JPH0220938B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas concentration measuring method and apparatus suitable for measuring ethane gas concentration at a location far away from a measurement point.

Ethane gas is a gas contained in LNG and LPG.
These gases are used as fuel gases and as useful gases in petrochemistry, and when handling these gases, serious accidents such as factory explosions and personal injury may occur if sufficient care is not taken to prevent leakage. It's possible. In fact, gas explosions and fire accidents on tankers and the like occur every year. For this purpose, it is desirable to develop a useful leak detection and alarm system for methane and propane, and we have already applied for a patent (Patent Application No. 58-205993).
Method and device for measuring propane gas concentration, patent application 166836/1983, 86770/1982, patent application 1986/1986
136727 Patent application regarding methane gas concentration measurement method and device). Recognizing that safety would be even higher if ethane gas, in addition to methane and propane gas, could be independently detected and alarmed, we investigated methods and devices for detecting ethane gas, and found that the methods and devices described below are effective. I made sure of that.

In addition, when considering the gas detection described above, flammable,
Since it is an explosive gas, it is desirable that the detection method be an essentially explosion-proof structure and method that does not have an ignition source, and that remote measurement from a central monitoring room can be carried out reliably.

Conventionally used semiconductor gas sensors, combustion gas sensors, optical interference detection methods, etc. have problems with gas selection detection, operational stability, humidity effects, dilute gas detection, etc., and are also difficult to maintain. There are some points that need to be taken into consideration. Furthermore, in the case of remote monitoring and telemetry, electrical signals are sent and received, so the risks of false alarms caused by electromagnetic induction and accidents caused by damage to cables cannot be ignored.

The present invention has been made in view of the above circumstances, and by reliably and quickly detecting the leakage of ethane gas and issuing an alarm, it is possible to prevent the leakage of not only ethane gas but also natural gases including ethane gas. We provide a method and device for measuring ethane gas concentration that is highly reliable even under severe measurement conditions, allows real-time measurement, allows measurement at extremely remote locations, and has no danger of inducing accidents. It is something to do.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method and apparatus for measuring ethane gas concentration of the present invention will be described in detail below with reference to the drawings.

The present invention utilizes an optical fiber, such as a quartz-based optical fiber, which has been developed in recent years for optical communications. This kind of optical fiber
Light transmission loss is low in the wavelength range of 1.0 to 1.8 μm.
On the other hand, ethane gas has a characteristic absorption band in a broad wavelength band of 1.64 to 1.71 μm within the wavelength band of 1.0 to 1.8 μm. Furthermore, a wavelength range in which light absorption by water vapor (H ₂ O) and carbon dioxide gas (CO ₂ ) is almost narrow can be selected within the above-mentioned characteristic absorption of ethane gas.

The present invention has been made based on the above new findings. That is, the present invention can be achieved by selecting a wavelength range within the characteristic absorption band of ethane gas, which has little loss due to the optical fiber during transmission, and is hardly affected by H ₂ O or CO ₂ . The purpose of this system is to accurately and quickly measure the concentration of ethane gas at a remote location.

FIG. 1 is a graph showing the transmission loss of a silica-based optical fiber in the wavelength range of 0.6 to 1.8 μm. As is clear from this figure, the transmission loss at a wavelength of 1.1 to 1.7 μm is less than 1 dB/Km, and it can be seen that it is practically effective for transmitting light in the wavelength range from the visible region to 1.8 μm. If such a low-loss optical fiber is used as an optical transmission line, it is possible to measure the concentration of ethane gas in a remote location by spectrophotometry.

FIG. 2 is a diagram showing the characteristic absorption of ethane gas, which is the object of the present invention, and is a measurement result obtained using a spectrometer with a pressure of 760 Torr, a measurement cell length of 50 cm, and a resolution of 3 Å or less. Broadly speaking, the characteristic absorption wavelength band of ethane gas can be considered as one broad wavelength range of 1.64 to 1.71 μm, but as shown in the figure, each wavelength shows its own absorption, and these overlap. It can be seen that a characteristic absorption wavelength band is formed. This characteristic absorption wavelength band was only measured up to 1.71 μm due to the light source, but from this figure it is estimated that it exists beyond 1.71 μm and extends up to about 1.75 μm. However, in the present invention, the wavelength range up to 1.71 μm, which has become clear through measurement, is treated as a characteristic absorption wavelength band.

