Laser gas analyzer

Abstract

Laser gas analyzer A laser gas analyzer 1 comprising a laser element 12; a modulated light generating unit (11); a light receiving element (20); a filtering unit; an analog-to-digital converter (114); a waveform analyzing unit (135); a subtraction circuit (115); and a measuring unit (130). Abstract: Fig. 2

Description

Description Title of the invention: Laser gas analyzer Background of the invention Scope of the invention The present invention relates to a laser gas analyzer, which analyzes the presence or absence and concentration of various types of gas to be measured in a space. Description of the related technique A laser gas analyzer uses a laser element to emit laser light at a specific absorption wavelength. This laser light is absorbed by the gas being measured, which consists of gas molecules. The gas absorbs the laser light, and the analyzer detects the presence or absence of the gas based on the amount of laser light absorbed at that wavelength. Furthermore, since the amount of laser light absorbed at the wavelength is proportional to the concentration of the gas being measured, the laser gas analyzer can also detect the concentration of the gas being measured. It is necessary to select only the specific gas to be measured from among the many gases present in the area being analyzed.Therefore, among the wavelengths of light absorption of the gas to be measured and other gases in the space to be measured, a wavelength of light absorption is selected, at which light is absorbed only by the gas to be measured, but is not absorbed by other gases. To measure trace gases, wavelength-modulated spectroscopy (WMSP) is generally used, as described, for example, in Japanese patent application No. 2012-177612. In WMSP, a wavelength is swept by a control current, a wavelength-variable laser light source emits laser light, which is modulated at a precise frequency. This laser light is detected by a photodetector, and a synchronous detection unit synchronously detects a signal with a frequency that is an integer multiple of the modulated frequency. Based on a correspondence, such as a proportionality relationship, between the concentration of the gas to be measured and the amplitude information of the synchronous detection waveform, it is possible to perform an arithmetic operation on the gas concentration. The detection signal, having a frequency that is an integer multiple of the modulated frequency, corresponds to the concentration of the gas being measured. The signal of detection is ideally a signal obtained only from absorption by the gas. However, due to the non-linearity of a laser diode or distortion in a signal processing circuit, an actual detection signal includes an unnecessary signal with a frequency that is the same as the frequency of the gas absorption signal. This unnecessary signal has no relation to the gas absorption signal. Therefore, among the detection signals, the gas absorption signal is relatively attenuated, which leads to a problem of insufficient resolution of the gas absorption signal and a problem of reduced measurement accuracy caused by this lack of resolution. In addition, in recent years there has been an increasing demand for trace gas analysis to provide a measurement in ppm units, which increasingly leads to a lack of resolution in a gas absorption signal. An object of the present invention, which was made to solve the problems mentioned above, is to provide a laser gas analyzer, in which the resolution in a detection signal and the measurement accuracy are increased by reducing the influence of a constituent that is not necessary. Summary of the invention According to one of its facets, the present invention relates to a laser gas analyzer, which performs an analysis of a gas to be measured, which is present in a space to be measured. The laser gas analyzer is characterized in that it comprises: a laser element configured to emit laser light in a wavelength band, which includes a wavelength of light absorption from an absorption line spectrum of the gas to be measured; a modulated light production unit, configured to supply a control current to the laser element, the control current being produced in such a way that a wavelength of the control current is swept and modulated repeatedly in the wavelength band, which includes the wavelength of light absorption from the absorption line spectrum of the gas to be measured; a light receiving element configured to receive the laser light, which passes into the object to be measured;a filtering unit configured to extract, from a detection signal output from the light receiving element, a frequency that is an integer multiple of a modulated frequency of the laser light, which is wavelength modulated; an analog-to-digital converter configured to transform from analog to digital a detection signal output from the filtering unit; a waveform analysis unit configured to calculate, using a portion of a detection signal, which is output from the analog-to-digital converter and which is yet to be subjected to sub-processing; traction, an amplitude information for a region which is not required, in which there is no absorption by the gas to be measured; a subtraction circuit, configured to perform the subtraction process of the amplitude information, for the region which is not required, from a detection signal output from the filtering unit; and a measurement unit configured to perform a gas analysis on the basis of a synchronous detection signal obtained by synchronous detection, at the frequency which is the integer multiple of the modulated frequency, from a detection signal which is output from the analog-to-digital converter, via the subtraction circuit and which has been subjected to the subtraction processing. According to one facet of the present invention, a digital-to-analog converter is provided between the waveform analysis unit and the subtraction circuit, the digital-to-analog converter being configured to transform from digital to analog the amplitude information for the region which is not needed, and the subtraction circuit performs a subtraction processing of the amplitude information, which is transformed from digital to analog. According to one facet, the present invention relates to a laser gas analyzer, which performs an analysis of a gas to be measured, which is present in a space to be measured, the laser gas analyzer being characterized in that it comprises: a laser element configured to emit laser light in a wavelength band, which includes a wavelength of light absorption from an absorption line spectrum of the gas to be measured; a modulated light production unit, configured to supply a control current to the laser element, the control current being produced, such that a wavelength of the control current is swept and modulated repeatedly in the wavelength band, which includes the wavelength of light absorption from the absorption line spectrum of the gas to be measured; a light receiving element configured to receive the laser light, which passes into the object to be measured;a filtering unit configured to extract, from a detection signal output from the light receiving element, a frequency that is an integer multiple of a modulated frequency of laser light, which is wavelength modulated; an analog-to-digital converter configured to convert from analog to digital a detection signal output from the filtering unit; a waveform analysis unit configured to calculate, using a portion of a detection signal output from the analog-to-digital converter that is yet to undergo subtraction processing, amplitude information for a region that is not required, in which there is no absorption by the gas to be measured; a subtraction circuit configured to perform the subtraction processing of the amplitude information, calculated by the waveform analysis unit, from the control current produced