JP6210195B2 - Laser oxygen analyzer - Google Patents

Description

  The present invention relates to a laser-type oxygen gas analyzer that measures the gas concentration of high-temperature oxygen gas used in combustion control applications by using the difference in gas temperature absorption intensity.

It is known that each gas molecule in gas has its own light absorption spectrum. For example, FIG. 17 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. As the absorption intensity on the vertical axis increases, the amount of light absorption increases. The laser type oxygen gas analyzer is equipped with a laser element that emits laser light with a wavelength that is absorbed by the oxygen gas to be measured, and the presence or absence of oxygen gas by absorbing the laser light with a specific wavelength into the oxygen gas. Can be detected. In addition, the laser oxygen gas analyzer can detect the concentration because the amount of absorption of the laser beam at a specific wavelength is proportional to the concentration of oxygen gas.

  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 also described in, for example, Patent Document 1 described later. The present invention also relates to a laser-type oxygen gas analyzer using a frequency modulation method.

  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, for example, as described in Patent Document 2 described later.

  Such a laser-type oxygen gas analyzer is particularly used for atmospheric environment measurement and control applications, and specifically, is often used mainly for combustion control of boilers such as garbage incinerators. The temperature of the measurement target gas targeted by the laser oxygen gas analyzer used for boiler combustion control is as high as 700 to 1200 ° C. Therefore, it is necessary to perform gas purging at all times in order to protect the device due to heat and prevent dirt from adhering to dust.

  FIG. 18 shows the external structure when a laser oxygen gas analyzer is installed at a measurement location such as a boiler, and the flow of flue gas and purge gas to be measured. In the wall 40, flue gas generated by combustion flows. Further, purge gas is introduced from the purge gas inlets 20 and 60, and the purge gas prevents contamination of the lens and glass window on the surface of the light emitting unit box 10 and the light receiving unit box 70. In the gas purge, the purge gas is discharged into the wall 40 through the companion flanges 30 and 50.

  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. However, the use of instrumentation nitrogen requires equipment and operation costs, so it is mainly used only in places where there is a risk of fire and explosion, such as steelworks and steelworks, and in general incinerators. Instrument air is used. When air is used, it is necessary that the oxygen gas in the air has no influence on the oxygen gas to be measured.

  The instrument air described above normally 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. In order to avoid this influence, a method is conceivable in which the oxygen amount of the oxygen gas contained in the instrument air is obtained and the concentration is converted in advance as an offset and measured. However, in general, the oxygen amount of the oxygen gas controlled in the boiler is several vol% (for example, 3 to 7 vol%), and the oxygen concentration contained in the instrument air becomes relatively high, so that the measurement accuracy is improved. It has an effect. In the worst case, sufficient S / N may not be obtained. For this reason, oxygen analyzers used in combustion control have not used the above-mentioned laser-type oxygen gas analyzers, but have used other types of oxygen meters (zirconia oxygen meters) with high maintenance frequency such as periodic cleaning. It was.

  Therefore, development of a laser-type oxygen gas analyzer capable of purging gas with instrument air even for applications used in combustion control is underway. This is based on the following principle. It was found that the absorption intensity varies depending on the temperature at a certain wavelength among many wavelengths that absorb gas. Use this principle to select a wavelength that shows sensitivity only to high-temperature oxygen gas contained in the combustion gas to be measured, with little sensitivity to purge gas and low-temperature (near room temperature) oxygen gas contained in the atmosphere. The concentration measurement is performed only for the oxygen gas contained in the measurement target gas.

Japanese Patent Laid-Open No. 7-151681 (paragraph [0005], FIG. 4 etc.) JP 2001-235418 A (paragraphs [0012] to [0024], FIG. 2, FIG. 11, etc.)

  Laser-type oxygen gas analyzers cause deviations in measured values due to changes over time, and therefore it is necessary to perform periodic correction every six months or one year. At this time, generally, the light receiving unit and the light emitting unit are removed from the installation site, and the light emitting unit and the light receiving unit are connected to both ends of a dedicated correction gas cell. Then, correction is performed by flowing a correction gas through the correction gas cell. However, it has been confirmed that correction is required for the laser oxygen gas analyzer that is used in combustion control and can be purged with instrument air. This point will be described.

  At the time of correction, light absorption by the gas is necessary, but in a laser oxygen gas analyzer that uses a wavelength that does not absorb normal temperature gas but only high temperature gas, the gas is heated to a high temperature at which absorption occurs, and the temperature The correction gas cell had to be heated in the same way as the gas so that was constant.

  For example, when correcting a shift due to a time-dependent change of a laser type oxygen gas analyzer using a wavelength having a high absorption intensity of high-temperature oxygen gas and a low absorption intensity of normal-temperature oxygen gas, the gas used is 400 ° C. or higher. It is necessary to heat to 400 ° C. or higher so that the gas temperature distribution pipe and the correction gas cell do not decrease. In order to do this, the apparatus becomes large-scale, such as heating a pipe using a ceramic heater, and although it can be performed in a laboratory, it cannot be easily performed in any environment. In addition, it is difficult to keep the temperature constant during the correction period, and it takes time until the temperature becomes stable. In reality, it is very difficult to correct by this method.

  As described above, it is very difficult to correct the laser oxygen gas analyzer that uses a wavelength with high absorption intensity of high-temperature oxygen gas and low absorption intensity of oxygen gas at normal temperature in an actual environment. Is expected. Since the above general correction cannot be performed when there is gas absorption at room temperature, there is a problem that correction is not easy.

  Therefore, the present invention has been made in view of the above-mentioned problems, and its purpose is to include a gas to be measured in gas analysis, although it hardly shows sensitivity to purge gas and low-temperature oxygen gas contained in the atmosphere. A laser oxygen gas analyzer that is sensitive only to high-temperature oxygen gas that can be corrected, and in particular, it can be easily corrected using low-temperature oxygen gas at the time of correction. It is in.

  The present invention expands the wavelength sweeping range by the current drive of the laser element in a laser-type oxygen gas analyzer that uses a wavelength that has almost no gas absorption at room temperature and gas absorption only at high temperature. Oxygen gas at a high temperature and a normal temperature as a wavelength scanning range including a target wavelength used for measuring the gas concentration of oxygen gas and a wavelength adjacent to the wavelength used for the concentration measurement and absorbing oxygen gas even at normal temperature Allow the concentration to be measured.

