JP2014102152A - Laser type gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser type gas analyzer capable of stably and accurately measuring gas concentration by automatically correcting deviation in an emission wavelength of a laser device without a reference gas cell about gas to be measured that does not exist in the air or exists only in a trace amount in the air.SOLUTION: Gas to be measured that indicates a certain absorption intensity or larger during measurement at each constant cycle is used to obtain a deviation width of an output wavelength of a synchronous detection section. A deviated wavelength is corrected by changing the temperature of a laser device. With this method, an error in concentration due to wavelength change can be prevented without the need of a reference gas cell, thereby achieving long-term stability.

Description

  The present invention relates to a laser gas analyzer that measures the concentration of a gas that does not exist in the atmosphere or a gas that exists only in a minute amount in the atmosphere using a laser beam.

It is known that each gas molecule in gas has its own light absorption spectrum. For example, FIG. 19 is an example of an absorption spectrum of NH ₃ (ammonia) gas, in which 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. A measurement object gas such as NH ₃ (ammonia) gas has a specific absorption spectrum.

  The laser gas analyzer is equipped with a laser element that emits laser light of a wavelength that is absorbed by the measurement target gas, and detects the presence or absence of the measurement target gas by absorbing the laser light of this specific wavelength into the measurement target gas. can do. In addition, since the absorption amount of the laser beam at a specific wavelength is proportional to the concentration of the measurement target gas, the laser gas analyzer can also detect the concentration.

  The gas concentration measuring method of the laser gas analyzer is 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 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 enclosed, The control method is also used, for example, as described in Patent Document 2 described later.

  Such laser gas analyzers are used especially for atmospheric environment measurement and control applications. Specifically, they mainly control combustion of boilers such as garbage incinerators, monitor hydrogen chloride gas in flue gas, and power facilities. Often used for ammonia monitoring. The measurement target gas has a relatively high temperature. For example, the temperature of the measurement target gas targeted by a laser gas analyzer used for boiler combustion control is as high as 700 to 1200 ° C. Laser gas analyzers are used in such environmental fields.

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.)

  A frequency modulation type laser gas analyzer needs to receive a signal having a double frequency component in order to measure the concentration. Therefore, a laser element that emits an absorption wavelength of the measurement target gas is selected. Specifically, there are a DFB laser (Distributed Feedback Laser), a DBR laser (Distributed Bragg Reflector Laser), a VCSEL (Vertical Cavity Surface Emitting Laser), and the like. These laser elements are elements whose wavelength changes with current and temperature. In general, the frequency modulation method scans the front and rear wavelengths centering on the absorption wavelength by current drive control, and controls the temperature to be a constant value by temperature control to prevent wavelength deviation due to temperature change of the laser element. .

  The output waveform of the synchronous detector has a shape as shown in FIG. 20, and the concentration of the measurement target gas is detected from the difference between the maximum value and the minimum value of the gas absorption waveform. A wavelength or current value indicating a point between the maximum value and the minimum value can be obtained in advance.

  Laser elements used in laser gas analyzers such as these have MTBF of several hundreds of thousands of hours or more, and the current required to emit the initial optical output that is considered to be a lifetime according to the optical standard is increased by 20%. It is a long-life device that can continue to emit light for several tens of thousands of hours to several hundreds of thousands of hours. However, the laser element gradually deteriorates when viewed on a yearly basis, and the wavelength changes over time even when controlled at the same current and the same temperature. The cause is that if the light emission time increases, the light emission end face is destroyed and deteriorated due to the influence of heat of light emission, the threshold for emitting laser light increases, the light output decreases, and the wavelength range for the current value to scan is reduced. It is to become.

  When the laser element is driven with the same current immediately after the start of use and after tens of thousands of hours have elapsed, the wavelength of the laser element after tens of thousands of hours after the threshold current has risen moves to the short-wave side. For example, in the output waveform A for the ammonia gas in the square frame in FIG. 4, it moves to the left on the time axis. In FIG. 21, the scan wavelength range for ammonia gas is shifted downward. If the concentration is detected in this state, a measurement error occurs. That is, the emission wavelength of ammonia gas emits light at a low current value, and the output waveform becomes small even if the ammonia gas has the same absorption intensity as the current value becomes low. This change gradually moves over several years, and is a long-term drift factor that is difficult to judge from the daily operating situation.

  In this way, the wavelength position to be measured is different from the actual wavelength position, and an instruction error occurs. Therefore, correction is necessary. Normally, maintenance is performed once every six months or once a year, the measurement target gas is flowed, the position of the output waveform of the synchronous detector is checked, and if there is a deviation, the position of the output waveform is determined by the laser temperature. Adjust.

  If there is a sufficient amount of gas in the atmosphere (for example, oxygen), the absorption intensity can always be obtained from the atmosphere in the device without a reference gas cell. Wavelength correction can be performed by changing the element temperature.

  However, the absorption intensity cannot always be obtained for a gas that does not exist in the atmosphere, such as hydrogen chloride gas or ammonia gas, or a gas that exists only in a minute amount in the atmosphere. In these devices for measuring hydrogen chloride gas and ammonia gas, the output waveform of the synchronous detection unit in FIG. 20 does not appear in a space where there is no measurement target gas.

  Therefore, in order to detect and correct the wavelength shift for such a gas, as shown in FIG. 22, the laser beam is incident on the beam splitter to divide the beam, and one of the beams is transmitted to the measurement target gas in the pipe. The other is transmitted through a reference gas cell filled with a gas having the same component as the gas to be measured, such as hydrogen chloride gas or ammonia gas, and the wavelength shift from the output waveform of the detection unit obtained from the light transmitted through the reference gas cell. Was detected. However, if the reference gas cell cannot be inserted due to structural problems, or if a gas that is adsorbent and cannot be enclosed in the reference gas cell, such as hydrogen chloride gas, is used, the wavelength change is detected by the reference gas cell. Difficult to do.

  Therefore, the present invention has been made in view of the above-described problems, and the object of the present invention is to perform laser measurement even when there is no reference gas cell for a measurement target gas that does not exist in the atmosphere or exists only in a minute amount in the atmosphere. It is an object of the present invention to provide a laser type gas analyzer that automatically corrects the emission wavelength deviation of the element and can measure the gas concentration stably and accurately.

