JP2014167451A - Apparatus and method for measuring gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple gas measuring apparatus that can be manufactured more easily and has high measurement accuracy, and a gas measuring method capable of saving power.SOLUTION: A gas measuring apparatus 100 displaying a concentration of a measured gas according to an amount of infrared radiation that reaches an infrared detection element 20 comprises: a measurement cell 30 capable of introducing a gas to be measured into an internal space 31; a calculation section 40 performing concentration determination for the gas to be measured in the internal space 31 on the basis of an output from the infrared detection element 20; and a control section 60 controlling a light source 10 and the calculation section 40. The light source 10 can emit both an infrared radiation in an absorption wavelength band absorbed by the gas to be measured and an infrared radiation in a non-absorption wavelength band not absorbed by the gas to be measured, simultaneously. The control section 60 acquires the output of the infrared detection element 20 multiple times during a period in which an emission spectrum of the infrared radiation emitted by the light source 10 changes continuously, and causes the calculation section 40 to perform calculation for the concentration determination of the gas to be measured on the basis of the output acquired.

Description

  The present invention relates to a gas measuring device and a gas measuring method, and more specifically, in an atmosphere of a measurement target gas introduced into an optical path, an infrared ray emitted from a light source is in accordance with an amount of infrared rays reaching an infrared detecting element, The present invention relates to a gas measuring device and a gas measuring method which are displayed as a concentration of a measurement target gas.

  Conventionally, as an infrared gas measuring device for measuring gas in the atmosphere, non-dispersed red is used to measure the gas concentration by detecting the amount of absorption using the difference in the wavelength of infrared rays absorbed by the type of gas. Non-Dispersive Infrared gas measuring devices are known. This gas measurement device combines a filter (transmission member) that transmits infrared light limited to a wavelength with which the gas to be detected has absorption characteristics and an infrared sensor, and measures the amount of absorption to measure the gas concentration. Is.

  This gas measuring device selectively transmits infrared light in a wavelength range in which infrared absorption by the measurement target gas does not occur and selective infrared light in a wavelength range in which infrared absorption by the measurement target gas occurs. A plurality of infrared detection elements each having a transmitting measurement filter are arranged, and the presence / absence or concentration of the measurement target gas is detected based on an output signal from each infrared detection element.

For example, what is described in Patent Document 1 is a gas measurement device and a CO ₂ detection method with improved detection accuracy and output stability. Hereinafter, it is also called a gas measuring device and a gas measuring method including these. The principle of operation is that the difference in the degree of absorption depending on the wavelength is applied to CO ₂ detection. Among infrared rays emitted from a ceramic heater as a light source, infrared rays having a wavelength of about 4.3 μm are absorbed by CO ₂ in the gas container, and the radiation intensity is reduced. On the other hand, infrared rays having a wavelength of 3.9 μm are not absorbed by CO ₂ and their radiation intensity does not decrease.

Then, from the infrared rays including different wavelengths that have passed through the gas container of the gas measuring device, two waves with a wavelength of 4.3 μm and a wavelength of 3.9 μm are two types of optical filters having passbands corresponding to the two waves respectively. Filter selection. Based on the radiant intensity of each of these infrared rays having different wavelengths, the concentration of CO ₂ in the gas container is calculated. Radiant intensity distribution of the ceramic heater comprises an infrared absorption spectrum of CO _2, a broad a wavelength range of 2Myuemu～50myuemu, with sufficient radiation intensity in the wavelength region near infrared absorption spectrum of CO _2. Therefore, the detection accuracy and output stability of the gas measuring device using a ceramic heater as the light source are improved.

  FIG. 1 is a configuration diagram for explaining a conventional gas measuring apparatus. The gas measuring device 300 has an outer shape constituted by a measuring cell 330 capable of introducing a measuring object gas (GAS in FIG. 1) into the internal space 331. Further, a distance from one light source 310 arranged at one end inside the measurement cell 330 to emit infrared rays (IR in FIG. 1) to two infrared detection elements 321 and 322 arranged side by side at the other end inside. The optical paths 332 and 333 are formed respectively. The gas measuring device 300 was introduced into the internal space 331 based on the output from the two different optical filters 351 and 352 and the infrared detection elements 321 and 322 inserted in these optical paths 332 and 333, respectively. It further includes a calculation unit 340 that performs concentration determination of the measurement target gas.