  Between the error caused by time-dependent change in oxygen concentration measured at a wavelength where oxygen gas absorption is at room temperature and the error caused by time-dependent change in oxygen concentration measured at a wavelength where gas absorption is only at high temperature There is a certain correlation. Using this relationship, the oxygen concentration measured at a wavelength at which oxygen gas is absorbed even at room temperature is corrected.

  This makes it possible to indirectly correct the oxygen concentration measured at a wavelength where gas is absorbed only at high temperatures. Therefore, it is not necessary to heat the gas used for the correction to a high temperature to directly correct the oxygen concentration measured at a wavelength at which the gas is absorbed only at a high temperature, and the correction gas cell circulates the gas so that the gas temperature is constant. Does not need to be heated as well.

  Therefore, in any environment, it is possible to correct if there is a correction gas cell and a correction gas, and since the correction is performed at room temperature, the gas temperature is also stable and more accurate than when corrected to high temperatures. It was made possible to correct.

That is, the laser oxygen gas analyzer according to claim 1 of the present invention is
A light emitting unit that emits detection light by laser light, a light receiving unit that receives detection light propagated through a space in which oxygen gas to be measured exists, and calculates a gas concentration from a detection peak of the received detection light; A laser oxygen gas analyzer for measuring a gas concentration of oxygen gas, having a correction unit that corrects a concentration error caused by a change with time by a correction coefficient,
The light emitting unit has a detection light for gas analysis with a laser beam having a wavelength such that the absorption intensity of the high-temperature oxygen gas to be measured is high and the absorption intensity of the oxygen gas at room temperature is small, and oxygen gas at room temperature. The detection light for correction by the laser light having a wavelength with a large absorption intensity, and the respective light emission,
The light receiving unit receives the detection light for gas analysis at the time of gas analysis and calculates the gas concentration of the high-temperature oxygen gas, and receives the detection light for correction at the time of correction to calculate the detection peak. And
The correction unit calculates a correction coefficient for correcting a change with time using a detection peak generated from correction detection light at the time of correction,
The light receiving unit indirectly corrects the gas concentration value generated by receiving the detection light for gas analysis using the correction coefficient calculated by the correction unit.

Further, a laser type oxygen gas analyzer according to claim 2 of the present invention provides:
A light emitting unit that emits detection light by laser light, a light receiving unit that receives detection light propagated through a space in which oxygen gas to be measured exists, and calculates a gas concentration from a detection peak of the received detection light; A light-emitting unit side purge unit that supplies purge gas by air to the light-emitting unit, a light-receiving unit side purge unit that supplies purge gas by air to the light-receiving unit, a correction unit that corrects a concentration error caused by a change with time, using a correction coefficient, A laser oxygen gas analyzer that measures the gas concentration of oxygen gas,
The light emitting unit
A wavelength at which the absorption intensity of the high-temperature oxygen gas to be measured is large and the absorption intensity of the normal-temperature oxygen gas contained in the purge gas of the light-emitting part side purge part and the light-receiving part side purge part is small, and the light-emitting part side purge Detection light for gas analysis and detection light for correction by a laser beam scanned at a scanning wavelength in a predetermined range including a wavelength at which the absorption intensity of room-temperature oxygen gas contained in the purge gas of the gas detector and the light-receiving-side purge unit is high A laser element emitting light,
A light emission side temperature stabilizing means for stabilizing the temperature of the laser element;
A high frequency modulation signal for modulating the emission wavelength with respect to a wavelength scanning drive signal including a variable drive signal for changing the emission wavelength of the laser element to a scanning wavelength within a predetermined range so as to scan the absorption wavelength of oxygen gas. A laser drive signal generator that combines and outputs the laser drive signal;
A current controller that converts the laser drive signal output from the laser drive signal generator into a current and supplies the current to the laser element;
With
The light receiving unit is
A light receiving element having sensitivity to detection light for gas analysis during gas analysis and detection light for correction during correction;
A synchronous detection unit that detects an amplitude of a second harmonic signal that is a double frequency component of a modulation signal in the light emitting unit from an output signal of the light receiving unit, and outputs a detection signal;
A filter circuit for removing noise from the output signal of the light receiving unit;
The calculation is based on the detection signal output from the filter circuit. During gas analysis, the gas concentration of high-temperature oxygen gas is calculated using the detection light for gas analysis, and the correction detection light is used during correction. A calculation unit for calculating the detection peak at
The correction unit calculates a correction coefficient for correcting a change with time using a detection peak generated from correction detection light at the time of correction,
The calculation unit of the light receiving unit indirectly corrects a gas concentration value generated by receiving detection light for gas analysis using the correction coefficient calculated by the correction unit.
It is a sign.

A laser oxygen gas analyzer according to claim 3 of the present invention is
In the laser type oxygen gas analyzer according to claim 1 or 2,
The wavelength at which the absorption intensity of the high-temperature oxygen gas to be measured is large and the absorption intensity of the oxygen gas at room temperature is small is a wavelength at which an absorption peak is included in the range of 759.63 nm to 759.64 nm. The wavelength at which the absorption intensity of the oxygen gas at room temperature is high is a wavelength at which an absorption peak is included in the range of 759.65 nm to 759.67 nm, or 759.60 nm to 75 9 . The wavelength is such that an absorption peak is included in a range of 62 nm.

According to the present invention, at the time of gas analysis, a laser-type oxygen that shows little sensitivity to the purge gas and the low-temperature oxygen gas contained in the atmosphere, but exhibits sensitivity only to the high-temperature oxygen gas contained in the measurement target gas. It is a gas analyzer, and in particular, it is possible to provide a laser-type oxygen gas analyzer that can easily perform correction using low-temperature oxygen gas at the time of correction.
As a result, when performing correction due to changes over time, it is not necessary to heat the gas used for correction to a high temperature, and correction can be performed at room temperature, so it can be easily performed in any environment and can be performed at a stable gas temperature. Therefore, accurate correction can be performed.

