JP2011117732A - Hydrocarbon concentration measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact, inexpensive hydrocarbon concentration measuring device reducing a measurement error without using any optical choppers. <P>SOLUTION: A THC measuring device 1 includes: an irradiation unit 10 emitting infrared rays of which the wavelength varies periodically; a cell 20 storing an exhaust gas; and a light reception unit 30 receiving intensity of infrared rays that are emitted from the irradiation unit 10 and are transmitted through the exhaust gas stored in the cell 20. The irradiation unit 10 includes: a light source 12 emitting infrared rays including a wavelength region absorbed by hydrocarbon included in the exhaust gas; a movable mirror 13 reflecting the infrared rays emitted from the light source 12 in a plurality of directions; a diffraction grating 14 generating middle-wavelength infrared rays, short-wavelength infrared rays, and long-wavelength infrared rays from infrared rays reflected by the movable mirror 13; and an optical slit plate 16 blocking the long-wavelength infrared rays. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hydrocarbon concentration measuring apparatus, and more particularly to a technique for measuring a concentration sum of hydrocarbons contained in exhaust gas based on an absorption amount of infrared rays irradiated to exhaust gas discharged from an engine.

  2. Description of the Related Art Conventionally, an apparatus using infrared spectroscopy is known as an apparatus for measuring the total concentration of hydrocarbons (Total Hydrocarbon: THC) contained in exhaust gas of an automobile or the like (see, for example, Patent Document 1).

The hydrocarbon concentration measuring device using infrared spectroscopy as described above irradiates exhaust gas with infrared rays, and based on the absorption amount of the infrared rays in a specific wavelength region, the concentration sum of hydrocarbons contained in the exhaust gas. Measure.
In the measurement, an infrared ray irradiated to the exhaust gas is periodically blocked using an optical chopper, and the zero point of the received light intensity of the infrared ray is grasped to correct the infrared oscillation intensity and the background light. The influence (noise) is removed.

  However, if an optical chopper is used to measure the concentration of hydrocarbons contained in the exhaust gas, the size of the hydrocarbon concentration measuring device will be increased, and a device for controlling the optical chopper will be required, leading to cost deterioration. Furthermore, if any deviation occurs in the control of the optical chopper, an error may occur in the hydrocarbon concentration finally measured.

JP 2009-115654 A

  An object of the present invention is to provide a hydrocarbon concentration measuring apparatus that is small and inexpensive and has reduced measurement error without using an optical chopper.

  The hydrocarbon concentration measuring apparatus of the present invention includes an irradiation unit that irradiates infrared rays whose wavelengths periodically change, a light receiving unit that detects the infrared rays and obtains the intensity of the infrared rays, and a measurement target gas. A cell that transmits infrared rays, irradiates infrared rays from the irradiation unit toward the measurement target gas accommodated in the cells, and detects the infrared rays transmitted through the measurement target gas by the light receiving unit, Obtaining the intensity of infrared light that has passed through the measurement target gas, and measuring the concentration of hydrocarbons contained in the measurement target gas based on the intensity of the infrared light, the irradiation unit, A light source that irradiates infrared rays including a wavelength range that is absorbed by hydrocarbons contained in the measurement target gas, and infrared rays emitted from the light sources are dispersed to measure the concentration of hydrocarbons contained in the measurement target gas. In order, a medium-wavelength infrared having a wavelength range necessary for performing, a short-wavelength infrared having a shorter wavelength range than the medium-wavelength infrared, and a long-wavelength infrared having a longer wavelength range than the medium-wavelength infrared A spectroscope that periodically changes the wavelength by taking out the light, and a blocking means that blocks at least one of the short wavelength infrared light and the long wavelength infrared light.

  In the hydrocarbon concentration measuring apparatus of the present invention, the spectroscope is composed of a reflecting means for reflecting incident infrared rays in a plurality of directions, and a diffracting means for diffracting incident infrared rays, and the blocking means. Is preferably a light-shielding member that is provided on at least one of the short-wavelength infrared light and the long-wavelength infrared light and blocks the light path.