by the unit; modulated light production; and a measuring unit (130) configured to perform gas analysis on the basis of a synchronous detection signal obtained by synchronous detection, at the frequency which is the integer multiple of the modulated frequency, of a detection signal, which is output from the digital-to-analog converter and which has been subjected to subtraction processing. According to one facet of the present invention, a digital-to-analog converter is provided between the subtraction circuit and the laser element, the digital-to-analog converter being configured to convert the control current, which has been subjected to the subtraction processing by the subtraction circuit, from digital to analog; and the control current, which is transformed from digital to analog, is sent to the laser element. According to the present invention, a laser gas analyzer can be provided which can analyze a gas to be measured with high precision. Brief description of the drawings Fig. 1 is a schematic diagram of the overall configuration of a laser gas analyzer according to the present invention; Fig. 2 is a schematic of the signal processing block of the laser gas analyzer according to a first embodiment; Figure 3(A) is a conceptual view of the waveform of a control current and Figure 3(B) is a conceptual view of the waveform of the synchronous sensing signal; The [Fig.4] is a larger scale view of the synchronous detection signal; Figure 5 is a schematic of the waveform of a detection signal, before the detection signal is transformed from analog to digital in a conventional laser gas analyzer, Figure 5(A) representing a detection signal in the case where there is no absorption by the gas, Figure 5(B) being a conceptual view re- representing a part of Figure 5(A) on a larger scale, and Figure 5(C) re- representing a detection signal (no subtraction processing) in the case where there is absorption by the gas; Figure 6 represents a synchronous detection signal obtained by synchronous detection of the detection signal shown in Figure 5(C); Figure 7 represents a detection signal, before the detection signal is transformed from analog to digital in the laser gas analyzer according to the present embodiment, Figure 7(A) representing a detection signal in the case where there is no absorption by the gas, the detection signal having been subjected to the subtraction treatment and Figure 7(B) representing a detection signal in the case where there is absorption by the gas, the detection signal having been subjected to the subtraction treatment; The [Fig.8] represents a synchronous detection signal obtained by synchronous detection of the detection signal which has been subjected to the subtraction processing shown in Figure 7 (B); The [Fig.9] is a flowchart representing the signal processing flow performed by the laser gas analyzer according to the first embodiment; Figure 10 is a diagram of the signal processing block of a laser gas analyzer according to a second embodiment; and The [Fig.11] is a diagram representing the signal processing course performed by the laser gas analyzer according to the second embodiment. Detailed description of preferred embodiments A laser gas analyzer according to an embodiment of the present invention will be described in detail below, with reference to the accompanying drawings. The present invention is not limited to the following embodiments and can be carried out by appropriate modifications without departing from the scope of the present invention. Diagram of an overall configuration of a laser gas analyzer. Fig. 1 is a schematic diagram of the overall configuration of a laser gas analyzer according to an embodiment of the present invention. As shown in [Fig.1], a laser gas analyzer 1 comprises a light emission unit 10 and a light reception unit 20 and a communication line 40. The laser gas analyzer analyzes a gas to be measured that is present in a space to be measured. In the laser gas analyzer 1, the gas to be measured, which passes through a space inside walls 50a, 50b (a space to be measured), is exposed to laser light 30 emitted by the light-emitting unit 10, the walls 50a, 50b forming a passage for the gas. The laser light 30, passing through the gas to be measured, is incident on the light-receiving unit 20, so it is possible to obtain the concentration of a precise gas based on the amount of light detected. Furthermore, when the gas concentration is zero or equal to or less than a predetermined value, it is possible to detect that the gas is not present. It is therefore also possible to detect the presence or absence of the gas. The light-emitting unit 10 and the light-receiving unit 20 are removably attached to the walls 50a, 50b forming the gas conduit. The walls 50a, 50b are the walls of flues or similar conduits, in which a specific gas is present, and each of the walls 50a, 50b has a hole. Flanges 51a, 51b are attached to these holes by welding or similar means. Optical axis adjustment flanges 52a, 52b, provided on the light-emitting unit 10 and the light-receiving unit 20, are mechanically removably attached to these flanges 51a, 51b. The light-emitting unit 10 and the light-receiving unit 20 are arranged in facing positions with walls 50a, 50b interposed between them. However, the positions of the light-emitting unit 10 and the light-receiving unit 20 can be adjusted by the optical axis adjustment flanges 52a, 52b. The optical axis adjustment flange 52a can adjust the emission angle of the laser beam 30°. The optical axis adjustment flange 52b can adjust the incidence angle of the laser beam 30°. Due to the optical axis adjustment flanges 52a and 52b, a maximum amount of the laser beam 30° emitted by the light-emitting unit 10 is received by the light-receiving unit 20. Unit 10 of light emission. The light-emitting unit 10 will be described. As shown in [Fig. 1], the light-emitting unit 10 is configured to include a modulated light-producing unit 11, a laser element 12, a collimating lens 13, a window plate 14 for the light-emitting unit, a housing 15 for the light-emitting unit, and the optical axis adjustment flange 52a. As shown in [Fig. 1], the modulated light-producing unit 11, the laser element 12, and the collimating lens 13 are arranged within the housing 15 of the light-emitting unit. The housing 15 of the light-emitting unit isolates the respective components incorporated in a housing 15 of the light-emitting unit from the outside air, thus protecting the respective components from wind and rain, dust and dirt, pollution or the like. The modulated light production unit 11 generates a control current, which is generated so that the wavelength of the control current is repeatedly swept and modulated within a wavelength band that includes the absorption wavelength of the absorption line spectrum of the gas being measured. The modulated light production unit 11 supplies the laser element 12 with the control current to emit modulated laser light. With this type of configuration, gas concentration analysis can be performed by exposing the gas to wavelength-modulated light corresponding to a specific absorption characteristic of the gas being measured. The laser element 12 emits light at a central wavelength λ1, designated here by a spectrum of a precise absorption line, and at wavelengths around the central wavelength, the gas being measured absorbing the light. The laser element 12 variably controls an emission wavelength by controlling a control current and temperature. The laser element 12 is temperature-adjusted so that a central emission wavelength takes the central wavelength A1 of the line spectrum absorption of the gas to be measured. Furthermore, the laser light 30 emitted by the laser element 12 is controlled so that wavelengths around the central wavelength of the absorption line spectrum of the gas to be measured are swept over time by