JP4460404B2 - Gas detector calibration device - Google Patents

Description

  The present invention relates to a gas detector calibration apparatus for calibrating a gas detector that detects a gas concentration in a measurement atmosphere in the atmosphere.

  It is already known that gases such as methane, carbon dioxide, acetylene, and ammonia have an absorption band that absorbs light of a specific wavelength according to molecular rotation, vibration between constituent atoms, and the like. Various types of gas detectors using this absorption band have been proposed. For example, in a gas concentration measuring apparatus having a gas detector disclosed in Patent Document 1 below, a laser beam frequency-modulated by a semiconductor laser of a light source unit is emitted toward a measurement atmosphere in the atmosphere where a gas to be measured exists. Then, the transmitted light that has passed through the measurement atmosphere as the laser light is emitted is received by the photo detector of the light receiving unit, and the gas concentration in the measurement atmosphere is measured from the received light signal.

  Here, a large offset due to intensity modulation occurs in a fundamental sensitive detection signal (hereinafter referred to as “1f signal”) having a modulation frequency detected from the output signal of the light receiving unit. For this reason, in order to measure a particularly minute gas concentration with high sensitivity, a second harmonic phase sensitive detection signal (hereinafter abbreviated as 2f signal) having a considerably smaller offset than the 1f signal is used.

  When actually measuring the gas concentration, if the measurement light with the wavelength matched to the measurement gas absorption line passes through the measurement atmosphere, the measurement light is absorbed by the measurement target gas, and the intensity corresponding to the concentration is twice the modulation frequency. Is generated, that is, 2f. Since the value of the intensity change ratio 2f / 1f between 2f and the original modulation frequency 1f is proportional to the gas concentration, the gas concentration is obtained by multiplying this value by a coefficient.

  By the way, this type of gas detector is not a sealed space, but passes a frequency-modulated laser beam to the measurement atmosphere in the atmosphere, and receives the laser beam absorbed in the measurement atmosphere to detect the gas concentration. It is the structure to perform. For example, when the measurement target gas is methane gas, the atmosphere contains about 2 ppm of methane gas, and the value also varies depending on the environment. For this reason, it is difficult to determine whether or not the gas concentration actually detected by the gas detector shows an accurate value. Therefore, in order to detect the gas concentration more accurately, it is necessary to calibrate the gas detector periodically.

Therefore, conventionally, when a gas detector is calibrated, for example, a gas cell in which a predetermined gas is sealed in a glass cylindrical tube having a small thermal shrinkage and a gas detector to be calibrated are set apart by a predetermined distance. And the gas concentration of a gas cell was measured with the gas detector, and the gas detector was calibrated with this measured value.
JP 2001-235418 A

  However, in the conventional gas detector calibration method, the detection result is difficult to stabilize due to the influence of variations such as the distance and orientation of the gas cell and the gas detection device, the atmospheric conditions, etc., and the gas sealed in the gas cell Concentrations also vary and it is difficult to perform accurate calibration. For this reason, provision of the apparatus which can calibrate a gas detector more correctly was desired.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a gas detector calibration device that can obtain an accurate gas concentration coefficient and can calibrate a gas detector more accurately. It is said.

In order to achieve the above object, the gas detector calibration apparatus according to claim 1 described in the present invention emits a laser beam whose frequency is stabilized to the gas absorption line into the atmosphere, and reflects the reflected light of the laser beam. A gas detector calibration apparatus 1 for calibrating a gas detector 3 that receives light and measures a gas concentration in the atmosphere,
The gas detector to be calibrated is disposed away from the position where the gas detector is placed along the optical axis CC of the laser beam generated by the gas detector by a predetermined length L0 or more, and is inclined with respect to the optical axis. A calibration gas cell 6 that is defined by a pair of transmission windows 21 and a peripheral wall that are provided and transmit a laser beam, and in which a detection gas having a predetermined concentration is filled.
Reflection means 27 for reflecting the laser light transmitted through the calibration gas cell from one of the pair of transmission windows to the other;
A purge means 4 for removing the gas to be detected from the optical path between the gas detector and the calibration gas cell is provided.