FIG. 3 shows the characteristic absorption wavelength band of methane gas near the same wavelength band, and FIG. 4 shows the characteristic absorption wavelength band of propane gas near the same wavelength band. Methane gas is
60Torr and cell length of 0.5m, and the propane gas in Figure 4 was obtained at 200Torr and cell length of 0.5m, but that wavelength band is different from that of methane gas.
It is a sharp wavelength band of 1.664 to 1.669 μm centered on 1.666 μm, and is included in the characteristic wavelength band of ethane gas.
It can be seen that there is a characteristic absorption wavelength band from 1.668 to 1.72 μm, which overlaps with that of ethane gas. Referring to these, if ethane gas exists alone and you want to detect its leak, all of the characteristic absorption wavelength bands shown in Figure 2 can be selected, but if it is mixed with methane gas or propane gas, the characteristic absorption wavelength range is 1.64 to 1.66 μm. It can be seen that by using the band, it is possible to detect the ethane gas concentration without being affected by the mixed methane and propane gases. That is, when measuring the concentration of ethane gas by spectrophotometry, a narrow wavelength band with at least one wavelength as the center wavelength is selected from among the characteristic absorption wavelength bands of ethane gas, and this is used as the measurement light. The amount of light absorbed when it passes through a measurement cell (absorption cell) where ethane gas is present is measured, and the ethane gas concentration can be detected from this absorption rate. Here, the measurement light having a narrow wavelength band is selected by, for example, a band transmission filter or a prism, and is, for example, light having a wavelength of 1.645 to 1.650 μm.

When measuring the concentration of ethane gas by spectrophotometry using one or more lights at the measurement wavelength (narrow wavelength band) as described above, the reference wavelength (reference light) is usually ethane gas, and the coexisting methane gas or A wavelength band other than the characteristic absorption wavelength band of propane gas, for example, a 1.60 to 1.64 μm band is selected. In other words, it is necessary to select a reference wavelength from a wavelength range in which light is not absorbed due to the presence of ethane gas. Moreover, H ₂ O
Since the presence of (water vapor) and CO ₂ (carbon dioxide) is also a concern, a wavelength band that is hardly affected (absorbed) by these is selected as the reference wavelength. Similarly to the measurement wavelength, the reference wavelength is also selected from a narrow wavelength band having one or more wavelengths as the center wavelength.

Using the measurement wavelength and reference wavelength selected as described above, the light intensity at each wavelength after passing through the measurement cell is measured. From these measured values, calculate one or more ratios between the measured value at the measurement wavelength and the measured value at the reference wavelength, and calculate the absorption rate and absorbance calculated in advance based on this and the known concentration of ethane gas. The concentration of ethane gas to be measured can be determined based on the relationship with the concentration.

According to the measurement method of the present invention, even if only one measurement wavelength and one reference wavelength are selected, results with higher precision and reliability can be obtained than with conventional gas detection methods. However, if light in one or more wavelength bands is used as the measurement wavelength, the reference wavelength, or both, measurement results with higher accuracy and reliability can be obtained. By selecting multiple wavelengths, multiple absorbance ratios can be obtained, and by comparing these values with each other, more reliable results can be obtained and the results can be determined due to the measurement equipment. It is now possible to detect errors and the effects of absorption by gases other than ethane gas, and by eliminating these sources of error, highly reliable measurements are possible, and it is also possible to detect extremely low concentrations of ethane gas. It will become.

FIG. 5 and FIG. 12 show absorption wavelength characteristic curves of H ₂ O. As is clear from these figures, the strong absorption band of H ₂ O is concentrated in the wavelength band of 1.350 to 1.393 μm in the range of 1.2 to 1.7 μm. Therefore, by excluding this wavelength band, measurement with less influence of H ₂ O becomes possible. Similarly, by using a wavelength band excluding the 4.0 to 4.6 μm wavelength band where the characteristic absorption of CO ₂ is strong, measurement with less influence of carbon dioxide gas becomes possible.

As is clear from the above, when a silica glass-based optical fiber is used as an optical transmission line, the characteristic absorption wavelength band of ethane gas shown in Fig. 2, and the coexisting absorption wavelength band shown in Figs. If you use the characteristic absorption wavelength band of ethane gas, excluding the characteristic absorption wavelength band of methane gas and propane gas, which are highly likely, the concentration of ethane gas in a remote area can be reduced to the above-mentioned gases, H ₂ O (water vapor, moisture), and CO that coexist. Measurements can be made with high accuracy and reliability, with almost no influence from ₂ or from optical loss in the optical transmission path.

