Laser gas analyzer

Abstract

Laser gas analyzer. Gas analyzer 1 comprising a light-emitting unit 10 having a laser element 12 for emitting laser light 30, a light-receiving unit 20, communication between the light-emitting element 10 and the light-receiving element 20 being effected by laser light 30. Figure for abbreviation: Fig. 1

Description

Title of the invention: Laser gas analyzer

[0001] Background of the invention Field of invention

[0002] The present invention relates to a laser gas analyzer, which analyzes the presence or absence and concentration of various types of gases to be measured in a space.

[0003] Description of the related art

[0004] A laser gas analyzer uses a laser element of a light emitting unit to emit laser light of a light absorption wavelength at which the laser light is absorbed by a gas to be measured, which consists of gas molecules of gas, causing the gas to be measured to absorb the laser light, and performs gas analysis of the gas to be measured by the light receiving unit, based on the absorption amount of the laser light at the light absorption wavelength.

[0005] As described in Japanese Patent Application Laid-Open No. 2017-106742 (Patent Document 1), for example, wavelength modulation spectroscopy is generally used for analysis of the gas to be measured. That is, according to Patent Document 1, laser light, which has a wavelength swept by a driving current and is modulated at a specific frequency, is emitted from a variable-wavelength laser light source, the laser light is detected by a photodetector, and a synchronous amplifier synchronously detects a signal having a frequency that is the integer multiple of the modulated frequency. Based on a correspondence (proportional relationship or the like) between the concentration of the gas to be measured and the amplitude of the waveform of the synchronous detection, it is possible to perform an arithmetic operation for the concentration of the gas.

[0006] The light-emitting unit and the light-receiving unit are connected to each other by a communication line for signal synchronization or for exchanging setting values. However, at an actual installation site, there may be cases in which the diameter of a duct is several meters. Therefore, an extremely long cable is required for the communication line, which connects the light-emitting unit and the light-receiving unit to each other. Furthermore, the laser gas analyzer is mounted outdoors, and therefore it is necessary to eliminate the influence of a sudden increase or an indirect lightning strike. Therefore, an isolated communication module is mounted on each of the light-emitting unit and the light-receiving unit. light, which form the laser gas analyzer, and these modules occupy a relatively large area for simple serial communication. It follows that it is difficult to reduce the size of the laser gas analyzer. An increase in the size of the laser gas analyzer also poses an explosion control problem proportional to the volume of the laser analyzer, for example.

[0007] The present invention, which has been made to solve the above-mentioned problem, provides a gas analyzer, which can exchange information, required between the light emitting unit and the light receiving unit, without connecting the light emitting unit and the light receiving unit by the communication line. Summary of the invention

[0008] 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 comprising a light emitting unit having a laser element, configured to emit laser light in a wavelength band, which includes an absorption wavelength of light of an absorption line spectrum of the gas to be measured, and a modulated light generating unit, configured to supply a driving current to the laser element, such that a wavelength of the driving current is scanned and modulated in the wavelength band, which includes the absorption wavelength of light of the absorption line spectrum of the gas to be measured;and a light receiving unit, having a light receiving element, configured to receive laser light, which passes into the space to be measured, and a light receiving signal processing unit, configured to analyze the gas to be measured on the basis of a detection signal outputted from the light receiving element, wherein communication between the light emitting unit and the light receiving unit is performed by the laser light. ;

[0009] One aspect of the present invention is characterized in that the light emitting unit produces, by the modulated light producing unit, information on the light emitting unit, in the form of a light modulation signal, the information being required by the light receiving unit, and superimposes the light modulation signal on the laser light, and the light receiving signal processing unit obtains a light modulation signal for gas analysis and a light modulation signal for communication from a detection signal output from the light receiving element.

[0010] One aspect of the present invention is characterized in that the information on the light emitting unit is a start time of the measurement where the gas analysis is performed, the information being required by the light receiving unit.

