JP2012108156A - Gas concentration measurement method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas concentration measurement method and a measurement device with which the concentration of gas generating in a sealed container such as a boiler, a garbage incinerator, a combustion chamber of a combustion engine or exhaust gas discharged from the sealed container to the outside can be measured by using laser light and the concentration of a plurality of gases can be efficiently measured with using a simple system.SOLUTION: In a gas concentration measurement method in which the gas concentration is measured from the laser light absorption amount of a specific wavelength through the irradiation of the gas atmosphere to be measured with laser light of a specific wavelength, the oscillating wavelengths of a plurality of laser diodes are set to the absorption wavelength corresponding to the plurality of gases, the oscillating lights from the respective laser diodes are subject to the time division and thus generated, the oscillating lights thus generated are irradiated by using the same laser beam, and the gas concentration is obtained from light receiving signals obtained by receiving the lights of the irradiation laser beam.

Description

  The present invention relates to a gas generated in a closed container such as a boiler, a garbage incinerator, a combustion chamber of a combustion engine, a gas discharged to the outside from the closed container, or a place where the discharged gas is highly likely to stay. The present invention relates to a measuring method and a measuring apparatus for measuring a gas concentration of gas or the like in the gas.

  2. Description of the Related Art Conventionally, a technique using a laser beam has been developed as a technique for measuring the concentration of gas generated in a closed container such as a boiler, a garbage incinerator, or a combustion chamber of a combustion engine. This gas concentration measurement technology using laser light utilizes the property of absorbing a specific wavelength for each gas type, and irradiates laser light of a specific wavelength in the gas atmosphere, and the laser light that has passed through the gas atmosphere. By analyzing the spectrum, the concentration of a specific gas type is grasped, which is called absorption spectroscopy.

  As an example, Patent Document 1 (Japanese Patent Laid-Open No. 10-142148) is known. In Patent Document 1, the concentration of a specific type of gas is accurately measured even under conditions with background light (background noise). The background noise is calculated by calculating the difference between the main measurement light and the background light using the main measurement light that is measured by frequency-modulating the laser light and the background light that is measured by another sensor so that it can be measured. A technique for reducing the above is shown.

  Moreover, in patent document 2 (patent 3342446 gazette), the difference of main measurement light and background light is calculated using main measurement light and the background light measured by another sensor similarly to the said patent document 1. (Difference circuit method) shows a technique for reducing background noise, and further, by modulating the laser light not at a single frequency but at two different frequencies (double modulation), Although modulation with a single frequency is likely to cause a drift in the measurement value due to multiple reflection (fringing) of the measurement laser, a technique for suppressing the drift in the measurement value is shown.

An outline of the gas concentration measuring apparatus disclosed in Patent Document 2 will be described with reference to FIG.
A light source composed of a semiconductor laser diode (LD) 01 for oscillating laser light is connected to a control circuit of an LD driver 02 so that the temperature and current of the LD are controlled. The oscillated laser beam is reflected by the half mirror 03, and the laser beam L enters the measurement region from one optical window toward the other optical window. The laser light that has passed through the measurement region is received by two photodiodes (PD2, PD3) 04 and 05 as light receiving means arranged in the vicinity of the other optical window.

  One photodiode 04 is arranged on the optical axis so as to receive the laser light L that has passed through the measurement region, and the other photodiode 05 is arranged at a position off the laser optical axis, and the measurement region The light emitted from the flame is received as background light. The light reception signals from the two photodiodes 04 and 05 are input to the AD converter 07 via the measurement unit 06 and then sent to the computer 08.

Japanese Patent Laid-Open No. 10-142148 Japanese Patent No. 3342446

However, the techniques disclosed in Patent Documents 1 and 2 are all techniques for measuring one kind of gas concentration, and are shown for one irradiation laser light L emitted from one laser diode. Yes.
In particular, Patent Document 2 shows that modulation is performed by two sine wave generators 09 and 010, but this is for preventing drift of a measurement value due to multiple reflection (fringe) of a laser. It is not a technique that enables measurement of various gas concentrations with a single irradiation laser beam L.
Therefore, in order to measure a plurality of types of gas concentrations, a system such as providing a plurality of irradiation laser beams must be provided, which may lead to deterioration in measurement efficiency, complication of the measurement apparatus, and increase in apparatus cost. There is a need for a technique for efficiently measuring a plurality of types of gas concentrations by using one irradiation laser beam and laser beams from one or a plurality of laser diodes.