It is an absorption spectrum characteristic view of O ₂ gas. It is explanatory drawing of the example of a general absorption spectrum according to oxygen gas temperature. It is explanatory drawing of oxygen concentration distribution and optical path length in the environment where a laser-type oxygen gas analyzer is used for combustion control. It is explanatory drawing of the absorption spectrum example according to oxygen gas temperature for combustion control. It is a block diagram of the laser type oxygen gas analyzer of the form for implementing 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. It is an explanatory view for explaining a detection by laser type oxygen gas analyzer mode for carrying out the present invention, FIG. 8 (a) illustrates the scan waveform and O ₂ gas absorption waveform of the laser element, Fig. FIG. 8B is a diagram showing an output waveform of the synchronous detection unit when there is a purge gas but no high-temperature oxygen gas, and FIG. 8C is an output waveform of the synchronous detection unit when there is a purge gas and a high-temperature oxygen gas. FIG. 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 semiconductor laser by a drive current. It is a figure which shows the change of the light emission wavelength of the semiconductor laser with temperature. It is explanatory drawing of correction | amendment of a laser type oxygen gas analyzer. The correlation between the zero point of the wavelength (λ _A ) where the absorption intensity of high-temperature oxygen gas is high and the absorption intensity of oxygen gas at room temperature is small and the wavelength (λ _B ) where absorption intensity is sufficiently large for oxygen gas at room temperature FIG. Correlation of the span coefficient between the wavelength (λ _A ) where the absorption intensity of high-temperature oxygen gas is large and the absorption intensity of oxygen gas at room temperature is small and the wavelength (λ _B ) where absorption intensity is sufficiently large for oxygen gas at room temperature FIG. Is an explanatory view for explaining the detection by other laser type oxygen gas analyzer mode for carrying out the present invention, FIG. 16 (a) illustrates the scan waveform and O ₂ gas absorption waveform of the laser element FIG. 16B is a diagram showing an output waveform of the synchronous detection unit when there is a purge gas but no high-temperature oxygen gas, and FIG. 16C shows the output of the synchronous detection unit when there is a purge gas and a high-temperature oxygen gas. It is a figure which shows an output waveform. It is an absorption spectrum characteristic view of O ₂ gas. It is explanatory drawing explaining the flow of purge gas.

Next, the laser oxygen gas analyzer of the present invention will be described below. First, the detection principle will be described.
FIG. 1 shows an absorption spectrum of oxygen gas (O ₂ gas). Each of the oxygen gas absorption lines is represented by a linear spectrum. In general, there is temperature dependence as shown in the absorption spectrum for each oxygen gas temperature in FIG. 2. Generally, as the temperature of the oxygen gas increases, the absorption intensity decreases even at the same oxygen concentration. The apparent density decreases.

  As described above, the laser oxygen gas analyzer performs a gas purge to protect the apparatus from the heat in the furnace and to prevent the adhesion of dust. If nitrogen is used as the purge gas, the oxygen concentration of the oxygen gas to be measured will not be affected, but since nitrogen requires equipment costs and running costs, instrument air is used.

  FIG. 3 is a general combustion control application, and shows the relationship between the oxygen concentration distribution and the optical path length of a laser oxygen gas analyzer when instrumented air is used as the purge gas. The gas concentration of the oxygen gas in the purge gas is 20.6 vol%, and the gas concentration of the oxygen gas in the measurement target gas is 3 to 7 vol%. The purge section distance in the section where the oxygen gas in the purge gas exists is 1 m × 2, and the flue distance in the section in which the oxygen gas in the measurement target gas exists is 2 to 4 m.

  The relationship between the oxygen concentration and the optical path length in a laser oxygen gas analyzer is based on Lambert-Beer's law, and the signal intensity obtained is proportional to the gas concentration and the distance in which the gas exists. The Lambert-Beer equation is shown in Equation 1.

[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, it can be understood that the signal intensity is influenced by the product of the gas concentration and the distance. In general, the measurement range can be set with a laser oxygen gas analyzer, but the range of the laser oxygen gas analyzer used for combustion control is 20.6 vol% in the atmosphere, so 25 vol% can be selected. The majority.

  In the model of FIG. 3, the oxygen concentration ratio of purge air with respect to the measurement range of 0 ° C. is expressed by (20.6 vol% × purge section distance) / (25 vol% × flue distance), but purge section distance = 2, smoke Since the road distance is 2 to 4, the oxygen concentration ratio is 0.41 to 0.82 times, which is 1 time or less.

  However, in an actual combustion control environment, the general oxygen gas absorption intensity according to temperature in FIG. 2 is followed, and the absorption intensity at 800 ° C. is about 15% of the absorption intensity at 0 ° C. In this case, The oxygen concentration of the purge air is expressed by (20.6 vol% × purge part distance) / (flue concentration vol% × flue distance × 0.15) with respect to the oxygen concentration to be measured. = 2, flue distance = 2-4, and concentration in the flue = 3-7, so that the oxygen concentration ratio is 9.8-45.8 times, and the influence of the purge gas is large.

  Moreover, although it represents with the absorption intensity of 800 degreeC measurement gas with respect to a 0 degreeC measurement range (concentration in flue vol% x 0.15) / 25x100, since the concentration in flue = 3-7, absorption intensity = 1.8 to 4.2% FS, which is only 2 to 4% of the full scale.

  From the above, under the combustion control environment, the oxygen absorption intensity of the purge air, which is a disturbance, becomes relatively large, and the absorption intensity of the measurement gas becomes small due to the influence of the gas temperature, so that a sufficient S / N cannot be obtained. .

  Therefore, in order to avoid such a problem, an absorption wavelength having gas temperature characteristics as shown in FIG. 4 is selected as an absorption line spectrum of oxygen used in combustion control. This absorption wavelength is, for example, a wavelength having an absorption peak within a predetermined range of 759.63 nm to 759.64 nm. The characteristic of the absorption line at this wavelength is that it absorbs almost no oxygen near room temperature, but oxygen absorption occurs when the gas temperature rises, and the absorption intensity at 400 to 1200 ° C. is sufficiently large with respect to room temperature. The amount of change also falls within the range of about 20% from the maximum absorption intensity.

  Therefore, when the absorption intensity at 400 ° C. is used as a reference, the oxygen concentration of the purge gas, which is a normal temperature atmosphere, can be almost ignored, and the oxygen concentration of the purge air under the actual combustion control environment in the model of FIG. The absorption intensity of the measurement gas at 800 ° C. with respect to the concentration range of 0 ° C. is 14 to 34% FS, and even if purge air is used, it is hardly affected by the concentration, and is sufficient. S / N can be obtained.

  In this way, the instrumentation air that flows into the purge unit using the difference in absorption intensity caused by the gas temperature difference of the specific wavelength between the oxygen gas contained in the purge gas that is instrumentation air that flows to the purge unit and the oxygen gas to be measured The laser-type oxygen gas analyzer that efficiently measures the high-temperature oxygen concentration of the measurement object without being almost affected by the oxygen gas contained in the apparatus and the oxygen gas in the apparatus such as the purge unit.