The gas detector calibration device according to claim 2 is the gas detector calibration device according to claim 1,
The purge means 4 has a cylindrical shape formed at both ends so as to surround the optical axis of measurement light that connects the gas detector 3 and the calibration gas cell so that the gas detector 3 and the calibration gas cell 6 are detachable. It has a tubular shape and is characterized in that the inside is held in a predetermined gas state.

The gas detector calibration device according to claim 3 is the gas detector calibration device according to claim 1,
In the calibration gas cell 6, an antireflection film is formed on the surface of the pair of transmission windows 21, and the pair of transmission windows are inclined at a predetermined angle θ with respect to the optical axis of the laser beam and have a predetermined interval L1. It is characterized by being arranged.

The gas detector calibration device according to claim 4 is the gas detector calibration device according to any one of claims 1 to 3,
The reflecting means 27;
An optical path length increasing / decreasing means 7 including a driving means 28 for driving the reflecting means so as to slightly increase / decrease the optical path length L of the laser light between the reflecting means and the gas detector 3 is provided. To do.

The gas detector calibration device according to claim 5 is the gas detector calibration device according to claim 4,
The reflecting means 27 is arranged such that the reflecting surface 27a is inclined at a predetermined angle with respect to the optical axis CC.
The driving means 28 is characterized in that the reflecting means is rotationally driven at a predetermined rotational speed.

The gas detector calibration device according to claim 6 is the gas detector calibration device according to claim 4,
The drive means 28 is characterized in that the reflection means 27 is finely driven in the direction of the optical axis CC.

The gas detector calibration device according to claim 7 is the gas detector calibration device according to any one of claims 1 to 6,
The reflection surface 27a of the reflection means 27 forms an irregular reflection surface.

  According to the gas detector calibration apparatus of the present invention, since the system in which the gas column density PL is determined is constructed, the undetermined gas concentration coefficient C can be determined and acquired from the determined gas column density PL. it can. If the determined gas concentration coefficient C is set in the gas detector 3 as a gas concentration coefficient parameter of the gas detector 3, the detected column density is calculated using the set gas concentration coefficient at the time of gas detection. By doing so, the calibrated gas concentration can be obtained. As a result, the gas concentration measurement value of the gas detector can be calibrated accurately in a short time compared to the conventional case.

  According to the gas detector calibration apparatus of the second aspect, since the atmospheric pressure in the purge pipe 5 is kept higher than the outside, it is possible to prevent extra gas from entering from the outside.

  According to the gas detector calibration apparatus of the third aspect, it is possible to prevent the influence of the reflection of the laser light and the interference of the laser light when the laser light passes through the transmission window 21.

  According to the gas detector calibration apparatus of the fourth to sixth aspects, the distance L between the light projecting / receiving surface of the gas detector 3 and the reflecting surface 27a of the reflecting plate 27 is slightly changed, so that the gas detector 3 and the reflecting plate are changed. The laser beam can be prevented from interfering with the laser beam 27 without resonating with the laser beam 27.

  According to the gas detector calibration apparatus of the seventh aspect, the laser beam transmitted through the calibration gas cell 6 can be irregularly reflected and reflected again to the calibration gas cell 6.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of a gas detector calibration device according to the present invention, showing a state in which a gas detector to be calibrated is attached, and FIG. 2 is a diagram of the gas detector calibration device of FIG. FIG. 3 is a cross-sectional view of the calibration standard gas cell.

  In particular, the gas detector calibration device of this example is not a sealed space, but the atmosphere including a measurement target gas such as methane gas is used as a measurement atmosphere, and the frequency of the gas absorption line is stabilized in the measurement atmosphere. Suitable for calibrating a gas detector that emits laser light and receives reflected light of the laser light absorbed in the measurement atmosphere to measure the gas concentration of the measurement target gas contained in the measurement atmosphere .

