JP2008298452A - Infrared gas analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared gas analyzer capable of grasping quantitatively a light quantity drift of a light source due to deterioration of the light source, or the like, compensating a concentration signal drift of a measuring component, and performing high-accuracy measurements. <P>SOLUTION: This infrared gas analyzer, having a measuring cell wherein sample gas is circulated for detecting the concentration of measuring component gas in the sample gas by utilizing a change of intensity of infrared light passing the measuring cell, is equipped with the light source controlled by a light source driving voltage control circuit for generating the infrared light; a measuring gas cell detection part for detecting the intensity of the infrared light passing the measuring cell; and the monitor gas cell detection part, to which the infrared light from the light source is guided for detecting an infrared ray absorption amount by gas other than the measuring component gas in the guided infrared light. The monitor gas cell detection part determines the deviation between a signal that detects the absorbed amount by gas other than the measuring component gas and a value set beforehand, and feedbacks a controlled variable based on the determined deviation amount to the light source drive voltage control circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an infrared gas analyzer that measures the concentration of a specific gas species by using a gas pressure fluctuation accompanying infrared spectrum absorption of a component gas to be measured.

  Infrared gas analyzers in the prior art generate a difference in the amount of light between the reference cell and the sample cell caused by the infrared absorption of the gas to be measured due to the pressure difference generated inside the gas cell absorption detector (gas cell detector). The flow rate is detected by a flow sensor, and the concentration of the measurement target gas is measured.

  As shown in FIG. 5, the double beam type infrared gas analyzer has an infrared light source 11 that emits infrared light, and a motor that periodically and alternately interrupts the infrared light beam emitted from the infrared light source 11. 12, a rotating sector 13 that is driven to rotate, a distribution cell 14 that distributes the infrared light beam interrupted by the rotating sector 13, and a measurement light source that is connected to one side of the distribution cell 14 and guided as a measurement light source. A sample cell 15; a reference cell 16 connected to the other side of the distribution cell and guided as a comparison light source to form a comparison optical line; and a reference cell disposed on the output side of the sample cell 15 and the reference cell 16 and receiving both rays A gas cell detector 17 having a side chamber 18 and a sample side chamber 19 and a gas flow provided in a flow passage 23 communicating with the reference side chamber 18 and the sample side chamber 19 are detected. A thermal flow sensor 21 which forms a gas detecting means, and an AC voltage amplifier 22 which generates a concentration signal by amplifying the signal detected by the thermal flow sensor 21 is largely constituted by.

  In the double beam type infrared gas analyzer configured as described above, first, infrared light emitted from an infrared light source is divided into two by a distribution cell 14 and is incident on a reference cell 16 and a sample cell 15, respectively. To do. The reference cell 16 is filled with an inert gas or the like that does not contain a measurement target component.

In addition, a measurement sample gas flows through the sample cell 15. The infrared light divided into two by the distribution cell 14 is absorbed by the measurement target component of the sample gas only in the sample cell 15 and reaches the gas cell detector 17.

  The gas cell detector 17 includes two chambers (a reference side chamber 18 and a sample side chamber 19) that receive light from the reference cell 16 and light from the sample cell 15, and the two chambers are connected by a flow passage 23. A thermal flow sensor 21 for detecting the flow of gas is attached to the flow passage 23.

  The gas cell detector 17 is filled with a gas containing the same component as the measurement target, and when the infrared light from the reference cell 16 and the sample cell 15 is irradiated, the measurement target component gas absorbs the infrared light. The gas expands thermally in it.

If the measurement sample in the sample cell 15 contains many components to be measured, the infrared light is mostly absorbed there. Therefore, the gas cell detector 17 irradiates the reference side chamber 19 with the reduced infrared light, Corresponding gas expansion occurs.

The infrared light is repeatedly blocked and irradiated by the rotating sector 13, and when the infrared light is blocked, neither the reference side chamber 18 nor the sample side chamber 19 is irradiated with infrared light, so that the gas does not expand and the infrared light is irradiated. The sample side chamber 19 of the gas cell detector 17 is irradiated with infrared light corresponding to the concentration of the measurement target component in the sample cell 15, and the reference side chamber 18 is irradiated with infrared light transmitted through the reference cell 16.

The reference side chamber 18 is irradiated with substantially constant infrared light, and the sample side chamber 19 is irradiated with infrared light according to the concentration of the measurement target component in the sample. A differential pressure is generated between the chambers, and gas flows back and forth through the flow passage 23 provided between the two chambers. The behavior of the gas is detected by the thermal flow sensor 21, amplified by the AC voltage amplifier 22, and output as a concentration signal.

  On the other hand, as shown in FIG. 6, the configuration of a single beam type NDIR equipped with a hot wire type flow sensor generally includes a light source unit 31 for generating infrared light, a cell unit 32 into which a sample gas is introduced, a cell unit. It is composed of three units of a gas cell detection unit 33 that finally measures the sample concentration by measuring the intensity of infrared light that has passed through 32.

  The light source unit 31 includes an infrared light source 30 responsible for generation of infrared light, and a chopper 34 for intermittently allowing the infrared light to enter the cell unit 32 and the detection unit 33.

  The chopper 34 includes, for example, a two-bladed rotating disc 35 in which a notch part is cut out to allow passage of light from a light source, and a motor that rotationally drives the rotating disc 35. 36, and the rotating disc 35 is rotated by the motor 36, so that when the uncut portion (light-shielding portion) of the rotating disc 35 is positioned in front of the light source, the red light from the light source When outside light is shielded and the notch is positioned in front of the light source, infrared light from the light source passes and is irradiated to the cell portion 32.

