JP2017067475A - Laser type oxygen gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser type oxygen gas analyzer that radiates to an inspection space as an inspection light that is adjusted to become a class 1 or class 1M laser output, as compared with a laser beam from a DFB laser element that becomes a class 3B equivalent laser output of a wavelength in the absorption wavelength region of an oxygen gas, the oxygen gas analyzer being designed to be safe to a user and have improved convenience.SOLUTION: Provided is a laser type oxygen gas analyzer comprising a light emission unit that includes a laser element 101e for radiating a laser beam of class 3B laser output with a wavelength in the absorption wavelength region of an oxygen gas and a collimator lens 102 for collimating the laser beam from the laser element 101e and radiating a detection light, the laser type oxygen gas analyzer radiating the laser beam of class 3B laser output, as a detection light, which is weakened to class 1 or class 1M equivalent laser output by being absorbed by an intra-optical path absorption unit 104.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a laser oxygen gas analyzer that determines the presence or absence of oxygen gas and measures the gas concentration.

It is known that each gaseous gas molecule has its own light absorption spectrum. For example, FIG. 14 is an example of a light absorption spectrum of O ₂ gas (oxygen gas), where the horizontal axis indicates the wavelength and the vertical axis indicates the absorption intensity. The greater the absorption intensity on the vertical axis, the greater the amount of light absorption.

  The laser-type oxygen gas analyzer is equipped with a laser element that emits laser light of a wavelength that is absorbed by the target oxygen gas, and detects the presence or absence of oxygen gas by absorbing the laser light of this specific wavelength into the oxygen gas. can do. In addition, the laser-type oxygen gas analyzer can detect the concentration because the amount of absorption (absorption intensity) of laser light of a specific wavelength is proportional to the concentration of oxygen gas. Such a laser-type oxygen gas analyzer is particularly used for atmospheric environment measurement and control applications, for example, for combustion control of boilers such as garbage incinerators.

  Gas concentration measurement methods for a laser oxygen gas analyzer are roughly classified into a two-wavelength difference method and a frequency modulation method. A concentration measuring apparatus using a frequency modulation method is described in Patent Document 1, for example.

  In addition, in the frequency modulation, it is necessary to change the emission wavelength. Regarding the control of the emission wavelength, for example, using a reference gas cell in which the same gas component as that of the measurement target gas is preliminarily sealed, the emission wavelength of the laser element is changed to the temperature. The control method is also used, and is described in Patent Document 2, for example.

JP 7-151681 A (paragraph [0005], FIG. 4 etc.) JP 2001-235418 A (paragraphs [0012] to [0024], FIG. 2, FIG. 11, etc.)

  Regarding laser equipment, in order to prevent the laser equipment from causing troubles to users, “Laser Product Radiation Safety Standard” JIS C 6802 is defined as a Japanese Industrial Standard. In this standard, lasers are classified and classified into class 1, class 1M, class 2, class 2M, class 3R, class 3B, and class 4 from safe classes.

  In general, the laser output of the laser-type oxygen gas analyzer is preferably class 1 or class 1M because the laser class is small and the user is safe and convenient to use. Class 1 is inherently safe by design and safe to hit the human body (eyes and skin) through the optical part.

  This laser-type oxygen gas analyzer uses a laser element that emits wavelengths from 760 nm to 780 nm because the absorption wavelength of the oxygen gas to be measured is in the near infrared region. As a type of this laser element, a surface emitting laser called VCSEL (Vertical Cavity Surface Emitting Laser) may be used, but a distribution called a DFB laser (Distributed Feedback Laser) whose output is several mW to several tens mW because of availability. A feedback type semiconductor laser is often used.

  However, this DFB laser element has an output of several mW or more even with a small output, and the output is high.

  The laser class has an upper limit output depending on the wavelength, and light having a wavelength of 1400 nm or more corresponds to class 1 if the laser output is 10 mW or less, but light having a wavelength of less than 1400 nm has an allowable output depending on the wavelength.

  For example, in the vicinity of a wavelength of 760 to 780 nm in the oxygen absorption wavelength range, it is about 0.52 mW or less, and if the output is not reduced to about 1/20 as compared with a laser beam having a wavelength of 1400 nm or more, it can be handled as class 1 or class 1M. Can not. Thus, the allowable output range varies greatly even in the same class depending on whether it is 1400 nm or more.

  Since the DFB laser element used in the laser oxygen gas analyzer corresponds to class 3B, it is dangerous to perform direct in-beam observation. The output of the DFB laser element is usually several mW to several tens mW, but the inventor of the present application has a power of 0.52 mW or less, which is smaller than the capability of the DFB laser element, between 760 and 780 nm in the oxygen absorption wavelength region. Based on the idea of making the analyzer more safe and easy to use, the present inventors have come up with the idea of the present invention.

