JP2019184277A - Concentration measurement device and concentration measurement method - Google Patents

Abstract

To accurately measure, without changing the configuration of the device, gas concentration by light absorption spectrometry using transmitted light of long optical length remaining after removal of transmission light of short optical length.SOLUTION: A closed optical path is formed by a first reflector 14 to a third reflector 18. A chopper type mirror 22 rotates around a rotation axis. Light passage portions through which light is allowed to pass are formed at equal intervals around the chopper type mirror. Portions other than the light passage portions 34 are light reflection members. The light passage portions 34 are arranged in positions where light in the closed optical path is allowed to pass. Gas concentration in a gas cell 20 is calculated based on a signal output by a light intensity detector 26 from when incidence of light from the closed optical path is allowed to when a signal output from a light intensity detector 26 indicates a smallest value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a concentration measuring apparatus and a concentration measuring method.

  Conventionally, a collection tube is provided at the front stage of the gas cell, and the gas component to be measured is adsorbed to the collection tube and collected, then the gas component is desorbed by heating with a heater, and the gas component is concentrated and enclosed in the gas cell. Then, an apparatus has been proposed in which interference gas is irradiated to the enclosed gas, the light emitted from the gas cell is detected by a detector, and the concentration of the gas is obtained based on the detected light intensity (Patent Document 1). ).

JP 07-270316 A

  When measuring a low-concentration gas in a concentration measuring apparatus, it is necessary to increase the absorbance by increasing the distance (optical path length) through which light passes through the gas cell in order to increase the detection sensitivity. In the above conventional apparatus, the optical path length is increased by raising a multiple reflection mirror in the gas cell and reciprocating the infrared light from the light source several times in the gas cell.

  However, in the above conventional apparatus, when the gas has a high concentration, infrared light is absorbed by the gas to be measured, so that light cannot be detected by a light intensity detector such as an infrared sensor, or the absorbance of the concentration change Sensitivity may not be guaranteed. The output signal of the light intensity detector can include transmitted light having a long optical path length and transmitted light having a short optical path length. The transmitted light having a short optical path length has a lower signal-to-noise ratio than the transmitted light having a long optical path length, so the gas concentration should be measured with the transmitted light having a long optical path length. In this apparatus, it is impossible to separate transmitted light having a long optical path length and short transmitted light.

  In view of the above, in order to accurately measure the gas concentration in the case where the concentration of the gas sealed in the gas cell is assumed to be high and in the case where it is assumed to be low, the device is changed, for example, by changing the detector. It is necessary to change the configuration.

  The present invention relates to a concentration measuring apparatus and a concentration measuring method for accurately measuring the concentration of a gas by absorption analysis using transmitted light having a long optical path length by excluding transmitted light having a short optical path length without changing the apparatus configuration. The purpose is to provide.

  In order to achieve the above object, the concentration measuring apparatus according to claim 1 of the present application is disposed in a light source, an optical system that forms a closed optical path of light incident from the light source, and an optical path of the closed optical path, A gas is supplied to the inside and light from the closed optical path passes through the interior and exits to the closed optical path, and allows light from the light source to enter the closed optical path, and by the permission A permitting device that permits the light that has passed through the container to exit from the closed optical path, and a light that exits from the closed optical path via the permitting device are arranged to be incident, according to the intensity of the incident light A light intensity detector that outputs a signal; and the permission state can be detected, and light from the light source incident on the closed optical path and light that has passed through the container a plurality of times through the closed optical path is the closed optical path The permitter to be emitted from And controlling the concentration of gas in the container based on the signal output from the light intensity detector until the intensity of the signal output from the light intensity detector indicates a minimum value from the time when the permission state is detected. And a controller for calculating.

  The optical system forms a closed optical path for light incident from the light source. In the optical path of the closed optical path, there is a container in which a gas to be measured is supplied, and light incident from the light source passes through the container. The permitter permits the light that has passed through the container to be emitted from the closed optical path.

  The controller controls the permitter so that the light that has passed through the container a plurality of times through the closed optical path is emitted from the closed optical path and causes the light to enter the light intensity detector, and the permitter enters the permitted state. The concentration of the gas in the container is calculated based on the signal output from the light intensity detector until the intensity of the signal output from the light intensity detector shows a minimum value from that time.

  As in the invention of claim 2, the controller is allowed to enter the gas when the gas supplied to the container has a low concentration, and is allowed to enter the closed optical path more than when the gas is high. The permitter may be controlled so that the number of times that the light passes through the container increases.

  As in the invention of claim 3, the permitter includes a moving member in which a portion through which light can pass is formed, a position where the light in the closed optical path can pass through the portion and exit from the closed optical path, A mechanism for moving the moving member to a position where light on the closed optical path is reflected by a predetermined portion other than the portion of the moving member and returns to the closed optical path, and the controller is supplied to the container. The mechanism may be controlled so that the number of times is adjusted according to the assumed concentration of the gas.

  According to a fourth aspect of the present invention, the moving member rotates about an axis, and a portion through which light can pass is formed. The rotating member is disposed at a position through which the light in the closed optical path can pass. The mechanism controls the rotation of the rotating member, and the controller controls the rotation speed of the rotating member when the assumed concentration of the gas supplied to the container is low than when it is high. You may make it control the said mechanism so that it may become small.

  According to a fifth aspect of the present invention, the apparatus further comprises a rotation angle detector that detects a rotation angle of the rotating member, and the controller is configured to allow the permission based on the rotation angle detected by the rotation angle detector. The state may be detected.