  As shown in FIG. 1, a gas detector calibration apparatus 1 includes a gas detector 3 to be calibrated, a purge pipe 5 that is a component of the purge means 4, a calibration gas cell 6, and a reflection mechanism 7 as an optical path length increasing / decreasing means. Is placed on the base 2 forming the main body. Hereinafter, each structure of the base 2, the purge means 4, the calibration gas cell 6, and the reflection mechanism 7 will be described with reference to the drawings.

  First, although not shown in detail, the base 2 includes, for example, a plurality of support members 2a for supporting the gas detector 3, the purge pipe 5, the calibration gas cell 6, and the reflection mechanism 7, and this support member 2a. Is movably provided with respect to the rail-shaped guide member 2b. In the example of FIG. 1, the calibration gas cell 6 is installed on the right side of the base 2, the gas detector 3 is mounted on the left end of the purge pipe 5, and the calibration gas cell 6 is mounted on the right end of the purge pipe 5. It is supported by the support member 2a. Further, the reflection mechanism 7 is supported by the support member 2a at a predetermined distance on the right side of the calibration gas cell 6. As a result, the components are positioned and arranged on the base 2 in the order of the gas detector 3, the purge pipe 5, the calibration gas cell 6, and the reflection mechanism 7 from the left in FIG. 1. The calibration gas cell 6 is disposed on the control box 8. In the control box 8, a controller for controlling the operation of the driving means 28 described later is housed.

  Next, the purge means 4 has an optical axis CC of the laser beam (measurement light) connecting the gas detector 3 and the calibration gas cell 6 so that the gas detector 3 and the calibration gas cell 6 are detachably attached to both ends (see FIG. A cylindrical shape formed so as to surround a broken line 1), and the inside is maintained in a predetermined gas state by a purge gas.

  More specifically, as shown in FIG. 1, the purge unit 4 includes a cylindrical purge pipe 5 and a purge gas cylinder 12 connected to the purge pipe 5 via a pipe 11. The purge pipe 5 is formed in a cylindrical shape by, for example, acrylic or glass, and the gas detector 3 is inserted and attached to one of both end openings, and the calibration gas cell 6 is inserted and attached to the other. The purge gas cylinder 12 is filled with, for example, inexpensive nitrogen gas (not including standard gas) as the purge gas. Further, the purge gas cylinder 12 has a valve 12 a that opens and closes the pipe 11.

  The purge unit 4 supplies the nitrogen gas in the purge gas cylinder 12 to the purge pipe 5 through the pipe 11 by opening the valve 12a, and keeps the purge pipe 5 in a gas state by the purge gas. At this time, the gas detector 3 and the calibration gas cell 6 are attached to both ends of the purge pipe 5 by insertion, and even if there is a gap in these attachment parts, the purge gas in the purge pipe 5 escapes from the gap, Since the pressure in the purge pipe 5 is kept higher than the outside, it is possible to prevent extra gas from entering from the outside. As a result, the purge pipe 5 only needs to have a shape in which the gas detector 3 and the calibration gas cell 6 can be inserted and held at both ends, and the purge pipe 5 itself can be easily manufactured.

  The inner diameter of the opening at both ends of the purge pipe 5 is appropriately determined according to the outer diameter of the light projecting / receiving portion of the gas detector 3 to be inserted and the outer diameter of the calibration gas cell.

  Further, the purge pipe 5 can be formed as an anti-reflection surface by forming the inner surface of, for example, a black matte surface. Thereby, when the laser beam passes through the purge tube 5, it is possible to suppress the inner surface of the purge tube 5 from being reflected as a mirror surface.

  Next, as shown in FIG. 3, the calibration gas cell 6 is formed with a gas atmosphere length L1 of, for example, 100 mm and an inner diameter L2 of, for example, 80 mm or more. The calibration gas cell 6 uses, as a cell body 6a, a cylindrical member made of a metal such as aluminum or glass having a small heat shrinkage. As shown in FIGS. 2 and 3, two hollow joints 13 and 14 having valves 13a and 14a, respectively, are attached to the upper portion of the cell body 6a. These two joints 13 and 14 have base end portions 13b and 14b communicating with the inside of the cell body 6a. Moreover, the front-end | tip part 13c of the coupling 13 is connected to the vacuum pump 16 via the pipe 15, as shown in FIG. Further, the tip end portion 14 c of the joint 14 is connected to a standard gas cylinder 18 through a pipe 17.

