based carbon oxide concentration measuring equipment

Abstract

The utility model discloses TDLAS (tunable diode laser absorption spectroscopy)-based carbon oxide concentration measuring equipment, which comprises an electrical unit and an optical unit, and the optical unit comprises a tunable laser, an optical detector and a gas absorption cell and is used for detecting absorption of gas to laser with specific wavelength; the electrical unit comprises a microprocessor, a signal excitation unit and a signal receiving unit; the signal excitation unit is connected with the microprocessor and generates a direct current sine wave tuning signal to drive the tunable laser to output a laser signal with a specific wavelength. The signal receiving unit carries out filtering amplification and analog-to-digital conversion on the received signal of the optical detector and sends the signal to the microprocessor. According to the equipment, a triangular sine wave tuning signal is replaced by a direct-current bias adjustable direct-current sine wave tuning signal, so that the influence of the RAM on the gas concentration test precision can be reduced to a certain extent.

Description

Technical Field

[0001] The utility model relates to the technical field of TDLAS, in particular to a carbon oxide concentration measuring device based on TDLAS. Background Art

[0002] In TDLAS technology, under ideal conditions when a semiconductor laser modulates its wavelength, the modulation signal only changes the laser's wavelength. However, in practical applications, the modulation signal also affects the laser intensity, which can lead to asymmetric and complex second harmonic waveforms, negatively impacting the accuracy of gas concentration measurements. The modulation signal in WMS (wavelength modulation spectroscopy) technology consists of a superposition of low-frequency and high-frequency signals. The triangular wave scanning signal input to the laser's modulation signal is the primary source of RAM (residual amplitude modulation effect) and other noise. Therefore, for WMS technology, RAM is one of the primary factors affecting its accuracy. Utility Model Content

[0003] In order to solve the above problems in the prior art, the present invention provides a carbon oxide concentration measurement device based on TDLAS to reduce the influence of triangle wave modulation on the gas concentration test accuracy.

[0004] The technical solution is as follows:

[0005] A carbon oxide concentration measuring device based on TDLAS, comprising an electrical unit and an optical unit;

[0006] The optical unit includes a tunable laser, an optical detector and a gas absorption cell; the laser light generated by the tunable laser is projected onto the optical detector after passing through the gas absorption cell;

[0007] The electrical unit includes a microprocessor, a signal excitation unit and a signal receiving unit;

[0008] The signal excitation unit is connected to the microprocessor to generate a DC sinusoidal wave tuning signal;

[0009] The tunable laser is connected to the signal excitation unit and outputs laser light of a specific wavelength according to a DC sinusoidal wave tuning signal;

[0010] The signal receiving unit is connected to the optical detector and performs filtering, amplification and analog-to-digital conversion on the received signal of the optical detector;

[0011] The microprocessor is connected to the signal receiving unit and processes the received signal.

[0012] Furthermore, the microprocessor includes an automatic amplitude modulation unit and an FFT operation unit; the automatic amplitude modulation unit is used to output a series of PWM signals with adjustable duty cycles; the FFT operation unit is used for signal processing, converting the received time domain signal into a frequency domain signal for spectrum analysis; the signal excitation unit includes a DC conversion unit, a Sin signal excitation unit, an adder and a laser driving circuit; the DC conversion unit is used to convert the PWM signal output by the microprocessor into a DC signal; the Sin signal excitation unit is used to generate a sinusoidal wave signal; the adder is used to superimpose the DC signal and the sinusoidal wave signal to generate a DC sinusoidal wave tuning signal.

[0013] Furthermore, the DC conversion unit includes a PWM to analog voltage integrated circuit.

[0014] Furthermore, the Sin signal excitation unit includes a precision oscillation integrated circuit with a sinusoidal waveform output.

[0015] Furthermore, the optical unit also includes a semiconductor cooler and a thermistor, which are arranged close to the tunable laser to constitute a constant temperature control circuit of the tunable laser; the electrical unit also includes a laser temperature control unit, which is connected to the constant temperature control circuit.

[0016] Furthermore, the electrical unit also includes a communication unit, which is used for communication connection between the microprocessor and external devices.

[0017] Furthermore, the electrical unit also includes a power management unit, which is used to connect to an external power supply device to supply power to each functional module of the electrical unit.

[0018] The utility model achieves the following technical effects:

[0019] The carbon oxide concentration measuring device based on TDLAS of the present invention adopts a DC sine wave signal with adjustable DC bias to replace the triangular sine wave signal, which can reduce the influence of RAM (residual amplitude modulation effect) on the gas concentration test accuracy to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a system block diagram of the carbon oxide concentration measuring device based on TDLAS of the present utility model;

[0021] Figure 2 This is a typical circuit diagram of the DC conversion unit of the utility model;

[0022] Figure 3 This is a typical circuit diagram of the ICL 8038 of the present utility model;

[0023] Figure 4 This is the detection principle block diagram of FFT-WMS technology. DETAILED DESCRIPTION

[0024] To further illustrate various embodiments, this utility model is provided with accompanying drawings. These drawings form part of the disclosure of this utility model and are primarily used to illustrate the embodiments and, in conjunction with the relevant description in the specification, to explain the operating principles of the embodiments. By referring to these drawings, those skilled in the art will be able to understand other possible implementations and the advantages of this utility model.