  As in the invention of claim 6, the permitter has a portion that can be changed between a passable state where light can pass and a non-passable state where light cannot pass, and is changed to the passable state. And selectively switching the portion of the light passage state changer to the passable state or the non-passable state. A light switch that is allowed to be incident when the assumed concentration of the gas supplied to the container is low than when it is high, and is incident on the closed optical path. The switch may be controlled so that the number of times that the gas passes through the inside of the container increases.

  The light passage state changer is an electronic shutter as in the invention of claim 7, and the controller detects the permission state based on transmission of a control signal for opening the electronic shutter. Also good.

  In addition, as for the said container, at least the incident part in which the light of the said closed optical path injects, and the emission part which passes through the said inside and radiate | emits to the said closed optical path may be transparent.

  The concentration measuring method according to claim 9 is arranged in a light source, an optical system that forms a closed optical path of light incident from the light source, and an optical path of the closed optical path, and a gas is supplied to the inside and the closed A container in which light in the optical path passes through the interior and exits to the closed optical path; and permits light from the light source to enter the closed optical path, and allows light that has passed through the container to pass through the closed optical path. A light intensity detector that allows the light emitted from the closed optical path to enter through the permission device, and outputs a signal corresponding to the intensity of the incident light; The permitter is capable of detecting the permission state, so that light from the light source is incident on the closed optical path and light that has passed through the container a plurality of times through the closed optical path is emitted from the closed optical path. And controlling the permission status Intensity from time out signal the light intensity detector is output to calculate the concentration of the gas in the container based on a signal output by said light intensity detector to indicate a minimum value.

  The present invention can accurately measure the gas concentration by absorption analysis using transmitted light having a long optical path length by excluding transmitted light having a short optical path length without changing the apparatus configuration.

It is the schematic which shows the structure of the density | concentration measuring apparatus of 1st Embodiment. (A) is a front view of the chopper type mirror 22, and (B) is a side view of the chopper type mirror 22. It is explanatory drawing which showed the mode of the density | concentration measuring apparatus when the infrared rays from the infrared light source 12 inject into a closed optical path. It is explanatory drawing which showed the position of the light passage part 34 of the chopper type | mold mirror 22 when the infrared rays from the infrared light source 12 enter into a closed optical path. It is explanatory drawing which showed a mode that the infrared rays which injected entered the closed optical path many times. It is explanatory drawing which showed the position of the light reflection part 32 of the chopper-type mirror 22 when the incident infrared rays go around the closed optical path many times. It is explanatory drawing which showed a mode that the infrared rays radiate | emitted from the closed optical path arrived at the light intensity detector 26. FIG. (A) is explanatory drawing which showed an example of the output signal 64 which shows the transmitted light intensity which the light intensity detector 26 detected, (B) is the signal (circumferential light signal) concerning the circulating light 60 contained in the output signal 64 ) 66 and a signal (one-round optical signal) 68 related to the one-round light 62. It is the schematic which shows the structure of the density | concentration measuring apparatus of 2nd Embodiment. It is explanatory drawing which showed a mode that the infrared rays from the light intensity detector 26 reached | attained the gas cell 20 via the chopper type mirror 22. FIG. It is explanatory drawing which showed a mode that infrared rays reciprocated between the chopper type | mold mirror 22 and the reflective mirror 44 through the inside of the gas cell 20 many times. Infrared rays that have reciprocated many times between the chopper type mirror 22 and the reflecting mirror 44 through the inside of the gas cell 20 pass through the light passing part 34 of the chopper type mirror 22 and the beam splitter 42 to obtain the light intensity. It is explanatory drawing which showed a mode that it reached | attained the detector 26. FIG. It is the schematic which shows the structure of the density | concentration measuring apparatus of 3rd Embodiment. (A) is explanatory drawing which showed an example of the output signal 80 which shows the transmitted light intensity which the light intensity detector 26 detected, (B) is the signal (circumferential light signal) concerning the circulating light 74 contained in the output signal 80 ) 82 and a signal (reflected light signal) 84 related to the reflected light 78 and a signal (one-round light signal) 86 related to the one-round light 76, respectively. It is the schematic which showed the structure of the density | concentration measuring apparatus of 4th Embodiment. It is explanatory drawing which showed the structure of the density | concentration measuring apparatus which concerns on a 1st modification. It is explanatory drawing which showed the structure of the density | concentration measuring apparatus which concerns on a 2nd modification.

  Embodiments of the present invention will be described below.

(First embodiment)
FIG. 1 shows the configuration of the concentration measuring apparatus according to the first embodiment. As shown in FIG. 1, the concentration measuring apparatus according to the first embodiment includes an infrared light source 12 that emits infrared light, and a first optical path that forms a closed optical path so that light incident from the infrared light source 12 circulates. Reflecting mirrors 14 to 3. The concentration measuring device is disposed in the optical path of the closed optical path formed by the first reflecting mirror 14 to the third reflecting mirror 18, and gas is supplied to the inside and light in the closed optical path passes through the inside and is closed. A gas cell 20 that exits to the optical path is provided. The gas cell 20 is transparent at least at the incident part where the light of the closed optical path enters and the outgoing part which passes through the inside and exits to the closed optical path. The gas cell 20 may be entirely transparent.

  The concentration measuring device includes a chopper-type mirror 22 that permits the infrared light from the infrared light source 12 to enter the closed optical path and allows the infrared light that has passed through the gas cell 20 to exit from the closed optical path by the permission. ing. The chopper type mirror 22 is formed in a disk shape that rotates about an axis. The concentration measuring apparatus includes a rotation speed adjustment mechanism 24 that controls the rotation speed (rotation speed) of the chopper type mirror 22 per unit time.