  Next, 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. 5 is a configuration diagram of the 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, a light receiving unit side purge unit 400, a communication line 500, and a correction unit 600.

The light emitting unit 100 further includes a laser light source unit 101, a collimating lens 102, which is a specific example of the light emitting unit side optical system, 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, which are specific examples of the light receiving unit side optical system.
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.
Walls 701a and 701b are walls of this pipe. The companion flanges 702a and 702b are fixed to the walls 701a and 701b by, for example, welding.

  The purge unit main body 301 of the light emitting unit side purge unit 300 including the angle adjustment mechanism unit is attached to one of the phase flanges 702a. The box cover 103 of the light emitting unit 100 is attached to the purge unit main body 301 of the light emitting unit side purge unit 300. The internal passage of the light emitting unit side purge unit 300 and the internal passage of the phase flange 702a communicate with each other, and further communicate with the inside of the pipe. A space is separated from the box cover 103 by a collimating lens 102.

  The purge portion main body 401 of the light receiving portion side purge portion 400 including the angle adjusting mechanism portion is attached to the other phase flange 702b. A box cover 204 of the light receiving unit 200 is attached to the purge unit main body 401 of the light receiving unit side purge unit 400. The internal passage of the light-receiving unit side purge unit 400 communicates with the internal passage of the phase flange 702b, and further communicates with the inside of the pipe. A space is separated from the box cover 204 by a condenser lens 201.

  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. Laser light emitted from the laser light source unit 101 is collimated into parallel light by the collimating lens 102. The collimated detection light 800 is incident on the inside of the walls 701a and 701b (inside the flue) through the center of the internal passage of the light emitting portion side purge portion 300 and the internal passage of the companion flange 702a.

  The detection light 800 is absorbed when it passes through the oxygen gas in the measurement target gas inside the walls 701a and 701b. In addition, when high-temperature oxygen gas to be measured exists in the phase flanges 702a and 702b, 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, the absorption is usually similarly performed. receive. However, although it will be described later, there is sensitivity for high-temperature oxygen gas during gas analysis, but for oxygen gas at room temperature by air purge and oxygen gas at room temperature contained in the atmosphere, a wavelength with low sensitivity is selected to absorb high-temperature gas. Make it happen. At the time of correction, a wavelength that is sensitive to room temperature oxygen gas is selected so that absorption occurs at room temperature oxygen gas.

  The detection light 800 is incident on 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. Detection light 800, which is parallel light transmitted through the inside of the walls 701a and 701b (inside the flue), passes through the center of the internal passage of the companion flange 702b 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, instrument air, which is compressed air, flows into the purge unit main body 301 from the inlet 302 into the light emitting unit side purge unit 300, and the light emitting unit side purge unit 300 The internal passage 300 is purged, and the internal passage of the companion flange 702a is purged through the outlet 303. After this purging, the purge gas is discharged into the walls 701a and 701b (inside the flue). Similarly, instrument air, which is compressed air, 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. Then, the internal passage of the companion flange 702b is purged. After this purging, the purge gas is discharged into the walls 701a and 701b (inside the flue).

  The instrument air blows away dust and the like that are included in the measurement target gas and adhere to each part, and the lens surfaces of the light emitting unit 100 and the light receiving unit 200 are kept clean. In addition, the instrument air flowing in for purge 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 702a and 702b are forcibly cooled.

  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. 6 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 measurement target gas. The wavelength scanning drive signal is transmitted to the arithmetic unit 203e via the communication line 500.
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 that is the measurement target gas.

  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. ing. 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. The laser element 101e is, for example, a laser element called a DFB laser (Distributed Feedback Laser) or a VCSEL (Vertical Cavity Surface Emitting Laser).

  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 absorbs heat by PID (proportional / integral / derivative) control of the temperature control unit 101d to change the temperature, and the resistance value of the thermistor 101f is set to a constant value. As a result, the temperature of the laser element 101e is stabilized.

  Here, as shown in FIG. 7, 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 O ₂ gas, the line width includes (1) a wavelength at which oxygen is absorbed even at room temperature and (2) a wavelength at which oxygen is absorbed only at a high temperature, and a line width of about 0.04 nm to 0.05 nm. Is a portion that enables scanning.

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. The value is set so as to be supplied to the 101 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 allows the Peltier element 101g to measure the oxygen gas that is the measurement target gas within the range of S1 of the wavelength scanning drive signal shown in FIG. 7 (so that a predetermined absorption characteristic can be obtained). The temperature of the laser element 101e is adjusted by controlling energization.
Thereafter, the laser element 101e is driven.

FIG. 8A shows a drive signal for the laser element, where the frequency of the high frequency modulation signal is 10 kHz, the frequency of the wavelength scanning drive signal is 50 Hz, λ ₁ is the wavelength corresponding to the offset, and λ ₂ (759 .63 nm) and λ ₃ (759.64 nm) are the upper and lower limits of the scanning wavelength corresponding to the absorption wavelength of oxygen gas (O ₂ gas) that has gas absorption only at high temperatures, and λ ₄ (759.65 nm), λ ₅ (759.67 nm) indicates the upper and lower limits of the scanning wavelength corresponding to the absorption wavelength of oxygen gas (O ₂ gas) that has gas absorption even at room temperature. λ _A indicates a wavelength corresponding to the absorption wavelength of oxygen gas only at a high temperature, and λ _B indicates a wavelength corresponding to the absorption wavelength of oxygen gas only at a normal temperature.
The laser element 101e irradiates the collimating lens 102 with the laser light scanned in such a wavelength to generate detection light 800 which is parallel light, and the detection light 800 is formed in the internal space of the walls 701a and 701b where the measurement target gas exists. The condensed light is incident on the light receiving element 202.

  Next, the light receiving unit 200 will be described. FIG. 9 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 detection unit 203b, and a gas waveform signal obtained by extracting only the amplitude of the second harmonic signal having the same phase of the emitted light is obtained. The output signal of the synchronous detection unit 203b is sent to a calculation unit 203e such as a CPU through a noise removal filter 203d. The calculation unit 203e detects the presence or absence of oxygen gas and calculates the oxygen concentration by various processes described below. The arithmetic unit 203e receives the wavelength scanning drive signal from the wavelength scanning driving signal generation unit 101a.