  The cell part 32 is a part into which the sample gas is introduced, and the front and rear of the measurement cell 37 are sealed with a window plate 38 made of infrared transmissive glass capable of transmitting infrared light in a wide spectral range, and the side surface of the sample cell Are provided with a sample gas inlet 41 and a sample gas outlet 42 so that the gas can flow from one end to the other end, and the inner surface is efficiently mirror-reflective or coated with gold to reflect infrared light efficiently. It has been subjected.

The gas cell detection unit 33 is divided into two chambers, a front chamber 43 and a rear chamber 44, and at least a front panel of the front chamber 43 and a partition between the front chamber 43 and the rear chamber 44 is a window plate 45 that transmits infrared light. These two chambers are structured to be connected by a communication passage 46 such as a capillary or a tunnel capable of moving gas.
In the communication path 46, a thin film type hot-wire flow sensor (thermal flow sensor) provided with a hot-wire resistance element for measuring the flow of the filling gas filled in both chambers generated by the pressure difference between the front and rear chambers 43 and 44 as a resistance change. 47) is arranged.
Further, these two chambers are filled with a gas that is a target of NDIR measurement, for example, a chemical species such as CO2 or a gas obtained by diluting this chemical species with an inert gas such as Ar, He, or N2. Yes.

In the single beam type NDIR having such a configuration, first, infrared light emitted from the light source unit 31 passes through the measurement cell 37 and enters the gas cell detection unit 33. At this time, if the component to be measured exists in the measurement cell 37, a part of the incident infrared light is absorbed by the gas in the measurement cell 37 according to the gas concentration in the measurement cell 37, and the remaining infrared light Enters the gas cell detector 33.
Infrared light incident from the front of the front chamber 43 of the gas cell detection unit 33 is absorbed by the front chamber 43 and the rear chamber 44, but most of it is absorbed by the front chamber 43. The absorbed light energy is converted into a translational movement of molecules, and expands to generate a pressure difference between the front and rear chambers 43 and 44, thereby filling (sealing) gas into the communication passage 46 that communicates both chambers. A flow occurs. Since the flow velocity of this gas flow depends on the intensity of incident light to the gas cell detector 33, it is measured as a resistance change of the hot wire resistance element of the thin film type hot wire flow sensor 47 disposed in the communication passage 46 of the front and rear chambers 43, 44. By doing so, it is possible to measure the infrared intensity before and after incidence on the gas cell detector 33, that is, the concentration of the component gas to be measured in the measurement cell 37.
Japanese Patent Laid-Open No. 2001-255269 (pages 3 to 4 and FIG. 1)

However, the measurement principle in the double beam type infrared analyzer shown in FIG. 5 or the single beam type infrared analyzer shown in FIG. 6 described in the prior art is based on the amount of infrared light emitted from the infrared light source.
That is, the measurement principle of the infrared analyzer is based on the relationship between the concentration of the measurement component in the sample gas and the amount of infrared absorption. Specifically, when the infrared absorption is based on the Lambert-Beer law and the intensity of incident light is used as a reference, the proportion of the amount of light absorbed is related to the concentration of the measurement target component in the sample gas. .

l (λ) = l ₀ (λ) × e ^{−α (λ) · L · C} (1)
here,
l (λ): Infrared intensity after passing through the sample gas. Function of wavelength λ.
l ₀ (λ): Infrared intensity incident on the sample gas. Function of wavelength λ.
α (λ): Absorption coefficient of the measurement component. Function of wavelength λ.
L: Sample gas absorption length C: Concentration of measurement component

Any form of the optical system of FIG. 5 and 6 of different measuring the emitted light quantity l ₀ emitted from the light source on the basis, the infrared light quantity, the infrared intensity l after being absorbed in the sample gas It is configured to measure.
Accordingly, the reference light intensity l ₀ emitted from the light source, when varied by life and other factors of the light source, the signal of the concentration of the component are also measured, varies in proportion to the amount of variation as can be seen from equation (1) End up.
In addition, it is known that an infrared light source made of a semiconductor material capable of modulating the amount of infrared light without a chopper has an unstable factor when the operating temperature is raised, and has a limitation on the operating temperature.
Stabilization technology is an issue for these new types of light sources, and countermeasures against fluctuation phenomena are essential when used.

  In order to solve the above-described problems, the infrared gas analyzer of the present invention has the following configuration.

(1) In an infrared gas analyzer that has a measurement cell through which a sample gas flows, and detects the concentration of a measurement component gas in the sample gas by using a change in intensity of infrared light that has passed through the measurement cell.
A light source controlled by a light source drive voltage control circuit to generate infrared light;
A gas cell detector for measurement that detects the intensity of infrared light that has passed through the measurement cell;
Infrared light from the light source is guided, and a monitor gas cell detection unit that detects an infrared absorption amount by a gas other than the measurement component gas in the guided infrared light, and
The monitor gas cell detection unit obtains a deviation between a signal obtained by detecting an absorption amount by a gas other than the measurement component gas and a preset value, and sets a control amount based on the obtained deviation amount to the light source driving voltage control. An infrared gas analyzer that feeds back to a circuit.

(2) The monitor gas cell detection unit is formed of two chambers before and after a gas other than the measurement component gas is sealed, and at least one of the chambers is disposed at a position on the optical axis for introducing infrared light into the measurement cell. The infrared gas analyzer according to (1), wherein

(3) The monitor gas cell detection unit is formed of two front and rear chambers in which a gas other than the measurement component gas is sealed, and the two front and rear chambers are positioned away from the optical axis for introducing infrared light into the measurement cell. The infrared gas analyzer according to (1), wherein the infrared gas analyzer is disposed at a position where the excess light of the infrared light communicates.