  The concentration measuring device includes a light intensity detector 26 that detects the intensity of light emitted from the closed optical path via the chopper type mirror 22.

  The concentration measuring device includes a controller 28 connected to the infrared light source 12, the rotation speed adjusting mechanism 24, and the light intensity detector 26. The controller 28 is constituted by a computer including a CPU, a ROM, a RAM, a display, etc. (not shown). The ROM stores a density measurement processing program to be described later. The density measurement processing program is read from the ROM, expanded in the RAM, and executed by the CPU to execute the density measurement process.

  The controller 28 is further connected with an infrared non-absorbing gas supply unit (not shown) for supplying an infrared non-absorbing gas to the gas cell 20 and a measurement target gas supply unit (not shown) for supplying a measurement target gas to the gas cell 20. Then, the controller 28 controls the infrared non-absorbing gas supply unit or the measurement target gas supply unit to supply the gas cell 20 with the infrared non-absorption gas or the measurement target gas.

  The controller 28 adjusts the number of times that the light incident on the closed optical path passes through the gas supplied to the gas cell 20 according to the assumed concentration of the gas supplied to the gas cell 20. Thus, the rotation speed adjusting mechanism 24 is controlled so as to be emitted from the closed optical path. The controller 28 calculates the gas concentration based on the light intensity detected by the light intensity detector 26.

  Next, the configuration of the chopper type mirror 22 will be described. FIG. 2 shows the configuration of the chopper type mirror 22. FIG. 2A shows a front view of the chopper type mirror 22, and FIG. 2B shows a side view of the chopper type mirror 22.

  As shown in FIG. 2, the chopper type mirror 22 is a rotating member that rotates about a rotating shaft 30. Around the chopper-type mirror 22, light passing portions 34 through which light can pass at equal intervals are formed. The chopper-type mirror 22 is disposed at a position where light on the closed optical path can pass through the light passage portion 34. A portion other than the light passage portion 34 of the chopper type mirror 22 is formed in the light reflection portion 32. The light passing part 34 is defined between the incident start edge 34A and the incident end edge 34B in the light reflecting part 32. The surface opposite to the surface on which the light reflecting portion 32 of the chopper mirror 22 is provided is a light absorbing portion 36 that absorbs light without reflecting it. As an example, the light absorbing portion 36 is subjected to a surface treatment such as black matte coating.

  Next, referring to FIG. 3 to FIG. 7, infrared light from the infrared light source 12 enters the closed optical path, and the incident infrared light circulates the closed optical path many times, and then reaches the light intensity detector 26. How to do is explained.

  FIG. 3 shows the state of the concentration measuring apparatus when the infrared light from the infrared light source 12 enters the closed optical path. FIG. 4 shows the position of the light passage portion 34 of the chopper-type mirror 22 when the infrared light from the infrared light source 12 is incident on the closed optical path. FIG. 5 shows how the incident infrared rays circulate around the closed optical path many times. FIG. 6 shows the position of the light reflecting portion 32 of the chopper-type mirror 22 when the incident infrared ray goes around the closed optical path many times. FIG. 7 shows how the infrared light emitted from the closed optical path reaches the light intensity detector 26.

  When the chopper-type mirror 22 rotates and the light passing portion 34 is positioned in the closed optical path as shown in FIG. 4 and infrared rays are irradiated from the infrared light source 12, the irradiated infrared rays are irradiated as shown in FIG. Passes through the light passage 34 and travels toward the first reflecting mirror 14. The infrared rays directed toward the first reflecting mirror 14 are incident on the gas cell 20 through the first reflecting mirror 14 as shown in FIG. The infrared rays from the first reflecting mirror 14 toward the gas cell 20 enter the gas cell 20 through the transparent incident portion of the gas cell 20, pass through the gas cell 20, and pass through the transparent emission portion of the gas cell 20. To the closed optical path. The infrared rays emitted to the closed optical path through the transparent emission part of the gas cell 20 reach the second reflecting mirror 16, are reflected by the second reflecting mirror 16, reach the third reflecting mirror 18, and the third Is reflected by the reflecting mirror 18 toward the chopper-type mirror 22. As shown in FIG. 6, when the light reflecting portion 32 is located in the closed optical path, the infrared light reflected by the third reflecting mirror 18 and directed to the chopper type mirror 22 is reflected by the light reflecting portion 32, It reaches the first reflecting mirror 14. Thereby, a closed optical path is formed. In this state, infrared rays go around the closed optical path many times and pass through the gas cell 20 many times. If a measurement target gas that absorbs infrared rays is supplied to the gas cell 20, a part of the infrared rays is absorbed by the measurement target gas in the gas cell 20. Therefore, when the infrared light circulates the closed optical path many times, the infrared light that has not been absorbed by the measurement target gas in one circulation is also absorbed by the measurement target gas.

  Thereafter, as shown in FIG. 7, when the light passing part 34 is positioned in the closed optical path, the circulating light 60 that is infrared light that has been circulated many times in the closed optical path and was not absorbed by the measurement target gas is converted into the light passing part. 34, and reaches the light intensity detector 26. Thereby, the light intensity detector 26 detects the light intensity of infrared rays and outputs a light intensity signal indicating the light intensity to the controller 28.

  However, it is not only the circulating light 60 that enters the light intensity detector 26. One-round light 62 incident on the light intensity detector 26 after only one round of the closed optical path is included. In the first embodiment, the absorbance is calculated by excluding light containing a large amount of one-round light 62 from the light incident on the light intensity detector 26.