  Therefore, the present invention has been made in view of such a background, and gas generated in a closed container such as a boiler, a garbage incinerator, a combustion chamber of a combustion engine, or the like, is discharged to the outside from the closed container. An object of the present invention is to provide a gas concentration measurement method and a measurement apparatus that can measure a gas concentration such as a gas using a laser beam and that can measure a plurality of types of gas concentrations with an efficient and simple system. .

  In order to solve the above-mentioned problem, the first invention includes a plurality of gas concentration measurement methods in which a measurement gas atmosphere is irradiated with laser light of a specific wavelength, and the gas concentration is measured from the amount of absorption of the laser light of the specific wavelength. The oscillation wavelength of each laser diode is set to an absorption wavelength corresponding to a plurality of types of gases, the oscillation light from each laser diode is generated in a time-sharing manner, and the generated oscillation light is irradiated with the same laser beam. The method is characterized in that a plurality of types of gas concentrations are obtained from a received light signal obtained by receiving irradiated laser light.

  The time division oscillation light may be generated by time division control of the drive current for driving each laser diode, or the laser light continuously oscillated from each laser diode may be generated by time division. Good.

According to this invention, since each laser beam is irradiated onto the light receiving means alternately in a time-division manner, it is easy to extract signals corresponding to each gas, and a plurality of types of gas concentrations can be calculated easily and reliably. It becomes possible.
Further, when laser light that is continuously oscillated is generated in a time-sharing manner, the light emission state is stabilized and highly accurate measurement is maintained.

  Next, a second invention is a gas concentration measurement method for irradiating a measurement gas atmosphere with laser light of a specific wavelength and measuring the gas concentration from the absorption amount of the laser light of the specific wavelength. The oscillation wavelength is set to an absorption wavelength corresponding to multiple types of gases, a drive current is applied so that each laser diode continuously oscillates, and the oscillation light from each laser diode is combined and irradiated with the same laser beam. The light receiving signal obtained by receiving the irradiated laser light is extracted from the signal for each gas based on the modulation frequency of each gas to obtain a plurality of types of gas concentrations.

According to the second aspect of the invention, the modulation frequencies of the respective gases are all made different, and the respective gases are electrically separated and taken out based on the modulation frequency after light reception. Each gas can be measured separately.
In addition, since the laser diode itself is in a continuous light emission state without repeatedly stopping and starting light emission, the light emission is stable, and highly accurate measurement is maintained.

  Next, a third invention is a gas concentration measurement method for irradiating a measurement gas atmosphere with laser light of a specific wavelength and measuring the gas concentration from the absorption amount of the laser light of the specific wavelength. The oscillation wavelength is set to an absorption wavelength corresponding to multiple types of gases, a drive current is applied so that each laser diode continuously oscillates, and the oscillation light from each laser diode is combined and irradiated with the same laser beam. The light receiving signal obtained by receiving the irradiated laser light is separated into signals for each gas by an optical filter or a deflecting surface before being received by the light receiving diode, and a plurality of types of gas concentrations are obtained. To do.

  According to the third aspect of the invention, since the laser light is separated into the signals for the respective gases by the optical filter or the deflecting surface before being input to the light receiving means, the apparatus does not require a complicated electric circuit. Is simplified.

  Further, the fourth invention is an apparatus invention for carrying out the method of the first invention, wherein the gas concentration is determined from the amount of absorption of the laser light of the specific wavelength by irradiating the measurement gas atmosphere with the laser light of the specific wavelength. In the gas concentration measuring device to measure, a plurality of the laser diodes, and time division means for generating the oscillation light from each laser diode whose oscillation wavelength is set to an absorption wavelength corresponding to a plurality of types of gas in a time division manner Irradiating laser light corresponding to a plurality of types of gases generated by the time division with the same laser beam, and receiving light from the irradiated laser light, and the light receiving signal received by the light receiving means Each gas concentration divided | segmented by the time division means is calculated | required, It is characterized by the above-mentioned.

  According to the fourth invention, similarly to the first invention, according to such an invention, each laser beam is alternately irradiated to the light receiving means in a time-division manner, and therefore, signals corresponding to the respective gases are taken out. Therefore, it is possible to calculate a plurality of types of gas concentrations easily and reliably.