[0011] One aspect of the present invention is characterized in that the light emitting unit transforms from digital to analog the light modulation signal for gas analysis and the light modulation signal for communication, which are produced by the modulated light producing unit, and the light emitting unit superimposes the light modulation signal for gas analysis and the light modulation signal for communication with laser light.

[0012] One aspect of the present invention is characterized in that the light reception signal processing unit transforms the detection signal output from the light reception element from analog to digital to obtain the light modulation signal for gas analysis and the light modulation signal for communication.

[0013] According to the present invention, it is possible, without passing through the communication line, to exchange various communication information, so that it is no longer necessary to connect the light emitting unit and the light receiving unit, through the communication line. It is thus possible to provide a laser gas analyzer, which can simplify the passage of cable or the like, carried out by a worker and achieve a reduction in size.

[0014] Brief description of the drawings

[0015] [Fig.l] is a diagram of the overall configuration of a laser gas analyzer according to one embodiment;

[0016] [Fig.2] is a diagram of the waveform of a synchronous detection signal;

[0017] [Fig.3] is a diagram of a signal processing block of the gas analyzer at laser according to this embodiment;

[0018] [Fig.4] is a diagram of the overall configuration of a gas analyzer classic; and

[0019] [Fig.5] is a diagram of the waveform of a control current, which includes a light modulation signal for gas analysis and a light modulation signal for communication.

[0020] Detailed Descriptions of Preferred Embodiments

[0021] A laser gas analyzer according to one 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 may be carried out by appropriate modifications without departing from the scope of the present invention.

[0022] Diagram of an overall configuration of a laser gas analyzer.

[0023] [Fig.l] is a diagram of the overall configuration of a laser gas analyzer according to an embodiment of the present invention.

[0024] As shown in [Fig.l], a laser gas analyzer 1 comprises a light emitting unit 10 and a light receiving unit 20.

[0025] The laser gas analyzer 1 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 into a space inside walls 50a, 50b (a space to be measured), is irradiated with laser light 30 emitted from the light emitting unit 10, the walls 50a, 50b forming a conduit for gas. The laser light 30, which passes into the gas to be measured, is incident on the light receiving unit 20, so that it is possible to obtain the concentration of a specific gas on the basis of the detected light quantity. Furthermore, when the concentration of the gas 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.

[0026] The light-emitting unit 10 and the light-receiving unit 20 are removably attached to the walls 50a, 50b forming the duct for gas. The walls 50a, 50b are the walls of ducts or the like, 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 the like. Optical axis adjusting 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 at positions facing each other with the walls 50a, 50b interposed therebetween. 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.

[0027] The optical axis adjustment flange 52a can adjust the emission angle of the laser light 30. The optical axis adjustment flange 52b can adjust the incident angle of the laser light 30. Due to the optical axis adjustment flanges 52a, 52b, a maximum amount of the laser light 30 emitted by the light emitting unit 10 is received by the light receiving unit 20.

[0028] Light emitting unit 10.

[0029] 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 generating unit 11, a laser element 12, a collimating lens 13, a light emitting unit window plate 14, a light emitting unit housing 15, and the optical axis adjusting flange 52a. As shown in [Fig. 1], the modulated light generating unit 11, the laser element 12, and the collimating lens 13 are disposed in the light emitting unit housing 15. The light emitting unit housing 15 isolates the respective components incorporated in a light emitting unit housing 15 from the outside air, thus protecting the respective components from wind and rain, dust and dirt, pollution or the like.

[0030] The modulated light generating unit 11 generates a drive current, which is generated in such a way that the wavelength of the drive current is repeatedly scanned and modulated in a wavelength band that includes the absorption wavelength of the light of the absorption line spectrum of the gas to be measured. The modulated light generating unit 11 supplies the laser element 12 with the drive current to emit modulated laser light. By such a configuration, for analyzing the gas concentration, it is possible to perform exposure to wavelength-modulated light corresponding to an absorption characteristic of the light of the gas to be measured.

