JPH10148613A - Gas concentration measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clearly distinguish absorption by a container itself from that by an internal gas, and to measure concentration accurately and continuously, by applying laser beams, of which oscillation wavelength is modulated, to a gas to be measured in a sealed type container and receiving laser beams that are transmitted. SOLUTION: A laser control part 2 controls a semiconductor laser diode(LD) 1 based on the modulation signal of a waveform generation part 3. Semiconductor laser beams 9 which have been modulated, are applied to a transparent container where a measurement target (a gas to be measured) 8 sealed and is transmitted through a gas in the container and a laser beams with a wavelength specific to the gas are absorbed, are converted to electrical signal by a photodiode(PD) 4, and are outputted to a lock-in amplifier 6 for phase-sensitive detection. The lock-in amplifier 6 detects an absorption constituent due to a gas from the output signal of the PD4. A signal obtained from the lock-in amplifier 6 becomes an n-order differential quantity regarding the wavelength of an original absorption spectrum, is transmitted to a data processing part, and is recorded and displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas concentration measuring device for detecting a gas concentration in a closed container.

[0002]

2. Description of the Related Art Conventionally, when detecting the gas concentration in a sealed transparent container represented by a glass ampule, a representative ampule is extracted from a large number of ampules, the ampule is destroyed, and the internal gas is taken out. It was measured by various densitometers such as gas chromatograph and mass spectrometer.

Further, when the gas concentration in the container in which the gas to be measured is enclosed is high and the container does not affect the measurement,
Non-destructive measurement such as FT-IR using absorption of infrared light has also been performed.

[0004]

In the above-mentioned conventional gas concentration measuring apparatus, in the measurement using various concentration meters such as a gas chromatograph and a mass spectrometer, a small number of samples are taken out of the whole, the samples are destroyed, and the internal Since the gas concentration is determined, there is a drawback that a continuous inspection of the gas concentration for all products is impossible.

[0005] In addition, in the measurement utilizing absorption of infrared light or the like, continuous measurement can be performed for all samples, but on the other hand, it is not suitable for measurement of a substance having a small light absorption amount or a trace amount of a substance. Absent. In such a case, measurement may not be possible due to absorption, scattering, dirt, etc. of the container itself in which the gas to be measured is sealed. In addition, when measuring gas in different containers, or when the laser beam is transmitted through different positions in the same container, the fringe changes will cause an error in the detection of the peak value of the gas concentration, which will greatly affect the measurement. give.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to measure a gas to be measured sealed in a container without destroying the container. It is an object of the present invention to provide a gas concentration measuring device which can clearly distinguish the absorption by itself and the absorption by an internal gas, and enables continuous measurement with high accuracy.

[0007]

According to the present invention, there is provided a gas concentration measuring apparatus comprising: a semiconductor laser light source for irradiating a sealed container enclosing a gas to be measured with laser light; A laser controller for emitting laser light, a waveform generator for generating a modulation signal for modulating the oscillation wavelength of the laser light emitted from the semiconductor laser light source, and the sealing by irradiation of the laser light. A light receiving unit for receiving a laser beam transmitted through the gas to be measured in the mold container; and n (n) of a frequency component of an output signal of the waveform generating unit.
≧ 2, n is an integer) a frequency multiplier for generating a signal having a multiple period, and a phase-sensitive detector for generating a detection signal based on an output signal of the frequency multiplier and an output signal of the light receiver. It is characterized by having done.

According to the gas concentration measuring device of the present invention, the following operations and effects are obtained. A semiconductor laser light source is used as the light source, and the wavelength of the laser light oscillated from the light source is modulated, only the component synchronized with the modulation signal is extracted from the received light signal, and the frequency-multiplied modulation signal is used at the time of synchronous detection. By obtaining a high-order differential absorption signal as its detection output, the detection sensitivity is improved, the influence on the measurement due to absorption / scattering or contamination of the container itself is eliminated, and the influence of the curvature of the container surface (optical standing) Waves, fringes) can be removed. The principle is as follows.