  When the laser element used is deteriorated, the wavelength of light emitted at the same current value and the same temperature is different. Therefore, a deviation occurs between the wavelength to be measured and the actual wavelength, which causes a density error. Therefore, in the laser gas analyzer of the present invention, the measurement target gas is used at regular intervals, the presence or absence of wavelength deviation of the laser element is determined from the detected waveform signal, and the wavelength of the laser element is changed by changing the temperature of the laser element. Correction was made to achieve long-term stability. This method does not require a reference gas cell, can prevent concentration errors due to wavelength changes, and can achieve long-term stability.

That is, the laser gas analyzer according to claim 1 of the present invention is:
A frequency modulation method for measuring the concentration of the measurement target gas, comprising: a light emitting unit that emits detection light by laser light; and a light receiving unit that receives detection light propagated through a space in which the measurement target gas exists. A laser gas analyzer,
The light emitting unit
A laser element that emits a laser beam having a wavelength at which the measurement target gas absorbs light, temperature control means for maintaining the laser element at a constant temperature by a thermo module, and a supply current to the laser element are changed to change the measurement target gas. Wavelength scanning drive signal generating means for generating a wavelength scanning drive signal for scanning light absorption characteristics, high frequency modulation signal generating means for generating a high frequency modulation signal, and modulating the wavelength scanning drive signal with the high frequency modulation signal, Current control means for generating a drive signal for the laser element,
The light receiving unit is
From the light receiving element sensitive to the laser wavelength that is the detection light in which the gas to be measured is absorbed, the reference signal generating means for generating the reference signal having the double frequency component of the high frequency modulation signal, and the output signal of the light receiving element Synchronous detection means for detecting the amplitude of the second harmonic signal, which is a double frequency component, and outputting a detection signal; calculation means for calculating the concentration of the gas to be measured based on the value of the detection signal from the synchronous detection means; Each with
This computing means is
It is determined whether or not there is a deviation between the gas absorption waveform of the detection signal and a reference waveform registered in advance, and if there is a deviation, the set temperature of the thermo module that controls the temperature of the laser element is changed to eliminate the deviation. To fix,
It is characterized by that.

A laser gas analyzer according to claim 2 of the present invention is
A frequency modulation method for measuring the concentration of the measurement target gas, comprising: a light emitting unit that emits detection light by laser light; and a light receiving unit that receives detection light propagated through a space in which the measurement target gas exists. A laser gas analyzer,
The light emitting unit
A laser element that emits a laser beam having a wavelength at which the measurement target gas absorbs light, temperature control means for maintaining the laser element at a constant temperature by a thermo module, and a supply current to the laser element are changed to change the measurement target gas. Wavelength scanning drive signal generating means for generating a wavelength scanning drive signal and trigger signal for scanning light absorption characteristics, high frequency modulation signal generating means for generating a high frequency modulation signal, and modulating the wavelength scanning drive signal by the high frequency modulation signal And current control means for generating a drive signal for the laser element,
The light receiving unit is
From the light receiving element sensitive to the laser wavelength that is the detection light in which the gas to be measured is absorbed, the reference signal generating means for generating the reference signal having the double frequency component of the high frequency modulation signal, and the output signal of the light receiving element Synchronous detection means for detecting the amplitude of the second harmonic signal, which is a double frequency component, and outputting a detection signal, and detection signals from the synchronous detection means when a predetermined time has elapsed with reference to the trigger signal input from the light emitting unit. Calculating means for calculating the concentration of the gas to be measured based on the value,
This computing means is
The presence or absence of deviation between the gas absorption waveform of the detection signal and the reference waveform is determined with reference to the trigger signal, and when there is a deviation, the set temperature of the thermo module that controls the temperature of the laser element is changed to correct the deviation. To fix it,
It is characterized by that.

A laser gas analyzer according to claim 3 of the present invention is
A frequency modulation method for measuring the concentration of the measurement target gas, comprising: a light emitting unit that emits detection light by laser light; and a light receiving unit that receives detection light propagated through a space in which the measurement target gas exists. A laser gas analyzer,
The light emitting unit
A laser element that emits a laser beam having a wavelength at which the measurement target gas absorbs light, temperature control means for maintaining the laser element at a constant temperature by a thermo module, and a supply current to the laser element are changed to change the measurement target gas. Wavelength scanning driving signal generating means for generating a wavelength scanning driving signal for scanning the light absorption characteristic so as to include a trigger signal, high frequency modulation signal generating means for generating a high frequency modulation signal, and the high frequency modulation of the wavelength scanning driving signal Current control means for modulating the signal to generate a drive signal for the laser element,
The light receiving unit is
From the light receiving element sensitive to the laser wavelength that is the detection light in which the gas to be measured is absorbed, the reference signal generating means for generating the reference signal having the double frequency component of the high frequency modulation signal, and the output signal of the light receiving element Synchronous detection means for detecting the amplitude of the second harmonic signal, which is a double frequency component, and outputting a detection signal, an extraction unit for extracting the trigger signal component from the output signal of the light receiving element, and the trigger signal as a reference A calculation means for calculating the concentration of the gas to be measured based on the value of the detection signal from the synchronous detection means when a predetermined time has elapsed,
This computing means is
The presence or absence of deviation between the gas absorption waveform of the detection signal and the reference waveform is determined with reference to the trigger signal, and when there is a deviation, the set temperature of the thermo module that controls the temperature of the laser element is changed to correct the deviation. To fix it,
It is characterized by that.

  According to the present invention, the emission wavelength shift of the laser element is automatically corrected for a measurement target gas that does not exist in the atmosphere or exists only in a minute amount in the atmosphere without a reference gas cell, and is stable. In addition, it is possible to provide a laser type gas analyzer capable of accurately measuring the gas concentration.

It is a block diagram of the laser type 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 embodiment of the present invention, showing the scanning waveform of the laser device, the absorption and output waveforms of the synchronous detector of the NH ₃ gas. 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 a drive current. 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 output signal of an I / V conversion part and a synchronous detection part. It is a figure which shows the output signal of an I / V conversion part and a synchronous detection part. It is a block diagram of the laser light source part of the laser type gas analyzer of the 2nd Embodiment of this invention. It is a block diagram of the light receiving element and signal processing part of the laser type gas analyzer of the 2nd Embodiment of this invention. It is explanatory drawing of the trigger signal sent to the output waveform of the wavelength scanning drive signal generation part of a laser element, and a signal processing part. It is a figure which shows the output signal of an I / V conversion part and a synchronous detection part. It is a figure which shows the output signal of an I / V conversion part and a synchronous detection part. It is a figure which shows the output signal of a synchronous detection part. It is a block diagram of the signal processing part of the laser type gas analyzer of the 3rd Embodiment of this invention. It is a wave form diagram of a received light signal. It is a wave form diagram of a received light signal. It is a figure which shows the output waveform of the synchronous detection part corresponding to FIG. 15A. It is a figure which shows the output waveform of the synchronous detection part corresponding to FIG. 15B. It is a figure which shows the relationship between the light-receiving light quantity level and the amplitude level of a gas absorption waveform. FIG. 15B is a waveform diagram of wavelength scanning signal components corresponding to FIG. 15A. It is a wave form diagram of the wavelength scanning signal component corresponding to Drawing 15B. It is an absorption spectrum characteristic view of NH ₃ gas. It is an output waveform of a synchronous detection part. It is the figure which showed the change by the time-dependent change of IR characteristic of a laser element. It is explanatory drawing of the wavelength detection which uses a reference cell.

