JP2010249726A - Gas analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas analyzer using a spectral absorption analysis method for checking an aging variation or the like of the device without using standard gas by a simple operation. <P>SOLUTION: A spectral absorption analyzer having a gas cell 1 includes a filter inserting/removing mechanism 5 that sequentially inserts one and a plurality of optical filters having the same absorbance into an optical path A of measuring light while changing the number of filters, and removes them from the insertion position. By this, the plurality of optical filters of different absorbance doubly, triply or more instead of standard gas is sequentially inserted into the optical path, and the checking of the performance the device can be easily performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gas analyzer that measures trace components in a gas by spectrophotometric analysis.

Hereinafter, a spectrophotometric analyzer using laser light will be described as an example.
For example, as described in Patent Document 1 as a prior art, a laser spectroscopic absorption spectrometer includes a wavelength tunable semiconductor laser device serving as a light source, a gas cell for passing laser light emitted from the laser light into a sample gas, and a gas cell. It consists of a photodetector that measures the light intensity of the laser beam that has passed through it, and has high sensitivity and accuracy, and therefore has applications such as measurement of trace moisture in semiconductor material gases. Since the wavelength of the laser beam can be controlled by the driving current or operating temperature of the semiconductor laser device, there is an advantage that an optical system such as a spectroscope is not required for the light source.

  FIG. 5 shows an example of a conventional configuration of a laser spectrophotometric analyzer for measuring trace moisture in a sample gas. As shown in the figure, the configuration of this apparatus is roughly divided into a gas cell 1 and an optical system chamber 2, and a laser light source 3 and a photodetector 4 are housed in the optical system chamber 2. The gas cell 1 is a sealed cylindrical metal container except for the gas inlet 13 and the gas outlet 14, and two spherical mirrors 11 and 12 facing each other are held on the inner surfaces of both ends.

  The gas cell 1 and the optical system chamber 2 are partitioned by light transmitting windows 15 and 16 made of a light transmissive material (quartz, sapphire, etc.), and the laser light emitted from the laser light source 3 is shown in the figure. As shown by an alternate long and short dash line, the optical path A is introduced into the gas cell 1 through one light transmission window 15, passes through the sample gas while being subjected to multiple reflections between the two spherical mirrors 11 and 12, and then the other light. The light reaches the photodetector 4 through the transmission window 16.

In the above configuration, a wavelength tunable laser device capable of wavelength scanning in a required wavelength range is used as the laser light source 3, and the output light is passed through the gas cell 1 filled with the sample gas, and then is detected by the photodetector 4 including a photodiode or the like. By receiving light, for example, a spectrum shown in FIG. 6 is obtained.
FIG. 6 shows a measurement example of trace moisture, and an absorption peak at a wavelength peculiar to moisture (1.3686 μm) is observed. In the figure, the vertical axis represents the received light intensity, the horizontal axis represents the wavelength, and the wavelength scale represents the difference from the peak center wavelength in wave numbers (cm-1).

JP 2001-21493 A

  In general, in a gas analyzer, calibration is periodically performed using a standard gas with a known concentration in order to check the time-dependent change of the apparatus and maintain accuracy. Since the output of the analyzer is not always proportional to the concentration, it is common to check linearity using two or more standard gases having different concentrations. However, for example, when measuring a trace amount of moisture at the ppm level, it is difficult to prepare several kinds of standard gases with stable concentrations.

  In the spectrophotometric analysis in the UV-visible region, mainly for liquid analysis, an optical filter with an accurate absorbance value is used for calibration instead of a standard sample, but in the infrared region for gas. This type of optical filter is generally difficult to obtain in absorbance analysis.

  The present invention has been made in view of the above circumstances, and it is intended to provide a gas analyzer using a spectrophotometric method capable of checking a change with time of the apparatus with a simple operation without using a standard gas. Objective.