  Next, the fifth aspect of the invention is an apparatus invention for carrying out the method of the second aspect of the invention, wherein a laser beam having a specific wavelength is irradiated in a measurement gas atmosphere, and the gas concentration is determined from the absorption amount of the laser beam having the specific wavelength. In the gas concentration measuring apparatus for measuring the gas, a driving current is supplied to the laser diode so as to continuously oscillate from the plurality of laser diodes and the laser diodes whose oscillation wavelengths are set to absorption wavelengths corresponding to a plurality of types of gases. A current driving circuit; a light receiving means for receiving the laser light irradiated by combining the oscillation light from each laser diode; and a gas based on the modulation frequency of each gas from the light reception signal received by the light receiving means. And a demodulating means for extracting a signal. The demodulating means extracts each gas signal to obtain the gas concentration.

The sixth invention is an apparatus invention for carrying out the method of the third invention, wherein the gas concentration is determined from the amount of absorption of the laser light of the specific wavelength by irradiating the measured gas atmosphere with the laser light of the specific wavelength. In the gas concentration measuring device that measures
A plurality of laser diodes; drive current control means for applying a drive current so as to continuously oscillate from each laser diode whose oscillation wavelength is set to an absorption wavelength corresponding to a plurality of gases; and oscillation from each laser diode A light receiving means for receiving the laser light irradiated by combining the light and a light separating means comprising an optical filter or a deflecting surface for separating a gas signal corresponding to each gas before receiving the light by the light receiving means. In addition, the gas concentration is obtained by taking out each gas signal by the light separation means.

According to the fifth and sixth inventions, since the laser light receiving means side separates the signals for the respective gases, the state on the light emitting unit side is stable, and stable measurement is maintained.
Furthermore, according to the sixth invention, the modulation frequencies of the respective gases are all made different so that each gas is electrically separated based on the modulation frequency after light reception. Gas can be measured separately.
Further, according to the eighth invention, the apparatus is simplified without requiring a complicated electric circuit.

  According to the present invention, the concentration of a gas generated in a closed container such as a boiler, a waste incinerator, or a combustion chamber of a combustion engine, or a gas discharged to the outside from the closed container is measured using laser light. Thus, it is possible to provide a gas concentration measurement method and a measurement apparatus that can measure a plurality of types of gas concentrations with a simple and efficient system.

1 is an overall configuration block diagram of a gas concentration measuring apparatus according to a first embodiment of the present invention. It is a whole block diagram of the gas concentration measuring apparatus which concerns on 2nd Embodiment. It is explanatory drawing about the wavelength switching means of 1st Embodiment. It is explanatory drawing about the wavelength switching means of 2nd Embodiment. It is a whole block diagram of the gas concentration measuring device concerning a 3rd embodiment. It is outline | summary explanatory drawing of the oscillation of wavelength (lambda) 1 from the 1st laser diode of 3rd Embodiment, and the oscillation of wavelength (lambda) 2 from a 2nd laser diode. It is a whole block diagram of the gas concentration measuring device which concerns on 4th Embodiment. It is a whole block diagram of the gas concentration measuring device concerning a 5th embodiment. It is a whole block diagram of the gas concentration measuring device concerning a 6th embodiment. It is explanatory drawing which shows a prior art.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Only.
(First embodiment)

FIG. 1 is an overall configuration block diagram showing an outline of a gas concentration measuring apparatus 2 according to the first embodiment of the present invention.
As shown in FIG. 1, a light source composed of a semiconductor laser diode (LD) 4 for oscillating a laser beam is connected to an LD current driving circuit 6 and an LD temperature driving circuit 8 of an LD driver. The temperature and current are controlled.
The LD current drive circuit 6 receives the direct current 10, the ramp wave 12, the modulation signal f, the modulation signal w, and the wavelength lock signal 16 from the wavelength switching means 14 and the wavelength lock signal via the adder 9. The switched wavelength signal 18 after switching is applied as the reference signal.

  The direct current 10 is a current for driving the semiconductor laser diode 4, the modulation signal f and the modulation signal w are signals applied to perform frequency modulation on the laser light, and the ramp wave 12 is This is a signal applied to slowly sweep the laser oscillation wavelength at the absorption spectrum unique to the measurement target gas.

The laser light oscillated from the semiconductor laser diode 4 is guided to the duplexer 22 through the laser optical path 20 of the optical fiber. The laser beam demultiplexed into the reference gas cell 24 and the measurement region by the demultiplexer 22 and demultiplexed into the measurement region is applied to the gas circulation region in the engine combustion chamber or the engine exhaust pipe by the laser beam L. The other collimator (optical lens) 28 is irradiated from one collimator (optical lens) 26.
The laser light that has passed through the measurement region is received by a photodiode (PD) (light receiving diode) of the light receiving means 30 disposed in the vicinity of the other collimator 28 and amplified by a preamplifier.