[0031] The laser element 12 emits light at a central wavelength XI of a spectrum of a specific absorption line and at wavelengths around the central wavelength, the gas to be measured absorbing the light. The laser element 12 variably controls an emission wavelength by controlling a control current and a temperature.

[0032] The laser element 12 is temperature-controlled so that a central emission wavelength takes the central wavelength XI of the absorption line spectrum 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 scanned in terms of time by the control current supplied by the modulated light generating unit 11. Furthermore, the laser light 30 is modulated by superimposing an appropriate sine wave so as to enable measurement with high sensitivity by wavelength modulation spectroscopy (WMS). Wavelength modulation spectroscopy is also referred to as 2f detection.

[0033] The laser element 12 to be used is not limited in any particular manner. However, the laser element 12 may be a DFB laser diode (diode-deferred feedback laser), a VCSEL (vertical cavity surface emitting laser) or a DBR laser diode (distributed Bragg refractor laser), for example.

[0034] The collimating lens 13 is a material having a large transmittance at the central wavelength XI of the absorption line spectrum of the gas to be measured and at wavelengths around the central wavelength XI. The laser light 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 suppressed.

[0035] The light emitting point of the laser element 12 is arranged at a position close to the focal point of the collimating lens 13. The light emitted by the laser element 12 is incident on the collimating lens 13 while diffusing, thereby being transformed into the laser light 30, which is substantially parallel light. In the present embodiment, the description is made on the assumption that the collimating lens 13 is used as a parallel light transformation unit. But it should not be considered that the parallel light transformation unit is limited to a collimating lens. It is, for example, also possible to use a parabolic mirror as the parallel light transformation unit, instead of the collimating lens 13.

[0036] The laser light 30, which is substantially parallel light, transmits through the window plate 14 of the light emitting unit and propagates into a space inside the walls 50a, 50b, i.e., a space in which gases, including the gas to be measured, are present. A hole is formed at 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 disposed 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 transmit through the window plate 14 of the light emitting unit.By such a configuration, the respective components arranged in the 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 the housing 15 of the light emitting unit.

[0037] Light receiving unit.

[0038] The light receiving unit 20 will be described.

[0039] The light receiving unit 20 is configured to comprise a unit 21 for processing a light receiving signal, a light receiving element 22, a condenser lens 23, a window plate 24 of the light receiving unit and a housing 25 of the light receiving unit. The housing 25 of the light receiving unit contains the light receiving element 22, optical components and an electrical and electronic circuit. The housing 25 of the light receiving unit isolates these components from the outside air, thereby protecting these components from wind and rain, dust and dirt, pollution or the like.

[0040] 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 which is absorbed by the gas to be measured due to a light absorption characteristic of the gas to be measured. A hole is formed at a portion of the housing 25 of the light receiving unit and the window plate 24 of the light receiving unit is provided to close this hole. The window plate 24 of the light receiving unit is disposed in the optical path of the laser light 30, and prevents gases, including the precise gas that is 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 disposed 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.But it is also possible to adopt a parabolic mirror, a doublet lens, a diffraction lens or the like, instead of the lens 23 forming the condenser.

[0041] The light receiving element 22 receives laser light 30, which passes into the gas to be measured. As the light receiving element 22, it is possible to select a light receiving element having sensitivity to the central wavelength XI of the absorption line spectrum of the gas to be measured and to wavelengths around the central wavelength XI. A light receiving signal output from the light receiving element 22 is transmitted to the light receiving signal processing unit 21 in the form of an electrical signal.

[0042] The condenser lens 23 is made of a material having a high transmittance at the central wavelength XI of the absorption line spectrum of the gas to be measured and at wavelengths around the central wavelength XI. The laser light 30 is thus condensed onto the light receiving element 22 by the condenser lens 23, and it is thus possible to obtain a high signal intensity.

