JP2010060485A - Gas cell, gas sample chamber and concentration measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas cell capable of preventing the irregular reflection of infrared rays from an inner peripheral surface to prevent the deterioration of the measuring precision of concentration, a gas sample chamber and a concentration measuring instrument. <P>SOLUTION: The gas cell 6 is formed into a cylindrical shape and guides infrared rays radiated from the light source 7 arranged at one end 6b to the infrared sensor arranged at the other end 6c through the interior and is formed of pure aluminum. Mirror polish treatment is applied to the inner peripheral surface 6d. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gas cell, a gas sample chamber, and a concentration measuring device including the gas sample chamber, which are used in a concentration measuring device that measures the concentration of a predetermined gas such as carbon dioxide, water vapor, or carbon monoxide. .

  For example, various gas sample chambers have conventionally been used for concentration measuring devices that measure the concentration of a predetermined gas such as carbon dioxide, water vapor, or carbon monoxide. Such a gas sample chamber comprises a hollow tube as a cylindrical gas cell sealed inside, a light source provided at one end of the hollow tube, and a light receiver provided at the other end of the hollow tube. I have.

  The hollow tube is formed, for example, by cutting a cylindrical metal body such as duralumin into a cylindrical shape and then performing mechanical polishing (such as buffing) to smooth the inner peripheral surface. The hollow tube is provided with a gas introduction hole into which an atmosphere containing a predetermined gas whose concentration is to be measured, and a gas outlet hole through which the atmosphere is discharged.

  The light source is an incandescent lamp and emits infrared rays (that is, infrared light). The light receiver includes an infrared sensor, and an optical bandpass filter (hereinafter referred to as “filter”) as a transmission member that is disposed between the infrared sensor and the light source and transmits only infrared rays having a predetermined wavelength. Yes. This infrared sensor outputs a voltage corresponding to the intensity of infrared rays. The wavelength of infrared light that passes through the filter is determined according to the gas whose concentration is to be measured. For example, if the concentration of the gas to be measured is within a relatively low concentration range of 0 ppm to several thousand ppm, the infrared wavelength that is most easily attenuated by the gas to be measured is selected as the wavelength of the infrared light that passes through the filter. The filter is appropriately selected according to the gas to be measured.

  Such a gas sample chamber, that is, a concentration measuring device, supplies an atmosphere into the hollow tube through the gas introduction hole, and measures the intensity of infrared rays from the light source received by the infrared sensor through the filter. The concentration of the gas to be measured included was measured.

  However, the filter described above is used in the gas sample chamber described above, which sorts (passes or blocks) infrared rays incident on the filter surface at an angle perpendicular to or close to the vertical according to the wavelength. Since the inner peripheral surface of the hollow tube is smoothed by mechanical polishing, the surface is formed rough when viewed optically, and the infrared rays are irregularly reflected (diffuse reflected) in various directions. Of the irregularly reflected infrared rays, those reflected at an angle close to a right angle with respect to the axial direction of the hollow tube are tanned with respect to the above-described filter surface (a direction close to parallel to the filter surface, that is, a direction not perpendicular). The filter does not function properly for each infrared wavelength by the filter, and the infrared light with the wavelength that is originally blocked by the filter passes through the filter. The accuracy of the concentration measurement there is a problem that becomes worse. Also, some of the infrared rays emitted from the light source are attenuated or extinguished before reaching the infrared sensor depending on the angle of irregular reflection, so that the amount of infrared light reaching the infrared sensor is reduced, and thus the concentration measurement. There was a problem that the accuracy of was deteriorated.

  The present invention aims to solve the above problems. That is, an object of the present invention is to provide a gas cell, a gas sample chamber, and a concentration measuring device that can prevent irregular reflection of infrared rays on the inner peripheral surface and prevent deterioration in accuracy of concentration measurement.

  In order to achieve the above-mentioned object, the invention described in claim 1 is formed in a cylindrical shape, and infrared rays emitted from a light source arranged at one end portion are infrared rays arranged at the other end portion through the inside. A gas cell led to a sensor, which is made of pure aluminum and has an inner peripheral surface polished in a mirror shape.

  The invention described in claim 2 is a gas cell formed in a cylindrical shape, a light source disposed at one end of the gas cell and emitting infrared light, a gas source disposed at the other end of the gas cell, and the light source The gas cell according to claim 1, further comprising: an infrared sensor that detects the infrared light from the light source, wherein the gas cell is a gas sample chamber that guides the infrared light from the light source to the infrared sensor through the gas cell. A gas sample chamber.

