JPH0943141A - Gas detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detecting device which can detect a gas at a plurality of locations. SOLUTION: Optical pulses from an optical pulse generating device 1 are made to enter a first light branching device 5a and part of the pulses is introduced to a first light sending device 6a as first optical pulses. Of the first optical pulses discharged to a space as a first light beam 12a, a specific spectral component is absorbed by a gas when the gas exists in the space, received by means of a first light receiving device 7a, and converted into two kinds of optical pulses of first and second wavelength components by means of a first reflection type wavelength separator 3a, an optical pulse delaying device 4, and a second reflection type wavelength selecting separator 3b after passing through a first photocoupler 8a and a directional photocoupler 2 and the optical pulses arrive at a photodetector 9 with a time lag. The photodetector 9 converts the optical pulses into electric signals and the signals are successively sampled by means of a sampling circuit 10 and processed as signals by means of the a signal processing circuit 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multipoint gas detector which optically detects gas at a plurality of locations.

[0002]

2. Description of the Related Art Conventional gas detectors that optically detect gas include those that detect the spectral spectrum of the gas and those that detect the absorption of light of a specific wavelength by the gas.

FIG. 12 is a block diagram of the first prior art, FIG. 13 is a diagram when gas is not present, and FIG.
Diagram showing the spectrum in the presence of gas, Fig. 1
FIG. 5 is a diagram showing a difference between the spectrums of FIGS. 12 and 13. In the figure, 20 is a white light source, 21 is an optical transmitter, and 2
2 is a light beam, 23 is a light receiver, 24 is a spectroscope, and 25 is a signal processing circuit. This conventional technique is a gas detection device that detects a spectrum.

In FIG. 12, the output light of the white light source 20 is converted into a light beam 22 by a light transmitter 21 and emitted into a space, and this light beam 22 is received by a light receiver 23,
The spectroscope 24 performs spectroscopic measurement, and the signal processing circuit 25 processes the spectroscopic spectrum waveform of the spectroscope 24.

The spectrum shown in FIG. 13 when there is no gas between the light transmitter 21 and the light receiver 23 becomes the spectrum of the white light source 20 itself, and the light spectrum width is wide. On the other hand, the spectral spectrum shown in FIG. 14 in the presence of gas is the absorption of light of a specific wavelength.
When the difference between the two spectra is calculated by the waveform processing circuit 25, the result shown in FIG.
The spectrum shown in FIG. The type of gas and its concentration can be specified by detecting the wavelength at which the absorption spectrum is generated and quantifying the amount of absorption on this difference spectrum.

However, in this prior art, an expensive spectroscope 24 is used, and when the number of measurement target points is increased, not only the optical transmitter 21 and the photodetector 23 are plural, but Since it is necessary to use the spectroscope 24 as many as the measurement points, the cost thereof becomes enormous. Furthermore, since a white light source is used as the light source 20, the absolute intensity of the output light thereof is weak, which causes a problem in measurement accuracy.

FIG. 16 is a block diagram of the second prior art, FIG. 17 is a sampling output of an optical signal having a wavelength which is absorbed by gas, and FIG. 18 is a sampling output of an optical signal having a wavelength which is not absorbed by gas. FIG. In the figure, 30 is a high output optical pulse generator, 31 is a Raman fiber, 32 is an optical transmitter, 33 is a light receiver, 34 is a wavelength selective optical demultiplexer, 35a,
Reference numeral 35b is a photodetector, 36a and 36b are sampling circuits, and 37 is a signal processing circuit. This prior art is a gas detection that detects the absorption of light of a specific wavelength by gas, displays the change in the intensity of the light beam as a waveform on the time axis, and detects the presence or absence of gas between the light transmitter and the light receiver. Device, which is disclosed in Japanese Patent Laid-Open No. 6-
It is known from Japanese Patent No. 229915.

In FIG. 16, a high power optical pulse generator 2
Reference numeral 0 is a laser using a solid-state laser or a rare earth element-doped optical fiber. The Raman fiber 31 is a dispersion-shifted fiber or an optical fiber to which a metal element is added. The Raman fiber 31 causes a stimulated Raman scattering phenomenon by injecting high-power light, and outputs a broadband light or shifts a specific wavelength. is there.

The output light of the high-power optical pulse generator 30 is converted into a light beam 38 by a light transmitter 32 via a Raman fiber 31 and emitted into space, and this light beam 38 is received by a light receiver 33, From the received light beam 38, two lights having a wavelength λ _a with absorption of light by the gas and a wavelength λ _b without absorption of the gas are extracted by the wavelength selective separator 34. The light having the wavelength λ _a and the light having the wavelength λ _b are respectively detected by the photodetectors 35a and 3a.
Sampling circuit 3 converts the intensity of the electric signal at 5b.
The signals sampled by 6a and 36b are processed by the signal processing circuit 37.

In the sampling outputs shown in FIGS. 17 and 18, the intensity of the sampling output P _a corresponding to the optical signal of wavelength λ _a absorbed by gas corresponds to the optical signal of wavelength λ _b not absorbed by gas. Is lower than the intensity of the sampling output P _b .

The above-mentioned second prior art gas detector is
Although the presence or absence of gas is detected, the signal processing circuit 37 of FIG. 16 is modified so as to compare and calculate the intensities of the sampled signals and measure the intensity difference between the sampling outputs P _a and P _b. It is also possible to detect the gas concentration.

However, even when the second conventional technique is modified as described above, in order to detect a plurality of kinds of gases at the same time, the number of wavelengths to be used is determined according to the number of kinds of measurement target gases. Need to increase. Further, the wavelength-selective optical demultiplexer 34 has a large internal configuration because the number of wavelengths to be selected increases as the number of wavelengths to be used increases, resulting in a large size and high cost. At the same time, the photo detectors 35 and the sampling circuits 36 corresponding to the number of wavelengths to be used are also required, which causes a problem that the entire apparatus becomes very large and expensive.

When measuring a flammable gas in an explosive range of concentration, it is desirable to keep the energy of the light pulse as low as possible for safety. However, this conventional technique has a problem that the measurement sensitivity is sacrificed when the output of the optical pulse is reduced. Further, when handling a high energy light pulse, there is also a problem that high energy durability is required for all optical components to which the pulse is transmitted, resulting in an increase in cost.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and a gas detection device for detecting gas at a plurality of locations by using light having a plurality of wavelengths, and further, a plurality of types of gas detection apparatus. An object of the present invention is to provide a gas detection device capable of detecting a gas and improving safety against an explosive gas without lowering measurement sensitivity.