  Next, a laser 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 type gas analyzer 1 of the present embodiment. The laser 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, and a communication line 500.

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.
The communication line 500 connects the light emitting unit 100 and the light receiving unit 200 in a communicable manner.

  As a specific example, the laser gas analyzer of this embodiment will be described as being fixed to facility piping. This pipe is a flue or the like in which a small amount of gas in the atmosphere or a gas to be measured that does not exist in the atmosphere passes inside. Such a measurement target gas is, for example, hydrogen chloride gas discharged from a flue such as a garbage incinerator or ammonia gas that has not reacted with NOx injected as a catalyst in a power facility. In the description of the present embodiment, it is assumed that ammonia gas is used as the measurement target gas for the sake of concreteness of the description, but the present invention can of course be applied to hydrogen chloride.

  The walls 601a and 601b are walls of this pipe. The companion flanges 602a and 602b are fixed to the walls 601a and 601b by, for example, welding.

  The purge unit main body 301 of the light emitting unit side purge unit 300 including the angle adjusting mechanism unit is attached to one of the phase flanges 602a. 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 emission unit side purge unit 300 and the internal passage of the phase flange 602a 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 602b. 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 and the internal passage of the phase flange 602b communicate with each other and further communicate 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 700 is incident on the inside of the walls 601a and 601b (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 602a.

  The detection light 700 is absorbed when it passes through ammonia gas or the like in the measurement target gas inside the walls 601a and 601b. The detection light 700 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 700, which is parallel light transmitted through the walls 601a and 601b (inside the flue), passes through the center of the internal passage of the companion flange 602b 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 602 a is purged through the outlet 303. After this purge, the purge gas is discharged into the walls 601a and 601b (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 602b is purged. After this purge, the purge gas is discharged into the walls 601a and 601b (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. Further, the instrument air 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 602a and 602b 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. 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 makes the emission wavelength of the laser element variable so as to scan the absorption wavelength of the measurement target gas.
The high frequency modulation signal generation unit 101b frequency-modulates the wavelength with a sine wave of about 10 kHz, for example, in order to detect the absorption wavelength of the ammonia 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), a DBR laser (Distributed Bragg Reflector Laser), or a VCSEL (Vertical Cavity Surface Emitting Laser).

  The laser element 101e is provided with temperature control means that is a thermo module. This temperature control 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. As a result, the temperature of the laser element 101e is set to a desired value. It operates to match the temperature. The temperature control unit 101d is communicably connected to the calculation unit 203e via the communication line 500.

  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 ammonia gas (NH ₃ gas), it is a portion that can scan a line width of about 0.2 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. 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 be able to measure ammonia gas, which is a measurement target gas, 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). The temperature of the laser element 101e is adjusted by controlling energization.
Thereafter, the laser element 101e is driven.

FIG. 4 shows the drive signal of the laser element, 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 and λ ₃ are ammonia. The upper and lower limit values of the scanning range corresponding to the absorption wavelength of gas (NH ₃ gas) are shown.
The laser element 101e irradiates the collimator lens 102 with such laser light to generate detection light 700 that is parallel light, and emits the detection light 700 to the internal space of the walls 601a and 601b 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. 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 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 detection 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 computing unit 203e detects the presence or absence of ammonia gas and calculates the ammonia concentration by various processes described below. The arithmetic unit 203e controls the set temperature for the temperature control unit 101d that is communicably connected via the communication line 500. The output signal of the I / V conversion unit 203a is input to the calculation unit 203e.

Here, the measurement principle of the frequency modulation type laser gas analyzer will be described with reference to the principle diagram of the frequency modulation type of the laser type gas analyzer of FIG. As shown in the absorption spectrum of ammonia gas (NH ₃ gas) in FIG. 19, since the absorption line of this ammonia gas is represented by a linear spectrum, concentration detection by a frequency modulation method is possible. Then, the laser gas analyzer of the frequency modulation scheme, center frequency f _c, by frequency-modulating the output light of the laser element at the modulation frequency f _m, is irradiated to the ammonia 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, a single-wavelength laser beam using a distributed feedback laser element (DFB laser), a distributed Bragg reflection laser (DBR laser), or a vertical cavity surface emitting laser (VCSEL) as described above. Only the gas is emitted 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 FIGS. 7A and 7B, the emission wavelength of the laser element varies 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. In this case, the wavelength before and after the absorption wavelength is scanned by current drive control, and the temperature is controlled to be a constant value by temperature control to prevent wavelength shift due to temperature change of the laser element.

  As described above, the wavelength of the 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, not all absorption lines as shown in FIG. 19 can 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. 6, 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 such a principle, when the laser beam is not absorbed by the measurement target gas in the synchronous detection unit 203b, the double detection signal is not detected by the synchronous detection unit 203b, and therefore the output of the synchronous detection unit 203b is almost linear. (See, for example, FIG. 8A).

  On the other hand, when there is absorption of laser light by the measurement target gas, a double wave signal that is a signal obtained by extracting only the amplitude of the double frequency component of the modulation signal of the emitted light is detected by the synchronous detection unit 203b. The output waveform is an output waveform of the synchronous detection unit 203b shown in the rectangular frame of FIG. 4 or a peak waveform as shown in FIG. 8B. Noise is removed from the peak waveform by the filter 203d, and the peak waveform is appropriately amplified and output to the arithmetic unit 203e such as a CPU or DSP in the subsequent stage. The computing unit 203e detects the presence or absence of ammonia gas and calculates the ammonia concentration by various processes described below.