FIG. 2 is a diagram of an infrared transmission spectrum example (wavelength band: 2.5 μm to 8 μm) in the CO ₂ atmosphere in the internal space of FIG. 1. In a specific band of this infrared transmission spectrum example, that is, a band having a wavelength of 4.2 to 4.4 μm (hereinafter also referred to as a CO ₂ absorption band), infrared absorption by CO ₂ occurs, and the infrared transmittance is local. It can be confirmed that

In the gas measuring device 300 has an optical filter 352 and the first infrared detecting element 321, selectively transmits infrared than CO ₂ absorption band with an optical filter 351 selectively transmits infrared CO ₂ absorption band Two pairs with the second infrared detecting element 322 are used. Although the output I _CO2 of the first infrared detection element changes according to the concentration of CO ₂ , the output I _ref of the second infrared detection element 322 does not change, so that the CO ₂ is based on the difference or ratio between these outputs. It becomes possible to measure the density | concentration of.
As a specific example, it is possible to derive the CO ₂ concentration based on the following equation.

(C _CO2 : CO ₂ concentration, ε _CO2 : CO ₂ absorption coefficient, l: optical path length)
Further, for example, the device described in Patent Document 2 is a small and low-cost wavelength-selective infrared detection element that secures assembly accuracy, and an infrared gas analyzer using the same. This infrared gas analyzer (hereinafter, also simply referred to as a gas measuring device) is an integral unit of a wavelength selection filter that selectively transmits infrared light from a light source and an infrared detection element that detects infrared light transmitted through the wavelength selection filter. A wavelength selective filter using a plurality of mirrors formed in the above is integrally formed with the infrared detecting element.

  Further, what is described in Patent Document 3 is a concentration measuring device (hereinafter simply referred to as a gas measuring device) capable of measuring a gas concentration with a pair of optical filters and an infrared detecting element. This gas measurement device uses a light source controlled to emit two different wavelengths of infrared rays discretely and selectively, and an optical filter that selectively transmits infrared rays emitted from the light source, One set of filter and infrared detection element is sufficient. In this gas measuring device, a wavelength of 4.257 μm is used for the detection infrared and a wavelength of 1.5 μm is used for the reference infrared.

JP-A-9-33431 Japanese Patent Laid-Open No. 2001-228022 JP-A-2005-49171

  In the gas measuring device disclosed in Patent Document 1 described above or the conventional gas measuring device shown in FIG. 1, the optical filter and the infrared detecting element are a combination of individual elements. It was difficult. As a result, measurement errors were likely to occur between measuring instruments due to variations in assembly accuracy. In addition, since a plurality of optical filters and infrared detection elements are used, it is inevitable to increase the size and cost of the apparatus.

  Although the problem of alignment accuracy is reduced to some extent by integrally forming the gas measuring device disclosed in Patent Document 2 described above, miniaturization is difficult because a plurality of infrared detection elements are used. In addition, in order to maintain the measurement accuracy of the gas measuring device, it is essential to maintain the optical characteristics of the wavelength selective filter using a plurality of mirrors in a uniform manner. Thus, there was a problem that the configuration was not simple.

In addition, the gas measuring device disclosed in Patent Document 3 described above requires a light source that is controlled so as to discretely and selectively emit reference infrared rays and infrared rays for detection. There was a drawback that it took. In addition, in order to maintain the measurement accuracy of the gas measuring device, an optical filter that selectively transmits the detection infrared wavelength range, the reference infrared wavelength range, and the discrete wavelength range infrared rays, respectively. It is essential to maintain the same optical characteristics. Since this optical filter is a special member and is not general, there is a problem that it is not easy to manufacture.
The present invention has been made in view of such problems, and an object of the present invention is to provide a gas measurement device that is simpler, easier to manufacture, and has higher measurement accuracy, and a gas measurement method that supports power saving.