  In the hydrocarbon concentration measuring apparatus according to the present invention, the spectroscope includes a reflecting unit that reflects incident infrared rays in a plurality of directions, and a diffracting unit that diffracts incident infrared rays, and the reflecting unit. Preferably functions as the blocking means by oscillating within a range including a position where the infrared rays emitted from the light source do not enter the diffraction means.

  According to the present invention, it is possible to reduce the size of the apparatus, reduce costs, and reduce errors in the measurement of hydrocarbons contained in exhaust gas.

The figure which shows a hydrocarbon concentration measuring apparatus. The figure which shows the structure of an irradiation part. The figure which shows the periodic fluctuation | variation of the infrared rays received intensity at the time of wavelength sweep. The figure which shows the structure of another form of an irradiation part. The figure which shows the periodic fluctuation | variation of the infrared rays received intensity at the time of wavelength sweep. The figure which shows the structure of another form of an irradiation part. The figure which shows the periodic fluctuation | variation of the infrared rays received intensity at the time of wavelength sweep. The figure which shows the structure of another form of an irradiation part. The figure which shows the periodic fluctuation | variation of the infrared rays received intensity at the time of wavelength sweep.

Hereinafter, the THC measuring apparatus 1 will be described with reference to FIG.
The THC measurement device 1 is a hydrocarbon concentration measurement device using infrared spectroscopy, which irradiates exhaust gas (measurement target gas) exhausted from an engine such as an automobile with infrared rays, in a specific wavelength region of the infrared rays. Based on the amount of absorption, the total concentration of hydrocarbons (total hydrocarbon: THC) contained in the exhaust gas is measured.

  As shown in FIG. 1, the THC measurement apparatus 1 includes an irradiation unit 10, a cell 20, a light receiving unit 30, and a control unit 40.

The irradiating unit 10 irradiates the infrared gas whose wavelength varies periodically toward the exhaust gas supplied into the cell 20.
The irradiation unit 10 includes a housing 11 that forms the exterior thereof.
The housing 11 is a housing that houses a plurality of members that constitute the irradiation unit 10, and holds the relative positional relationship between the plurality of members.
Note that details of a plurality of members housed in the housing 11 and constituting the irradiation unit 10 will be described later.

  The cell 20 is a substantially cylindrical member, and is disposed in the middle of the exhaust path of an automobile or the like, and introduces exhaust gas flowing through the exhaust path into the inside. The cell 20 is configured to be able to transmit infrared rays in a predetermined direction (a direction perpendicular to the axial direction of the cell 20 and the left-right direction in FIG. 1), and has passed through the exhaust gas introduced into the cell 20. Later infrared rays (hereinafter referred to as “transmitted light”) can be acquired. That is, transmitted light that has passed through the exhaust gas is acquired on the side (right side in FIG. 1) where infrared rays are introduced and on the opposite side (also on the left side). The transmitted light acquired by the cell 20 is received by the light receiving unit 30.

  The light receiving unit 30 includes a photodetector such as a photodiode, and detects the infrared light after passing through the exhaust gas irradiated from the irradiation unit 10 and introduced into the cell 20, that is, the intensity of the transmitted light. (Infrared intensity) is obtained.

The control unit 40 is electrically connected to the irradiation unit 10 and the light receiving unit 30.
The control unit 40 controls the irradiation unit 10 so that infrared rays having a desired wavelength range can be emitted from the irradiation unit 10. Further, the control unit 40 acquires the intensity of the transmitted light from the light receiving unit 30, and calculates the concentration sum of the hydrocarbons contained in the exhaust gas based on the intensity of the transmitted light.

  As described above, in the THC measurement device 1, infrared rays irradiated from the irradiation unit 10 are irradiated toward the exhaust gas introduced into the cell 20, and infrared rays (transmitted light) transmitted through the exhaust gas are received. The intensity is detected by the unit 30. And based on the intensity | strength of the said transmitted light, the control part 40 calculates the density | concentration sum of the hydrocarbon contained in exhaust gas.

  Below, with reference to FIGS. 2-3, the structure of the irradiation part 10 is demonstrated in detail.

  As shown in FIG. 2, the irradiation unit 10 includes a light source 12, a movable mirror 13, a diffraction grating 14, a fixed mirror 15, and an optical slit plate 16. These members are accommodated in the housing 11 (see FIG. 1) and are fixed in a state in which the relative positional relationship is maintained.