(4) The gas other than the measurement component gas sealed in the monitor gas cell detection unit is a gas having an absorption spectrum close to or overlapping with an absorption spectrum of the measurement component gas (1) to The infrared gas analyzer according to any one of (3).

In the present invention, by attaching a device that can detect in advance the variation in the amount of infrared light emitted from the light source, the light amount drift of the light source caused by the deterioration of the light source is quantitatively grasped, the reliability is displayed, and the lifetime is displayed. Self-diagnosis is possible.
By using the light amount drift amount and feeding back to the driving voltage of the light source, it is possible to obtain a light source system in which the light amount input to the analyzer does not vary. This enables highly accurate measurement.
By using a gas that has an absorption spectrum that is close to or overlaps with the absorption spectrum of the measurement component gas, it is possible to measure without affecting the amount of light in the wavelength range that the measurement component gas absorbs in the infrared light emitted from the light source. It becomes.

  Next, an embodiment of an infrared gas analyzer according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated to the same thing as what was demonstrated by the prior art.

The measurement principle of the present invention is that a monitor gas cell detector is disposed on the optical path of infrared light emitted from a light source. The structure of the monitor gas cell detection unit is basically the same as that of a normally used gas cell detection unit. However, an enclosed gas having an absorption wavelength (wavelength λm) different from that of the measurement component is previously placed in the gas cell. . Using the signal from the monitor gas cell detector, feedback control is performed on the light source drive voltage control circuit that generates the infrared light source to compensate the infrared light source.
As shown in FIG. 2, the absorption wavelength λm of the gas sealed in the monitor gas cell (monitor gas cell detector) is different from the absorption wavelength λs of the measurement gas cell.

  The infrared gas analyzer according to the first embodiment of the present invention is a single beam type NDIR equipped with a heat ray type flow sensor, and its configuration is a light source unit 31 for generating infrared light as shown in FIG. The monitor gas cell detection unit 51 that measures the intensity of infrared light on the infrared light path at a position closest to the light source unit 31, the cell unit 32 that includes the measurement cell 37 into which the sample gas is introduced, and the measurement cell 37. 4 units of the gas cell detection unit 33 that finally measures the sample concentration by measuring the intensity of the infrared light and the first signal obtained from the infrared absorption detected by the gas cell detection unit 33 are input. A correction calculation output unit 52 that calculates and outputs the concentration of the measurement target component gas, an amplitude measurement circuit 79 that receives the second signal obtained from the infrared absorption detected by the monitor gas cell detector 51, and measures the amplitude; , Shake An amplitude setter 80 that presets and stores set values, a comparison unit 81 that compares the amplitude calculated by the amplitude measurement circuit 79 with the amplitude set value set in the amplitude setter 80, and an infrared light source The light source power supply 82 to be generated and a light source drive voltage control circuit 83 that controls the infrared light source based on a control amount calculated according to the deviation amount obtained by comparison by the comparison unit 81 are roughly configured.

  The light source unit 31 includes an infrared light source 30 that is responsible for generating infrared light, and a chopper 34 that intermittently transmits the infrared light at a predetermined period to enter the monitor gas cell detection unit 51, the measurement cell 37, and the gas cell detection unit 33. ing.

  The chopper 34 is, for example, a two-bladed rotating disc 35 in which a notch part is cut out so as to allow the passage of infrared light from the infrared light source 30, and the rotating disc 35. And a motor 36 that rotates and rotates the rotating disk 35 with the motor 36 so that the uncut portion (light-shielding part) of the rotating disk 35 is positioned in front of the light source. Shields (chops) the infrared light from the light source, and when the notch is positioned in front of the light source, the infrared light from the infrared light source 30 passes through and irradiates the cell portion 32.

The monitor gas cell detection unit 51 has the same configuration as the gas cell detection unit 33, and is divided into two front chambers 54 and a rear chamber 55 so that one front chamber 54 transmits infrared light from the infrared light source 30. In the front chamber 54, an infrared window 48a is formed on the infrared light source side, and the same infrared window 48b is formed on the other side. The two front chambers 54 and the rear chamber 55 are connected by a communication path 56 such as a capillary or a tunnel capable of moving gas.
The communication path 56 is a thin film type hot-wire flow sensor having a hot-wire resistance element for measuring the flow of the filling gas filled in the chamber generated by the pressure difference between the two front chambers 54 and the rear chamber 55 as a resistance change ( (Thermal flow sensor) 57 is arranged.
The two front chambers 54 and the rear chamber 55 are filled with a gas other than the measurement component, and in the embodiment, filled with a gas having an absorption wavelength (λm) (see FIG. 2).
The gas other than the measurement component sealed in the monitor gas cell detection unit 51 is a gas having an absorption spectrum that is close to or overlaps with the absorption spectrum of the measurement component gas. By using such a gas, it is possible to perform measurement without affecting the light quantity in the wavelength region absorbed by the measurement component gas in the infrared light emitted from the light source.

  The cell part 32 is a part into which the sample gas is introduced, and the measurement cell 37 is sealed with a window plate 45 made of infrared transmissive glass capable of transmitting infrared rays in a wide spectral range. A sample gas inlet 41 and a sample gas outlet 42 are provided on the side surface so that gas can flow from one end to the other, and the inner surface is coated with a mirror finish or gold to efficiently reflect infrared light. Yes.