  The invention described in claim 3 is based on a gas sample chamber including a light source that emits infrared rays and an infrared sensor that detects the infrared rays from the light source, and the intensity of the infrared rays detected by the infrared sensor. A concentration measuring device comprising: a concentration calculating unit that calculates a predetermined gas concentration in the gas sample chamber, wherein the gas sample chamber according to claim 2 is provided as the gas sample chamber. This is a characteristic concentration measuring device.

  According to the first, second, and third aspects of the present invention, the gas cell that transmits infrared rays is made of pure aluminum, and the inner peripheral surface thereof is polished in a mirror shape. Therefore, infrared rays can be prevented from entering the filter (transmission member) from an angle nearly parallel to the filter surface, and the amount of infrared light reaching the infrared sensor can be reduced. This prevents the deterioration of density measurement accuracy. Moreover, since infrared rays are mirror-reflected, the heat absorption rate on the inner peripheral surface is low, so that infrared rays can be guided efficiently. In addition, since pure aluminum used for the gas cell is inexpensive, the gas cell, the gas sample chamber including the gas cell, and the concentration measuring device including the sample chamber can be provided at low cost. .

  Hereinafter, a concentration measuring apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6.

  As shown in FIG. 2, the concentration measuring apparatus 1 includes a gas sample chamber 2 filled with an atmosphere containing a gas whose concentration is to be measured, a control circuit unit 3, a light receiving circuit unit 4, and a concentration calculating unit. And a microcomputer 5 (hereinafter referred to as μcom).

  As shown in FIG. 1, the gas sample chamber 2 includes a measurement cell 6 as a gas cell, a light source 7, a light receiving unit 8, a radiator 9 as a heat radiating member, and a heat absorber 10 as a temperature adjusting member, It has.

  The measurement cell 6 is a conduit that guides infrared rays from one end 6b to the other end 6c through the inside thereof. The measurement cell 6 is made of, for example, pure aluminum having a purity of 99.99% or more and is formed in a cylindrical shape. The inner peripheral surface 6d of the outer wall 6a of the measurement cell 6 is polished in a mirror shape so that infrared rays are not irregularly reflected.

  The measurement cell 6 is formed in a cylindrical shape by cutting a columnar base material made of pure aluminum into a predetermined length, and providing a hole penetrating the inside in the axial direction by cutting. Then, in order to polish the inner peripheral surface 6d in a mirror shape, for example, (1) mechanical polishing (buff polishing) performed by pressing a polishing softener such as leather or resin while rotating, (2) in the chemical polishing liquid (3) The measurement cell 6 is immersed in the electrolytic polishing liquid, and a terminal is arranged inside the measurement cell 6 by immersing the measurement cell 6 in the electrode and moving at least one of the cell and the chemical polishing liquid. Then, a positive potential is applied to the measurement cell 6 and a negative potential is applied to the terminal and the electrode containing the electrolytic polishing liquid, respectively, and electrolytic polishing performed by moving at least one of the cell and the electrolytic polishing liquid is sequentially performed. In the case where sufficient mirror-like polishing can be performed by chemical polishing, electrolytic polishing may be omitted. In this way, the measurement cell 6 in which the inner peripheral surface 6d is polished in a mirror shape is obtained. If the purity of pure aluminum is low, the electric resistance is high and sufficient current cannot flow, so that the effect of electrolytic polishing does not appear and a mirror surface that can prevent irregular reflection of infrared rays cannot be obtained. Therefore, the purity of pure aluminum, which is the material of the measurement cell 6, needs to be high enough that the inner peripheral surface can be polished into a mirror surface by electrolytic polishing, and more than 99.99%. As the material of the measurement cell 6, pure aluminum which is cheaper and can be easily processed (polished) than the metal (alloy) such as duralumin is suitable. The surface roughness of the inner peripheral surface 6d of the measurement cell 6 is desirably Rz = 0.11 μm or less and Ra = 0.111 μm or less.

  A gas introduction hole (not shown) and a gas lead-out hole (not shown) are provided in each of the one end 6b and the other end 6c of the measurement cell 6, and a gas supply part (not shown) is connected to the gas introduction hole. Yes. The gas supply unit forcibly sends the atmosphere containing the gas to be measured into the measurement cell 6 from the gas introduction hole. Then, the atmosphere sent into the measurement cell 6 is discharged from the gas outlet hole.

  The light source 7 is provided in the measurement cell 6 and at one end 6 b of the measurement cell 6. The light source 7 emits infrared light as light toward the other end of the measurement cell 6 by applying a voltage. As the light source 7, for example, a black body furnace or an incandescent lamp is used. A reflector 30 is attached to the light source 7. That is, the concentration measuring apparatus 1 includes a reflector 30. The reflector 30 reflects the light emitted from the light source 7 into parallel light directed toward the light receiving unit 8. The light source 7 performs pulse lighting that repeats lighting and extinguishing at predetermined intervals such as lighting 0.7 seconds and lighting 2.7 seconds.