  The calculation unit 203e functions as follows. First, A in the peak waveform of FIG. 8B is a portion (gas absorption waveform) that has been absorbed by the measurement target gas, and the maximum value C or minimum value B, D of this absorption waveform A corresponds to the concentration of the measurement target gas. To do. Therefore, the calculation unit 203e measures the peak value of the waveform corresponding to the concentration of the measurement target gas using the gas absorption waveform A that is the output of the synchronous detection unit 203b shown in FIG. It functions as a means for measuring the amplitude difference between the maximum value C or the minimum values B and D and detecting the concentration of ammonia gas that is the measurement target gas. Alternatively, it functions as means for integrating a part or all of the gas absorption waveform A and detecting the concentration of ammonia gas as a measurement object from the integrated value. Also, it functions as means for determining that there is no ammonia gas when the gas concentration is lower than a predetermined value.

  An output unit (not shown) is connected to the calculation unit 203e. The output unit corrected the concentration converted value by the calculation unit 203e into a concentration value corresponding to a change in gas temperature or gas pressure, and a display unit for displaying 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 calculation unit 203e performs output control, and the density value corrected by the correction function display unit is displayed on the display unit. This is the case of gas analysis using a laser gas analyzer.

  Next, automatic correction of wavelength shift using such a laser gas analyzer will be described. Such correction is performed by the calculation unit 203e. First, as a premise, the calculation unit 203e flows a reference gas having a specific concentration in the walls 601a and 601b in advance, and registers the waveform obtained at that time. For example, the waveform is as shown by the signal Sb in FIG. 8B, and the maximum value C and the minimum values B and D, which are the peaks of the waveform, are stored in a memory unit (not shown). Also, the time at which the maximum value C and the minimum values B and D appear is registered with reference to the falling portion of the signal Sa. At this time, the waveform is used as a reference gas having a concentration that provides a sufficiently large output waveform capable of detecting the wavelength shift, so that the wavelength position can be easily grasped. The reference gas is ammonia gas having a predetermined concentration. This reference may be acquired when the apparatus is started up or at the time of factory shipment.

  Then, at the time of a regular medical examination performed after a predetermined period (for example, 6 months), the calculation unit 203e compares the measurement target gas, which is the same gas as the reference gas, through the walls 601a and 601b. First, one maximum value and two minimum values, which are waveform peaks, are stored from waveform data acquired as digital data by sampling, and the time at which the maximum value and minimum value appear with reference to the falling portion of the signal Sa is stored. .

  If the peak appearance time is shorter than the reference gas having a specific concentration acquired in advance as shown in the rectangular frame in FIG. 4 and the shift to the left on the time axis occurs, the shift occurs. The amount is displayed on the display unit of the output unit, and the worker confirms the amount of deviation. Further, the calculation unit 203e changes the set temperature by controlling the temperature control unit 101d of the temperature control unit via the communication line 500. The calculation unit 203e changes the set temperature of the temperature control unit 101d so as to reduce the time deviation, detects the previous measurement target gas, performs the same comparison, repeats the same control, and finally performs the time deviation. The temperature control unit 101d controls the temperature control unit 101d to newly register the temperature at which 0 becomes 0 as the set temperature in the temperature control unit 101d.

  When the wavelength shift occurs in this way, automatic adjustment is performed so that the temperature of the laser element is controlled and the initial output waveform position is obtained. Conventionally, it has been performed manually at regular checkups every predetermined period (for example, 6 months). However, the present invention is excellent in that maintainability is improved by enabling automatic adjustment. Further, correction is performed by the same method for the laser element for hydrogen chloride gas. The detection of the wavelength shift is not limited to the measurement target gas. For example, even when detection is performed using a calibration gas having the same concentration and different concentration as the reference gas, the position where the peak appears shifts to the left. Since the occurrence can be detected, temperature control may be performed at such time.

  The present embodiment has been described above. In the prior art, the laser element used in the laser gas analyzer shifts to the short wavelength side even if it is controlled at the same current and the same temperature when used for a long time. When a wavelength change occurs, a density error occurs unless it is controlled by temperature or the like so that the original state is obtained. In the case of a gas that does not exist in the atmosphere, a reference cell or the like is built in the apparatus and the wavelength is corrected. However, it is difficult to seal the gas in the cell if the gas has strong adsorptivity. . If the reference cell cannot be used, it is necessary to correct the deviation during regular maintenance. Therefore, maintenance workers have performed wavelength adjustment using an adjustment device or the like during regular maintenance, and automatic correction has been performed using a reference gas cell.

  However, according to the present invention, there is provided a laser gas analyzer for measuring a gas to be measured that does not exist in the atmosphere or exists only in a minute amount in the atmosphere, for example, hydrogen chloride gas or ammonia gas. Even in a structure without a reference gas cell sealed with the target gas, correction of measurement error due to wavelength shift due to degradation of the laser element can be made by measuring the wavelength shift width from the absorption waveform of the measurement target gas above a certain value and then measuring the wavelength shift from the absorption waveform. The temperature is corrected by changing the set temperature of the thermo module that controls the temperature of the laser element, and the wavelength that is affected by the wavelength fluctuation due to laser degradation is automatically corrected. By solving the problem, a laser gas analyzer having long-term stability can be provided. Further, long-time adjustment by a person is not necessary, and parts such as a reference cell are not necessary, so that cost can be greatly reduced. Also. By eliminating the wavelength shift, a laser gas analyzer can be obtained in which measurement errors hardly occur.

  Next, a second embodiment of the present invention will be described with reference to the drawings. Compared with the previous first embodiment, this embodiment basically has the same configuration as that of FIG. 1, but more specifically, as shown in FIG. 9, the wavelength scanning drive signal generation section of the laser light source section 101 ′. The trigger signal S4 (see FIG. 11) of the wavelength scanning drive signal is extracted from 101a and output, and as shown in FIG. 10, the output from the I / V conversion unit 203a to the calculation unit 203e is eliminated. The operation unit 203e of the signal processing unit 203 ′ receives the trigger signal S4 and is synchronized using the trigger signal S4 (see FIG. 11). The laser light source unit 101 ′ of the light emitting unit 100 in FIG. 9 and the signal processing unit 203 ′ of the light receiving unit 200 in FIG. 10 are compared with the laser light source unit 101 in FIG. 2 and the signal processing unit 203 in FIG. Although it has the same configuration, it is different in that the trigger signal S4 is input / output instead of the output of the I / V conversion unit, and the calculation unit 203e performs calculation processing based on the trigger signal S4. Are given the same reference numerals and redundant descriptions are omitted, and only the differences are described.