  The present invention has been made in view of the above problems, and its object is to class 1 or to a laser beam from a DFB laser element having a laser output equivalent to class 3B at a wavelength in the absorption wavelength region of oxygen gas. An object of the present invention is to provide a laser-type oxygen gas analyzer that emits detection light adjusted to have a class 1M laser output to a detection space and is improved in safety and convenience for the user.

A laser type oxygen gas analyzer according to claim 1 of the present invention includes:
A light emitting side including a laser light source unit that emits laser light of class 3B laser output at a wavelength in the absorption wavelength region of oxygen gas, and a collimating lens that collimates the laser light from the laser light source unit and emits detection light A light emitting part having an optical part;
A light receiving unit that receives detection light propagated through a space where oxygen gas to be measured exists,
A laser oxygen gas analyzer comprising:
The light emitting side optical unit has a function of emitting laser light of class 3B laser output as detection light weakened corresponding to laser output of class 1 or class 1M.

Further, a laser type oxygen gas analyzer according to claim 2 of the present invention provides:
The laser oxygen gas analyzer according to claim 1,
A laser-type light-absorbing portion that is disposed on the surface of a collimating lens or other optical element included in the light-emitting side optical portion and is substantially at the center of the laser light passage surface to absorb the laser light. An oxygen gas analyzer was used.

A laser oxygen gas analyzer according to claim 3 of the present invention is
In the laser type oxygen gas analyzer according to claim 2,
The laser light source unit and the light emitting side optical unit are arranged apart from the focal length so that a part of the laser light radiated from the laser light source unit and reaches the light transmitting side optical unit is transmitted through the light emitting side optical unit. The laser oxygen gas analyzer is characterized in that it emits as weakened detection light.

A laser type oxygen gas analyzer according to claim 4 of the present invention includes:
In the laser type oxygen gas analyzer according to claim 3,
A laser-type oxygen gas analyzer is provided, which is provided around the light-emitting side optical unit and includes an off-optical path absorption unit that absorbs laser light incident on the outside of the light-emitting side optical unit.

  According to the present invention, detection light adjusted to have a laser output of class 1 or class 1M with respect to laser light from a DFB laser element having a laser output equivalent to class 3B at a wavelength in the absorption wavelength region of oxygen gas. As described above, it is possible to provide a laser-type oxygen gas analyzer that is emitted to the detection space and has improved safety and convenience for the user.

It is a block diagram of the laser type oxygen gas analyzer of the 1st Embodiment of this invention. It is a block diagram of a laser light source part. It is a figure which shows the output waveform of the wavelength scanning drive signal generation part of a laser element. For explaining the operation of the first embodiment of the present invention, it is a diagram showing a scanning waveform, absorption and output waveforms of the synchronous detector of the O ₂ gas laser device. It is a block diagram of a light receiving element and a signal processing part. It is a principle diagram of a frequency modulation system. It is a figure which shows the change of the light emission wavelength of the laser element by temperature. It is a figure which shows the change of the light emission wavelength of the laser element by a drive current. It is explanatory drawing of the laser element and collimating lens of a normal structure. It is explanatory drawing of 1st Embodiment made into the light emission part of a class 1 or a class 1M using a class 3B DFB laser element and a collimating lens. It is explanatory drawing of 2nd Embodiment made into the light emission part of a class 1 or a class 1M using a class 3B DFB laser element and a collimating lens. It is explanatory drawing of 3rd Embodiment made into the light emission part of a class 1 or a class 1M using a class 3B DFB laser element and a collimating lens. It is explanatory drawing of 4th Embodiment made into the light emission part of a class 1 or a class 1M using a class 3B DFB laser element and a collimating lens. It is an absorption spectrum characteristic view of O ₂ gas.

  A laser oxygen gas analyzer according to a first embodiment for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a laser oxygen gas analyzer 1 of the present embodiment. The laser oxygen gas analyzer 1 includes a light emitting unit 100, a light receiving unit 200, a light emitting unit side purge unit 300, and a light receiving unit side purge unit 400.

The light emitting unit 100 further includes a laser light source unit 101, a collimating lens 102, and a box cover 103.
The light receiving unit 200 includes a condenser lens 201, a light receiving element 202, a signal processing unit 203, and a box cover 204.

The light emission unit side purge unit 300 includes a purge unit main body 301, an inlet 302, and an outlet 303.
The light receiving unit side purge unit 400 includes a purge unit main body 401, an inflow port 402, and an outflow port 403.

In the laser-type oxygen gas analyzer of this embodiment, a specific example will be described on the assumption that a measurement target gas containing oxygen gas is fixed to a pipe such as a flue that passes through the inside. The measurement target gas is, for example, exhaust gas generated during combustion.
The walls 501a and 501b are walls of this pipe. The phase flanges 502a and 502b are fixed to the walls 501a and 501b by, for example, welding.