the control current supplied by the modulated light production unit 11. In addition, the laser light 30 is modulated by superimposing a suitable sine wave, so as to allow measurement with high sensitivity by wavelength modulation spectroscopy (WMS). Wavelength modulation spectroscopy is also referred to as 2f detection. The laser element 12 to be used is not limited in any particular way. However, the laser element 12 can be a DFB laser diode (deferred reaction laser diode), a VCSEL (vertical cavity surface emission laser) or a DBR laser diode (distributed Bragg refractor laser diode), for example. The collimating lens 13 is made of a material with a high transmission factor at the central wavelength λ1 of the absorption line spectrum of the gas to be measured and at wavelengths around the central λ1. The laser light 30 is transformed into substantially parallel light by the collimating lens 13 and can be transmitted to the light receiving unit, while a loss caused by scattering is eliminated. The light emission point of the laser element 12 is positioned near the focal point of the collimating lens 13. The light emitted by the laser element 12 is incident on the collimating lens 13 while scattering, thus being transformed into laser light 30, which is substantially parallel light. In this embodiment, the description assumes that the collimating lens 13 is used as the unit for transforming light into parallel. However, it should not be assumed that the unit for transforming light into parallel is limited to a collimating lens. For example, it is also possible to use a parabolic mirror as the unit for transforming light into parallel, instead of the collimating lens 13. The laser light 30, which is substantially parallel light, is transmitted through the window plate 14 of the light-emitting unit and propagates into a space within the walls 50a, 50b, i.e., a space in which gases, including the gas to be measured, are present. A hole is formed in a portion of the housing 15 of the light-emitting unit, and the window plate 14 of the light-emitting unit is provided to close this hole. The window plate 14 of the light-emitting unit is positioned in the optical path of the light 30 and prevents gases, including the precise gas to be measured, from entering the light-emitting unit 10, while allowing the laser light 30 to be transmitted through the window plate 14 of the light-emitting unit. By such a configuration, the respective components arranged in housing 15 of the light-emitting unit are prevented from coming into direct contact with the gas and thus it is possible to protect the respective components in housing 15 of the light-emitting unit. Light receiving unit. We will describe unit 20 of light reception. The light-receiving unit 20 is configured to include a light-receiving signal processing unit 21, a light-receiving element 22, a condenser lens 23, a light-receiving unit window plate 24, and a light-receiving unit housing 25. The light-receiving unit housing 25 contains the light-receiving element 22, optical components, and an electrical and electronic circuit. The light-receiving unit housing 25 isolates these components from the outside air, thus protecting them from wind and rain, dust and dirt, pollution, or the like. The light-receiving unit 20 receives the laser light 30, which passes through the window plate 24 of the light-receiving unit, and analyzes the light absorbed by the gas to be measured due to a light-absorption characteristic of the gas. A hole is formed in a portion of the housing 25 of the light-receiving unit, and the window plate 24 of the light-receiving unit is designed to close this hole. The window plate 24 of the light-receiving unit is positioned in the optical path of the laser light 30 and prevents gases, including the specific gas to be measured, from entering the light-receiving unit 20, while allowing the laser light 30 to pass through the window plate 24 of the light-receiving unit.By such a configuration, the respective components arranged in the light-receiving unit 20 are prevented from coming into direct contact with the gas, and thus it is possible to protect the respective components in the light-receiving unit 20. The light 30 is condensed by the condenser lens 23 and is incident on the light-receiving element 22. In the present embodiment, the condenser lens 23 is used. However, it is also possible to use a parabolic mirror, a doublet lens, a diffraction lens, or something similar, instead of the condenser lens 23. The light-receiving element 22 receives the laser light 30, which passes through the gas to be measured. As a light-receiving element 22, it is possible to select a light-receiving element having sensitivity to the central wavelength λ1 of the absorption line spectrum of the gas to be measured and to wavelengths around the central wavelength λ1. A light-receiving signal The light output from element 22 is transmitted to processing unit 21 as a light reception signal in the form of an electrical signal. The condensing lens 23 is made of a material with a high transmission factor at the central wavelength λ1 of the absorption line spectrum of the gas to be measured and at wavelengths around the central wavelength λ1. The laser light 30 is thus condensed onto the light-receiving element 22 by the condensing lens 23, and it is therefore possible to obtain a high signal intensity. The light reception signal processing unit 21 processes the electrical signal received by the light reception element 22 to calculate the gas concentration. The harmonic component of the frequency-modulated wavelength-modulated laser light 30 is detected by synchronous detection, and the amplitude information of the detected waveform is calculated, thus enabling highly sensitive gas detection. As shown in [Fig. 1], the communication line 40 is connected to the light-emitting unit 10 and the light-receiving unit 20. Communication between the light-emitting unit 10 and the light-receiving unit 20 is made via electrical signals. A communication unit for wireless communication, or optical communication, can be used instead of the communication line. Description of a block forming a laser gas analyzer according to a first embodiment The laser gas analyzer according to the first embodiment will be described below with reference to [Fig.2]. Figure 2 is a schematic diagram of the signal processing block of the laser gas analyzer 1 according to the first embodiment. The light emission unit 10 and the light reception unit 20 of the laser gas analyzer 1 shown in Figure 1 will be described in particular detail with reference to the block diagram shown in Figure 2. The modulated light production unit 11 and the light reception signal processing unit 21 of the laser gas analyzer 1 shown in Figure 1 will also be described. Although components that are usually included in the laser gas analyzer 1 are not shown in Figure 2, it is assumed that such components are present. As shown in [Fig. 2], the light-emitting unit 10 is configured to include the modulated light-producing unit 11, the laser element 12, and a laser element temperature control circuit 112. The modulated light-producing unit 11 is configured to include a wavelength-swept and modulated current-fixing unit 113 and a digital-to-analog converter 114. The wavelength-swept and modulated current-fixing unit 113 controls a control current for the laser element, such that the wavelength of the laser light 30 emitted by the laser element 12 is swept near an absorption line at the central wavelength λ1 of the absorption line spectrum of the gas to be measured and is modulated by a predetermined signal. Furthermore, a control method for the wavelength-swept and modulated current-fixing unit 113 is selected based on an instruction from a control unit 160 for the light-receiving unit 20. This is how, for example, the wavelength-swept and