JP2009063311A - Gas detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detection device having a simple constitution of an optical part, and dispensing with strict optical axis adjustment. <P>SOLUTION: This gas detection device has a laser diode 1 for emitting laser light into an atmosphere of measuring object gas; a photodiode 2 for receiving the laser light, and converting it into an electric signal; an elliptically spherical reflector 8 facing to the laser diode 1 and the photodiode 2 across the gas atmosphere, for reflecting the laser light from the laser diode 1, and guiding it to the photodiode 2; and a gas concentration calculation means for calculating the concentration of the measuring object gas based on an output signal from the photodiode 2. The laser diode 1 is disposed so that its emission surface is positioned on one focal point of the elliptically spherical reflector 8, and the photodiode 2 is disposed so that its incident surface is positioned on the other focal point of the elliptically spherical reflector 8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas detector that measures the concentration of a gas to be measured by using light absorption by the gas when the gas to be measured is irradiated with laser light.

Conventionally, gas chromatography is known as a means for analyzing gas. However, the gas chromatography has a problem that the sampling time is as long as several tens of minutes and it takes a long time to analyze the gas.
In view of this, a gas detection device that detects the concentration of gas flowing in a pipe or container in real time has been proposed (see, for example, Patent Document 1).

  The gas detection device disclosed in Patent Document 1 includes a light source unit and a light receiving unit that are separated by a predetermined distance, passes laser light that is frequency-modulated by a semiconductor laser of the light source unit through the atmosphere of the measurement target gas, and transmits the transmitted light. The gas concentration of the measurement target gas is measured from the output signal when the light is received by the light receiving unit.

  In the gas detection device disclosed in Patent Document 1, when the laser light from the light source unit is reflected unnecessarily while passing through the measurement optical path and returns to the light source unit, the return light becomes noise and causes measurement errors. Therefore, it is necessary to give an angle to the light source and the optical component. FIG. 4 is a cross-sectional view of an optical unit of the gas detection device disclosed in Patent Document 1. In the optical unit 41a shown in FIG. 4, the laser light emitted from the light source side optical fiber 44a is reflected by the prism 51a, further reflected by the prism 51b, and enters the light receiving side optical fiber 44b. The laser light incident on the optical fiber 44b is guided to a light receiver (not shown). In this optical part 41a, the optical components exposed to the gas atmosphere are a glass plate 56 and a pair of prisms 51a and 51b arranged on the surface of the glass plate 56.

  In the optical unit 41a, as an anti-reflection measure, the incident angle from the optical fiber 44a on the light source side to the prism 51a is set to a predetermined angle (for example, 4) with respect to the vertical incidence (incident angle 0 °) on the incident surface of the prism 51a. It is slanted. At that time, the emission angle with respect to the reflecting surface of the prism 51b is the same as the incident angle, and the laser light incident on the prism 51a and the laser light emitted from the prism 51b are parallel to each other. This eliminates measurement noise components due to reflection (stray light).

JP 2007-1113948 A

  As described above, in the gas detection device disclosed in Patent Document 1, it is necessary to provide an angle between the light source and the optical component in order to prevent measurement error due to noise (self-coupling effect) of the return light. Since it is necessary to make the laser beam a thin beam in order to realize the resolution, there are problems that there are many parts and it is difficult to adjust the optical axis of the optical parts.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a gas detection device in which the configuration of the optical unit is simple and strict optical axis adjustment is unnecessary.

The gas detector of the present invention includes a light projecting unit that emits laser light into an atmosphere of a measurement target gas, a light receiving unit that receives the laser light and converts the laser light into an electrical signal, and the light projecting across the gas atmosphere. An ellipsoidal reflector that reflects the laser light from the light projecting means and guides it to the light receiving means, and a gas that calculates the concentration of the measurement target gas based on the output signal of the light receiving means Density calculating means, and the light projecting means is disposed such that its exit surface is positioned at one focal point of the elliptical spherical reflector, and the light receiving means has its incident surface having the elliptical spherical reflector. It is arrange | positioned so that it may be located in the other focus.
In one configuration example of the gas detection device of the present invention, the light projecting means includes a laser diode that emits the laser light, and a first light that emits light emitted from the laser diode into the gas atmosphere. The light receiving means receives a second optical fiber that receives the reflected light from the ellipsoidal reflecting mirror, and receives light from the second optical fiber and converts it into an electrical signal. The first optical fiber is disposed such that an exit surface thereof is positioned at one focal point of the elliptical spherical reflector, and the second optical fiber includes an incident surface thereof. Is arranged so as to be located at the other focal point of the elliptical spherical reflecting mirror.