[0015]

According to a first aspect of the present invention, in a gas detector, an optical pulse generator is connected to the optical pulse generator, and the optical pulse is branched into m optical pulses. A light branching unit, m light transmitters connected to the light branching unit, which convert a light pulse into a light beam and emit the light beam into a space, and m light receiving units which receive the light beam emitted from the light transmitter unit. Device, an optical coupling unit connected to the m light receiving units, for coupling m light pulses, an optical directional coupler connected to the optical coupling unit, and the optical directional couplers in series. It is connected to the optical coupling part by being connected, and is connected between n reflection-type wavelength selective demultiplexers for separating an optical pulse into n different wavelengths from each other and the n reflection-type wavelength selective demultiplexers. N−1 optical pulse delay devices, and by connecting to the optical directional coupler. A photodetector coupled to the n reflection-type wavelength selective demultiplexers for converting light pulses into electric signals in a time-sequential manner; and a sampling circuit for sampling the output of the photodetectors on a time axis, The present invention is characterized by having a signal processing unit for processing the output of the sampling circuit and detecting the gas between the m light transmitters and the light receivers.

According to the second aspect of the present invention, in the gas detection device, an optical pulse generator, an optical branching unit connected to the optical pulse generator and branching the optical pulse into m optical pulses, The m optical directional couplers for each optical transmitter / receiver connected to the optical branching unit and the optical directional couplers for each optical transmitter / receiver are coupled to the optical branching unit to couple the optical pulses. M light transmitters / receivers for converting the light beam into a light beam and emitting the light beam to the space, receiving the return light of the light beam, m reflectors for reflecting the light beam as the return light, and the m light An optical coupling unit that is coupled to the m optical transmitters / receivers by being connected to the optical directional couplers for each of the transmitters / receivers, and couples the m optical pulses, and the optical direction connected to the optical coupling unit. Directional coupler and the optical directional coupler connected in series to the optical coupler. Is, n number of reflective wavelength selective separator for separating light pulses different in the n wavelengths from each other, the n
N-1 optical pulse delay devices connected between the reflection type wavelength selective demultiplexers, and coupled to the n reflection type wavelength selective demultiplexers by being connected to the optical directional coupler, One photodetector for converting an optical pulse into an electric signal in time sequence, a sampling circuit for sampling the output of the photodetector on the time axis, and m optical transmitters for processing the output of the sampling circuit And a signal processing unit for detecting the gas between the light receivers.

According to a third aspect of the present invention, in the gas detection device, an optical pulse generator, an optical directional coupler connected to the optical pulse generator, and a tandem connection to the optical directional coupler. By being connected to the optical pulse generator, and is connected between n reflection-type wavelength selective demultiplexers for separating an optical pulse into n different wavelengths and the n reflection-type wavelength selective demultiplexers. N−1 optical pulse delay devices, and the n optical pulse delay devices connected to the optical directional coupler.
And an optical branching unit which is coupled to the reflection type wavelength selective separators and branches the optical pulse into m optical pulses, and m units which are connected to the optical branching unit and convert the optical pulse into a light beam and emit it to the space. Optical transmitters, m light receivers for receiving the light beams emitted from the light transmitters, an optical coupling unit connected to the m light receivers for coupling m light pulses, A photodetector connected to the optical coupling section for converting the optical pulse into an electrical signal;
A sampling circuit for sampling the output of the photodetector on a time axis, and a signal processing unit for processing the output of the sampling circuit and detecting gas between m light transmitters and photodetectors. To do.

According to a fourth aspect of the invention, in the gas detection device, an optical pulse generator, an optical directional coupler connected to the optical pulse generator, and a tandem connection to the optical directional coupler. By being connected to the optical pulse generator, and is connected between n reflection-type wavelength selective demultiplexers for separating an optical pulse into n different wavelengths and the n reflection-type wavelength selective demultiplexers. N−1 optical pulse delay devices, and the n optical pulse delay devices connected to the optical directional coupler.
An optical branching unit which is coupled to the reflection type wavelength selective demultiplexer and branches the optical pulse into m optical pulses, and m optical transmitter / receiver-specific optical directional couplers connected to the optical branching unit. , M units that are coupled to the optical branching unit by being connected to the optical directional couplers for each optical transmitter / receiver, convert optical pulses into optical beams and emit them into space, and receive return light of the optical beams Optical transmitters / receivers, m reflectors that reflect the light beam as the return light, and the m optical transmitters / receivers are connected to the optical directional couplers. Coupled to the receiver,
An optical coupling unit for coupling m optical pulses, one photodetector connected to the optical coupling unit for converting the optical pulses into an electrical signal, and sampling for sampling the output of the photodetector on the time axis It is characterized by having a circuit and a signal processing unit for processing the output of the sampling circuit and detecting the gas between the m light transmitters and the light receivers.

According to a fifth aspect of the present invention, in the gas detection device according to any one of the first to fourth aspects, the light branching section is m-1 number of light branches for sequentially branching light pulses. Optical coupler, and the optical coupling section has m-1 optical couplers for sequentially coupling optical pulses.

According to a sixth aspect of the present invention, in the gas detection device according to any one of the first to fifth aspects, at least one of the reflection type wavelength selective separators is absorbed by a gas to be detected. The signal processing unit selectively separates the wavelengths that are not separated, and the signal processing unit intensifies the sampling output corresponding to the optical pulse of the wavelength absorbed by the detection target gas and the sampling output corresponding to the optical pulse of the wavelength not absorbed by the detection target gas. It is characterized by obtaining a ratio.