  FIG. 8A is an explanatory diagram showing an example of the output signal 64 indicating the transmitted light intensity detected by the light intensity detector 26, and FIG. 8B shows the output signal 64 shown in FIG. It is explanatory drawing which each showed the signal (circumferential light signal) 66 which concerns on the included circulating light 60, and the signal (1 optical signal) 68 which concerns on the 1 round light 62.

  As described above, the light incident on the light intensity detector 26 is a mixture of the circulating light 60 and the one-round light 62. In order for the circulating light 60 to enter the light intensity detector 26, a chopper is placed in the closed optical path. It is necessary for the chopper type mirror 22 to be switched from the “reflection state” to the “incident state” by positioning the light passing portion 34 of the type mirror 22. In such a case, the light emitted from the infrared light source 12 enters the closed optical path and becomes the one-round light 62. However, when the light passage part 34 is positioned in the closed optical path, the circulating light 60 reaches the light intensity detector 26, but the one-round light 62 is irradiated from the infrared light source 12 and is closed via the light passage part 34. In this state, the light is incident on the optical path. Accordingly, the circulating light 60 enters the light intensity detector 26 earlier than the one-round light 62.

  Further, since the circulating light 60 passes through the gas cell 20 a plurality of times, the light absorption by the measurement target gas becomes more conspicuous than the one-round light. Further, the intensity is different due to reflection by each reflecting mirror.

  Considering the time difference between each of the circulating light 60 and the one-round light 62 reaching the light intensity detector 26, the intensity of the circulating light 60 is attenuated as time passes after entering the incident state. As long as the chopper-type mirror 22 is in the incident state, the irradiation from the infrared light source 12 to the closed optical path is continued, so that the intensity of the one-round light 62 is increased or constant after the intensity of the circulating light 60 is attenuated. To maintain.

  As described above, the transmitted light intensity detected by the light intensity detector 26 becomes a minimum value mainly after the circulating light 60 reaches the light intensity detector 26, and then becomes a minimum value. Increased by reaching the light intensity detector 26.

  As shown in FIG. 8A, the curve of the output signal 64 of the transmitted light intensity detected by the light intensity detector 26 shows a local minimum value A after showing a local maximum value in an upwardly convex manner. . Further, the curve of the output signal 64 turns to a monotonous increase after showing the minimum value A.

  The components of the output signal 64 are as shown in FIG. The output signal 64 in FIG. 8A includes a circulating optical signal 66 and a one-round optical signal 68. Therefore, by adopting the output signal 64 from the time when the chopper-type mirror 22 is switched from the reflection state to the incident state until the time when the output signal 64 indicating the transmitted light intensity becomes the minimum value A, the light intensity detector 26 is used. Absorbance can be calculated by excluding light containing a lot of one-round light 62 from the incident light. As a result, it is possible to calculate the absorbance based on the output signal having a high S / N ratio, and the concentration of the measurement target gas can be measured more accurately.

  The time when the chopper type mirror 22 is switched from the reflection state to the incident state is a state in which the chopper type mirror 22 permits light emission from the closed optical path. The permission state can be estimated from the fact that the output signal 64 starts monotonically increasing as shown in FIG. 8A, but the surface of the chopper mirror 22 facing the light intensity detector 26 is infrared. The light from the light source 12 may be reflected, and in such a case, it is difficult to accurately detect the permission state. In the first embodiment, as an example, the rotation speed adjustment mechanism 24 is provided with a rotation angle sensor (not shown) for detecting the rotation angle of the chopper type mirror, such as a magnetoresistive (MR) sensor or a rotary encoder, The controller 28 calculates the rotation position of the chopper type mirror 22 from the rotation angle of the chopper type mirror 22 detected by the rotation angle sensor, and detects a permission state in which the chopper type mirror 22 starts emission from the closed optical path from the rotation position. To do. The detection of the permission state using the rotation angle sensor is also effective in the second to fourth embodiments described later.

  In order to calculate the concentration of the target gas in the gas cell 20 from the output signal of the light intensity detector 26, the output signal 64 indicating the transmitted light intensity is a minimum value from the time when the chopper-type mirror 22 switches from the reflective state to the incident state. Although it is based on the integral value with respect to the time of the output signal 64 up to the time when A is reached, since it is a known calculation method, a detailed description is omitted.

  When the concentration of the measurement target gas in the gas cell 20 is high, the maximum value due to the circulating optical signal 66 shown in FIGS. 8A and 8B decreases, but as described above, the circulating optical signal 66. Since the SN ratio is high, the concentration of the measurement target gas can be measured more accurately even if the maximum value of the circulating light signal 66 detected by the light intensity detector 26 decreases.

  Also, the concentration of the measurement target gas can be accurately measured by controlling the rotation speed of the chopper mirror 22 according to the concentration of the measurement target gas.

  When the rotation speed of the chopper type mirror 22 is decreased, the time for forming the closed optical path is increased, and the number of times that infrared rays pass through the gas cell 20 is increased. Conversely, when the rotation speed of the chopper type mirror 22 is increased, the time for forming the closed optical path is shortened, and the number of times that infrared rays pass through the gas cell 20 is reduced.

  Further, when the assumed concentration of the gas supplied to the gas cell 20 is low, the infrared light absorption by the gas is increased by increasing the number of infrared rays that pass through the measurement target gas supplied to the gas cell 20 as compared with the case where the concentration is high. Is prominently shown.

  When the assumed concentration of the gas supplied to the gas cell 20 is high, by reducing the number of infrared rays that pass through the gas supplied to the gas cell 20, it is possible to prevent excessive absorption of infrared rays by the gas. it can.