As shown in FIG. 1, the signal received by the light receiving means 30 is then sent to the demodulation processing means 32. The part of the demodulation processing means 32 is inputted from two places. From one input side, a band pass filter (BPF) 34, an AC amplifier 36, a first lock-in amplifier (demodulation means based on the modulation signal f) 38, and The second lock-in amplifier (demodulating means based on the modulation signal w) 40 and the DC amplifier 42 are connected in series.
Further, a low-pass filter (LPF) 44 and a DC amplifier 46 are connected in series from the other input side. Outputs from the DC amplifiers 42 and 46 are input to an AD converter 48 and sent to the computer 50 from there.

  The received light signal from one input side is passed through a signal of a certain frequency band by a band pass filter 34 and amplified by an AC amplifier 36. Thereafter, the signal is input to a first lock-in amplifier (demodulation means based on the modulation signal f) 38, and the first lock-in amplifier 38 receives the modulation signal f as a reference signal and extracts a signal synchronized with the modulation signal f. It is. Further, the signal is input to a second lock-in amplifier (demodulation means based on the modulation signal w) 40, and the second lock-in amplifier 40 receives the modulation signal w as a reference signal and extracts a signal synchronized with the modulation signal w. It is.

  In this way, the target signal component is extracted from the laser light that is doubly frequency-modulated with the modulation signals f and w by the first lock-in amplifier 38 and the second lock-in amplifier 40. Yes.

Further, the received signal from the other input side of the demodulation processing means 32 passes only the low frequency component by the low pass filter 44, is amplified by the DC amplifier 46, and is AD converted as the detected value of the DC component in the received light signal. Is input to the device 48.
The digital signal after passing through the AD converter 48 is input to the computer 50, and the target gas concentration is analyzed based on the measurement results of the signal components from the 138 and the second lock-in amplifier 40 and the DC component. Processing is performed.

  On the other hand, the laser beam demultiplexed from the demultiplexer 22 to the reference gas cell 24 is input to the standard signal processing means 52. Laser light is circulated in a standard gas of a known concentration at a constant pressure enclosed in a reference gas cell 24, received by a light receiving means 54, subjected to signal processing similar to that of the demodulation processing means 32, and sent to an AD converter 48. Is output. Then, it is used for processing such as gas concentration verification and correction.

  Among the standard signal processing means 52, as shown in FIG. 1, a band pass filter (BPF) 56, an AC amplifier 58, a third lock-in amplifier (demodulation means based on the modulation signal f) 60, and a fifth lock-in amplifier. (Demodulation means based on modulation signal w) 62 and a DC amplifier 64 are connected in series to extract a target signal modulated by modulation signals f and w from a standard gas. Based on the signal, wavelength switching is performed. The wavelength lock signal 16 of the means 14 is set. Further, a switched wavelength signal 18 is formed by adding a certain value to the wavelength lock signal 16.

The wavelength switching means 14 will be described with reference to FIG. For example, when the types of gases to be measured are NH ₃ gas and H ₂ O gas, the respective wavelengths are in the vicinity of 1.512 μm, and in the case of N ₂ O gas and NH ₃ gas, the wavelength is about 1.517 μm. Therefore, the light absorption of these two gases can be observed within the wavelength sweep range by the current of one laser diode.

For example, when measuring two kinds of gases, NH ₃ gas and H ₂ O gas, the ammonia NH ₃ gas is sealed in the reference gas cell 24 using the absorption center wavelength λ1 of ammonia NH ₃ as a standard, The bandpass filter (BPF) 56, the AC amplifier 58, the third lock-in amplifier 60, the fifth lock-in amplifier 62, and the DC amplifier 64 of the standard signal processing means 52 from a circuit connected in series. The absorption wavelength calculated from the output is set as the lock wavelength λ1.

Then, as shown in FIGS. 3A and 3B, a current I1 for oscillating the absorption center wavelength λ1 of ammonia NH ₃ and a current I2 for oscillating the absorption center wavelength λ2 of water vapor H ₂ O are timed. Oscillation is performed by alternately switching at the division Δt. The current I2 is I2 = I1 + ΔI, and is set as the wavelength signal 18 after switching.
The wavelength lock signal 16 and the switched wavelength signal 18 are alternately generated as a pulsed switching current by the wavelength switching means 14 and input to the adder 9.
By detecting the gas absorption signal at λ1 when the current I1 is applied and by detecting the gas absorption signal at the wavelength λ2 when the current I2 is applied, the single laser diode 4 causes NH ₃ to be detected. Two types of gas concentrations, gas and H ₂ O gas, can be measured.