The gas cell detector 33 is divided into two chambers, a front chamber 43 and a rear chamber 44. At least the front surface of the front chamber 43 and the partition between the front chamber 43 and the rear chamber 44 are window plates 38 that transmit infrared light. These two chambers are structured to be connected by a communication passage 46 such as a capillary or a tunnel capable of moving gas.
A thin film type hot-wire flow sensor 47 having a hot-wire resistance element for measuring the flow of the filling gas filled in both chambers generated by the pressure difference between the front and rear chambers 43 and 44 as a resistance change is disposed in the communication path 46. ing.
Further, in these two chambers, for example, only a chemical species such as CO2 to be measured by NDIR, or an absorption wavelength (λs) obtained by diluting this chemical species with an inert gas such as Ar, He, or N2. Is filled with gas.

  In the single beam type NDIR having such a configuration, first, infrared light emitted from the light source unit 31 is first absorbed through the infrared window 48a of the monitor gas cell detection unit 51 except for the measurement component enclosed therein. It is absorbed by the sealed gas of wavelength (λm).

Infrared light incident and absorbed from the front of the front chamber 54 of the monitor gas cell detector 51 is expanded by being converted into the translational movement of molecules of the absorbed light energy, and the front chamber 54 and the rear chamber of both of them are expanded. A pressure difference is generated between the first and second chambers 55, whereby a flow of filled (enclosed) gas is generated in the communication passage 56 communicating with both chambers. Since the flow velocity of this gas flow depends on the incident light intensity to the monitor gas cell detection unit 51, the resistance change of the hot wire resistance element of the thin film type hot wire flow sensor 57 disposed in the communication path 56 of both chambers 54 and 55 is obtained. By measuring, the light intensity itself emitted from the light source unit 31 can be measured.

  Then, the infrared light transmitted through the monitor gas cell detection unit 51 enters the measurement cell 37. At this time, if a component to be measured (gas having an absorption wavelength (λs)) is present in the measurement cell 37, a part of the incident infrared light is gas in the measurement cell 37 according to the gas concentration in the measurement cell 37. The remaining infrared light is incident on the gas cell detector 33.

  Infrared light incident from the front of the front chamber 43 of the gas cell detection unit 33 is absorbed by the front chamber 43 and the rear chamber 44, but most of it is absorbed by the front chamber 43. The absorbed light energy is converted into a translational movement of molecules, thereby generating a pressure difference between the front and rear chambers 43 and 44, and thereby filling (encapsulating) gas into the communication passage 46 communicating with both chambers 43 and 44. The flow of

Since the flow velocity of this gas flow depends on the intensity of incident light to the gas cell detector 33, it is measured as a resistance change of the hot wire resistance element of the thin film type hot wire flow sensor 47 disposed in the communication passage 46 of the front and rear chambers 43, 44. By doing so, it is possible to measure the infrared intensity before and after incidence on the gas cell detection unit 33, that is, the concentration of the component gas to be measured in the measurement cell 37.

In this way, the infrared light having the spectrum as shown in FIG. 2 is first absorbed by the enclosed gas (wavelength λm) through the infrared window 48a of the monitor gas cell detector 51. ), Transmitted through the opposite infrared window 48 b and enters the measurement cell 37.
When measurement component gas is contained in the measurement cell 37, infrared absorption of the measurement component occurs here (wavelength λs). Infrared light that has passed through the light enters the gas cell detector 33. The gas cell detection unit 33 is filled with the same gas as the measurement component, and when the measurement component is present in the measurement cell 37, the amount of infrared light centered on the wavelength λs decreases. This change is detected by the gas cell detector 33 and output as a concentration signal of the measurement component. Specifically, the amplitude of the AC waveform generated corresponding to the intermittent timing by the sector changes. Through such a process, the thermal flow sensor signal (second signal) of the monitor gas cell detector 51 and the flow sensor signal (first signal) of the gas cell detector 33 are obtained.

  Since these two signals are both based on the light emission amount Io of the infrared light source, the component concentration signal detected by the gas cell detection unit 33 when a decrease in the amount of infrared light occurs due to a drift such as deterioration of the infrared light source. (First signal) decreases. At the same time, the amplitude of the second signal detected by the monitor gas cell detector 51 also decreases.

Therefore, as shown in FIG. 1, when the amplitude setting value of the second signal is provided in the amplitude setting device 80, and the second signal obtained from the actual light source has a deviation from this amplitude setting value, The second signal is always controlled to maintain the same level by performing feedback control to the light source drive voltage control circuit 83 so that the deviation becomes zero. That is, the amount of light input to the measurement cell 37 is maintained at a constant value. Therefore, even if the light emission characteristics of the light source alone fluctuate due to deterioration or aging, the analysis value of the analyzer is not affected, and high-precision measurement without drift is possible.
However, it is necessary to assume that the light amount drift of the light source occurs at the same ratio between the absorption wavelength λm of the monitor gas cell detector 51 and the absorption wavelength λs of the sample gas in the measurement cell 37. However, unless the light emission temperature of the light source changes significantly, the shape of the emission spectrum of blackbody radiation does not change greatly, so this assumption is considered to hold.

  Note that the absorption wavelength λs of the measurement component and the absorption wavelength λm of the sealed gas of the monitor gas cell detection unit 51 are in different wavelength bands. For this reason, mounting the monitor gas cell detection unit 51 does not affect the measurement of the measurement component other than the influence of the transmittance of the window material and the surface reflection.

  Next, an infrared gas analyzer of the second embodiment will be described with reference to the drawings.