Next, a description will be given of an apparatus of the present invention constructed based on the ethane gas concentration measuring method of the present invention described in detail above.

Before explaining the apparatus of the present invention, a light source used in the apparatus, that is, a light source that emits light in the near-infrared region corresponding to the characteristic absorption wavelength band of ethane gas will be explained. Light sources in this wavelength range generally include semiconductor laser diodes (LDs), light emitting diodes (LEDs), discharge tubes (such as xenon lamps), and heating wires. In any case, it is preferable to use a device that continuously or pulsedly emits light that covers the measurement wavelength range and has a higher emission energy intensity because it allows detection of low concentration gases.

Since LDs are easy to obtain high output and have strong monochromaticity, it is desirable that the oscillation wavelength can be easily selected in the case of a broad wavelength band such as the characteristic wavelength band of ethane gas. However, care must be taken to ensure that the oscillation wavelength does not fluctuate due to fluctuations in power supply voltage or temperature changes. Also, when using an LD as a light source, at least two wavelengths are used, one for the reference wavelength and one for the characteristic absorption wavelength (measurement wavelength).
Although it is necessary to use two different LDs, there is no need to use a spectrometer such as a bandpass filter. Note that by using a plurality of LDs with different emission wavelengths as one or both of the LD for the characteristic wavelength and the LD for the reference wavelength, measurement with higher sensitivity and accuracy becomes possible.

In addition, LEDs and discharge tubes have low output, but have good output stability and long life. Furthermore, since the emission spectrum is broad, when using these light sources, a spectrometer is used to narrow the detection wavelength band and capture the amount of change in the selected wavelength in the desired characteristic absorption wavelength band or reference wavelength band. Then, the ethane gas concentration may be measured. In this case, an inexpensive bandpass filter, prism, etc. can be used as the spectrometer. This band-pass filter is used in the embodiments of the device of the invention described later. The transmission width of this bandpass filter is generally wide, on the order of 1 to several nm, and if the characteristic absorption wavelength range of the gas to be measured is narrower than this transmission width, it will be disadvantageous in terms of efficiency. However, since the characteristic absorption wavelength band of ethane gas is broad as described above, measurement can be carried out satisfactorily even with such a band transmission filter.

In Figure 6, the center wavelength is 1.6475μm and the half width is 5nm.
FIG. 2 is a diagram schematically showing the intensity distribution of light after passing through a band transmission filter having a Gaussian distribution type transmission characteristic. In this figure, the broken line represents the case where ethane gas is contained at a pressure of 760 Torr in a measurement cell with an optical path length of 50 cm, and the solid line represents the case where ethane gas is not present. By dividing the difference in area within each curve in this figure by the area surrounded by the solid line, the extinction ratio A due to ethane gas can be determined. This filter may have a half width of 3 nm or 10 nm, for example.