  The light source 12 is a member that irradiates the movable mirror 13 with broadband infrared light including a wavelength range absorbed by hydrocarbons contained in the exhaust gas introduced into the cell 20 (see FIG. 1).

The movable mirror 13 functions as means for reflecting the infrared rays emitted from the light source 12 and is a member that enters the diffraction grating 14 at an appropriate angle. As the movable mirror 13, a so-called MEMS (Micro Electro Mechanical Systems) mirror or the like can be applied.
The movable mirror 13 is swingably provided on an appropriate fixed shaft, and the control unit 40 (so as to swing a predetermined range around the fixed shaft (between the position P1 and the position P2 shown in FIG. 2). 1). Assuming that the position P1 shown in FIG. 2 is the initial position of the movable mirror 13, the period until the movable mirror 13 rotates to the position P2 and returns to the position P1 is the rotation period (one period) of the movable mirror 13.
The swing range of the movable mirror 13 is set so that infrared rays can enter the diffraction grating 14 at all positions.
In this way, the movable mirror 13 periodically changes the angle of infrared rays incident on the diffraction grating 14.

  The diffraction grating 14 functions as means for diffracting the infrared light reflected by the movable mirror 13, and is a member that separates the infrared light for each wavelength and reflects it toward the fixed mirror 15. As the diffraction grating 14, it is possible to apply a metal plate or the like in which a large number of grooves parallel to each other are formed on the surface (the surface on which infrared rays are incident).

The diffraction grating 14 is disposed at a position where the infrared ray reflected by the movable mirror 13 is incident. Depending on the swing position of the movable mirror 13 from the incident infrared ray, the “medium wavelength infrared ray” and the “short wavelength infrared ray”. , And “long wavelength infrared”.
The medium-wavelength infrared light is a part of the infrared light dispersed by the diffraction grating 14 and is an infrared light in a wavelength region that is absorbed by the hydrocarbons contained in the exhaust gas introduced into the cell 20. Used to measure.
The short wavelength infrared ray forms a part of the infrared ray dispersed by the diffraction grating 14 and is an infrared ray having a shorter wavelength range than the medium wavelength infrared ray. The short wavelength infrared ray is an infrared ray in a wavelength region that is not absorbed by the hydrocarbons contained in the exhaust gas introduced into the cell 20.
The long-wavelength infrared light is a part of the infrared light dispersed by the diffraction grating 14 and has a longer wavelength range than the medium-wavelength infrared light. The long wavelength infrared ray is an infrared ray in a wavelength region that is not absorbed by hydrocarbons contained in the exhaust gas introduced into the cell 20.

The fixed mirror 15 is a member that reflects the infrared light dispersed by the diffraction grating 14 toward the optical slit plate 16.
The fixed mirror 15 is arranged on an optical path of medium wavelength infrared light, short wavelength infrared light, and long wavelength infrared light generated by the diffraction grating 14.

The optical axes of the medium-wavelength infrared light, the short-wavelength infrared light, and the long-wavelength infrared light reflected by the fixed mirror 15 are substantially parallel to each other at a predetermined interval.
As described above, the movable mirror 13 reflects the infrared rays emitted from the light source 12 toward the diffraction grating 14 while swinging within a predetermined range (between the position P1 and the position P2 shown in FIG. 2). This is because infrared rays incident on the diffraction grating 14 at a plurality of angles are dispersed. However, the installation position of the light source 12 and the swing range of the movable mirror 13 are set so that the optical axes of the medium wavelength infrared ray, the short wavelength infrared ray, and the long wavelength infrared ray are substantially parallel to each other with a predetermined interval therebetween. In addition, the installation position, the installation position of the diffraction grating 14, the installation position of the fixed mirror 15, and the like are appropriately set.
In this way, the movable mirror 13 and the diffraction grating 14 function as a spectroscope, and in synchronization with the swinging of the movable mirror 13, irradiation is performed by sequentially extracting medium-wavelength infrared light, short-wavelength infrared light, and long-wavelength infrared light. The wavelength of infrared rays emitted from the unit 10 fluctuates, and wavelength sweeping is realized.