It should be noted that the timing when I1 is applied and the current I2 is applied so that the processing in the demodulation processing means 32 can be performed with respect to which of NH ₃ gas and H ₂ O gas is processed. In other words, the timing of time division (Δt) is automatically taken into the computer 50, and the two gases are distinguished and calculated in the calculation of the measured concentration.

  The wavelength switching means 14 detects a wavelength shift signal when the current I1 for oscillating the wavelength λ1 is applied, generates a signal for correcting the wavelength shift, and shifts from the lock wavelength λ1. Is used to stabilize the wavelength.

Note that the time division (Δt) interval is set according to the gas to be measured, and when the combustion chamber of the engine is to be measured, the time division (Δt) is decreased with increasing engine speed, for example, according to the engine speed. Further, it is possible to set Δt so that two types of gas can be measured within one cycle of explosion combustion.
Moreover, although the absorption center wavelength λ1 of the NH ₃ gas has been described as the lock wavelength, the current may be set using the absorption center wavelength λ2 of the H ₂ O gas as the lock wavelength.

As described above, the drive currents I1 and I2 are alternately switched between the adjacent gas absorption wavelengths λ1 and λ2 within the wavelength sweep range by the drive current of one laser diode 4, and one laser diode 4 is switched. Since the laser beams corresponding to the two kinds of gases are irradiated with time division (Δt), two gas concentrations can be measured simultaneously by the same laser beam L with one laser diode, thus simplifying the system. The cost of the gas measuring device can be reduced.
(Second Embodiment)

Next, a second embodiment will be described with reference to FIGS.
The second embodiment differs from the first embodiment only in that the wavelength lock signal is locked to the absorption wavelength of the gas enclosed in the first reference gas cell 70 and the second reference gas cell 72, respectively. Since the components are the same as those in the first embodiment, the same reference numerals are given and the description thereof is omitted.

In the standard signal processing means 74, a first reference gas cell 70 and a second reference gas cell 72 are arranged in series. For example, the first reference gas cell 70 is filled with NH ₃ gas having a known concentration, and second The reference gas cell 72 is filled with a known concentration of H ₂ O gas, and includes a band pass filter (BPF) 76, an AC amplifier 78, a third lock-in amplifier 80, a fifth lock-in amplifier 82, and a DC amplifier 84. Are sent to the wavelength switching means 86, and the absorption wavelengths based on the respective reference gases are set as the first lock wavelength λ1 and the second lock wavelength λ2.

  In the wavelength switching means 86, as shown in FIGS. 4A and 4B, the drive currents I1 and I2 are set based on the lock wavelengths λ1 and λ2, and the first wavelength lock signal 88 and the second wavelength lock are set. As a signal 90, a pulsed switching current is alternately generated by time division (Δt) and output to the adder 9.

The second embodiment has the same effect as the first embodiment, and further oscillates the current I1 for oscillating the absorption center wavelength λ1 of ammonia NH ₃ and the absorption center wavelength λ2 of H ₂ O. Since the current I2 is set based on the standard gas sealed in the reference gas cell, an accurate reference current value is set as compared with the case where I2 is obtained by adding the switching amount ΔI as in the first embodiment. Errors are less likely to occur and accuracy is improved.

(Third embodiment)
Next, a third embodiment will be described with reference to FIG.
In the first and second embodiments, the case where two types of gas concentrations are measured by one laser diode 4 has been described, but in the third embodiment, two types of laser diodes 100 and 102 are used, The case of measuring the gas concentration will be described.
The third and fourth embodiments are improvements on the laser beam irradiation side, and the fifth, sixth, and seventh embodiments are improvements on the laser beam reception side.
In addition, about the same component as 1st Embodiment and 2nd Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In order to oscillate the laser beam, the light source includes a first laser diode (LD1) 100 and a second laser diode (LD2) 102. The first laser diode 100 is connected to the LD1 current driving circuit 104 and the LD1 temperature driving circuit 106. The temperature and current are controlled by being connected, and the second laser diode 102 is connected to the LD2 current driving circuit 108 and the LD2 temperature driving circuit 110 to control the temperature and current.

