Laser Gas Analyzer

Abstract

To provide a laser gas analyzer that can simplify the handling performed by a user and reduce size.SOLUTION: A laser gas analyzer 1 performs gas analysis of gas to be measured that is present in a space to be measured. The laser gas analyzer comprises: a light emitting section 10 including a laser element 12 that emits laser light 30 in a wavelength band including a light absorption wavelength of an absorption line spectrum of the gas to be measured, and a modulated light generation section 11 that supplies a drive current to the laser element so as to sweep and modulates a wavelength in the wavelength band including the light absorption wavelength of the absorption line spectrum of the gas to be measured; and a light receiving section 20 including a light receiving element 22 that receives the laser light passing through the space to be measured, and a light reception signal processing section 21 that analyzes the gas to be measured on the basis of a detection signal output from the light receiving element 22. The light emitting section 10 and the light receiving section 20 communicate with each other using the laser light 30.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a laser gas analyzer that analyzes the presence and concentration of various target gases in a space. [Background technology]

[0002] In a laser gas analyzer, a laser element on the light-emitting side emits laser light at an optical absorption wavelength that is absorbed by the measurement target gas, which is a gaseous gas molecule, and the laser light is absorbed by the measurement target gas.On the light-receiving side, gas analysis of the measurement target gas is performed based on the amount of laser light absorbed at that optical absorption wavelength.

[0003] For example, as described in Patent Document 1, wavelength modulation spectroscopy is commonly used for gas analysis of a measurement target gas. That is, according to Patent Document 1, a wavelength-tunable laser light source sweeps the wavelength using a drive current and emits laser light modulated at a specific frequency, a photodetector detects the laser light, and a lock-in amplifier locks in and detects the signal at an integer multiple of the modulation frequency. Then, the gas concentration can be calculated based on the correspondence (e.g., proportionality) between the gas concentration of the measurement target gas and the amplitude of the lock-in detection waveform. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-106742 A Summary of the Invention [Problem to be solved by the invention]

[0005] The light-emitting unit and the light-receiving unit are connected by a communication line to synchronize signals and exchange setting values. However, in actual installation sites, the flue diameter can be several meters, which requires a very long cable to connect the light-emitting unit and the light-receiving unit. Furthermore, because laser gas analyzers are installed outdoors, it is necessary to eliminate the effects of surges and induced lightning. For this reason, the light-emitting unit and the light-receiving unit that make up the laser gas analyzer are equipped with an insulated communication module, and this module occupies a relatively large area even for simple serial communication. As a result, it has been difficult to miniaturize laser gas analyzers. The increase in size of laser gas analyzers has also created problems with measures such as explosion protection, which are proportional to the volume of the laser gas analyzer.

[0006] Therefore, the present invention has been made to solve the above problems, and provides a laser gas analyzer that enables the exchange of necessary information between the light-emitting unit and the light-receiving unit without connecting the two units with a communication line. [Means for solving the problem]

[0007] The present invention is a laser gas analyzer for performing gas analysis of a measurement target gas present in a measurement target space, comprising: a light-emitting unit having a laser element that emits laser light in a wavelength band that includes an optical absorption wavelength of the absorption line spectrum of the measurement target gas; and a modulated light generating unit that sweeps the wavelength in the wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the measurement target gas and supplies a drive current to the laser element so that the wavelength is modulated; a light-receiving unit that has a light-receiving element that receives the laser light that has passed through the measurement target space; and a light-receiving signal processing unit that analyzes the measurement target gas based on a detection signal output from the light-receiving element; the modulated light generating unit generates an optical modulation signal for gas analysis and an optical modulation signal for communication, the optical modulation signal for communication being a synchronization signal for starting measurement of gas analysis, having a pattern of a plurality of pulses, and the optical modulation signal for communication is superimposed on the laser light together with the optical modulation signal for gas analysis, Communication between the light-emitting unit and the light-receiving unit The light receiving signal processing unit acquires the optical modulation signal for gas analysis and the synchronization signal, and when the pulse pattern of the synchronization signal is correctly received, the gas analysis is started. It is characterized by the following.