The optical slit plate 16 is a plate material made of a material that does not transmit infrared rays emitted from the light source 12, and functions as a light shielding member that blocks infrared rays in a predetermined wavelength region. The optical slit plate 16 is disposed on the optical path of the medium wavelength infrared, the short wavelength infrared, and the long wavelength infrared reflected by the fixed mirror 15. A slit 16 a is formed in the optical slit plate 16.
The slit 16a is a fine hole penetrating the front and back surfaces of the optical slit plate 16, and is disposed in a portion where an optical path of medium-wavelength infrared light and short-wavelength infrared light is located. The medium-wavelength infrared light and the short-wavelength infrared light pass through the slit 16a of the optical slit plate 16, and the long-wavelength infrared light is blocked by the portion of the optical slit plate 16 where the slit 16a is not formed.

  As described above, in the irradiation unit 10, an optical path that sequentially follows the light source 12, the movable mirror 13, the diffraction grating 14, the fixed mirror 15, and the optical slit plate 16 is formed.

The infrared light emitted from the light source 12 is swept in wavelength by the movable mirror 13 that swings within a predetermined range (between the position P1 and the position P2 shown in FIG. 2) and the diffraction grating 14 that splits the infrared light. Of the infrared rays that have reached the plate 16, only medium-wavelength infrared rays and short-wavelength infrared rays are selected by the optical slit plate 16 and irradiated from the irradiation unit 10.
The infrared rays that have passed through the slit 16a of the optical slit plate 16 are appropriately adjusted by a collimator lens or the like, and then irradiated toward the exhaust gas supplied into the cell 20 (see FIG. 1). At this time, since the irradiated infrared rays are partially blocked by the optical slit plate 16, the intensity is lower than that in the case where the optical slit plate 16 is not installed, but the exhaust gas supplied into the cell 20 is exhausted. It is set so as to have a strength capable of measuring hydrocarbons contained in the gas.

Thus, as shown in FIG. 3, the long wavelength infrared rays are blocked during the infrared wavelength sweep, and the portions where the intensity of the infrared rays received by the light receiving unit 30 (see FIG. 1) is zero for a certain period are periodically It becomes possible to form.
This makes it possible to grasp the zero point of the infrared light reception intensity without periodically blocking the infrared light using an optical chopper, to correct the infrared oscillation intensity, and to remove the influence (noise) of the background light. It can be carried out. Therefore, the THC measuring device 1 can be configured to be small and inexpensive, and errors in measuring hydrocarbons contained in the exhaust gas can be reduced.
In addition, although the optical slit plate 16 in this embodiment has the structure which has the slit 16a and interrupts | blocks only long wavelength infrared rays, it is not limited to this, It has a slit which interrupts | blocks only short wavelength infrared rays. It is good also as a structure which has both a structure or the slit which interrupts | blocks short wavelength infrared rays, and the slit which interrupts | blocks long wavelength infrared rays.

As another form of the irradiation unit according to the present invention, the irradiation unit 110 can be applied in place of the irradiation unit 10.
Below, with reference to FIGS. 4-5, the structure of the irradiation part 110 is demonstrated in detail.

  As shown in FIG. 4, the irradiation unit 110 includes a light source 112, a movable mirror 113, a diffraction grating 114, a half mirror 115, and an optical slit plate 116.

  The light source 112 is configured in substantially the same manner as the light source 12 of the irradiating unit 10, and the half-mirror 115 emits broadband infrared light including a wavelength range absorbed by hydrocarbons contained in the exhaust gas introduced into the cell 20 (see FIG. 1). This is a member that irradiates the diffraction grating 114 via

The movable mirror 113 is configured in substantially the same manner as the movable mirror 13 of the irradiating unit 10, functions as a means for reflecting infrared rays dispersed by the diffraction grating 114, and is a member that is incident on the diffraction grating 114 again at an appropriate angle.
The movable mirror 113 is swingably provided on an appropriate fixed shaft, and the control unit 40 (so as to swing within a predetermined range (between position P3 and position P4 shown in FIG. 4) around the fixed shaft. 1). Assuming that the position P3 shown in FIG. 4 is the initial position of the movable mirror 113, the period until the movable mirror 113 rotates to the position P4 and returns to the position P3 is the rotation period (one period) of the movable mirror 113.