  The present invention has been made to achieve such an object, and the invention according to claim 1 is emitted from the light source (10) in the atmosphere of the measurement target gas introduced into the optical path (32). In the gas measurement device (100) in which the concentration of the measurement target gas is displayed according to the amount of infrared rays that have reached the infrared detection element (20), the measurement target gas can be introduced into the internal space (31). A measurement cell (30), a calculation unit (40) for determining the concentration of the gas to be measured in the internal space (31) based on the output from the infrared detection element (20), and the light source (10) And a control unit (60) for controlling the unit (40), and the light source (10) simultaneously emits both an infrared ray in an absorption wavelength band absorbed by the measurement target gas and an infrared ray in a non-absorption wavelength band that is not absorbed. Is possible and The unit (60) acquires the output of the infrared detection element (20) a plurality of times within a period in which the emission spectrum of the infrared light emitted from the light source (10) is continuously changing, and converts the output to the acquired output. Based on this, the calculation unit (40) is caused to execute a calculation for determining the concentration of the gas to be measured. (Figure 3)

According to a second aspect of the present invention, in the first aspect of the present invention, the control unit (60) is configured such that the emission spectrum is based on a continuous change in an infrared peak emitted from the light source (10). It is characterized by controlling the continuous change of the. (FIGS. 3, 5, 6 to 8)
According to a third aspect of the present invention, in the first or second aspect of the present invention, the control unit (60) is configured to continue the emission spectrum based on a continuous change in the temperature of the light source (10). It is characterized by controlling the change of the eye. (FIGS. 3, 5, 6 to 8)

The invention according to claim 4 is the invention according to claim 1, 2 or 3, wherein the control unit (60) is within a predetermined period after the light source (10) is controlled to start lighting, The continuous change of the emission spectrum is controlled within any period of a predetermined period after the light source (10) is controlled to be turned off. (FIGS. 3, 5, 6 to 8)
According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects of the present invention, the calculation unit (40) includes an infrared detection element (20) when the light source (10) is not emitting light. The offset due to infrared radiation from other than the light source (10) is canceled based on the output. (FIGS. 3, 5, 6 to 8)

The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the gas to be measured is CO ₂ . (FIGS. 5, 7, and 8)
According to a seventh aspect of the present invention, there is provided an optical path (32) between the light source (10) and the infrared detection element (20) according to any of the first to sixth aspects. The optical filter (50) further comprises a continuous wavelength band in which the transmittance for infrared rays in the absorption wavelength band and the non-absorption wavelength band is greater than 50% of the maximum transmittance. It is contained in. (Fig. 5)

The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the control unit (60) has an infrared detecting element within a period in which the emission spectrum continuously changes. The timing for acquiring the output from (20) is controlled. (FIGS. 3, 5, 6 to 8)
The invention according to claim 9 is the invention according to claim 8, wherein the controller (60) controls the temperature of the light source (10) or the elapsed time after the lighting of the light source (10) is started, and the turn-off control. The timing for acquiring the output from the infrared detection element (20) is controlled based on either the elapsed time or the post-elapsed time. (Fig. 3, Fig. 5)

According to the tenth aspect of the present invention, in the atmosphere of the measurement target gas introduced into the optical path (32), the infrared rays emitted from the light source (10) correspond to the amount of infrared rays that have reached the infrared detection element (20). Then, in the gas measurement method that is displayed as the concentration of the gas to be measured, the light emitting step (S10) that emits both the infrared of the absorption wavelength band and the infrared of the non-absorption wavelength band from the light source (10) simultaneously. ), And obtaining the output group (I _{all (T, C)} ) by acquiring the output from the infrared detecting element (20) a plurality of times during the continuous change of the emission spectrum of the infrared light emitted from the light source (10). A light emission output acquisition step (S20) to be obtained, and a gas concentration calculation step (S30) for performing a calculation for determining the concentration of the gas to be measured based on the output group (I _{all (T, C)} ). Features And (Fig. 4)

The invention described in claim 11 is the invention described in claim 10, characterized in that the continuous change of the emission spectrum is due to the continuous change of the temperature of the light source (10). (FIGS. 3, 5, 6 to 8)
According to a twelfth aspect of the present invention, in the invention of the eleventh aspect, a non-light-emitting output acquisition step of acquiring the output of the infrared detection element (20) acquired when the light source (10) is not emitting light ( The gas concentration calculation step (S30) further includes an output of the infrared detection element (20) acquired when the light source (10) is not emitting light by the non-light emitting output acquisition step (S25), The calculation is performed based on the output group (I _{all (T, C)} ). (Fig. 4)
The invention according to claim 13 is the invention according to claim 10, 11 or 12, wherein the calculation is derived by the following expression (1) relating to the output group (I _{all (T, C)} ). It is performed based on the transmittance A _{λi (c)} .