[0025] The present invention will now be further described with reference to the accompanying drawings and specific implementation methods.

[0026] like Figure 1 As shown, the present invention provides an embodiment of a device for measuring carbon oxide concentration based on TDLAS. The device includes an electrical unit 10 and an optical unit 20, wherein:

[0027] The optical unit 20 includes functional modules such as a laser 201, an optical detector 204 and a gas absorption cell 205 (also known as a detection cavity). In this application, the laser 201 adopts a tunable laser (abbreviated as TDLAS in English. A tunable laser refers to a laser that can continuously change the laser output wavelength within a certain range); the laser generated by the tunable laser is projected onto the optical detector 204 after passing through the gas absorption cell.

[0028] The electrical unit 10 includes functional modules such as a power management unit 101 , a microprocessor 102 , a signal excitation unit 103 , a laser temperature control unit 104 , a filter and amplifier unit 105 , an ADC unit 106 and a communication unit.

[0029] The signal excitation unit 103 further includes functional modules such as a DC conversion unit 1031, a Sin signal excitation unit 1032, an adder 1033, and a laser driving circuit 1034. The DC conversion unit 1031 converts the PWM wave signal output by the microprocessor 102 into a DC signal; the Sin signal excitation unit 1032 outputs a sine wave signal; and the adder 1033, with its two inputs connected to the outputs of the DC conversion unit 1031 and the Sin signal excitation unit 1032, superimposes the DC signal and the sine wave signal, and outputs a DC sine wave tuning signal. This DC sine wave tuning signal is sent to the laser driving circuit 1034, driving the frequency sweep output of the laser 201.

[0030] In this embodiment, the DC conversion unit 1031 may adopt a dedicated PWM to analog voltage integrated circuit, or may construct a PWM to DC circuit by using components such as an operational amplifier and resistors and capacitors. Figure 2 Shown is a typical circuit example of the application-specific integrated circuit GP8101.

[0031] In this embodiment, the core processing unit of the sin signal excitation unit 1032 is the ICL 8038. The ICL 8038 is a precision oscillator integrated circuit with a variety of waveform outputs. By simply adjusting individual external components, it can generate low-distortion sine, triangle, and rectangular wave pulse signals ranging from 0.001 Hz to 300 kHz. The frequency and duty cycle of the output waveform can be controlled by current or resistance. The typical circuit of the ICL 8038 as a sin generator is shown in the figure below. Figure 3 shown.

[0032] The filter amplifier unit 105 and the ADC unit 106 constitute a signal receiving unit. The filter amplifier unit 105 and the ADC unit 106 are configured as needed. The filter amplifier unit 105 amplifies the received signal to the desired level to ensure data accuracy when input into the microprocessor. In specific applications, the ADC unit 106 can also be a built-in ADC unit of the microprocessor.

[0033] In this embodiment, the communication unit 107 is a serial port, which can communicate data between the device and an external PC. In other embodiments, the communication unit 108 can also use a communication module such as RS485 or CAN to communicate data with an external management device (such as a PC) via a bus and accept management from the external management device.

[0034] In this embodiment, the power management unit may include some power modules and circuits such as buck modules and LDO modules to convert external DC power or AC power into the operating voltage of the electrical unit 10, such as 3.3V, 5V, etc.

[0035] To ensure high reliability of the laser, the optical unit 20 also includes functional modules such as a semiconductor cooler 202 (TEC) and a thermistor 203. The semiconductor cooler 202 and the thermistor 203 constitute a constant temperature control circuit for the laser. The constant temperature control circuit is connected to the laser temperature control unit 104 in the electrical unit 10. The laser temperature control unit 104 adjusts the cooling intensity of the semiconductor cooler 202 according to the temperature value fed back by the thermistor 203, thereby providing a constant temperature working environment for the laser 201.

[0036] The light output by the laser 201 is projected into the gas absorption cell 204 and then into the photodetector 204. The gas in the gas absorption cell 204 (such as CO (carbon monoxide) and CO2 carbon dioxide) absorbs the laser light of the characteristic wavelength (frequency band), so that the electrical signal output by the photodetector 204 is sent to the microprocessor 102 after passing through the filter amplifier unit 105 and the ADC circuit unit 106 in the electrical unit 10 to read the signal waveform and identify whether the gas entering the gas washing basin contains carbon monoxide gas and / or carbon dioxide gas based on the waveform, and measure the concentration of carbon monoxide gas and carbon dioxide gas. Through absorption spectrum analysis, it can be obtained that CO and CO2 have independent absorption peaks, that is, the absorption wavelength corresponding to CO is different from the absorption wavelength of CO2. Therefore, the concentrations of CO and CO2 can be detected simultaneously in one detection, and there will be no interference between the two gases when they are measured simultaneously.

