CN106872401A - A kind of distributed infrared laser multi-parameter gas on-line detecting system - Google Patents

Abstract

The invention relates to a distributed infrared laser multi-parameter gas online detection system, which includes a light source drive module, a receiving optical fiber, an absorbing gas chamber, a sending optical fiber, a photoelectric conversion and a signal processing module; it also includes a plurality of laser light sources and a light source conversion These laser light sources have different central wavelengths, and the light source conversion module realizes the switching between different laser light sources so that only one laser light source emits light waves at the same time, which are collimated by a set of coupling lenses and then focused into the receiving optical fiber The receiving fiber is connected to one end of the absorbing gas chamber, and the other end of the absorbing gas chamber is connected to the sending fiber, and the light wave transmitted by the sending fiber is collimated by another group of coupling lenses and then output to the photoelectric conversion and signal processing module, so as to detect the second harmonic component of the measured gas and calculate the concentration of the measured gas. The solution solves the problems of long detection period and low efficiency in single parameter measurement in the prior art.

Description

A distributed infrared laser multi-parameter gas online detection system

technical field

The invention relates to the technical field of infrared laser spectroscopy, in particular to a distributed infrared laser multi-parameter gas online detection system.

Background technique

Metal smelting is essentially a circulation process of raw materials, fuels and finished products, and a large amount of gas is produced during the circulation. On-line detection and analysis of these process gases is an essential key technology for the optimization control of production processes, safety and environmental monitoring in the metallurgical industry One, it plays a very important role in reducing energy consumption and ensuring production safety.

In the traditional gas concentration measurement method, the principle of direct absorption measurement technology is to invert Unknown information such as gas concentration. This method is easy to judge the interference between spectral lines and various external noise interference, and can obtain the concentration signal results visually and intuitively. However, although gas chromatography has high sensitivity and reliability, errors may be introduced during the sampling process, thereby affecting the measurement accuracy. In order to achieve the best measurement effect, it is necessary to carry out multiple experiments and calculate the average value. The follow-up processing workload is heavy, and the analysis time is long, so it is difficult to realize online real-time detection.

Based on the absorption of specific wavelengths of light by gas molecules, and the intensity of absorbed light is proportional to the gas concentration, the distributed infrared gas laser online detection technology is currently a relatively advanced gas detection method at home and abroad. It has the advantages of high detection sensitivity, fast response, good selectivity, large detection range, good stability, etc., and is suitable for industrial control fields. However, the commonly used single-gas measurement equipment can only detect a single gas, and the online measurement of multi-parameter gases is a development trend.

Contents of the invention

The purpose of the present invention is to provide a distributed infrared laser multi-parameter gas online detection system, which can solve the problems of long detection period and low efficiency in single parameter measurement.

Technical scheme of the present invention is as follows:

A distributed infrared laser multi-parameter gas online detection system, which includes a light source drive module, a receiving optical fiber, an absorbing gas chamber, a sending optical fiber, a photoelectric conversion and a signal processing module; it also includes a plurality of laser light sources and a light source conversion module, these The laser light sources have different central wavelengths, and the light source conversion module realizes the switching between different laser light sources so that at the same time only one laser light source emits light waves that are collimated by a set of coupling lenses and then focused into the receiving optical fiber; the receiving optical fiber It is connected to one end of the absorbing gas chamber, and the other end of the absorbing gas chamber is connected to the sending optical fiber, and the light wave transmitted by the sending optical fiber is collimated by another set of coupling lenses and then output to the photoelectric conversion and signal processing module, thereby The second harmonic component of the measured gas is detected, and the concentration of the measured gas is calculated.

The present invention uses multiple light sources with different central wavelengths to realize on-line detection of various gas concentrations. Due to the switching and selection function of the source conversion module, the present invention only needs one set for the peripheral coupling lens and optical fiber, and for the peripheral absorbing gas chamber and Only one photoelectric conversion and signal processing module is needed, and it is time-division multiplexed, which not only realizes the online detection of multiple parameters, but also simplifies the system structure and reduces the system cost.

Further, the light source conversion module uses a flange to fix the multiple laser light sources, and the flange is driven by a motor to switch between different laser light sources by rotating a corresponding angle, and the absorption gas chamber is fixed to the measured on site.