Here, the measurement principle of the frequency modulation type laser oxygen gas analyzer will be described with reference to the principle diagram of the frequency modulation type of the laser oxygen gas analyzer of FIG. As shown in the absorption spectrum of oxygen gas (O ₂ gas) in FIG. 1, since the absorption line of this oxygen gas is represented by a linear spectrum, concentration detection by a frequency modulation method is possible. Then, the laser type oxygen gas analyzer of the frequency modulation method, the center frequency f _c, the light emitted from 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 system, as described above, only a single wavelength laser beam is emitted using a distributed feedback semiconductor laser (DFB laser) or a vertical cavity surface emitting laser (VCSEL), and the gas concentration is measured. In this case, since the spectral line width at which the laser element emits light is smaller than the absorption line width of the measurement target gas, it is necessary to match the emission wavelength of the laser with the absorption wavelength of the measurement target gas. Therefore, the emission wavelength is controlled by controlling the temperature and current of the laser element.

  As shown in FIG. 11 and FIG. 12, the laser element changes its emission wavelength depending on the drive current and temperature. Since the 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 laser element that emits light in the vicinity of the absorption wavelength of the measurement target gas. Due to the wavelength-selective nature of this laser element, all absorption lines as shown in FIG. 1 cannot be measured, and the absorption lines used for measurement have a relatively large absorption intensity and One or two absorptions do not overlap.

As shown in FIG. 10, since 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 double modulation frequency f _m A frequency signal (second harmonic 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 gas concentration to be measured can be obtained without being affected by the signal having the same frequency component.

  Based on this principle, the following output is made when gas analysis is performed. First, there is no high-temperature oxygen gas in the measurement target gas and there is a normal-temperature purge gas. In this case, the output of the synchronous detector 203b is as shown in FIG.

First, at a wavelength λ _A in which oxygen is absorbed only at high temperature and there is no oxygen absorption at room temperature, since there is no high-temperature oxygen gas in the gas to be measured, the second harmonic signal is not detected by the synchronous detector 203b. As shown by an enclosure A in FIG. 8B, the output of the synchronous detection unit 203b is substantially a straight line.
In addition, in λ _B where oxygen is absorbed at both high temperature and normal temperature, only the oxygen gas at normal temperature contained in the purge gas is present, so only the amplitude of the double frequency component of the modulation signal of the emitted light is extracted by the synchronous detection unit 203b. Since a second harmonic signal, which is a signal, is detected, the output waveform has a peak waveform as shown by an enclosure B in FIG. 8B. This detection peak represents the concentration of oxygen gas at room temperature.

  Subsequently, there is a case where there is a high-temperature oxygen gas in the measurement target gas and a normal-temperature purge gas. In this case, the output of the synchronous detector 203b is as shown in FIG.

First, at a wavelength λ _A where oxygen is absorbed only at a high temperature and there is no oxygen absorption at a normal temperature, since there is a high-temperature oxygen gas in the measurement target gas, the amplitude of the double frequency component of the modulated signal of the emitted light by the synchronous detector 203b Since the second harmonic signal, which is only the extracted signal, is detected, the output waveform has a peak waveform as indicated by an enclosure A in FIG. This detection peak represents the concentration of high-temperature oxygen gas.
In addition, at λ _B where oxygen is absorbed at both high temperature and normal temperature, there is a purge gas at normal temperature, so that the double is a signal obtained by extracting only the amplitude of the double frequency component of the modulated signal of the emitted light by the synchronous detector 203b. Since a wave signal is detected, the output waveform has a peak waveform as shown by an enclosure B in FIG.

  In either case of the output waveform of FIG. 8B or FIG. 8C, this output waveform is noise-removed by the filter 203d, is appropriately amplified, and is output to the arithmetic unit 203e which is a subsequent CPU, DSP or the like. Is done. The calculation unit 203e functions as follows. The calculation unit 203e that measures the density receives the wavelength scanning drive signal from the light emitting unit 100, and performs timing synchronization by, for example, extracting S3 of the wavelength scanning driving signal, thereby performing FIGS. ) So that only the detected peak waveform at the timing of the enclosure A can be selected. At the time of gas analysis, the detection peak of the enclosure B in FIGS. 8B and 8C is not considered. The detection peak waveform A of the enclosure A in FIGS. 8B and 8C is a portion (gas absorption waveform) that has been absorbed by high-temperature oxygen gas in the measurement target gas, and the maximum of the detection peak waveform A The value or the minimum value corresponds to the gas concentration of the high-temperature oxygen gas in the measurement target gas.

  Therefore, the calculation unit 203e uses the detection peak waveform A of the high-temperature oxygen gas, which is the output of the synchronous detection unit 203b shown in the square frames of FIGS. 8B and 8C, to detect the high-temperature oxygen gas. Measure the peak value of the waveform corresponding to the concentration, measure the amplitude difference between the maximum value and the minimum value of the detection peak waveform A of the high-temperature oxygen gas, or part of the detection peak waveform A of the high-temperature oxygen gas Alternatively, it integrates all and functions as means for detecting the concentration of high-temperature oxygen gas in the measurement object from the integrated value. Also, it functions as means for determining that there is no oxygen gas when the gas concentration is lower than a predetermined value.

  A correction unit 600 is connected to the calculation unit 203e. The correction unit 600 displays a concentration value correction unit that corrects the value converted by the arithmetic unit 203e to a concentration value corresponding to a change in gas temperature or gas pressure, and a display that displays the concentration value corrected by the concentration value correction unit. And an external transmission unit for transmitting the corrected density value in analog and digital signals. The calculation unit 203e performs output control, and the density value corrected by the correction function display unit is displayed on the display unit. Gas analysis by the laser oxygen gas analyzer 1 is performed in this way.

  Next, a periodic correction method of the laser oxygen gas analyzer 1 will be described. When performing periodic correction, the light receiving unit and the light emitting unit are generally removed from the installation site, and the light emitting unit and the light receiving unit are connected to both ends of a dedicated correction gas cell 900 as shown in FIG. Nitrogen gas and oxygen gas are usually supplied from a nitrogen cylinder 901 or an oxygen cylinder 902. The temperature of the nitrogen gas or oxygen gas passed through the correction gas cell is the same as the ambient temperature (0 to 35 ° C.).

In order to check the deviation of the zero point, a correction nitrogen (N ₂ ) gas is supplied from the nitrogen cylinder 901 to the correction gas cell 900, and the deviation width of the zero point is measured compared with the time of shipment or the previous correction. If there is a deviation from zero, correction is performed, the zero coefficient is changed so that the value becomes zero, and correction is performed so that the value becomes the same as the gas cylinder concentration value.