modulated current-fixing unit 113 is controlled so that a control current passes and is interrupted repeatedly, thus causing the laser light 30 to pass and be interrupted repeatedly.During such an operation, the wavelength is repeatedly scanned at a predetermined rate, at which the laser light passes. At this operating point, it is preferable that the modulated frequency, which is modulated by a sine wave, be set to a value higher than the wavelength scanning frequency. The digital-to-analog converter 114 transforms a digital signal into an analog signal. The analog-to-digital converter 114 therefore transforms a control current transmitted by the wavelength-swept and modulated current-fixing unit 113 and transmits the control current to the laser element 12. The laser element temperature control circuit 112 sets the output signal and wavelength of the laser element 12 to fixed values, thereby stabilizing both the output signal and wavelength. The output signal and wavelength of the laser element 12 fluctuate with temperature. Therefore, to prevent these fluctuations due to changes in ambient temperature, the laser element 12 is set to a fixed temperature by the laser element temperature control circuit 112. The laser element temperature control circuit 112 is controlled based on an instruction from the light receiver control unit 160. The laser element 12 emits laser light 30, while the wavelength is scanned and modulated by a sweep control current, so that the wavelength passes through the entire absorption line at the central wavelength A1 of the absorption line spectrum of the gas to be measured. The laser light 30 is modulated by superimposing a sine wave onto the control current. The light 30 shown in [Fig. 2] is partially absorbed by the gas being measured. The laser light 30, which is incident on the light-receiving element 22, is light that remains and is not absorbed by the gas being measured. This means that the laser light 30, which is incident on the light-receiving element 22 of the Light is transmitted light. The light-receiving element 22 is sensitive to the wavelength of the laser light 30. A photodiode, for example, can be appropriately selected as the light-receiving element 22, depending on the wavelength and intensity of the laser light 30 signal. There may be a case where the light-receiving element 22 also receives light emitted from a space containing gas, for example. Furthermore, if the light-receiving element 22 is a photodiode, a dark current is produced. To ensure that the fluctuation of the light-receiving signal, caused by the reception of light or a dark current, is sufficiently longer than the repeated scan period of the laser light 30, a short repeated scan period is chosen. As shown in [Fig. 2], the light reception signal processing unit 21 comprises a voltage converter circuit 122, a high-pass filter 123, a first amplifier circuit 124, a band-pass filter 125, a subtraction circuit 126, a second amplifier circuit 127, an analog-to-digital converter 128, a measurement unit 130, a waveform analysis unit 135, a digital-to-analog converter 150, and a control unit 160. The measurement unit 130 comprises a synchronous detection unit 131, a peak-to-ground arithmetic unit 133, and a gas concentration arithmetic correction unit 134. The peak-to-ground arithmetic unit 133 calculates, from the synchronous detection signal, a signal that corresponds to the gas concentration. The conversion circuit 122 IV is a circuit that converts a current signal output from the light-receiving element 22 into a voltage signal. When the light-receiving element 22 is a photodiode, it is possible, for example, to select a transimpedance amplifier, which amplifies a current signal output from the photodiode, while simultaneously converting the current signal into a voltage signal. In this case, provided that the laser light 30 is only slightly attenuated, i.e., provided that there is no dust or similar debris in the optical path, a signal can be appropriately amplified by an amplifier circuit not shown in the drawing, as long as the signal is not saturated. The high-pass filter 123 removes a DC component from the detection signal transmitted by the conversion circuit 122 IV. The detection signal transmitted by the conversion circuit 122 IV generally includes a DC component. This DC component is caused, for example, by light emitted from the space in which the gas is present. Furthermore, when the light-receiving element 22 is the photodiode, the DC component is also caused, for example, by a dark current produced in the photodiode. Even though these DC components fluctuate, their time constants are sufficiently longer than the period with which the laser light scan is repeated. This means that these DC components have a low frequency, and thus the DC components are eliminated by the high-pass filter, resulting in a waveform that passes through the 0 V reference voltage. For a repetition frequency (the inverse of the repetition period) at which the laser light 30 passes and is interrupted, and for the frequency of the scanning and wavelength modulation signal of the laser light 30, the cutoff frequency of the high-pass filter 123 is selected to allow the frequencies to fall within the bandwidth of the high-pass filter 123. It follows that the signal for passing and interrupting the laser light 30 and the signal for scanning and wavelength modulation of the laser light 30 pass through the high-pass filter 123 without being substantially altered. The purpose of placing the high-pass filter 123 immediately downstream of the conversion circuit 122 IV is as follows. If a signal is amplified into a DC signal by the first amplifier circuit 124, as described below, and the measurement conditions are less than ideal—for example, if the light emitted from the space containing the gas is very intense, resulting in a large dark current and a low light transmission factor (30), then the gas absorption signal, which is effective for measurement, is significantly attenuated, thus reducing the detection sensitivity. To prevent such a situation, the high-pass filter 123 is placed immediately downstream of the conversion circuit 122 IV to remove the DC component beforehand. The waveform of a signal output from the 123 high-pass filter primarily comprises a signal for passing and stopping the 30 laser light and a signal for scanning and modulating the wavelength of the 30 laser light. The 30 laser light is scattered and attenuated due to fluctuations in the amount of dust present in the space where gas is present, for example. Consequently, among these signals, the waveform for scanning and modulating the wavelength fluctuates as the 30 laser light passes. This fluctuation, caused by the scattering and attenuation of the scanning and modulating signal, is independent of the wavelength within the range in which the 30 laser light is scanned and modulated, and the signal passes through the 123 high-pass filter.The first circuit 124 amplifier amplifies the detection signal which passes through the high-pass filter 123, with an amplification factor. appropriate, which ensures that the detection signal is not saturated. The 125 bandpass filter forms a filtering unit that extracts, from the detection signal output by the light receiving element 22, a frequency that is an integer multiple of the modulated frequency of the wavelength-modulated laser light 30. The 125 bandpass filter extracts a signal having a frequency that is, for example, twice as high as the modulated frequency (hereafter referred to as "signal 2f"). In the wavelength modulation process, the gas concentration is detected using a signal that is an integer multiple of a modulation signal, as the gas absorption signal. As described above, the 2f signal is used, for example. However, this signal is significantly smaller than the wavelength modulation and