  The vacuum pump 16 evacuates the cell main body 6 a of the calibration gas cell 6 including the path of the pipe 17 to the standard gas cylinder 18. The standard gas cylinder 18 is filled with methane gas that has been accurately calibrated in advance as a standard gas. In the example of FIG. 1, the standard gas cylinder 18 is composed of three, and 1000 ppm, 2000 ppm, and 5000 ppm of methane gas are enclosed. The standard gas cylinder 18 is provided with a valve 18a for opening and closing between the pipe 17 and the standard gas cylinder 18, respectively. The standard gas filled in these standard gas cylinders 18 is supplied to the cell body 6a of the calibration gas cell 6 through the pipe 17 by opening any one of the valves 18a.

  A pair of glass windows 21 and 21 as transmission windows are attached to the opening ends 6b and 6b of the cell body 6a so that the laser light can pass therethrough. Each glass window 21 is formed of, for example, a wedge glass made of BK7. Each glass window 21 is attached to both ends 6b of the opening with an inclination of a predetermined angle θ (for example, around 10 °) with respect to the central axis (optical axis of the gas detector 3) CC. The surface of each glass window 21 is provided with an AR coating for a wavelength of 1.65 μm, for example, as an antireflection film 22. Further, a gasket 23 made of, for example, silicon rubber or the like for sealing the inside is disposed outside each glass window 21 at the opening both ends 6b. The pair of glass windows 21 and the gasket 23 are fixed by fixing means 24.

  In this example, the fixing means 24 includes a screw portion 24a having a screw formed at both ends 6b of the opening and an annular nut 24b having a screw formed on the outer periphery so as to be fastened to the screw portion 24a. The glass window 21 and the gasket 23 are fixed by fastening an annular nut 24b to the threaded portion 24a after being attached to the open ends 6b of the cell body 6a from the outside.

  Further, the cell body 6a is provided with a pressure sensor 25 as pressure detecting means for detecting the internal pressure within a range of, for example, 0 to 2 atmospheres. In this example, the internal pressure of the calibration gas cell 6 is normally set to 1 atm. The base 2 is provided with a digital display 26 as display means for displaying a pressure value based on a detection signal from the pressure sensor 25. Thus, the user can easily recognize the internal pressure of the calibration cell 6 by visually confirming the value displayed on the digital display 26.

  In the present example, the configuration in which the pressure sensor 25 is provided in the cell body 6a is illustrated, but a meter-type pressure gauge having an analog display function may be provided in the cell body 6a. In this case, a digital display as the display means 26 provided on the base 2 becomes unnecessary.

  The calibration gas cell 6 configured in this way is configured so that a standard gas (a gas to be detected) having a predetermined concentration is filled in a space defined by the pair of transmission windows 21 and the peripheral wall of the cell body 6a. . The calibration gas cell 6 has a predetermined length L0 (for example, 1000 mm) or more along the optical axis CC of the laser beam generated by the gas detector 3 from the position where the gas detector 3 to be calibrated is placed. Disposed on the base 2 at a distance.

  Next, the reflection mechanism 7 as an optical path length increasing / decreasing unit includes a reflection plate 27 as a reflection unit and a driving unit 28 that finely moves the reflection plate 27 in the direction of the optical axis CC of the laser light. The reflecting plate 27 reflects the laser beam that has passed through the calibration gas cell 6 from one of the pair of glass windows 21 through the other to the calibration gas cell 6 again. Further, in the reflection plate 27 in FIG. 1, the reflection surface 27a is inclined at a predetermined angle (for example, around 10 °) with respect to the optical axis CC of the laser beam. Further, the reflecting plate 27 is rotatably provided by the driving means 28, and the center of rotation is located slightly deviated from the optical axis CC.

  The driving means 28 rotates the reflecting plate 27 at a predetermined speed (for example, 600 rpm). The driving means 28 can be constituted by various motors, actuators, vibrators, and the like, for example. And the irradiation position of a laser beam changes by rotating the reflecting plate 27 inclined with respect to the optical axis CC by the drive means 28 by predetermined speed. Thereby, the distance L between the light projecting / receiving surface of the gas detector 3 and the reflecting surface 27a of the reflecting plate 27 changes minutely, and the laser beam does not resonate between the gas detector 3 and the reflecting plate 27. Laser beam interference can be prevented.

  In the reflection mechanism 7 in the example of FIG. 1, the reflection plate 27 is inclined by a predetermined angle with respect to the optical axis C-C, and the reflection plate 27 is rotated by the driving unit 28. However, the configuration is limited to this configuration. It is not a thing. For example, the reflecting surface 27a of the reflecting plate 27 is arranged perpendicularly to the optical axis CC, and the reflecting plate 27 is moved minutely in the direction of the optical axis CC by the driving means 28, so that the gas detector 3 and the reflecting plate 27 The distance L between the two can be slightly increased or decreased. The amount of movement of the reflecting plate 27 at that time may be slightly larger than the laser light at a distance different from the wavelength of the laser light to be used so that the phases of the light are not aligned. For example, if the wavelength of the laser beam to be used is 1 to 3 μm, the moving amount of the reflection plate 27 is 5 to 100 μm.

  In addition, the reflection surface 27a of the reflection plate 27 can be an irregular reflection surface formed of, for example, a minute uneven surface. As a result, the laser beam transmitted through the calibration gas cell 6 can be diffusely reflected and reflected again to the calibration gas cell 6. Further, the reflecting means is not limited to the reflecting plate 27, and may not be a plate shape as long as the reflecting surface 27a is provided on the side facing the glass window 21 of the calibration gas cell 6. .

Next, the calibration principle of the gas detector calibration apparatus 1 of this example will be described.
The gas detection method of the gas detector 3 emits gas measurement laser light, receives weak laser light reflected from the measurement object, analyzes the light reception signal, and detects the gas column density in the optical path.

  If a measurement gas having a partial pressure P is present in the measurement optical path and the measurement optical path length is L, Ir = IR (exp (−αPL)). In Equation 1, Ir: received laser beam intensity, I: emitted laser beam intensity, R: attenuation of measurement light, α: absorption coefficient of measurement gas, P: partial pressure of measurement gas, L: measurement optical path length is there.

The emitted laser beam intensity I is expressed as I = I ₀ + I ₁ cos (2πft + φ) (2) (where I _{0 is} bias laser beam intensity, I _{1 is} modulated laser beam intensity, f is modulation frequency, φ is modulation phase), The emission laser beam frequency ω is set to ω = ω ₀ + ω ₁ cos (2πft + φ ′) Equation 3 (where ω is the emission laser beam wavelength, ω _{0 is the} bias laser beam wavelength, ω _{1 is the} modulated laser beam wavelength half-width, f: If αPL and ω ₁ / Δω take a value sufficiently smaller than 1, the detection 1f intensity and the detection 2f intensity are obtained by performing Fourier expansion of Equation 1 when αPL and ω ₁ / Δω have values sufficiently smaller than 1, I _1f = RI ₁ cos (2πft + φ ₁ ) (4), I _2f = RI ₀ α ₀ PL (ω ₁ / Δω) ² cos (4πft + 2φ ₁ ′) / 2 (5)

In Equation 4, I _{1f is the} detection 1f intensity, R is the attenuation amount of the measurement light, I _{1 is the} modulation laser light intensity, f is the modulation frequency, and φ ₁ is the detection phase. Further, in Equation 5, I _2f : detected 2f intensity, R: measurement light attenuation, I ₀ : bias laser light intensity, α ₀ : absorption coefficient at the center of the measurement gas absorption line, P: partial pressure of measurement gas, L : Measurement optical path length, ω ₁ : Modulated laser light wavelength half width, Δω: Measurement gas absorption line half width, f: Modulation frequency, φ ₁ ′: Detection phase.