  Accordingly, when the assumed concentration of the gas supplied to the gas cell 20 is low, the rotational speed of the chopper-type mirror 22 is reduced, and when the concentration of the measurement target gas supplied to the gas cell 20 is assumed to be high, By increasing the rotation speed of the chopper-type mirror 22, the concentration of the measurement target gas can be measured with high accuracy.

  As described above, according to the first embodiment, the gas concentration can be accurately measured without changing the apparatus configuration even when the concentration of the measurement target gas is high or low.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. Since the configuration of the second embodiment has the same parts as the configuration of the first embodiment (see FIG. 1), the same parts are denoted by the same reference numerals, the description thereof is omitted, and is different. Only the part will be described.

  FIG. 9 shows the configuration of the concentration measuring apparatus according to the second embodiment. As shown in FIG. 9, in the concentration measuring apparatus according to the second embodiment, a beam splitter 42 is disposed between the infrared light source 12 and the chopper type mirror 22. The beam splitter 42 is configured by combining two triangular prisms so that the bottom surfaces are in contact with each other. The beam splitter 42 is not limited to the combination of two triangular prisms, and for example, a polarizing beam splitter may be adopted.

  In the second embodiment, instead of the first reflecting mirror 14 to the third reflecting mirror 18 of the first embodiment, a single reflection is provided with the gas cell 20 sandwiched between the chopper type mirror 22. A mirror 44 is provided. When the light reflecting portion 32 of the chopper type mirror 22 is positioned directly below the gas cell 20, a closed optical path in which light reciprocates is formed.

  FIG. 10 shows how the infrared rays from the light intensity detector 26 reach the gas cell 20 via the chopper-type mirror 22. FIG. 11 shows a state in which infrared rays reciprocate between the chopper type mirror 22 and the reflecting mirror 44 many times through the inside of the gas cell 20. In FIG. 12, infrared rays reciprocated many times between the chopper type mirror 22 and the reflecting mirror 44 through the inside of the gas cell 20 pass through the light passing part 34 of the chopper type mirror 22 and the beam splitter 42. The state of reaching the light intensity detector 26 is shown.

  As shown in FIG. 10, a part of the infrared light incident from one inclined surface of the two triangular prisms of the beam splitter 42 passes through the bottom surface of one triangular prism and passes through the bottom surface of the other triangular prism to the other triangular prism. Incident on the triangular prism. Thereafter, the light is emitted through the slope of the other triangular prism and reaches the chopper-type mirror 22. When the light passing part 34 of the chopper type mirror 22 is positioned in the closed optical path when reaching the chopper type mirror 22, the light emitted from the other triangular prism passes through the gas cell 20 and reaches the reflection mirror 44 to reach the reflection mirror. And pass through the gas cell 20 and reach the chopper-type mirror 22. As shown in FIG. 11, when the light reflecting portion 32 of the chopper type mirror 22 is located in the closed optical path when reaching the chopper type mirror 22, infrared rays pass between the chopper type mirror 22 and the reflecting mirror 44 in the gas cell 20. Go back and forth many times through the interior. Then, as shown in FIG. 12, a part of infrared rays reciprocating between the chopper type mirror 22 and the reflecting mirror 44 through the inside of the gas cell 20 many times is a light passage part 34 of the chopper type mirror 22. Then, the light is reflected by the bottom surface of the other triangular prism of the beam splitter 42 and reaches the light intensity detector 26 via the slope of the other triangular prism.

  Also in the second embodiment, it is not only the circulating light 70 that enters the light intensity detector 26. One-round light 72 that enters the light intensity detector 26 after only one round of the closed optical path is included. In the second embodiment, an output signal from the time when the chopper-type mirror 22 is switched from the reflection state to the incident state until the time when the output signal indicating the transmitted light intensity becomes a minimum value is employed. By adopting such an output signal, the absorbance can be calculated using an output signal having a high S / N ratio obtained by excluding the output signal of the light intensity detector 26 due to light containing a large amount of the one-round light 72. .

  Therefore, even in the second embodiment, the gas concentration can be accurately measured without changing the apparatus configuration even when the assumed gas concentration is high or low. Also in the second embodiment, even if the concentration of the measurement target gas supplied to the gas cell 20 changes, the concentration of the gas can be accurately measured.

  Similarly to the first embodiment, in order to accurately measure the concentration of the measurement target gas, when the assumed concentration of the gas supplied to the gas cell 20 is low, the rotation speed of the chopper mirror 22 is set to be low. If it is assumed that the concentration of the measurement target gas supplied to the gas cell 20 is high, the rotational speed of the chopper mirror 22 may be increased.

  Furthermore, in the second embodiment, instead of the first reflecting mirror 14 to the third reflecting mirror 18 of the first embodiment, one reflection is performed with the gas cell 20 sandwiched between the chopper type mirror 22. A mirror 44 is provided to constitute a closed optical path. Therefore, in the second embodiment, the number of parts can be reduced as compared with the configuration of the first embodiment.

(Third embodiment)
Next, a third embodiment of the present invention will be described. Since the configuration of the third embodiment has the same parts as the configuration of the first embodiment (see FIG. 1), the same parts are denoted by the same reference numerals, the description thereof is omitted, and is different. Only the part will be described.

  As shown in FIG. 13, in the third embodiment, the chopper-type mirror 122 is a mirror-reflected light reflecting the light-absorbing portion 36 in the first embodiment. This is different from the first embodiment in that it is a part 136. Therefore, the chopper type mirror 122 according to the third embodiment has a mirror surface on both sides except for the light passing part 34.