  A purge unit main body 301 of a light emitting unit side purge unit 300 including an angle adjustment mechanism unit (not shown) is attached to one phase flange 502a. A box cover 103 of the light emitting unit 100 is attached to the purge unit main body 301. The box cover 103 incorporates an electronic board and optical components that will be described in detail later. The internal passage of the light emitting unit side purge unit 300 communicates with the internal passage of the companion flange 502a, and further communicates with the inside of the pipe. The space between the box cover 103 and the internal passage of the purge unit main body 301 is separated by a window (not shown).

  A purge unit main body 401 of the light receiving unit side purge unit 400 including an angle adjustment mechanism unit (not shown) is attached to the other phase flange 502b. A box cover 204 of the light receiving unit 200 is attached to the purge unit main body 401. The box cover 204 also incorporates an electronic board and optical components that will be described in detail later. The internal passage of the light receiving unit side purge unit 400 communicates with the internal passage of the phase flange 502b, and further communicates with the inside of the pipe. The box cover 204 and the internal passage of the purge unit main body 401 are separated by a window (not shown).

  A box cover 103 of the light emitting unit 100 includes a laser light source unit 101 mounted on an electronic substrate and a collimating lens 102 which is an optical component. The laser light source unit 101 incorporates a DFB laser element. Laser light emitted from the laser light source unit 101 is collimated into parallel light by the light-emitting side optical unit including the collimating lens 102. Further, the light-emitting side optical unit including the collimating lens 102 weakens the laser light of the class 3B laser output corresponding to the laser output of the class 1 or class 1M in the oxygen absorption wavelength region between 760 and 780 nm. Details of the light emitting side optical unit will be described later in detail with reference to the drawings. The collimated detection light 600 is incident on the inside of the walls 501a and 501b (inside the flue) through the center of the internal passage of the light emitting unit side purge unit 300 and the center of the internal passage of the companion flange 502a.

  The detection light 600 is absorbed when the oxygen gas in the measurement object gas inside the walls 501a and 501b is transmitted. Further, when oxygen gas to be measured is present in the interior of the companion flanges 502 a and 502 b, the internal passage of the light emitting unit side purge unit 300, and the internal passage of the light receiving unit side purge unit 400, it is similarly absorbed.

  Detection light 600 that is substantially parallel light that has passed through the interior of the flue enters the light receiving unit 200. The box cover 204 of the light receiving unit 200 includes a condenser lens 201 that is an optical component, a light receiving element 202 mounted on an electronic substrate, and a signal processing unit 203. The detection light 600, which is parallel light transmitted through the walls 501a and 501b (inside the flue), passes through the center of the internal passage of the companion flange 502b and the internal passage of the light-receiving unit-side purge unit 400, and the inside of the box cover 204. The light is condensed by the condenser lens 201 and received by the light receiving element 202. This light is converted into an electrical signal by the light receiving element 202 and input to the signal processing unit 203 at the subsequent stage.

  At this time, in order to prevent heat, corrosion, and contamination due to the measurement target gas, purge gas flows into the light emission unit side purge unit 300 from the inlet 302 into the purge unit main body 301 and purges the internal passage of the light emission unit side purge unit 300. In addition, the internal passage of the companion flange 502a is purged through the outlet 303. After this purging, the purge gas is discharged into the walls 501a and 501b (inside the flue). Similarly, purge gas flows into the light receiving unit side purge unit 400 from the inlet 402 into the purge unit main body 401, purges the internal passage of the light receiving unit side purge unit 400, and passes through the outlet 403 to the phase flange 502 b. Purge the internal passage. After this purging, the purge gas is discharged into the walls 501a and 501b (inside the flue).

  This purge gas blows away dust and the like that are included in the measurement target gas and adhere to each part, and keeps the window surfaces (not shown) of the light emitting unit 100 and the light receiving unit 200 clean. Further, the purge gas flowing in for purging is at a normal temperature (for example, 25 ° C.), and the inside of the purge unit main bodies 301 and 401 and the inside of the phase flanges 502a and 502b are forcibly cooled.

  As this purge gas, instrumentation nitrogen is desirable. For this reason, if instrument air is used, the instrument air contains oxygen gas, and the analysis of the oxygen gas in the flue is affected by the oxygen gas in the purge gas. If nitrogen gas is used as the purge gas, the oxygen concentration of the oxygen gas to be measured is not affected. The use of instrumentation nitrogen requires equipment and operating costs, but it is still used in places where there is a risk of fire and explosion, such as steelworks and steelworks.