Here, when the ratio between the detected 2f intensity and the detected 1f intensity is obtained, | I _2f | / | I _1f | = (I ₀ / I ₁ ) (ω ₁ / Δω) ² α ₀ PL / 2. but here introduced gas concentration conversion coefficient C, C = obtains the magnitude of the gas column density PL as _{((I 0 / I 1)} (ω 1 / Δω) 2 α 0/2) -1 ... equation 7 PL = C * (| I _2f | / | I _1f |)...

In Equation 6, I _2f / I _1f : ratio of detected 2f intensity to detected 1f intensity, I ₀ : bias laser beam intensity, I ₁ : modulated laser beam intensity, ω ₁ : modulated laser beam wavelength half width, Δω: measurement Gas absorption line half-width, α ₀ : absorption coefficient at the center of the measurement gas absorption line, P: partial pressure of the measurement gas, and L: measurement optical path length.

  Thus, since the gas column density PL is defined as the product of the measurement gas concentration and the measurement distance, the gas concentration coefficient C can be accurately determined if there is a gas having a determined measurement distance and an accurate concentration. Therefore, in order to obtain an accurate gas column density, the gas concentration coefficient C may be precisely measured and set.

  Therefore, in the gas detector calibration apparatus 1 of this example, a system in which the gas column density PL is determined is constructed in order to accurately measure the gas concentration coefficient C based on the calibration principle described above. The undetermined gas concentration coefficient C is determined from the density PL.

  The calibration gas cell 6 provided in the gas detector calibration apparatus 1 of this example has a measurement optical path length L1 set to 100 mm. Further, standard gases of 1000 ppm, 2000 ppm, and 5000 ppm are prepared, and the calibration gas cell 6 can be filled with a standard gas of 1 atm accurately.

  If a standard gas of 1000 ppm is filled, the gas column density PL = 1000 ppm × 0.1 m = 100 ppm · m, and the column density of 100 ppm · m is set in the calibration apparatus 1. Similarly, a column density of 200 ppm · m is set for a standard gas of 2000 ppm, and a column density of 500 ppm · m is set for a standard gas of 5000 ppm.

  In the gas detector calibration apparatus of this example, the gas detector 3 to be calibrated is mounted, and the | 2f | / | 1f | value is measured by the gas detector 3 at the three types of column densities. Then, the gas concentration coefficient C is obtained using the measured | 2f | / | 1f | value and the column density PL. The acquired gas concentration coefficient C is set in the gas detector 3 from a personal computer or the like as a gas concentration coefficient parameter of the gas detector 3. Thus, the gas detector 3 can obtain the calibrated column density by calculating the detected column density using the set gas concentration coefficient at the time of gas detection.

  Hereinafter, the acquisition method of the gas concentration coefficient C using the gas detector calibration apparatus 1 of the present example will be specifically described along the procedure.