  As a result, the reflected light 78 from the light reflecting section 136 reaches the light intensity detector 26 in addition to the circulating light 74 and the one-round light 76.

  FIG. 14A is an explanatory diagram showing an example of the output signal 80 indicating the transmitted light intensity detected by the light intensity detector 26, and FIG. 14B shows the output signal 80 shown in FIG. FIG. 5 is an explanatory diagram showing a signal (circumferential light signal) 82 related to the ambient light 74, a signal (reflected light signal) 84 related to the reflected light 78, and a signal (one optical signal) 86 related to the one-round light 76. is there.

  In the third embodiment, when the light passing part 34 is positioned in the closed optical path and the chopper-type mirror 122 is switched from the reflecting state to the incident state, the area of the light reflecting part 136 is reduced. The intensity of 78 is gradually attenuated. As shown in FIG. 4, when the optical axis portion is completely included in the light passage portion 34, the intensity of the reflected light 78 becomes zero.

  In the third embodiment, as shown in FIG. 13, in addition to the reflected light 78, the light incident on the light intensity detector 26 includes the circulating light 74 and the one-round light 76. In order for the circulating light 74 to enter the light intensity detector 26, it is necessary that the light passing portion 34 of the chopper-type mirror 122 is positioned in the closed optical path. In such a case, the light irradiated from the infrared light source 12 is not emitted. Then, the light enters the closed optical path and becomes one-round light 76. However, when the light passing part 34 is located in the closed optical path, the circulating light 74 reaches the light intensity detector 26, but the one-round light 76 is irradiated from the infrared light source 12 and is closed via the light passing part 34. In this state, the light is incident on the optical path. Therefore, the circulating light 74 enters the light intensity detector 26 earlier than the one-round light 76.

  Since the circulating light 74 passes through the gas cell 20 a plurality of times, the light absorption by the measurement target gas becomes more conspicuous than the one-round light 76. Further, the intensity is different due to reflection by each reflecting mirror.

  Considering the time difference between each of the circulating light 74 and the one-round light 76 reaching the light intensity detector 26, the intensity of the circulating light 74 is attenuated as time passes after entering the incident state. As long as the chopper-type mirror 122 is in the incident state, the irradiation from the infrared light source 12 to the closed optical path is continued. Therefore, even after the intensity of the circulating light 74 is attenuated, the intensity of the one-round light 76 increases or is constant. To maintain.

  Further, since the optical path length of the optical system of the concentration measuring apparatus according to the third embodiment is finite, the intensity of the one-round light 76 becomes maximum after the intensity of the reflected light 78 becomes zero.

  From the above, the transmitted light intensity detected by the light intensity detector 26 is the minimum value (time) when the intensities of the circulating light 74 and the one-round light 76 are the same or when the intensity of the circulating light 74 is zero. Minimum value) B.

  As shown in FIG. 14A, the curve of the transmitted light intensity output signal 80 detected by the light intensity detector 26 gradually decreases when the chopper-type mirror 122 is switched from the reflecting state to the incident state. The minimum value B is shown. The curve of the output signal 80 increases after showing the minimum value B.

  The output signal 80 component is as shown in FIG. The output signal 80 in FIG. 14A includes a circulating light signal 82, a reflected light signal 84, and a one-round light signal 86. Accordingly, by adopting the output signal 80 from the time when the chopper-type mirror 122 is switched from the reflection state to the incident state until the time when the output signal 80 indicating the transmitted light intensity becomes the minimum value B, the light intensity detector is adopted. It is possible to calculate the absorbance by excluding light including a lot of one-round light 76 from the light incident on the light 26. As a result, it is possible to calculate the absorbance based on the output signal having a high S / N ratio, and the concentration of the measurement target gas can be measured more accurately.

  Similarly to the first embodiment, in order to accurately measure the concentration of the measurement target gas, when the assumed concentration of the gas supplied to the gas cell 20 is low, the rotation speed of the chopper mirror 22 is set to be low. If it is assumed that the concentration of the measurement target gas supplied to the gas cell 20 is high, the rotational speed of the chopper mirror 22 may be increased.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. The configuration of the fourth embodiment has the same parts as the configurations of the second and third embodiments (see FIG. 13). Description is omitted and only different parts are described.

  FIG. 15 shows the configuration of the concentration measuring apparatus according to the fourth embodiment. As shown in FIG. 15, the concentration measuring apparatus according to the fourth embodiment is related to the second embodiment in that it includes a chopper-type mirror 122 having a light reflecting portion 136 similar to that of the third embodiment. Although different from the concentration measuring apparatus, other configurations are the same as those of the concentration measuring apparatus according to the second embodiment.

  Also in the fourth embodiment, it is not only the circulating light 88 that enters the light intensity detector 26. One-round light 90 incident on the light intensity detector 26 after only one round of the closed optical path and reflected light generated by reflection of the infrared light emitted from the infrared light source 12 by the light reflecting portion 136 of the chopper-type mirror 122 92. In the fourth embodiment, the transmitted light intensity is shown from the time when the chopper-type mirror 122 is switched from the reflection state to the incident state from the light incident on the light intensity detector 26, as in the third embodiment. The output signal up to the time when the output signal becomes the minimum value is adopted. By adopting such an output signal, the absorbance can be calculated using an output signal having a high S / N ratio obtained by excluding the output signal of the light intensity detector 26 due to light containing a large amount of the one-round light 90. .

  Therefore, also in the fourth embodiment, the gas concentration can be measured with high accuracy without changing the apparatus configuration even when the assumed gas concentration is high or low. Also in the fourth embodiment, even when the concentration of the measurement target gas supplied to the gas cell 20 changes, the concentration of the gas can be measured with high accuracy.