The diffraction grating 114 is configured in substantially the same manner as the diffraction grating 14 of the irradiation unit 10, functions as a means for diffracting infrared light irradiated from the light source 112 and transmitted through the half mirror 115, and the infrared light is dispersed for each wavelength. It is a member that reflects toward the movable mirror 113 and reflects the infrared rays reflected by the movable mirror 113 toward the half mirror 115. The diffraction grating 114 is disposed at a position where the infrared light irradiated from the light source 112 and transmitted through the half mirror 115 is incident and the infrared light reflected by the movable mirror 113 is incident.
Similar to the diffraction grating 14 of the irradiation unit 10, the diffraction grating 114 generates medium-wavelength infrared light, short-wavelength infrared light, and long-wavelength infrared light from incident infrared light according to the swing position of the movable mirror 113.

The half mirror 115 is a member that reflects a part of incident light and transmits the remaining part. The half mirror 115 transmits a part of infrared rays emitted from the light source 112 to be incident on the diffraction grating 114. The infrared rays dispersed by the light are reflected toward the optical slit plate 116.
The half mirror 115 is disposed on the optical path of the infrared light emitted from the light source 112 and generated by the diffraction grating 114 on the optical path of the medium wavelength infrared light, the short wavelength infrared light, and the long wavelength infrared light. Yes.

The optical axes of the medium-wavelength infrared light, the short-wavelength infrared light, and the long-wavelength infrared light reflected by the half mirror 115 are substantially parallel to each other at a predetermined interval.
As described above, this is because the movable mirror 113 swings within a predetermined range (between the position P3 and the position P4 shown in FIG. 4) and the infrared light that is spectrally reflected and reflected by the diffraction grating 114 is directed to the diffraction grating 114 again. This is because infrared rays reflected and incident on the diffraction grating 114 at a plurality of angles are dispersed.

Specifically, the medium-wavelength infrared light, the short-wavelength infrared light, and the long-wavelength infrared light generated by the diffraction grating 114 have different angles toward the movable mirror 113 (reflection angles at the diffraction grating 114). When the incident angles with respect to the oscillating movable mirror 113 are 0 degrees, that is, in the state where the medium wavelength infrared ray, the short wavelength infrared ray, and the long wavelength infrared ray, the respective optical axes and the movable mirror 113 are orthogonal to each other. , And follow the same optical path between the movable mirror 113 and the diffraction grating 114, respectively, and enter the half mirror 115 in a state in which the respective optical axes are substantially parallel with a predetermined distance from each other. However, the installation position of the light source 112 and the swing range of the movable mirror 113 are set so that the optical axes of the medium wavelength infrared rays, the short wavelength infrared rays, and the long wavelength infrared rays are substantially parallel to each other with a predetermined interval therebetween. In addition, the installation position, the installation position of the diffraction grating 114, the installation position of the half mirror 115, and the like are set as appropriate.
In this way, the movable mirror 113 and the diffraction grating 114 function as a spectroscope, and in synchronization with the swinging of the movable mirror 113, irradiation is performed by sequentially extracting medium wavelength infrared rays, short wavelength infrared rays, and long wavelength infrared rays. The wavelength of infrared rays emitted from the unit 110 varies, and wavelength sweeping is realized.

The optical slit plate 116 is configured in substantially the same manner as the optical slit plate 16 of the irradiation unit 10 and is a plate material made of a material that does not transmit infrared rays emitted from the light source 112, and serves as a light shielding member that blocks infrared rays in a predetermined wavelength range. Function. The optical slit plate 116 is disposed on the optical path of the medium-wavelength infrared light, the short-wavelength infrared light, and the long-wavelength infrared light reflected by the half mirror 115. The optical slit plate 116 is formed with a slit 116a.
The slit 116a is a fine hole penetrating the front and back surfaces of the optical slit plate 116, and is disposed in a portion where an optical path of medium-wavelength infrared light and long-wavelength infrared light is located. The medium-wavelength infrared light and the long-wavelength infrared light pass through the slit 116a of the optical slit plate 116, and the short-wavelength infrared light is blocked by a portion of the optical slit plate 116 where the slit 116a is not formed.