scanning signal of the laser light. Therefore, the 2f signal can be extracted by the 125 bandpass filter and amplified by an appropriate amplification factor by the amplifier circuit without saturating the signal. Consequently, after converting the 2f signal into a digital signal, it can be used to detect the gas concentration with high accuracy. The second amplifier circuit 127 amplifies the detection signal output from the bandpass filter 125 with an appropriate amplification factor without saturating the signal. As described below, in this embodiment, an unnecessary component is removed by the subtraction circuit 126 from the detection signal output from the bandpass filter 125. Before removing the unnecessary component, it has a high signal intensity, and therefore, a process is performed to fix the amplification factor to a small value to prevent overshoot. After removing the unnecessary component, a process is performed to adjust the amplification factor to a high value to transmit the gas absorption signal to the analog-to-digital converter 128, after increasing the signal intensity as much as possible.An amplification process is controlled by the control unit 160. The analog-to-digital converter 128 converts the detection signal output from the bandpass filter 125. The analog-to-digital converter 128 converts an analog signal transmitted from the second amplifier circuit 127 into a digital signal. As shown in [Fig. 2], there is a branch from the analog-to-digital converter 128 into two, i.e., into the synchronous detection unit 131 and the waveform analysis unit 135, so as to transmit the digital signal to either the synchronous detection unit 131 or the waveform analysis unit 135. The analog-to-digital converter 128 appropriately selects an element with a sampling rate, which This allows for sufficient detection of a modulation component. For example, if the laser's modulation component is 50 kHz, a frequency component of 100 kHz, twice the frequency of 50 kHz, is detected in the 2f detection method. To ensure sufficient detection of these frequency components, an analog-to-digital converter with a sampling rate of 1 MHz or higher is chosen. The waveform analysis unit 135 calculates amplitude information (an unnecessary component) for a region where there is no absorption by the gas being measured, using a portion of the detection signal output from the analog-to-digital converter 128. The waveform analysis unit 135 transmits to the analog-to-digital converter 150 a signal whose phase and frequency are synchronized with the phase and frequency of the signal 2f, which corresponds to the calculated amplitude information. The digital-to-analog converter 150 is positioned between the waveform analysis unit 135 and the subtraction circuit 126. The digital-to-analog converter converts the output signal from the waveform analysis unit 135. In this configuration, the digital-to-analog converter 150 converts the amplitude information for an unnecessary region, calculated by the waveform analysis unit 135, from digital to analog and transmits this amplitude information to the subtraction circuit 126. The subtraction circuit 126 performs a subtraction of the amplitude information for the unnecessary region, calculated by the waveform analysis unit 135, from the detection signal output of the bandpass filter 125. As described above, based on the result of the waveform analysis unit 135's calculation, a signal corresponding to the amplitude information for the unnecessary region, in which there is no absorption by the gas being measured, is removed. It is therefore possible to reduce the signal intensity of the unnecessary component to a level less than or equal to that of a gas absorption signal. The synchronous detection unit 131 performs phase detection (synchronous detection) at a frequency twice as high as the modulated frequency set by the wavelength-swept current-modulated unit 131, the modulation frequency being included by the signal output from the second amplifier circuit 127. Peak-to-bottom arithmetic unit 133 performs an arithmetic operation on a peak and a bottom of the synchronous detection signal, the peak and bottom being necessary to calculate a signal that corresponds to the gas concentration. Gas concentration arithmetic correction unit 134 performs detection processing, arithmetic processing, and gas concentration correction processing based on the signal processed by synchronous detection unit 131 and unit 133. peak-bottom arithmetic. The processing carried out by unit 134 for arithmetic correction of the gas concentration is controlled by the control unit 160. Based on information about the gas to be measured, the control unit 160 controls the wavelength-swept and modulated current-fixing unit 113, the laser element temperature adjustment circuit 112, the second amplifier circuit 127, the waveform analysis unit 135, the synchronous detection unit 131, and the arithmetic gas concentration correction unit 134. Arithmetic processing for gas analysis Figure 3(A) is a conceptual view of the waveform of a control current αl, and Figure 3(B) is a conceptual view of the waveform of a synchronous detection signal β1. The control current αl, shown in Figure 3(A), is generated by the modulated light production unit 11, such that the wavelength of the control current αl is swept and modulated repeatedly in a band of length that includes the central wavelength α1 of the absorption line spectrum of the gas to be measured. Figure 3(B) corresponds to a waveform after detection is performed by the synchronous detection unit 131, shown in [Fig. 2]. Figure 4 is a larger-scale view of the synchronous detection signal b1 from Figure 3(B). It is desirable that the synchronous detection signal b1 have a waveform with extreme values ​​based on the absorption line of the component of the gas to be measured, as shown in Figure 3(B) and Figure 4. A difference D in signal intensity of the synchronous detection signal bl, shown in [Fig. 4], between the background and the peak, correlates with the gas concentration. Consequently, by performing a calibration with a standardized gas fixed at each concentration in advance, it is possible to measure the gas concentration by detecting the difference D. Problems in classical technique In a gas analysis of the gas to be measured, a detection signal (signal 2f) having a frequency that is an integer multiple of the modulated frequency corresponds to the concentration of the gas to be measured. Ideally, the detection signal (signal 2f) is a signal obtained solely by absorption by the gas to be measured. However, in real-world analysis, due to the nonlinearity of a laser diode and distortion in a signal processing circuit, a detection signal (signal 2f) includes an unnecessary signal 2f (unnecessary component) having a frequency that is the same as the frequency of the gas absorption signal. This unnecessary signal 2f has a relationship to the gas absorption signal. When this unnecessary component is larger than the gas absorption signal, an amplification factor for the amplifier circuit is applied. determined at a level at which the unnecessary component is not saturated, and thus the gas absorption signal is relatively attenuated. Figure 5 is a waveform diagram of a detection signal before the absorption signal is converted from analog to digital in a conventional laser gas analyzer. Figure 5(A) represents a detection signal in the case where there is no absorption by the gas, and Figure 5(B) is a conceptual view showing a portion of Figure 5(A) enlarged. Unlike the configuration of the present embodiment shown in [Fig. 2], the conventional laser gas analyzer does not include the subtraction circuit 126 or the waveform analysis unit 135, so that a detection signal from the bandpass filter 125, shown in [Fig. 2], is transmitted directly to the synchronous detection unit 