  The LD1 current drive circuit 104 is connected to the first DC current 114, the ramp wave 12, the modulation signal f, the modulation signal w, the pulse signal 118 constituting the time division means 116, and the wavelength lock via the adder 112. Each of the signals 120 is applied. A similar signal is also input to the LD2 current drive circuit 108 via the adder 122.

The current applied to the first laser diode 100 (added current of the first DC current 114 and the pulse signal 118) oscillates at the wavelength λ1 so that the first laser diode 100 and the second laser diode oscillate alternately. The current applied to the second laser diode 102 (the added current of the second DC current 124 and the pulse signal 118) is set so that the wavelength λ2 oscillates.
The oscillating laser from the first laser diode 100 and the oscillating laser from the second laser diode 102 are merged by the multiplexer 125, pass through the laser optical path 20 of the optical fiber, and from the demultiplexer 27 to the gas flow region. Irradiated by the same laser beam.

An outline of oscillation of the wavelength λ1 from the first laser diode 100 shown in FIG. 6 and oscillation of the wavelength λ2 from the second laser diode 102 is shown.
In FIG. 6, the pulse width is ramp-shaped, but it may be a flat output state. Further, the time division (Δt) can be set as appropriate when applied to the engine as described in the first embodiment in accordance with the measurement gas.

Since the respective laser beams are alternately irradiated onto the light receiving means 30 in a time-division manner, it is easy to extract signals corresponding to the respective gases, and it is possible to calculate a plurality of types of gas concentrations easily and reliably, and the wavelength λ1 The concentration of the first gas can be measured from the gas absorption signal at the time when the gas oscillates, and the concentration of the second gas can be measured from the gas absorption signal at the time when the wavelength λ2 oscillates.
Note that the correspondence between the timing of time division (Δt) and the extracted gas signal is automatically calculated by the computer 50.

(Fourth embodiment)
Next, a fourth embodiment will be described with reference to FIG.
Compared with the third embodiment, the fourth embodiment is not the drive current of the first laser diode 100 and the second laser diode 102 but the first laser diode 100 and the second laser diode 102 that are time-divided by the pulse signal. Is different in that it oscillates continuously and is time-divided by optical modulators 134 and 136 in the middle of the optical fiber that guides the oscillated laser light to one collimator (optical lens) 26. Therefore, the same reference numerals are given and description thereof is omitted.

  The laser beams oscillated from the first laser diode 100 and the second laser diode 102 are sent to the first optical polarization plane controller 130 and the second optical polarization plane controller 132, respectively. Then, the light is guided to the first optical modulator 134 and the second optical modulator 136. The optical polarization plane controllers 130 and 132 adjust the plane of polarization of the laser light to ensure the modulation action by the pulse signal 138 in the next optical modulators 134 and 136.

  The first laser diode 100 and the second laser diode 102 are continuously oscillated, and the laser light oscillated by the first laser diode 100 according to the pulse signal 138 constituting the time division means 135 is passed through the optical modulator 134. The laser light oscillated by the laser diode 102 passes through the optical modulator 136 alternately by time division (time Δt). After passing, the laser light is combined by the multiplexer 139 and the laser of the same optical fiber. The light is input to the duplexer 140 through the optical path 20, and is demultiplexed by the duplexer 140 into a flow to the first reference gas cell 70 and a flow to the measurement region of the standard signal processing means 74.

The concentration of the first gas can be measured from the gas absorption signal at the time when the wavelength λ1 oscillates, and the concentration of the second gas can be measured from the gas absorption signal at the time when the wavelength λ2 oscillates.
Compared with the third embodiment, according to the fourth embodiment, the activation of the first and second laser diodes 102 and 102 itself is not controlled, and the light emission from the laser diode is continuously performed. Therefore, the light emission state is stable and measurement with high accuracy is possible.

(Fifth embodiment)
Next, a fifth embodiment will be described with reference to FIG.
In the fifth embodiment, the first laser diode 100 and the second laser diode 102 are continuously oscillated, and the signals of the wavelengths λ1 and λ2 are electrically separated from the received signals based on the modulation frequencies, respectively. Is.
In addition, the same code | symbol is attached | subjected about the component same as 3rd Embodiment and 4th Embodiment, and description is abbreviate | omitted.

  In the case of measuring one kind of gas, in order to improve the measurement accuracy, it is modulated with two modulation frequencies f and w (f = 10 KHz, w = 500 Hz) and sequentially demodulated by the demodulation means 150 and 152. When measuring two kinds of gases, the signals are separated by setting the respective modulation frequencies to different frequencies.