In order to solve the above-mentioned problems, the present invention provides a spectrophotometric apparatus equipped with a gas cell, wherein one or a plurality of optical filters having the same absorbance are sequentially changed in the optical path of measurement light. A filter insertion / removal mechanism is provided for insertion and removal from the insertion position.
With this configuration, it is possible to easily check the performance of the apparatus by sequentially inserting a plurality of optical filters having different absorbances of 2 times, 3 times, etc. in the optical path instead of the standard gas.

  Since the present invention is configured as described above, it is possible to easily check the change over time of the apparatus without using a standard gas, so that the reliability of measurement can be maintained.

It is a figure which shows one Example of this invention. It is a figure which shows a part of one Example of this invention. It is a figure which shows the modification of this invention. It is operation | movement explanatory drawing of this invention apparatus. It is a figure which shows the example of a conventional structure. It is a figure which shows the example of an actual measurement by a spectral absorption analysis.

  The best mode of the present invention is a laser spectroscopic absorption comprising a filter insertion / removal mechanism that sequentially inserts / removes one or a plurality of optical filters having the same absorbance in the optical path of measurement light. It is an analysis device.

  FIG. 1 shows an embodiment of the present invention. In the figure, the same components as those in FIG. The present embodiment is different from the conventional example shown in FIG. 5 in that a filter insertion / removal mechanism 5 is provided, and a rotating disk 51 that is a part thereof crosses the optical path A. FIG. 2 shows the configuration of the filter insertion / removal mechanism 5 in more detail. FIG. 2 (a) is a front view and FIG. 2 (b) is a plan view.

  As shown in FIG. 2, a single filter window 52 out of four windows opened at 90 ° intervals on a rotating disc 51 rotated around a shaft B (in this example, the rotating shaft of the motor 55) by a motor 55. Is attached with a plurality of (two in this example) quartz plates 6 on the plurality of filter windows 53 located diagonally thereto, and the remaining two windows ( The blank window 54) is transparent. The quartz plate 6 functions as an optical filter, and has a size of, for example, a diameter of about 10 mm and a thickness of about 1 mm, all having the same optical characteristics, but the absorbance value need not be known.

  As shown in FIG. 1, the filter insertion / removal mechanism 5 is disposed at a position where the rotating disk 51 crosses the optical path A at a right angle and the measurement light passes through one of the windows. With this configuration, each time the motor 55 rotates 90 °, the blank window 54, the single filter window 52, the blank window 54, and the plurality of filter windows 53 are inserted into the optical path A in this order.

  When performing normal measurement with the apparatus of FIG. 1, the filter insertion / removal mechanism 5 is stopped at a position where one of the blank windows 54 crosses the optical path A. In this state, the measurement light reaches the photodetector 4 without being affected by the optical filter, unlike the conventional configuration shown in FIG.

When performing a performance check, first, the wavelength of the laser beam is fixed to a wavelength that is not absorbed by the moisture to be measured. That is, in the actual measurement example of FIG. 6, a wavelength as close as possible to the water absorption peak wavelength is selected within the wavelength region R1 or R2 deviated from the water absorption peak. The wavelength can be set by changing the driving current of the laser beam or the operating temperature.
Next, the filter insertion / removal mechanism 5 is operated to insert the blank window 54, the single filter window 52, the blank window 54, and the plurality of filter windows 53 in this order into the optical path A, and measure the light intensity received by the photodetector 4. .

FIG. 4 is a diagram schematically showing the result. As shown in the figure, assuming that the light intensity I ₀ of the transmitted light through the blank window 54, the light intensity I ₁ of the transmitted light through the single filter window 52, and the light intensity I ₂ of the transmitted light through the multiple filter windows 53, the single filter window 52. The absorbance D _{1 at} the wavelength and the absorbance D _{2 at the} wavelength of the plurality of filter windows 53 are calculated by the following equations.
D ₁ = Log (I ₀ / I ₁ ) (1)
D ₂ = Log (I ₀ / I ₂ ) (2)
Since the absorbance of the optical filter can be regarded as constant, the performance check result, if the temporal change is observed in the measured values of D ₁ or D ₂ are to be considered to be due to aging of the apparatus.
Further, according to the known Lambert-Beer law, the absorbance of the optical filter on which the quartz plates 6 are stacked is proportional to the thickness, that is, the number of sheets, so the following relationship must be established between D ₁ and D _2. .
_{D 1 = D 2 / N ······················} (3)
N is the number of quartz plates 6 of the plurality of filter windows 53 (N = 2 in this embodiment).
When the equations (1) to (3) are combined, the following equation is derived.
Log (I ₀ / I ₁ ) = (1 / N) × Log (I ₀ / I ₂ ) (4)