[0021]

FIG. 1 is a block diagram of a first embodiment of the present invention. FIG. 2 is a diagram showing a spectrum of light emitted from the optical pulse generator. FIG. 3 is a diagram showing a spectrum of light received when methane gas is present. 4, FIG. 5, and FIG. 6 are diagrams showing the spectra of incident light, reflected light, and transmitted light, respectively, of the prototype wavelength selective separator. FIG. 7 is a first explanatory diagram of sampling output corresponding to an optical signal, and FIG. 8 is a second explanatory diagram thereof. In the figure, 1 is an optical pulse generator, 2 is an optical directional coupler, 3a and 3b are first and second reflection type wavelength selective separators, 4 is an optical pulse delay device, 5a and 5b are first and first optical pulse delay devices. 2 optical branching devices, 6a, 6b and 6c are first to third optical transmitters, 7a, 7b and 7c are first to third optical receivers, and 8
a, 8b are first and second optical couplers, 9 is a photodetector, 10
Is a sampling circuit, 11 is a signal processing unit, and 12a, 12
Reference numerals b and 12c are first to third light beams. This embodiment is a gas detection device that can detect gas at three locations by using one photodetector 9 and one sampling circuit 10.

The overall structure will be described with reference to FIG. The optical pulse generator 1 is configured to operate via an optical transmission line such as an optical fiber.
It is connected to the first optical branching device 5a of branching type, and the first output is connected to the second optical branching device 5b of two branching type via the same optical transmission line. The second output of the first optical branching device 5a is connected to the first optical transmitter 6a via an optical transmission line. The first light beam 12a is emitted into the space from the first light transmitter 6a, the first light receiver 7a receives the first light beam 12a, and the first coupler is connected via the light transmission path. 8a
Is connected to the second input of.

Similarly, the second output of the second optical branching device 5b is connected to the second optical transmitter 6b via the optical transmission line. The second light beam 12b is emitted into the space from the second light transmitter 6b, and the second light receiver 7b receives the second light beam 12b and then the second coupler via the optical transmission line. 8b
Is connected to the second input of.

The first branch output of the second optical branching device 5b is
It is connected to the third optical transmitter 6c via an optical transmission line. The third light beam 12c is emitted from the third light transmitter 6c into the space, and the third light receiver 7c receives the third light beam 12c.
c of the second coupler 8b is received via the optical transmission line.
Connected to the input of.

The output of the second optical coupler 8b is connected to the first input of the first optical coupler 8a via the optical transmission line, and the output of the first optical coupler 8a is connected to the optical transmission line. Connected to the first port of the optical directional coupler 2 via the optical directional coupler 2
The second port of is connected to the first reflection type wavelength selective demultiplexer 3a which reflects only the light of wavelength λ ₁ through the optical transmission line, and the first reflection type wavelength selective demultiplexer 3a is It is connected to the second reflection type wavelength selective demultiplexer 3b which reflects only the light of wavelength λ ₂ via the delay device 4. Optical directional coupler 2
The third port of is connected to the photodetector 9 via the optical transmission line, and the electric signal output of the photodetector 9 is connected to the signal processing unit 11 via the sampling circuit 10.

FIG. 1 is a block diagram of the gas detecting device when the number m of gas detecting points is 3, but when the number m of gas detecting points is 2, the number of gas detecting points may be increased. Similarly, m optical transmitters 6 and optical couplers 8 are provided in parallel, and optical branching devices 5 and optical receivers 7 are provided m-1 in accordance with the number of m which is an integer of 2 or more. .

The configuration of each part of the block diagram of FIG. 1 will be described. The optical pulse generator 1 generates a high output pulse, but the output intensity of the optical pulse is preferably as high as possible in order to improve the measurement sensitivity. Further, the wavelength spectrum is preferably spread in the wavelength range in which the light absorption of the gas to be measured exists, in particular,
It is desirable to have as broad a spectrum as possible when making measurements on many different gases.

As this specific example, for example, the same combination of the high output pulse generator 30 and the Raman fiber 31 in the second conventional technique can be used. That is, it is an optical pulse generator that combines an erbium-doped fiber and a fiber for generating stimulated Raman scattered light.

A wavelength of 148
When excited by a 0 nm pumping light source and oscillated by Q-switch, a light pulse having a spectrum in the wavelength range from 1530 nm to 1560 nm and having an output of several tens to several hundreds of watts can be obtained.

A fiber for generating stimulated Raman light scattering, for example, an optical fiber doped with GeO ₂ or P
_When input to an optical fiber doped with ₂ O ₅ or B ₂ O _{3 or} an optical fiber doped with another metal element, a nonlinear phenomenon represented by stimulated Raman scattering occurs in the optical fiber, and the type and length of the optical fiber Depending on the length, the spectrum of the light pulse is broadened to 1530 nm to 1700 nm, or a part of the energy of the light pulse is shifted to a specific wavelength. When a dispersion shift fiber is used as a fiber for generating stimulated Raman scattered light, an optical pulse generator 1
The output light spectrum of is as shown in FIG.

When there is a gas that absorbs light in the space between the light transmitters 6a-6c and the light receivers 7a-7c, the light receiver 7
The spectra in a to 7c are shown in FIG.
Will be shown in.

The optical directional coupler 2 has a first port and a second port.
It has only to have a directional coupling function of coupling the second port to the third port.

As the reflection type wavelength selective separator 3, a dielectric multilayer film filter, a fiber grating or the like is used.
In particular, the fiber grating is a Ge-doped optical fiber whose core portion is irradiated with an interference pattern of ultraviolet light having a wavelength of around 240 nm to form a striped refractive index change. It is excellent in terms of matching with optical fiber transmission lines and cost. Using a fiber grating, a reflective wavelength selective separator with a wavelength of 1667 nm was prototyped. With respect to the incident light spectrum shown in FIG. 4, the spectrum of reflected light is as shown in FIG. 5, and the spectrum of transmitted light is as shown in FIG.

As the optical pulse delay device 4, it is simplest and efficient to use a single mode optical fiber. For example, when using an optical pulse with a wavelength of 1550 nm to 1700 nm, a dispersion shift fiber is suitable in order to minimize an increase in transmission loss due to bending of the optical fiber itself.

The operation of this embodiment will be described. One pulse generated by the optical pulse generator 1 is incident on the first optical branching device 5a via the optical transmission line, and a part of the pulse is guided to the first optical transmitter 6a as a first optical pulse, The rest is second
To the optical branching device 5b. The first light pulse emitted into the space as the first light beam 12a from the first light transmitter 6a absorbs a specific spectral component when the gas is present in the space, and the first light receiver 7a. Is guided again to the optical transmission line.

When there is no gas that absorbs light in this space, the spectrum of the first light pulse received by the first light receiver 7a is emitted from the light pulse generator 1 shown in FIG. The pulse spectrum is almost the same. When there is a gas that absorbs light, for example, when there is methane gas, the spectrum of the first light pulse received by the first light receiver 7a has the largest light near the wavelength of 1667 nm shown in FIG. It is the absorbed spectrum.