[0037] Microprocessor 102 includes a program-implemented automatic amplitude modulation unit and an FFT operation unit. The automatic amplitude modulation unit is used to execute an automatic amplitude modulation program, outputting a series of PWM signals with adjustable duty cycles. After passing through DC conversion unit 1031, these signals generate a series of DC sinusoidal tuning signals with varying DC offsets to modulate the laser wavelength, thereby achieving full coverage of the central wavelength of gas absorption. Those skilled in the art can easily implement the automatic amplitude modulation program based on given input and output conditions to implement the functions of this automatic amplitude modulation unit and output PWM signals with adjustable duty cycles. This technical solution does not involve improvements to the automatic amplitude modulation program; therefore, the automatic amplitude modulation unit can be considered a known functional module disclosed in the prior art. The FFT operation unit is used to execute an FFT-based signal processing method, converting time-domain signals into frequency-domain signals for spectral analysis. This method can effectively extract the spectral features required for gas concentration information, which can be used for filtering, denoising, and spectral feature extraction. This technical solution does not involve improvements to the FFT algorithm itself; therefore, the FFT operation unit can be considered a known functional module disclosed in the prior art.

[0038] The carbon oxide concentration measurement device can measure the carbon oxide concentration through FFT-WMS (Fast Fourier Transform-Wavelength Modulation Spectroscopy) technology. The detection principle of FFT-WMS technology is as follows: by changing the DC bias value, the transmitted light intensity is continuously FFT transformed to obtain the second harmonic value under different DC biases. Then, the discrete second harmonic peak is reconstructed to obtain a complete second harmonic-like waveform. Figure 4 Then, by analyzing the second harmonic waveform, the concentration information of gases such as CO and CO2 can be obtained.

[0039] Using a DC sine wave signal with adjustable DC bias instead of a triangular sine wave signal can reduce the impact of RAM (residual amplitude modulation effect) on the gas concentration test accuracy to a certain extent.

[0040] At the same time, the circuit of the electrical unit of the device is simpler and easier to integrate, which can achieve miniaturization of the product.

[0041] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, those skilled in the art should understand that various changes can be made to the form and details of the present invention without departing from the spirit and scope of the present invention as defined by the appended claims, and all of these changes are within the scope of protection of the present invention.

Claims

1. A device for measuring carbon oxide concentration based on TDLAS, characterized by: Including electrical unit and optical unit, The optical unit includes a tunable laser, an optical detector and a gas absorption cell; the laser light generated by the tunable laser is projected onto the optical detector after passing through the gas absorption cell; The electrical unit includes a microprocessor, a signal excitation unit and a signal receiving unit; The signal excitation unit is connected to the microprocessor to generate a DC sinusoidal wave tuning signal; The tunable laser is connected to the signal excitation unit and outputs laser light of a specific wavelength according to a DC sinusoidal wave tuning signal; The signal receiving unit is connected to the optical detector and performs filtering, amplification and analog-to-digital conversion on the received signal of the optical detector; The microprocessor is connected to the signal receiving unit and processes the received signal.

2. The carbon oxide concentration measuring device based on TDLAS according to claim 1, characterized in that: The microprocessor includes an automatic amplitude modulation unit and an FFT operation unit; the automatic amplitude modulation unit is used to output a series of PWM signals with adjustable duty cycles; the FFT operation unit is used for signal processing, converting the received time domain signal into a frequency domain signal for spectrum analysis; the signal excitation unit includes a DC conversion unit, a Sin signal excitation unit, an adder and a laser driving circuit; the DC conversion unit is used to convert the PWM signal output by the microprocessor into a DC signal; the Sin signal excitation unit is used to generate a sine wave signal; the adder is used to superimpose the DC signal and the sine wave signal to generate a DC sine wave tuning signal.

3. The carbon oxide concentration measuring device based on TDLAS according to claim 2, characterized in that: The DC conversion unit includes a PWM to analog voltage integrated circuit.

4. The carbon oxide concentration measuring device based on TDLAS according to claim 2, characterized in that: The Sin signal excitation unit includes a precision oscillation integrated circuit with a sinusoidal waveform output.

5. The carbon oxide concentration measuring device based on TDLAS according to claim 1, characterized in that: The optical unit also includes a semiconductor cooler and a thermistor, which are arranged close to the tunable laser to form a constant temperature control circuit for the tunable laser; the electrical unit also includes a laser temperature control unit, which is connected to the constant temperature control circuit.

6. The carbon oxide concentration measuring device based on TDLAS according to claim 1, characterized in that: The electrical unit further includes a communication unit, which is used for communication connection between the microprocessor and external devices.

7. The carbon oxide concentration measuring device based on TDLAS according to claim 1, characterized in that: The electrical unit further includes a power management unit, which is used to connect to an external power supply device to supply power to each functional module of the electrical unit.

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