131 via the analog-to-digital converter 128. In the case where the laser light 30 is not absorbed by the gas, a detection signal (signal 2f) from the bandpass filter 125 is not produced, and thus, the signal intensity is ideally zero. However, in actual operation, an unnecessary signal 2f, unrelated to the gas absorption signal, is present, as shown in Figure 5(A) and Figure 5(B). Figure 5(C) is a waveform diagram of a conventional detection signal, in the case where the laser light is absorbed by the gas. A region represented by (I) in Figure 5(C) shows a signal in a region where the laser light is absorbed by the gas to be measured. Conversely, regions represented by (II) in Figure 5(C) are signals in regions that are not needed, where there is no absorption by the gas. When a signal from gas absorption is smaller than the signal in the region that is not needed, a detection signal has a shape represented in the diagram in Figure 5(C), and an amplification factor for the second amplifier circuit, before the signal enters the analog-to-digital converter, is set at a level at which the signals in the regions that are not needed are not saturated.This is why the gas absorption signal cannot be amplified sufficiently. Figure 6 represents a conventional synchronous detection signal, after the signal has been synchronously detected. As shown in Figure 6, in the synchronous detection signal, the difference D in signal intensity is relatively small in a region where there is gas absorption, the region being represented by (IIT). Therefore, a problem arises: sufficient resolution cannot be achieved in the gas absorption signal, which reduces the measurement accuracy. In view of the above, in the present embodiment, as shown in [Fig. 2], the waveform analysis unit 135 and the circuit 126 of Subtractions are performed downstream of the bandpass filter 125. The waveform analysis unit 135 calculates amplitude information for unnecessary regions where there is no gas absorption, and the subtraction circuit 126 subtracts this amplitude information for the unnecessary regions from the detection signal output by the bandpass filter 125. Through operations of this kind, a control is applied so that the amplitude information for the unnecessary regions is attenuated to a level less than or equal to the gas absorption signal. By proceeding in this way, it is possible to perform a gas analysis of the gas to be measured with high precision. Subtraction processing in this embodiment In the present embodiment, as shown in [Fig.2], when a detection signal from the bandpass filter 125 passes through the subtraction circuit 126 without being subjected to the subtraction process, the detection signal is converted from analog to digital by the analog-to-digital converter 128 and then is transmitted to the waveform analysis unit 135. In this case, where there is absorption by the gas, the waveform diagram of the detection signal, which is still to be processed by the subtraction and which comes out of the bandpass filter 125, is essentially the same as the waveform diagram shown in Figure 5(C), for example. As described above, the region represented by (I) in Figure S(C) represents a signal in a region where there is absorption by the gas, and the region represented by (IT) represents signals in regions where there is no absorption by the gas. The waveform analysis unit 135 calculates amplitude information for the regions where there is no absorption, represented by (IT) in Figure 5(C), and the digital-to-analog converter 150 outputs a signal with a phase and frequency synchronized with the phase and frequency of the signal 2f, which corresponds to the amplitude information.The subtraction circuit 126, shown in [Fig.2], subtracts the output signal from the digital-to-analog converter 150 from the output signal from the bandpass filter 125, thereby removing the amplitude information for the regions that are not needed, represented by (II) in Figure 5(C). Figure 7 is a waveform diagram of a detection signal before the detection signal is converted from analog to digital in the laser gas analyzer according to this embodiment. Figure 7(A) represents a detection signal in the case where there is no absorption by the gas, the detection signal having undergone subtraction processing, and Figure 7(B) represents a detection signal in the case where there is absorption by the gas, the detection signal having undergone subtraction processing. As shown in Figure 7(A), the unnecessary component is removed of the signal from the 125 bandpass filter, and in the case where there is no absorption by the gas, the intensity of the signal is therefore sufficiently reduced, that is to say that it is essentially zero, before transforming the signal from analog to digital. In contrast, Figure 7(B) represents the signal intensity in the case of gas absorption. The unnecessary component has been subjected to subtraction processing, making it possible to sufficiently amplify a gas absorption signal as long as the signal is not saturated. As will be clearly understood by comparing it with Figure 5(C), it is possible to obtain a detection signal with extreme values. Figure 8 represents a synchronous detection signal obtained by synchronous detection of the detection signal that has undergone subtraction processing, the detection signal being shown in Figure 7(B). The synchronous detection signal obtained in this embodiment can exhibit a difference D in signal intensity compared to a conventional example shown in Figure 6. Such a large difference D can be obtained, thus enabling high resolution in the gas absorption signal and increasing the accuracy of the gas analysis. A component that is not necessary We will now describe amplitude information (a component that is not necessary) for regions that are not needed, in which there is no absorption by the gas, regions that are not needed being represented by (LI) in Figure 5(C). In this embodiment, before performing a gas analysis, for example, when a setting is made in a factory, before an analyzer is sent, a laser control current is set in the length-swept and modulated current-setting unit 113, and a setting value for the laser element temperature control circuit 112 is set using a gas (standardized gas), which is the object to be measured, such that a gas absorption waveform is produced substantially at a central position in the laser scanning portion. Thus, a region (time domain) in which the gas absorption waveform is present and a region in which the gas absorption waveform is not present in the scanning portion (pre-determined scanning time period) are stored in the control unit 160.To perform, for example, a wavelength-sweeping and modulated current adjustment and to set a temperature based on the output results of the components, from unit 131 of synchronous detection to unit 134 of arithmetic correction of gas concentration, information from unit 131 of synchronous detection and unit 134 of arithmetic correction of gas concentration is collected at unit 130 of. command and information on the component which is not needed can be transmitted from the control unit 160 to the waveform analysis unit 135. Description of a flowchart in which a laser gas analyzer is used according to the first embodiment Figure 9 is a flowchart in which the laser gas analyzer is used according to the first embodiment. As shown in stage SO1 in Figure 9, the modulated light production unit 11 generates a control current. The modulated light production unit 11 sends the control current to the laser element 12, the control current being generated such that the wavelength of the control current is swept and modulated repeatedly in a wavelength band that includes the central wavelength Δ1 of the absorption line spectrum of the gas to be measured. The unit 113 for fixing the swept wavelength and modulated current, forming the unit 