The infrared gas analyzer of the second embodiment of the present invention is a single-beam NDIR equipped with a hot-wire flow sensor, and has a structure in which the chambers of the gas cells constituting the monitor gas cell detector are arranged in series on the optical axis. A gas cell is used.
As shown in FIG. 3, the configuration includes a light source unit 31 for generating infrared light, a monitor gas cell detection unit 61 that measures the intensity of infrared light on the infrared optical path at a position closest to the light source unit 31, 4 units of a cell unit 32 having a measurement cell 37 into which a sample gas is introduced, a gas cell detection unit 33 for finally measuring a sample concentration by measuring the intensity of infrared light that has passed through the measurement cell 37, and a gas cell A correction calculation output unit 52 that inputs the first signal obtained from the infrared absorption amount detected by the detection unit 33 and calculates and outputs the concentration of the measurement target component gas, and the infrared absorption detected by the monitor gas cell detector 51 An amplitude measurement circuit 79 that inputs the second signal obtained from the quantity and measures the amplitude, an amplitude setter 80 that presets and stores the amplitude setting value, and the amplitude calculated by the amplitude measurement circuit 79 And amplitude setter 80 The comparison unit 81 for comparing with the set amplitude set value, the light source power source 82 for generating the infrared light source, and the infrared light source based on the control amount calculated according to the deviation amount obtained by comparison by the comparison unit 81 The light source driving voltage control circuit 83 is generally configured.

  The light source unit 31 includes an infrared light source 30 responsible for generation of infrared light, and a chopper 34 for intermittently allowing infrared light to enter the monitor gas cell detection unit 61, the measurement cell 37, and the gas cell detection unit 33.

  The chopper 34 includes, for example, a two-bladed rotating disc 35 in which a notch part is cut out to allow passage of light from a light source, and a motor that rotationally drives the rotating disc 35. 36, and the rotating disc 35 is rotated by the motor 36, so that when the uncut portion (light-shielding portion) of the rotating disc 35 is positioned in front of the light source, the red light from the light source When outside light is shielded and the notch is positioned in front of the light source, infrared light from the light source passes and is irradiated to the cell portion 32.

The monitor gas cell detection unit 61 has the same configuration as the gas cell detection unit 33, is divided into two front chambers 64 and a rear chamber 65, and allows infrared light from the infrared light source 30 to pass through the front chamber 64. The infrared light is arranged to pass through the rear chamber 65. The front chamber 64 has an infrared window 58a on the infrared light source 30 side, the same infrared window 58b on the other side, and a front chamber and a rear chamber. An infrared window 58c is formed between them. The two front chambers 64 and the rear chamber 65 are connected by a communication path 66 such as a capillary or a tunnel capable of moving gas.
A thin film type hot-wire flow sensor (including a hot-wire resistance element for measuring the flow of the filling gas filled in the chamber generated by the pressure difference between the two front chambers 64 and the rear chamber 65 as a resistance change is provided in the communication path 66. A thermal flow sensor) 67 is disposed.
The two front chambers 64 and the rear chamber 65 are filled with a gas different from the measurement component, and are filled with a gas having an absorption wavelength (λm) in the embodiment.
The gas other than the measurement component sealed in the monitor gas cell detection unit 51 is a gas having an absorption spectrum that is close to or overlaps with the absorption spectrum of the measurement component gas. By using such a gas, it is possible to perform measurement without affecting the light quantity in the wavelength region absorbed by the measurement component gas in the infrared light emitted from the light source.

  The cell part 32 is a part into which the sample gas is introduced, and the measurement cell 37 is sealed with a window plate 45 made of infrared transmissive glass capable of transmitting infrared rays in a wide spectral range. A sample gas inlet 41 and a sample gas outlet 42 are provided on the side surface so that gas can flow from one end to the other, and the inner surface is coated with a mirror finish or gold to efficiently reflect infrared light. Yes.

The gas cell detector 33 is divided into two chambers, a front chamber 43 and a rear chamber 44. At least the front surface of the front chamber 43 and the partition between the front chamber 43 and the rear chamber 44 are window plates 38 that transmit infrared light. The two chambers 43 and 44 are partitioned and connected to each other through a communication passage 46 such as a capillary or a tunnel capable of moving gas.
In the communication path 46, there is a thin film type hot-wire flow sensor 47 provided with a hot-wire resistance element for measuring the flow of the filling gas filled in both chambers caused by the pressure difference between the front chamber 43 and the rear chamber 44 as a resistance change. Has been placed.
Further, in these two chambers 43 and 44, for example, only a chemical species such as CO2 to be measured by NDIR, or an absorption wavelength obtained by diluting this chemical species with an inert gas such as Ar, He or N2 is used. (Λs) gas is filled.

  In the single beam type NDIR having such a configuration, first, infrared light emitted from the light source unit 31 is first absorbed through the infrared window 58a of the monitor gas cell detection unit 61 except for the measurement component enclosed therein. It is absorbed by the sealed gas of wavelength (λm).

Infrared light incident and absorbed from the front of the front chamber 64 of the monitor gas cell detector 61 expands by converting the absorbed light energy into the translational movement of the molecules. A pressure difference is generated between the two chambers 65, and a flow of filling (enclosed) gas is generated in the communication passage 66 that communicates the two chambers 64, 65. Since the flow velocity of this gas flow depends on the intensity of incident light to the monitor gas cell detector 61, the resistance change of the hot wire resistance element of the thin film type hot wire flow sensor 67 disposed in the communication passage 66 of both chambers 64 and 65 is obtained. By measuring, the gas concentration of the absorption wavelength (λm) other than the measurement component can be measured.

  Then, the infrared light transmitted through the monitor gas cell detector 61 enters the measurement cell 37. At this time, if a component to be measured (gas having an absorption wavelength (λs)) is present in the measurement cell 37, a part of the incident infrared light is gas in the measurement cell 37 according to the gas concentration in the measurement cell 37. The remaining infrared light is incident on the gas cell detector 33.