[0010] One aspect of the present invention is characterized in that the light emitting unit digitally converts an optical modulation signal for gas analysis and an optical modulation signal for communication generated by the modulated light generating unit and superimposes the converted signal on the laser light.

[0011] One aspect of the present invention is characterized in that the light receiving signal processing unit converts the detection signal output from the light receiving element from analog to digital to obtain an optical modulation signal for gas analysis and an optical modulation signal for communication. [Effects of the Invention]

[0012] According to the present invention, various communication information can be exchanged without using a communication line, and there is no need to connect the light-emitting unit and the light-receiving unit with a communication line. This simplifies the handling of wiring by the worker, and also makes it possible to provide a laser gas analyzer that can be made smaller. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an overall configuration diagram of a laser gas analyzer according to an embodiment of the present invention. [Figure 2] FIG. 10 is a waveform diagram of a lock-in detection signal. [Figure 3] FIG. 2 is a block diagram of signal processing of the laser gas analyzer according to the present embodiment. [Figure 4] FIG. 1 is an overall configuration diagram of a conventional laser gas analyzer. [Figure 5] FIG. 2 is a waveform diagram of a driving current including an optical modulation signal for gas analysis and an optical modulation signal for communication. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a laser gas analyzer according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiment, and can be modified appropriately within the scope of the present invention.

[0015] <Overall configuration of laser gas analyzer> 1 is a diagram showing the overall configuration of a laser gas analyzer according to an embodiment of the present invention. As shown in FIG. 1, the laser gas analyzer 1 includes a light emitting unit 10 and a light receiving unit 20.

[0016] The laser gas analyzer 1 analyzes a target gas present in a target space. In the laser gas analyzer 1, a laser beam 30 emitted from a light-emitting unit 10 is irradiated onto the target gas flowing through the interior (target space) of walls 50a and 50b that form the gas pipe. The laser beam 30 passes through the target gas and enters a light-receiving unit 20, and the concentration of a specific gas can be determined from the detected light intensity. If the gas concentration is 0 or below a predetermined value, it can be detected that the gas is absent, and therefore the presence or absence of the gas can also be detected.

[0017] The light-emitting unit 10 and the light-receiving unit 20 are detachably attached to walls 50a, 50b that constitute a gas pipe. The walls 50a, 50b are walls of a pipe or the like in which a specific gas is present, and each has a hole drilled therein. The flanges 51a, 51b are fixed to the holes by welding or the like. The optical axis adjustment flanges 52a, 52b provided on the light-emitting unit 10 and the light-receiving unit 20 are mechanically detachably attached to these flanges 51a, 51b. The light-emitting unit 10 and the light-receiving unit 20 are disposed in opposing positions across the walls 50a, 50b, but their positions can be adjusted by the optical axis adjustment flanges 52a, 52b.

[0018] The optical axis adjusting flange 52a adjusts the emission angle of the laser beam 30, and the optical axis adjusting flange 52b adjusts the incident angle of the laser beam 30. The optical axis adjusting flanges 52a and 52b allow the laser beam 30 emitted from the light emitting unit 10 to be received by the light receiving unit 20 with the maximum amount of light.

[0019] [Light-emitting unit 10] The light-emitting unit 10 will now 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 container 15, and an 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 inside the light-emitting unit container 15. The light-emitting unit container 15 isolates the built-in components from the outside air to protect them from wind, rain, dust, dirt, and the like.

[0020] The modulated light generating unit 11 generates a drive current that is generated so that the wavelength is repeatedly swept and modulated in a wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the measurement target gas. The modulated light generating unit 11 then supplies the drive current for emitting modulated laser light to the laser element 12. This makes it possible to irradiate modulated light that is wavelength-modulated in accordance with the absorption characteristics of the measurement target gas for gas concentration analysis.

[0021] The laser element 12 emits light at a central wavelength λ1 of a specific absorption line spectrum absorbed by the gas to be measured and at wavelengths around that central wavelength λ1. The laser element 12 variably controls the emission wavelength by controlling the drive current and temperature.