Next, each embodiment of the ethane gas concentration measuring device of the present invention will be described. FIG. 7 is a diagram showing the configuration of a first embodiment of the ethane gas concentration measuring device of the present invention, which is configured to perform measurements using two measurement wavelengths and one reference wavelength. In this figure, 1 is a light emitting source made of, for example, an LED, and 3 is a light emitting source 1.
For example, 1.65μm (half width 0.1μm)
A low-loss optical fiber (for example, a silica optical fiber), that is, a first optical fiber, transmits the light through the optical coupler 2, and 4 is an optical transmission line formed of a first optical fiber. The cylindrical body 4a of this measuring cell 4 is
is made of porous sintered metal or plastic foam with a continuous pore structure to allow natural flow of atmospheric gas (gas to be measured).
The measuring cell 4 used has, for example, an optical path length (distance between the optical couplers 4b and 4b') of 50 to 100 cm. However, when the concentration of the gas to be detected is low, it is better to increase the optical path length of the measurement cell.
In this case, a well-known multi-optical path type absorption cell or the like may be used. Reference numeral 5 indicates an optical transmission line consisting of a second optical fiber such as a low transmission loss optical fiber, such as a quartz-based optical fiber, which transmits the light from the measurement cell 4 via the optical coupler 4b'; a beam splitter that splits the light coming through the transmitted optical coupler 6 into a first beam 8 and a second beam 10; 9 is a first bandpass filter disposed in the first beam 8; 11 is a beam splitter placed in the second beam 10 and splits it into a third beam 12 and a fourth beam 13; 14 is a second band pass filter placed in the third beam 12; ,
15 is a third band pass filter placed in the fourth light beam 13. These bandpass filters 9, 14, and 15 are interference filters that utilize the light interference effect of thin films, for example, and multilayer film interference filters are preferably used, and the transmittance of the center wavelength is as high as possible, and the half-width is 2 to 2. A narrow one of 5 nm is desirable. For example, the center wavelength of the first band-pass filter 9 is 1.6475 μm, and the center wavelength of the second band-pass filter 14 is 1.675 μm (on the contrary, the center wavelength of the first band-pass filter 9 is 1.6475 μm).
The center wavelength of the second band-pass filter 9 is 1.675 μm, and the center wavelength of the second band-pass filter 14 is 1.675 μm.
1.6475 μm) In other words, the wavelength is within the characteristic absorption wavelength band of ethane gas and is the wavelength selected as the measurement wavelength. Further, the third band transmission filter 15 has a wavelength other than the characteristic absorption wavelength of ethane gas (reference wavelength).
For example, 1.610 μm is selected. Note that the center wavelength of these filters is naturally selected to be a wavelength that does not exhibit the characteristic absorption of H ₂ O and CO ₂ .

Further, 16, 17, and 18 are the first, third, and fourth, respectively.
first, second and third photodetectors arranged in the optical paths 8, 12 and 13 of the photodetectors, such as avalanche photodiodes (APDs), photodiodes (PDs) (e.g. Ge semiconductor or PbS detectors), etc. is used.
19, 20, 21 are amplifiers, 22 are each photodetector 1
Electrical signals from 6, 17, and 18 are used to connect amplifier 1, respectively.
This is an arithmetic processing device that performs calculations to determine the absorption ratio of the gas to be detected and also the concentration of the gas to be detected based on the signals amplified at 9, 20, and 21.

In the first embodiment configured as described above, light from a light source 1 is sent to a measuring cell 4 through an optical coupler 2 and transmitted through an optical transmission line 3. The cylindrical body 4a of the measurement cell 4 has a structure through which atmospheric gas can flow in and out, as described above, so that when placed at a location to be measured, the cylindrical body 4a is filled with the atmospheric gas at that location. Therefore, the light from the light source 1 is transmitted through the optical transmission path 5 after being absorbed by the atmospheric gas within the measurement cell 4 . Next, the first beam 8 of the lights split by the beam splitter 7
The first band transmission filter 9 transmits only a narrow band of light centered around the measurement wavelength of 1.6475 μm, which is received by the first photodetector 16 and output as an electrical signal corresponding to the amount of received light. The signal is amplified by an amplifier 19 and then input to an arithmetic processing unit 22 .

Similarly, the third light beam 12 divided by the beam splitters 7 and 11 is passed through the second band pass filter 14, where only a narrow band of light having a center wavelength of 1.675 μm, which is the other measurement wavelength, is transmitted. Second
The light is received by the photodetector 17, and its output signal is amplified by the amplifier 20 and then input to the arithmetic processing unit 22.

Furthermore, the fourth light beam 13 separated by the beam splitters 7 and 11 is transmitted by a third band transmission filter 15, in which only light in a narrow band with the center wavelength of 1.610 μm, which is the reference wavelength, is transmitted, and a third light beam is generated. The signal is detected by the detector 18 and its output signal is amplified by the amplifier 21 and then input to the arithmetic processing unit 22 .

In this manner, the ratio of the electrical signal from the first photodetector 16 to the electrical signal from the third photodetector 18 among the electrical signals input to the arithmetic processing unit 22 is determined. In other words, the measurement wavelength is 1.6475μm and the reference wavelength is
The extinction ratio A ₁ of ethane gas at 1.610 μm is determined. From this and the relationship between the extinction ratio A ₀ and the ethane gas concentration P ₀ determined in advance based on standard ethane gas, the measured value P ₁ of the ethane gas concentration in the gas present in the measurement cell is determined by calculation processing. can get.

Similarly, based on the electrical signal from the second photodetector 17 and the electrical signal from the third photodetector 18, the ratio of the other measurement wavelength 1.675μm and the reference wavelength 1.610μm is used to determine the wavelength 1.675μm. The extinction ratio A ₂ is determined,
Based on this, the ethane gas concentration P ₂ can be obtained by calculation.

The two ethane gas concentration measurements obtained in this way based on two different measurement wavelengths are compared, and if both are within the error range, the average value of these values or the maximum value if necessary , the minimum value is displayed on the display 23 as the ethane gas concentration at the measurement point. Additionally, if there is a deviation greater than a predetermined value between the two measured values, this deviation may indicate that the measurement cell contains gas other than ethane gas, such as propane gas or other hydrocarbon gas, and this deviation is due to the characteristics of this gas. This may be due to overlap with the absorption wavelength, or the parts of the measuring device after the optical coupler 6, namely the beam splitters 9, 14, 15, and the photodetectors 16, 1.
7, 18, or amplifiers 19, 20, and 21, and a message to that effect is shown on the display 23. In this case, a test light source is provided between the optical coupler 6 and the beam splitter 7, the light from the optical coupler 6 is blocked in the above abnormality, and the test light source is made to emit light for measurement. If abnormalities in the device itself can be determined, abnormalities in the optical and electrical systems after the beam splitter can be detected at least, which increases the reliability of the device.

If no abnormality is found in the optical or electrical system after beam splitter 7, it is thought that the difference in gas concentration at the two measurement wavelengths occurred due to light absorption by propane gas, which tends to mix with ethane gas.
From the comparison between Fig. 4 and Fig. 4, it is estimated that the influence of propane gas appears in the gas concentration detection at the measurement wavelength of 1.675 μm. From this, 1.6475μ
Assuming that the gas concentration at the measurement wavelength of m is correct, at 1.675 μm (ethane gas + propane gas)
It is also possible to determine the propane gas concentration by considering it as the concentration of the mixed gas.

FIG. 8 is a diagram showing the configuration of a second embodiment of the ethane gas concentration measuring device of the present invention. This second
In this embodiment, the light that exits the measurement cell 4 and is transmitted through the optical transmission path 5 is divided into three beams by the optical branching path 24, and each divided beam is sent to the optical coupler 2.
5, 26, 27 and the chopper 28 to the first, third and second band pass filters 9, 15,
14 to the first, third, and second photodetectors 1
6, 18, and 17, and among the electrical signals from these photodetectors, the electrical signals from the first photodetector 16 and the third photodetector 18 are both amplified by the amplifier 29 and sent to the arithmetic processing unit. 22, and the electrical signals from the second photodetector 17 and the third photodetector 18 are different from the first embodiment in that they are amplified by the amplifier 30 and then input to the arithmetic processing unit 22. They are different. Since the other configurations are substantially the same as those in the first embodiment, parts having the same functions are designated by the same reference numerals and illustrated.

This second embodiment has the advantage that amplification and the like are facilitated because the output electric signals from each photodetector become alternating current due to the use of the chopper 28.

In addition, in these embodiments, if the light from the light source 1 is divided into a plurality of light beams by an optical branch path and these light beams are guided to measurement cells placed at different points by separate optical transmission paths, different results can be obtained. It is also possible to adopt a configuration in which the concentration of the detected gas at multiple points can be measured simultaneously.

FIG. 9 shows a third embodiment of the ethane gas concentration measuring device of the present invention. In this third embodiment, by using a microcomputer as the arithmetic processing device, this arithmetic processing device 2
Light source 1 consisting of LED based on the signal from 2
The point is to emit pulse light instead of continuous light, and each band pass filter 9, 14, 15 is rotated in sector 3.
The photodetector 16 is configured with only one photodetector and one amplifier, so that the light of the measurement wavelength and the reference wavelength transmitted through these filters are made to enter the photodetector 16 alternately (sequentially at different times). This embodiment differs from the above-mentioned embodiments 1 and 2 in that the above-mentioned embodiments are obtained. That is, the light from the light source 1 that emits pulse light based on the signal from the arithmetic processing unit 22 is transmitted by the optical transmitter 5 through the measurement cell 4 and then sent to the optical coupler 6.
After passing through the first band-pass filter 9 at successive time intervals due to the rotation of the rotating sector 31,
The light passes through the second band pass filter 14 and enters the photo detector 16, and passes through the third band pass filter 15 and enters the photo detector 16. Based on this, the photodetector 16 sequentially outputs electrical signals for the measurement wavelength and reference wavelength according to the transmission band of each band pass filter, and after being amplified by the amplifier 19, the arithmetic processing unit 22
is input to. Reference numerals 32, 33, and 34 designate synchronizing signal generators consisting of a light receiver such as a photodiode and a lamp installed in the vicinity of the rotating sector 31. Based on the signal, it is determined which signal is the electric signal inputted from the amplifier 19, and based on this, the concentration of the gas to be detected is determined by the same calculation as in each of the above-described embodiments. Other than the above, this embodiment is substantially the same as the previous embodiment. In this embodiment, only one photodetector and one amplifier are required, resulting in an inexpensive configuration. Especially in recent years, microcomputers have become extremely popular and inexpensive, making them extremely effective in practice.

FIG. 10 is a diagram showing a fourth embodiment of the ethane gas concentration measuring device of the present invention. This fourth embodiment uses an LD as a light emission source, and has a wavelength within the characteristic absorption wavelength band of ethane gas, for example.
First light emitting source 1 whose center wavelength of light emission is 1.647 μm
By using two light emitting sources, a is the light source for the measurement wavelength, and the second light source 1b, whose center wavelength of light emission is 1.610 μm, which is a wavelength other than the ethane gas characteristic absorption wavelength, is the light source for the reference wavelength. This embodiment differs from the other embodiments described above in that it does not use a bandpass filter (spectroscope) such as a multilayer interference filter.

Further, in this fourth embodiment, the first light emitting source 1a
A chopper 28 is arranged in front of the second light emitting source 1b, and the light from these light emitting sources is alternately guided to the measurement cell 4 through the optical transmission line 3a or 3b and the optical transmission line 3c. Further, a synchronizing signal generator 32 consisting of a lamp and a light receiver such as a photodiode is arranged near the chopper 28, and the output signal from the synchronizing signal generator 32 is inputted to the signal processing device 22.
Based on this signal, it is determined whether the signal from the detector 16 via the amplifier 19 is from the first light emitting source 1a or the second light emitting source 1b, and the signal processing device 22 calculates the detected gas. I'm trying to find the concentration. The other configurations are substantially the same as the other embodiments.

In this fourth embodiment, the first and second light emitting sources 1
Even when LEDs are used for a and 1b, the ethane gas concentration can be measured without using a bandpass filter (spectroscope) by the means described below. That is,
Although the emission wavelength of LED is broader than that of LD, its width (half width) is about 0.1 μm. Therefore, a light emitting diode with a center wavelength of 1.68μm and
By using a light emitting diode with a center wavelength of 1.60 μm as a light source for the measurement light and a light source for the reference light, the measurement device having the configuration of the fourth embodiment can detect ethane gas (without using a bandpass filter). Concentration can be measured. In this case, there is an advantage that the energy for detection is large, but since the wavelength is not selective and the wavelength width is relatively wide, there is a risk that the influence of other gases may become somewhat large.

FIG. 11 shows the configuration of a fifth embodiment of the ethane gas concentration measuring device of the present invention.

Since the purpose of the present invention is to measure the concentration of a gas to be detected at a remote location, the length of the optical fiber serving as the optical transmission path is long. Since this optical fiber is used back and forth, it requires longer length.

In this fifth embodiment, a spectrometer 36, an optical multiplexer 37
By using the optical fiber 3, it is possible to transmit the incident light and the emitted light with low loss without interference even if the same optical fiber 3 is used for both the outward and return paths. It is possible to cut the cost in half. Figure 11a shows measurement cell 4.
After transmitting the light through the optical fiber 5' and inputting it into the optical transmission line 3 via the optical multiplexer 37, using most of the optical transmission line 3 as the return path,
The light is sent to the photodetector side via the optical demultiplexer 36. In this way, the first to fourth embodiments
By using only a small portion of the optical transmission line 5' which is the return path used in the embodiment described above, most of the optical transmission line 3 which is the outgoing path is also used.

In FIG. 11b, a reflecting mirror 4c is arranged inside the measuring cell 4, so that the light incident on the measuring cell 4 is
After being reflected by the reflecting mirror 4c, the light is returned to the incident side and is made to enter the optical transmission line 3 via the optical multiplexer 37. In the case of this example b, since the light travels back and forth within the measurement cell 4, the optical path length within the measurement cell is longer than the size of the measurement cell 4.