  Infrared light incident from the front of the front chamber 43 of the gas cell detection unit 33 is absorbed by the front chamber 43 and the rear chamber 44, but most of it is absorbed by the front chamber 43. The absorbed light energy is converted into a translational movement of molecules, thereby generating a pressure difference between the front and rear chambers 43 and 44, and thereby filling (encapsulating) gas into the communication passage 46 communicating with both chambers 43 and 44. The flow of

Since the flow velocity of this gas flow depends on the intensity of incident light to the gas cell detector 33, it is measured as a resistance change of the hot wire resistance element of the thin film type hot wire flow sensor 47 disposed in the communication passage 46 of the front and rear chambers 43, 44. By doing so, it is possible to measure the infrared intensity before and after incidence on the gas cell detection unit 33, that is, the concentration of the component gas to be measured in the measurement cell 37.

In the infrared analyzer of the second embodiment configured as described above, similarly to the infrared analyzer described in the first embodiment, infrared light having a spectrum as shown in FIG. 61 is absorbed by the enclosed gas enclosed in the infrared window 58a (wavelength λm), passes through the opposite infrared window 58b, and enters the measurement cell 37.
When measurement component gas is contained in the measurement cell 37, infrared absorption of the measurement component occurs here (wavelength λs). Infrared light after passing through the light enters the gas cell detector 33. The gas cell detection unit 33 is filled with the same gas as the measurement component, and when the measurement component is present in the measurement cell 37, the amount of infrared light centered on the wavelength λs decreases. This change is detected by the gas cell detector 33 and output as a concentration signal of the measurement component. Specifically, the amplitude of the AC waveform generated corresponding to the timing at which the chopper 34 is interrupted changes. Through such a process, the thermal flow sensor signal (second signal) of the monitor gas cell detector 61 and the flow sensor signal (first signal) of the gas cell detector 33 are obtained.

  Since these two signals are based on the light emission amount Io of the infrared light source, the component concentration signal detected by the gas cell detection unit 33 when a decrease in the amount of infrared light occurs due to a drift such as deterioration of the infrared light source. (First signal) decreases. At the same time, the amplitude of the second signal detected by the monitor gas cell detector 61 also decreases.

Therefore, as shown in FIG. 3, when the amplitude setting value of the second signal is provided in the amplitude setting device 80 and the second signal obtained from the actual light source has a deviation from this amplitude setting value, The second signal is always controlled to maintain the same level by performing feedback control to the light source drive voltage control circuit 83 so that the deviation becomes zero. That is, the amount of light input to the measurement cell 37 is maintained at a constant value. Therefore, even if the light emission characteristics of the light source alone fluctuate due to deterioration or aging, the analysis value of the analyzer is not affected, and high-precision measurement without drift is possible.
However, it is necessary to assume that the light amount drift of the light source occurs at the same ratio between the absorption wavelength λm of the monitor gas cell detector 51 and the absorption wavelength λs of the sample gas in the measurement cell 37. However, unless the light emission temperature of the light source changes significantly, the shape of the emission spectrum of blackbody radiation does not change greatly, so this assumption is considered to hold.

  The absorption wavelength λs of the measurement component and the absorption wavelength λm of the sealed gas of the monitor gas cell detection unit 61 are in different wavelength bands. For this reason, mounting the monitor gas cell detector 61 does not affect the measurement of the measurement component other than the influence of the transmittance of the window material and the surface reflection.

  Next, an infrared gas analyzer of the third embodiment will be described with reference to the drawings.

  The infrared gas analyzer of the third embodiment of the present invention is a single beam type NDIR equipped with a hot-wire flow sensor, and the monitor gas cell detector is formed of two chambers before and after the gas other than the measurement component is enclosed, The two front and rear chambers are arranged at positions that are out of the optical axis through which infrared light communicates and are irradiated with excess infrared light.

  As shown in FIG. 4, the configuration includes a light source unit 31 for generating infrared light, and a monitor gas cell detection unit arranged at a position where infrared light is irradiated at a position closest to the light source unit 31. 71, four units of a cell unit 32 including a measurement cell 37 into which a sample gas is introduced, a gas cell detection unit 33 that finally measures the sample concentration by measuring the intensity of infrared light that has passed through the measurement cell 37, and A correction calculation output unit 52 that inputs the first signal obtained from the infrared absorption detected by the gas cell detection unit 33 and calculates and outputs the concentration of the measurement target component gas, and the monitor gas cell detector 51 detects An amplitude measurement circuit 79 that inputs the second signal obtained from the infrared absorption amount and measures the amplitude, an amplitude setter 80 that presets and stores the amplitude setting value, and the amplitude measurement circuit 79 calculate the amplitude. Amplitude and amplitude setter The comparison unit 81 for comparing with the amplitude setting value set to 0, the light source power source 82 for generating the infrared light source, and the infrared ray based on the control amount calculated according to the deviation amount obtained by the comparison by the comparison unit 81 A light source driving voltage control circuit 83 that controls the light source is roughly configured.

  The light source unit 31 includes an infrared light source 30 responsible for generation of infrared light, and a chopper 34 for intermittently allowing the infrared light to enter the measurement cell 37 and the gas cell detection unit 33.

  The chopper 34 is, for example, a two-bladed rotating disc 35 in which a notch part is cut out so as to allow passage of light from the light source, and the rotating disc 35 is rotationally driven. When the rotating disk 35 is rotated by the motor 36 and the uncut portion (light-shielding part) of the rotating disk 35 is positioned in front of the light source, When infrared light is shielded (chopped) and the notch is positioned in front of the light source, the infrared light from the light source passes through and is irradiated to the cell unit 32.