  In addition, instrument air, which is compressed air, can be used as the purge gas. Instrument air is used in general incinerators. Instrument air typically contains about 20.6 vol% oxygen. The laser oxygen gas analyzer is affected by the oxygen of about 20.6 vol% when measuring air is used as the purge gas. When air is used, it is necessary that the oxygen gas in the air has no influence on the oxygen gas to be measured. In order to avoid this influence, the oxygen amount of the oxygen gas contained in the instrument air may be obtained, and the concentration may be converted and measured in advance as an offset.

  Next, detailed configurations of the light emitting unit 100 and the light receiving unit 200 will be described. First, the light emitting unit 100 will be described in detail with reference to FIGS. FIG. 2 shows details of the laser light source unit 101. The laser light source unit 101 includes a laser drive signal generation unit 101s having a wavelength scanning drive signal generation unit 101a and a high frequency modulation signal generation unit 101b.

  The wavelength scanning drive signal generator 101a outputs a wavelength scanning drive signal for making the emission wavelength of the laser element variable so as to scan the absorption wavelength of the oxygen gas to be measured.

  The high-frequency modulation signal generation unit 101b outputs a high-frequency modulation signal for frequency-modulating the wavelength with a sine wave of about 10 kHz, for example, in order to detect the absorption wavelength of the oxygen gas to be measured.

  The laser scanning signal is generated by synthesizing the high frequency modulation signal from the high frequency modulation signal generating unit 101b with the wavelength scanning driving signal output from the wavelength scanning driving signal generating unit 101a and performing frequency modulation. The laser drive signal output from the laser drive signal generation unit 101s is converted into a current by the current control unit 101c and supplied to the laser element 101e made of a semiconductor laser. Specifically, the laser element 101e is a DFB laser element as described above.

  The laser element 101e is provided with a temperature stabilizing means. This temperature stabilization means includes a temperature control unit 101d, a thermistor 101f, and a Peltier element 101g. A thermistor 101f as a temperature detecting element is disposed in the vicinity of the laser element 101e, and a Peltier element 101g is disposed in the vicinity of the thermistor 101f. The Peltier element 101g is subjected to PID (proportional / integral / differential) control by the temperature control unit 101d so that the resistance value of the thermistor 101f becomes a constant value, and as a result, the temperature of the laser element 101e is stabilized. It is what makes it operate.

  Here, as shown in FIG. 3, the wavelength scanning drive signal output from the wavelength scanning drive signal generation unit 101a becomes a substantially trapezoidal unit waveform due to the variable drive signal S1 and the offset signal S2. Is a signal repeated at a constant period.

  The variable drive signal S1 of the wavelength scanning drive signal is a signal for scanning the absorption wavelength, and is a part that linearly changes the magnitude of the current supplied to the laser element 101e via the current control unit 101c. This signal S1 is a signal for scanning the absorption wavelength by gradually shifting the emission wavelength of the laser element 101e. The emission wavelength can be scanned in the sub-nm to several nm range according to the slope of the signal S1, that is, the amount of change in the supply current. For example, in the case of oxygen gas, it is a portion that can scan a line width of about 0.02 nm.

The offset signal S2 of the wavelength scanning drive signal is an offset portion that does not scan the absorption wavelength but causes the laser element 101e to emit light, and has a value equal to or greater than a threshold current value at which the light emission of the laser element 101e of the light source unit 101 is stabilized. 101 is set to be supplied to the laser element 101e. The signal S1 and the signal S2 are inserted so as to be switched alternately.
The signal S3 is a portion where the drive current is almost zero.

Next, light emission by the light emitting unit 100 will be described.
First, the temperature of the laser element 101e is detected in advance by the thermistor 101f. Further, the temperature control unit 101d energizes the Peltier element 101g so that the measurement target oxygen gas can be measured at the central portion of S1 of the wavelength scanning drive signal shown in FIG. 3 (so that a predetermined absorption characteristic can be obtained). To adjust the temperature of the laser element 101e. Thereafter, the laser element 101e is driven to emit laser light into the internal space of the walls 501a and 501b where the oxygen gas to be measured is present, and the condensed light is incident on the light receiving unit 200.

FIG. 4 shows a drive signal for the laser element when oxygen gas is detected. It is a figure for demonstrating the signal which the laser element drive signal production | generation part 101s outputs, the frequency of a high frequency modulation signal is 10 kHz, the frequency of a wavelength scanning drive signal is 50 Hz, (lambda) ₁ is a wavelength equivalent to an offset, (lambda) ₂ , Λ ₄ is the upper and lower limit values of the scanning wavelength corresponding to the absorption wavelength of oxygen gas (O ₂ gas), and λ ₃ is the wavelength of the peak of the absorption waveform.

The laser element 101e irradiates the collimating lens 102 with the laser light changing from the wavelength λ ₂ to λ _{4 in} this way to generate the detection light 600 that is parallel light, and the wall 501a on which the measurement target gas containing oxygen gas is present. The detection light 600 is emitted into the internal space 501 b and the collected light is incident on the light receiving element 202.