  FIG. 11 is a diagram for explaining the trigger signal S4. The trigger signal S4 is input from the wavelength scanning drive signal generation unit 101a to the calculation unit 203e. As shown in the figure, the trigger signal S4 is a pulse-like signal output from the wavelength scanning drive signal generation unit 101a in synchronization with one period of the wavelength scanning driving signal including S1, S2, and S3. For example, the trigger signal S4 may be generated in synchronization with the timing of the wavelength scanning drive signal (the generation timing of the signal S3) that makes the drive current of the laser element 101e zero. A trigger signal S4 is output from the wavelength scanning drive signal generation unit 101a and input to the arithmetic circuit 203e via the communication line 500.

  Next, a method for calculating the concentration of oxygen gas by the calculation unit 203e of the signal processing unit 203 of this embodiment will be described. As shown in FIG. 9, in the laser light source unit 101, the temperature control unit 101d controls energization of the Peltier element 101g so that the measurement target gas can be measured at the central portion of the wavelength scanning drive signal S1, and the temperature of the laser element 101e. Adjust. The laser element 101e is driven to emit laser light into the internal space of the walls 601a and 601b where the measurement target gas exists.

  The laser beam is condensed by the condensing unit 201 and the collected light is incident on the light receiving element 202. Ammonia gas is measured as a measurement target gas. The light receiving element 202 converts it into a detection signal based on an electric signal according to the amount of received light and sends it to the signal processing unit 203. For example, the signal processing unit 203 performs amplification or noise filtering on the detection signal to detect the density. In the signal processing unit 203, when the laser light is not absorbed by the measurement target gas, as shown in FIG. 12A, the double frequency signal is not detected by the synchronous detection unit 203b. Therefore, the output of the synchronous detection unit 203b is almost linear. Become.

  On the other hand, when there is absorption of laser light by the measurement target gas, the double frequency signal is detected by the synchronous detection unit 203b. FIG. 12B is a waveform diagram showing the output signal Sb of the synchronous detection unit 203b together with the output signal Sa of the I / V conversion unit 203a. In FIG. 12B, the portion surrounded by the dotted line is the gas absorption waveform A.

Here, when there is an offset in the output signal Sb of the synchronous detection portion 203b by some cause, as shown in FIG. 13, offset is not the original output signal Sb ₀ signal Sb ₁ appears added. As a result, an error occurs in the detection based on the maximum or minimum value of the gas absorption waveform A in FIG. 12B or the integral value of the waveform, and the gas concentration may not be detected accurately. Therefore, in this embodiment, the following method is used in order to detect the gas concentration with higher accuracy and stability.

  As described above, in the case shown in FIG. 12A where the measurement target gas does not exist, the double frequency signal is not detected by the synchronous detection unit 203b, and the output of the synchronous detection unit 203b is almost a straight line. However, since various noises exist, even if the measurement target gas does not exist, the output signal Sb of the synchronous detection unit 203b has a slightly uneven waveform as shown in FIG. 12A. In the case of such a waveform, in a method of simply detecting only the maximum value or the minimum value of the waveform, there is a possibility that the uneven portion due to noise is misidentified as a gas absorption waveform and the maximum value or the minimum value is erroneously detected. Similarly, when an integral value of a waveform is obtained, there is a possibility of erroneous detection. In particular, when the measurement target gas has a low concentration, the uneven portion becomes a large error factor when detecting the gas concentration.

  For this reason, in this embodiment, in order not to misidentify the uneven portion due to noise as a gas absorption waveform, the trigger signal S4 output from the wavelength scanning drive signal generator 204a as shown in FIG. Identifies the position where the maximum or minimum value should be. The trigger signal S4 is synchronized with one cycle of the wavelength scanning drive signal, and is particularly synchronized with S3 of the wavelength scanning drive signal. There is a certain temporal correlation between the trigger signal S4 and the output signal Sb of the synchronous detector 203b.

  That is, when the measurement target gas exists, the timing at which the gas absorption waveform A, the maximum value C, and the minimum values B and D in FIGS. 12A and 12B are generated with respect to the timing of the trigger signal S4 is detected almost accurately in advance. Is possible. Therefore, measurement is performed on the assumption that the minimum value B at point B, the maximum value C at point C, and the minimum value D at point D appear in the synchronous detector output waveform when a predetermined time tb, tc, td has elapsed from the trigger signal. . These predetermined times tb, tc, and td are preliminarily calculated experimentally before factory shipment or at the time of calibration, and are registered in a memory (not shown). The concentration is calculated using this value.

  When measuring the gas concentration, the synchronous detector at the predetermined times tb, tc and td at which the maximum value C and the minimum values B and D should be generated with reference to the trigger signal S4 received from the wavelength scanning drive signal generator 204a. The maximum value and the minimum value are measured from the output signal Sb of 203b (the output signal of the filter 203d).

  As a result, even when the concentration of the measurement target gas is as low as possible, the calculation unit 203e detects the gas absorption waveform A, the maximum value C, and the minimum values B and D based on the trigger signal S4. Functions as a means to The calculation unit 203e can accurately detect and measure these values. Therefore, the gas concentration can be calculated with high accuracy without being affected by the uneven portions of the waveform due to noise.

  The calculation unit 203e functions as a means for reading and storing the value of the synchronous detection unit output waveform when a predetermined time tb, tc, td elapses from the trigger signal, and thereafter calculating the concentration. For example, the maximum value at the peak of the waveform directly represents the gas concentration, so that the maximum value is output as the concentration. Alternatively, the difference value obtained by subtracting the minimum value from the maximum value is used as the density. The concentration is measured using these ABCD. The calculation unit 203e in FIG. 10 detects a maximum value C and minimum values B and D before and after the gas absorption waveform A shown in FIG. 12A, and calculates the gas concentration by the following formula 1 or formula 2. Function as.

[Equation 1]
Gas concentration = α × | BC

[Equation 2]
Gas concentration = α × | C−D |

  In Equations 1 and 2, α is a gas concentration conversion coefficient. The gas concentration conversion coefficient α is determined by calibrating in advance with a gas whose concentration of the gas component to be measured is known. For example, the zero gas with the concentration of the measurement target gas component of 0 ppm and the span gas with the concentration of the measurement target gas component being the maximum concentration in the desired measurement range are measured, and the measured values of the zero gas and the span gas are measured as the first calibration point, Two calibration points are set, and a straight line connecting the two points is set as a reference calibration curve. The slope of the reference calibration curve is defined as a gas concentration conversion coefficient α. The gas concentration is calculated in this way. Further, in the case of the synchronous detection unit output as shown in FIG. 12A, it is determined that the oxygen gas concentration is not more than a predetermined value and there is no measurement target gas (ammonia gas). The calculation unit 203e functions as means for performing such processing.