  As shown in FIGS. 3 and 4, the light receiving unit 8 includes a unit main body 11 and a plurality of light receivers 12. The unit main body 11, that is, the light receiving unit 8 is provided in the measurement cell 6 and at the other end 6 c of the measurement cell 6. The unit body 11 is formed in a cylindrical shape along the inner peripheral surface 6 d of the outer wall 6 a of the measurement cell 6. In the illustrated example, four light receivers 12 are provided. Each of the light receivers 12 includes a thermopile type infrared sensor 14 as an infrared sensor and a transmission member 15.

  A thermopile type infrared sensor (hereinafter also referred to as “infrared sensor”) 14 is also called a thermopile type infrared sensor, and is a known thermal-voltage energy conversion element in which a plurality of thermocouples are connected in series to increase the output voltage. It is. The warm contact point of the infrared sensor 14 is disposed so as to face the transmission member 15 so as to receive infrared rays from the light source, and the cold junction is thermally connected to a case of the infrared sensor 14 (not shown). ing. The infrared sensor 14 is attached to the unit main body 11. That is, the cold junction of the infrared sensor 14 is thermally connected to the other end 6 c of the measurement cell 6. The infrared sensors 14 of the plurality of light receivers 12 are arranged on the same plane. The infrared sensor 14 receives infrared rays emitted from the light source 7 and transmitted through the transmission member 15 and converts the heat of the infrared rays into electric energy. The infrared sensor 14 converts infrared heat into electrical energy, and outputs it to the μcom 5 as a sensor output.

  The transmission member 15 is a known optical bandpass filter, is attached to the unit main body 11, and is disposed between the infrared sensor 14 and the light source 7. The transmission members 15 of the plurality of light receivers 12 are arranged on the same plane. Each of the transmissive members 15 transmits only infrared rays having a predetermined wavelength out of infrared rays from the light source 7 and guides the infrared rays having the transmitted wavelengths to the infrared sensor 14. The transmission members 15 of the plurality of light receivers 12 have different wavelengths of infrared rays that pass through each other.

  The wavelength of infrared light transmitted through the transmission member 15 is determined according to the gas whose concentration is to be measured by the concentration measuring device 1. In the illustrated example, the concentration range of measurement of the gas to be measured can be detected at a low concentration within the range of 0 ppm to several thousand ppm, and the wavelength of the infrared ray transmitted through the transmission member 15 is the concentration measurement target. The transmittance for the gas is set to a small infrared wavelength. The light receiver 12 uses water vapor and carbon monoxide as the measurement target gas in addition to carbon dioxide. In the illustrated example, for example, one light receiver 12 is used as a reference, and the transmitting member 15 transmits only infrared rays having a wavelength of 1.5 μm or 4.0 μm that does not attenuate at all in the atmosphere. In the illustrated example, for example, another one of the light receivers 12 is used for measuring the concentration of carbon dioxide, and the transmission member 15 only receives infrared rays having a wavelength of 4.27 μm that is easily attenuated in carbon dioxide. To Penetrate. In the illustrated example, for example, still another light receiver 12 is used for measuring the concentration of water vapor, and the transmission member 15 transmits only infrared light having a wavelength of 1.9 μm that is easily attenuated in the water vapor. In the illustrated example, for example, another light receiver 12 is used to measure the concentration of carbon monoxide, and only the infrared ray whose wavelength is easily attenuated in the above-described carbon monoxide by the transmitting member 15 is 4.64 μm. Transparent. The transmissive member 15 accurately transmits only a predetermined wavelength when the angle of incident infrared rays is nearly perpendicular to the surface, and when the angle of incident infrared rays is nearly horizontal to the surface, Wavelengths other than the predetermined wavelength are also transmitted.

  6 shows the infrared transmittance for carbon dioxide, the horizontal axis in FIG. 6 indicates the wavelength of infrared rays (μm), and the vertical axis in FIG. 6 indicates the infrared transmittance (%). ing. FIG. 6 shows that the transmittance of infrared rays having a wavelength of 4.27 μm in carbon dioxide is substantially zero, and infrared rays having a wavelength of 4.27 μm hardly pass through carbon dioxide ( It is almost absorbed).