The monitor gas cell detection unit 71 has the same configuration as that of the gas cell detection unit 33, and is divided into two front chambers 74 and a rear chamber 75, and one of the front chambers 74 receives infrared light of excess light from an infrared light source. An infrared window 78 is formed in the front chamber 74 on the infrared light source side. The two front chambers 74 and the rear chamber 75 are connected by a communication path 76 such as a capillary or a tunnel capable of moving gas.
In the communication path 76, a thin film type hot-wire flow sensor 77 provided with a hot-wire resistance element for measuring the flow of the filling gas filled in the chamber generated by the pressure difference between the two front chambers 74 and the rear chamber 75 as a change in resistance. Is arranged.
The two front chambers 74 and the rear chamber 75 are filled with a gas other than the measurement component, and in the embodiment, filled with a gas having an absorption wavelength (λm).
The gas other than the measurement component sealed in the monitor gas cell detection unit 51 is a gas having an absorption spectrum that is close to or overlaps with the absorption spectrum of the measurement component gas. By using such a gas, it is possible to perform measurement without affecting the light quantity in the wavelength region absorbed by the measurement component gas in the infrared light emitted from the light source.

  A chopper 35 ′ similar to the chopper 34 is provided between the monitor gas cell detection unit 71 and the infrared light source 30, and performs the passage and blocking of the infrared light with respect to the monitor gas cell detection unit 71.

  The cell part 32 is a part into which the sample gas is introduced, and the measurement cell 37 is sealed with a window plate 45 made of infrared transmissive glass capable of transmitting infrared rays in a wide spectral range. A sample gas inlet 41 and a sample gas outlet 42 are provided on the side surface so that gas can flow from one end to the other, and the inner surface is coated with a mirror finish or gold to efficiently reflect infrared light. Yes.

The gas cell detection unit 33 is divided into two chambers, a front chamber 43 and a rear chamber 44, and at least a front surface of the front chamber 43 and a partition between the front chamber and the rear chamber are partitioned by a window plate 38 that transmits infrared light. The two chambers 43 and 44 are connected by a communication passage 46 such as a capillary or a tunnel capable of moving gas.
A thin film type hot-wire flow sensor 47 having a hot-wire resistance element for measuring the flow of the filling gas filled in both chambers generated by the pressure difference between the front and rear chambers 43 and 44 as a resistance change is disposed in the communication path 46. ing.
Further, in these two chambers 43 and 44, for example, only a chemical species such as CO2 to be measured by NDIR, or an absorption wavelength obtained by diluting this chemical species with an inert gas such as Ar, He or N2 is used. (Λs) gas is filled.

  In the single beam type NDIR having such a configuration, first, the infrared light of the surplus light emitted from the light source unit 31 is first measured in an infrared window 78 of the monitor gas cell detection unit 71. It is absorbed by the sealed gas having an absorption wavelength (λm) other than the components.

The infrared light incident and absorbed from the front of the front chamber 74 of the monitor gas cell detector 71 expands by being converted into the translational movement of the molecules of the absorbed light energy, and the front chamber 74 and the rear chamber of both of them are expanded. A pressure difference is generated between the two chambers 75, and a flow of filling (enclosed) gas is generated in the communication passage 76 that communicates the two chambers 74 and 75. Since the flow velocity of this gas flow depends on the intensity of incident light to the monitor gas cell detector 71, the resistance change of the hot wire resistance element of the thin film type hot wire flow sensor 77 disposed in the communication path 76 of both chambers 74 and 75 is obtained. By measuring, the gas concentration of the absorption wavelength (λm) other than the measurement component can be measured.

  At the same time, infrared light from the light source unit 31 enters the measurement cell 37. At this time, if a component to be measured (gas having an absorption wavelength (λs)) is present in the measurement cell 37, a part of the incident infrared light is gas in the measurement cell 37 according to the gas concentration in the measurement cell 37. The remaining infrared light is incident on the gas cell detector 33.

  Infrared light incident from the front of the front chamber 43 of the gas cell detection unit 33 is absorbed by the front chamber 43 and the rear chamber 44, but most of it is absorbed by the front chamber 43. The absorbed light energy is converted into a translational movement of molecules, thereby generating a pressure difference between the front and rear chambers 43 and 44, and thereby filling (encapsulating) gas into the communication passage 46 communicating with both chambers 43 and 44. The flow of

Since the flow velocity of this gas flow depends on the intensity of incident light to the gas cell detector 33, it is measured as a resistance change of the hot wire resistance element of the thin film type hot wire flow sensor 47 disposed in the communication passage 46 of the front and rear chambers 43, 44. By doing so, it is possible to measure the infrared intensity before and after being incident on the gas cell detector 33, that is, the concentration of the component gas to be measured in the measurement cell 33.

Now, in this way, the infrared light of the surplus light having the spectrum as shown in the figure is absorbed by the enclosed gas (wavelength λm) enclosed therein through the infrared window 78 of the monitor gas cell detector 71. receive.
At the same time, when infrared light from the light source unit 31 is incident on the measurement cell 37 and the measurement component gas is contained in the measurement cell 37, infrared absorption of the measurement component occurs here (wavelength λs). Infrared light after passing through the light enters the gas cell detector 33. The gas cell detection unit 33 is filled with the same gas as the measurement component, and when the measurement component is present in the measurement cell 37, the amount of infrared light centered on the wavelength λs decreases. This change is detected by the gas cell detector 33 and output as a concentration signal of the measurement component. Specifically, the amplitude of the AC waveform generated corresponding to the timing at which the chopper 34 is interrupted changes. Through such a process, the thermal flow sensor signal (second signal) of the monitor gas cell detector 71 and the signal (first signal) of the flow sensor of the gas cell detector 33 are obtained.