[0022] The temperature of the laser element 12 is controlled so that the central wavelength of the emitted light coincides with the central wavelength λ1 of the absorption line spectrum of the gas to be measured. The laser light 30 emitted from the laser element 12 is controlled by a drive current supplied from the modulated light generating unit 11 so as to sweep wavelengths around the central wavelength of the absorption line spectrum of the gas to be measured over time, and is further modulated by superimposing an appropriate sine wave so that high-sensitivity measurement can be performed by wavelength modulation spectroscopy (WMS). Wavelength modulation spectroscopy is also known as 2f detection.

[0023] The laser element 12 used is not particularly limited, but may be, for example, a DFB laser diode (Distributed Feedback Laser Diode), a VCSEL (Vertical Cavity Surface Emitting Laser), or a DBR laser diode (Distributed Bragg Reflector Laser Diode).

[0024] The collimating lens 13 is made of a material that has high transmittance at the central wavelength λ1 of the absorption line spectrum of the gas to be measured and at wavelengths around that wavelength. The collimating lens 13 converts the laser light 30 into a substantially parallel light, which can be transmitted to the light receiving unit 20 while suppressing loss due to diffusion.

[0025] The light emitting point of the laser element 12 is located near the focal point of the collimator lens 13. The light emitted from the laser element 12 is diffused and enters the collimator lens 13, where it is converted into laser light 30, which is substantially parallel light. Note that in this embodiment, the collimator lens 13 is used as the parallel light converting unit, but this is not intended to be limited to a collimator lens. For example, a parabolic mirror can be used as the parallel light converting unit instead of the collimator lens 13.

[0026] The laser light 30, which is a substantially parallel beam, passes through the light-emitting unit window plate 14 and propagates inside the walls 50a, 50b, i.e., into the space where gas containing the target gas is present. The light-emitting unit window plate 14 is provided to close a hole drilled in part of the light-emitting unit container 15. The light-emitting unit window plate 14 is located in the optical path of the laser light 30, and while allowing the laser light 30 to pass through, it prevents gas containing the specific target gas from entering the light-emitting unit 10. This prevents the components arranged inside the light-emitting unit container 15 from coming into direct contact with the gas, protecting the components inside the light-emitting unit container 15.

[0027] [Light receiving section 20] The light receiving unit 20 will now be described. 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 container 25. The light receiving unit container 25 houses the light receiving element 22, optical components, and electrical and electronic circuits, and isolates them from the outside air to protect them from wind, rain, dust, dirt, and the like.

[0028] The light receiving unit 20 receives the laser light 30 that has passed through the light receiving unit window plate 24 and analyzes the light absorbed due to the absorption characteristics of the target gas. The light receiving unit window plate 24 is provided to cover a hole drilled in a part of the light receiving unit container 25. The light receiving unit window plate 24 is located in the optical path of the laser light 30 and transmits the laser light 30 while preventing gas, including the specific target gas, from entering the interior of the light receiving unit 20. This prevents the components arranged inside the light receiving unit 20 from direct contact with the gas, thereby protecting the interior. The laser light 30 is focused by the condenser lens 23 and enters the light receiving element 22. Note that although the condenser lens 23 is used in this embodiment, a parabolic mirror, a doublet lens, a diffractive lens, or the like may be used instead of the condenser lens 23.

[0029] The light receiving element 22 receives the laser light 30 that has passed through the gas to be measured. A light receiving element having sensitivity at the central wavelength λ of the absorption line spectrum of the gas to be measured and its surrounding wavelengths can be selected. The light receiving signal from the light receiving element 22 is sent to the light receiving signal processing unit 21 as an electrical signal.

[0030] The condenser lens 23 is made of a material that has high transmittance at the central wavelength λ1 of the absorption line spectrum of the gas to be measured and at wavelengths around it. The condenser lens 23 condenses the laser beam 30 onto the light receiving element 22, thereby obtaining a high signal intensity.

[0031] The light receiving signal processing unit 21 processes the electrical signal received by the light receiving element 22 to calculate the gas concentration. It performs lock-in detection of the harmonics of the modulation frequency of the wavelength-modulated laser light 30 and calculates amplitude information of the detected waveform, enabling highly sensitive gas detection.

