JPH02124448A - Method and apparatus for detecting concentration of fluorocarbon gas - Google Patents

Abstract

PURPOSE:To suppress erroneous detection with other gas and to make it possible to detect the concentration of low-concentration fluorocarbon gas by projecting infrared rays on a sample cell through which fluorocarbon gas passes and a comparing cell in which gas that does not absorb the infrared rays is sealed. CONSTITUTION:The infrared rays which are generated in an infrared-ray source 11 are guided into a filter 12. Only the infrared rays having the wavelength in C-F stretching vibration mode of fluorocarbon gas pass through the filter 12. Said infrared rays are projected on a sample cell 13 and a comparing cell 14. A gas to be measured incorporating fluorocarbon gas is introduced into the sample cell 13 through an inlet port 15 and exhausted through an outlet port 16. In the comparing cell 14, a gas which does not absorb the infrared rays is sealed. In this constitution, the fluorocarbon gas selectively absorbs the wavelength in the C-F stretch vibration mode. The intensities of the infrared rays which have passed through the cells 13 and 14 are separately measured and compared with a detecting means 17. Thus the signal matching the concentration of the fleon gas can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for detecting the concentration of fluorocarbon gas, and in particular to a method and apparatus for detecting a low concentration of fluorocarbon gas, for example on the order of ppm. Regarding.

Conventional technology To detect the concentration of fluorocarbon gas, for example, when constructing a main city gas pipeline, nitrogen mixed with fluorocarbon gas (0.2% in terms of fluorocarbon gas concentration) is pressurized into the pipe buried underground.
Airtightness tests are conducted by drilling detection holes underground to detect fluorocarbon gas leaks.

Therefore, it is desirable to be able to easily detect low-concentration fluorocarbon gas, and to have excellent selectivity without causing false detection due to other gases.

A typical prior art is shown in No. 6I21. In this prior art, the electric heater 1 heats the temperature to about 800°C, for example.
Platinum @[i2, which is heated to a high temperature, is used as an anode to apply a positive potential, and a cathode 3 is placed nearby, and a negative potential is applied to the cathode 3. When there is fluorocarbon gas between the anode 2 and the cathode 3, the radiation of positive ions increases rapidly and the current increases significantly.

In the prior art shown in FIG. 6, T4 flowing between the anode 2 and the cathode 3 is caused not only by fluorocarbon gas but also by other halides and hydrocarbons.
The flow changes.

Therefore, there is a problem in that the concentration of only fluorocarbon gas cannot be measured with high precision.

Ike's prior art is shown in FIG. A radiation source 7 of a radioactive isotope, such as Trinauno, is sealed in a small cell 4, and the inside is filled with an inert gas such as nitrogen gas.The nitrogen gas is ionized by the β rays from the isotope. When a voltage is applied to the anode 6 supported by the ceramic insulator 5, an ionic current flows. The cell 4 is provided with an inlet 8 and an outlet 9. When a molecule with a strong ability to absorb electrons (II electronic molecule), such as a fluorocarbon gas, enters, the molecule absorbs the electron and becomes an ion. Since the charged molecules move at a slower speed than free electrons, it takes a longer time to reach the anode 6, and the degree of recombination with positive ions is higher, so that the ionic current decreases. This decrease in ionic current is proportional to the concentration of electrophilic molecules in the inert gas when the concentration is low. Therefore, by connecting the outlet of the column of the gas chromad bluff to this cell 4, it is possible to know the concentration of the electrophilic gas in the carrier gas flowing out from the column every moment. Such a configuration is suitable for gas chromad bluffs.
It is called an electron capture detector.

The prior art shown in FIG. 7 requires a gas chromatograph and uses radioactive isotopes, so
Due to legal requirements, it is actually impossible to construct such a device in a portable manner.

Problems to be Solved by the Invention An object of the present invention is to provide a method and device for detecting fluorocarbon gas concentration so that low concentrations of fluorocarbon gas can be detected without false detection due to pond gas and with a simple configuration. It is to provide.

Means for Solving the Problems The present invention provides a sample cell through which a gas to be measured containing fluorocarbon gas flows, and a comparison cell filled with a gas that does not absorb infrared rays including the wavelength of the C-p side line vibration mode of fluorocarbon gas. A method for detecting a fluorocarbon gas concentration, comprising: irradiating the infrared rays, and detecting the fluorocarbon gas concentration based on the intensity of the infrared rays that have passed through a sample cell and a comparison cell, respectively.

The present invention also provides an infrared light source that generates infrared rays including a wavelength of the C-F stretching vibration mode of fluorocarbon gas, a sample cell that is irradiated with infrared rays from the light source, and through which a gas to be measured containing fluorocarbon gas flows; Infrared rays from a light source are irradiated, and the intensity of the infrared rays that has passed through a comparison cell filled with a comparison gas that does not absorb light at the wavelength of the C-F stretching vibration mode of fluorocarbon gas, a sample cell, and a specific axis cell is detected. a detection means, interposed in the optical path from the light source to the detection means,
This is a fluorocarbon gas concentration detection device characterized by including an optical selective passage means for passing only light having a wavelength in the C-F stretching vibration mode of fluorocarbon gas.

Further, an example of the detection means of the present invention includes two parts formed airtightly from each other by a displaceable partition member.
One room is irradiated with infrared rays that have passed through a sample cell, and the other room is filled with a gas that absorbs light at the C-1 (II) torsional vibration mode wavelength of CFC gas. , such a casing is irradiated with infrared rays that have passed through a comparison cell and is filled with a gas that does not absorb light in the wavelength of the C-F stretching vibration mode of fluorocarbon gas; and means for detecting displacement of the partition member and deriving an electrical signal.

Function According to the present invention, a sample cell through which a gas to be measured, which is a fluorocarbon gas, flows is irradiated with infrared rays having a wavelength of the C-p offshore 1ii vibration mode of the fluorocarbon gas. This wavelength is approximately 900-1200 cm-'.

This type of C-1 gas? The wavelength of the ll11 contraction vibrational mode is selectively absorbed by chlorofluorocarbon gas, and other gases such as N2, 02... N20. Co.

It is not absorbed by CO, halides other than chlorofluorocarbons, and hydrocarbons.

Another comparison cell is filled with a gas that does not absorb infrared rays.The sample cell and comparison cell are irradiated with infrared rays from an infrared light source, and the intensity of the infrared rays that has passed through the sample cell and comparison cell is individually measured. Measure to. Based on the intensity of the infrared rays that passed through the Sun Arcel and the intensity of the infrared rays that passed through the comparison cell, the concentration of fluorocarbon gas contained in the gas to be measured can be detected without depending on the output intensity of the infrared light source. . In this way, it becomes possible to measure the fluorocarbon gas concentration with high accuracy.

Moreover, such a configuration can be realized relatively easily and can be made into a m-type, which is advantageous.

Example FIG. 1 is a block diagram of one embodiment of the present invention.

The infrared light source 11 generates infrared rays including the wavelength of the C-F stretching vibration mode of the fluorocarbon gas, and the wavelength of the C-F (I11 contraction vibration mode) of the generated fluorocarbon gas is, for example, 900 nm.
~1200 cm-', and its maximum spectral intensity is obtained at about 900 cm-'. The infrared rays from this infrared light source 11 are guided to a filter 12. This filter 1
2 allows only the wavelength of the C-F stretching vibration mode of the fluorocarbon gas to pass through.

The light from the filter 12 illuminates a sample cell 13 made of an infrared transparent material I':I, such as rock salt, and a comparison cell 14 made of an infrared transparent material 1'4 f4.
be done. A gas to be measured including fluorocarbon gas is introduced into the sample cell 13 from an inlet 15 and is discharged from an outlet 16. In the comparison cell 14, a gas such as N2. Co□.

1-120, CO□, Go, or other gases are sealed in advance.

Infrared light passed through sandal cell 13 and comparison cell 14
The intensity of each infrared ray that has passed is detected by the detection means 17.

FIG. 2 is a sectional view showing a specific configuration of the detection means 17. For example, there is a chopper 23 that is made of an infrared transparent material such as rock salt and an infrared opaque material, and cuts off the infrared rays that have passed through the sample cell 13 and the comparison cell 14 by rotating the chopper 23. There is a casing 18 made of an infrared transparent material, in which a flexible membrane-like partition member 10 is fixed, thereby forming airtight rooms 20 and 21, respectively. Ru. One room 204i→r is irradiated with infrared rays that have passed through Arcel 13. The other room 21 is irradiated with infrared rays that have passed through the comparison cell 14. One of the chambers 20 is filled with a fluorocarbon gas having the same composition as the fluorocarbon gas whose concentration is to be detected in the gas to be measured led to the Sun Arcel 13. 11! ! The other chamber 21 is filled with a gas that does not absorb infrared rays, such as the aforementioned N2, which is filled in the comparison cell 14. Partition member 19
can be displaced 1 m above and below No. 2121 depending on the pressure in the room 20.21. This displacement of the f-soil cutting member 19 is electrically detected by a detection element 22 such as a strain gauge, and the amount of displacement of the partition member 19 is derived as an electrical signal. The output of the detection element 22 is given to a processing circuit 27 shown in FIG.
displays the concentration of fluorocarbon gas in the measured gas. The chopper 23 has a through hole 25 in a disc 24 made of a light-shielding material.
is formed and driven to rotate around an axis 26.

FIG. 3 is a front view of the chopper 23 seen from the cell 13, 14 side. The through holes 25 are formed with a 180 degree shift in the circumferential direction.

During operation, when a gas to be measured containing fluorocarbon gas is supplied from the inlet 15 of the sample cell 13, the fluorocarbon gas absorbs infrared rays depending on the concentration, thereby causing the detector f117 to
One of the rooms 20 is irradiated with the remaining infrared rays.

The infrared radiation passing through the comparison cell 14 is applied to the other chamber 21 of the detection means 17 without its intensity being weakened. One of the chambers 20 is filled with fluorocarbon gas as described above, and therefore infrared rays are transmitted to that chamber 20.
When the room 20 is irradiated, the infrared rays are absorbed, the temperature rises, and the pressure inside the room 20 rises. Since the gas in the other room 21 does not absorb infrared rays, there is no temperature rise. Therefore, one partition member is displaced toward the other room 21 side. Further, since the chopper 23 cuts off the infrared rays irradiated to the gauging 18, when the infrared rays are cut off, the gauging 18 cools down by radiating heat to the surroundings, and the partition member 19 returns to its original state. This partition member 1
The magnitude of the displacement of 9 is detected by the detection element 22.

The amount of displacement of the partition member 19 corresponds to the concentration of fluorocarbon gas in the gas to be measured supplied into the sample cell 13.

By providing the comparison cell 14 and the other room 21, the detection means 17 can detect the ratio of the infrared intensities, and therefore, the detection means 17 can detect the ratio of the infrared rays of the fluorocarbon gas without depending on the intensity of the infrared rays from the infrared rays [11]. It is possible to obtain an electrical signal corresponding to the concentration from the detection element 22.

FIG. 4 is a graph showing the experimental results of the FTIR spectrophotometer (Fourier transform infrared spectrophotometer) of the present inventor. The gas to be measured is N2 containing 100 p p rn of fluorocarbon gas.
It's gas. The absorbance, that is, the peak p1 of the spectral intensity indicates the wavelength having the maximum spectral intensity of the C-Fll contraction vibration mode of the Freon 12, and the peak p2 exists close to this. Furthermore, there are beaks p3, p4, etc. unique to this Freon 12. these beak p1
~p4 is a wavelength unique to Freon 12 gas, and it is confirmed that there is no adverse effect of air, ie, N2, Ox + HtO, CO, Co, etc.

According to the present invention, preferably, by detecting the peak p1 of the wavelength having the maximum spectral intensity, the concentration of freon corresponding to the spectral intensity can be detected, but other peaks p2. p3. Alternatively, the spectral intensity of p4 or the like may be detected, and the concentration of fluorocarbon gas corresponding to the spectral intensity may be detected.

FIG. 5 is an enlarged view of the spectral intensity at the baseline of the experiment shown in FIG. 4, that is, in a state where the spectral intensity is small. By making the waveform B corresponding to the concentration of fluorocarbon gas larger than the noise component A, low concentration fluorocarbon gas can be detected with high accuracy. To detect fluorocarbon gas concentration with high accuracy, use Sun Arcel 1.
The optical path length 11 through which the infrared rays of the cells 1 and 14 pass should be made sufficiently long.
3.14 may be configured to be long in a straight line, or the optical path length may be increased by repeating reflection multiple times using a low-loss reflecting mirror having a reflective surface made of gold or the like.

In another embodiment of the invention, filter 12 includes cell 13.1.
4 and the detection means 17, and the infrared light source 11 is configured to emit infrared light at a wavelength in the C-F stretching vibration mode, that is, about 900 to 1200 cm −'. Alternatively, the detection means 17 may be configured to detect only the intensity of such infrared radiation, and the filter 12 may be omitted.
Effects of the Invention As described above, according to the present invention, it is possible to extract only the wavelength of the C-F stretching vibration mode of the fluorocarbon gas using a spectrometer instead of 2. It is possible to perform detection with high precision without being affected, and the structure is simple and can be configured to be portable.

[Brief explanation of drawings]

1 [2I is an overall block diagram of an embodiment of the present invention, 2I 121 is a sectional view showing a specific configuration of the detection means 17, FIG. 3 is a front view of the chopper 23, and FIGS. 4 and 5 [
21 is the inventor I? Graphs showing experimental results of the TIR spectrophotometer, FIG. 6 is a cross-sectional view of the prior art, and FIG. 7 is a cross-sectional view of another prior art. 11... Infrared light source, 12... Filter, 13...
- Sample cell, 14... Comparison cell, 17... Detection means, 23... Chopper, 27... Processing means, 28
...Display means Fig. Fig. Fig.

Claims (3)

[Claims] (1) A sample cell through which a gas to be measured containing fluorocarbon gas flows, and a comparison cell filled with a gas that does not absorb infrared rays including the wavelength of the C-F stretching vibration mode of fluorocarbon gas,
A method for detecting fluorocarbon gas concentration, comprising: irradiating the infrared rays, and detecting the fluorocarbon gas concentration based on the intensity of the infrared rays that have passed through a sample cell and a comparison cell, respectively. (2) an infrared light source that generates infrared rays including the wavelength of the C-F stretching vibration mode of fluorocarbon gas; a sample cell that is irradiated with the infrared rays from the light source and through which the gas to be measured including the fluorocarbon gas flows; a comparison cell filled with a comparison gas that is irradiated with infrared rays and does not absorb light at a wavelength in the C-F stretching vibration mode of the fluorocarbon gas; and a detection means that detects the intensity of the infrared rays that have passed through the sample cell and the comparison cell, respectively. , interposed in the optical path from the light source to the detection means,
A fluorocarbon gas concentration detection device comprising: a light selection passage means for passing only light having a wavelength in the C-F stretching vibration mode of fluorocarbon gas. (3) The detection means are formed airtightly from each other by displaceable partition members.
One room is filled with a gas that is irradiated with infrared rays that have passed through the sample cell and absorbs light at the wavelength of the C-F stretching vibration mode of the fluorocarbon gas, and the other room is filled with a comparison cell. The C-
Such a casing is filled with a gas that does not absorb light with wavelengths in the F stretching vibration mode, a chopper that irradiates the casing with infrared rays intermittently, and detects displacement of the partition member and derives an electrical signal. 3. The fluorocarbon gas concentration detection device according to claim 2, further comprising means for detecting the concentration of fluorocarbon gas.