(Where I _{all (T, c)} represents the output group (I _{all (T, C)} ) of the infrared detection element (20) at a light source temperature T [° C.] and a gas concentration c, and A _{λi (c)} represents gas Infrared transmittance of the wavelength band λi at the concentration c, I _{λi (T)} indicates the output of the infrared detection element (20) for the infrared of the wavelength band λi at a gas concentration of zero and temperature T [° C.], n is infrared (An integer greater than or equal to 2 is shown by the number which divides | segments the range of the infrared spectrum which injects into a detection element (20).)
The invention according to claim 14 is the invention according to claim 13, wherein the number of the output groups (I _{all (T, C)} ) is equal to or more than n, and is represented by the formula (1). Infrared transmittance A _{λi (c)} in each wavelength band λi is derived from the output group (I _{all (T, C)} ) using the least square method.

Further, in the invention described in claim 15, in the invention described in claim 13, the number of the output groups (I _{all (T, C)} ) is equal to the n, and is represented by the formula (1). Infrared transmittance A _{λi (c)} in each wavelength band λi is derived by solving an inverse matrix of the output group (I _{all (T, C)} ).
The invention of claim 16 is the invention according to claim 13, wherein the transmittance _A λi _(c), the parameter for the reference transmittance A _{.lambda.ref (c)} without wavelength band lambda _ref of gas absorption The gas measurement method according to claim 13, wherein a calculation for obtaining a ratio with the transmittance of another wavelength band is performed. (Fig. 8)

  ADVANTAGE OF THE INVENTION According to this invention, the gas measuring apparatus and gas measuring method corresponding to power saving which are simpler, easy to manufacture, and have high measurement accuracy can be realized.

It is a block diagram for demonstrating the conventional gas measuring apparatus. It is a diagram of the infrared transmission spectrum example in the CO ₂ atmosphere in the space of FIG. It is a block diagram for demonstrating Example 1 of the gas measuring device which concerns on this invention. It is a figure which shows the flowchart for demonstrating the gas measuring method by the gas measuring device of FIG. It is a block diagram for demonstrating Example 2 of the gas measuring device which concerns on this invention. It is a figure of the infrared emission spectrum shown according to the temperature of a light source. FIG. 7 is an enlarged view in the vicinity of a wavelength of 3.8 μm to 4.4 μm in the emission spectrum of FIG. 6. Source temperature 1200 ° C., in the CO ₂ concentration 0～6000Ppm, illustrates the amount of infrared incident on the infrared detector.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 3 is a configuration diagram for explaining the first embodiment of the gas measuring device according to the present invention. The gas measurement apparatus 100 according to the first embodiment introduces a measurement target gas into the internal space 31 from the introduction unit 33 and discharges it from the extraction unit 34, the light source 10, the infrared detection element 20 that receives infrared rays emitted from the light source 10. A measurement cell 30 that can perform the calculation, a calculation unit 40 that determines the concentration of the gas to be measured in the internal space 31 based on an output from the infrared detection element 20, and a control unit 60 that controls them. Yes.

<Measurement cell>
The measurement cell 30 is not particularly limited as long as the measurement target gas can be introduced into the internal space 31. The introduction part 33 and the lead-out part 34 may be at least one in combination with some ventilation function part for the internal space 31 of the measurement cell 30. In addition, from the viewpoint of improving the measurement accuracy of the gas concentration over time, it is preferable that the gas introduction part 33 and the derivation part 34 are provided respectively.

<Light source>
The light source 10 is not particularly limited as long as the light source 10 can emit both infrared rays in the absorption wavelength band and non-absorption wavelength band by the measurement target gas, and can continuously change the emission spectrum. For example, an incandescent light bulb, a MEMS (micro electro mechanical systems) heater, an LED, and the like can be given. The light source 10 may be either a point light source or a surface light source.
The absorption wavelength band here may be a wavelength band in which the infrared transmittance (hereinafter also simply referred to as transmittance) varies depending on the concentration of the measurement target gas.