[0032] When the composition of multiple gases present in the measurement space is fixed, the amplitude of the lock-in detection wavelength obtained by the absorption of the measurement gas is a function of the wavelength modulation amplitude and has a maximum value. Therefore, when calibrating the standard gas, the wavelength modulation amplitude can be adjusted so that the amplitude of the lock-in detection waveform is maximized, thereby maximizing the signal-to-noise ratio.

[0033] Figure 2 shows the waveform of the lock-in detection signal. As shown in Figure 2, the lock-in detection signal has a waveform with extrema based on the absorption lines of the gas components being measured. The range of width W is the detection signal due to gas absorption.

[0034] The difference D between the bottom and peak of the signal intensity in the lock-in detection signal shown in Figure 2 correlates with the gas concentration. Therefore, by performing calibration in advance using standard gases set to each concentration, the difference D can be detected to measure the gas concentration.

[0035] The width W of the lock-in detection signal can be used to perform correction calculations depending on, for example, the type of gas.

[0036] <Description of blocks constituting the laser gas analyzer of this embodiment> Fig. 3 is a block diagram of signal processing of the laser gas analyzer according to this embodiment. Signal processing of the laser gas analyzer according to this embodiment will be described using Fig. 3. Note that the block diagram of Fig. 3 particularly describes in detail the modulated light generating unit 11 and the received light signal processing unit 21 of the light emitting unit 10 and the light receiving unit 20 of the laser gas analyzer 1 shown in Fig. 1, but it is assumed that the laser gas analyzer 1 also includes components that are normally included in Fig. 3, even if not shown in Fig. 3.

[0037] As shown in FIG. 3, the light emitting unit 10 includes a laser element 12 and a modulated light generating unit 11, and the modulated light generating unit 11 includes a laser element temperature control circuit 112, a wavelength sweep / modulation current setting unit 113, and a DA converter 114.

[0038] The wavelength sweep / modulation current setting unit 113 controls the drive current of the laser element 12 so that the wavelength of the laser light 30 emitted by the laser element 12 is swept near the absorption line of the central wavelength λ1 of the absorption line spectrum of the measurement target gas, and so that the laser light 30 is modulated with a predetermined signal. As will be described later, the wavelength sweep / modulation current setting unit 113 also generates information of the light emitter 10 required by the light receiver 20 as an optical modulation signal.

[0039] The DA converter 114 converts the digital signal into an analog signal, and sends the optical modulation signal sent from the wavelength sweep and modulation current setting unit 113 to the laser element 12 after DA conversion.

[0040] The laser element temperature control circuit 112 controls and stabilizes the output and wavelength of the laser element 12. Since the output and wavelength of the laser element 12 vary depending on the temperature, the laser element temperature control circuit 112 controls the temperature to a constant value so that the output and wavelength do not vary due to changes in the ambient temperature.

[0041] The light receiving unit 20 is configured with a light receiving element 22 and a light receiving signal processing unit 21, and the light receiving signal processing unit 21 includes an IV conversion circuit 122, a gas absorption measurement circuit 123, an AD converter 125, a gas concentration calculation correction unit 124, a demodulator / decoder 127, and a control unit 126.

[0042] The light receiving element 22 is an element that is sensitive to the wavelength of the laser light 30, and the light receiving element 22 can be selected appropriately depending on the wavelength of the laser light 30 and the signal intensity, such as a photodiode.

[0043] The IV conversion circuit 122 is a circuit that converts the current signal from the light receiving element 22 into a voltage signal. For example, if the light receiving element 22 is a photodiode, a transimpedance amplifier that amplifies the current from the photodiode while converting it into a voltage can be selected. Here, under conditions where the laser light 30 is least attenuated, i.e., under conditions where there is no dust or the like on the optical path, amplification may be performed as appropriate by an amplifier circuit (not shown) to the extent that the signal does not saturate.