This first optical pulse is transmitted to the first optical coupler 8
via a, it passes from the first port of the optical directional coupler 2 in the direction of the second port, and only the optical pulse of the first wavelength component λ ₁ is reflected by the first reflection type wavelength demultiplexer 3a. Then, the light travels backward in the optical transmission path, passes from the second port of the optical directional coupler 2 to the third port, and reaches the photodetector 9.

On the other hand, the optical pulse of the remaining wavelength component that has passed through the first reflection type wavelength selective demultiplexer 3a is guided to the optical pulse delay device 4 and is then transmitted by the second reflection type wavelength selective demultiplexer 3b.
Only the light pulse of the second wavelength component λ ₂ is reflected, and the light pulse of the remaining wavelength component is terminated by the non-reflection end, or if there is no non-reflection end, it passes through as it is and is emitted to the space. It The reflected optical pulse of the _second wavelength component λ ₂ passes through the optical pulse delay device 4 again, passes through the first reflection type wavelength demultiplexer 3a without being reflected, and then returns to the optical directional coupler 2 From the second port to the third port and reaches the photodetector 9.

First wavelength component λ ₁ and second wavelength component λ ₂
The two light pulses of 1 arrive at the photodetector 9 with a time difference, are converted into an electric signal corresponding to the light intensity by the photodetector 9, and are sequentially sampled by the sampling circuit 10.

On the other hand, a part of the optical pulse reaching the second optical branching device 5b is guided to the second optical transmitter 6b as a second optical pulse, and the rest is a third optical pulse. 3 to the optical transmitter 6c. The second light pulse emitted into the space as the second light beam 12b from the second light transmitter 6b is the second light receiver 7b, the second light combiner 8b, and the first light combiner 8b.
Of the second optical pulse and the second wavelength component of the second optical pulse having the first wavelength component λ ₁ of the second optical pulse and following the same path as the _first optical pulse. The light pulses of λ ₂ reach the photodetector 9 and are sampled by the sampling circuit 10.

The third light beam 1 from the third light transmitter 6c
The third light pulse emitted into the space as 2c is the third light receiver 7c, the second light combiner 8b, and the first light combiner 8a.
And then first follows the same path as the light pulse,
The optical pulse of the first wavelength component λ ₁ of the third optical pulse and the optical pulse of the second wavelength component λ ₂ of the third optical pulse reach the photodetector 9 and are sampled by the sampling circuit 10. It

In FIG. 7, the sampling output P ₁ corresponds to the optical pulse of the first wavelength component λ ₁ of the _first optical pulse, and thereafter, the second wavelength component λ of the first optical pulse. A sampling output P ₂ corresponding to ₂ light pulses arrives. The same applies to the sampling outputs corresponding to the second and third optical pulses, and in FIG. 8, the sampling outputs Q ₁ and Q ₂ are the _first and _second sampling pulses of the second optical pulse.
Corresponding to the optical pulses of the wavelength components λ ₁ and λ ₂ , and the sampling outputs R ₁ and R ₂ correspond to the optical pulses of the first and second wavelength components λ ₁ and λ ₂ of the third optical pulse.

In order to completely separate the sampling output of each first wavelength component λ _{1 from} the sampling output of each second wavelength component λ ₂ in each of the first to third optical pulses, an optical pulse delay device The length of the optical fiber of 4 is L _d
And then, the width of the optical pulses in the optical fiber as L _p, may be the _{L d ≧ L p / 2 (} 1).

At this time, assuming that the arrival time difference between the optical pulse of the first wavelength component λ _{1 and} the optical pulse of the second wavelength component λ ₂ is T ₁ , the light speed in the optical fiber is c, and T ₁ = 2L It becomes _d / c (2). In FIG. 7, this arrival time difference T ₁ is shown on the sampling output.

On the other hand, the time difference T ₂ at which the first light pulse and the second light pulse having the same wavelength component reach the photodetector 9 is
This is in accordance with the optical path difference of the optical transmission path through which the first and second optical pulses pass, and similarly, the time difference between the second optical pulse and the third optical pulse having the same wavelength component reaching the photodetector 9. T ₃ depends on the optical path difference of the optical transmission path through which the second and third optical pulses pass. In FIG. 8, the arrival time differences T ₂ and T ₃ are shown on the sampling output. Since such arrival time differences T ₂ and T ₃ are usually larger than the width L _{p of the} optical pulse, it is possible to separate the optical pulses having the same wavelength component.

Next, the time difference between the different wavelength components of the first light pulse and the second light pulse reaching the photodetector 9 will be described. The block diagram of FIG. 1 is an example in which two reflection-type wavelength selective demultiplexers 3b and one optical pulse delay device 4 are provided to selectively demultiplex two wavelength components. However, n is an integer of 2 or more. , N general reflection type wavelength selective demultiplexers 3a to 3n and n-1 optical pulse delay circuits 4 will be considered.

In order to separate the sampling output of the optical pulse of the nth wavelength component λ _n of the first optical pulse and the sampling output of the optical pulse of the first wavelength component λ ₁ of the second optical pulse, The wavelength component of the second optical pulse after the optical pulse of the _nth wavelength component λ _n reflected by the nth reflection type wavelength selective separator for the first optical pulse passes through the first wavelength selective separator 3a. The optical pulse of λ ₁ may be configured to reach the first wavelength selective demultiplexer 3a.