  According to the present invention, the ellipsoidal reflecting mirror is provided so as to face the light projecting means and the light receiving means across the gas atmosphere, and the light projecting means is arranged so that the exit surface thereof is located at one focal point of the ellipsoidal reflecting mirror. By disposing the light receiving means so that the incident surface is positioned at the other focal point of the elliptic spherical reflector, the gas detection device can be configured with a simple optical unit and does not require strict optical axis adjustment. Can be realized.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A is a side sectional view of an optical part of the gas detection device according to the first embodiment of the present invention, FIG. 1B is a sectional view taken along line AA in FIG. (C) is the BB sectional drawing of FIG. 1 (A). The optical part of the gas detector of the present embodiment includes a laser diode 1 that emits laser light, a photodiode 2 that receives the laser light and converts it into an electrical signal, and a bottom part of a container into which a gas to be measured flows. A bottom member 3, a top member 4 constituting the top surface of the container, a side member 5 constituting the side of the container, a holder 6 for fixing the laser diode 1 to the top member 4, and a photodiode 2 And a holder 7 fixed to the upper surface member 4. The laser diode 1 constitutes light projecting means, and the photodiode 2 constitutes light receiving means.

The bottom surface member 3 is formed with an elliptical spherical reflecting mirror 8 that is concave with respect to the top surface of the container in which the laser diode 1 and the photodiode 2 are disposed.
The side member 5 fixes the top member 4 on the bottom member 3 with a predetermined distance. Further, the side member 5 is formed with a vent hole 9 serving as an inlet of the container and a vent hole 10 serving as an outlet of the container.

  The laser diode 1 is fixed to the upper surface member 4 by the holder 6, and the photodiode 2 is fixed to the upper surface member 4 by the holder 7. At this time, the laser diode 1 is fixed so that its emission surface is located at one focal point f1 of the elliptical spherical reflecting mirror 8, and the photodiode 2 has its incident surface at the other focal point f2 of the elliptical spherical reflecting mirror 8. It is fixed to be positioned. The laser diode 1 is connected to a laser driver described later via an electric wire 11, and the photodiode 2 is connected to a signal detection unit described later via an electric wire 12.

FIG. 2 is a block diagram illustrating a configuration of a detection unit of the gas detection device according to the present embodiment. The detection unit of the gas detection device includes a laser driver 13, a signal detection unit 14, a gas concentration calculation unit 15, and a display unit 16.
Next, operation | movement of the gas detection apparatus of this Embodiment is demonstrated using FIG. 1, FIG. The gas to be measured flows into the container through the vent hole 9, flows in the direction of the arrow 17 in FIG. 1A, and flows out of the container from the vent hole 10.

The laser driver 13 emits frequency-modulated laser light from the laser diode 1. At this time, the laser driver 13 controls the laser diode 1 so that the oscillation center wavelength of the laser light coincides with the measurement wavelength (absorption line wavelength) of the measurement target gas. The light projecting means may be configured to emit laser light that is frequency-modulated to a wavelength that includes at least the absorption line of the gas to be measured.
The laser light emitted from the laser diode 1 passes through the gas atmosphere in the container, is reflected by the elliptic spherical reflector 8, passes through the gas atmosphere again, and enters the photodiode 2. When passing through the gas atmosphere, the laser beam is absorbed by the gas.

The photodiode 2 converts the received reflected light into an electrical signal. The signal detection unit 14 converts the output current of the photodiode 2 into a voltage and amplifies it, and a fundamental wave signal having a modulation frequency of the laser diode 1 and a double wave signal having a frequency twice that of the fundamental wave signal from the amplified signal. And phase sensitive detection.
Then, the gas concentration calculation unit 15 calculates the concentration of the gas to be measured based on the intensity ratio between the fundamental wave signal and the second harmonic signal. Since the intensity ratio between the fundamental wave signal and the second harmonic signal is proportional to the gas concentration, the gas concentration can be calculated from this ratio. The calculation result of the gas concentration calculation unit 15 is displayed on the display unit 16.

  In the gas detection apparatus as described above, the optical path in the gas atmosphere needs to be a known constant value. In the present embodiment, the laser diode 1 is arranged at one focal point f1 of the elliptical spherical reflecting mirror 8, and the photodiode 2 is arranged at the other focal point f2, so that the elliptical spherical reflecting mirror 8 is arranged from the laser diode 1. The lengths of all optical paths that reach the photodiode 2 via the same path are the same.

  Also, with this arrangement, even if the position and angle of the laser diode 1 vary, no return light is geometrically generated to the laser diode 1, and all the light emitted from the laser diode 1 is another focal point. Gathered in the photodiodes 2 arranged in Therefore, it is not necessary to use collimated light in order to improve the light receiving sensitivity, and it is not necessary to incline the optical component at a predetermined angle in order to prevent return light noise, so that the optical axes of the laser diode 1 and the photodiode 2 can be changed. There is no need to adjust strictly.