[0043] The light receiving signal processing unit 21 performs processing on the electrical signal received by the light receiving element 22 to calculate the concentration of the gas. The harmonic component of the modulated frequency of the wavelength modulated laser light 30 is detected by synchronous detection, and the amplitude information of the detected waveform is calculated, and thus it is possible to detect the gas with high sensitivity.

[0044] In the case where a plurality of gases, which are present in the space to be measured, have a fixed composition, the amplitude of a synchronous detection wavelength, obtained, by absorption of light by the gas to be measured, is a function of the wavelength modulation amplitude and has a maximum value. Accordingly, in a calibration of a standardized gas, it is possible to maximize a signal-to-noise ratio by adjusting the wavelength modulation capability, of so that the amplitude of a synchronous detection waveform takes a maximum value.

[0045] [Fig.2] is a diagram of the waveform of a synchronous detection signal. As shown in [Fig.2], the synchronous detection signal has a waveform with extreme values, based on the absorption line of the gas component to be measured. The range of width W shows the synchronous detection signal caused by absorption by the gas.

[0046] A difference D of the intensity of the synchronous detection signal, shown in [Fig.2], between the bottom and the peak has a correlation with the gas concentration. Therefore, by performing a calibration with a standardized gas, set for each concentration in advance, it is possible to measure the gas concentration by detecting the difference D.

[0047] The width W of the synchronous detection signal can be used to perform an arithmetic correction operation depending on the nature of the gas, for example.

[0048] Description of a block forming a laser gas analyzer according to the present embodiment.

[0049] [Fig. 3] is a diagram of the signal processing block of the laser gas analyzer according to this embodiment.

[0050] The signal processing performed by the laser gas analyzer according to the present embodiment will be described with reference to [Fig. 3]. Of the light emitting unit 10 and the light receiving unit 20 of the laser gas analyzer 1 shown in [Fig. 1], the modulated light generating unit 11 and the light receiving signal processing unit 21 will be described in particular detail with reference to the block diagram shown in [Fig. 3]. Even if components that the laser gas analyzer 1 usually includes are not shown in [Fig. 3], it will be assumed that such components are included.

[0051] As shown in [Fig.3], the light emitting unit 10 is configured to include the laser element 12 and the modulated light generating unit 11, and the modulated light generating unit 11 is configured to include a circuit 112 for adjusting the temperature of the laser element, a unit 113 for fixing the wavelength-swept and modulated current, and a digital-to-analog converter 114.

[0052] The wavelength-swept and modulated current setting unit 113 controls a control current of the laser element 12, so that the wavelength of the laser light emitted by the laser element 12 is scanned near an absorption line of the central wavelength XI of the absorption line spectrum of the gas to be measured, and is modulated by a predetermined signal. Furthermore, as will be described below, the wavelength-swept and modulated current setting unit 113 modulated produces information on the light emitting unit 10 in the form of a light modulation signal, the information on the light emitting unit 10 being required by the light receiving unit 20.

[0053] The digital-to-analog converter 114 transforms a digital signal into an analog signal. The analog-to-digital converter 114 transforms a light modulation signal transmitted from the modulated wavelength-scanned current fixing unit 113, and transmits the light modulation signal to the laser element 12.

[0054] The laser element temperature adjustment circuit 112 controls an output of the laser element 12 and a wavelength to fixed values, thereby stabilizing the output of the laser element 12 and the wavelength. The output of the laser element 12 and the wavelength fluctuate depending on the temperature. Therefore, to prevent the output and the wavelength from fluctuating due to a change in the ambient temperature, the laser element 12 is set to a fixed temperature by the laser element temperature adjustment circuit 112.

[0055] The light receiving unit 20 is configured to include the light receiving element 22 and the light receiving signal processing unit 21, and the light receiving signal processing unit 21 is configured to include an IV conversion circuit 112, a gas absorption measuring circuit 123, an analog-to-digital converter 125, a gas concentration arithmetic correction unit 124, a demodulator / decoder 127, and a control unit 126.