As described above, in the irradiating unit 110, an optical path that sequentially follows the light source 112, the half mirror 115, the diffraction grating 114, the movable mirror 113, the diffraction grating 114, the half mirror 115, and the optical slit plate 116 is formed.
In the irradiating unit 110, since the optical path passes through the diffraction grating 114 twice, infrared rays can be more favorably dispersed as compared with the irradiating unit 10.

The infrared rays emitted from the light source 112 are swept in wavelength by the movable mirror 113 that swings within a predetermined range (between the position P3 and the position P4 shown in FIG. 4) and the diffraction grating 114 that divides the infrared rays, and the optical slit Of the infrared rays that have reached the plate 116, only the medium-wavelength infrared rays and the long-wavelength infrared rays are selected by the optical slit plate 116 and irradiated from the irradiation unit 110.
The infrared rays that have passed through the slit 116a of the optical slit plate 116 are appropriately adjusted by a collimating lens or the like and then irradiated toward the exhaust gas supplied into the cell 20 (see FIG. 1). At this time, the irradiated infrared rays are partially reflected and transmitted by the half mirror 115 and partially blocked by the optical slit plate 116, so that compared with the case where the half mirror 115 and the optical slit plate 116 are not installed. Thus, the strength is lowered, but the strength is set such that hydrocarbons contained in the exhaust gas supplied into the cell 20 can be measured.

Thus, as shown in FIG. 5, the infrared light having a short wavelength is blocked during the wavelength sweeping of the infrared light, and the portion where the intensity of the infrared light received by the light receiving unit 30 (see FIG. 1) is zero for a certain period is periodically It becomes possible to form.
This makes it possible to grasp the zero point of the infrared light reception intensity without periodically blocking the infrared light using an optical chopper, to correct the infrared oscillation intensity, and to remove the influence (noise) of the background light. It can be carried out. Therefore, the THC measuring device 1 can be configured to be small and inexpensive, and errors in measuring hydrocarbons contained in the exhaust gas can be reduced.
The optical slit plate 116 in the present embodiment has the slit 116a and is configured to block only short-wavelength infrared, but is not limited thereto, and has a slit that blocks only long-wavelength infrared. It is good also as a structure which has both a structure or the slit which interrupts | blocks short wavelength infrared rays, and the slit which interrupts | blocks long wavelength infrared rays.

Further, as another form of the irradiation unit according to the present invention, the irradiation unit 210 can be applied in place of the irradiation unit 110.
Below, with reference to FIGS. 6-7, the structure of the irradiation part 210 is demonstrated in detail.
In addition, the same code | symbol is attached | subjected to the part which is common with the irradiation part 110, and the description is abbreviate | omitted.

As shown in FIG. 6, the irradiation unit 210 includes a light source 112, a movable mirror 113, a diffraction grating 114, a half mirror 115, and a light shielding plate 216.
The irradiation unit 210 is different from the irradiation unit 110 in that it includes a light shielding plate 216 instead of the optical slit plate 116.

  The light shielding plate 216 is a plate material that functions as a light shielding member that blocks infrared rays emitted from the light source 112. The light shielding plate 216 is disposed on the short-wavelength infrared light path that forms a part of the infrared light that is split by the diffraction grating 114 and reflected toward the movable mirror 113. The short wavelength infrared rays are blocked by the light shielding plate 216 and cannot enter the movable mirror 113.

As described above, in the irradiation unit 210, an optical path that sequentially follows the light source 112, the half mirror 115, the diffraction grating 114, the light shielding plate 216 (only short-wave infrared light), the movable mirror 113, the diffraction grating 114, and the half mirror 115 is formed. Is done.
In the irradiating unit 210, similarly to the irradiating unit 110, the optical path passes through the diffraction grating 114 twice, and therefore, infrared rays can be more favorably dispersed as compared with the irradiating unit 10.

Infrared rays emitted from the light source 112 are swept in wavelength by a movable mirror 113 that swings within a predetermined range (between the position P3 and the position P4 shown in FIG. 6) and a diffraction grating 114 that divides the infrared rays, and a light shielding plate. Since the short wavelength infrared ray is blocked by 216, only the medium wavelength infrared ray and the long wavelength infrared ray are selected and irradiated from the irradiation unit 210.
The infrared light reflected by the half mirror 115 is appropriately adjusted by a collimator lens or the like, and then irradiated toward the exhaust gas supplied into the cell 20 (see FIG. 1). At this time, the irradiated infrared rays are partially reflected and transmitted by the half mirror 115 and partially blocked by the light shielding plate 216, so that compared to the case where the half mirror 115 and the light shielding plate 216 are not installed. Although the strength is lowered, the strength is set so that hydrocarbons contained in the exhaust gas supplied into the cell 20 can be measured.