[0044] The gas absorption measurement circuit 123 performs various processes in gas absorption measurement. Although not shown, the gas absorption measurement circuit 123 is provided with various filters, an amplifier circuit, a lock-in detection unit, and the like. Lock-in detection is performed by detecting the phase at a frequency that is an integer multiple (e.g., twice) of the modulation frequency in the wavelength sweep / modulation current setting unit 113 included in the detection signal output from the light receiving element 22. The lock-in detection signal obtained by lock-in detection is sent to an AD converter 125 and converted from analog to digital. The gas concentration calculation correction unit 124 calculates the gas concentration based on the correspondence (e.g., proportionality) between the gas concentration of the measurement target gas and the amplitude of the lock-in detection waveform. While the AD converter 125 is connected after the gas absorption measurement circuit 123 in FIG. 3 , the AD converter 125 may be connected before the gas absorption measurement circuit 123.

[0045] Furthermore, the gas absorption measurement circuit 123 can extract an optically modulated signal for gas analysis and an optically modulated signal for communication from the detection signal output from the light receiving element 22. Of these, the optically modulated signal for gas analysis is used for gas analysis by the above-mentioned lock-in detection, while the optically modulated signal for communication is, for example, a synchronization signal for the measurement start timing of gas analysis, as will be described later.

[0046] The demodulator / decoder 127 demodulates / decodes the communication information signal into a format compatible with the analyzer of this embodiment.

[0047] The control unit 126 controls each processing unit (gas absorption measurement circuit 123, gas concentration calculation correction unit 124) of the light receiving unit 20. The control unit 126 can control each processing unit based on information about the gas to be measured and communication information sent from the light emitting unit 10.

[0048] <Background to this embodiment> Fig. 4 is an overall configuration diagram showing a conventional laser gas analyzer 2. In the conventional configuration shown in Fig. 4, various communication information, such as synchronization of the timing at which concentration measurement starts between the light-emitting unit 10 and the light-receiving unit 20, is exchanged via a communication line 40.

[0049] 4, a communication line 40 connects between a modulated light generating unit 31 and a received light signal processing unit 32. Conventionally, the communication line 40, the modulated light generating unit 31, and the received light signal processing unit 32 are configured based on, for example, Patent Document 1.

[0050] As described above, in the conventional configuration, the light-emitting unit 10 and the light-receiving unit 20 are connected by a communication line 40 for signal synchronization and exchange of setting values. However, the conventional configuration has problems such as increasing the size of the laser gas analyzer 2 and making the wiring arrangement complicated.

[0051] 1, in the laser gas analyzer 1 of this embodiment, communication between the light-emitting unit 10 and the light-receiving unit 20 is performed by laser light 30, without using a communication line 40 between the light-emitting unit 10 and the light-receiving unit 20. In this way, in this embodiment, there is no need to connect the light-emitting unit 10 and the light-receiving unit 20 with the communication line 40, which simplifies the handling of wiring by an operator and also enables the laser gas analyzer 1 to be made more compact.

[0052] <Communication between the light-emitting unit 10 and the light-receiving unit 20> In the laser gas analyzer 1 of this embodiment, a communication signal between the light-emitting unit 10 and the light-receiving unit 20 can be generated as an optical modulation signal by the wavelength sweep / modulation current setting unit 113 shown in Fig. 3. The communication signal is preferably information from the light-emitting unit 10 that is required by the light-receiving unit 20.

[0053] The wavelength sweep / modulation current setting unit 113 can generate an optical modulation signal for gas analysis and an optical modulation signal for communication. For example, the optical modulation signal for communication is a synchronization signal for matching phases during lock-in detection. The synchronization signal is, for example, a pulsed intensity modulation signal, and can synchronize the modulated light generation unit 11 and the received light signal processing unit 21 at the time of receiving the pulse.

[0054] When detecting gas concentrations by lock-in detection, a phase shift occurs in the detected waveform unless the measurement start timing is synchronized between the modulated light generating unit 11 and the received light signal processing unit 21. Therefore, in this embodiment, in order to match the phases, a synchronization signal is superimposed on the laser light instead of the conventional communication line 40, and communicated between the modulated light generating unit 11 and the received light signal processing unit 21. This makes it possible to synchronize the measurement start timing between the modulated light generating unit 11 and the received light signal processing unit 21, thereby suppressing the occurrence of a phase shift.