  In order to check the displacement of the span, oxygen gas corresponding to the span is caused to flow from the oxygen cylinder 902 to the correction gas cell 900, and the displacement width of the span is measured. If the concentration value deviates from the concentration of the oxygen cylinder 902, correction is performed and the span coefficient is changed.

  Such correction can be easily performed with a laser oxygen gas analyzer for normal use that is not used in combustion control of the prior art. However, with a new type of laser-type oxygen gas analyzer that does not absorb room temperature oxygen gas and detects only the wavelength that absorbs only high-temperature oxygen gas, it is equivalent to the span at room temperature, especially when checking the deviation of the span. Even if oxygen gas was flowed, there was a possibility that the absorption could not be obtained and correction could not be made.

  On the other hand, the laser oxygen gas analyzer 1 of the present invention performs correction as follows. The laser-type oxygen gas analyzer 1 of the present invention scans as shown in FIG. 8A described above, but this is a case where only oxygen gas at normal temperature for correction is present. In this case, the output of the synchronous detector 203b is as shown in FIG.

First, at the wavelength λ _A where oxygen is absorbed only at high temperature and there is no oxygen absorption at room temperature, since there is no high-temperature oxygen gas, the second harmonic signal is not detected by the synchronous detection unit 203b. As indicated by an enclosure A in b), the output of the synchronous detector 203b is substantially a straight line.
In addition, at λ _B where oxygen is absorbed at both high temperature and normal temperature, there is only oxygen gas at normal temperature, so that only the amplitude of the double frequency component of the modulated signal of the emitted light is extracted by the synchronous detector 203b 2. Since the harmonic wave signal is detected, the output waveform has a peak waveform as shown by an enclosure B in FIG. 8B. This detection peak represents the concentration of oxygen gas at normal temperature for correction.

  This output waveform is noise-removed by the filter 203d, is appropriately amplified, and is output to the arithmetic unit 203e, which is a subsequent CPU, DSP, or the like. The calculation unit 203e functions as follows. The calculation unit 203e for measuring the density receives the wavelength scanning drive signal from the light emitting unit 100, and can select the peak waveform at the timing of the enclosure B in FIG. 8B by the timing synchronization as described above. Yes. Switching between different timings for gas analysis and correction can be selected by, for example, a switch (not shown) connected to the calculation unit 203e. The detected peak waveform B in the enclosure B in FIG. 8B is a portion (gas absorption waveform) absorbed by the correction oxygen gas, and the maximum or minimum value of the detected peak waveform B is the correction oxygen. Corresponds to gas concentration.

  Accordingly, the calculation unit 203e corresponds to the concentration of oxygen gas at room temperature using the detection peak waveform B of room temperature oxygen gas, which is the output of the synchronous detection unit 203b shown in the square frame of FIG. 8B. Measure the peak value of the waveform, measure the amplitude difference between the maximum or minimum value of the detection peak waveform B of oxygen gas at normal temperature, or integrate part or all of the detection peak waveform B of oxygen gas at normal temperature Thus, it functions as a means for detecting the concentration of oxygen gas at room temperature from the integrated value. Correction is performed using the density of the absorption waveform B.

Note that the rate of change with time of the zero point at 400 ° C. between the wavelength at which oxygen is absorbed even at room temperature (λ _B ) and the wavelength at which oxygen is absorbed only at high temperature (λ _A ) is correlated as shown in FIG.
Further, the time-dependent change rate of the span at 400 ° C. between the wavelength at which oxygen is absorbed even at room temperature (λ _B ) and the wavelength at which oxygen is absorbed only at high temperature (λ _A ) is correlated as shown in FIG. is there.

From the above, the wavelength (λ _B ) is corrected by using the following relational expression 2 for the wavelength (λ _B ) where oxygen is absorbed even at room temperature and the wavelength (λ _A ) where oxygen is absorbed only at high temperature. This makes it possible to indirectly correct the wavelength (λ _A ).

[Equation 2]
Wavelength (λ _A ) zero point correction value = k × wavelength (λ _B ) zero point correction value Wavelength (λ _A ) span correction value = k ′ × wavelength (λ _B ) span correction value

A span correction value of the zero-point correction value and the wavelength of the wavelength (λ _A) (λ _A) is calculated as a correction coefficient, the correction unit 600 transmits to the arithmetic 203e of the light receiving portion 200. The calculation 203e of the light receiving unit 200 registers these correction coefficients in a built-in memory, and thereafter outputs the correction after correcting the gas concentration value of the high-temperature oxygen gas using the correction coefficient. Therefore, after correction, the influence of the secular change can be canceled and an accurate gas concentration value can be obtained. Such correction makes it possible to correct the deviation at normal temperature without heating the gas and the piping. Such a laser oxygen gas analyzer 1 has an advantage that correction is easy.

Next, another form of apparatus will be described with reference to FIG. In this embodiment, the scanning range of the laser beam is changed. First, as shown by the laser element drive signal in FIG. 8A in the previous embodiment, the frequency of the high frequency modulation signal is 10 kHz, the frequency of the wavelength scanning drive signal is 50 Hz, λ ₁ is the wavelength corresponding to the offset, λ ₂ (759.63 nm) and λ ₃ (759.64 nm) are the upper and lower limits of the scanning wavelength corresponding to the absorption wavelength of oxygen gas (O ₂ gas) that has gas absorption only at high temperatures, and λ ₄ (759.65 nm). ), Λ ₅ (759.67 nm) indicates the upper and lower limit values of the scanning wavelength corresponding to the absorption wavelength of oxygen gas (O ₂ gas) that absorbs gas even at room temperature. λ _A indicates a wavelength corresponding to the absorption wavelength of oxygen gas only at a high temperature, and λ _B indicates a wavelength corresponding to the absorption wavelength of oxygen gas only at a normal temperature.

On the other hand, in the present embodiment, as shown in FIG. 16, the laser element drive signal has a high frequency modulation signal frequency of 10 kHz and a wavelength scanning drive signal frequency of 50 Hz, λ ₁ is a wavelength corresponding to an offset, and λ ₂ ( 759.60 nm) and λ ₃ (759.62 nm) are the upper and lower limits of the scanning wavelength corresponding to the absorption wavelength of oxygen gas (O ₂ gas) that has gas absorption even at room temperature, and λ ₄ (759.63 nm), λ ₅ (759.64 nm) indicates the upper and lower limits of the scanning wavelength corresponding to the absorption wavelength of oxygen gas (O ₂ gas) having gas absorption only at high temperatures. λ _A indicates a wavelength corresponding to the absorption wavelength of oxygen gas only at a high temperature, and λ _B indicates a wavelength corresponding to the absorption wavelength of oxygen gas only at a normal temperature. Such a laser scanning range is employed.

  Based on this principle, the following output is made. First, there is no high-temperature oxygen gas in the measurement target gas and there is a normal-temperature purge gas. In this case, the output of the synchronous detector 203b is as shown in FIG.

First, at λ _B where oxygen is absorbed at both high temperature and normal temperature, only the oxygen gas at normal temperature contained in the purge gas is present, so only the amplitude of the double frequency component of the modulated signal of the emitted light is extracted by the synchronous detection unit 203b. Since the second harmonic signal, which is a signal, is detected, the output waveform has a peak waveform as indicated by an enclosure B in FIG. This detection peak represents the concentration of oxygen gas at room temperature.
In addition, at the wavelength λ _A where oxygen is absorbed only at high temperature and there is no oxygen absorption at room temperature, since there is no high-temperature oxygen gas in the gas to be measured, the second harmonic signal is not detected by the synchronous detection unit 203b, so its output waveform As shown by an enclosure A in FIG. 17 (b), the output of the synchronous detector 203b is substantially a straight line.

  Subsequently, there is a case where there is a high-temperature oxygen gas in the measurement target gas and a normal-temperature purge gas. In this case, the output of the synchronous detector 203b is as shown in FIG.

First, in λ _B where oxygen is absorbed at both high temperature and normal temperature, since there is a purge gas at normal temperature, the synchronous detector 203b is a signal obtained by extracting only the amplitude of the double frequency component of the modulated signal of the emitted light. Since a wave signal is detected, the output waveform has a peak waveform as shown by an enclosure B in FIG.
In addition, at a wavelength λ _A where oxygen is absorbed only at high temperature and there is no oxygen absorption at room temperature, there is a high-temperature oxygen gas in the gas to be measured. Since the second harmonic signal, which is only the extracted signal, is detected, the output waveform has a peak waveform as indicated by an enclosure A in FIG. This detection peak represents the concentration of high-temperature oxygen gas.

  In either case of the output waveform of FIG. 16B or FIG. 16C, this output waveform is noise-removed by the filter 203d, is appropriately amplified, and is output to the arithmetic unit 203e which is a subsequent CPU, DSP or the like. Is done. The calculation unit 203e functions as follows. The calculation unit 203e that measures the concentration receives the wavelength scanning drive signal from the light emitting unit 100, and generates the detection peak waveform A at the timing of the enclosure A in FIGS. 16B and 16C by the timing synchronization as described above. It is made available for selection. The detection peak waveform A of the enclosure A in FIGS. 16B and 16C is a portion (gas absorption waveform) that has been absorbed by high-temperature oxygen gas in the measurement target gas, and the maximum of the detection peak waveform A The value or the minimum value corresponds to the gas concentration of the high-temperature oxygen gas in the measurement target gas.

  Accordingly, the calculation unit 203e uses the detection peak waveform A of the high-temperature oxygen gas that is the output of the synchronous detection unit 203b shown in the square frames of FIGS. Measure the peak value of the waveform corresponding to the concentration, measure the amplitude difference between the maximum value and the minimum value of the detection peak waveform A of the high-temperature oxygen gas, or part of the detection peak waveform A of the high-temperature oxygen gas Alternatively, it integrates all and functions as means for detecting the concentration of high-temperature oxygen gas in the measurement object from the integrated value. Also, it functions as means for determining that there is no oxygen gas when the gas concentration is lower than a predetermined value.

  A correction unit 600 is connected to the calculation unit 203e. The correction unit 600 displays a concentration value correction unit that corrects the value converted by the arithmetic unit 203e to a concentration value corresponding to a change in gas temperature or gas pressure, and a display that displays the concentration value corrected by the concentration value correction unit. And an external transmission unit for transmitting the corrected density value in analog and digital signals. The calculation unit 203e performs output control, and the density value corrected by the correction function display unit is displayed on the display unit. Gas analysis by the laser oxygen gas analyzer 1 is performed in this way.

  On the other hand, the laser oxygen gas analyzer 1 of the present invention performs correction as follows. In the laser type oxygen gas analyzer 1 of the present invention, scanning is performed as shown in FIG. 16A, but there is only a room temperature oxygen gas for correction. In this case, the output of the synchronous detector 203b is as shown in FIG.

First, in λ _B where oxygen is absorbed at both high temperature and normal temperature, there is only oxygen gas at normal temperature, so that only the amplitude of the double frequency component of the modulated signal of the emitted light is extracted by the synchronous detector 203b 2. Since the harmonic wave signal is detected, the output waveform becomes a detected peak waveform B as indicated by an enclosure B in FIG. This detection peak waveform B represents the concentration of oxygen gas at normal temperature for correction.
Further, since there is no high-temperature oxygen gas at the wavelength λ _A where oxygen is absorbed only at high temperature and there is no oxygen absorption at room temperature, the second harmonic signal is not detected by the synchronous detection unit 203b. As indicated by an enclosure A in b), the output of the synchronous detector 203b is substantially a straight line.

  This output waveform is noise-removed by the filter 203d, is appropriately amplified, and is output to the arithmetic unit 203e, which is a subsequent CPU, DSP, or the like. The calculation unit 203e functions as follows. The calculation unit 203e that measures the concentration receives the wavelength scanning drive signal from the light emitting unit 100, and can select the detection peak waveform B at the timing of the enclosure B in FIG. 16B by the timing synchronization described above. Yes. Timing switching can be selected by, for example, a switch (not shown) connected to the calculation unit 203e. The detection peak waveform B of the enclosure B in FIG. 16B is a portion (gas absorption waveform) that has been absorbed by the normal-temperature oxygen gas for correction, and the maximum or minimum value of the detection peak waveform B is for correction. This corresponds to the concentration of oxygen gas.

  Therefore, the calculation unit 203e corresponds to the concentration of oxygen gas at room temperature using the detection peak waveform B of oxygen gas at room temperature, which is the output of the synchronous detection unit 203b shown in the square frame of FIG. 16B. Measure the peak value of the waveform, measure the amplitude difference between the maximum or minimum value of the detection peak waveform B of oxygen gas at normal temperature, or integrate part or all of the detection peak waveform B of oxygen gas at normal temperature Thus, it functions as a means for detecting the concentration of oxygen gas at room temperature from the integrated value. Correction is performed using the density based on the detected peak waveform B. And it correct | amends as mentioned above and obtains a correction coefficient like said Formula 3.