(1) Improvement of detection sensitivity The gas concentration measuring device of the present invention uses phase sensitive detection. That is, the laser oscillation wavelength is modulated by modulating the injection current to the semiconductor laser light source, and only the component synchronized with the modulation signal is extracted from the received light signal. Generally, noise coming from the outside is not synchronized with the modulation signal, and thus can be removed during analysis of the received light signal, and the phase-sensitive detection signal is a signal affected only by gas absorption. Therefore, high-sensitivity density detection becomes possible.

(2) Elimination of the influence on the measurement due to absorption, scattering, dirt, etc. of the container itself enclosing the gas to be measured. As shown in FIG. The horizontal axis indicates the wavelength, and the vertical axis indicates the transmittance. In FIG. 3, a plurality of straight lines extending in the vertical direction are gas absorption lines. In the present invention,
Since only one absorption line is to be measured, the wavelength scanning / modulation range is very narrow.

On the other hand, the influence of absorption / scattering, contamination, and the like of the container is much wider than the wavelength range to be measured, and therefore, the wavelength range of the gas absorption line to be measured is wavelength-dependent. Can be considered as having no dependencies.

For this reason, when one absorption line in FIG. 3 is enlarged, it becomes as shown in FIG. From FIG. 4, the absorption by gas can be calculated by the following equation, and the gas concentration can be detected from the amount of absorption.

Phase-sensitive detection signal = (absorption peak) − (absorption / scattering by container) = absorption by gas On the other hand, the output of the phase-sensitive detection is a value at both ends of the modulation width, that is, a gas absorption peak and a base in FIG. Is equivalent to the difference Therefore, as long as the gas concentration does not change, the difference between the gas absorption peak and the base does not change, and is not affected by the absorption of the container itself which has no wavelength dependency. Further, since a semiconductor laser light source is used as the light source, accurate wavelength control can be performed.

Accordingly, the gas concentration can be accurately detected without being affected by the absorption of the container itself. (3) Removal of the influence of the curvature of the container surface (optical standing wave, fringe) FIG. 5 shows an example of measurement of an absorption spectrum obtained by the present invention in 2f detection and 4f detection. The horizontal axis indicates the wavelength, and the vertical axis indicates the measured value.

FIG. 5A is a diagram showing an absorption spectrum in 2f detection. Only gas is present in the optical path of the semiconductor laser, that is, the object to be measured is directly measured without being sealed with a container or the like. Is the case. In this case, it is possible to obtain a linear base line (0 value line) and a differential absorption spectrum, and it can be confirmed that the gas concentration can be easily detected from the peak value at the absorption center wavelength of the spectrum.

Also, when a measurement target whose gas to be measured is sealed in a transparent container such as glass is measured by 2f detection in the same manner as in FIG. 5 (a), a linear baseline is obtained as in FIG. 5 (a). And the differential absorption spectrum can be obtained,
The gas concentration could be detected.

On the other hand, under the same conditions, ie, 2f detection,
When the gas to be measured is sealed in a transparent container,
In some cases, the zero-value line cannot be observed with high accuracy, and an example of absorption spectrum measurement in that case is shown in FIG. FIG.
In the case of (b), the linear base line as shown in FIG. 5A does not appear due to the multiple reflection of light inside the glass and the influence of the container curvature, and the differential line is differentiated on the wavy base line, that is, on the fringe. A spectrum in which the absorption spectra overlap. For example, when measuring different containers, or when the same container has a different laser transmitting position, FIG.
As shown in (c), the baseline fluctuates, and the 0 value level changes. This change in the zero value level makes it difficult to detect the peak value at the absorption center wavelength with high accuracy, and causes an error in detecting the gas concentration.