[0055] 5 is a waveform diagram of the drive current generated by the wavelength sweep / modulation current setting unit 113, in which a synchronization / measurement ID signal as an optical modulation signal (I) for communication is provided before an optical modulation signal (II) for gas analysis. The optical modulation signal (II) is an optical modulation signal that sweeps the wavelength in a wavelength band including the optical absorption wavelength of the absorption line spectrum of the gas to be measured.

[0056] The optical modulation signal (III) shown in FIG. 5 is information of the light emitting unit 10 required by the light receiving unit 20, which is different from the optical modulation signal (I), and includes, but is not limited to, characteristic change information such as laser element temperature information of the laser element 12, degradation information, information on the gas to be measured, etc.

[0057] The optical modulation signal generated by the wavelength sweep / modulation current setting unit 113 shown in Fig. 3 can be converted into a digital signal, and the optical modulation signal is converted from digital to digital by the DA converter 114 and sent to the laser element 12. In this embodiment, optical modulation signals (I) and (III) for communication and an optical modulation signal (II) for gas analysis are superimposed on the laser light 30.

[0058] In the light receiving unit 20, the gas absorption measurement circuit 123 acquires an optical modulation signal for gas analysis and an optical modulation signal for communication from the detection signal output from the light receiving element 22, and synchronizes the measurement start timing of the lock-in detection. This makes it possible to correct the phase shift of the lock-in detection waveform in the gas absorption measurement circuit, enabling accurate gas concentration detection. Furthermore, it is preferable to perform synchronization using the optical modulation signal (I) for each gas measurement and then perform gas concentration detection using the optical modulation signal (II), since this allows detection without phase shift for each measurement.

[0059] If the synchronization and measurement ID signal generated by the wavelength sweep and modulation current setting unit 113 is a simple single pulse, there is a possibility that the correct timing cannot be acquired when the laser light 30 is blocked by dust or the like. Therefore, by using a predetermined pattern of multiple pulses in the light emitting unit 10 and the light receiving unit 20, concentration measurement can be performed only when the pattern is correctly received, enabling stable measurement.

[0060] The exact same pulse pattern may be used, but in that case, it is assumed that measurements will continue under the same conditions. When measuring multiple gas components, such as changing the gas component to be measured, the light-emitting unit 10 can tell the light-receiving unit 20 which gas component is being measured, so by being able to predict the next pulse pattern based on the pulse pattern received by the light-receiving unit 20, it becomes possible to perform measurements under multiple conditions. The gas concentration calculation correction unit 124 is notified by the control unit 126 of which component concentration to calculate.

[0061] For example, if two pulse patterns, 10001 and 10101, are provided, measurements can be made under two conditions, and predictability can be achieved by using consecutive numbers such as 10001, 10010, 10011, etc.

[0062] 5 shows an example of communication using a pulse pattern, i.e., communication using intensity modulation, but it is also possible to use an optical communication method using a general single laser, and it is also possible to use binary communication such as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), or Phase Shift Keying (PSK), or multi-level communication using amplitude or the like (QASK, QPSK, etc.). In that case, the signals are matched by the demodulator / decoder 127 shown in FIG. 4. This can also be achieved by introducing an optical heterodyne detection mechanism into the light receiving unit 20.

[0063] In this embodiment, an optical 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. The optical modulation signal (III) can be transmitted periodically or irregularly, but it is preferable that communication be performed periodically between the light-emitting unit 10 and the light-receiving unit 20 to exchange setting values, etc. In this embodiment, the optical modulation signal (III) is transmitted periodically after performing concentration detection multiple times using the optical modulation signal (I) and the optical modulation signal (II). Since this is one-way communication from the light-emitting unit 10 to the light-receiving unit 20, it is possible to handle this by determining in advance the information required by the light-receiving unit 20 and having the light-emitting unit 10 periodically transmit (broadcast) this information.

[0064] Furthermore, as mentioned above, it is expected that the pulse pattern may be corrupted by disturbances such as dust, so adding redundancy such as a checksum will enable more reliable communication.