A span correction value of the zero-point correction value and the wavelength of the wavelength (λ _A) (λ _A) is calculated as a correction coefficient, the correction unit 600 transmits to the operation unit 203e of the light receiving portion 200. The calculation unit 203e of the light receiving unit 200 registers these correction coefficients in a built-in memory, and thereafter uses the correction coefficient to correct the gas concentration value of the high-temperature oxygen gas and output the corrected gas concentration value. Therefore, after correction, the influence of the secular change can be canceled and an accurate gas concentration value can be obtained. Such correction makes it possible to correct the deviation at normal temperature without heating the gas and the piping.
The laser oxygen gas analyzer of this embodiment is such a thing. This embodiment can also achieve the same effect as the laser oxygen gas analyzer described above.

The laser oxygen gas analyzer of the present invention has been described above.
The laser oxygen gas analyzer of the present invention uses a physical phenomenon that absorption intensity differs when the temperature of oxygen gas is different, and absorbs light at a specific wavelength where the absorption intensity of high-temperature oxygen gas is particularly high. Of the oxygen gas contained in the gas to be measured, low-temperature oxygen gas in instrument air used for purge gas for the purpose of protecting the device and preventing dust adhesion, and in the air inside the device that is not purge gas For example, the gas concentration of a high-temperature oxygen gas of 400 ° C. or higher among the measurement target gas in a boiler such as a garbage incineration facility is measured by a laser beam without being affected by the low-temperature oxygen gas. In particular, at the time of correction, since correction can be easily performed using low-temperature oxygen gas, a laser type oxygen gas analyzer that is easy to operate is obtained.

  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 generating unit 102: Collimating lens 103: Box cover 200: Light receiving unit 201: Condensing lens 202: Light receiving element 203: Signal processing unit 204: Box cover 300: Light emitting unit side purge unit 301: Purge Main part 302: Inlet 303: Outlet 400: Light receiving part side purge part 401: Purge part main body 402: Inlet 403: Outlet 500: Communication line 600: Correction part 701a, 701b: Wall 702a, 702b: Companion flange 800 : Detection light 900: Correction gas cell 901: Nitrogen cylinder 02: oxygen cylinder

Claims (3)

A light emitting unit that emits detection light by laser light, a light receiving unit that receives detection light propagated through a space in which oxygen gas to be measured exists, and calculates a gas concentration from a detection peak of the received detection light; A laser oxygen gas analyzer for measuring a gas concentration of oxygen gas, having a correction unit that corrects a concentration error caused by a change with time by a correction coefficient,
The light emitting unit has a detection light for gas analysis with a laser beam having a wavelength such that the absorption intensity of the high-temperature oxygen gas to be measured is high and the absorption intensity of the oxygen gas at room temperature is small, and oxygen gas at room temperature. The detection light for correction by the laser light having a wavelength with a large absorption intensity, and the light emission,
The light receiving unit receives the detection light for gas analysis at the time of gas analysis and calculates the gas concentration of the high-temperature oxygen gas, and receives the detection light for correction at the time of correction to calculate the detection peak. And
The correction unit calculates a correction coefficient for correcting a change with time using a detection peak generated from correction detection light at the time of correction,
The laser-type oxygen gas analyzer, wherein the light receiving unit indirectly corrects a gas concentration value generated by receiving detection light for gas analysis using the correction coefficient calculated by the correction unit. A light emitting unit that emits detection light by laser light, a light receiving unit that receives detection light propagated through a space in which oxygen gas to be measured exists, and calculates a gas concentration from a detection peak of the received detection light; A light-emitting unit side purge unit that supplies purge gas by air to the light-emitting unit, a light-receiving unit side purge unit that supplies purge gas by air to the light-receiving unit, a correction unit that corrects a concentration error caused by a change with time, using a correction coefficient, A laser oxygen gas analyzer that measures the gas concentration of oxygen gas,
The light emitting unit
A wavelength at which the absorption intensity of the high-temperature oxygen gas to be measured is large and the absorption intensity of the normal-temperature oxygen gas contained in the purge gas of the light-emitting part side purge part and the light-receiving part side purge part is small, and the light-emitting part side purge Detection light for gas analysis and detection light for correction by a laser beam scanned at a scanning wavelength in a predetermined range including a wavelength at which the absorption intensity of room-temperature oxygen gas contained in the purge gas of the gas detector and the light-receiving-side purge unit is high A laser element emitting light,
A light emission side temperature stabilizing means for stabilizing the temperature of the laser element;
A high frequency modulation signal for modulating the emission wavelength with respect to a wavelength scanning drive signal including a variable drive signal for changing the emission wavelength of the laser element to a scanning wavelength within a predetermined range so as to scan the absorption wavelength of oxygen gas. A laser drive signal generator that combines and outputs the laser drive signal;
A current controller that converts the laser drive signal output from the laser drive signal generator into a current and supplies the current to the laser element;
With
The light receiving unit is
A light receiving element having sensitivity to detection light for gas analysis during gas analysis and detection light for correction during correction;
A synchronous detection unit that detects an amplitude of a second harmonic signal that is a double frequency component of a modulation signal in the light emitting unit from an output signal of the light receiving unit, and outputs a detection signal;
A filter circuit for removing noise from the output signal of the light receiving unit;
The calculation is based on the detection signal output from the filter circuit. During gas analysis, the gas concentration of high-temperature oxygen gas is calculated using the detection light for gas analysis, and the correction detection light is used during correction. A calculation unit for calculating the detection peak at
The correction unit calculates a correction coefficient for correcting a change with time using a detection peak generated from correction detection light at the time of correction,
The laser oxygen, wherein the calculation unit of the light receiving unit indirectly corrects a gas concentration value generated by receiving detection light for gas analysis using a correction coefficient calculated by the correction unit Gas analyzer. In the laser type oxygen gas analyzer according to claim 1 or 2,
The wavelength at which the absorption intensity of the high-temperature oxygen gas to be measured is large and the absorption intensity of the oxygen gas at room temperature is small is a wavelength at which an absorption peak is included in the range of 759.63 nm to 759.64 nm. The wavelength at which the absorption intensity of the oxygen gas at room temperature is high is a wavelength at which an absorption peak is included in the range of 759.65 nm to 759.67 nm or 759.60 nm to 75 9 . A laser type oxygen gas analyzer characterized by having a wavelength that includes an absorption peak within a range of 62 nm.

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