In this way, as shown in FIG. 7, the short wavelength infrared rays are blocked during the infrared wavelength sweep, and the portions where the intensity of the infrared rays received by the light receiving unit 30 (see FIG. 1) is zero for a certain period are periodically It becomes possible to form.
This makes it possible to grasp the zero point of the infrared light reception intensity without periodically blocking the infrared light using an optical chopper, to correct the infrared oscillation intensity, and to remove the influence (noise) of the background light. It can be carried out. Therefore, the THC measuring device 1 can be configured to be small and inexpensive, and errors in measuring hydrocarbons contained in the exhaust gas can be reduced.
In addition, although the light shielding plate 216 in the present embodiment is disposed so as to block only short-wavelength infrared, it is not limited thereto, and may be disposed so as to block only long-wavelength infrared, A plurality of short wavelength infrared rays and long wavelength infrared rays may be arranged so as to be blocked.

Further, as another form of the irradiation unit according to the present invention, the irradiation unit 310 can be applied in place of the irradiation unit 10.
Below, with reference to FIGS. 8-9, the structure of the irradiation part 310 is demonstrated in detail.

  As shown in FIG. 8, the irradiation unit 310 includes a light source 312, a movable mirror 313, a diffraction grating 314, and a fixed mirror 315.

  The light source 312 is configured in substantially the same manner as the light source 12 of the irradiation unit 10, and a movable mirror 313 emits broadband infrared light including a wavelength range absorbed by hydrocarbons contained in exhaust gas introduced into the cell 20 (see FIG. 1). It is a member which irradiates toward.

The movable mirror 313 is configured in substantially the same manner as the movable mirror 13 of the irradiating unit 10, functions as a means for reflecting infrared rays emitted from the light source 312, and is a member that enters the diffraction grating 314 at an appropriate angle.
The movable mirror 313 is swingably provided on an appropriate fixed shaft, and the control unit 40 (so as to swing within a predetermined range around the fixed shaft (between position P5 and position P6 shown in FIG. 8). 1). Assuming that the position P5 shown in FIG. 8 is the initial position of the movable mirror 313, the period until the movable mirror 313 rotates to the position P6 and returns to the position P5 is the rotation period (one period) of the movable mirror 313.

The swing range of the movable mirror 313 (between the position P5 and the position P6 shown in FIG. 8) is set so that infrared rays do not enter the diffraction grating 314 in a part thereof.
For example, when the movable mirror 313 is located at the position P5 shown in FIG. 8, the infrared rays reflected by the movable mirror 313 are directed to the left in FIG. 8 rather than the diffraction grating 314 and do not enter the diffraction grating 314. Further, when the movable mirror 313 is positioned at the position P6 shown in FIG. 8, the infrared rays reflected by the movable mirror 313 are directed to the right side in FIG. 8 rather than the diffraction grating 314 and do not enter the diffraction grating 314.

  The diffraction grating 314 is configured in substantially the same manner as the diffraction grating 14 of the irradiation unit 10 and functions as means for diffracting the infrared light reflected by the movable mirror 313. The infrared light is dispersed for each wavelength and directed to the fixed mirror 315. It is a member to be reflected. The diffraction grating 314 is disposed at a position where infrared rays reflected by the movable mirror 313 are incident.

The fixed mirror 315 is a member that is configured in substantially the same manner as the fixed mirror 15 of the irradiating unit 10 and reflects infrared rays that are spectrally separated by the diffraction grating 314.
The fixed mirror 15 is disposed on the optical path of the medium wavelength infrared light generated by the diffraction grating 314.

  As described above, in the irradiation unit 310, an optical path that follows the light source 312, the movable mirror 313, the diffraction grating 314, and the fixed mirror 315 in order is formed.