(1) The light projecting / receiving portion of the gas detector 3 to be calibrated is inserted into the purge pipe 5 and the gas detector 3 is positioned on the base 2.
(2) The reflecting plate 27 is rotated by the driving means 28 at a specified speed.
(3) The valve 12 a of the purge gas cylinder 12 is opened and the purge gas is caused to flow into the purge pipe 5. Thus, the purge pipe 5 is filled only with the purge gas.
(4) Close all the valves 13c, 14c, 18a of the calibration gas cell 6 and the standard gas cylinder 18.
(5) The valve 14c connected to the standard gas cylinder 18 of the calibration gas cell 6 is opened.
(6) The valve 13c connected to the vacuum pump 16 of the calibration gas cell 6 is opened.
(7) The vacuum pump 16 is operated to evacuate the calibration gas cell 6.
(8) The valve 13c connected to the vacuum pump 16 of the calibration gas cell 6 is closed.
(9) Open the valve 18a of the standard gas cylinder 18 of 1000 ppm.
(10) The standard gas is put into the calibration gas cell 6 until it reaches 1 atm.
(11) The valve 18a of the standard gas cylinder 18 is closed.
(12) The valve 14c connected to the standard gas cylinder 18 of the calibration gas cell 6 is closed.
(13) The operations (3) to (12) are repeated a plurality of times. This operation is performed in order to eliminate the previous gas by the operation of the vacuum pump 16 and eliminate the measurement error due to the influence of the previous residual gas.
(14) The | 2f | / | 1f | value (gas concentration) is measured and recorded by the gas detector 3 to be calibrated.
(15) The 1000 ppm standard gas cylinder 18 is replaced with a 2000 ppm standard gas cylinder 18, and the operations (3) to (14) are repeated a plurality of times.
(16) The standard gas cylinder 18 of 2000 ppm is replaced with the standard gas cylinder 18 of 5000 ppm, and the operations (3) to (14) are repeated a plurality of times.
(17) Stop the rotation of the reflecting plate 27 by the driving means 28.
(18) Close the valves 12a and 18a of all the gas cylinders 12 and 18.
(19) Open the valves 13c and 14c of the calibration gas cell 6.
(20) Remove the gas detector 3 to be calibrated from the base 2.

  As described above, in the gas detector calibration apparatus of this example, since a system in which the gas column density PL is determined is constructed, the undetermined gas concentration coefficient C can be determined from the determined gas column density PL. That is, the gas detector 3 to be calibrated is mounted on the base 2 of the gas detector calibration apparatus 1 of this example, and | 2f | / | at three column densities of 100 ppm · m, 200 ppm · m, and 500 ppm · m. The 1f | value is measured by the gas detector 3. The gas concentration coefficient C can be obtained from Equation 8 using the measured | 2f | / | 1f | value and the column density PL. Accordingly, if the acquired gas concentration coefficient C is set in the gas detector 3 as a gas concentration coefficient parameter of the gas detector 3, the detection column density is calculated using the set gas concentration coefficient at the time of gas detection. By doing so, the calibrated gas concentration can be obtained. Thereby, compared with the past, the gas concentration measured value of a gas detector can be correctly calibrated in a short time.

  In the gas detector calibration apparatus of this example, three types of standard gases of 1000 ppm, 2000 ppm, and 5000 ppm are provided so that the offset amount of the gas concentration and voltage (| 2f | / | 1f | value) that are proportional to each other can be corrected. However, it is sufficient to prepare at least two types of standard gases.

  In the gas detector calibration apparatus of this example, the purge means 4 includes an optical axis C− of the measurement light that connects the gas detector 3 and the calibration gas cell 6 so that the gas detector 3 and the calibration gas cell 6 are detachable at both ends. It is a configuration in which a cylindrical tube formed so as to surround C is formed and the inside is held in a predetermined gas state. Thereby, since the atmospheric pressure in the purge pipe 5 is kept higher than the outside, it is possible to prevent extra gas from entering from the outside.

  In the calibration gas cell 6, an antireflection film is formed on the surface of the pair of transmission windows 21, and the pair of transmission windows 21 is inclined at a predetermined angle θ with respect to the optical axis CC of the laser beam, and at a predetermined interval L1. Therefore, the influence of the reflection of the laser beam and the interference of the laser beam when the laser beam passes through the transmission window 21 can be prevented.

  Further, the reflecting mechanism 7 as the optical path length increasing / decreasing means includes the reflecting plate 27 as the reflecting means and the reflecting plate 27 so as to slightly increase / decrease the optical path length L of the laser light between the reflecting plate 27 and the gas detector 3. And driving means 28 for driving the motor. Specifically, the reflecting means 27 having the reflecting surface 27a inclined at a predetermined angle with respect to the optical axis C-C is rotationally driven by the driving means 28 at a predetermined rotational speed, and the reflecting plate 27 is driven by the driving means 28. Thus, it is finely driven in the direction of the optical axis CC. Thereby, the distance L between the light projecting / receiving surface of the gas detector 3 and the reflecting surface 27a of the reflecting plate 27 is changed minutely, and the laser beam does not resonate between the gas detector 3 and the reflecting plate 27. Laser beam interference can be prevented.