  Similarly to the first embodiment, in order to accurately measure the concentration of the measurement target gas, when the assumed concentration of the gas supplied to the gas cell 20 is low, the rotation speed of the chopper mirror 22 is set to be low. If it is assumed that the concentration of the measurement target gas supplied to the gas cell 20 is high, the rotational speed of the chopper mirror 22 may be increased.

  Furthermore, in the fourth embodiment, instead of the first reflecting mirror 14 to the third reflecting mirror 18 of the third embodiment, a single reflection is performed with the gas cell 20 sandwiched between the chopper type mirror 22. A mirror 44 is provided to constitute a closed optical path. Therefore, in the fourth embodiment, the number of parts can be reduced as compared with the configuration of the third embodiment.

(Modification)
Next, a modified example will be described.

(First modification)
FIG. 16 shows the configuration of the concentration measuring apparatus according to the first modification. As shown in FIG. 16, the configuration of the first modification example has the same part as the configuration of the first embodiment (see FIG. 1). Description is omitted and only different parts are described.

  In the first modification, instead of the chopper-type mirror 22, there is a portion that can be changed to a passable state in which light can pass and a non-passable state in which light cannot pass, and is changed to a passable state. Depending on the pulse width of the signal from the high-speed optical shutter 52 and the signal from the controller 28, the above-mentioned portion of the high-speed optical shutter 52 can pass or cannot pass. And a pulse width adjusting mechanism 54 that selectively switches to a state.

  The controller 28 can adjust the number of times the infrared rays pass through the gas cell 20 depending on whether the concentration of the measurement target gas supplied to the gas cell 20 is assumed to be high or low. Specifically, when the assumed concentration of the gas supplied to the gas cell 20 is low, the pulse width is adjusted so that the number of infrared rays passing through the gas supplied to the gas cell 20 is larger than when the concentration is high. The pulse width adjusting mechanism 54 may be controlled by the signal thus generated.

  Even in the first modification, it is not only the circulating light 94 that is incident on the light intensity detector 26. Included is one-round light 96 that enters the light intensity detector 26 with only one round of the closed optical path. In the first modification, the transmitted light intensity is shown from the time when the high-speed light shutter 52 is switched from a closed state where light does not pass through to an incident state where light passes through and is allowed to emit light from the closed optical path. The output signal up to the time when the output signal becomes the minimum value is adopted. By adopting such an output signal, the absorbance can be calculated using an output signal having a high S / N ratio obtained by excluding the output signal of the light intensity detector 26 due to light containing a lot of one-round light 96. . The time when the high-speed light shutter 52 is switched to the incident state is calculated from the timing at which the controller 28 controls the pulse width adjustment mechanism 54. For example, a time obtained by adding a time lag from when the high-speed light shutter 52 is actually opened to the incident state to the time when the control signal for switching the high-speed light shutter 52 to the incident state is transmitted from the controller 28 to the pulse width adjusting mechanism 54 Is the time when the high-speed light shutter 52 is switched to the incident state (permitted state).

  Even in the first modification, the gas concentration can be accurately measured without changing the apparatus configuration even when the assumed gas concentration is high or low. Further, even in the first modified example, even if the concentration of the measurement target gas supplied to the gas cell 20 changes, the concentration of the gas can be measured with high accuracy.

(Second modification)
FIG. 17 shows the configuration of the concentration measuring apparatus according to the second modification. As shown in FIG. 17, the configuration of the second modified example has the same parts as the configurations of the second embodiment (see FIG. 9) and the first modified example (see FIG. 16). Parts are denoted by the same reference numerals, description thereof is omitted, and only different parts are described. In the second modification, a high-speed optical shutter 52 and a pulse width adjustment mechanism 54 are provided instead of the chopper type mirror 22.

  The controller 28 can adjust the number of times the infrared rays pass through the gas cell 20 depending on whether the concentration of the measurement target gas supplied to the gas cell 20 is assumed to be high or low. Specifically, when the assumed concentration of the gas supplied to the gas cell 20 is low, the pulse width is adjusted so that the number of infrared rays passing through the gas supplied to the gas cell 20 is larger than when the concentration is high. The pulse width adjusting mechanism 54 may be controlled by the signal thus generated.

  Even in the second modification, not only the circulating light 98 is incident on the light intensity detector 26. One-round light 100 incident on the light intensity detector 26 after only one round of the closed optical path is included. In the second modified example, the output signal from the time when the high-speed optical shutter 52 is switched from the closed state where light does not pass through to the incident state where light passes through until the time when the output signal indicating the transmitted light intensity becomes a minimum value. Is adopted. By adopting such an output signal, the absorbance can be calculated using an output signal having a high S / N ratio obtained by excluding the output signal of the light intensity detector 26 due to light containing a large amount of the one-round light 100. .

  In the second modified example, as in the first modified example, the high-speed optical shutter 52 is actually transmitted at the time when the control signal for switching the high-speed optical shutter 52 to the incident state is transmitted from the controller 28 to the pulse width adjusting mechanism 54. Is the time when the high-speed optical shutter 52 is switched to the incident state (permitted state).

  Even in the second modification, the gas concentration can be accurately measured without changing the apparatus configuration even when the assumed gas concentration is high or low. In the second modified example, the gas concentration can be accurately measured even if the concentration of the measurement target gas supplied to the gas cell 20 changes.

(Other variations)
Instead of the chopper-type mirror 22 in the first embodiment and the second embodiment, a moving member in which a hole or notch is formed may enter or retreat into the closed optical path.