Multiple laser light sources are installed in this way, which is easy to use and can withstand high pressure. The two ends of the absorption gas chamber are connected to the output end of the light source and the signal collection end through optical fibers, and the conversion of the flange plate is used to complete the adjustment of different laser light sources. The switching of the light source realizes the multi-parameter gas online detection.

Further, the laser light source adopts a tunable diode laser, and the light source drive module includes a signal generation circuit, a modulation circuit and a temperature control circuit, the signal generation circuit generates a triangular wave current that drives the laser light source to emit light, and the modulation circuit modulates The DC component of the triangular wave current makes the central wavelength of the light wave emitted by the laser light source just aligned with the absorption peak of the gas to be measured. The modulation circuit modulates the AC component of the triangular wave current so that the frequency scanning range of the light emitted by the laser light source just covers the measured gas. A certain absorption peak of the gas; the temperature control circuit performs constant temperature control on the laser light source.

According to the wavelength corresponding to the absorption peak of the measured gas, a distributed feedback semiconductor laser is selected as the light source, which has a good linear and tunable relationship, and the laser spectral line width is much smaller than the absorption line width, which can effectively avoid the influence of interference. The modulation circuit precisely modulates the amplitude and DC component of the triangular wave current, so that the measured gas has a strong absorption peak at the measurement line. Distinguished, and the cross-interference generated by other gases is small or even non-existent, thus improving the measurement accuracy.

Further, the laser light source includes three tunable diode lasers with central wavelengths of 1567nm, 1601nm and 1665nm.

This system uses three semiconductor lasers with different center wavelengths as light sources, which are used to detect carbon monoxide, carbon dioxide and methane gases produced in the metallurgical industry.

Further, the photoelectric conversion and signal processing module includes a photodetector, a preamplifier circuit, a harmonic detection circuit, a data acquisition circuit, and a DSP processor.

Using the principle of photoelectric effect to convert the input optical signal into an output electrical signal, the light from the absorption gas chamber contains gas information, which is converted into an electrical signal by a photodetector, and then processed by pre-amplification, and then processed by DSP data , detect the second harmonic component, perform calculation or processing, and complete signal analysis and display.

Further, the photodetector is made of TO-type InGaAs planar photodiode, which has low noise, high reliability and low price.

The invention proposes a method for realizing multi-parameter gas on-line detection by switching a plurality of laser light sources with different central wavelengths, which has a distributed structure, low cost, simple device and long service life. It can realize online real-time detection of carbon monoxide, carbon dioxide and methane produced in the production process of the metallurgical industry, overcoming the shortcomings of long detection period and low efficiency in single parameter measurement; The device has the advantages of distributed, easy installation and commissioning, low cost, and long service life.

Description of drawings

Fig. 1 is a structural schematic diagram of a distributed infrared laser multi-parameter gas online detection system of the present invention;

Fig. 2 is a schematic structural diagram of a light source conversion module in the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

A distributed infrared laser multi-parameter gas online detection system, as shown in Fig. A laser light source and a light source conversion module, these laser light sources have different central wavelengths, and the light source conversion module realizes the switching between different laser light sources so that the light waves emitted by only one laser light source are collimated by a group of coupling lenses 4 at the same time After focusing into the receiving optical fiber; the receiving optical fiber is connected to one end of the absorbing gas chamber 6, and the other end of the absorbing gas chamber 6 is connected to the sending optical fiber, and the light wave transmitted by the sending optical fiber is collimated by another group of coupling lenses 4 It is directly output to the photoelectric conversion and signal processing module, so as to detect the second harmonic component of the measured gas and calculate the concentration of the measured gas.

The light source conversion module uses a flange 2 to fix, connect and switch the multiple laser light sources. The light source conversion module uses a flange plate 2 to fix the multiple laser light sources, and the flange plate 2 is driven by a motor to realize switching between different laser light sources by rotating a corresponding angle, and the absorption gas chamber 6 is fixed on the measured on site. Taking three laser light sources 31, 32, 33 as an example, as shown in Figure 2, the laser light sources 31, 32, 33 are fixed on the flange plate 2 in equal arcs, driven by a motor, and the flange plate 2 only rotates for three minutes at a time. One of the radians, in one detection, switching three times can complete the detection of three gas parameters. When more laser light sources with different center wavelengths are designed, multi-parameter gas online detection can be realized. The three laser light sources used in the present invention reach a pressure of more than four kilograms, and the flange plate 2 adopts the form of a welding flange.

