JPH0229980B2 - PUROPANGASUNODONOSOKUTEIHOHOOYOBISONOSOCHI - Google Patents

Description

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

Propane gas is used as a fuel gas for automobiles,
Although it is a useful gas that is widely used for general home cooking, etc., when handling this gas, if sufficient care is not taken to prevent leakage, serious accidents may occur. In fact, propane explosions in households and fires in tankers occur every year. It is desired to develop useful propane gas detection and alarm equipment for this disaster prevention measure.

Furthermore, when considering gas leak detection in LPG tanks, LPG tankers, etc., remote measurement from a central monitoring room is desired, and an essentially explosion-proof detection method that does not have an ignition source is essential.

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 is intended to reliably and quickly detect propane gas leakage and issue an alarm, and to ensure reliability even under severe measurement conditions. The purpose of the present invention is to provide a propane gas concentration measuring method and apparatus that have a high level of propane gas concentration, can perform real-time measurements, can be measured at extremely remote locations, and are completely free from the danger of inducing accidents.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The detailed content of the propane gas concentration measuring method and apparatus of the present invention will be explained 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, propane gas has wavelengths of 1.50 to 1.57 μm and 1.668 to 1.668 μm.
There is a characteristic absorption band in the broad wavelength band of 1.720μm band. Furthermore, a narrow wavelength range in which there is almost no absorption of light by water vapor H ₂ O and carbon dioxide gas CO ₂ can be selected within the above-mentioned characteristic absorption band of propane gas.

The present invention has been made based on the above new findings. In other words, by selecting a wavelength range that is within the characteristic absorption band of propane gas, where there is little loss due to the optical fiber during transmission, and which is hardly affected by H ₂ O or CO ₂ , The purpose of the invention is to make it possible to accurately and quickly measure the concentration of propane 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 wavelengths 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 propane gas in a remote location by spectrophotometry.

Figures 2 to 5 show the characteristic absorption of propane gas, which is the subject of the present invention.
The figure shows the case where the propane gas pressure is 200 Torr and the length of the measuring cell is 50 cm. Figures 3 and 5 are when the propane gas pressure is 1 atm and the length of the measuring cell is 50 cm. Of these figures, FIGS. 2 and 3 show that the characteristic wavelength band of propane gas is one broad wavelength band. Its area is 1.668 ~
1.720 μm (see Figure 2) and approximately 1.50-1.57 μm (see Figure 3). However, regarding the characteristic absorption wavelength band of approximately 1.668 to 1.720 μm, due to the relationship of the light emitting source,
Although measurements were only made up to 1.720 μm, it is estimated that the characteristic absorption band exists up to approximately 1.74 μm. For this reason, in FIG. 2, the measured area up to 1.720 μm is shown as a solid line, and the area beyond that is shown as a broken line.
In the present invention, 1.720μm revealed by measurement
is treated as the characteristic absorption band. Figures 4 and 5 show the second wavelength range shown as a broad wavelength band.
This is a diagram showing the actual absorption characteristics that are the basis for the graphs in Figures 3 and 3, and is the result of measurement using a spectrometer with a resolution of 0.5 nm or less.

As is clear from these figures, the
The characteristic absorption band of 1.668 to 1.720 μm has a maximum absorption rate of about 25% even at a propane gas pressure of 200 Torr, and is effective if used as a practical measurement wavelength band. On the other hand, the characteristic absorption wavelength band of 1.50 to 1.57 μm in FIG. 5 shows the transmittance when the measurement cell is filled with propane gas at 1 atm, and the absorption is small.
However, if you use a light source that emits strong light, and considering that the only light emission wavelength range of currently commercially available light sources is from visible light to about 1.55 μm, it should be used for measurement. It is a wavelength band.

As is clear from the considerations based on the measurement results of the characteristic absorption of propane gas described above, when measuring the concentration of propane gas by spectrophotometry, first the characteristic absorption of 1.668 to 1.720 μm or 1.50 to 1.57 μm Light having a center wavelength of at least one wavelength from one or both of the wavelength bands is selected as the measurement light, and when these lights pass through a measurement cell (detection cell) where propane gas is present, The concentration of propane gas can be detected from this absorption rate.
The light used at this time is a narrow wavelength band with the selected measurement wavelength as the center wavelength, for example, light in a narrow wavelength band of 1.68 to 1.69 μm or 1.53 to 1.54 μm selected by a band pass filter. be.

When measuring the concentration of propane gas by spectrophotometry using one or more lights at the measurement wavelength (narrow wavelength band) as described above, the characteristic absorption of propane gas is usually used as the reference wavelength (reference light). It is necessary to select from a wavelength range other than the wavelength ranges of 1.668 to 1.720 μm and 1.50 to 1.57 μm. In other words, it is necessary to select a reference wavelength from a wavelength range where light is not absorbed due to the presence of propane gas. For example, a wavelength range other than the characteristic absorption wavelength of propane gas, around 1.65, 1.75 μm, or 1.59 μm, which is in the vicinity thereof, and which is hardly affected by H ₂ O or CO ₂ may be selected as the reference wavelength. Furthermore, the characteristic absorption wavelength band of methane gas, which has a strong possibility of coexisting with propane gas, is 1.664 to 1.669 μm.
It is desirable to select a wavelength range excluding . That is, light in a narrow wavelength band whose center wavelength is one or more wavelengths in the above-mentioned wavelength bands may be selected as the reference light.

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, which has been determined in advance based on this and the known concentration of propane gas. The concentration of propane gas to be measured can be determined based on the relationship between and 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 propane gas, and by eliminating these sources of error, highly reliable measurements are possible, and it is also possible to detect extremely low concentrations of propane gas. It becomes possible.

FIG. 6 shows data obtained by measuring characteristic absorption at a wavelength of 1.69 to 1.72 μm when commercially available propane gas at 1 atmosphere is placed in a detection cell (measuring cell) with an optical path length of 50 cm.

In this figure, curve A shows the measured value when the inside of the measurement cell is vacuum, that is, there is no absorption by propane gas, and curve B shows the light intensity when commercially available propane gas is present at 1 atm. It is.

The graphs shown in Figures 2 to 5 show the values when data corresponding to curves A and B in Figure 6 are obtained, the ratio B/A is determined, and A = 1 is always set. be. If B/A is determined based on this FIG. 6, it will be seen that the absorption characteristics of propane gas for general household use also show a tendency similar to the characteristics shown in FIGS. 2 and 4. Therefore, it can be seen that by using the method of the present invention, it is possible to detect leaks of propane gas for general household use.

FIG. 7 shows an absorption wavelength characteristic curve of H ₂ O. As is clear from this figure, the strong absorption band of H ₂ O is from 1.350 to 1.350 at 1.2 to 1.7 μm.
It is concentrated in the 1.393μm wavelength band. Therefore, by excluding this wavelength band, measurement with less influence of H ₂ O becomes possible. Similarly, by using a wavelength band excluding the 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, if a silica glass-based optical fiber is used as an optical transmission line and the characteristic absorption wavelength bands of propane gas as shown in Figures 2 to 6 are utilized, propane gas can be transmitted to remote locations. H ₂ O (water vapor, moisture) and coexisting gas concentrations
Measurements can be made with high accuracy and reliability, with almost no effects from CO ₂ or optical loss in the optical transmission path.

Next, the apparatus of the present invention constructed based on the propane gas concentration measuring method of the present invention described in detail above will be explained.

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 propane gas will be explained. Light sources in this wavelength range are generally semiconductor laser diode LDs and light emitting diodes.
Examples include LEDs, discharge tubes (such as xenon lamps), and heating wires. In any case, it is desirable to emit light that covers the measurement wavelength range continuously or in a pulsed manner, and the higher the intensity of the emitted energy, the more low-concentration gas can be detected.

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 propane 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 propane gas concentration can 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 that will be described later. The transmission width of this band pass filter is generally wide, about 1 to several nm, and if the characteristic absorption wavelength range of the gas to be measured is narrower than this transmission width, it is disadvantageous in terms of efficiency. However, since the characteristic absorption wavelength band of propane gas is broad as described above, measurements can be carried out satisfactorily even with such a band pass filter.

FIG. 8 is a diagram schematically showing the intensity distribution of light after passing through a bandpass filter having a Gaussian distribution type transmission characteristic with a center wavelength of 1.684 μm and a half width of 5 nm. In this figure, the broken line represents the case where propane gas is contained at a pressure of 200 Torr in a measurement cell with an optical path length of 50 cm, and the solid line represents the case where propane 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 propane gas can be determined. This filter may have a half width of 3 nm or 10 nm, for example.

Next, each embodiment of the propane gas concentration measuring device of the present invention will be described. FIG. 9 is a diagram showing the configuration of a first embodiment of the propane 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 such as an LED, and 3 is a light emitting source of 1.65 μm (half-value width) emitted from the light source 1.
An optical transmission line 4 is made of a low-loss optical fiber (for example, a silica optical fiber) that transmits light (0.1 μm) through an optical coupler 2, and optical couplers 4b and 4b' are provided at both ends of a cylindrical body 4a. The cylindrical body 4a of the measuring cell 4 is made of porous sintered metal or plastic foam with a continuous pore structure to enable natural flow in and out of the atmospheric gas (measured gas). It is configured. Also, this measurement cell 4
As an example, one having an optical path length (distance between optical couplers 4b and 4b') of 50 to 100 cm is used. However, when the concentration of propane gas 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 made of a low transmission loss optical fiber, such as a quartz optical fiber, which transmits the light from the measurement cell 4 via an optical coupler 4b'; a beam splitter that splits the incoming light into a first beam 8 and a second beam 10;
Reference numeral 9 denotes a first band transmission filter placed in the first beam 8; 11 a beam splitter placed in the second beam 10 and splitting it into a third beam 12 and a fourth beam 13; , 14 is the third luminous flux 12
a second bandpass filter disposed in 15;
is a third bandpass 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, a first bandpass filter 9
The center wavelength of is 1.684 μm, the center wavelength of the second band pass filter 14 is 1.695 μm (conversely, the center wavelength of the first band pass filter 9 is 1.695 μm, and the center wavelength of the second band pass filter 14 is 1.684 μm). In other words, the wavelength is within the characteristic absorption wavelength band of propane gas and is selected as the measurement wavelength. Further, the third band pass filter 15 is configured to use a wavelength (reference wavelength) other than the characteristic absorption wavelength of propane gas, for example.
1.650μm is chosen. 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.
The first, second, and third photodetectors arranged in the optical paths 8, 12, and 13 are an avalanche photodiode APD, a photodiode PD (for example, a Ge semiconductor or a PbS detector), or the like. 19,2
0, 21 are amplifiers, 22 are each photodetectors 16, 1
Electrical signals from 7 and 18 are used to connect amplifiers 19 and 2, respectively.
This is an arithmetic processing device that performs calculations to determine the absorption ratio of propane gas and also the concentration of propane gas based on the signal amplified by 0.0 and 21.

In the first embodiment configured as described above, light from the light source 1 passes through the optical coupler 2 and is transmitted by the optical transmission line 3 and sent to the measurement cell 4. 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, it 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 1.684 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 then amplified by an amplifier 19 and then input to an arithmetic processing unit 22 .

Similarly, the third beam 12 separated by the beam splitters 7 and 11 is passed through the second band pass filter 14 and has a different measurement wavelength. Only light in a narrow band with a center wavelength of 1.695 μm is transmitted and received by the second photodetector 17 , and its output signal is amplified by the amplifier 20 and then input to the arithmetic processing unit 22 .

Further, 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 1.650 μm, which is the reference wavelength, is transmitted. 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 1.684μm and the reference wavelength is
The extinction ratio A ₁ of propane gas at 1.650 μm is determined. Based on the relationship between this and the absorption wave A ₀ determined in advance based on standard propane gas and the propane gas concentration P ₀ , the measured value of the propane gas concentration in the gas existing in the measurement cell is calculated by calculation processing. P ₁ is obtained.

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 of 1.695 μm and the reference wavelength of 1.650 μm is used to determine the wavelength of 1.695 μm. The extinction ratio A ₂ is determined,
Based on this calculation, the propane gas concentration P ₂
is obtained.

Two propane gas concentration measurements based on two different measurement wavelengths obtained in this way are compared, and if both are within the error range,
the average or maximum value of these values if desired,
The minimum value is displayed on the display 23 as the propane gas concentration at the measurement point. Also, if there is a deviation greater than a predetermined value between the two measured values, this deviation indicates that the measurement cell contains a gas other than propane gas, such as a hydrocarbon gas, and this deviation overlaps with the characteristic absorption wavelength of this gas. This may be due to the fact that the parts of the measuring device after the optical coupler 6, that is, the beam splitters 7, 11, the bandpass filters 9, 14, 15,
Photodetectors 16, 17, 18, amplifiers 19, 20,
21, 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.

FIG. 10 is a diagram showing the configuration of a second embodiment of the propane gas concentration measuring device of the present invention. In this second embodiment, the light exiting the measurement cell 4 and transmitted through the optical transmission path 5 is divided into three beams by an optical branching path 24, and each divided beam is sent to an optical coupler. 25, 26, 27 and the chopper 28 to the first, third, and second band transmission filters 9, 11.
5, 14 and is received by the first, third, and second photodetectors 16, 18, 17, and among the electrical signals from these photodetectors, the first photodetector 16 and the third
The electrical signals from the photodetector 18 are both sent to the amplifier 29.
The electrical signals from the second photodetector 17 and the third photodetector 18 are amplified by the amplifier 30 and then input to the signal processing device 22. This is in agreement with the first embodiment in this respect. The rest of the configuration is substantially the same as the first embodiment, so parts with the same functions are shown with the same reference numerals.

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 configure the device so that the propane gas concentration at multiple points can be measured simultaneously.

FIG. 11 shows a third embodiment of the propane gas concentration measuring device of the present invention. This third
The embodiment uses a microcomputer as a signal processing device, so that the light source 1 made of an LED emits pulse light rather than continuous light emission based on the signal from the signal processing device 22, and each band transmission filter 9 . This is different from the first and second embodiments described above in that it can be configured with only one. That is, the light from the light source 1 that emits pulses based on the signal from the arithmetic processing unit 22 passes through the measurement cell 4, is transmitted by the optical transmission line 5, passes through the optical coupler 6, and then is transmitted by the rotation of the rotation sector 31. At sequential time intervals, the light passes through the first band-pass filter 9 to the photodetector 16, passes through the second band-pass filter 14 to the photodetector 16, and passes through the third band-pass filter 15. and enters the photodetector 16. Based on this, photodetector 1
Electric signals corresponding to the measurement wavelength and the reference wavelength corresponding to the transmission band of each band pass filter are sequentially output from 6, amplified by an amplifier 19, and then input to the arithmetic processing unit 22. 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 propane gas concentration 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. 12 is a diagram showing a fourth embodiment of the propane gas concentration measuring device of the present invention. This fourth embodiment uses an LD as a light emitting source, and has a wavelength within the characteristic absorption wavelength of propane gas, for example.
First light emitting source 1 whose center wavelength of light emission is 1.695 μm
Two light emitting sources are used: a is the light source for the measurement wavelength, and the second light source 1b, whose center wavelength of light emission is 1.650 μm, which is a wavelength other than the propane gas characteristic absorption wavelength, is the light source for the reference wavelength. Band-pass filters (spectroscopes) such as multilayer interference filters
This embodiment differs from the other embodiments described so far in that it does not use a configuration.