[0065] To simultaneously achieve the above-described concentration measurement function and communication function, it is desirable to provide a low-distortion DA converter 114 between the modulated light generating unit 11 and the laser element 12. Conventional laser gas analyzers utilize the fact that optically modulated laser light is distorted by absorption by the gas being measured, and detect concentration by measuring the harmonic components (generally the second harmonic) of the modulation frequency. Therefore, low-distortion analog oscillators that oscillate at specific frequencies have often been used. Even with such analog oscillators, communication is relatively easy using a mixer / multiplexer (AND) or the like if intensity modulation (ASK) is used. However, there are concerns that communication using modulation such as PSK or FSK or multi-level modulation will complicate the peripheral circuitry and increase the circuit size. Therefore, in this embodiment, a low-distortion DA converter with a total harmonic distortion significantly lower than that of conventional low-distortion analog oscillators (approximately -90 to -80 dB) is used, enabling the laser to be driven with any waveform while maintaining the low-distortion modulation performance required for gas concentration measurement. This makes it possible to accommodate communication including multi-value communication between the light emitting unit 10 and the light receiving unit 20 without increasing the scale of the circuit. [Industrial Applicability]

[0066] The laser gas analyzer of the present invention is ideal for measuring and controlling combustion exhaust gases from boilers, waste incineration plants, etc. It is also useful for steel gas analysis (blast furnaces, converters, heat treatment furnaces, sintering (pellet plants), coke ovens), fruit and vegetable storage and aging, biochemistry (microorganisms) (fermentation), air pollution (incinerators, flue gas desulfurization and denitrification), exhaust gases from internal combustion engines of automobiles and ships (detester), disaster prevention (explosive gas detection, toxic gas detection, combustion gas analysis of new building materials), plant cultivation, chemical analysis (oil refineries, petrochemical plants, gas generating plants), environmental applications (ground concentration, tunnel concentration, parking lots, building management), and various physical and chemical experiments. [Explanation of symbols]

[0067] 1. Laser gas analyzer 2 Laser gas analyzer 10 Light-emitting part 11 Modulated light generation unit 12 Laser element 13 Collimating lens 14 Light-emitting window plate 15. Light-emitting container 20 Light receiving section 21 Light receiving signal processing section 22 Photodetector 23 Condenser lens 24 Light receiving window plate 25 Light receiving unit container 30 Laser light 40 Communication lines 50a, 50b walls 51a, 51b flanges 52a, 52b Optical axis adjustment flange 112 Laser element temperature control circuit 113 Wavelength sweep and modulation current setting section 114 DA converter 122 IV conversion circuit 123 Gas absorption measurement circuit 124 Gas concentration calculation correction unit 125 AD converter 126 Control Unit 127 Demodulator / Decoder

Claims

1. A laser gas analyzer that performs gas analysis of a measurement target gas present in a measurement target space, a laser element that emits laser light in a wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the measurement target gas; a modulated light generating unit that sweeps a wavelength in a wavelength band including an optical absorption wavelength of the absorption line spectrum of the measurement target gas and supplies a drive current to the laser element so that the wavelength is modulated; a light emitting section having a light receiving element that receives the laser light that has passed through the measurement target space; a light-receiving signal processing unit that analyzes the measurement target gas based on the detection signal output from the light-receiving element; a light receiving unit having the modulated light generating unit generates an optical modulated signal for gas analysis and an optical modulated signal for communication; the optical modulation signal for communication is a synchronization signal for starting measurement of gas analysis, the synchronization signal having a pattern of multiple pulses; an optical modulation signal for communication is superimposed on the laser light together with the optical modulation signal for gas analysis, thereby enabling communication between the light emitting unit and the light receiving unit; The laser gas analyzer is characterized in that the light receiving signal processing unit acquires the optical modulation signal for the gas analysis and the synchronization signal, and the gas analysis is started when the pulse pattern of the synchronization signal is correctly received.

2. 2. The laser gas analyzer according to claim 1, wherein the light emitting unit digitally converts the optical modulation signal for gas analysis generated by the modulated light generating unit and the optical modulation signal for communication, and superimposes the converted signal on the laser light.

3. 3. The laser gas analyzer according to claim 1, wherein the light receiving signal processing unit performs analog-to-digital conversion on the detection signal output from the light receiving element to obtain an optically modulated signal for gas analysis and an optically modulated signal for communication.

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