[0056] The light receiving element 22 is an element having sensitivity to the wavelength of the laser light 30. For the light receiving element 22, it is possible to suitably select a photodiode, for example, depending on the wavelength of the laser light 30 or an intensity of a signal.

[0057] The IV conversion circuit 122 is a circuit that transforms a current signal output from the light receiving element 22 into a voltage signal. Thus, for example, when the light receiving element 22 is a photodiode, it is possible to select a trans-impedance amplifier, which amplifies a current signal output from the photodiode, while transforming the current signal into a voltage signal. In this case, provided that the light 30 is little attenuated, that is, provided that there is no dust or the like in the optical path, a signal can be amplified in a suitable manner by an amplifier circuit not shown in the drawings, as long as the signal is not saturated.

[0058] The gas absorption measuring circuit 123 performs various types of processing to measure gas absorption. Although not shown in the drawings, the gas absorption measuring circuit 123 is provided with various types of filters, an amplifier circuit, a synchronous detection unit, for example. In the synchronous detection signal, phase detection is performed at a frequency which is an integer multiple (e.g., twice) of the modulated frequency included in the detection signal output from the light receiving element 22, the modulated frequency being set in the modulated wavelength swept current setting unit 113. The synchronously detected synchronous detection signal is transmitted to the analog-to-digital converter 125 and is converted from analog to digital. The gas concentration arithmetic correction unit 124 performs an arithmetic operation for the gas concentration based on a correspondence (proportional relationship or the like) between the concentration of the gas to be measured and the amplitude of the synchronous detection waveform. In [Fig.3], the analog to digital converter 125 is connected downstream of the gas absorption measuring circuit 123. However, the analog to digital converter 125 may be connected upstream of the gas absorption measuring circuit 123.

[0059] The gas absorption measuring circuit 123 can extract a light modulation signal for gas analysis, and a light modulation signal for communication from the detection signal outputted from the light receiving element 22. Among these signals, the light modulation signal for gas analysis is subjected to gas analysis in the above-mentioned synchronous detection. On the other hand, as will be described below, the light modulation signal for communication is a synchronization signal for a measurement start time in the gas analysis, for example.

[0060] The demodulator / decoder 127 demodulates / decodes a signal of communication information into a form that can correspond to the analyzer of the present embodiment.

[0061] The control unit 126 controls the respective processing units (the gas absorption measuring circuit 123, the gas concentration arithmetic correction unit 124) of the light receiving unit 20. The control unit 126 can control the respective processing units on the basis of information on the gas to be measured and the communication information transmitted by the light emitting unit 10.

[0062] Process for obtaining the present embodiment.

[0063] [Fig.4] is a diagram showing the overall configuration of an analyzer 2 of conventional laser gas. In the conventional configuration, shown in [Fig.4], various communication information, such as a synchronization of a start time of the concentration measurement, is exchanged between the emission unit 10 of the light and the light receiving unit 20 via the communication line 40.

[0064] As shown in [Fig.4], the communication line 40 connects a modulated light generating unit 31 and a light receiving signal processing unit 32 to each other. In the conventional configuration, the communication line 40, the modulated light generating unit 31 and the light receiving signal processing unit 32 are formed based on the patent document 1, for example.

[0065] As described above, in the conventional configuration, the light-emitting unit 10 and the light-receiving unit 20 are connected to each other by the communication line 40 for signal synchronization or for exchanging setting values. But the conventional configuration results in an increase in the size of the laser gas analyzer 2 and has the difficulty that the wiring routing becomes, for example, complicated.

[0066] In view of the above, in the laser gas analyzer 1 according to the present embodiment, as shown in [Fig. 1], communication between the light emitting unit 10 and the light receiving unit 20 is performed via the laser light 30, without using the communication line 40 between the light emitting unit 10 and the light receiving unit 20. As described above, in the present embodiment, it is not necessary to connect the light emitting unit 10 and the light receiving unit 20 by the communication line 40 and therefore the routing of analogous wiring performed by a worker is simplified, it is also possible to achieve a reduction in the size of the laser analyzer 1.

[0067] Communication between the light emitting unit 10 and the light receiving unit 20.

[0068] In the laser gas analyzer 1 according to the present embodiment, a communication signal between the light-emitting unit 10 and the receiving unit 20 can be produced by the wavelength-swept and modulated current fixing unit 113, shown in [Fig. 3], in the form of a light modulation signal. It is preferable that the communication signal is information on the light-emitting unit 10, the information being required by the light-receiving unit 20.

[0069] The wavelength-swept and modulated current fixing unit 113 can produce a light modulation signal for gas analysis and a light modulation signal for communication. The light modulation signal for communication is, for example, a synchronization signal for aligning phases when performing synchronous detection. The light modulation signal synchronization may be an intensity modulation signal, such as a pulse, for example, and may cause the unit 11 for producing a modulated signal and the unit 21 for processing a light reception signal to be able to synchronize with each other at the clock time at which a pulse is received.

[0070] When the gas concentration is detected by the synchronous detection, if a measurement start time is not synchronized between the modulated light generating unit 11 and the light receiving signal processing unit 21, a phase shift is produced in the detected waveform. In view of the above, in the present embodiment, communication between the modulated light generating unit 11 and the light receiving signal processing unit 21 is performed by superimposing a synchronization signal on the laser light to align phases, instead of using the conventional communication line 40. By such a configuration, it is possible to synchronize the measurement start time between the modulated light generating unit 11 and the light receiving signal processing unit 21, and thus the occurrence of a phase shift can be suppressed.

[0071] [Fig. 5] is a diagram of the waveform of a control current output by the wavelength-swept and modulated current setting unit 113. A synchronization / measurement signal ID, in the form of a light modulation signal (I) for communication, is provided before each light modulation signal (II) for gas analysis. The light modulation signal (II) is a light measurement signal, which scans a wavelength in a wavelength band, which includes the light absorption wavelength of the absorption line spectrum of the gas to be measured.

[0072] A light modulation signal (III), shown in [Fig. 5], is different from the light modulation signal (I) and is information on the light emitting unit 10, the information being required by the light receiving unit 20. Although not a limitation, the light modulation signal (III) may be information on a change in characteristics, such as information on the temperature of the laser element 12, deterioration information, information on the gas to be measured, for example.

[0073] The wavelength-swept and modulated current fixing unit 113, shown in [Fig. 3], can produce a light modulation signal in the form of a digital signal. The light modulation signal is converted from digital to analog by the digital to analog converter 114, and is transmitted to the laser element 12. In the present embodiment, the light modulation signals (I), (III) for communication and the light modulation signal (II) for gas analysis are superimposed on the laser line 30.

[0074] In the light receiving unit 20, the gas absorption measuring circuit 123 obtains a light modulation signal for gas analysis, and a light modulation signal for communication from the detection signal outputted by the light receiving element 22 to synchronize a measurement start time in the synchronous detection. By such a configuration, it is possible to correct the phase shift of the synchronous detection waveform in the gas absorption measuring circuit, and thus the gas concentration can be detected with high accuracy. Furthermore, synchronization is performed by the light modulation signal (I) for each gas measurement, and then the gas concentration is detected by the light modulation signal (II), and thus the gas concentration can be detected without producing a phase shift for each measurement. Therefore, such a configuration is preferred.

[0075] When a timing / measurement ID signal output by the modulated wavelength swept current setting unit 113 is given as a simple single pulse, there is a possibility of not obtaining the correct timing, in the case where the laser light 30 is interrupted by dust or the like. In view of the above, a plurality of pulse patterns are determined in advance and a signal is used for measurement, only if the light emitting unit 10 and the light receiving unit 20 can correctly receive such a pattern. By such a pattern, it is possible to measure the concentration in a stable manner.