  In this way, the peak position can be accurately detected by synchronizing the trigger signal compared to the case where only the maximum value, minimum value, or integral value of the gas absorption waveform is detected. Improved. In particular, since ammonia gas often has a low concentration, the measurement accuracy can be further improved by adopting the above configuration.

In addition, since the loss is low, the peak can be surely displayed, and the detection ability of low concentration ammonia gas is improved.
In particular, it is synchronized with the timing of the wavelength scanning drive signal that makes the drive current of the laser element zero, and the synchronization signal can be discriminated.

  In particular, when the gas concentration is low, the effects of noise caused by interference of laser light from optical window materials and lenses, etc., become stronger, and these noises are detected as peaks, making it difficult to find peaks. However, in the present invention, since the portion where gas absorption occurs is set in advance and the gas absorption peak is detected based on the trigger signal, accurate gas concentration detection can be performed without being affected by noise or the like. There is an advantage.

  Next, automatic correction of wavelength shift using such a laser gas analyzer will be described. Such correction is performed by the calculation unit 203e. First, as a premise, the calculation unit 203e flows a reference gas having a specific concentration in the walls 601a and 601b in advance, and registers the waveform obtained at that time. For example, the waveform is as shown by the signal Sb in FIG. 8B, and in particular, the maximum value C and the minimum values B and D, which are the peaks of the waveform, are stored in a memory unit (not shown) of the calculation unit 203e. In addition, the times tc, tb, and td at which the maximum value C and the minimum values B and D appear with the trigger signal S4 as a reference are also registered. At this time, the waveform is used as a reference gas having a concentration that provides a sufficiently large output waveform capable of detecting the wavelength shift, so that the wavelength position can be easily grasped. The reference gas is ammonia gas having a predetermined concentration. This reference may be acquired when the apparatus is started up or at the time of factory shipment.

  Then, at the time of a regular medical examination performed after a predetermined period (for example, 6 months), the calculation unit 203e compares the measurement target gas, which is the same gas as the reference gas, through the walls 601a and 601b. First, one maximum value and two minimum values, which are waveform peaks, are stored from waveform data acquired as digital data by sampling, and the time at which the maximum value and minimum value appear with reference to the trigger signal S4 is stored.

  Then, as shown in the rectangular frame in FIG. 4, the peak appearance time with reference to the trigger signal S4 is shortened compared to the reference gas having a specific concentration in advance, resulting in a shift to the left on the time axis. In this case, the amount of deviation is displayed on the display unit of the output unit, and the worker confirms the amount of deviation. Further, the calculation unit 203e changes the set temperature by controlling the temperature control unit 101d of the temperature control unit via the communication line 500. The calculation unit 203e changes the set temperature of the temperature control unit 101d so as to reduce the time deviation, detects the previous measurement target gas, performs the same comparison, repeats the same control, and finally performs the time deviation. The temperature control unit 101d controls the temperature control unit 101d to newly register the temperature at which 0 becomes 0 as the set temperature in the temperature control unit 101d.

  When the wavelength shift occurs in this way, automatic adjustment is performed so that the temperature of the laser element is controlled and the initial output waveform position is obtained. Further, correction is performed by the same method for the laser element for hydrogen chloride gas. Conventionally, it has been performed manually at regular checkups every predetermined period (for example, 6 months). However, the present invention is excellent in that maintainability is improved by enabling automatic adjustment. The detection of the wavelength shift is not limited to the measurement target gas. For example, even when detection is performed using a calibration gas having the same concentration and different concentration as the reference gas, the position where the peak appears shifts to the left. Since the occurrence can be detected, temperature control may be performed at such time.

  According to the present invention, a measurement target gas is sealed in a laser gas analyzer that measures a measurement target gas, such as hydrogen chloride gas or ammonia gas, that is present in a minute amount or not present in the atmosphere. Even if the reference gas cell is not built in, the measurement error correction due to wavelength deviation due to laser element degradation is corrected by measuring the wavelength deviation width from the absorption waveform of the gas to be measured above a certain value and detecting the wavelength deviation from the absorption waveform. Long-term stability by changing the set temperature of the thermo module that controls the temperature of the element, correcting the wavelength, and automatically correcting and solving the problem that affects the concentration value due to wavelength fluctuation due to laser degradation A laser gas analyzer having the characteristics can be provided. In particular, since the trigger signal is used as a reference, the wavelength shift can be detected more accurately. Further, long-time adjustment by a person is not necessary, and parts such as a reference cell are not necessary, so that cost can be greatly reduced. Also. By eliminating the wavelength shift, a laser gas analyzer can be obtained in which measurement errors hardly occur.

  Next, a third embodiment of the present invention will be described with reference to the drawings. Compared to the previous first embodiment, this embodiment has the same structure as the laser gas analyzer of FIG. 1 as an overall configuration, and the light emitting unit 100 has the same configuration as the laser light source unit of FIG. However, with respect to the light receiving unit 200, the signal processing unit 203 ″ of the light receiving unit 200 in FIG. 14 further includes an extraction unit 203f connected to the I / V conversion unit 203a and the calculation unit 203e. The difference is that the received light amount level extracted in 203f is input to the arithmetic unit 203e of the signal processing unit 203 and the received light amount level is obtained as a reference value, with the same components as in FIGS. Are denoted by the same reference numerals and the description thereof is omitted. In the following description, different parts will be mainly described.

  In FIG. 14, the output of the light receiving element 202 is a current signal, and this current signal is converted into a voltage signal by the I / V conversion unit 203a. This voltage signal is called a light reception signal, and an example of the waveform is shown in FIGS. 15A and 15B. FIG. 15A is a light reception signal waveform in a clean space where there is no dust in the measurement environment, and FIG. 15B is a light reception signal waveform in a space where dust exists. As is apparent from these drawings, the amount of received light (received light signal level) decreases because the laser beam is blocked when dust is present.

As described above, only the amplitude of the second harmonic signal, which is the second frequency component of the modulated signal of the emitted light, is extracted by the synchronous detection unit 203b. For example, when the received light signals shown in FIGS. 15A and 15B are synchronously detected, waveforms as shown in FIGS. 16A and 16B are obtained, respectively.
A in FIG. 16A is the same as the gas absorption waveform, it is possible to measure the gas concentration by detecting the amplitude w (= w _a) of this waveform.
On the other hand, in FIG. 16B when dust is present, the amplitude w (= w _b ) is also reduced corresponding to FIG. 15B.
Thus, since the amplitude of the gas absorption waveform varies depending on the amount of received light, it is difficult to accurately measure the gas concentration particularly in an environment where the amount of dust varies.

