JP2007101303A - Infrared gas analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NDIR stable in performance by storing a pressure sensor package in an airtight space shielded from the outside air in a block and filling the airtight space with a sensitive gas of the same components as the sensitive gas filled in a front and rear chambers of a detecting section. <P>SOLUTION: The infrared analyzer comprises a cell section 30 for introducing a sample gas onto the optical path of infrared rays projected from a light source 21, and the detecting section 40 formed in a block 47 adjacent to the cell section and detecting infrared rays having passed through the cell section 30. The detecting section 40 comprises a front chamber 41 and a rear chamber 42, and a pressure sensor package S for detecting pressure difference between the sensitive gases filled into these two chambers. The package S is stored in an airtight space 54 shielded from the outside air in the block 47, and the airtight space 54 is filled with the sensitive gas of the same components as the sensitive gas filled in the front and rear chambers of the detecting section 30. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an infrared gas analyzer for measuring a sample gas concentration (concentration of a specific gas species) using gas pressure fluctuations accompanying absorption of an infrared spectrum of a component gas to be measured. The present invention relates to the configuration of the gas detector used.

  Many heteronuclear molecules composed of two or more different atoms undergo a transition in the vibrational and rotational kinetic energy levels peculiar to the chemical species when irradiated with infrared light having a wavelength of 1 to 20 μm. Absorbs the spectrum and causes thermodynamic changes such as an increase in internal energy, volume or pressure. A non-dispersive infrared gas analyzer (hereinafter referred to as NDIR) is an analytical instrument that measures the concentration by utilizing the characteristics of such gas components. For example, those shown in Patent Documents 1 to 3 There is.

  FIG. 2 shows the basic configuration of this type of single-beam NDIR. This NDIR is finally measured by measuring the intensity of infrared light that has passed through the light source unit 20 for generating infrared light, the cell unit 30 into which the sample gas (gas to be measured) is introduced, and the cell unit 30. It is comprised from three elements of the detection part 40 which measures a sample density | concentration.

  The light source unit 20 is responsible for generation of infrared light, and includes a heater 21 that is a light source, and a chopper 22 that is rotated by a motor 23 to intermittently cause infrared light to enter the cell unit 30 and the detection unit 40. Yes.

  The cell part 30 is a part into which the sample gas is introduced, and the pipe 31 is sealed at the front and rear ends thereof with an infrared transmissive window plate 32 such as CaF2. A gas outlet / inlet 33 is formed on the side surface of the pipe 31 so that the gas flows from one end to the other end. The inner surface of the pipe 31 is coated with a mirror finish or gold plating in order to reflect infrared light efficiently.

The detection unit 40 is composed of an aluminum block 47, and a front chamber 41 and a rear chamber 42 filled with sensitive gas are formed in the block 47, and a pressure difference between the two rear chambers is detected before and after this. A sensor 44 is disposed in a communication passage 43 that communicates the front chamber 41 and the rear chamber 42. The front (infrared incident side) of the front chamber 41 is sealed with an infrared transmissive window plate 49 such as CaF2, and the front chamber 41 and the rear chamber 42 are similarly partitioned by an infrared transmissive window plate such as CaF2. The back side of 42 is blocked by, for example, a black back plate 46 in order to prevent the incidence of infrared light from the outside. The sensitive gas sealed in the front chamber 41 and the rear chamber 42 is a high-concentration gas such as CO _{2 to} be measured by NDIR, or a gas diluted with an inert gas such as Ar, He, or N _2. used. This sensitive gas is filled after the front and rear chambers 41 and 42 are evacuated by the gas introduction pipe 48, and after filling, the opening of the gas introduction pipe 48 is closed by means such as caulking.

  In measuring the sample gas concentration, infrared light that has passed through the cell unit 30 into which the sample gas has been introduced is incident on the front chamber 41 and the rear chamber 42 of the detection unit 40. At this time, most of the infrared light corresponding to the absorption spectrum of the sensitive gas is absorbed by the sensitive gas in the anterior chamber as molecular vibrational energy, and this vibrational energy is converted into translational kinetic energy by relaxation. Pressure increases. At this time, since a pressure difference is generated between the front chamber and the rear chamber, this pressure difference detected by the sensor 44 disposed between the communication passages 43 and 43 depends on the intensity of infrared rays passing through the sample gas. Since the infrared intensity depends on the concentration of the infrared absorbing gas in the sample gas, the infrared absorbing gas concentration in the sample gas can be measured based on the pressure difference detected by the sensor.