The absorption gas chamber 6 is fixed on the site to be tested. In the present invention, the laser light source part is separated from the absorbing gas chamber 6, and the absorbing gas chamber 6 is fixed on the metallurgical industry site. During detection, the two ends of the absorbing gas chamber 6 are connected to the output end of the laser generating part and the signal acquisition end through an optical fiber. connected with each other for on-line detection, so that the detection system is easy to carry, store and maintain, and reduces the cost.

During the detection work, the laser light source is switched through the flange 2 device, and under the action of the light source drive module 1, the light modulated into different central wavelengths is emitted, enters the receiving optical fiber 51 through the optical coupling lens 4, and reaches the absorbing optical fiber 51 through the receiving optical fiber 51. Air chamber6. When the light passes through the absorbing gas chamber 6, different gases absorb light intensities of different wavelength components, and then the optical signal carrying the gas absorption information is transmitted to the photoelectric conversion and signal processing module through the sending optical fiber 52 and converted into an electrical signal, which is detected after processing. The second harmonic component of the measured gas is used to calculate the concentration of the gas. The design uses optical fiber as the long-distance transmission medium of the laser, which is easy to multiplex, shortens the measurement cycle, and simplifies the measurement operation.

The selection of the absorption wavelength of the gas to be measured should meet the following principles: (1) The intensity of the absorption line can affect the minimum detection limit that the system can achieve, so there must be a strong absorption peak at the measurement line of the gas to be measured; (2) The laser manufacturing technology of the selected wavelength is relatively mature, cheap, and easy to implement; (3) The wavelength must be compatible with the wavelength required by the tunable diode laser and photodetector, so that the use of hardware and software can reach the best state; (4) ) at this wavelength, the intensity of the absorption line of the characteristic gas should be more prominent than that of other gases, and can be clearly distinguished from the intensity of other gases, and the cross-interference generated by other background gases should be small or even non-existent, so as to improve the measurement accuracy.

The laser light source adopts a tunable diode laser, and when it is used as a light source to detect a certain gas, three conditions need to be satisfied: (1) the wavelength at the selected absorption peak of the measured gas can be output; (2) it can be within the closed value range There is a good linear tunable relationship with the injection current; (3) The line width of the laser spectrum is much smaller than that of the absorption line.

The light source drive module 1 includes a signal generation circuit, a modulation circuit and a temperature control circuit. The signal generation circuit generates a triangular wave current that drives the laser light source to emit light. The modulation circuit makes the amplitude and DC component of the triangular wave current accurately adjustable. By modulating the triangular wave The current amplitude controls the center wavelength of the laser source. The triangular wave current is used to drive the light source to emit light. Precise modulation of the DC component of the triangular wave current can make the central wavelength of the light emitted by the tunable diode laser exactly aligned with the absorption peak of the measured gas, and precisely modulate the AC component of the triangular wave current. The frequency scanning range of the light emitted by the tunable diode laser can just cover a certain absorption peak of the measured gas. Since the wavelength drift of the tunable diode laser is serious due to the influence of temperature, a temperature control circuit is used to control the constant temperature of the tunable diode laser to make it work at a constant temperature.

Therefore, according to the above principles, by analyzing the gas absorption spectrum, in order to avoid the influence of interference, the absorption wavelengths of the three gases released in the metallurgical industry, carbon monoxide, carbon dioxide and methane, are selected: select 1567nm as the characteristic absorption of carbon monoxide (CO) Peak, choose 1601nm as carbon dioxide (CO2) characteristic absorption peak, choose 1665nm as methane (CH4) characteristic absorption peak. That is, the laser light source includes three tunable diode lasers emitting central wavelengths of 1567nm, 1601nm and 1665nm.