In this case, assuming that the total length of the n-1 optical pulse delay units 4 is Ld _(TOTAL) , Ld _(TOTAL) = _Ld1 + _Ld2 + ... + Ld _(n-1) (3 ) And the first light pulse and the second light pulse are detected by the photodetector 9
Time difference T ₂ reaching the optical path and the total length L of the optical pulse delay device 4
_{d (TOTAL)} must satisfy the following equation. However, the width L _{p of the} optical pulse is ignored as it is sufficiently smaller than L _{d (TOTAL)} . T ₂ > 2 × L _{d (TOTAL)} / c (4) Time difference T _{3 at which} the second optical pulse and the third optical pulse reach the photodetector 9 and the total length L _{d (TOTAL) of the} optical pulse delay device 4
Similarly, it is necessary to satisfy the following equation. T ₃ > 2 × L _{d (TOTAL)} / c (5)

When the above conditional expression is satisfied, as shown in FIG. 8, from the sampling circuit 10, the sampling output P ₁ corresponding to the optical pulse of the first wavelength component λ ₁ of the _first optical pulse, Similarly, a sampling output P ₂ corresponding to the optical pulse of the second wavelength component λ ₂ , a sampling output Q ₁ corresponding to the optical pulse of the first wavelength component λ ₁ of the second optical pulse, and the same second wavelength component λ sampling the output Q ₂ to which corresponds to the _second light pulses, corresponding to the third sampling output R ₁ corresponding to the first wavelength component lambda ₁ of the optical pulse of the optical pulse, likewise the second wavelength component lambda ₂ of the optical pulse The sampling output R ₂ is supplied to the signal processing unit 1 in this time order.
It is output to 1.

The order in which the light pulses of the respective wavelength components of the plurality of light pulses from the plurality of detection target locations reach the photodetector is not limited to the above example. For example, it may be set such that the optical pulse of the first wavelength component λ ₁ of each optical pulse arrives first, and then the optical pulse of the second wavelength component λ ₂ of each pulse arrives later. it can.
Even in this case, each wavelength component of each of the plurality of optical pulses may be temporally separated.

In the signal processing section 11, the sampling outputs which are temporally separated from each other are sequentially processed to detect the presence or absence of gas or the concentration in the three spaces where the light beams 12a, 12b and 12c are emitted. To do. The optical pulse generator 1 has a predetermined time interval,
A pulse can be generated periodically, and the signal processing unit 1
1 is to detect the presence or absence of gas or the concentration after performing statistical processing such as averaging of sampling signals of a plurality of light pulses detected by the photodetector 9 for each cycle for a plurality of cycles. However, in the following description, one pulse generated by the optical pulse generator 1 will be described to simplify the description.

In the first example of detecting the presence or absence of gas or detecting the concentration, the first wavelength component λ ₁ is the absorption wavelength peculiar to the first gas, for example, methane gas, and the second wavelength component λ ₂ Is set to a unique absorption wavelength of the second gas, for example, propane gas.

When there is no gas to be detected, the intensity of the sampling output corresponding to each of the optical pulse of the first wavelength component λ _{1 and} the optical pulse of the second wavelength component λ ₂ is measured in advance, and these are used as a reference. Store it as a value. During the gas detection operation, the intensities of the two measured sampling outputs are compared with individual reference values, and, for example, if the difference from the reference value is equal to or more than a predetermined value, it is determined that gas is present. And the presence of the second gas can be detected.

The gas concentration can be detected, for example, by theoretically obtaining the difference between the reference value and the gas concentration in advance. Alternatively, the intensity of the sampling output may be measured in advance for each gas concentration, the correlation between the two may be stored, and the concentration may be detected from the measured intensity of the sampling output based on the stored correlation.

To further increase the sensitivity of the detection device,
It is necessary to constantly correct temporal changes in the optical pulse intensity of the optical pulse generator 1, temporal characteristic variations of various components in the transmission path, temporal changes in the sensitivity of the photodetector 9, and the like. There is.

Therefore, as a second example of detecting the presence or absence of gas or detecting the concentration, the first wavelength component λ ₁ is the wavelength absorbed by the gas, and the second wavelength component λ ₂ is not absorbed by the gas. Set to the wavelength.

When there is no gas, the intensity ratio of the sampling output corresponding to each of the optical pulses of the first wavelength component λ ₁ and the second wavelength component λ ₂ is measured in advance and stored as a reference value. To do. After that, the presence or absence of gas can be detected by comparing the intensity ratio of the two measured sampling outputs with a reference value.

The gas concentration can be accurately detected by, for example, theoretically obtaining the correlation between the gas concentration and the intensity ratio of the sampling output. Alternatively, the intensity ratio of the sampling output is measured in advance for each gas concentration and the correlation is stored in advance,
It is also possible to detect the concentration based on the stored correlation from the intensity ratio of the two measured sampling outputs.

The sampling output of FIG. 8 described above is, as an example, the first sampling output of the device configuration of the block diagram of FIG.
Absorption wavelength 166 peculiar to methane gas as the wavelength component λ ₁ of
7 shows the sampling output on the time axis when 7 nm is the wavelength 1658 nm that is not absorbed by methane gas as the second wavelength component λ ₂ .

The detection of the presence or absence of gas and the detection of concentration are
They may be performed at the same time, or the presence or absence of gas may be detected by detecting the concentration.

In the above description, the case where two reflection type wavelength selective demultiplexers 3a and 3b and one optical pulse delay device 4 are provided has been described. However, one reflection type wavelength demultiplexer and one One set or a plurality of sets of the combined optical pulse delay devices 4 may be connected to the second reflection type wavelength selective demultiplexer 3b in a predetermined number of columns. With such a cascade connection, more wavelength components are sequentially extracted, are made incident on the photodetector 9 with a time shift, and the sampling output corresponding to various wavelength components of the optical pulse is subjected to signal processing,
It is obvious that more kinds of gases can be detected.

In this case, n is an integer of 2 or more and n reflection type wavelength selective separators 3a to 3n are provided.
The optical pulse delay circuit 4 includes reflection type wavelength selective demultiplexers 3a to 3n.
N-1 pieces will be provided between them. The photodetector 9 is m
Light pulses of the 1st to nth wavelength components of the 1st to mth light pulses from the light receiver 7 at a certain position, that is, a total of n × m reflected by the reflection type wavelength selective separators 3a to 3n. Will be converted into electrical signals in time sequence. The signal processing unit 11 can detect the presence or absence of gas or the concentration of gas at m locations from the signal intensity or signal intensity ratio of sampling outputs corresponding to these light pulses.

In the second example of detecting the presence or absence of gas or detecting the concentration, the first wavelength component λ ₁ absorbed by the gas and the second wavelength component not absorbed by the gas are detected for plural kinds of gases. Although the wavelength component λ ₂ may be set individually, the second wavelength component λ ₂ common to at least two kinds of gases may be set.
Can also be set.