  FIG. 3 shows the details of the sensor 44 used in NDIR. The micron-order silicon diaphragm 1 processed by the micromachining technology is fixed by applying tension to the substrate 2 such as glass. The change of the diaphragm 1 due to the pressure is detected as a change in capacitance. The sensor 44 is rarely marketed as a single sensor from the viewpoint of protection of the main body, and is generally packaged and supplied to the market.

FIG. 4 shows a packaged pressure sensor S, which is incorporated in an inseparable manner in a state in which the sensor 44 is disposed on the electronic circuit board 4 in an integrally molded resin mold member 3. ing. The interior of the mold member 3 is separated into an upper space 5 connected to the communication hole 8 and a lower space 6 connected to the pressure introducing hole 9 by a sensor 44 and an electronic circuit board 4 having a through hole. 7 so that the pressure difference between the pressures P1 and P2 introduced from the pressure introduction holes 8 and 9 can be sensed. Further, a signal processed in the previous stage by the circuit of the electronic circuit board 4 is output from the terminal 10. As shown in FIG. 5, the pressure sensor package S is attached by inserting cylindrical insertion portions 11, 11 each having pressure introduction holes 8, 9 into communication holes 43 communicating with the front chamber 41 and the rear chamber 42.
JP 09-049797 A Japanese Patent Laid-Open No. 09-304278 JP 2003-83891 A

  However, in the above-described configuration, the space 6 isolated by the cover 7, that is, the pressure sensing side can be said to be an action system of the detection unit, and the space 12 that is inevitably formed outside the cover 7. Since the electronic circuit board 4 and the mold member 3 and the electronic circuit board 4 and the cover 10 are not completely sealed because they are open to the outside atmosphere, for example, the sealing agent is a polymer material having gas permeability. In some cases, leakage occurs due to the gas passing through the inside of the sensitive gas or the sealing material due to gas diffusion, etc., or the outside air flows into the interior and gas exchange occurs, resulting in a change in the sensitive gas component, which degrades the measurement accuracy. There was a problem such as.

  Therefore, the present applicant has made a prototype of an NDIR detection unit as shown in FIG. 6A is a metal block 47 of the detection unit not mounted with a pressure sensor, and a storage chamber 49 that only accommodates the pressure sensor package S to be incorporated is opened below the block 47. FIG. . A sensor lead wire extraction hole 50 is provided in the side wall of the storage chamber 49. As shown in FIG. 6B, the pressure sensor package S is stored in the storage chamber 49 from below, and the lid 52 is joined in a state where the outer periphery thereof is filled with the epoxy adhesive layer 51 without a gap. The storage chamber opening is closed and the pressure sensor package S is shut off from the outside air.

  However, with this means, since the atmosphere remains in the space 20 inside the pressure sensor package S, the remaining atmosphere diffuses into the action system of the detection unit due to the slow leak, and the interference response and sensitivity change of the detection unit due to impurities can be avoided. There wasn't.

  Therefore, the present invention accommodates the pressure sensor package in an airtight space that is shielded from the outside air in the block, and in this airtight space, a sensitive gas having the same composition as the sensitive gas filled in the front chamber and the rear chamber of the detection unit is stored. The main object is to provide an NDIR that overcomes the above-described conventional problems by filling.

  In order to achieve the above object, the present invention takes the following technical means. That is, the present invention provides an infrared ray including a cell portion into which a sample gas is introduced on an optical path of infrared rays projected from a light source, and a detection portion that is formed in a block adjacent to the cell portion and detects infrared rays that have passed through the cell portion. In the analyzer, the detection unit includes a front chamber and a rear chamber surrounded by a wall surface of the block, and a pressure sensor package for detecting a pressure difference between the sensitized gas filled in the two chambers. The sensor package is housed in an airtight space that is blocked from the outside air in the block, and the airtight space is filled with the same sensitive gas as that in the front and rear chambers of the detector. It is.

  Since the infrared gas analyzer of the present invention is configured as described above, there is no remaining air in the airtight space containing the pressure sensor package, and the airtight space receives the same components as the sensitized gas in the front chamber and the rear chamber of the detector. Because it is filled with gas sensitivities, even if leaks occur in the confidential space from the isolated part in the pressure sensor package, the interference gas of the detection part due to impurities is not affected by the interference of the same components, and the sensitivity changes In addition, it is possible to obtain an infrared gas analyzer that is stable in terms of performance, and that a commercially available pressure sensor package can be used as it is as a detection element of the infrared gas analyzer, thereby reducing costs. is there. Note that “the same sensitive gas” refers to gases having almost the same component ratio. More preferably, the pressure is almost the same as the sensitivity gas in the front and rear chambers.

(Means and effects for solving other problems)
In the above invention, a storage space in which the pressure sensor package can be mounted from the outside is formed in the lower part of the block, and after the pressure sensor package is stored in the storage space, the opening of the storage space is sealed with a lid. It is preferable that an airtight space is formed.
As a result, the pressure sensor package can be easily assembled to the block, and an airtight space can be easily formed.

  The NDIR according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing an NDIR detector according to the present invention. The other configurations of NDIR, that is, the configurations of the light source unit and the cell unit are omitted because they are the same as those shown in FIG. The detection unit 40 ′ is also configured with the same structure as that shown in FIG. 2 except for the portion that houses the pressure sensor package S. Therefore, in order to avoid complication, the same components as those in FIG. Was attached.

The detection unit 40 ′ is composed of an aluminum block 47 ′, and a front chamber 41 and a rear chamber 42 in which a sensitive gas is sealed are formed in the block 47 ′. A continuous communication path 43 is provided. The front chamber 41 and the rear chamber 42 are partitioned by an infrared light transmissive window plate, and the back of the rear chamber 42 is blocked by, for example, a black back plate 46 to prevent infrared light from entering from the outside. As the back plate, a metal plate such as aluminum may be used depending on the case, or an infrared transmitting window plate may be used when a detector in which a different kind of sensitive gas is sealed is connected. The sensitive gas sealed in the front chamber 41 and the rear chamber 42 is a high-concentration gas such as CO _{2 to} be measured by NDIR, or a gas diluted with an inert gas such as Ar, He, or N _2. used. This sensitive gas is filled after the front and rear chambers 41 and 42 are evacuated by the gas introduction pipe 48, and after filling, the opening of the gas introduction pipe 48 is closed by means such as caulking.

  A storage space for storing the pressure sensor package S having the same structure as that shown in FIGS. 3 and 4 is provided at the lower part of the block 47 ′. The pressure sensor package S is mounted in the storage space by being inserted into the communication hole 43 communicating with the chamber 41 and the rear chamber 42. A slight space 54 is left between the pressure sensor package S and the space 54 is hermetically sealed with a lid 55.

  This space 54 (airtight space), which is blocked from the outside air, is filled with a sensitive gas after being evacuated by the gas introduction pipe 56 in the same manner as the gas filling to the front chamber 41 and the rear chamber 42. The gas inlet tube 56 is sealed by closing the opening of the gas inlet tube 56 by means such as caulking. As the sensitized gas to be filled, those having the same components as the sensitized gas filled in the front chamber 41 and the rear chamber 42 are used.

  A lead wire 57 for connecting a power supply and a signal from the electronic circuit board 4 of the sensor 44 of the pressure sensor package S is connected, and a hole 58 formed in the block 47 ′ for taking out the lead wire 57 is formed by a sealing material 59. It is completely sealed.

  With the above configuration, the remaining atmosphere is eliminated from all the spaces in the block 47 ′ including the pressure sensor package, and the airtight space 54 has a sensitized gas having the same component as the sensitized gas in the front chamber 41 and the rear chamber 42. Even if gas leaks from the isolated part in the pressure sensor package S, that is, between the electronic circuit board 4 and the mold member 3 or from the joint part of the cover 7, the same component is perceived. By simply mixing the gases, there is no interference response or sensitivity change of the detection part due to impurities, and a stable NDIR can be obtained.

  The present invention can be used when manufacturing a NDIR that can be used as a performance-stable sensing element using a commercially available pressure sensor package.

Sectional drawing which shows the structure of the detection part of the infrared gas analyzer which is one Example of this invention. The schematic block diagram of the conventional infrared gas analyzer. The expanded sectional view of a pressure sensor. Sectional drawing of a pressure sensor package. Sectional drawing which shows the detection part of the conventional infrared gas analyzer equipped with the pressure sensor package. The other example of the conventional mounting | wearing with the pressure sensor package is shown, (A) is before mounting | wearing, (B) shows after mounting | wearing.

Explanation of symbols

S pressure sensor package 20 light source unit 21 light source 30 cell unit 40 detection unit 41 front chamber 42 rear chamber 47 block 54 space (airtight space)

Claims (1)

An infrared analyzer including a cell part into which a sample gas is introduced onto an optical path of infrared light projected from a light source, and a detection part that detects infrared light that is formed in a block adjacent to the cell part and passes through the cell part,
The detection unit includes a front chamber and a rear chamber surrounded by a wall surface of the block, and a pressure sensor package for detecting a pressure difference between the sensitized gases filled in the two chambers, and the pressure sensor package is included in the block. An infrared gas analyzer, wherein the infrared gas analyzer is housed in an airtight space cut off from outside air, and the airtight space is filled with the same sensitive gas as the sensitive gas charged in the front chamber and the rear chamber.

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