Since these two signals are both based on the emission amount Io of the infrared light source,
When a decrease in the amount of infrared light occurs due to a drift such as deterioration of the infrared light source, the component concentration signal (first signal) detected by the gas cell detection unit 33 decreases. At the same time, the amplitude of the second signal detected by the monitor gas cell detector 71 also decreases.

Therefore, as shown in FIG. 4, when the amplitude setting value of the second signal is provided in the amplitude setting device and the second signal obtained from the actual light source has a deviation from this amplitude setting value, By performing feedback control to the light source drive voltage control circuit 83 so that this deviation becomes zero, the second signal is always controlled to maintain the same level. That is, the amount of light input to the measurement cell 37 is maintained at a constant value. Therefore, even if the light emission characteristics of the light source alone fluctuate due to deterioration or aging, the analysis value of the analyzer is not affected, and high-precision measurement without drift is possible.
However, it is necessary to assume that the light amount drift of the light source occurs at the same ratio between the absorption wavelength λm of the monitor gas cell detector 51 and the absorption wavelength λs of the sample gas in the measurement cell 37. However, unless the light emission temperature of the light source changes significantly, the shape of the emission spectrum of blackbody radiation does not change greatly, so this assumption is considered to hold.

  Note that the absorption wavelength λs of the measurement component and the absorption wavelength λm of the sealed gas in the monitor gas cell detection unit 71 are in different wavelength bands. For this reason, mounting the monitor gas cell detection unit 71 does not affect the measurement of the measurement component other than the influence of the transmittance of the window material and the surface reflection.

By providing a monitor gas cell detection unit that guides infrared light from the light source unit and detects the amount of gas absorption of the guided infrared light other than the measurement component, the light amount drift of the light source that occurs due to deterioration of the light source, etc. To provide an infrared gas analyzer that enables quantitative measurement, compensates for concentration signal drift of measurement components, and enables high-precision measurement.

It is explanatory drawing which shows the concept of the infrared gas analyzer of 1st Example of this invention. It is explanatory drawing which showed the absorption peak of the emission spectrum of an infrared light source. It is explanatory drawing which showed the concept of the infrared gas analyzer of 2nd Example of this invention. It is explanatory drawing which showed the concept of the infrared gas analyzer of 3rd Example of this invention same as the above. It is explanatory drawing which showed the concept of the double beam type infrared gas analyzer in a prior art. It is explanatory drawing which showed the concept of the single beam type infrared gas analyzer in a prior art.

Explanation of symbols

11 Infrared light source 12 Motor 13 Rotating sector 14 Distribution cell 15 Sample cell 16 Reference cell 17 Gas cell detector 18 Reference side chamber 19 Sample side chamber 21 Thermal flow sensor 22 AC voltage amplifier 23 Flow path 30 Infrared light source 31 Light source unit 32 Cell unit 33 Gas cell detection Section 34 Chopper 35 Rotating disk 36 Motor 37 Measurement cell 38 Window plate 41 Sample gas inlet 42 Sample gas outlet 43 Front chamber 44 Rear chamber 45 Window plate 46 Communication passage 47 Thermal flow sensor 48a Infrared window 48b Infrared window 51 Monitor gas cell Detection section 52 Correction calculation output section 54 Front chamber 55 Rear chamber 56 Communication path 57 Thermal flow sensor 58a Infrared window 58b Infrared window 61 Monitor gas cell detection section 64 Front chamber 65 Rear chamber 66 Communication path 67 Thermal flow sensor 71 Monitor gas cell detection Part 74 front chamber 75 rear chamber 76 communication passage 77 Row sensors 78 infrared window 79 the amplitude measuring circuit 80 the amplitude setter 81 comparison unit 82 light source power supply 83 light source drive voltage control circuit

Claims (4)

In an infrared gas analyzer that has a measurement cell through which a sample gas circulates and detects the concentration of a measurement component gas in the sample gas by using a change in intensity of infrared light that has passed through the measurement cell.
A light source controlled by a light source drive voltage control circuit to generate infrared light;
A gas cell detector for measurement that detects the intensity of infrared light that has passed through the measurement cell;
Infrared light from the light source is guided, and a monitor gas cell detection unit that detects an infrared absorption amount by a gas other than the measurement component gas in the guided infrared light, and
The monitor gas cell detection unit obtains a deviation between a signal obtained by detecting an absorption amount by a gas other than the measurement component gas and a preset value, and sets a control amount based on the obtained deviation amount to the light source driving voltage control. An infrared gas analyzer that feeds back to a circuit.   The monitor gas cell detection unit is formed of two chambers before and after a gas other than the measurement component gas is sealed, and at least one of the chambers is arranged at a position on the optical axis for introducing infrared light into the measurement cell. The infrared gas analyzer according to claim 1.   The monitor gas cell detection unit is formed of two front and rear chambers filled with a gas other than the measurement component gas, and the two front and rear chambers are at a position off the optical axis for introducing infrared light into the measurement cell. The infrared gas analyzer according to claim 1, wherein the infrared gas analyzer is disposed at a position where the excess light of the infrared light communicates.   4. The gas other than the measurement component gas sealed in the monitor gas cell detection unit is a gas having an absorption spectrum close to or overlapping with an absorption spectrum of the measurement component gas. An infrared gas analyzer as described in the above.

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