  The performance check in the present invention is performed based on the equation (4). That is, the linearity of the output value is checked by verifying that the expression (4) holds, and the measurement accuracy is confirmed by the value of the left side (or right side) of the expression (4) being a constant value. . As a result, when it is determined that the device is abnormal, for example, mathematical correction such as correction of the correction coefficient value is performed in the course of data processing, and in some cases, hardware adjustment is performed to make the device in a normal state. And the reliability of measurement can be maintained.

The filter insertion / removal mechanism 5 is not limited to that shown in FIG.
FIG. 3 is a diagram illustrating some modified examples of the filter insertion / removal mechanism 5.
FIG. 6A is a simplified diagram in which the blank window 54 is omitted from the rotating disk 51 in FIG. 2A because it is not necessary to pass through the measurement light to pass through the window. . A single filter window 52 and a plurality of filter windows 53 similar to those shown in FIG. 2 are provided on a rectangular rotating plate 56, and are rotated around an axis B as in FIG. There is no change.

  FIG. 3B is a modification in which the rotary motion in FIG. 2 is changed to a linear reciprocating motion. A slide plate 57 having a single filter window 52, a blank window 54, and a plurality of filter windows 53 is moved left and right by a slide drive unit 59. In this structure, one of the windows is inserted / removed into / from the optical path A.

  FIG. 3C shows a plurality of (three in the figure) oscillating plates 58 having only a single filter window 52 oscillated around an axis B within a certain angle range. The window is inserted into the optical path A at the lower end position, and the swing plate 58 is configured not to block the optical path A at the upper end position. With this configuration, by individually controlling each swing plate 58, a required number of optical filters can be inserted into and removed from the optical path A. As a drive source for the swing motion, for example, a solenoid (not shown) or the like may be installed on each swing plate 58.

  2 and 3 are not limited to one, and a plurality of filter windows 53 having different numbers of quartz plates 6 to be attached may be provided. This makes it possible to perform a linearity check with higher accuracy.

  As described above, the laser spectrophotometric analyzer has been described as an example. However, the present invention is not limited to this, and the present invention can be applied to various gas spectrophotometric gas analyzers such as a Fourier transform infrared spectrophotometer. Moreover, although the said Example is an example using a multiple reflection cell, it is obvious that this invention is applicable not only when this but using a direct-through type cell.

  INDUSTRIAL APPLICABILITY The present invention can be used for a gas analyzer that measures trace components in a gas by spectrophotometric analysis.

DESCRIPTION OF SYMBOLS 1 Gas cell 2 Optical system chamber 3 Laser light source 4 Photo detector 5 Filter insertion / extraction mechanism 6 Quartz plate 11 Spherical mirror 12 Spherical mirror 13 Gas inlet 14 Gas outlet 15 Light transmissive window 16 Light transmissive window 51 Rotating disk 52 Single filter window 53 Multiple Filter window 54 Blank window 55 Motor 56 Rotating plate 57 Slide plate 58 Oscillating plate 59 Slide drive part A Optical path B axis

Claims (1)

  A plurality of optical filters having the same absorbance in a gas analyzer using a spectrophotometric method in which a variable wavelength measurement light is passed through a gas cell filled with a sample gas and then the light intensity is detected by a photodetector. A gas analyzer comprising a filter insertion / removal mechanism that sequentially inserts or removes one or a plurality of the plurality of sheets into or from the optical path of the measurement light.

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