For example, the first laser diode 100 modulates with f1 = 10 KHz and w1 = 500 Hz, and the second laser diode 102 modulates with f2 = 12 KHz and w2 = 600 Hz.
That is, the electric signal amplified by the preamplifier of the light receiving means 30 is input to the first demodulation processing means 154 and the second demodulation processing means 156, and the modulation frequency f1 by the eleventh lock-in amplifier 150 of the first demodulation processing means 154. The signal synchronized with the modulation frequency w1 is demodulated by the twelfth lock-in amplifier 152, and the absorption signal of the first laser diode 100 is detected.
Similarly, a signal synchronized with the modulation frequency f2 is demodulated by the 21st lock-in amplifier 158 of the second demodulation processing means 156, and a signal synchronized with the modulation frequency w2 is demodulated by the 22nd lock-in amplifier 160. An absorption signal is detected.
The first demodulation processing means 154 is provided with first standard signal processing means 162 for gas concentration stabilization and wavelength stabilization, and the second demodulation processing means 156 is provided with second standard signal processing means 164. ing.

As described above, according to the fifth embodiment, the modulation frequencies f1, w1, f2, and w2 are all made different so that the two gases are electrically separated after light reception. Since the light emission is performed continuously, the light emission state is stable and highly accurate measurement is maintained.
In addition, since electrical processing is performed by setting the modulation frequencies f1, w1, f2, and w2, it is possible to reliably separate and measure the two types of gases.

(Sixth embodiment)
Next, a sixth embodiment will be described with reference to FIG.
In the sixth embodiment, the first laser diode 100 and the second laser diode 102 are continuously oscillated and received by the light receiving means 170, 172 before being received by the wavelength filter (light separating means) 174. And the signal of wavelength λ2.
In addition, the same code | symbol is attached | subjected about the component same as embodiment described so far, and description is abbreviate | omitted.

  As shown in FIG. 9, the laser light having passed through the gas flow region and incident on the collimator (optical lens) 28 is allowed to pass, for example, the laser light having the wavelength λ1 by the wavelength filter 174, and the laser light having the wavelength λ2 is reflected. In this way, the incident laser light is separated, and then the laser light with the wavelength λ 1 is sent to the first light receiving means 170, and the laser light with the wavelength λ 2 is sent to the second light receiving means 172.

Thereafter, the first light receiving means 170 inputs the first demodulation processing means 154, the second light receiving means 172 inputs the second demodulation processing means 156, and then the first demodulation processing means 154 and the second demodulation processing. Each of the means 156 demodulates based on the modulation signals f and w as described in the first embodiment, and takes out a signal synchronized with the modulation signals f and w.
The gas absorption signal at λ1 is detected from the signal extracted by the first demodulation processing means 154, and the gas absorption at the wavelength λ2 is detected from the signal extracted by the second demodulation processing means 156. A signal is detected and the concentration of the second gas is measured.

According to the sixth embodiment, since the wavelength filter 174 is used to separate the signals having the wavelengths λ1 and λ2 before being input to the light receiving means 170 and 172, a complicated electric circuit is not required and the apparatus is simple. It becomes.
The wavelength filter 174 is effective when the wavelengths are separated from each other. However, if the wavelength is close, sufficient separation capability cannot be obtained. Therefore, a deflection surface filter may be used instead of the wavelength filter 174. Good.

  In the first to sixth embodiments, the semiconductor laser diode 4 has been described as an example of the light source. However, the present invention can be applied to other laser oscillators capable of wavelength modulation and amplitude modulation.

  According to the present invention, the concentration of a gas generated in a closed container such as an inner boiler, a waste incinerator, or a combustion chamber of a combustion engine, or a gas discharged to the outside from the closed container is measured using a laser beam. Since it is possible to measure a plurality of types of gas concentrations with a simple and efficient system, it is useful for application to a gas concentration measurement method and a measurement apparatus.