11 for producing modulated light, selects a method for controlling the unit 113 for fixing the swept wavelength and modulated current and the circuit 112 for adjusting the temperature of the laser element, based on an instruction from the control unit 160.An example of the control current is shown in Figure 3(A). The digital-to-analog converter 114, shown in [Fig.2], transforms a digital signal transmitted by the wavelength-swept current-fixing unit 113 into an analog signal, and transmits the analog signal to the laser element 12. Next, as shown in stages S02 and S03 of [Fig. 9], the laser element 12 emits laser light 30 in the wavelength band that includes the central wavelength Å1 of the absorption line spectrum of the gas to be measured, and the light-receiving element 22 receives the laser light 30, which passes through a space to be measured, the gas being present in the space to be measured. The conversion circuit 122, the high-pass filter 123, and the first amplifier circuit 124 perform signal processing on the signal received by the light-receiving element 22, and the signal is then transmitted to the band-pass filter 125. As shown in stage SO4 of [Fig.9], the 125 bandpass filter extracts a signal (signal 2f) having a frequency that is an integer multiple of the modulated frequency, for example a signal having a frequency twice as high as the modulated frequency. As shown in stage S05 of [Fig.9], the analog-to-digital converter 128, shown in [Fig.2], converts the signal 2f from the bandpass filter 125 from analog to digital. Next, as shown in stage S06 of [Fig.9], the process branches depending on whether or not the detection signal is transformed from analog to digital in stage S05 has undergone a subtraction operation. This means that, as shown in [Fig. 2], the subtraction circuit 126 is located upstream of the analog-to-digital converter 128. If a predetermined subtraction operation has been performed by the subtraction circuit 126 (after subtraction [OUT]), the process proceeds to stage S09. Conversely, if the predetermined subtraction operation has not been performed by the subtraction circuit 126 (before subtraction [NOT]), the process proceeds to stage S07. At stage S07, the waveform analysis unit 135 calculates amplitude information for regions that are not required, where there is no absorption by the gas being measured. This means that at stage S07, the waveform analysis unit 135 calculates amplitude information for the region that is not required, where there is no absorption by the gas being measured, using a portion of the detection signal output from the bandpass filter 125. As previously described, in this embodiment, the regions that are not required, represented by (II) in Figure 5(C), are selected in advance, thus enabling the calculation of amplitude information for these regions. The 150 digital-to-analog converter converts the amplitude information signal for the region that is not needed, the amplitude information, which is calculated by the waveform analysis unit 135, and the 150 digital-to-analog converter transmits the signal to the subtraction circuit 126. In stage 508 shown in [Fig. 9], the subtraction circuit 126 performs a subtraction operation, in which it subtracts the amplitude information, calculated by the waveform analysis unit 135, from the signal 2f output of the bandpass filter 125 in stage S04. Through this operation, it is possible to reduce the intensity of the amplitude information signal in the detection signal output from the bandpass filter 125, in the region where there is no gas absorption, to a level lower than or equal to the gas absorption signal. This makes it possible to obtain a detection signal shown in Figure 7(B), for example. After performing the subtraction processing, the process returns to S05, where the detection signal that underwent the subtraction processing is converted from analog to digital, and the process then proceeds to stage S06. At stage S06, it is determined that the signal has undergone the subtraction processing, and therefore the process proceeds to stage S09. At stage S09, the measuring unit 130, shown in [Fig. 2], performs an arithmetic operation to concentrate the detection signal output from the bandpass filter 125. Note that the control unit 160 can variably change the amplification factor setting of the second amplifier circuit depending on the subtraction processing. traction was either performed or it wasn't. Diagram of the block forming the laser gas analyzer of the second implementation mode Figure 10 shows the signal processing block diagram of a laser gas analyzer according to a second embodiment used to carry out the present invention. The following description will only describe those parts that make the second embodiment different from the first embodiment. As shown in [Fig. 10], a subtraction circuit 115 is provided between the wavelength-swept and modulated current-fixing unit 113 and the laser element 12. The subtraction circuit 115 performs a subtraction operation, in which the amplitude information, which is calculated by waveform analysis 135, is subtracted from the control current signal output from the wavelength-swept and modulated current-fixing unit 113. The digital-to-analog converter 114 is located between the subtraction circuit 115 and the laser element 12. The signal that has undergone subtraction processing by the subtraction circuit 115 is converted from digital to analog by the digital-to-analog converter 114. The converted digital-to-analog signal is then transmitted to the laser element 12. In the second embodiment, a signal corresponding to data obtained by the waveform analysis unit 135 is transmitted to the light emission unit 10, and the subtraction circuit 115 subtracts the signal from a signal output by the wavelength-swept and modulated current-fixing unit 113, so that an unnecessary component is removed from the light emission unit 10. Other detection operations and signals to be obtained correspond mainly to the operations and corresponding signals obtained in the first embodiment. In the laser gas analyzer according to the first embodiment, the subtraction processing is performed in the light-receiving unit 20, and therefore there is little influence from noise or similar factors on the transmission path, thus allowing for the detection of the gas concentration to be measured with high precision. In contrast, in the laser gas analyzer 2 of the second embodiment, unlike the first embodiment, the light-receiving unit 20 does not require the digital-to-analog converter 150, and it is possible to perform the subtraction operation by digital signal processing carried out by a microcomputer, FPGA, or similar device, mounted in advance on the light-emitting unit 10. Consequently, fewer parts are required, and this is why the laser gas analyzer 2 of the second embodiment has an advantage in terms of scale. circuit. Figure 11 is a flowchart of the signal processing performed by the laser gas analyzer according to the second embodiment. The following description will only describe those parts that distinguish the second embodiment from the first. In the second embodiment, after stage S07 is performed, the subtraction circuit 115 carries out a subtraction operation, removing amplitude information (an unnecessary component), as calculated by the waveform analysis unit 135, from the control current signal output from the wavelength-swept current-fixing unit 113, which was modulated in the SOI stage (stage S10). In such an operation, amplitude information (an unnecessary component) is removed for a region where there is no gas absorption from the control current signal output from the wavelength-swept current-fixing unit 113, which was modulated. Furthermore, the digital-to-analog converter 114 converts the signal that underwent the subtraction operation by the subtraction circuit 