  Therefore, in the present embodiment, as shown in FIG. 17, the phase adjustment of the synchronous detection is performed so that the received light amount level and the amplitude level of the gas absorption waveform are in a substantially proportional relationship, and the received light amount level is obtained in the calculation unit 203e. By correcting the amplitude of the gas absorption waveform with reference to the wavelength scanning drive signal component, it is possible to accurately detect the gas concentration even in an environment where dust or the like is present.

  That is, as shown in FIG. 14, the received light signal output from the I / V conversion unit 203a is input to the extraction unit (filter) 203f to extract the wavelength scanning drive signal component. Then, the calculation unit 203e calculates the ratio between the wavelength scanning drive signal component and the received light amount setting value as the received light amount correction coefficient β, and corrects the amplitude of the gas absorption waveform output from the filter 203d by the correction coefficient β. I did it.

  For example, when the received light signal shown in FIGS. 15A and 15B is input to the extraction unit (filter) 203f to extract the wavelength scanning drive signal component, waveforms as shown in FIGS. 18A and 18B are obtained. FIG. 18A shows a case where there is no dust and the amount of received light is not reduced, and FIG. 18B is a case where there is dust and the amount of received light is reduced.

As shown in FIG. 18A, the level P (= P _max ) of the received light signal (the wavelength scanning drive signal output from the filter 203f) when there is no dust and the received light amount is maximum at a certain point in time is the received light amount setting value. Is previously set and registered in the calculation unit 203e. The calculation unit 203e detects the received light signal level P when there is dust as shown in FIG. 18B, and calculates the ratio between this P and P _max at the same time as the received light amount correction coefficient β by Equation 3.

[Equation 3]
β = P _max / P

By multiplying or dividing the correction coefficient β by the amplitude w of the gas absorption waveform (for example, w _{b in} FIG. 16B), the amplitude w _h in which the variation in the amount of received light caused by dust is corrected, as shown in Equation 4. Can be obtained.

[Equation 4]
w _h = w × β

Thus by measuring the gas concentration by using the amplitude w _h of the corrected gas absorption waveform, if reduction of the amount of received light at the amount of dust is large environment as flue significant also, to accurately measure the gas concentration be able to.

  According to such a laser type gas analyzer, an extraction unit (filter) that extracts the component of the wavelength scanning drive signal from the output signal of the light receiving unit is provided, and the output signal is output to the arithmetic unit. The calculation unit compares the output signal of the extraction unit (filter) with the received light amount setting value (for example, the output signal level of the extraction means when the received light amount is maximum when measured in a clean environment free from dust). The amplitude of the gas absorption waveform is corrected using the received light quantity correction coefficient.

  Next, automatic correction of wavelength shift using such a laser gas analyzer will be described. Such correction is performed by the calculation unit 203e. First, as a premise, the calculation unit 203e flows a reference gas having a specific concentration in the walls 601a and 601b in advance, and registers the waveform obtained at that time. For example, the waveform is as shown by the signal Sb in FIG. 8B, and in particular, the maximum value C and the minimum values B and D, which are the peaks of the waveform, are stored in a memory unit (not shown) of the calculation unit 203e. In addition, times tc, tb, and td at which the maximum value C and the minimum values B and D appear are registered with reference to the trigger signal S4 included in the component of the wavelength scanning drive signal extracted by the extraction unit 203f. At this time, the waveform is used as a reference gas having a concentration that provides a sufficiently large output waveform capable of detecting the wavelength shift, so that the wavelength position can be easily grasped. The reference gas is ammonia gas having a predetermined concentration. This reference may be acquired when the apparatus is started up or at the time of factory shipment.

  Then, at the time of a regular medical examination performed after a predetermined period (for example, 6 months), the calculation unit 203e compares the measurement target gas, which is the same gas as the reference gas, through the walls 601a and 601b. First, one maximum value and two minimum values, which are waveform peaks, are stored from waveform data acquired as digital data by sampling, and the time at which the maximum value and minimum value appear with reference to the trigger signal S4 is stored. The trigger signal S4 is included in the component of the wavelength scanning drive signal extracted by the extraction unit, and can detect the synchronization timing.

  Then, as shown in the rectangular frame in FIG. 4, the peak appearance time with reference to the trigger signal S4 is shortened compared to the reference gas having a specific concentration in advance, resulting in a shift to the left on the time axis. In this case, the amount of deviation is displayed on the display unit of the output unit, and the worker confirms the amount of deviation. Further, the calculation unit 203e changes the set temperature by controlling the temperature control unit 101d of the temperature control unit via the communication line 500. The calculation unit 203e changes the set temperature of the temperature control unit 101d so as to reduce the time deviation, detects the previous measurement target gas, performs the same comparison, repeats the same control, and finally performs the time deviation. The temperature control unit 101d controls the temperature control unit 101d to newly register the temperature at which 0 becomes 0 as the set temperature in the temperature control unit 101d.

When the wavelength shift occurs in this way, automatic adjustment is performed so that the temperature of the laser element is controlled and the initial output waveform position is obtained. Further, correction is performed by the same method for the laser element for hydrogen chloride gas. Conventionally, it has been performed manually at regular checkups every predetermined period (for example, 6 months). However, the present invention is excellent in that maintainability is improved by enabling automatic adjustment. The detection of the wavelength shift is not limited to the measurement target gas. For example, even when detection is performed using a calibration gas having the same gas as the reference gas but having a different concentration, the position where the peak appears shifts to the left. Therefore, the temperature control may be performed at such time.

  According to the present invention, a reference gas cell in which a measurement target gas is sealed in a laser gas analyzer that measures a measurement target gas, for example, ammonia gas, in which a trace amount exists in the atmosphere or does not exist in the atmosphere. Even in a structure without a built-in, the measurement error correction due to wavelength shift due to laser element degradation is measured by measuring the wavelength shift width from the absorption waveform of the gas to be measured above a certain value, detecting the wavelength shift from the absorption waveform, and adjusting the temperature of the laser element. A laser with long-term stability by changing the set temperature of the thermo module being controlled and correcting the wavelength, and automatically correcting and solving the problem that affects the concentration value due to wavelength fluctuations due to laser degradation. A gas analyzer can be provided. In particular, since the trigger signal is used as a reference, the wavelength shift can be reliably detected. Further, long-time adjustment by a person is not necessary, and parts such as a reference cell are not necessary, so that cost can be greatly reduced. Also. By eliminating the wavelength shift, a laser gas analyzer can be obtained in which measurement errors hardly occur.