  Next, the light receiving unit 200 will be described. FIG. 5 shows the configuration of the light receiving element 202 and the signal processing unit 203. The signal processing unit 203 further includes an I / V conversion unit 203a, a synchronous detection unit 203b, an oscillator 203c, a filter 203d, and a calculation unit 203e.

  The light receiving element 202 is configured by a photodiode, for example, and a light receiving element having sensitivity to the light emission wavelength of the laser element 101e of the light emitting unit 100 is used. The output current of the light receiving element 202 is input to the I / V conversion unit 203a. The output current of the light receiving element 202 is converted into a voltage by the I / V conversion unit 203a. The output signal of the I / V conversion unit 203a is input to the synchronous detection unit 203b. The 2f signal from the transmitter 203c is added to the synchronous detector 203b, and an output waveform signal obtained by extracting only the amplitude of the double frequency component of the modulated signal of the emitted light is obtained. The output waveform signal of the synchronous detection unit 203b is sent to a calculation unit 203e such as a CPU via a noise removal filter 203d. The calculation unit 203e detects the presence or absence of oxygen gas and calculates the gas concentration of oxygen gas by various processes described below.

Here, the measurement principle of the frequency modulation type laser oxygen gas analyzer will be described with reference to the principle diagram of the wavelength modulation type of the laser type oxygen gas analyzer of FIG. As shown in the absorption spectrum of oxygen gas in FIG. 14, the oxygen gas absorption line is represented by a linear spectrum, so that concentration detection by a frequency modulation method is possible. Then, the laser type oxygen gas analyzer of the frequency modulation, the center wavelength f _c, the output light of the semiconductor laser element and frequency-modulated at a modulation frequency f _m, is irradiated to the oxygen gas to be measured. Here, the frequency modulation is to modulate the waveform of the drive current supplied to the laser element 101e into a sine wave.

  In this frequency modulation method, as described above, only a single wavelength laser beam is emitted using the DFB laser element, and the gas concentration is measured. In this case, since the spectral line width emitted by the DFB laser element is smaller than the absorption line width of the oxygen gas to be measured, it is necessary to match the emission wavelength of the laser with the absorption wavelength of the oxygen gas. Therefore, the emission wavelength is controlled by controlling the temperature and current of the DFB laser element.

  As shown in FIGS. 7 and 8, the emission wavelength of the DFB laser element varies depending on temperature and drive current. Since the DFB laser element can emit a specific wavelength according to a constant value of temperature and current, it can be adjusted to the absorption wavelength according to a preset temperature and current value. By performing frequency modulation, the emission wavelength is modulated in accordance with the modulation of the drive current.

  As described above, the wavelength of the semiconductor laser element can be changed depending on the current and temperature, but the wavelength range is several nm, and it is necessary to use a DFB laser element that emits light in the vicinity of the absorption wavelength of oxygen gas. Due to the wavelength-selective nature of this DFB laser element, not all absorption lines as shown in FIG. 14 can be measured, and the absorption lines used for the measurement have a relatively large absorption intensity and other gases. And one or two that do not overlap the absorption.

As shown in FIG. 6, since one of the absorption lines of the gas is almost quadratic function with respect to the modulation frequency, the absorption line plays the role of a discriminator, the light receiving portion of the modulation frequency f _m A signal having a double frequency (double wave signal) is obtained. Since the modulation frequency f _m good at any frequency, for example, using Selecting a modulation frequency f _m to several kHz, a digital signal processing device (DSP) or general-purpose processor, extraction of the second harmonic signal It is possible to perform advanced signal processing such as.

  Further, if the envelope detection is performed by the light receiving unit, the fundamental wave by amplitude modulation can be estimated, and the ratio between the amplitude of the fundamental wave and the amplitude of the second harmonic signal is detected in phase synchronization, so that it exists in addition to the concentration. A signal proportional to the oxygen gas concentration can be obtained without being affected by the signal of the same frequency component.

  Based on such a principle, when there is no absorption of laser light by oxygen gas, the synchronous detection unit 203b does not detect the second harmonic signal, and therefore the output of the synchronous detection unit 203b is substantially linear.

  On the other hand, when there is absorption of laser light by oxygen gas, the synchronous detection unit 203b detects a second harmonic signal that is a signal obtained by extracting only the amplitude of the second frequency component of the modulation signal of the emitted light. The output waveform becomes the signal intensity of the peak waveform which is the output of the synchronous detection unit 203b shown in the dotted circle in FIG. This signal intensity is appropriately filtered after noise is removed by the filter 203d and output to the arithmetic unit 203e such as a CPU or DSP in the subsequent stage. The calculation unit 203e detects the presence or absence of oxygen gas and calculates the gas concentration of oxygen gas by various processes described below.