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, the optical coupler 35, and the optical transmission line 3c. Furthermore, a synchronization 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 this synchronization signal generator 32 is inputted to the arithmetic processing unit 22, and the signal is detected using this signal. It is determined whether the signal from the device 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 concentration of propane gas. ing. The other configurations are substantially the same as the other embodiments.

Even if LEDs are used as the first and second light emitting sources 1a and 1b in this fourth embodiment, the propane gas concentration can be measured without using a band transmission 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 1.7μm and
By using light-emitting diodes with a center wavelength of 1.6 μm as a light source for measurement light and a light source for reference light, respectively, the measurement device having the configuration of the fourth embodiment can transmit propane gas (without using a bandpass filter). The concentration of 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. 13 shows the configuration of a fifth embodiment of the propane gas concentration measuring device of the present invention.

Since the purpose of the present invention is to measure propane gas concentration 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, an optical demultiplexer 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 13a shows measurement cell 4.
The resulting light is transmitted through the optical fiber 5' and inputted into the optical transmission line 3 via the optical multiplexer 37. After being transmitted using most of the optical transmission line 3 as the return path, the light is transmitted via the optical demultiplexer 36. The signal is sent to the photodetector side. In this way, by using only a small portion of the optical transmission line 5' which is the return path used in the first to fourth embodiments, most of the optical transmission line 3 which is the outgoing path is also used.

In FIG. 13b, 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 the example shown in FIG. 13b, 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 the propane gas concentration of the present invention, in the characteristic absorption wavelength band of propane gas, the absorption band of CO ₂ and H ₂ O is almost present in the wavelength range where the optical fiber has the lowest loss. Since the propane gas concentration is measured by selecting a narrow wavelength band that does not contain CO ₂ ,
Highly accurate measurement is possible with almost no influence from 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 centrally monitored. In addition, since the measurement uses spectrophotometry, real-time measurement is possible, and rapid response to changes in propane gas concentration is possible, making it highly practical, highly reliable, and highly reliable. We can provide precision equipment. 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]

Figure 1 is a graph showing the transmission loss of the silica optical fiber used in the present invention, Figures 2 and 3 are diagrams schematically showing the broad characteristic absorption band of propane gas, Figures 4 and 5. is a graph showing the actual characteristic absorption wavelength of propane gas in detail, Figure 6 is a graph showing measured values of commercially available propane gas, and Figure 7 is a graph showing H ₂ O.
FIG. 8 is a diagram showing the intensity distribution of light passing through a Gaussian distribution type band pass filter, and FIGS. 9 to 13 are diagrams showing the absorption wavelength characteristics of the device of the present invention, respectively. It is a figure showing the composition of a 5th example. 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 light flux, 14...Second band transmission filter, 15...Third band transmission filter, 16...First photodetector, 17...Second photodetector, 18...Third photodetection instrument, 19, 20, 21... amplifier, 22
...Arithmetic processing unit, 23...Display device, 25, 26, 2
7... Optical coupler, 28... Chopper, 29, 30...
Amplifier, 31...Rotating sector, 32, 33, 34
...Synchronizing 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. This method uses a photodetector to detect the concentration and spectrophotometrically detects the concentration, which is the characteristic absorption wavelength band of propane gas of 1.668-1.720 μm or 1.50-1.50 μm.
The light whose center wavelength is at least one wavelength within at least one wavelength band of 1.57 μm is used as the measurement light, and the light whose center wavelength is at least one wavelength outside the characteristic absorption wavelength band is used as the reference light. A method for measuring propane gas concentration, characterized in that the concentration is measured by detecting the measurement light and the reference light with a detector and determining a ratio thereof. 2 1.668, which is the characteristic absorption wavelength band of propane gas
A light emitting source that emits light in a wavelength range that includes at least wavelengths in the wavelength range of ~1.720 μm or 1.50 to 1.57 μm, and a measurement cell into which atmospheric gas flows in and out;
a first optical fiber with low transmission loss in the wavelength range used for transmitting light from the light emitting source to the measurement cell; and a first optical fiber with low transmission loss in the wavelength range for transmitting light from the measurement cell. another second optical fiber with a smaller wavelength, measurement light having a central wavelength of at least one wavelength within the characteristic absorption wavelength band of the light from the measurement cell transmitted by the second optical fiber, and a characteristic absorption wavelength band. a spectrometer that spectrally separates light having at least one wavelength as a center wavelength into a reference light in a wavelength band outside the absorption wavelength band; and a photodetector that detects the measurement light and the reference light spectrally separated by the spectrometer. , calculate the propane gas concentration by calculating the ratio of the electrical signal of the measurement light detected by the photodetector and the electrical signal of the reference light, and compare these propane gas concentrations to determine whether any interfering gas other than propane gas is detected. A propane gas concentration measuring device equipped with an arithmetic processing device that determines the presence or absence of a propane gas concentration. 3 All the light from the light source is transmitted through an optical demultiplexer, one optical fiber with low transmission loss, and an optical multiplexer to the measurement cell where atmospheric gas flows in and out,
After passing through the measurement cell, the method involves transmitting the light from the other optical fiber to the optical multiplexer, one optical fiber, and the optical demultiplexer, detecting with a photodetector, and detecting the concentration by spectrophotometry. So, the characteristic absorption wavelength band of propane gas is 1.668~1.720μm or 1.50~
The measurement light is light whose center wavelength is at least one wavelength within at least one wavelength within the 1.57 μm wavelength band, and the reference light is light whose center wavelength is at least one wavelength outside the characteristic absorption wavelength band. A method for measuring propane gas concentration, characterized in that the concentration is measured by detecting the measurement light and the reference light with a detector and determining a ratio thereof. 4 1.668, which is the characteristic absorption wavelength band of propane gas
A light emitting source that emits light in a wavelength range that includes at least a wavelength within the wavelength range of ~1.720 μm or 1.50 ~ 1.57 μm, and the light from the light emitting source is incident,
An optical demultiplexer outputs to one optical fiber with low total transmission loss, an optical multiplexer to which the other end of the optical fiber is connected, and light from the optical multiplexer enters, and atmospheric gas flows out. A measurement cell that enters the input cell and the other optical fiber with low transmission loss that transmits light from this measurement cell are connected to the optical multiplexer, and the light is sent back from the measurement cell via the optical demultiplexer. a spectrometer that splits the light into a measurement light whose center wavelength is at least one wavelength within the characteristic absorption wavelength band and a reference beam whose center wavelength is at least one wavelength outside the characteristic absorption wavelength band; A photodetector detects the measurement light and reference light separated by the spectrometer, and calculates the propane gas concentration by calculating the ratio between the electrical signal of the measurement light and the electrical signal of the reference light detected by the photodetector. A propane gas concentration measuring device comprising: a processing unit that calculates the propane gas concentration, and compares these propane gas concentrations to determine whether or not there is interference by a hydrocarbon gas other than propane gas. 5 1.668, which is the characteristic absorption wavelength band of propane gas
A laser diode that emits light to serve as measurement light having a center wavelength of at least one wavelength in the wavelength band of ~1.720 μm or 1.50 to 1.57 μm, and a reference having a center wavelength of at least one wavelength outside the characteristic absorption wavelength band. a light emitting source consisting of at least two laser diodes, including a laser diode that emits light as light, a measurement cell through which atmospheric gas flows in and out, and a transmission for transmitting the light from the light emission source to the measurement cell. a first optical fiber with low loss; a second optical fiber with low transmission loss for transmitting the light after passing through the measurement cell; and a light for detecting the light transmitted by the second optical fiber. What is claimed is: 1. A propane gas concentration measuring device, comprising: a detector, and measures the concentration by alternately detecting the measurement light and the reference light and determining an intensity ratio of the two. 6. The propane gas concentration measuring device according to claim 5, wherein the first optical fiber also serves as a part of the second optical fiber.