The photoelectric conversion and signal processing module includes a photodetector 7 , a preamplifier circuit 8 , a harmonic detection circuit 9 , a data acquisition circuit 10 and a DSP processor 11 . Among them, the photodetector 7 is an important component in the gas on-line detection system, and its performance is directly related to the performance of the entire system. The photoelectric effect principle is used to convert the input optical signal into an output electrical signal. The photodetector 7 used in the system should meet the following conditions: (1) match the light intensity and spectral characteristics passing through the gas absorption cell, and should match the preamplifier circuit; (2) the detector is linear in the working spectral range The accuracy is very good and the sensitivity is relatively high; (3) low price, fast response speed, long-term stable performance, wide response frequency bandwidth, and good dynamic characteristics; (4) the device's own noise is relatively low, and it is not affected by humid environment and external temperature. The fidelity performance and reliability of the signal are high. According to the above conditions and requirements, this invention selects the photodiode of TO type InGaAs planar structure produced by Beijing Minguang Technology Co., Ltd. Its response time is 40ns, and the spectral response range is 800-1700nm, which can meet the needs of this system. Its characteristics include: low noise, high reliability and low price. The light coming out of the gas chamber contains gas information, which is converted into an electrical signal by the photodetector 7, then pre-amplified, and then processed by DSP to detect the second harmonic component for calculation or processing to complete signal analysis and processing. show.

The operation mode when detecting gas is as follows:

Connect the laser light source and other parts with the absorption gas chamber 6 fixed on the metallurgical industry site through optical fibers. When the absorption gas chamber 6 does not contain the gas produced by the industrial process, turn the flange 2 to switch light sources with different central wavelengths. At this time The signal received by the photodetector 7 is a modulation signal of the light source without any distortion. At this time, the frequency spectrum calculated by the data acquisition and DSP processor 11 only has the first harmonic component of the detected gas corresponding to the light source, without the second harmonic component. When we open the valve and fill the industrial process gas into the absorption gas chamber 6, the signal received by the photodetector 7 is distorted, and the second harmonic component of the corresponding gas also appears in the spectrum diagram.

Claims (6)

1. A distributed infrared laser multi-parameter gas online detection system, comprising a light source drive module, a receiving optical fiber, an absorbing gas chamber, a sending optical fiber, a photoelectric conversion and a signal processing module, characterized in that it also includes a plurality of laser light sources and a light source A conversion module, these laser light sources have different central wavelengths, and the light source conversion module realizes the switching between different laser light sources so that at the same time only one laser light source emits light waves that are collimated by a set of coupling lenses and then focused to the receiving optical fiber Inside; the receiving fiber is connected to one end of the absorbing gas chamber, and the other end of the absorbing gas chamber is connected to the sending fiber, and the light wave transmitted by the sending fiber is collimated by another group of coupling lenses and then output to the photoelectric conversion and signal The processing module detects the second harmonic component of the measured gas and calculates the concentration of the measured gas. 2. A distributed infrared laser multi-parameter gas online detection system according to claim 1, characterized in that: the light source conversion module uses a flange to fix the multiple laser light sources, and the flange is mounted on the motor Switching between different laser light sources is realized by rotating corresponding angles under driving, and the absorption gas chamber is fixed on the site to be tested. 3. A distributed infrared laser multi-parameter gas online detection system according to claim 1 or 2, characterized in that: the laser light source is a tunable diode laser, and the light source drive module includes a signal generation circuit and a modulation circuit and a temperature control circuit, the signal generation circuit generates a triangular wave current that drives the laser light source to emit light, and the modulation circuit makes the central wavelength of the light wave emitted by the laser light source just aligned with the absorption peak of the gas to be measured by modulating the DC component of the triangular wave current, The modulation circuit modulates the AC component of the triangular wave current so that the frequency scanning range of the light emitted by the laser light source just covers a certain absorption peak of the measured gas; the temperature control circuit performs constant temperature control on the laser light source. 4. A distributed infrared laser multi-parameter gas on-line detection system according to claim 3, characterized in that: said laser light source includes three tunable diode lasers with emission center wavelengths of 1567nm, 1601nm and 1665nm. 5. A distributed infrared laser multi-parameter gas online detection system according to claim 4, characterized in that: the photoelectric conversion and signal processing module includes a photodetector, a preamplifier circuit, a harmonic detection circuit and a data Acquisition circuit and DSP processor. 6 . A distributed infrared laser multi-parameter gas on-line detection system according to claim 5 , wherein the photodetector is made of a TO-type InGaAs planar photodiode.