FIG. 9 is a block diagram of the second embodiment of the present invention. In the figure, the same parts as those in FIG. 15a, 15b, 15c are the first
To a third optical directional coupler for each optical transmitter / receiver, 13a, 1
3b and 13c are first to third optical transmitters / receivers, 14a,
14b and 14c are first to third reflectors. FIG.
Compared with the first embodiment described with reference to FIG. 8 to FIG. 8, regarding the emission and light reception of the light beams 12a to 12c, in the first embodiment, the light transmitters 6a to 6c and the light receivers 7a to 7c. In this embodiment, the optical transmitters / receivers 13a to 13c and the reflectors 14a to 1 are used.
4c, the optical directional couplers 15a to 15c for each light transmitting and receiving device are used. Optical directional couplers 15a to 15
15c couples the first port to the second port and
It has only to have a directional coupling function of coupling the above port to the third port.

The first optical pulse branched by the first optical branching / coupling device 5a is the optical directional coupler 1 for each first optical transmitter / receiver.
5a passes from the first port to the second port and is guided to the first optical transmitter / receiver 13a, where the first light beam 12
It is released into the space as a. The first light beam 12a is reflected by the first reflector 14a to become return light, which is received by the first optical transmitter / receiver 13a and is then received by the second optical directional coupler 15a of the first optical transmitter / receiver. The light passes from the port toward the third port and is guided to the first optical coupler 8a. The same applies to the second light pulse and the third light pulse. Once the second and third light beams 12b and 12c are formed,
It is guided to the third optical couplers 8b and 8c. The subsequent operation is similar to that of the first embodiment described with reference to FIGS. 1 to 8.

FIG. 10 is a block diagram of the third embodiment of the present invention. In the figure, the same parts as those in FIG. Compared with the first embodiment described with reference to FIGS. 1 to 8, this embodiment has an optical directional coupler 2, first and second reflection type wavelength selective demultiplexers 3a and 3b, The optical pulse delay device 4 is connected after the optical coupler 8a in the first embodiment, whereas
In this embodiment, the optical pulse generator 1 is connected immediately after.

The first optical pulse generated by the optical pulse generator 1 passes from the first port of the optical directional coupler 2 toward the second port thereof, and is passed by the first reflection type wavelength demultiplexer 3a. Only the optical pulse of the first wavelength component λ ₁ is reflected, travels backward in the optical transmission line, passes from the second port of the optical directional coupler 2 toward the third port, and is transmitted to the optical branching device 5a. To reach.

On the other hand, the optical pulse of the remaining wavelength component that has passed through the first reflection type wavelength selective demultiplexer 3a is guided to the optical pulse delay device 4 and is then transmitted by the second reflection type wavelength selective demultiplexer 3b.
Only the light pulse of the second wavelength component λ ₂ is reflected, and the light pulse of the remaining wavelength component is terminated by the non-reflection end, or if there is no non-reflection end, it passes through as it is and is emitted to the space. It The reflected optical pulse of the _second wavelength component λ ₂ passes through the optical pulse delay device 4 again, passes through the first reflection type wavelength demultiplexer 3a without being reflected, and then returns to the optical directional coupler 2 To reach the second port of.

The optical pulses of the first wavelength component λ ₁ and the second wavelength component λ ₂ pass from the second port of the optical directional coupler 2 toward the third port, and the first light component is sequentially transmitted. Turnout 5
a and a part of each optical pulse is guided to the first optical transmitter 6a as a first optical pulse having the first wavelength component λ ₁ and the second wavelength component λ ₂ . The remaining part of each optical pulse is guided to the second optical branching device 5b. Each of the first light pulses includes a first light transmitter 6a and a first light receiver 7
a, passing through the first optical coupler 8a and reaching the photodetector 9.

On the other hand, a part of the optical pulse reaching the second optical branching device 5b is further converted into a second optical pulse having a first wavelength component λ ₁ and a second wavelength component λ ₂ , respectively.
To the optical transmitter 6b of the
Of the wavelength component λ ₁ and the second wavelength component λ ₂ of the third pulse are guided to the third optical transmitter 6c. Each second light pulse is emitted into the space as a second light beam 12b by the second light transmitter 6b, and the second light receiver 7b, the second light combiner 8b, and the first light combiner 8a. After that, the second optical pulse having the first wavelength component λ ₁ and the second wavelength component λ ₂ reaches the photodetector 9 after following the same path as the first optical pulse. The same applies to the third light pulse. Once the second light beam 12b is formed, the first wavelength component λ ₁
The third light pulse of the wavelength component λ ₂ of the light reaches the photodetector 9.

The subsequent sampling and signal processing are the first.
This is the same as the embodiment. In addition, in the case of this embodiment, since the wavelength component unrelated to the measurement is removed in advance, only the minimum energy is emitted into the space from each of the optical transmitters 6a to 6c without lowering the measurement accuracy. The Rukoto.

FIG. 11 is a block diagram of the fourth embodiment of the present invention. In the figure, the same parts as those in FIGS. Compared with the third embodiment described with reference to FIG. 10, this embodiment is different from the third embodiment in terms of emission and reception of the light beams 12a to 12c, and in the third embodiment, the light transmitters 6a to 6c. Light receiver 7a
7c are used, in this embodiment, as in the second embodiment described with reference to FIG. 9, the optical transmitters / receivers 13a to 13c, the reflectors 14a to 14c, and the optical receivers 13a to 13c. The optical directional couplers 15a to 15c for each of the light-transmitting and light-receiving devices are used.

The first optical pulses of the first wavelength component λ ₁ and the second wavelength component λ ₂ respectively branched by the optical branching device 5a are transmitted to the first optical directional coupler 15a for each optical transmitter / receiver. First
From the port to the second port, is guided to the first optical transmitter / receiver 13a, and is emitted into the space as the first light beam 12a. The first light beam 12a is reflected by the first reflector 14a to become return light, is received by the first light transmitter / receiver 13a, and is again transmitted via the first light transmitter / receiver 13a. The optical directional coupler 15a for each light receiver passes from the second port toward the third port and is guided to the first coupler 8a. On the other hand, the second optical pulse having the first wavelength component λ ₁ and the second wavelength component λ ₂ respectively branched by the second optical branching device 5b, and the first wavelength component λ ₁ and the second wavelength component The third light pulse of λ ₂ follows the same path and reaches the photodetector 9 with a predetermined time difference. Subsequent sampling and signal processing are the same as those in the first embodiment.