As explained above, according to the method for measuring ethane gas concentration of the present invention, the characteristic absorption wavelength band of ethane gas is a narrow wavelength region where the optical fiber has the lowest loss, and where absorption bands of CO ₂ and H ₂ O are almost non-existent. Since the ethane gas concentration is measured by selecting a wavelength band, it is possible to measure with high precision from an extremely remote location with almost no influence from CO ₂ , H ₂ O, etc. Furthermore, according to the device of the present invention, an LD or a highly stable LED is used as a light emitting source, a quartz optical fiber with low transmission loss is used as an optical transmission line, and an inexpensive band pass filter is used for wavelength selection, so that it can be used at a remote location. Measurements can be made without electromagnetic induction or short circuits caused by cable breaks. Furthermore, since measurements can be made at a single point in a plurality of cells arranged over a wide area, it is suitable for cases where measurements at a plurality of points are to be viewed in a concentrated manner. In addition, since the measurement uses spectrophotometry, real-time measurement is possible, and rapid response to fluctuations in the concentration of the detected gas is possible. High precision equipment can be provided. It should be noted that if the device is configured to use optical fibers as in the fifth embodiment, the amount of optical fibers can be saved. Furthermore, by selecting an appropriate laser diode as the light emitting source as in the fourth embodiment, the spectroscope can be omitted and the apparatus can be simplified.

[Brief explanation of drawings]

Fig. 1 is a graph showing the transmission loss of the silica-based optical fiber used in the present invention, Fig. 2 is a graph showing the characteristic absorption wavelength band of ethane gas, and Fig. 3 is a graph showing the characteristic absorption wavelength band of methane gas.
Figure 4 shows the characteristic absorption wavelength bands of propane gas above 1.64 μm, Figure 5 shows the absorption wavelength characteristics of H ₂ O in the 1.3 μm band, and Figure 6 shows Gaussian distribution type band transmission. 7 to 11 are diagrams showing the configurations of the first to fifth embodiments of the apparatus of the present invention, and FIG. 12 is 1.1 to 1.7. in μm band
FIG. 2 is a diagram showing characteristic absorption of H ₂ O. 1, 1a, 1b,... light emitting source, 2... optical coupler, 3
...Optical fiber, 4...Measuring cell, 5...Optical fiber, 6...Optical coupler, 7, 11...Beam splitter, 8...First light beam, 9...First band transmission filter, 10...Second light beam , 12...Third luminous flux, 1
3...Fourth luminous flux, 14...Second band pass filter, 15...Third band pass filter, 1
6...First photodetector, 17...Second photodetector, 1
8... Third photodetector, 19, 20, 21... Amplifier, 22... Arithmetic processing unit, 23... Display, 25,
26, 27...Optical coupler, 28...Chopper, 2
9, 30...Amplifier, 31...Rotating sector, 32,
33, 34... Synchronization signal generator, 35... Optical coupler,
36... Optical demultiplexer, 37... Optical multiplexer.

Claims (1)