In the first and second modified examples, instead of the high-speed optical shutter 52, a mechanically controlled shutter, a lens shutter that opens and closes shutter blades that block light installed in the lens (leaf) A shutter) may be employed.
In addition, the case where the concentration of the measurement target gas is measured using the output signal in the section from the time when the state is switched to the incident state to the time when the output signal becomes the minimum value or the minimum value is described as an example. It is not limited, and the start time of the section may be shifted back and forth by a predetermined time as long as it corresponds to the time when the section is switched to the incident state. Further, if the end time of the section corresponds to the time when the output signal becomes the minimum value or the minimum value, it may be shifted back and forth by a predetermined time.

DESCRIPTION OF SYMBOLS 12 Infrared light source 14 1st reflective mirror 16 2nd reflective mirror 18 3rd reflective mirror 20 Gas cell 22 Chopper type mirror 24 Rotational speed adjustment mechanism 26 Light intensity detector 28 Controller 30 Rotating shaft 32 Light reflection part 34 Light Passing part 34A Incident start edge 34B Incident end edge 36 Light absorbing part 42 Beam splitter 44 Reflector 52 High-speed optical shutter 54 Pulse width adjusting mechanism 60 Circulating light 62 1-circular light 64 Output signal 66 Circulating optical signal 68 1-circular optical signal 70 Light 72 Round light 74 Round light 76 Round light 78 Reflected light 80 Output signal 82 Round light signal 84 Reflected light signal 86 Round light signal 88 Round light 90 Round 1 light 92 Reflected light 94 Round light 96 Round 1 light 98 Loop Light 100 Round light 122 Chopper type mirror 136 Light reflection part A Minimal value B Minimum value

Claims (9)

A light source;
An optical system that forms a closed optical path of light incident from a light source;
A container that is disposed in the optical path of the closed optical path, is supplied with gas therein, and the light of the closed optical path passes through the interior and exits to the closed optical path;
A permitter that permits the light from the light source to enter the closed optical path, and permits the light that has passed through the container to be emitted from the closed optical path by the permission;
A light intensity detector arranged so that light emitted from the closed optical path through the permitter enters, and outputting a signal according to the intensity of the incident light; and
The permitter is capable of detecting the permission state, so that light from the light source is incident on the closed optical path and light that has passed through the container a plurality of times through the closed optical path is emitted from the closed optical path. And the light intensity detector outputs in a section from a time corresponding to the time when the permission state is switched to a time corresponding to a time when the intensity of the signal output by the light intensity detector shows a minimum value. A controller for calculating the concentration of the gas in the container based on the received signal;
Concentration measuring device with   The controller allows the incident light to enter the closed optical path and pass through the interior of the container when the assumed concentration of the gas supplied to the container is low than when the concentration is high. The concentration measuring apparatus according to claim 1, wherein the permitter is controlled so that the number of times to be performed increases. The permitter is
A moving member formed with a portion through which light can pass;
A position where the light of the closed optical path passes through the portion and can be emitted from the closed optical path; and a position where the light of the closed optical path is reflected by a predetermined portion other than the portion of the moving member and returns to the closed optical path. A mechanism for moving the moving member;
With
The concentration measuring apparatus according to claim 2, wherein the controller controls the mechanism so that the number of times is adjusted in accordance with an assumed concentration of gas supplied to the container. The moving member is a rotating member that rotates about an axis and is formed with a portion through which light can pass, and is disposed at a position through which the light in the closed optical path can pass.
The mechanism controls the rotation of the rotating member;
The controller controls the mechanism so as to reduce the rotation speed of the rotating member when the assumed concentration of the gas supplied to the container is low than when it is high.
The concentration measuring apparatus according to claim 3. A rotation angle detector for detecting a rotation angle of the rotation member;
The concentration measuring apparatus according to claim 4, wherein the controller detects the permission state based on a rotation angle detected by the rotation angle detector. The permitter is
A position having a portion that can be changed between a passable state where light can pass and a non-passable state where light cannot pass, and the light in the closed optical path can pass through the portion changed to the passable state A light passage state changer disposed in
A switch for selectively switching the portion of the light passage state changer to the passable state or the non-passable state;
With
The controller allows the incident light to enter the closed optical path and pass through the interior of the container when the assumed concentration of the gas supplied to the container is low than when the concentration is high. Controlling the switch so as to increase the number of times
The concentration measuring apparatus according to claim 1. The light passage state changer is an electronic shutter,
The concentration measuring apparatus according to claim 6, wherein the controller detects the permission state based on transmission of a control signal for opening the electronic shutter. In the container, at least an incident part where light of the closed optical path enters and an outgoing part which passes through the inside and exits to the closed optical path are transparent.
The concentration measuring apparatus according to any one of claims 1 to 7. A light source;
An optical system that forms a closed optical path of light incident from a light source;
A container that is disposed in the optical path of the closed optical path, is supplied with gas therein, and light of the closed optical path passes through the interior and exits to the closed optical path;
A permitter that permits the light from the light source to enter the closed optical path, and permits the light that has passed through the container to be emitted from the closed optical path by the permission;
A light intensity detector that is arranged so that light emitted from the closed optical path through the permitter enters, and outputs a signal corresponding to the intensity of the incident light;
The permitter is capable of detecting the permission state, so that light from the light source is incident on the closed optical path and light that has passed through the container a plurality of times through the closed optical path is emitted from the closed optical path. And the concentration of the gas in the container based on the signal output from the light intensity detector until the intensity of the signal output from the light intensity detector indicates a minimum value from the time when the permission state is detected. A controller for calculating
A concentration measuring method in a concentration measuring apparatus comprising: