JP3274656B2 - Gas spectroscopic analysis method and spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for analyzing a trace component to be measured contained in a gas to be measured by infrared spectroscopy using a semiconductor laser as a light source.

[0002]

2. Description of the Related Art Conventionally, infrared spectroscopy has been often used as a method for analyzing a gaseous sample. Infrared spectroscopy analyzes the light absorption spectrum by transmitting light in the infrared region to the gas to be measured, and analyzes the light absorption spectrum.The analysis is performed based on the wavelength of the absorbed light. The component to be measured can be identified, and the component to be measured can be quantified from the amount of light absorbed.

FIG. 9 is a schematic diagram showing an example of a conventional gas spectrometer. In the figure, reference numeral 1 denotes a tunable semiconductor laser 1 from which laser light is oscillated. After the laser beam is collimated by the condenser lens system 2, a part thereof is transmitted through the beam splitter 3 and introduced into the sample cell 4. After passing through the sample cell 4, the amount of the laser light is reduced by the first photodetector 5. The signal is measured and output. The remaining laser light is reflected by the beam splitter 3, and the second light detector 6 measures the amount of the light and outputs a signal. Signals output from the first and second photodetectors 5 and 6 are converted from current signals to voltage signals by a converter 7 having an I / V converter and a preamplifier and amplified, and then locked. The signal is processed by the in-amplifier 8, sent to the computer device 9, and subjected to data processing as required. The signal output from the signal detecting means (photodetectors 5 and 6) is easily affected by electrical noise if transmitted through a signal line with a small amount of signal. By providing the amplifiers (converters 7, 7) at positions close to each of 5, 6, the influence of electric noise can be reduced.

At both ends of the sample cell 4, windows 41, 41 arranged at Brewster's angle with respect to the laser beam are provided, and a gas to be measured is introduced into the sample cell 4 at a constant flow rate. It is configured to be evacuated by a vacuum pump (not shown). A length obtained by subtracting an optical path length in the sample cell 4 from an optical path (hereinafter, also referred to as a measurement line) from the semiconductor laser 1 to the first photodetector 5 via the beam splitter 3; The optical path from 1 to the second photodetector 6 via the beam splitter 3 (hereinafter also referred to as a cancel line) is configured to be equal in length. Therefore, by subtracting the signal output from the second photodetector 6 from the signal output from the first photodetector 5, the influence of light absorption occurring in a portion other than the sample cell 4 in the measurement line is canceled. Can be.

[0005] The semiconductor laser 1 is a distributed feedback semiconductor laser, and the oscillation wavelength is controlled by the drive current and the temperature. In the figure, reference numeral 10 denotes a temperature controller for controlling the temperature of the laser element, and 11 denotes a current driver for controlling the drive current of the semiconductor laser 1, which are controlled by the computer 9. An oscillator (frequency modulation means) 12 is provided in the lock-in amplifier 8, and a modulation signal (AC component) based on a frequency modulation method is introduced from the oscillator 12 to a current driver 11, and an injection current to the laser 1 is By superimposing this modulation signal (AC component) on the (DC component), the laser light oscillated from the laser 1 is directly frequency-modulated. By modulating the laser light in this manner, the oscillation wavelength from the laser 1 periodically changes with a constant width, and the signals output from the first and second photodetectors 5 and 6 are also changed. It becomes a modulated signal. Therefore, a reference signal is introduced from the oscillator 12 to the lock-in amplifier 8 to detect the amount of attenuation of the laser beam intensity proportional to the concentration of the component to be measured in the gas to be measured. Then, only the double frequency signal synchronized with the modulation signal is extracted from the output signals of the photodetectors 5 and 6. By performing the phase detection in this manner, a second derivative spectrum of the light absorption spectrum is obtained.

When the gas to be measured in the sample cell 4 is 10
By maintaining a reduced pressure of about 0 Torr, the width of the peak in the light absorption spectrum is 1/10 of that at atmospheric pressure.
And a sharp peak is obtained. Therefore, in the measurement line, the peak of the light absorption by the component inside the sample cell 4 is distinguished from the peak of the light absorption by the atmospheric pressure component existing in a portion other than the sample cell 4 so that the two can be easily distinguished. Can be.

FIG. 10 shows an example of a second derivative spectrum obtained when HCl gas is introduced into the sample cell 4 and a small amount of water contained in the gas is measured. In this figure, X is the second derivative spectrum based on the signal measured by the first photodetector 5, Y is the second derivative spectrum based on the signal measured by the second photodetector 6, and (X− Y) is the second derivative spectrum obtained by performing the XY operation (the same applies hereinafter). The horizontal axis indicates the oscillation wavelength (unit: nm), and the vertical axis indicates the light absorption intensity (arbitrary unit). X, Y, and (X−Y) are appropriately shifted from each other in the vertical axis direction to prevent overlap. Is shown. Since the spectrum (XY) is obtained by subtracting the spectrum Y representing the light absorption generated in the cancel line from the spectrum X representing the light absorption generated in the measurement line, the spectrum (XY) is other than the sample cell 4 in the measurement line. The effect of light absorption occurring in the portion, for example, light absorption due to moisture in the atmosphere is eliminated. Then, in the spectrum (XY) obtained in this manner, the absorption intensity of the peak ｛(2a) determined from the peak a and the valleys b and c on both sides thereof.
Since the value of -bc) / 2 is proportional to the water concentration in the gas to be measured, the water concentration can be measured using this. For example, when the automatic measurement is performed using the computer device 9, the values of the peak a and the valleys b and c on both sides of the peak a in the spectrum (XY) are read, and the absorption intensity of the peak is calculated. What is necessary is just to design a program so that the value of intensity | strength may be converted into a water concentration.

[0008]

In such a measuring method, the value of the peak a and the values of the valleys b and c in the spectrum (XY) are automatically read. As shown in −Y), it is desirable to obtain a good second-order differential spectrum having a steep peak a and having a small difference between the values of the valleys b and c on both sides thereof. However, there is a problem that such a good spectrum is not always obtained. FIG. 11 shows that HCl was purified to remove water.
FIG. 4 shows an example of a second derivative spectrum when a measurement is performed by introducing a gas into the sample cell 4 as a gas to be measured. In this case, since no moisture is contained in the gas to be measured, the spectrum X and the spectrum Y coincide with each other, and the spectrum (XY) is ideally a straight line parallel to the horizontal axis. However, the spectrum (X-
Y) does not have a water peak, but has undulations. This undulation is noise generated in the optical path after the laser light, such as the inner wall of the sample cell 4 and the window 41, has passed through the beam splitter 3, and is due to fringe noise not generated in the cancel line. In FIG. 11, a large peak seen in the spectrum X in the measurement line and the spectrum Y in the cancel line is light absorption due to moisture in the atmosphere, and has been canceled by the XY arithmetic processing. FIG. 12 shows the result of measuring HCl gas containing water at a concentration of 100 ppb with the same apparatus. In this figure, it can be seen that the valley of the spectrum (XY) is distorted, and the difference between the values of the valleys b and c is large. When the valley is distorted in this manner, the peak absorption intensity ｛(2a−b−c) /
The value of 2｝ cannot be obtained accurately, and the measurement accuracy deteriorates.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and transmits a frequency-modulated semiconductor laser beam through a gas to be measured and measures the second derivative spectrum of the light absorption intensity to thereby measure the frequency of the semiconductor laser in the gas to be measured. In the method for measuring the concentration of a measurement component, fringe noise that cannot be canceled by a method of subtracting a second derivative absorption spectrum Y obtained on a cancel line without a sample cell from a second derivative absorption spectrum X obtained on a measurement line having a sample cell It is an object of the present invention to improve the measurement accuracy by reducing the measurement accuracy.

[0010]

In order to solve the above-mentioned problems, a gas spectroscopic analysis method according to the present invention provides a method for analyzing a secondary spectrum of light absorption intensity obtained by transmitting a frequency-modulated semiconductor laser beam through a gas to be measured. In a gas spectral analysis method for measuring the concentration of a component to be measured in the gas to be measured by using a differential spectrum, a background is obtained by transmitting laser light to a purified gas to be measured in which the component to be measured is removed from the gas to be measured. give a spectrum, was measured using the corrected second derivative spectrum obtained from the second derivative spectrum by subtracting the background spectrum, the corrected second derivative spectrum
To obtain the toll, the background data stored in the storage
Using the sound spectrum, the buffer stored in the storage means is used.
The background spectrum is updated at regular intervals, and the background
Measure the time interval for updating the background spectrum
Of the same concentration as the lower detection limit in the analyzer used for
For the measured gas containing the measured component,
The measured value of the measured component concentration when
Set based on the comparison with the detection lower limit, the detection lower limit,
Measured gas with known concentration
Standard deviation of measured values when component concentration measurement is performed multiple times
It is characterized by setting based on . The spectral component of the present invention
In the analysis method, the time interval at which the background spectrum is updated, the measured component concentration was continuously measured for the measured gas containing the measured component having the same concentration as the lower limit of detection in the analyzer used for the measurement. Sometimes, it is preferable to set the time to be shorter than the time from when the measurement is started until the measured value of the concentration of the component to be measured reaches + 10% or -10% of the lower limit of detection.

According to the gas spectrometer of the present invention, a tunable semiconductor laser, frequency modulation means for performing frequency modulation on the semiconductor laser, and a laser beam oscillated from the semiconductor laser are transmitted through a gas to be measured. Means, means for measuring the intensity of laser light transmitted through the gas to be measured, means for obtaining a second derivative spectrum from the measurement result of the intensity of the laser light, and means for purifying the gas to be measured by removing the component to be measured from the gas to be measured. Means for transmitting laser light through the measurement gas, means for measuring the intensity of the laser light transmitted through the purified gas to be measured, means for obtaining a background spectrum from the measurement result of the laser light intensity, and the second derivative spectrum Means for obtaining a corrected second derivative spectrum by subtracting the background spectrum from Means for calculating the amount of concentration, the
Storage means for storing the background spectrum;
Means for transmitting a laser beam to the gas to be measured, and
Means for transmitting semiconductor laser light to the purified gas to be measured
Are integrated, and one sample cell and the sample
In the pull cell, the measured gas and the purified measured gas are
Introduction means for switchably introducing the sample cell;
Means for transmitting laser light,
For each time interval for updating the background spectrum,
As the purified gas to be measured is introduced into the sample cell,
Switch the introduction means to a new background
Measure the spectrum and obtain the new background
Storing the vector in the storage means;
After the ground spectrum is obtained the sample cell
Turn off the introduction means so that the gas to be measured is introduced into
Switching means, the control means comprising:
The time interval for updating the spectrum is used for measurement.
Component to be measured at the same concentration as the lower detection limit in the analyzer
Concentration of the component to be measured is continuously measured for the gas to be measured containing
The measured value of the concentration of the component to be measured when
And the lower limit of detection is set at a known concentration.
Concentration of the component to be measured for the gas to be measured containing the component to be measured
Based on the standard deviation of the measurements when taking multiple measurements
It is characterized in that it can be set . In the spectroscopic analyzer of the present invention, the introduction unit may be configured to measure
To obtain the purified gas to be measured by removing the measured components of the constant gas
And manufacturing apparatus, the sample cell cycle by bypassing the purifier the gas to be measured
Guide bypass line and gas to be measured or purified gas to be measured
Equipped with a flow controller that controls the flow rate of
If the controller is installed upstream of the bypass line
The configuration that has been used can be adopted.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 is a schematic configuration diagram showing an embodiment of the gas spectroscopic analyzer of the present invention. In this figure, the same components as those of the apparatus of FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted.
This apparatus is significantly different from the conventional apparatus of FIG. 9 in that the optical system is housed in one purge box 20;
The point is that the replacement gas line 30 is provided in the sample cell 4, and the storage unit and the control unit described later are built in the computer device 9.

The purge box 20 is air-tight, and includes at least a measurement line from the semiconductor laser 1 as a light source to the first photodetector 5 and a second light detection from the semiconductor laser 1. The optical system of the cancel line up to the detector 6 is accommodated, and in this embodiment, the conversion device 7 arranged near the photodetectors 5 and 6 is also accommodated.
The inside of the purge box 20 is filled with a purge gas such as an inert gas whose moisture concentration is reduced as much as possible, and is preferably adjusted to a purified nitrogen gas atmosphere. Although components other than those described above may be accommodated in the purge box 20, it is better to minimize the components accommodated in the purge box 20 and make the purge box 20 as small as possible, so that the purge gas consumption is reduced. This is preferable because it requires only a small amount of time and the time required for filling the purge gas is short.

As shown in FIG. 2, for example, the replacement gas line 30 includes an introduction line (introduction means) 31 for introducing a gas into the sample gas 4 and an exhaust line for exhausting the gas from the sample gas 4. It consists of a line 32.
The exhaust line 32 is provided with a pressure gauge 33 and a flow control valve 34, and is connected to a vacuum pump (not shown). In the introduction line 31, a three-way branch valve 35, a purifier 36, an on-off valve 37,
A flow controller 38 is provided and connected to a supply source (not shown) of the gas to be measured. Opening / closing valve 3
A bypass line 39 branched from between the valve 7 and the flow controller 38 is connected to the three-way branch valve 35. As the three-way branch valve 35 and the on-off valve 37, a pneumatic drive valve is preferably used.

An introduction line 31 is provided in the sample cell 4
It is configured such that a gas to be measured that has not been purified and a gas to be measured that has been purified (a purified gas to be measured) can be switchably introduced. That is, in order to introduce the purified gas to be measured into the sample cell 4, the on-off valve 37 is opened, and the bypass line 39 side of the three-way branch valve 35 is closed. In this state, while the flow rate of the gas to be measured is controlled by the flow rate controller 38, the gas to be measured is introduced into the purifier 36 via the on-off valve 37, where the component to be measured is removed. Then, the purified measured gas from which the measured component has been removed is introduced into the sample cell 4 via the three-way branch valve 35. On the other hand, to introduce the gas to be measured that is not purified into the sample cell 4, the on-off valve 37 is closed,
The bypass line 39 side of the three-way branch valve 35 is opened. In this state, the measured gas is introduced into the sample cell 4 through the bypass line 39 and the three-way branch valve 35 while the flow rate is controlled by the flow rate controller 38. Exhaust line 32
In, the gas pressure in the sample cell 4 is measured by the pressure gauge 33, and the exhaust amount is adjusted by the flow rate adjusting valve 34, so that the gas at a constant pressure flows through the sample cell 4 at a constant flow rate.

Next, an embodiment of a method for measuring the concentration of the component to be measured in the gas to be measured using this apparatus will be described. Here, a hydrogen chloride (HCl) gas containing a trace amount of water will be described as an example of the gas to be measured. First, HCl gas is introduced into the sample cell 4 via the purifier 36 for removing moisture, and the second derivative spectrum of the light absorption intensity of the purified HCl gas is measured. The measurement uses a method of subtracting the second derivative spectrum Y obtained on the cancel line from the second derivative spectrum X obtained on the measurement line, as in the related art. The second derivative spectrum obtained by XY in a state where the inside of the sample cell 4 is sufficiently replaced with the purified HCl gas and no moisture is detected is used as a background spectrum B, and the computer device 9
Is stored in a storage means such as a semiconductor memory built in the CPU. FIG. 3 shows a background spectrum B obtained in this example.

Next, the gas to be introduced into the sample cell 4 is switched from the purified HCl gas to the non-purified HCl gas, and the measurement of the water concentration is started. That is, the measurement is performed by switching the introduction line 31 of the replacement gas line 30 to a flow path passing through the bypass line 39. To calculate the moisture concentration,
A corrected second derivative spectrum (XY) obtained by subtracting the second derivative spectrum Y obtained by the cancel line from the second derivative spectrum X obtained by the measurement line, and further subtracting the background spectrum B stored in the storage means. -B) is used. The measured moisture concentration is
The information is displayed on a monitor of the computer device 9 or output as appropriate by printing out. The corrected second derivative spectrum (XYB) obtained in the present embodiment is also shown in FIG. This figure also shows the second derivative spectrum (XY) before the background spectrum B is subtracted. As can be seen from the measurement results in FIG. 3, the distortion of the valley can be reduced by performing the correction for subtracting the background spectrum B.

Since the background spectrum B is not always constant and changes with time even under the same measurement conditions, it is necessary to update the background spectrum B stored in the storage means at regular intervals. preferable. That is, in the present embodiment, the background spectrum B is a noise generated in the optical path after the laser light has passed through the beam splitter 3, and is a fringe noise that is not generated in the cancel line. The fringe noise changes over time due to expansion and contraction of the sample cell 4 and the purge box 20 due to a change over time in the ambient temperature, and fluctuations in the driving temperature of the semiconductor laser 1. Therefore, every time an appropriate time elapses, the introduction line 31 of the replacement gas line 30 is switched to introduce the purified gas to be measured into the sample cell 4, and the background spectrum is newly measured, and the storage means of the computer device 9 is stored. , The background spectrum is preferably rewritten and updated. In order to perform such an updating operation automatically, the computer 9 controls the switching of the open / close valve 37 and the three-way branch valve 35 of the replacement gas line 30 and the acquisition of a new background spectrum and the rewriting to the storage means. It is preferable to incorporate a control device such as a sequence controller that can be used. Then, at every preset time interval, the introduction line 31 is switched so that the purified gas to be measured is introduced into the sample cell 4, a new background spectrum is measured, and the obtained new background spectrum is stored. After the new background spectrum is obtained, the program is set so that the introduction line 31 is switched so that the gas to be measured is introduced into the sample cell 4 and the measurement of the gas to be measured is restarted. Good.

The rewriting and updating of the background spectrum stored in the storage means of the computer device 9 are as follows:
Each time measurement is performed, that is, the second derivative spectrum (X-
Y) is ideally performed each time it is measured, but it is time-consuming, time-consuming, uneconomical and cannot be analyzed quickly. It is preferable to set so that the update is performed every time. For example, when the measurement of the measured component concentration is continuously performed on the measured gas containing the measured component having the same concentration as the lower detection limit in the analyzer, after the measurement is started, the measured value of the measured component concentration is measured. It is preferable to measure in advance the time during which the variation is kept to some extent small, and to update the background spectrum within this time. As the upper limit of the variation of the measured values of the measured component concentration is set smaller, the reliability of the analysis result increases, but the continuity of the analysis is greatly impaired because the time interval of the update is reduced. Therefore, for example, the time until the measured value of the measured component concentration reaches the concentration at the time of preparation, that is, + 10% or -10% of the lower limit of detection, can be preferably set as the upper limit of the update time interval.

The time interval for updating the background spectrum can be preferably set specifically by the following procedure. First, the lower limit of detection in the analyzer is determined in advance. In the present specification, the lower limit of detection is the standard deviation value of the variation of the measured value when the measurement of the concentration of the measured component is performed a plurality of times continuously for the measured gas containing the measured component of the known concentration. This is a value obtained by multiplying by three. For example,
With respect to the gas to be measured (for example, HCl gas) containing 1 ppm of the component to be measured (for example, water), the measurement of the water concentration is continuously performed. The number of measurements can be arbitrary, but 18
About 0 to 200 times is preferable. This measurement is performed by a method using a second derivative spectrum (XY) obtained by subtracting a second derivative spectrum Y obtained on the cancel line from a second derivative spectrum X obtained on the measurement line. Then, it is assumed that the average of the measured values (voltage values) obtained by a plurality of measurements is, for example, 100 mV, the dispersion of the measured values is 5 mV, and the value three times the standard deviation of the dispersion is 10 mV. Average value of measured value 100mV, water concentration 1ppm
When a value three times the standard deviation of the variation is converted into a water concentration corresponding to the above equation, 10 mV = 100 ppb, and the lower limit of detection is 100 ppb.

After obtaining the detection lower limit in this way, a time interval for updating the background spectrum is set. First, purified HC from which moisture has been removed is placed in the sample cell 4.
Immediately after the introduction of 1 gas and the background spectrum B was measured, the sample cell 4 was immediately charged with HC containing water having the same concentration as the lower detection limit (100 ppb in the above example).
The water concentration is measured by replacing with 1 gas. The background spectrum B measured first is stored in the storage means, and the measurement of the moisture concentration is performed using the corrected second derivative spectrum (XYB) obtained by subtracting the background spectrum B in the storage means. . Then, from the start of the concentration measurement, the variation of the measured value of the water concentration gradually increases, and the measured value becomes the lower limit of detection (100 pp in the above example).
The time until the value of b) reaches + 10% or -10% is set as the upper limit of the update time interval. The lower limit of the update time interval may be longer than the sum of the time required to obtain the background spectrum and the time required to perform at least one measurement on the gas to be measured after obtaining the background spectrum. Although it is necessary, if the interval of the update time is too short, the continuity of the analysis is impaired, and the efficiency of the analysis is deteriorated.

FIG. 4 shows a case where the water content is 100 ppb (=
When measurement was performed for HCl gas at the lower detection limit),
It shows the relationship between the passage of time and the measured moisture concentration. In this graph, the vertical axis represents the measured value of the water concentration, and is displayed such that the water concentration of 1 ppm is 1. On the horizontal axis, the time when the measurement of the gas to be measured is started immediately after the measurement of the background spectrum B is set to 0. For the measurement, a method was used in which a background spectrum B measured first was stored in a storage means, and a corrected second derivative spectrum was obtained using the background spectrum B. If the noise detected in the background spectrum does not fluctuate with time, the water concentration of the gas to be measured is 100 ppb.
Therefore, the graph of FIG. 4 is ideally a straight line passing through the point (0, 0.1) and parallel to the horizontal axis. However, in this figure, the variation in the measured value increases with the passage of time, and after about 100 minutes, the measured moisture concentration becomes less than the detection lower limit of 0.1 (= 100 pp).
It reaches 0.9 (= 90 ppb) which is -10% of b). Therefore, the time interval for updating the background spectrum is preferably set to less than 100 minutes.

FIG. 5 shows the relationship between the passage of time and the measured moisture concentration when the background gas update time interval is set to 90 minutes and the HCl gas having a moisture concentration of 100 ppb is automatically measured. . In this figure, the portion where the graph is broken is the time period during which the background spectrum is updated. As shown in this figure, if the background spectrum is updated at regular time intervals, it is possible to prevent the variation in the analysis result from increasing with the elapse of time.
It is recognized that measurement can be performed for a long time with an accuracy of about pb.
In addition, such setting of the time interval for updating the background spectrum is preferably performed at the time of final calibration after assembling the analyzer, and it is not necessary to reset the setting even if the gas to be measured changes. When the calibration is performed again, for example, when it is added, it is necessary to set again.

FIG. 6 and FIG.
Ground spectrum fluctuations over time and their analysis
These are the results of examining the effect on the results.
You. That is, first, purified HCl gas is stored in the sample cell 4.
And the background spectrum B₁Measure
Subsequently, the inside of the sample cell 4 was adjusted to a water concentration of 100 ppb.
HCl gas and the second derivative spectrum (X₁-Y₁)
Of the previous background spectrum.
Background spectrum B again after 10 minutes from the measurement
_Two, And then the second derivative spectrum (X_Two−
Y_Two) Was repeated. the first
Background spectrum B obtained in ₁Is storage means
And was not rewritten. In FIG.
And B₁Is the background spectrum first obtained
Backgrounds obtained every 10 minutes thereafter.
The spectrum is measured in order from the earliest measurement time to B_Two, B_Three, B_Four, B_Five, B
₆As shown. Back as shown in this figure
The position and size of the peak in the ground spectrum
It is changing every moment.

FIG. 7 shows the second derivative scan obtained by the above operation.
The vectors are sorted in the order of measurement time ₁-Y₁), (X_Two−
Y_Two), (X_Three-Y_Three), (X_Four-Y_Four), (X_Five-Y_Five),
(X₆-Y₆) And each second derivative spectrum
The first background stored in the storage means
Spectrum B₁Second derivative obtained by subtracting
It shows the spectrum. You can see from the result of this figure
Thus, the first corrected second derivative spectrum (X₁-Y₁-B
₁In), the portion other than the peak due to moisture is flat.
Fringe noise has been effectively removed, and
The amount has also been reduced. This is the second derivative spectrum (X₁
-Y₁) And the balance used to correct this
Background spectrum (B₁) Measurement time interval
Is considered short. And the second derivative spectrum
Fringe noise increases as measurement time is delayed
And the strain on the valley is increasing. this
As shown in the graph, the background spectrum
Therefore, when measuring the moisture concentration in the HCL gas,
Backgrounds for obtaining positive second derivative spectra
The background spectrum obtained first as a vector
Kuturu B₁If you continue using for a long time, the second derivative spectrum
The background spectrum from the image
The effect of improving the measurement accuracy is reduced.

FIG. 8 shows the corrected second derivative spectrum (X ₆ -Y ₆ -B ₁ ) shown at the bottom of the graph of FIG. 7 and the second derivative spectrum before subtracting the background spectrum B _1. (X ₆ −Y ₆ ). In this example, by subtracting the background spectrum B _1, doubled fringe noise has increased strain Valley also rather, subtracting the background spectrum B ₁ is becomes counterproductive.

As described above, according to the above-described embodiment, for example, when measuring the water concentration in the HCl gas, the second derivative spectrum Y obtained on the measurement line is replaced with the second derivative spectrum Y obtained on the cancel line. And the corrected second derivative spectrum (XYB) obtained by further subtracting the background spectrum B cannot be removed even by using a cancel line. For example, the inner wall or the window 41 of the sample cell 4 Can be removed. Sample cell 4
The optical system for measurement is housed in the purge box 20, and the purge box 20 is filled with a purge gas having a reduced moisture concentration, so that noise due to moisture in the atmosphere is removed. That is, moisture exists in the atmosphere at a concentration level of several percent, and the moisture concentration fluctuates greatly. Therefore, it is difficult to sufficiently remove the moisture in the atmosphere and the fringe noise due to the light source only by using the cancel line. However, these noises can be effectively reduced by providing the purge box 20.

In this embodiment, the gas introduced into the sample cell 4 is switched to purified HCl gas to measure the background spectrum, and the obtained background spectrum is stored in the storage means. Since the configuration is such that the gas introduced into the cell 4 can be switched to an unpurified HCl gas to measure the moisture concentration, both the purified gas to be measured and the gas to be measured can be measured using one sample cell 4. Can be automatically measured. Therefore, it is not necessary to provide a new sample cell in order to measure the background spectrum, and it is not necessary to increase the size of the analyzer. The background spectrum stored in the storage means is used to correct the second derivative spectrum of the gas to be measured, and the background spectrum of the storage means is automatically updated at regular intervals to obtain a background spectrum. It is possible to prevent a decrease in measurement accuracy due to a temporal variation of the spectrum, and to maintain a high measurement accuracy even in a long-time automatic measurement.

In the above-described embodiment, an example in which an apparatus having a cancel line is used as shown in FIG. 1 has been described. However, in the present invention, a configuration without a cancel line can be adopted. For example, when the moisture concentration in the gas to be measured is measured using an apparatus having a cancel line as shown in FIG. 1, the spectrum X obtained from the measurement line includes light absorption x due to moisture in the gas to be measured and sample Since the noise a generated outside the cell 4 and the other fringe noise f are included, it can be expressed as X = x + a + f, and the spectrum Y obtained from the cancel line is Y
= A. Also, since the background spectrum B is obtained by XY when x = 0, B =
(A + f) -a = f. Therefore, when performing the analysis, by using XYB, (x + a + f)-
a−f = x, and a light absorption spectrum from which noise has been removed is obtained. On the other hand, when no cancel line is provided, the spectrum X obtained on the measurement line is X = x + a +
f, but the background spectrum B is x
B = a + f because the spectrum is obtained on the measurement line when = 0. When performing the analysis, X-B
As a result, (x + a + f)-(a + f) = x, and a light absorption spectrum due to moisture from which noise has been removed is also obtained. However, if there is a cancel line, the value of a measured on the cancel line is used at the same time as the measurement of the measurement line to remove noise a outside the sample cell 4. When there is no line, the value of the noise a when the background spectrum is acquired is used for a certain period of time. Therefore, when the noise a changes over time, higher analysis accuracy can be obtained by using the cancel line. . If a configuration without a cancel line is employed, the analysis accuracy may be slightly inferior, but the analyzer can be made more compact. In addition, it is a device without a cancel line,
When measuring the lower detection limit, the corrected second derivative spectrum (X-B) is obtained by subtracting the background spectrum B obtained using only the measurement line from the second derivative spectrum X obtained on the measurement line. Do it in the way you get.

In the present invention, it is also possible to adopt a configuration in which no storage means is provided. In this case, it is necessary to provide a new line for measuring the light absorption spectrum by transmitting laser light to the sample cell into which the purified gas to be measured is introduced, separately from the measurement line containing the gas to be measured. is there. In this case, the replacement gas line 30 in this embodiment becomes unnecessary. Also, since the background spectrum can be measured simultaneously with the measurement of the second derivative spectrum by the measurement line, there is no need to store the background spectrum, and a control means for automatically updating the background spectrum Is also unnecessary. However, since the sample cell is newly provided, the analyzer becomes large, and the sample cell in the measurement gas line and the sample cell used for the measurement of the background spectrum are separate. The fringe noise generated in each cell has some error, and the analysis result includes this error.

In the above embodiments, HCl gas was used as an example of the gas to be measured, and water was used as an example of the component to be measured. However, the present invention is applicable to any combination in which the gas to be measured and the component to be measured do not react with each other. Applicable to analysis of any gas. For example, it can be applied to measurement of moisture in ammonia gas, and is also effective when the absorption wavelength by ammonia and the absorption wavelength by moisture are extremely high. In addition, it is suitable for analyzing moisture in nitrogen gas, carbon monoxide gas, carbon dioxide gas, and hydrogen bromide gas.

[0032]

As described above, the gas analysis method of the present invention uses the second derivative spectrum of the light absorption intensity obtained by transmitting the frequency-modulated semiconductor laser light through the gas to be measured. In the gas spectral analysis method for measuring the concentration of the component to be measured in, a background spectrum is obtained by transmitting a laser beam to a purified gas to be measured in which the component to be measured has been removed from the gas to be measured, and from the second derivative spectrum Since the measurement is performed using the corrected second derivative spectrum obtained by subtracting the background spectrum, the fringe noise contained in the second derivative spectrum of the gas to be measured is effectively removed to achieve high accuracy. A measurement can be made. If the background spectrum is stored in the storage means and the method of obtaining the corrected second derivative spectrum using the background spectrum of the storage means is used, the second derivative of the gas to be measured can be obtained using one sample cell. Since both a spectrum and a background spectrum can be measured, it is preferable in reducing the size of the apparatus.

By updating the background spectrum stored in the storage means at regular time intervals,
It is possible to prevent a decrease in measurement accuracy due to a temporal change in the background spectrum, and to maintain a high measurement accuracy for a long time. The time interval at which the background spectrum is updated is determined when the measurement of the concentration of the component to be measured is continuously performed for the gas to be measured containing the component to be measured having the same concentration as the lower limit of detection in the analyzer used for the measurement. By setting the time shorter than the time from the start of the measurement until the measured value of the concentration of the component to be measured reaches + 10% or -10% of the lower limit of detection, the error of the measured value is always ± 10% or less. The measurement can be carried out.

The gas spectrometric analyzer of the present invention also includes a wavelength-variable semiconductor laser, frequency modulation means for performing frequency modulation on the semiconductor laser, and means for transmitting laser light oscillated from the semiconductor laser to the gas to be measured. And means for measuring the intensity of the laser light transmitted through the gas to be measured, and means for obtaining a second derivative spectrum from the measurement result of the intensity of the laser light, and measuring the concentration of the component to be measured contained in the gas to be measured A gas spectroscopic analyzer, wherein means for transmitting laser light to the purified gas to be measured after removing the component to be measured, and means for measuring the intensity of the laser light transmitted through the purified gas to be measured,
Means for obtaining a background spectrum from the measurement result of the laser light intensity, means for obtaining a corrected second derivative spectrum by subtracting the background spectrum from the second derivative spectrum of the gas to be measured, and measurement using the corrected second derivative spectrum It is provided with means for calculating the concentration of the component to be measured in the gas. According to this analyzer, the concentration of the component to be measured in the gas to be measured is measured using the corrected second derivative spectrum from which the fringe noise included in the second derivative spectrum has been removed, so that the accuracy of the measurement is improved. Highly reliable analysis results can be obtained.

If a storage means for storing the background spectrum is provided and the background spectrum stored in the storage means is used to obtain the corrected second derivative spectrum, it is not always necessary to measure the gas to be measured. Since it is not necessary to measure the purified gas to be measured at the same time,
It is possible to obtain both the second derivative spectrum and the background spectrum of the gas to be measured by using one sample cell, so that the apparatus can be made compact. Preferably, the means for transmitting laser light to the gas to be measured and the means for transmitting semiconductor laser light to the purified gas to be measured are integrated into one sample cell, and the gas to be measured and the gas to be purified are placed in the sample cell. By providing a switchable introduction means and a means for transmitting laser light to the sample cell, the measurement of the second derivative spectrum and the measurement of the background spectrum of the gas to be measured can be quickly switched and performed. In addition, it is possible to preferably achieve a compact device.

Further, at each time interval for updating the preset background spectrum, the introduction means is switched so that the purified gas to be measured is introduced into the sample cell, and a new background spectrum is measured. The new background spectrum is stored in the storage means, and after the new background spectrum is obtained, the control means for switching the introduction means so that the gas to be measured is introduced into the sample cell is provided. The measurement of the second derivative spectrum of the gas and the measurement of the background spectrum can be automatically switched, and a long-time automatic measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a gas spectrometer of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an example of a replacement gas line according to the present invention.

FIG. 3 is a graph showing a measurement example of a corrected second derivative spectrum according to the present invention.

FIG. 4 is a graph showing a measurement result when a water concentration measurement is continuously performed on an HCl gas containing water having the same concentration as the lower detection limit in the example according to the present invention.

FIG. 5 is a graph showing measurement results when the background spectrum is updated and the water concentration in the HCl gas is measured in the example according to the present invention.

FIG. 6 is a graph showing a background spectrum measured at regular intervals as a reference example.

FIG. 7 is a graph showing a corrected second derivative spectrum measured at regular intervals as a reference example.

FIG. 8 is a graph showing, as a reference example, an example in which a corrected second derivative spectrum is obtained using a background spectrum that has passed for a long time after measurement.

FIG. 9 is a schematic configuration diagram showing an example of a conventional gas spectroscopic analyzer.

FIG. 10 is a graph showing an example of a second derivative spectrum obtained by a conventional analysis method.

FIG. 11 is a graph showing an example of a second derivative spectrum obtained by measuring a purified HCl gas by a conventional analysis method.

FIG. 12 is a graph showing an example of a second derivative spectrum obtained by measuring HCl gas containing a trace amount of water by a conventional analysis method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 4 ... Sample cell, 9 ... Computer device, 12 ... Oscillator (frequency modulation means), 5 ... First photodetector, 6 ... Second photodetector, 30 ... Substitution gas line, 31 ... Introduction line (introduction means).

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-338805 (JP, A) JP-A-11-83535 (JP, A) JP-A-3-2647 (JP, A) JP-A-8-835 15150 (JP, A) Actually open 1982-186846 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/00-21/61 G01J 3/00-3/52 JICST File (JOIS)

Claims (4)

(57) [Claims] 1. A gas spectrometer for measuring the concentration of a component to be measured in a gas to be measured using a second derivative spectrum of light absorption intensity obtained by transmitting a frequency-modulated semiconductor laser beam through the gas to be measured. In the analysis method, a corrected secondary gas obtained by transmitting a laser beam to a purified gas to be measured obtained by removing a component to be measured from the gas to be measured to obtain a background spectrum, and subtracting the background spectrum from the second derivative spectrum. The measurement is performed using the derivative spectrum, and in obtaining the corrected second derivative spectrum,
Using the stored background spectrum, the background spectrum stored in the storage means is
Updated every predetermined time, the time interval for updating of the background spectrum
Is the same as the lower detection limit of the analyzer used for measurement.
The measured gas containing the component of the same concentration
Measurement of the concentration of the component to be measured when measuring the partial concentration continuously
Value based on a comparison with the lower limit of detection , and the lower limit of detection is determined based on the measured gas containing the component to be measured having a known concentration.
When the concentration of the component to be measured is measured multiple times
A gas spectroscopic analysis method, wherein the method is set based on a standard deviation of a constant value . 2. A method for continuously measuring the concentration of a component to be measured with respect to a gas to be measured containing a component to be measured having the same concentration as a lower limit of detection in an analyzer used for measurement, wherein the time interval at which the background spectrum is updated is measured. 2. The gas according to claim 1, wherein when the measurement is started, the time is set to be shorter than the time from when the measurement is started until the measured value of the concentration of the component to be measured reaches + 10% or -10% of the lower limit of detection. Spectroscopic analysis method. 3. The concentration of a component to be measured contained in a gas to be measured.
What is claimed is: 1. A gas spectrometer for measuring a degree, comprising: a wavelength-variable semiconductor laser; frequency modulation means for frequency-modulating the semiconductor laser; and transmitting laser light oscillated from the semiconductor laser to a gas to be measured. Means, and means for measuring the intensity of laser light transmitted through the gas to be measured,
A means for obtaining a second derivative spectrum from the measurement result of the laser light intensity; a means for transmitting a laser beam to a purified gas to be measured obtained by removing a component to be measured from the gas to be measured; and a laser having transmitted the gas to be purified. Means for measuring light intensity, means for obtaining a background spectrum from the measurement result of the laser light intensity, means for subtracting the background spectrum from the second derivative spectrum to obtain a corrected second derivative spectrum, and the correction means for calculating the concentration of the measured component in the measurement gas using the second derivative spectrum, said back
Storage means for storing background spectra.
For example, the purification means for transmitting the laser light to the measurement gas
Means for transmitting semiconductor laser light to the gas to be measured are integrated
One sample cell and the sample cell
Switch between the gas to be measured and the purified gas to be measured
Introducing means capable of introducing the laser light into the sample cell
Means for transmitting background light, and updates a preset background spectrum.
At each time interval, the purified gas to be measured is stored in the sample cell.
Switch the introduction means so that the
Background spectrum was measured and the new
Background spectrum in the storage means,
After the new background spectrum is obtained
Before the gas to be measured is introduced into the sample cell,
Control means for switching the introduction means, and the control means updates the background spectrum.
Time interval is determined by the detector used for the measurement.
Gas containing a component to be measured with the same concentration as the
To be measured when the concentration of the component to be measured is measured continuously
Set based on measurement of concentration and comparison with the lower limit of detection
The lower limit of detection is set to
When the concentration of the component to be measured is measured multiple times for gas
Can be set based on the standard deviation of the measurements
A gas spectrometric analyzer characterized by the fact that: 4. The measuring device according to claim 1, wherein
A purifier that obtains a purified gas to be measured by removing
Bypass line, which bypasses the purifier to the sample cell.
Control the flow rate of the gas to be measured or purified gas to be measured.
Equipped with a flow controller, This flow controller is located upstream of the bypass line.
4. The gas according to claim 3, wherein the gas is provided in
Spectrometer.