[Claims] 1. Light from a light emitting source is transmitted through an optical fiber with low transmission loss to a measurement cell where atmospheric gas flows in and out, and after passing through the measurement cell, it is transmitted through another optical fiber. In this method, the concentration is detected using a photodetector and spectrophotometry.The measurement light uses light whose center wavelength is at least one wavelength within the wavelength band of 1.64 to 1.71 μm, which is the characteristic absorption wavelength band of ethane gas. By using a light whose center wavelength is at least one wavelength outside the characteristic absorption wavelength band as a reference light, detecting the measurement light and the reference light with the photodetector and determining their intensity ratio. A method for measuring ethane gas concentration, the method comprising: measuring the concentration using ethane gas. 2 1.64~ which is the characteristic absorption wavelength band of ethane gas
A light emitting source that emits light in a wavelength range that includes at least a wavelength within the wavelength range of 1.71 μm, a measurement cell through which atmospheric gas flows in and out, and a measurement cell used for transmitting the light from the light emission source to the measurement cell. a first optical fiber with low transmission loss in the wavelength range; a second optical fiber with low transmission loss in the wavelength range for transmitting light from the measurement cell; measurement light whose center wavelength is at least one wavelength within the characteristic absorption wavelength band; and measurement light whose center wavelength is at least one wavelength in a wavelength band outside the characteristic absorption wavelength band. A spectrometer that separates light into reference light and a reference light, a photodetector that detects the measurement light and reference light separated by the spectrometer, and an electrical signal of the measurement light detected by the photodetector and the reference light. An ethane gas concentration measuring device comprising an arithmetic processing device for calculating a ratio with an electric signal to obtain an ethane gas concentration. 3. Light from a light source is input into an optical demultiplexer, and the entire amount of the incident light is transmitted sequentially through a first optical fiber with low transmission loss and an optical multiplexer to a measurement cell where atmospheric gas flows in and out. After passing through the measurement cell, the optical multiplexer, the first optical fiber, and the optical demultiplexer are fed back from the second optical fiber to the optical demultiplexer and detected by a photodetector, and the concentration is determined by absorption photometry. 1.64, which is the characteristic absorption wavelength band of ethane gas.
A light whose center wavelength is at least one wavelength within the wavelength band of ~1.71 μm is used as the measurement light, a light whose center wavelength is at least one wavelength outside the characteristic absorption wavelength band is used as the reference light, and the measurement light and the A method for measuring ethane gas concentration, characterized in that the concentration is measured by detecting a reference light with the photodetector and determining the intensity ratio thereof. 4 1.64~ which is the characteristic absorption wavelength band of ethane gas
a light emitting source that emits light in a wavelength range that includes at least wavelengths in the wavelength range of 1.71 μm;
an optical demultiplexer into which light from the light emitting source enters and outputs it to one end of a first optical fiber with low total transmission loss; an optical multiplexer to which the other end of the first optical fiber is connected; A measurement cell into which the light from the optical multiplexer enters and into which atmospheric gas flows in and out; and a second optical fiber with low transmission loss, the other end of which transmits the light from the measurement cell, is connected to the optical multiplexer. , the center wavelength of the light sent back from the measurement cell to the second optical fiber, optical multiplexer, first optical fiber, and optical demultiplexer is at least one wavelength within the characteristic absorption wavelength band. A spectrometer that splits the light into a measurement light and a reference light whose center wavelength is at least one wavelength outside the characteristic absorption wavelength band, and a photodetector that detects the measurement light and the reference light split by the spectrometer. 1. An ethane gas concentration measuring device, comprising: an ethane gas concentration measuring device; and an arithmetic processing device for calculating the ratio of the electrical signal of the measurement light detected by the photodetector and the electrical signal of the reference light to obtain the ethane gas concentration. 5 1.64~ which is the characteristic absorption wavelength band of ethane gas
A laser diode that emits light that serves as a measurement light having a center wavelength of at least one wavelength in the 1.71 m wavelength band, and a light that serves as a reference light that has a center wavelength of at least one wavelength outside the characteristic absorption band. A light emitting source consisting of a laser diode, a measuring cell through which atmospheric gas flows in and out, a first optical fiber with low transmission loss for transmitting light from the light emitting source to the measuring cell, and a first optical fiber with low transmission loss for transmitting light from the light emitting source to the measuring cell; a second optical fiber with low transmission loss for transmitting the second optical fiber; a photodetector for detecting the light transmitted by the second optical fiber; and measurement light alternately detected by the photodetector. An ethane gas concentration measuring device comprising: an arithmetic processing device for calculating the ratio between the electric signal of the reference light and the electric signal of the reference light to determine the ethane gas concentration. 6 1.64~ which is the characteristic absorption wavelength band of ethane gas
A laser diode that emits light serving as a measurement light having a center wavelength at least one wavelength in the 1.71 μm wavelength band, and light serving as a reference light having a center wavelength at least one wavelength outside the characteristic absorption band. A light emitting source consisting of a laser diode, and a first
An optical demultiplexer emitting light from one end of the first optical fiber, an optical multiplexer connected to the other end of the first optical fiber, and measurement in which light from the optical multiplexer enters and atmospheric gas flows in and out. a second optical fiber with low transmission loss, the other end of which transmits light from the measurement cell is connected to the optical multiplexer; the second optical fiber is closer to the measurement cell, the optical multiplexer; a first optical fiber and an optical demultiplexer, and a photodetector that detects the intensity of the measurement light and the reference light that are sent back, and an electrical signal of the measurement light and a reference that are alternately detected by the photodetector. An ethane gas concentration measuring device comprising an arithmetic processing device for calculating the ratio of light to an electrical signal to determine the ethane gas concentration.