This absorption wavelength band can be arbitrarily determined depending on the measurement target gas. For example, when the measurement target gas is CO ₂ , infrared absorption occurs specifically at an absorption wavelength band of about 4.2 μm to about 4.4 μm. A non-absorption wavelength band is arbitrarily selected from a band other than the absorption wavelength band. That is, the non-absorption wavelength band is set to a band other than about 4.2 μm to about 4.4 μm. It should be noted that the absorption wavelength band and the non-absorption wavelength band are preferably as close as possible to each other as long as the conditions for making a large difference in transmittance are satisfied in the atmosphere of the measurement target gas. That is, when infrared rays having different wavelength bands are emitted using a single light source 10, the closer the different wavelength bands are, the more advantageous the required performance for the light source 10 is. . As a result, the light source 10 can be easily manufactured and simple. From a similar point of view, the closer the non-absorption wavelength band is to the absorption wavelength band, the easier the calculation, for example, the concentration can be derived with a small amount of calculation. As a result, the required performance for the arithmetic unit 40 is advantageous because it is sufficient to be more general and simple.

<Infrared detector>
The infrared detection element 20 is not particularly limited as long as it has sensitivity to infrared rays emitted from the light source 10. The infrared detection element 10 is preferably a thermal infrared sensor such as a pyroelectric sensor, a thermopile, a bolometer, a quantum infrared sensor, or the like.
In the gas measuring apparatus 100 of the first embodiment, the absorption wavelength band included in the infrared rays emitted from the light source 20 during the period in which the emission spectrum of the light source 20 continuously changes by the single infrared detection element 20 and The output of the infrared detection element 20 for the non-absorption wavelength band is acquired at least twice. Since the concentration of the measurement target gas can be determined based on these two or more outputs obtained, the number of the infrared detection elements 20 is sufficient, and the measurement cell 30 can be further downsized.

<Calculation unit>
The calculation unit 40 acquires the output of the infrared detection element 20 at least twice within a period in which the emission spectrum of infrared rays emitted from the light source 10 continuously changes, and based on the acquired output, the measurement target gas There is no particular limitation as long as the calculation for density determination can be executed. For example, an analog IC, a digital IC, and a CPU (Central Processing Unit) are suitable for the calculation unit 40. The control unit 60 may include the function of the calculation unit 40.

The calculation unit 40 is comprehensively controlled by the control unit 60 together with the light source 10 and derives the transmittance Aλi in each wavelength band based on the output acquired from the infrared detection element 20. Then, in order to determine the density, it is effective to execute arithmetic processing exemplified in the following (1) to (4).
(1) The transmittance Aλi (α) at a desired concentration α is stored as a threshold value, and the concentration with respect to the measurement target gas in the space, for example, CO ₂ is compared by comparing the threshold value and the derived transmittance Aλi. Processing for determining whether or not is greater than or equal to a threshold value.
(2) A calculation process for quantitatively determining the concentration of gas to be measured, for example, CO ₂ in the space, by storing the transmittance at each concentration and comparing the derived transmittance Aλi.

(3) In addition, calculation processing for offsetting offset due to infrared radiation from other than the light source 10 based on the output of the infrared detection element 20 when the light source 10 is not emitting light.
(4) In addition, during the light emission of the light source 20, two types of outputs are acquired from the infrared detection element 20 at least once each, a total of two or more times. These outputs are of two types, an output in the absorption wavelength band for the measurement target gas and an output in the non-absorption wavelength band. A calculation process executed for determining the concentration of the measurement target gas based on these two types of outputs. According to this calculation process, the absorption wavelength band and the non-absorption wavelength band are almost uniformly reduced as long as the light source 20 is deteriorated with the condition that the measurement target gas does not exist. It is possible to easily correct a decrease in output due to deterioration with time.

<Control unit>
The control unit 60 comprehensively controls light emission of the light source 10 and calculation processing of the calculation unit 40 while measuring appropriate timing, and determines the concentration of the measurement target gas based on the output acquired from the infrared detection element 20. For this purpose, the calculation unit 40 is caused to execute the calculation. Note that the function of the control unit 60 may be included in the calculation unit 40.
The control unit 60 can control to continuously change the emission spectrum emitted from the light source 10, and also has a function of controlling the timing for acquiring the output of the infrared detection element 20. And this control part 60 controls the timing of output acquisition so that the output of the infrared detection element 20 may be acquired synchronizing with the period when the emission spectrum emitted from the light source 10 is changed continuously. Such a function of the control unit 60 enables more accurate gas concentration determination. In other words, the output corresponding to the infrared rays of two or more different wavelength ranges necessary for the gas concentration determination is acquired more than once by one set of the light source 10 and the infrared detection element 20, thereby achieving higher accuracy. Gas concentration determination is possible.