In each of the above-mentioned embodiments, the optical branching device 5a,
5b is used to branch one optical signal into two, and optical couplers 8a and 8b are used to combine two optical signals into one. However, depending on the number m of gas detection points, an optical branching section for branching m as a whole and an optical coupling section for m coupling again may be used. This optical branching unit may be composed of one optical branching device or a combination of a plurality of optical branching devices. The same applies to the optical coupling section.

For example, an optical branching device for branching one optical signal into three is used to output an optical pulse to the first to third optical transmitters 6a.
The optical pulses from the first to third photodetectors 7a to 7c may be combined by using an optical coupler that splits the optical signals into 6 to 6c and combines the three optical signals into one.

However, as described with reference to FIG.
It is necessary to provide an optical path difference between the optical transmission paths of the optical pulses so that the optical pulses passing through the respective gas detection points do not overlap in the photodetector 9. For that purpose, for example, an optical pulse delay device for giving an optical path difference may be appropriately inserted in an optical transmission line through which only the second optical pulse passes, an optical transmission line through which only the third optical pulse passes, and the like. Good.

In each of the above-described embodiments, at least one optical branching device 5 and at least one optical coupler 8 are used to detect gas at two or more locations, and at least one optical pulse is detected. The delay device 4 is used to detect two or more optical pulses having different wavelengths and perform signal processing. However, even if the optical branching device 5 and the optical coupler 8 are not used, the gas can be detected at one place. Further, even when the single reflection type wavelength selective separator 3 is used without the optical pulse delay device 4, the gas can be detected by detecting the optical pulse of one wavelength and processing the signal.

[0078]

As is apparent from the above description, according to the invention described in claims 1 to 4, the optical branching unit for branching the optical pulse into m optical pulses and the m optical pulses are combined. Since it has an optical coupling section, the optical pulse from the optical pulse generator becomes m optical pulses, passes between the optical transmitters and the optical receivers at m points, and reaches one optical detector. The required time depends on the length of each transmission line, but normally the lengths of these transmission lines do not match, so that m light pulses arrive at the photodetector with a time shift and are sampled. Therefore,
One set of the light source, the photodetector, and the sampling circuit can detect the gas at a plurality of locations, which is economical, and has the effect of reducing the size and weight.

Further, an optical directional coupler, n reflection type wavelength selective demultiplexers which are connected in series to the optical directional coupler and separate the optical pulse into n different wavelengths, and n
Since there are n-1 optical pulse delay devices connected between the reflective wavelength selective demultiplexers, a plurality of wavelength components are extracted and separated, and the time is delayed for each wavelength component. Each light pulse arrives at the photodetector at different times and is sampled at different times. Therefore, there is also an effect that one photodetector can detect the gas by the light pulse for each wavelength component.

According to the invention of claim 2 or 4,
An optical transmitter / receiver that is connected to an optical directional coupler for each optical transmitter / receiver, converts a light pulse into a light beam, emits the light beam into a space, and receives return light of the light beam; and the light beam as the return light. Since it has a reflector for reflecting it, there is an effect that a reflection type light beam can be formed at a place where gas is detected.

According to the invention of claim 3 or 4,
An optical directional coupler connected to the optical pulse generator, and coupled to the optical pulse generator by being cascade-connected to the optical directional coupler to separate the optical pulse into n different wavelengths. Since it has n reflection-type wavelength selective demultiplexers and n-1 optical pulse delay devices connected between the n reflection-type wavelength selective demultiplexers, there are n wavelength selective demultiplexers and n-1. The optical pulse delay devices will be connected in cascade immediately after the optical pulse generator.

Therefore, it is possible to eliminate the wavelength component of the light not related to the detection of the gas in advance and emit it as a light beam. As a result, the energy of the light pulse emitted into the gas to be measured can be suppressed to the required minimum without lowering the measurement sensitivity, and the safety against explosive gas can be enhanced. In addition, as a result of reducing the number of optical components through which high energy light pulses pass, there is an effect that inexpensive optical components that do not require high energy durability can be used.

According to the invention described in claim 5, the optical branching unit has m-1 optical branching devices for sequentially branching the optical pulse,
Since the optical coupling unit has m-1 optical couplers that sequentially couple the optical pulses, the length of the transmission path through which each of the m optical pulses passes is sequentially and reliably lengthened. Has the effect of reliably reaching the photodetector with a time shift and being sampled.

According to the sixth aspect of the invention, at least one of the reflection type wavelength selective demultiplexers selectively separates a wavelength which is not absorbed by the gas to be detected, and the signal processing unit absorbs the wavelength which is absorbed by the gas to be detected. In order to obtain the intensity ratio of the sampling output corresponding to the optical pulse of the optical pulse and the sampling output corresponding to the optical pulse of the wavelength that is not absorbed by the gas to be detected, the temporal change of the optical pulse intensity of the optical pulse generator, Since it is possible to constantly correct the temporal change of the optical signal intensity due to the temporal characteristic change of the parts, the temporal change of the sensitivity of the photodetector, etc., it is possible to increase the sensitivity of the detection device.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a spectrum of light emitted from an optical pulse generator.

FIG. 3 is a diagram showing a spectrum of light received when methane gas is present.

FIG. 4 is a diagram showing a spectrum of incident light of a prototype wavelength selective separator.

FIG. 5 is a diagram showing a spectrum of reflected light of a prototype wavelength selective separator.

FIG. 6 is a diagram showing a spectrum of transmitted light of a prototype wavelength selective separator.

FIG. 7 is a first explanatory diagram of sampling output corresponding to an optical signal.

FIG. 8 is a second explanatory diagram of sampling output corresponding to an optical signal.

FIG. 9 is a block diagram of a second embodiment of the present invention.

FIG. 10 is a block diagram of a third embodiment of the present invention.

FIG. 11 is a block diagram of a fourth embodiment of the present invention.

FIG. 12 is a block diagram of a first conventional technique.

FIG. 13 is a diagram showing a spectral spectrum in the absence of gas.

FIG. 14 is a diagram showing a spectrum in the presence of gas.

FIG. 15 is a diagram showing a difference between the spectrums of FIGS. 12 and 13.

FIG. 16 is a block diagram of a second conventional technique.

FIG. 17 is an explanatory diagram of sampling output of an optical signal having a wavelength absorbed by gas.