115. The process then proceeds to stage S02. The signal, converted from digital to analog, is transmitted to the laser element 12, and the process proceeds to stage SO2. It then progresses from stage SO2 to stage SO9, passing through stage SO6, and the concentration of a specific gas within the gas being measured is analyzed. It should be noted that the control unit 160 can variably adjust the amplification factor setting of the second amplifier circuit 127, depending on whether the subtraction processing has been performed. The laser gas analyzer according to the present invention is optimal for measuring combustion exhaust gases or for controlling combustion in a boiler or waste incineration plant, for example. Furthermore, the laser gas analyzer according to the present invention is preferably used as an analyzer for gases used in iron and steel (blast furnaces, converter furnaces, heat treatment furnaces, sintering, pelletizing devices, coke ovens (for storing and ripening fruits and vegetables)), in biochemistry (microorganisms) by fermentation, for air pollution (incinerators, flue gases, desulfurization / denitrification (for exhaust gases from internal combustion engines of automobiles), ships or the like (disposal of a testing device)), for disaster prevention (detection of explosive gases, detection of toxic gases, analysis of combustion gases from new building materials).for growing plants, for chemical analysis (oil refineries, petroleum chemistry plants, gas production plants), for environmental concentration (baseline level), concentration in tunnels, in parking lots, building management and for, various experiments in physics and chemistry, for example. List of reference points 1 laser gas analyzer 2 laser gas analyzers 10 units of light emission 11 units for producing modulated light 12 laser elements 13 collimation lens 14 Light Emitting Unit Window Plate 15. Light-emitting unit housing 20 light receiving unit 21 light signal processing unit 22 light receiving element 23 condenser lens 24 light receiving unit window plate 25 Light receiving unit housing 30 laser lights 40 communication lines 50a, 50b wall 51a, 51b flange 52a, 52b optical axis adjustment flange 112 Laser element temperature control circuit 113 Wavelength-swept and modulated current fixing unit 114 digital to analog converter 115 subtraction circuit 122 Conversion Circuit IV 123 high-pass filter 124 amplifier circuit 125 bandpass filter 126 subtraction circuit 127 amplifier circuit 128 analog-to-digital converter 131 synchronous detection circuit 132 detection frequency fixing unit 133 arithmetic unit of peak — bottom 134 arithmetic correction unit for gas concentration 135 units of waveform analysis 150 digital-to-analog converter order number

Claims

Demands

1. Laser gas analyzer (1), which performs an analysis of a gas at to measure, which is present in a space to be measured, the gas analyzer (1) laser is characterized in that it comprises: a laser element (12) configured to emit laser light into a band of wavelength, which includes a wavelength light absorption of a gas absorption line spectrum measure, a modulated light production unit (11), configured for supply a control current to the laser element (12), the current of order being produced, in such a way that a wavelength of the control current is swept and modulated repeatedly in the wavelength band, which includes the absorption length of the light from the absorption line spectrum of the gas to be measured; a light receiving element (20) configured to receive the laser light, which passes through the object to be measured; a filtering unit configured to extract, from a detection signal exiting the light receiving element (22), a frequency, which is an integer multiple of a modulated light frequency laser, which is wavelength modulated; an analog-to-digital converter (114) configured for converting an analog detection signal from analog to digital the filtering unit; a waveform analysis unit (135) configured to calculate, in using a portion of a detection signal, which is output from the analog-to-digital converter (114) which is still at to subject to a subtraction process, information of amplitude for a region that is not needed, in which there is no absorption by the gas to be measured; a subtraction circuit (115), configured to perform the process of subtraction of amplitude information, for the region that is not necessary, from a detection signal output by the filtering unit; and a measuring unit (130) configured to perform a gas analysis based on a synchronous detection signal obtained by detection synchronous, at the frequency which is the integer multiple of the frequency modulated, of a detection signal that came out of the analog-to-digital converter, via the circuit (126) of subtraction and which has been subjected to the subtraction treatment.

2. Laser gas analyzer (1) according to claim 1, characterized in that a digital-to-analog converter (150) is planned between the waveform analysis unit (135) and the sub-circuit (126) traction, the digital-to-analog converter (150) being configured to convert digital information into analog of amplitude for the region that is not needed, and The subtraction circuit (126) performs a subtraction operation of the amplitude information, which is transformed from digital to analog.

3. Laser gas analyzer (1), which performs an analysis of a gas at to measure, which is present in a space to be measured, the gas analyzer (1) laser being characterized in that it comprises: a laser element (12) configured to emit laser light in a wavelength band, which includes a wavelength light absorption of a gas absorption line spectrum measure; a modulated light production unit (11), configured for supply a control current to the laser element (12), the current of order being produced, in such a way that a wavelength of the control current is swept and modulated repeatedly in the wavelength band, which includes the absorption length of the light from the absorption line spectrum of the gas to be measured; a light receiving element (20) configured to receive the laser light, which passes through the object to be measured; a filtering unit configured to extract, from a detection signal exiting the light-receiving element (22), a frequency which is an integer multiple of a modulated frequency of laser light, which is modulated in wavelength; an analog-to-digital converter (114) configured for converting an analog detection signal from analog to digital the filtering unit; a waveform analysis unit (135) configured to calculate, in using a portion of a detection signal, which is output from the analog-to-digital converter (114) which is still subjected to a subtraction process, information of amplitude for a region that is not needed, in which there is no absorption by the gas to be measured; a subtraction circuit (126) configured to perform the processing of subtraction of amplitude information, calculated by the unit (135) waveform analysis of the control current produced by the unit (11) modulated light production; and a measuring unit (130) configured to perform a gas analysis based on a synchronous detection signal obtained by detection synchronous, at the frequency which is the integer multiple of the frequency modulated, of a detection signal that came out of the digital-to-analog converter (150) which has been subjected to subtraction process. [Claim: Laser gas analyzer (1) according to claim 3, characterized in that that a digital-to-analog converter is planned between the circuit {115) of subtraction and the laser element (12), the converter (150) of digital to analog being configured to convert digital in analog the control current, which has been subjected to processing subtraction by the subtraction circuit (126); and the control current, which is transformed from digital to analog, is sent to the laser element (12).