Therefore, similarly to FIGS. 5B and 5C,
FIG. 5D shows a measurement example in which the order of detection is increased (in this case, 4f detection) when the measurement target is enclosed in a transparent container such as glass. As shown in FIG. 5D, the order of differentiation is increased by increasing the order of detection, so that the effect of fringe seen in the cases of FIGS. 5B and 5C can be suppressed. Therefore, even when measuring a different container or changing the laser transmission position, the zero-value line can be easily observed, and the peak value at the absorption center wavelength can be measured with high accuracy.

As described above, the semiconductor laser light source is used as the light source, the oscillation laser light is modulated, and the synchronous detection is performed by the frequency-multiplied modulation signal when the laser light is received. And the n-th order differential quantity with respect to the wavelength of the absorption spectrum. For this reason, even when the containers are different or the same container has different laser transmitting positions, the influence of the fringe can be suppressed, and accurate gas concentration measurement can be performed.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a gas concentration measuring device according to one embodiment of the present invention. FIG.
As shown in the figure, the gas concentration measuring device
, A semiconductor laser diode 1 (hereinafter referred to as LD1) that emits light toward the measurement target 8, a laser control unit 2 that controls the LD1 and emits laser light of a desired wavelength, and modulation of a desired wavelength. A waveform generator 3 for generating a signal, a frequency multiplier 5 for frequency-multiplying the modulated signal, a lock-in amplifier 6 for phase-sensitive detection, and a light-receiving unit 4 for receiving laser light transmitted through the measurement target 8 (photodiode and photodiode And a data processing unit 7 for recording and displaying measured values.

The operation of the above embodiment will be described below. The waveform generator 3 generates a modulation signal for modulating the oscillation wavelength of the semiconductor laser light 9 oscillated from the LD 1 and outputs the modulation signal to the laser controller 2. The laser controller 2 controls the LD 1 based on the modulation signal of the waveform generator 3.
The LD 1 emits the modulated semiconductor laser light 9 toward the measurement target 8, that is, the transparent container in which the gas to be measured is sealed, under the control of the laser control unit 2. This semiconductor laser light 9 permeates the gas in the transparent container,
The light is received by PD4. Here, when the light passes through the measurement target 8, laser light having a wavelength specific to the gas in the transparent container is absorbed. The PD 4 converts the received laser light into an electric signal, amplifies the electric signal, and outputs the electric signal to the lock-in amplifier 6 for phase sensitive detection.

On the other hand, the frequency multiplier 5 converts the modulated signal generated by the waveform generator 3 into n (n ≧ 2,
(n is an integer) and outputs the signal multiplied by n to the lock-in amplifier 6 for phase sensitive detection.

The lock-in amplifier 6 for phase sensitive detection is
The component absorbed by the gas is detected from the output signal of D4. At the time of such detection, a component synchronized with the output signal of the frequency multiplier 5 is extracted. The signal obtained by the lock-in amplifier 6 becomes an n-th order differential quantity relating to the wavelength of the original absorption spectrum, and is sent to the data processing unit 7 to be recorded and displayed.

As a verification of the effectiveness of the present invention, an experiment was conducted using the gas concentration measuring device shown in FIG. In the experiment, four types of glass ampules were used as the measurement target 8, and the internal oxygen concentrations of the glass ampules were 0, 2, 10, 21.
[%]. Further, in order to confirm the effect of the high-magnification f detection, the frequency multiplier 5 doubles the modulation signal of the waveform generator 3 by two times.
The frequency was multiplied by 4 times (2f detection, 4f detection), and an experiment was performed under the following experimental conditions.

[0025]

[Table 1]

In the experimental results under the above experimental conditions,
First, in the experiment with 2f detection, when the measurement was performed without changing the container mounting position, that is, the laser beam transmission position, the reproducibility of the measurement was good, but when the container mounting position was different for each measurement, , The reproducibility of the measurement was very poor. This is because the measurement value indicating the concentration 0 in the container fluctuated due to the fact that the state of the light incident surface curvature (surface of the container) was different for each measurement.