That is, in this embodiment, it is not necessary to strictly adjust the tilt of the optical axis of the laser diode 1 (α, α ′ in FIG. 1), and the tilt of the optical axis of the photodiode 2 (β in FIG. 1) is strictly adjusted. There is no need to make adjustments. Further, if the accuracy of the optical axes of the laser diode 1 and the photodiode 2 is a general machining accuracy level, there is a slight displacement (d1, d2 in FIG. 1) of the laser diode 1 and the photodiode 2 in the optical axis direction. There is no problem.
In the present embodiment, since the elliptical spherical reflecting mirror 8 has a large area, it has good resistance to noise caused by dust adhering to the elliptical spherical reflecting mirror 8.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. 3A is a side sectional view of an optical part of a gas detection device according to a second embodiment of the present invention, FIG. 3B is a sectional view taken along line AA in FIG. 3A, and FIG. FIG. 3C is a cross-sectional view taken along the line B-B in FIG. 3A, and the same reference numerals are given to the same components as those in FIGS. 1A to 1C. 3A to 3C, 18 and 19 are optical fibers, and 20 and 21 are holders. The optical fiber 18 and a laser diode (not shown) constitute a light projecting means, and the optical fiber 19 and a photodiode (not shown) constitute a light receiving means.

  In the gas detection device of the present embodiment, light emitted from the laser diode is guided to the optical part by the optical fiber 18, and reflected light from the elliptic spherical reflector 8 is guided to the photodiode by the optical fiber 19. The optical fiber 18 is fixed to the upper surface member 4 by a holder 20, and the optical fiber 19 is fixed to the upper surface member 4 by a holder 21. At this time, the optical fiber 18 is fixed so that its exit surface is located at one focal point f1 of the elliptical spherical reflecting mirror 8, and the optical fiber 19 has its incident surface at the other focal point f2 of the elliptical spherical reflecting mirror 8. It is fixed to be positioned.

As in the first embodiment, the gas to be measured flows into the container from the vent hole 9, flows in the direction of the arrow 17 in FIG. 3A, and flows out of the container from the vent hole 10.
The light emitted from the laser diode is guided to the optical unit by the optical fiber 18, and the laser light emitted from the optical fiber 18 passes through the gas atmosphere in the container and is reflected by the ellipsoidal reflecting mirror 8, and again the gas. The light passes through the atmosphere and enters the optical fiber 19. The optical fiber 19 guides the reflected light from the elliptic spherical reflector 8 to the photodiode.

  The laser diode is connected to the laser driver 13 in FIG. 2, and the photodiode is connected to the signal detection unit 14. The configuration and operation of the detection unit are the same as those in the first embodiment. Thus, also in this embodiment, the same effect as that of the first embodiment can be obtained.

  The present invention can be applied to a gas detection device.

It is sectional drawing of the optical part of the gas detection apparatus which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the detection part of the gas detection apparatus which concerns on the 1st Embodiment of this invention. It is sectional drawing of the optical part of the gas detection apparatus which concerns on the 2nd Embodiment of this invention. It is sectional drawing of the optical part of the conventional gas detection apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser diode, 2 ... Photodiode, 3 ... Bottom member, 4 ... Upper surface member, 5 ... Side member, 6, 7, 20, 21 ... Holder, 8 ... Elliptical spherical reflector, 9, 10 ... Vent hole, 11 , 12 ... Electric wire, 13 ... Laser driver, 14 ... Signal detection unit, 15 ... Gas concentration calculation unit, 16 ... Display unit, 18, 19 ... Optical fiber.

Claims (2)

A light projecting means for emitting laser light into the atmosphere of the gas to be measured;
A light receiving means for receiving the laser beam and converting it into an electrical signal;
An elliptical spherical reflector that faces the light projecting means and the light receiving means across the gas atmosphere, reflects the laser light from the light projecting means, and guides it to the light receiving means;
Gas concentration calculating means for calculating the concentration of the measurement target gas based on the output signal of the light receiving means;
The light projecting means is arranged so that its exit surface is located at one focal point of the elliptical spherical reflector, and the light receiving means is such that its incident surface is located at the other focal point of the elliptical spherical reflector. A gas detection device arranged in The gas detection device according to claim 1,
The light projecting means includes a laser diode that emits the laser light, and a first optical fiber that emits light emitted from the laser diode into the gas atmosphere,
The light receiving means includes a second optical fiber that receives the reflected light from the elliptic spherical reflector and a photodiode that receives the light from the second optical fiber and converts it into an electrical signal. ,
The first optical fiber is disposed so that an exit surface thereof is positioned at one focal point of the elliptical spherical reflector, and an incident surface of the second optical fiber is the other of the elliptical spherical reflector. A gas detector arranged to be located at a focal point.

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