  The calculation unit 203e functions as follows. First, the analysis principle of oxygen gas using this signal intensity will be described. The point that the signal intensity obtained by the Lambert-Beer law is determined by the gas concentration and the distance at which the gas exists will be described. The Lambert-Beer equation is shown in Equation 1 below.

[Equation 1]
I (L) = I (0) · exp [−ks · ns · Ls]
I (L): received light quantity ks: gas coefficient
I (0): Light emission quantity ns: Gas concentration
Ls: Flue or cell length

  Therefore, the signal intensity is the amount of received light, and the gas coefficient ks, gas concentration ns, and flue length Ls are parameters. The emitted light quantity I (0) is registered in advance after measurement, the gas coefficient ks is a value unique to the gas, and the flue length Ls is a constant determined by design. That is, if the amount of received light I (L) can be measured, the gas concentration ns is calculated. The detection principle is like this.

  Next, calculation of the gas concentration ns by the calculation unit 203e will be described. First, the peak waveform in the dotted circle in FIG. 4 is the gas absorption waveform A of the portion that has been absorbed by oxygen gas, and the maximum value or the minimum value of the gas absorption waveform A corresponds to the signal intensity. Therefore, the calculation unit 203e measures the peak value of the waveform corresponding to the signal intensity using the gas absorption waveform A that is the output of the synchronous detection unit 203b shown in the circle of FIG. The signal intensity is calculated by measuring the amplitude difference between the maximum value and the minimum value of the signal or by integrating a part or all of the gas absorption waveform A. The gas concentration ns of the oxygen gas is calculated from the signal intensity that is the amount of received light and the above equation (1).

  Then, concentration analysis is performed based on the obtained gas concentration ns of oxygen gas. Further, when the gas concentration is lower than a predetermined value, it can be determined that there is no oxygen gas. A converter (not shown) is connected to the calculation unit 203e. The converter corrects the gas concentration calculated by the calculation unit 203e to a concentration value corresponding to a change in gas temperature or gas pressure, and a display unit that displays the concentration value corrected by the correction unit on the display. And an external transmission unit for transmitting the analog density value and digital signal. The density value corrected by the correction unit is displayed on the display unit. The detection of oxygen gas is performed in this way.

  Next, adjustment of the laser output that characterizes the present invention will be described. The light-emitting side optical unit, which characterizes the present invention, weakens the laser light of the class 3B laser output within the oxygen absorption wavelength range of 760 to 780 nm by the DFB laser element to the equivalent of the laser output of class 1 or class 1M. Detection light.

  In the prior art, as shown in FIG. 9, the light emitted from the normal laser element 101e is substantially collimated by the collimating lens 102 and is irradiated outside the apparatus into the flue in the walls 501a and 501b. Most of them reach the light receiving unit 200.

  Further, when the reflected light is incident on the laser element 101e as reflected light by the collimating lens 102, the laser oscillation state becomes unstable and becomes a noise source. Noise is particularly large in a DFB laser having a large output of several mW to several tens of mW.

  As described above, the output of the DFB laser element of usually several mW to several tens of mW must be emitted from the light emitting unit 100 at 0.52 mW or less corresponding to class 1 or class 1M at a wavelength in the absorption wavelength region of oxygen gas. Don't be.

  Therefore, the light-emitting side optical unit of the present invention employs a light-emitting side optical unit that lowers the laser output to be equivalent to class 1 or class 1M. Such a light-emitting side optical unit is shown in FIG. The light-emitting side optical unit includes a collimator lens 102 and an in-light absorption unit 104. The intensity of the laser light emitted from the laser element 101e has a shape like a normal distribution with the strongest central portion. At this time, the laser output is obtained by the spread angle of the laser beam and the focal length of the collimating lens 102. Usually, the light emitting surface of the laser element 101e is arranged near the focal length of the collimating lens 102, and all the outputs of the laser element 101e are output. The diameter of the collimating lens 102 is set so that is emitted.

  Then, an in-optical path light absorbing portion 104 such as a sheet that absorbs laser light is attached to the central portion of the lens surface of the collimating lens 102, and the light is absorbed at the central portion where the intensity is particularly high, thereby reducing the laser output. The in-light absorption section 104 absorbs about 99% of the laser beam having the same wavelength, and does not generate return light. The collimating lens 102 emits laser light having a ring-shaped cross section and low light intensity.

  By absorbing the light in this way, the laser output is reduced, and the detection light is equivalent to class 1 or class 1M, and is safe light.

  In FIG. 10, the light path absorption unit 104 is arranged on the lens surface on the downstream side (purge unit side) of the collimating lens 102, but it is not shown on the lens surface on the upstream side (laser element side) of the collimating lens 102. You may arrange | position the light absorption part 104 in an optical path.