However, in the experiment of 4f detection, the reproducibility of the measurement is good, and the high-magnification f detection shows that the influence of a change in the state of the container, which differs every measurement, can be eliminated.
FIG. 2 shows the experimental result of the 4f detection.

FIG. 2 shows the oxygen concentrations 0, 2, and 1 in the 4f detection.
It is a figure which shows the measurement result in 0,21 [%]. The vertical axis indicates the measured value, and the horizontal axis indicates the oxygen concentration in the ampoule.
The solid line in the figure is a calibration curve created from the measurement results of the oxygen concentration of 0.21 [%] since the measured value and the oxygen concentration theoretically have a quadratic function in the case of 4f detection. It is. As is clear from FIG. 2, the measurement results of the oxygen concentration of 2,10 [%] almost coincide with the calibration curve, and it is clear that the oxygen concentration in the unknown ampoule can be measured using this measurement device and the calibration curve. It is.

As described above, accurate wavelength control can be achieved by using a semiconductor laser light source as a light source. In addition, the wavelength of the laser light oscillated from this semiconductor laser light source is modulated, only the component synchronized with the modulation signal is extracted from the received light signal, and the frequency-multiplied modulation signal is used at the time of synchronous detection. By obtaining a high-order differential absorption signal, the detection sensitivity is improved,
It is possible to remove the influence on the measurement due to scattering, dirt, and the like, and to remove the influence on the measurement of the curvature of the container surface or the like.

In this embodiment, the case where the measuring object 8 is a sealed transparent container is shown. However, the present invention can be applied to a sealed container whose part is transparent. Of course. Also, the case where the frequency multiplier 5 multiplies the modulation signal of the waveform generator 3 by 2 times and 4 times has been described, but the present invention is applicable even when the modulation signal is multiplied to a higher magnification. Of course, it is.

[0031]

As described above, according to the present invention, the oscillation laser light is modulated, and upon receiving the laser light, synchronous detection is performed by the frequency-multiplied modulation signal, and the higher-order differential is output as the output. By obtaining the absorption signal, the absorption of the container itself and the absorption by the internal gas can be clearly distinguished without destroying the sealed container that encloses the gas to be measured, and the gas concentration is continuously measured with high accuracy. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an entire configuration of a gas concentration measurement device according to an embodiment of the present invention.

FIG. 2 is a view showing an experimental result by the gas concentration measuring device in the embodiment.

FIG. 3 is a view for explaining a measurement principle of the gas concentration measurement device in the embodiment.

4 is an enlarged view of one of the absorption lines in the absorption spectrum in FIG.

FIG. 5 is a diagram showing a measurement example of an absorption spectrum by the gas concentration measurement device according to one embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor laser diode (LD) 2 laser controller 3 waveform generator 4 light receiver (PD) 5 frequency multiplier 6 lock-in amplifier for phase sensitive detection 7 data processor 8 measurement target 9 semiconductor laser light

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masayuki Tabata 1-8-1 Koura, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture, Mitsubishi Heavy Industries, Ltd.

Claims (1)

[Claims] A semiconductor laser light source for irradiating a laser beam to a sealed container in which a gas to be measured is sealed; a laser control unit for controlling the semiconductor laser light source to emit laser light of a desired wavelength; A waveform generator that generates a modulation signal for modulating the oscillation wavelength of the laser light emitted from the semiconductor laser light source; and a laser light that has passed through the gas to be measured in the sealed container by irradiating the laser light. A light receiving unit for receiving light, and n (n ≧ 2, n) of a frequency component of an output signal of the waveform generating unit.
(n is an integer) a frequency multiplier for generating a signal having a multiple period, and a phase-sensitive detector for generating a detection signal based on the output signal of the frequency multiplier and the output signal of the light receiver. Characteristic gas concentration measurement device.