The infrared light emitted from the light source 312 has a wavelength in a state where a part of the infrared light reflected by the movable mirror 313 oscillating within a predetermined range (between the position P5 and the position P6 shown in FIG. 8) does not enter the diffraction grating 314. Since it is swept, only the medium wavelength infrared rays are selected and irradiated from the irradiation unit 310. That is, the movable mirror 313 functions as a means for blocking a part of the optical path of the infrared rays dispersed by the diffraction grating 314.
The infrared light reflected by the fixed mirror 315 is appropriately adjusted by a collimating lens or the like, and then irradiated toward the exhaust gas supplied into the cell 20 (see FIG. 1). At this time, the irradiated infrared rays are not partially blocked by a light shielding member or the like, and thus the strength does not decrease.

In this way, as shown in FIG. 9, only the middle-wavelength infrared light is selected at the time of the infrared wavelength sweep, and the portion where the intensity of the infrared light received by the light receiving unit 30 (see FIG. 1) is zero for a certain period is periodically Can be formed.
This makes it possible to grasp the zero point of the infrared light reception intensity without periodically blocking the infrared light using an optical chopper, to correct the infrared oscillation intensity, and to remove the influence (noise) of the background light. It can be carried out. Therefore, the THC measuring device 1 can be configured to be small and inexpensive, and errors in measuring hydrocarbons contained in the exhaust gas can be reduced.
In addition, since it is not necessary to block infrared rays using a light blocking member or the like, the THC measuring apparatus 1 can be configured at a lower cost.
Note that the movable mirror 313 in this embodiment swings between the position P5 and the position P6 shown in FIG. 8 and selects only the infrared light having the medium wavelength. However, the present invention is not limited to this. The movable mirror 313 may be swung within a range in which infrared rays and short-wavelength infrared rays are selected, or medium-wavelength infrared rays and long-wavelength infrared rays are selected.

DESCRIPTION OF SYMBOLS 1 THC measuring apparatus 10 Irradiation part 11 Case 12 Light source 13 Movable mirror 14 Diffraction grating 15 Fixed mirror 16 Optical slit plate 16a Slit 20 Cell 30 Light receiving part 40 Control part

Claims (3)

An irradiating unit for irradiating infrared light whose wavelength varies periodically;
A light receiving unit that detects the infrared rays and obtains the intensity of the infrared rays;
Containing a measurement target gas and transmitting the infrared rays,
By irradiating infrared rays toward the measurement target gas contained in the cell from the irradiation unit, and detecting the infrared rays transmitted through the measurement target gas by the light receiving unit, the intensity of the infrared rays transmitted through the measurement target gas is determined. Obtaining, based on the intensity of the infrared rays, a hydrocarbon concentration measuring device that measures the concentration of hydrocarbons contained in the measurement object gas,
The irradiation unit is
A light source that emits infrared light including a wavelength range that is absorbed by hydrocarbons contained in the measurement target gas;
Spectroscopying the infrared rays emitted from the light source, a medium wavelength infrared ray having a wavelength range necessary for measuring the concentration of hydrocarbons contained in the measurement target gas, a wavelength range shorter than the medium wavelength infrared ray A spectroscope that periodically varies the wavelength by sequentially taking out short-wavelength infrared light and long-wavelength infrared light having a longer wavelength range than the medium-wavelength infrared light,
A blocking means for blocking at least one of the short wavelength infrared rays and the long wavelength infrared rays;
A hydrocarbon concentration measuring apparatus comprising: The spectrometer is
Reflecting means for reflecting incident infrared rays in a plurality of directions;
Diffracting means for diffracting incident infrared rays to diffract, and
The blocking means is
The hydrocarbon concentration measuring apparatus according to claim 1, wherein the hydrocarbon concentration measuring apparatus is a light shielding member that is provided on at least one of an optical path of the short wavelength infrared and the long wavelength infrared and blocks the optical path. The spectrometer is
Reflecting means for reflecting incident infrared rays in a plurality of directions;
Diffracting means for diffracting incident infrared rays to diffract, and
2. The hydrocarbon concentration measuring apparatus according to claim 1, wherein the reflecting unit functions as the blocking unit by swinging in a range including a position where the infrared light emitted from the light source does not enter the diffracting unit.

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