  Further, in the gas detector calibration apparatus of this example, the reflecting surface 27a of the reflecting means 27 forms a diffusely reflecting surface, so that the laser beam transmitted through the calibration gas cell 6 is irregularly reflected and reflected again to the calibration gas cell 6. Can do.

It is the schematic which shows the whole structure of the gas detector calibration apparatus which concerns on this invention, Comprising: It is a figure which shows the state with which the gas detector of calibration object was attached. It is an external view of the standard gas cell for calibration of the gas detector calibration apparatus of FIG. It is sectional drawing of the standard gas cell for calibration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas detector calibration apparatus 2 Base 2a Support member 2b Guide member 3 Gas detector 4 Purge means 5 Purge pipe 6 Gas cell for calibration 6a Cell main body 6b Both ends 7 Reflection mechanism (optical path length increase / decrease means)
8 Control box 11 Pipe 12 Purge gas cylinder 12a Valve 13, 14 Joint 13a, 14a Valve 13b, 14b Base end 13c, 14c Tip 15 Pipe 16 Vacuum pump 17 Pipe 18 Standard gas cylinder 21 Glass window (transmission window)
DESCRIPTION OF SYMBOLS 22 Antireflection film 23 Gasket 24 Fixing means 24a Screw part 24b Nut part 25 Pressure detection means 26 Display means 27 Reflecting plate (reflection means)
27a Reflecting surface 28 Driving means

Claims (7)

For calibrating the gas detector (3) for emitting a laser beam whose frequency is stabilized to the gas absorption line into the atmosphere and receiving the reflected light of the laser beam to measure the gas concentration in the atmosphere. A gas detector calibration device (1) comprising:
The gas detector to be calibrated is disposed at a predetermined length ( L0 ) or more along the optical axis (CC) of the laser beam generated by the gas detector from the position where the gas detector is placed, A calibration gas cell (6) that is provided with a pair of transmission windows (21) that are respectively inclined and transmit laser light, and a peripheral wall, and in which a gas to be detected having a predetermined concentration is filled.
Reflection means (27) for reflecting the laser light transmitted through the calibration gas cell from one of the pair of transmission windows to the other;
A gas detector calibration apparatus comprising purge means (4) for removing the gas to be detected from an optical path between the gas detector and the calibration gas cell. The purge means (4) surrounds the optical axis of the measurement light connecting the gas detector and the calibration gas cell so that the gas detector (3) and the calibration gas cell (6) are detachable at both ends. The gas detector calibration device according to claim 1, wherein the gas detector calibration device is formed in a cylindrical shape and holds the inside in a predetermined gas state. In the calibration gas cell (6), an antireflection film is formed on the surface of the pair of transmission windows (21), and the pair of transmission windows are inclined at a predetermined angle (θ) with respect to the optical axis of the laser beam, 2. The gas detector calibration device according to claim 1, wherein the gas detector calibration device is arranged at a predetermined interval (L1). The reflecting means (27);
Optical path length increasing / decreasing means (7) including drive means (28) for driving the reflecting means so as to slightly increase / decrease the optical path length (L) of the laser beam between the reflecting means and the gas detector (3). The gas detector calibration device according to any one of claims 1 to 3, further comprising: The reflecting means (27) is arranged such that the reflecting surface (27a) is inclined at a predetermined angle with respect to the optical axis (CC),
5. The gas detector calibration device according to claim 4, wherein the driving means (28) rotationally drives the reflecting means at a predetermined rotational speed. 5. The gas detector calibration apparatus according to claim 4, wherein the driving means (28) finely drives the reflecting means (27) in the direction of the optical axis (CC). The gas detector calibration device according to any one of claims 1 to 6, wherein the reflection surface (27a) of the reflection means (27) forms an irregular reflection surface.

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