  The radiator 9 is a well-known heat radiating member that releases heat generated from a heat source to the surrounding atmosphere. The radiator 9 is made of, for example, a material having high thermal conductivity such as aluminum or copper, and includes a rectangular parallelepiped main body 9a and a plurality of fins 9b erected from the outer surface thereof. In the illustrated example, the radiator 9 is provided with a plurality of fins 9b. However, the present invention is not limited to this. For example, a plurality of pin-shaped protrusions can increase the surface area to efficiently dissipate heat. If so, the shape is arbitrary. The radiator 9 is disposed in close contact with the one end 6b of the measurement cell 6 so that the thermal resistance between the heat sink 9 and the measurement cell 6 becomes small. Thereby, the heat radiator 9 can discharge | release the heat | fever of the measurement cell 6 heated by the light source 7 in atmosphere, and can reduce the temperature of the light source 7 and the measurement cell 6 rapidly.

  Similarly to the radiator 9, the heat absorber 10 is made of a material having high thermal conductivity such as aluminum or copper, and includes a rectangular parallelepiped main body 10 a and a plurality of fins 10 b erected from the outer surface. In the illustrated example, the heat absorber 10 includes a plurality of fins 10b. However, the heat absorber 10 is not limited to this, and for example, a plurality of pin-shaped protrusions or the like can increase the surface area to efficiently dissipate heat. If so, the shape is arbitrary. The heat absorber 10 is disposed in close contact with the other end 6 c of the measurement cell 6 so that the thermal resistance between the heat absorber 10 and the measurement cell 6 becomes small. That is, the heat absorber 10 is thermally connected to the cold junction of the infrared sensor 14, so that the heat of the surrounding atmosphere can be absorbed and transmitted to the cold junction, and the temperature of the cold junction can be It can quickly follow changes in the temperature of the atmosphere. In addition, although it is preferable to install the radiator 9 and the heat absorber 10, it does not necessarily need to provide and the installation is arbitrary.

  As shown in FIG. 2, the control circuit unit 3 includes an oscillator 16, a clock frequency dividing circuit 17, a constant voltage circuit 18, and the like, and blinks the light source 7 at a predetermined frequency according to a command of μcom5.

  As shown in FIG. 5, the light receiving circuit unit 4 includes a plurality of amplifiers 19, a switcher 20, and an A / D converter 21. The amplifiers 19 are respectively provided in one-to-one correspondence with the light receivers 12. The amplifier 19 amplifies the signal from the infrared sensor 14 of the corresponding light receiver 12 and outputs it to the A / D converter 21 via the switcher 20. The A / D converter 21 converts the signal from the infrared sensor 14 into a digital signal and outputs it to the μcom 5.

  The μcom 5 is connected to the control circuit unit 3 and the light receiving circuit unit 4 and controls these operations, thereby controlling the operation of the concentration measuring apparatus 1 as a whole. μcom5 is a computer that operates according to a predetermined program. As is well known, this μcom 5 is a central processing unit (CPU) that performs various processes and controls in accordance with a predetermined program, a ROM that is a read-only memory storing a program for the CPU, and various data. And a RAM that is a readable / writable memory having an area necessary for processing operations of the CPU.

  The μcom 5 is connected to an electrically erasable / rewritable read-only memory capable of retaining stored contents even when the concentration measuring apparatus 1 itself is in an OFF state. The memory stores various information such as an extinction coefficient, measurement distance, and concentration conversion coefficient, which will be described later, necessary for calculating the concentration, and stores the calculated concentration in a time series so that it can be read from the outside.

  The concentration measuring apparatus 1 having the above-described configuration supplies an atmosphere into the measurement cell 6, and makes the gas in the measurement cell 6, that is, the gas sample chamber 2, equal to the atmosphere. Then, the concentration measuring apparatus 1 blinks the light source 7 (pulse lighting), and receives the infrared light from the light source 7 by the infrared sensor 14 of each light receiver 12. Then, μcom 5 of the concentration measuring apparatus 1 determines the potential difference between the intensity of infrared light received by the infrared sensor 14 (that is, the output voltage of the infrared sensor 14 when the light source 7 is turned on and the output voltage of the infrared sensor 14 when the light source 7 is turned off). ) And the like, the concentration of a predetermined gas (for example, carbon dioxide, water vapor, carbon monoxide, etc.) in the gas sample chamber 2 is measured. Specifically, the μcom 5 of the concentration measuring apparatus 1 determines the intensity of infrared light received by the infrared sensor 14 of the light receiver 12 used as a reference, and the infrared light of the light receiver 12 for measuring carbon dioxide, water vapor, and carbon monoxide. The concentration of carbon dioxide, water vapor, and carbon monoxide to be measured is measured by comparing the intensity of infrared rays received by the sensor 14. As described above, the gas sample chamber 2 of the concentration measuring apparatus 1 is formed so as to guide the infrared rays from the light source 7 to the light receiver 12, and the inner peripheral surface of the measurement cell 6 is polished into a mirror shape. Therefore, the infrared rays from the light source 7 can be guided to the light receiver 12 so as to be substantially parallel to the axial direction of the measurement cell 6 without irregular reflection.

  As described above, according to the present invention, the measurement cell 6 that transmits infrared rays is made of pure aluminum and the inner peripheral surface thereof is polished into a mirror surface. Diffuse reflection can be prevented, so that infrared rays can be prevented from entering the transmissive member 15 from an angle nearly parallel to the surface, and the amount of infrared rays reaching the infrared sensor can be prevented from decreasing, and the density measurement accuracy can be prevented. Can be prevented. Moreover, since infrared rays are mirror-reflected, the heat absorption rate at the inner peripheral surface 6a is low, so that infrared rays can be efficiently guided. Moreover, since pure aluminum used for the measurement cell 6 is inexpensive, the measurement cell 6, the gas sample chamber 2, and the concentration measuring device 1 can be provided at low cost.

  In the above-described embodiment, the wavelength of the infrared ray transmitted through the transmission member 15 when the concentration of the measurement target gas is low is shown. However, in the present invention, the measurement target gas has a low concentration to a high concentration (0 ppm). The length of the measurement cell 6 is changed, or the transmitting member 15 transmits only infrared light having a wavelength with a small amount of infrared absorption in the measurement target gas. Or you can do it.

Furthermore, in the embodiment, the concentration measuring device 1 measures the concentrations of carbon dioxide, water vapor, and carbon monoxide. However, in the present invention, the concentration measuring apparatus 1 may measure the concentrations of various gases other than carbon dioxide such as NOx, SOx, H ₂ S, O ₃ , CH ₄ , NO, water vapor, and carbon monoxide. In the present invention, the measurement cell 6 may be formed in various cylindrical shapes other than the cylindrical shape.

  Further, in the embodiment, the thermoelectric stack type infrared sensor is provided as the infrared sensor, but the invention is not limited thereto. For example, as the infrared sensor, a well-known quantum infrared sensor using a photoconductive effect or the like is used. Other types of infrared sensors may be used. Even in such a quantum infrared sensor, measurement errors and the like can be eliminated by quickly adjusting itself to the ambient temperature by the heat control member. This type of quantum infrared sensor is suitable for measurement at room temperature, uses PbSe as the material for the photoconductive element, and is suitable for measurement at a low temperature, and uses PbS as the material for the photoconductive element. There are things used.

  In addition, embodiment mentioned above only showed the typical form of this invention, and this invention is not limited to embodiment. That is, various modifications can be made without departing from the scope of the present invention.

It is a perspective view showing typically composition of a gas sample room of a concentration measuring device concerning one embodiment of the present invention. It is explanatory drawing which shows the structure of the density | concentration measuring apparatus shown by FIG. It is explanatory drawing which shows typically the front of the light-receiving unit of the gas sample chamber shown by FIG. It is explanatory drawing which shows typically the cross section of the VI-VI line in FIG. It is explanatory drawing which shows the structure of the light-receiving circuit of the density | concentration measuring apparatus shown by FIG. 3 is a graph showing an absorption spectrum of carbon dioxide.

Explanation of symbols

1 Concentration measuring device 2 Gas sample chamber 5 Microcomputer (concentration calculator)
6 Measurement cell (gas cell)
7 Light source 9 Radiator 10 Heat absorber 11 Unit body 12 Light receiver 14 Thermoelectric infrared sensor 15 Transmissive member 30 Reflector

Claims (3)

A gas cell that is formed in a cylindrical shape and guides infrared rays emitted from a light source arranged at one end to an infrared sensor arranged at the other end through the inside,
A gas cell comprising pure aluminum and having an inner peripheral surface polished in a mirror shape. A gas cell formed in a cylindrical shape, a light source disposed at one end of the gas cell and emitting infrared light, an infrared sensor disposed at the other end of the gas cell and detecting the infrared light from the light source; In a gas sample chamber for guiding the infrared light from the light source to the infrared sensor through the inside of the gas cell,
A gas sample chamber comprising the gas cell according to claim 1 as the gas cell. A gas sample chamber comprising a light source that emits infrared light and an infrared sensor that detects the infrared light from the light source, and a predetermined value in the gas sample chamber based on the intensity of the infrared light detected by the infrared sensor. In a concentration measuring device comprising a concentration calculating unit for calculating the concentration of gas,
A concentration measuring apparatus comprising the gas sample chamber according to claim 2 as the gas sample chamber.

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