2 Gas concentration measuring device 4 Laser diode (LD)
6 Current drive circuit (LD current drive circuit)
8 Temperature drive circuit (LD temperature drive circuit)
14, 86 Wavelength switching means 24 Reference gas cell 26, 28 Collimator (optical lens)
30, 170, 172 Light receiving means 32 Demodulation processing means 38 First lock-in amplifier (demodulation means)
40 Second lock-in amplifier (demodulation means)
52, 74 Standard signal processing means 70 First reference gas cell 72 Second reference gas cell 100 First laser diode (LD1)
102 Second laser diode (LD2)
104 1st current drive circuit (LD1 current drive circuit)
106 First temperature driving circuit (LD1 temperature driving circuit)
108 Second current drive circuit (LD2 current drive circuit)
110 Second temperature driving circuit (LD2 temperature driving circuit)
116, 135 Time division means 118, 138 Pulse signal 174 Wavelength filter (light separation means)
f, f1, f2, w, w1, w2 modulation signal

Claims (8)

In a gas concentration measurement method of irradiating a measurement gas atmosphere with laser light of a specific wavelength and measuring the gas concentration from the amount of absorption of the laser light of the specific wavelength,
The oscillation wavelength of a plurality of laser diodes is set to an absorption wavelength corresponding to a plurality of types of gases, the oscillation light from each laser diode is generated by time division, and the generated oscillation light is irradiated by the same laser beam. A gas concentration measuring method characterized in that a plurality of types of gas concentrations are obtained from a received light signal obtained by receiving irradiated laser light.   2. The gas concentration measuring method according to claim 1, wherein the time division oscillation light is generated by time division control of a drive current for driving each laser diode.   2. The gas concentration measuring method according to claim 1, wherein the time division oscillation light is generated by time division of laser light continuously oscillated from each laser diode. In a gas concentration measurement method of irradiating a measurement gas atmosphere with laser light of a specific wavelength and measuring the gas concentration from the amount of absorption of the laser light of the specific wavelength,
Set the oscillation wavelength of multiple laser diodes to the absorption wavelength corresponding to multiple gases, apply drive current so that each laser diode continuously oscillates, and combine the oscillation light from each laser diode to make them the same The light reception signal obtained by irradiating with the laser beam and receiving the irradiated laser light is extracted from the signal for each gas based on the modulation frequency of each gas, and a plurality of types of gas concentrations are obtained. Gas concentration measurement method. In a gas concentration measurement method of irradiating a measurement gas atmosphere with laser light of a specific wavelength and measuring the gas concentration from the amount of absorption of the laser light of the specific wavelength,
Set the oscillation wavelength of multiple laser diodes to the absorption wavelength corresponding to multiple gases, apply drive current so that each laser diode continuously oscillates, and combine the oscillation light from each laser diode to make them the same The light reception signal obtained by irradiating with the laser beam and receiving the irradiated laser light is separated into signals for each gas by an optical filter or deflecting surface before being received by the light receiving diode, and a plurality of gas concentrations A gas concentration measuring method characterized by obtaining In a gas concentration measurement device that irradiates a measurement gas atmosphere with laser light of a specific wavelength and measures the gas concentration from the amount of absorption of the laser light of the specific wavelength,
A plurality of the laser diodes, time division means for generating time-division oscillation light from each laser diode whose oscillation wavelength is set to an absorption wavelength corresponding to a plurality of types of gases, and the time division generation The laser beams corresponding to the plurality of kinds of gases are combined and irradiated with the same laser beam, and the light receiving means for receiving the irradiated laser light, and the time division means from the light reception signal received by the light receiving means. A gas concentration measuring device for obtaining a concentration of each divided gas. In a gas concentration measurement device that irradiates a measurement gas atmosphere with laser light of a specific wavelength and measures the gas concentration from the amount of absorption of the laser light of the specific wavelength,
A plurality of the laser diodes, a current drive circuit for supplying a drive current to the laser diodes so as to continuously oscillate from the laser diodes whose oscillation wavelengths are set to absorption wavelengths corresponding to a plurality of types of gases, and A light receiving means for receiving the laser beam irradiated by combining the oscillation light and a demodulating means for extracting each gas signal from the light reception signal received by the light receiving means based on the modulation frequency of each gas. A gas concentration measuring device for obtaining a gas concentration by taking out each gas signal by the demodulation means. In a gas concentration measuring apparatus that irradiates a laser beam with a specific wavelength into the gas atmosphere to be measured and measures the gas concentration from the amount of absorption of the laser light with the specific wavelength,
A plurality of laser diodes; drive current control means for applying a drive current so as to continuously oscillate from each laser diode whose oscillation wavelength is set to an absorption wavelength corresponding to a plurality of gases; and oscillation from each laser diode A light receiving means for receiving the laser light irradiated by combining the light and a light separating means comprising an optical filter or a deflecting surface for separating a gas signal corresponding to each gas before receiving the light by the light receiving means. And a gas concentration measuring device for obtaining a gas concentration by taking out each gas signal by the light separation means.

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