The laser type gas analyzer of the present invention has been described above.
In conventional laser gas analyzers, even with laser elements controlled at the same current and temperature, wavelength shifts are inevitably generated due to deterioration of the elements, and in the case of gases that do not exist in the atmosphere, such as hydrogen chloride gas or ammonia gas, the reference cell Gas was sealed inside and wavelength shift correction was performed. However, according to the present invention, wavelength deviation is detected and automatic correction is performed without using a reference cell, so that long-term stability can be obtained. In addition, since a simple structure can be constructed and the number of parts can be reduced, the cost can be reduced.

  The laser 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, 1 ′, 1 ″: Laser gas analyzer 100: Light emitting unit 101, 101 ′: Laser light source unit 101a: Wavelength scanning drive signal generation unit 101b: High frequency modulation signal generation unit 101c: Current control unit 101d: Temperature control unit 101e: Laser element 101f: Thermistor 101g: Peltier element 101s: Laser drive signal generation unit 102: Collimator lens 103: Box cover 200: Light receiving unit 201: Condensing lens 202: Light receiving elements 203, 203 ′, 203 ″: Signal processing unit 202: Light receiving element 203: Signal processing unit 203a: I / V conversion unit 203b: Synchronous detection unit 203c: Oscillator 203d: Filter 203e: Calculation unit 203f: Extraction unit (filter)
204: Box cover 300: Light emission unit side purge unit 301: Purge unit main body 302: Inlet 303: Outlet 400: Light receiving unit side purge unit 401: Purge unit main body 402: Inlet 403: Outlet 500: Communication line 601a, 601b: walls 602a, 602b: companion flange 700: detection light

Claims (3)

A frequency modulation method for measuring the concentration of the measurement target gas, comprising: a light emitting unit that emits detection light by laser light; and a light receiving unit that receives detection light propagated through a space in which the measurement target gas exists. A laser gas analyzer,
The light emitting unit
A laser element that emits a laser beam having a wavelength at which the measurement target gas absorbs light, temperature control means for maintaining the laser element at a constant temperature by a thermo module, and a supply current to the laser element are changed to change the measurement target gas. Wavelength scanning drive signal generating means for generating a wavelength scanning drive signal for scanning light absorption characteristics, high frequency modulation signal generating means for generating a high frequency modulation signal, and modulating the wavelength scanning drive signal with the high frequency modulation signal, Current control means for generating a drive signal for the laser element,
The light receiving unit is
From the light receiving element sensitive to the laser wavelength that is the detection light in which the gas to be measured is absorbed, the reference signal generating means for generating the reference signal having the double frequency component of the high frequency modulation signal, and the output signal of the light receiving element Synchronous detection means for detecting the amplitude of the second harmonic signal, which is a double frequency component, and outputting a detection signal; calculation means for calculating the concentration of the gas to be measured based on the value of the detection signal from the synchronous detection means; Each with
This computing means is
It is determined whether or not there is a deviation between the gas absorption waveform of the detection signal and a reference waveform registered in advance, and if there is a deviation, the set temperature of the thermo module that controls the temperature of the laser element is changed to eliminate the deviation. To fix,
A laser gas analyzer characterized by that. A frequency modulation method for measuring the concentration of the measurement target gas, comprising: a light emitting unit that emits detection light by laser light; and a light receiving unit that receives detection light propagated through a space in which the measurement target gas exists. A laser gas analyzer,
The light emitting unit
A laser element that emits a laser beam having a wavelength at which the measurement target gas absorbs light, temperature control means for maintaining the laser element at a constant temperature by a thermo module, and a supply current to the laser element are changed to change the measurement target gas. Wavelength scanning drive signal generating means for generating a wavelength scanning drive signal and trigger signal for scanning light absorption characteristics, high frequency modulation signal generating means for generating a high frequency modulation signal, and modulating the wavelength scanning drive signal by the high frequency modulation signal And current control means for generating a drive signal for the laser element,
The light receiving unit is
From the light receiving element sensitive to the laser wavelength that is the detection light in which the gas to be measured is absorbed, the reference signal generating means for generating the reference signal having the double frequency component of the high frequency modulation signal, and the output signal of the light receiving element Synchronous detection means for detecting the amplitude of the second harmonic signal, which is a double frequency component, and outputting a detection signal, and detection signals from the synchronous detection means when a predetermined time has elapsed with reference to the trigger signal input from the light emitting unit. Calculating means for calculating the concentration of the gas to be measured based on the value,
This computing means is
The presence or absence of deviation between the gas absorption waveform of the detection signal and the reference waveform is determined with reference to the trigger signal, and when there is a deviation, the set temperature of the thermo module that controls the temperature of the laser element is changed to correct the deviation. To fix it,
A laser gas analyzer characterized by that. A frequency modulation method for measuring the concentration of the measurement target gas, comprising: a light emitting unit that emits detection light by laser light; and a light receiving unit that receives detection light propagated through a space in which the measurement target gas exists. A laser gas analyzer,
The light emitting unit
A laser element that emits a laser beam having a wavelength at which the measurement target gas absorbs light, temperature control means for maintaining the laser element at a constant temperature by a thermo module, and a supply current to the laser element are changed to change the measurement target gas. Wavelength scanning driving signal generating means for generating a wavelength scanning driving signal for scanning the light absorption characteristic so as to include a trigger signal, high frequency modulation signal generating means for generating a high frequency modulation signal, and the high frequency modulation of the wavelength scanning driving signal Current control means for modulating the signal to generate a drive signal for the laser element,
The light receiving unit is
From the light receiving element sensitive to the laser wavelength that is the detection light in which the gas to be measured is absorbed, the reference signal generating means for generating the reference signal having the double frequency component of the high frequency modulation signal, and the output signal of the light receiving element Synchronous detection means for detecting the amplitude of the second harmonic signal, which is a double frequency component, and outputting a detection signal, an extraction unit for extracting the trigger signal component from the output signal of the light receiving element, and the trigger signal as a reference A calculation means for calculating the concentration of the gas to be measured based on the value of the detection signal from the synchronous detection means when a predetermined time has elapsed,
This computing means is
The presence or absence of deviation between the gas absorption waveform of the detection signal and the reference waveform is determined with reference to the trigger signal, and when there is a deviation, the set temperature of the thermo module that controls the temperature of the laser element is changed to correct the deviation. To fix it,
A laser gas analyzer characterized by that.

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