FIG. 18 is an explanatory diagram of sampling output of an optical signal having a wavelength that is not absorbed by gas.

[Explanation of symbols]

1 ... Optical pulse generator, 2 ... Optical directional coupler, 3a, 3
b ... 1st, 2nd reflection type wavelength selective demultiplexer, 4 ... Optical pulse delay device, 5a, 5b ... 1st, 2nd optical branching device, 6a, 6
b, 6c ... First to third light transmitters 7a, 7b, 7
c ... 1st thru | or 3rd light receiver, 8a, 8b ... 1st, 2nd
Optical coupler, 9 ... Photo detector, 10 ... Sampling circuit,
Reference numeral 11 ... Signal processing unit, 12a, 12b, 12c ... First to third light beams, 15a, 15b, 15c ... First to third optical transmitter / receiver-based optical directional couplers, 13a, 13
b, 13c ... First to third optical transmitter / receivers, 14a, 1
4b, 14c ... 1st thru | or 3rd reflector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsuro Senshiro 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka Within Osaka Gas Co., Ltd.

Claims (6)

[Claims] 1. An optical pulse generator, an optical branching unit that is connected to the optical pulse generator and branches the optical pulse into m optical pulses, and an optical branching unit that is connected to the optical branching unit to convert the optical pulse into a light beam. M light transmitters that convert and emit into the space, m light receivers that receive the light beam emitted from the light transmitters, and m light receivers that are connected to the m light receivers An optical coupling section for coupling, and an optical directional coupler connected to the optical coupling section,
N reflection-type wavelength selective demultiplexers, which are coupled to the optical coupling section by being connected in series to the optical directional coupler, to separate an optical pulse into n different wavelengths, and the n reflections N-1 optical pulse delay devices connected between the wavelength-type wavelength selective demultiplexers and the n-directional reflection type wavelength selective demultiplexers by being connected to the optical directional coupler to generate optical pulses. One photodetector for time-sequential conversion into an electrical signal, a sampling circuit for sampling the output of the photodetector on the time axis, and m optical transmitters and photodetectors for processing the output of the sampling circuit A gas detection device having a signal processing unit for detecting gas between the gas detection devices. 2. An optical pulse generator, an optical branching unit connected to the optical pulse generator and branching the optical pulse into m optical pulses, and m optical transmitters / receivers connected to the optical branching unit. An optical directional coupler for each device and an optical directional coupler for each optical transmitter / receiver, which is connected to the optical branching unit, converts an optical pulse into a light beam, and emits the light beam into a space. Connected to the m optical transmitters / receivers for receiving the return light, the m reflectors for reflecting the light beam as the return light, and the m optical transmitter / receiver-specific optical directional couplers. The optical coupling unit is coupled to the m optical transmitters / receivers to couple m optical pulses, the optical directional coupler is connected to the optical coupling unit, and the optical directional couplers are cascaded. N coupled to the optical coupling part by connecting to n to separate optical pulses into n different wavelengths. Reflection type wavelength selective demultiplexer, n-1 optical pulse delay devices connected between the n number of reflective type wavelength selective demultiplexers, and the n number of optical pulse delay devices connected to the optical directional coupler. , A photodetector coupled to the reflection type wavelength selective demultiplexer for time-sequentially converting an optical pulse into an electric signal, a sampling circuit for sampling the output of the photodetector on a time axis, and the sampling circuit A gas detection device having a signal processing unit for processing the output of the above and detecting a gas between m light transmitters and light receivers. 3. An optical pulse generator, an optical directional coupler connected to the optical pulse generator, and a tandem connection to the optical directional coupler to couple to the optical pulse generator, N reflection-type wavelength selective demultiplexers for separating an optical pulse into n different wavelengths, and n-1 optical pulse delay devices connected between the n reflection-type wavelength selective demultiplexers,
An optical branching unit that is coupled to the n reflection-type wavelength selective demultiplexers by being connected to the optical directional coupler, and branches an optical pulse into m optical pulses, and is connected to the optical branching unit.
M light transmitters for converting a light pulse into a light beam and emitting it into a space, m light receivers for receiving the light beam emitted from the light transmitters, and connected to the m light receivers, an optical coupling part for coupling m light pulses, and connected to the optical coupling part,
One photodetector for converting an optical pulse into an electric signal, a sampling circuit for sampling the output of the photodetector on a time axis, and m optical transmitters and photodetectors for processing the output of the sampling circuit A gas detection device having a signal processing unit for detecting gas between the gas detection devices. 4. An optical pulse generator, an optical directional coupler connected to the optical pulse generator, and a tandem connection to the optical directional coupler to couple the optical pulse generator to the optical pulse generator. N reflection-type wavelength selective demultiplexers for separating an optical pulse into n different wavelengths, and n-1 optical pulse delay devices connected between the n reflection-type wavelength selective demultiplexers,
An optical branching unit that is coupled to the n reflection-type wavelength selective demultiplexers by being connected to the optical directional coupler and that branches an optical pulse into m optical pulses, and is connected to the optical branching unit. The m optical directional couplers for each optical transmitter / receiver and the optical directional couplers for each optical transmitter / receiver are coupled to the optical branching unit to convert the optical pulse into a light beam and convert it into a space. Release
M optical transmitters / receivers for receiving the return light of the light beam,
M reflectors for reflecting the light beam as the return light, and m optical transmitter / receiver-specific optical directional couplers are connected to couple the m optical transmitters / receivers. An optical coupling part for coupling the optical pulses, one photodetector connected to the optical coupling for converting the optical pulses into an electric signal, and a sampling circuit for sampling the output of the photodetector on the time axis. And a signal processing unit for processing the output of the sampling circuit and detecting the gas between the m light transmitters and the light receivers. 5. The optical branching unit has m−1 optical branchers that sequentially branch optical pulses, and the optical coupling unit includes m−1 optical couplers that sequentially couple optical pulses. The gas detection device according to any one of claims 1 to 4, further comprising: 6. At least one of the reflection-type wavelength selective demultiplexers selectively separates wavelengths that are not absorbed by the detection target gas, and the signal processing unit responds to optical pulses of wavelengths that are absorbed by the detection target gas. 6. The gas detection device according to claim 1, wherein an intensity ratio between a sampling output that corresponds to the sampling output and a sampling output that corresponds to an optical pulse having a wavelength that is not absorbed by the detection target gas is obtained.