  Next, a laser oxygen gas analyzer according to a second embodiment of the present invention will be described with reference to the drawings. Compared with the previous first embodiment, this embodiment is basically a laser oxygen gas analyzer having the same configuration as that shown in FIG. 1, but only the emission side optical unit is different. Also in the light-emitting side optical unit, the laser light of the class 3B laser output in the oxygen absorption wavelength region of 760 to 780 nm by the DFB laser element is used as the detection light weakened corresponding to the laser output of class 1 or class 1M. For having an optical system. As shown in FIG. 11, the light-emitting side optical unit includes a collimator lens 102, an optical path light absorption unit 104, and a transparent plate 105.

  In the first embodiment, as shown in FIG. 10, the in-light-absorbing portion 104 is provided on the lens surface of the collimating lens 102, but in this embodiment, as shown in FIG. An in-light-absorbing portion 104 is formed on a transparent plate 105 that is an element, and this transparent plate 105 is disposed adjacent to the collimating lens 102. The in-light-absorbing part 104 is located in the central part where the intensity is particularly high and reduces the laser output.

  The in-light-absorbing part 104 absorbs about 99% of the light having the same wavelength, and thus is safe light of class 1 or class 1M. The transparent plate 105 emits laser light having a ring-shaped cross section and low light intensity. In FIG. 11, the transparent plate 105 is disposed on the downstream side (purge portion side) of the collimating lens 102, but although not shown, the transparent plate 105 and the light path absorption portion on the upstream side (laser element side) of the collimating lens 102. 104 may be arranged. This also has the same effect.

  Next, a laser oxygen gas analyzer according to a third embodiment of the present invention will be described with reference to the drawings. Compared with the previous first embodiment, this embodiment is basically a laser oxygen gas analyzer having the same configuration as that shown in FIG. 1, but only the emission side optical unit is different. Also in the light-emitting side optical unit, the laser light of the class 3B laser output in the oxygen absorption wavelength region of 760 to 780 nm by the DFB laser element is used as the detection light weakened corresponding to the laser output of class 1 or class 1M. For having an optical system. As shown in FIG. 12, the light-emitting side optical unit includes a collimator lens 102, an in-light absorption unit 104, and an out-of-light absorption unit 106.

  In the first embodiment, as shown in FIG. 10, all the laser light from the laser element 101e is incident on the lens surface of the collimating lens 102. However, in this embodiment, as shown in FIG. The laser element 101e is disposed at a position separated by a predetermined distance longer than the focal length of the laser beam so that only a part of the laser beam is incident on the collimating lens 102, thereby reducing the laser output of the laser beam equivalent to class 3B. ing. Further, an optical path light absorbing portion 104 such as a sheet that absorbs laser light is attached to the central portion of the lens surface of the collimating lens 102 and absorbed at the central portion having a high intensity, and the laser output is also lowered. The in-light-absorbing part 104 absorbs about 99% of the light having the same wavelength, and therefore corresponds to class 1 or class 1M. The collimating lens 102 emits laser light having a ring-shaped cross section and low light intensity.

  Further, an off-optical path light absorption unit 106 such as a sheet that absorbs laser light is attached inside the box cover 103 and particularly around the collimating lens 102 to reduce reflected light. Further, by shifting the focal length between the laser element 101e and the collimating lens 102, the collimating laser output is reduced. Therefore, the light emitted from the laser element 101e and reaching the outside of the collimating lens 102 is absorbed by the off-light-absorbing unit 106 and is not reflected. Because of the in-light absorption part 104 and the out-of-light absorption part 106, the influence of the return light on the oscillation of the laser element is reduced.

  In FIG. 12, the light path absorption unit 104 is disposed on the lens surface on the downstream side (purge unit side) of the collimating lens 102. However, although not shown, the lens surface on the upstream side (laser element side) of the collimating lens 102 is disposed. You may arrange | position the light absorption part 104 in an optical path. This also has the same effect.

  Next, a laser type oxygen gas analyzer according to a fourth embodiment of the present invention will be described with reference to the drawings. Compared with the previous first embodiment, this embodiment is basically a laser oxygen gas analyzer having the same configuration as that shown in FIG. 1, but only the emission side optical unit is different. Also in the light-emitting side optical unit, the laser light of the class 3B laser output in the oxygen absorption wavelength region of 760 to 780 nm by the DFB laser element is used as the detection light weakened corresponding to the laser output of class 1 or class 1M. For having an optical system. As shown in FIG. 13, the light-emitting side optical unit includes a collimator lens 102, an optical path light absorption unit 104, a transparent plate 105, and an optical path light absorption unit 106.

  In the third embodiment, as shown in FIG. 12, the light-absorbing portion 106 outside the optical path is provided inside the box cover 103 and outside the collimating lens 102. However, in this embodiment, as shown in FIG. In FIG. 103, no light absorbing portion is provided, and an optical path light absorbing portion 106 is formed at other locations, leaving a circular transparent portion on the transparent plate 105, which is an optical element, and this transparent plate 105 is adjacent to the collimating lens 102. To the upstream side (laser element side). The laser light that has passed through the transparent part is incident on the collimator lens 102, while the other laser light reaches the off-light-absorbing part 106.

The light absorption part 104 in the optical path of the collimator lens 102 absorbs about 99% of light having the same wavelength, and therefore corresponds to class 1 or class 1M. The collimating lens 102 emits laser light having a ring-shaped cross section and low light intensity.
Further, the off-light absorption unit 106 also absorbs about 99% of the light having the same wavelength, thereby suppressing reflection.

  In FIG. 13, the light path absorption unit 104 is arranged on the lens surface on the downstream side (purge unit side) of the collimating lens 102, but not shown on the lens surface on the upstream side (laser element side) of the collimating lens 102. You may arrange | position the light absorption part 104 in an optical path.

  Further, the transparent plate 105 transmits laser light at the center thereof, but the transparent plate 105 may not be a transparent plate as long as the transmission portion is made a simple hole. For example, an optical element such as a diaphragm having a hole in a plate-like light path absorption part may be used.

  Also in this embodiment, the light-absorbing part 106 outside the optical path may be provided inside the box cover 103. This also has the same effect.

  The present invention has been described above. In the present invention, the light-emitting side optical unit outputs laser light of class 3B laser output in the oxygen absorption wavelength region between 760 and 780 nm as detection light corresponding to class 1 or class 1M. The laser type oxygen gas analyzer can be handled more safely.

The laser oxygen gas analyzer of the present invention is optimal for measuring combustion exhaust gas such as boilers and garbage incineration.
In addition, gas analysis for steel [blast furnace, converter, heat treatment furnace, sintering (pellet equipment), coke oven], fruit and vegetable storage and ripening, biochemistry (microorganism) [fermentation], air pollution [incinerator, flue gas desulfurization / Denitration], automobile exhaust gas (remove tester), disaster prevention [explosive gas detection, toxic gas detection, new building material combustion gas analysis], plant growth, chemical analysis [oil refinery plant, petrochemical plant, gas generation plant], It is also useful as an analyzer for environmental [landing concentration, tunnel concentration, parking lot, building management], and various physics and chemistry experiments.

1: Laser oxygen gas analyzer 100: Light emitting unit 101: Laser light source unit 101a: Wavelength scanning drive signal generating unit 101b: High frequency modulation signal generating unit 101c: Current control unit 101d: Temperature control unit 101e: Laser element 101f: Thermistor 101g : Peltier element 101 s: Laser drive signal generator 102: Collimator lens 103: Box cover 104: Intra-optical path absorber 105: Transparent plate 106: Out-optical path absorber 200: Light receiver 201: Condensing lens 202: Light receiver 203: Signal Processing unit 203a: I / V conversion unit 203b: synchronous detection unit 203c: oscillator 203d: filter 203e: calculation unit 204: box cover 300: light emission unit side purge unit 301: purge unit body 302: inlet 303: outlet 400: Light-receiving-unit-side purge unit 401: purge unit body 402: inflow port 4 3: outlet 501a, 501b: walls 502a, 502b: companion flanges 600: the detection light

Claims (4)

A light emitting side including a laser light source unit that emits laser light of class 3B laser output at a wavelength in the absorption wavelength region of oxygen gas, and a collimating lens that collimates the laser light from the laser light source unit and emits detection light A light emitting part having an optical part;
A light receiving unit that receives detection light propagated through a space where oxygen gas to be measured exists,
A laser oxygen gas analyzer comprising:
The light emission side optical unit has a function of emitting laser light of class 3B laser output as detection light weakened corresponding to laser output of class 1 or class 1M. The laser oxygen gas analyzer according to claim 1,
A laser-type light-absorbing portion that is disposed on the surface of a collimating lens or other optical element included in the light-emitting side optical portion and is substantially at the center of the laser light passage surface to absorb the laser light. Oxygen gas analyzer. In the laser type oxygen gas analyzer according to claim 2,
The laser light source unit and the light emitting side optical unit are arranged apart from the focal length so that a part of the laser light radiated from the laser light source unit and reaches the light transmitting side optical unit is transmitted through the light emitting side optical unit. A laser-type oxygen gas analyzer that emits as a weakened detection light. In the laser type oxygen gas analyzer according to claim 3,
A laser-type oxygen gas analyzer, comprising an off-optical path absorption unit that is provided around the light-emitting side optical unit and absorbs laser light incident on the outside of the light-emitting side optical unit.

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