[0076] For the pulse pattern, exactly the same pulse pattern can be used. However, such a case is based on a premise that the measurement is carried out continuously under the same conditions. In the case where a plurality of gaseous constituents are measured, such as the case in which a gaseous constituent to be measured is changed, to enable the light receiving unit 20 to identify the gaseous constituent to be measured, pulse patterns are set so that the next pulse pattern can be predicted on the basis of the pulse pattern received by the light receiving unit 20 from the light emitting unit 10. Such a configuration makes it possible to carry out measurement under multiple conditions.The gas concentration arithmetic correction unit 124 receives notification from the control unit 126 that the gas concentration arithmetic correction unit 124 is to calculate the concentration of the constituent in question.

[0077] Thus, for example, when two patterns of 10001 and 10101 are predicted as pulse patterns, the measurement can be performed under two conditions. By adopting sequential numbers, such as 10001, 10010 and 10011, it is possible to predict a next pulse pattern.

[0078] [Fig. 5] shows an example, in which communication is carried out with a pulse configuration, i.e., communication is carried out by intensity modulation. However, it is possible to use a general optical communication system, which uses a single laser. It is also possible to use binary communication, such as Amplitude Shift Keying (ASK), Frequency Shift Keying (SFK) or Phase Shift Keying (PSK) or to use multi-value processing (QASQ, QPSK or the like), which uses amplitude or the like. In such a case, the demodulator / decoder 12, shown in [Fig. 4], causes signal matching. Alternatively, by introducing the mechanism of heterodyne optical detection to the light receiving unit 20, it is possible to cause signal matching.

[0079] In the present embodiment, the light modulation signal (III), for communication between the light emitting unit and the light receiving unit, is transmitted from the modulated light generating unit 11 to the light receiving signal processing unit 21. It is possible to transmit the light modulation signal (III) periodically or non-periodically. However, it is preferable to carry out communication periodically between the light emitting unit 10 and the light receiving unit 20 to exchange setting values ​​or the like. In the present embodiment, a concentration is detected several times by the light modulation signal (I) and the light modulation signal (II), and then the light modulation signal (III) is transmitted periodically.At this point of operation, one-way communication is carried out from the light-emitting unit 10 to the light-receiving unit 20. It is, therefore, possible to handle this case by a method, in which information which is required by the light-receiving unit 20 is determined in advance and the light-emitting unit 10 transmits (radio broadcasts) this information periodically.

[0080] Furthermore, as described above, it is anticipated that a pulse pattern is broken due to a disturbance factor, such as dust. Therefore, by adding redundancy, such as a checksum, it is possible to achieve communication with greater reliability.

[0081] To simultaneously provide the above-mentioned function of measuring a concentration and the communication function, it is desirable to provide a low-distortion digital-to-analog converter 114 between the unit 10 for producing a modulated light and the laser element 12. The conventional laser gas analyzer has the property that, by utilizing the fact that distortion is produced in the optically modulated laser light due to absorption by the gas to be measured, the concentration is detected by measuring a harmonic component (second harmonic in general) of a modulated frequency. Therefore, the conventional laser gas analyzer often uses a low-distortion analog oscillator that oscillates at a specific frequency. Even when using such an analog oscillator, intensity modulation (ASK) allows communication to be carried out relatively easily using a mixer / multiplexer (AND) or the like. On the other hand, when communication is carried out by modulation, such as PSK or FSK or by multi-valued processing, there is a risk that peripheral circuits may become complicated, which leads to an increase in circuit scale.In view of the above, in the present embodiment, a digital-to-analog converter is used, which has a small distortion factor, much lower than the total harmonic distortion factor (approximately -90 to -80 dB) of the conventional low-distortion analog oscillator, and therefore the laser can be driven by a desired waveform, while having a low-distortion modulation performance, which is required for measuring the gas concentration. It is thus possible not to have to increase the scale of a circuit, even for communication that includes multi-value processing between the light-emitting unit 10 and the light-receiving unit 20.

[0082] The laser gas analyzer according to the present invention is optimal for measuring combustion exhaust gases or for controlling combustion for a boiler or waste incineration, for example. Furthermore, the laser gas analyzer according to the present invention is preferably used as an analyzer of gases used for iron and steel (blast furnaces, converter furnaces, heat treatment furnaces, sintering, pelletizing device, coke ovens (for storing and ripening fruits and vegetables), in biochemistry (microorganisms) by fermentation), for air pollution (incinerator, flue gas, desulfurization / denitrification (for exhaust gases from internal combustion engines of automobiles), ships or the like (elimination of a test apparatus), for preventing disasters (explosive gas detection, toxic gas detection, flue gas analysis of new building materials),for growing plants, for chemical analysis (oil refining plants, petroleum chemical plants, gas production plants), for concentration in the environment (background level), concentration in tunnels, in parking lots, building management and for various experiments in physics and chemistry, for example.

[0083] Enumeration of benchmarks

[0084] 1 laser gas analyzer

[0085] 2 laser gas analyzer

[0086] 10 light emitting unit

[0087] 11 unit for producing modulated light

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] [YES] 12 laser element 13 collimating lens 14 window plate of light emitting unit 15 housing of light emitting unit 20 light receiving unit 21 light receiving signal processing unit 22 light receiving element 23 condenser lens 24 window plate of light receiving unit 25 light receiving unit housing 30 laser light 40 communication line 50a, 50b wall 51a, 51b flange 52a,52b optical axis adjustment flange 112 laser element temperature adjustment circuit 113 wavelength swept and modulated current fixing unit 114 digital to analog converter 122 IV conversion circuit 123 gas absorption measuring circuit 124 gas concentration arithmetic correction unit 125 analog to digital converter 126 control unit 127 demodulator / decoder,

Claims

1.

2. Claims A laser gas analyzer (1) which performs an analysis of a gas to be measured, which is present in a space to be measured, the laser gas analyzer (1) being characterized in that it comprises: a light emitting unit (10) having a laser element (12), configured to emit laser light (30) in a wavelength band, which includes an absorption wavelength of light of an absorption line spectrum of the gas to be measured, and a modulated light generating unit (11), configured to supply a driving current to the laser element (12), such that a wavelength of the driving current is scanned and modulated in the wavelength band, which includes the absorption wavelength of the light of the absorption line spectrum of the gas to be measured; and a light receiving unit (20), having a light receiving element (22), configured to receive laser light (30), which passes into the space to be measured, and a light receiving signal processing unit (21), configured to analyze the gas to be measured on the basis of a detection signal output from the light receiving element (22), wherein communication between the light emitting unit (10) and the light receiving unit (20) is performed by the laser light (30) emitted by the laser element (12). Laser gas analyzer (1) according to claim 1, characterized in that the light emitting unit (10) produces, by the modulated light producing unit (11), information on the light emitting unit (10), in the form of a light modulation signal, the information being required by the light receiving unit (20), and superimposes the light modulation signal on the laser light (30), and the light reception signal processing unit (21) obtains a light modulation signal for gas analysis and a light modulation signal for communication from a detection signal output from the light receiving element (22).

3. Laser gas analyzer (1) according to claim 2, characterized in that the information on the light emitting unit (10) is a start time of the measurement at which the gas analysis is carried out, the information being required by the light receiving unit (20).

4. A laser gas analyzer (1) according to any one of claims 1 to 3, characterized in that the light emitting unit (11) transforms from digital to analog the light modulation signal for gas analysis and the light modulation signal for communication, which are produced by the modulated light producing unit (11), and the light emitting unit (10) superimposes the light modulation signal for gas analysis and the light modulation signal for communication on the laser light (30).

5. A laser gas analyzer (1) according to any one of claims 1 to 3, characterized in that the light reception signal processing unit (21) transforms the detection signal output from the light reception element (22) from analog to digital to obtain the light modulation signal for gas analysis and the light modulation signal for communication.

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