Further, according to the control unit 60, the continuous change in the emission spectrum of the infrared light emitted from the light source 10 can be controlled based on the continuous change in the peak of the infrared light emitted from the light source 10.
Moreover, according to the control part 60, the continuous change of the emission spectrum mentioned above can be controlled based on the continuous change of temperature, when the light source 10 is an incandescent light bulb or a MEMS (microelectromechanical systems) heater. .
Further, according to the control unit 60, the above-described continuous change in the emission spectrum is either within a predetermined period after the light source 10 is controlled to start lighting, or within a predetermined period after the light source 10 is controlled to be turned off. It can be performed on the basis of a continuous change in the emission spectrum of infrared rays within a period of.

  In addition, the control unit 60 acquires the output from the infrared detection element 20 based on either the temperature of the light source 10 or the elapsed time after the lighting of the light source 10 starts and the elapsed time after the extinction control. That is, when the light source 10 is turned on and off, the wavelength spectrum of the emitted infrared light changes as the temperature of the light source 10 changes. It is possible to get the output. In this way, by controlling the timing for acquiring the output from the infrared detection element 20, it is possible to determine the gas concentration with higher accuracy.

In addition, regarding timing control based on the temperature of the light source 10 described above, for example, there is a method of monitoring information based on the temperature of the light source 10. Here, the light source 10 of a tungsten filament sphere is illustrated. Since the temperature and electrical resistance of tungsten have a correlation, it is possible for the control unit 60 to monitor the electrical resistance of tungsten and obtain temperature information of the light source 10. The output from the infrared detection element 20 is controlled at the timing when the light source 10 is at a desired temperature by controlling the timing for acquiring the output from the infrared detection element 20 based on the temperature information thus acquired. It becomes possible to get.
The gas measuring apparatus 100 according to the first embodiment is capable of saving power as compared with the conventional gas measuring apparatus shown in FIG. 1 and the like because only one infrared detecting element 20 for determining the concentration of the measurement target gas is required. It becomes possible.
Thus, according to the gas measuring device of the present invention, it is possible to realize power saving and higher measurement accuracy.

Next, a gas measurement method using the gas measurement device 100 of Example 1 will be described.
FIG. 4 is a flowchart for explaining a gas measuring method by the gas measuring apparatus of FIG. The gas measurement method of the first embodiment is a gas measurement method that utilizes infrared absorption caused by the measurement target gas introduced into the optical path 32 while the infrared rays emitted from the light source 10 reach the infrared detection element 20. is there. As shown in FIG. 4, the gas measurement method includes a light emission step (S10), an output acquisition step during light emission (S20), and a gas concentration calculation step (S30).

First, in the light emitting step (S10), both infrared rays in the absorption wavelength band and infrared rays in the non-absorption wavelength band are emitted from the light source 10 simultaneously. Also, the output from the infrared detection element 20 is acquired a plurality of times during the period of continuous change of the emission spectrum of the infrared rays emitted from the light source 10 by the output output acquisition step (S20), and the output group I _{all (T, C )} Then, in the gas concentration calculation step (S30), the concentration of the measurement target gas is determined by executing a calculation based on the output group I _{all (T, C)} . According to the gas measurement method described above, it is possible to perform highly accurate gas concentration determination based on the output from the single infrared detection element 20.

Note that the continuous change of the emission spectrum may be controlled by the control unit 60 based on the continuous change of the temperature of the light source 10. Furthermore, from the viewpoint of reducing offset due to infrared radiation from other than the light source 10, it further includes a non-light-emitting output acquisition step (S25) for acquiring the output of the infrared detection element 20 acquired when the light source 10 is not emitting light, and the gas concentration In the calculation step (S30), the output of the infrared detection element 20 acquired when the light source 10 is not emitting light by the non-light-emitting output acquisition step (S25), and the output group acquired a plurality of times in the light-emitting output acquisition step (S20) It is preferable to perform the operation based on I _{all (T, C)} .

According to the gas measurement method for performing the steps (S20) to (S30) using the gas measurement device 100 of the first embodiment, only one infrared detection element 20 for determining the concentration of the measurement target gas is sufficient. Therefore, it becomes possible to cope with power saving as compared with a gas measuring method using the conventional gas measuring apparatus shown in FIG.
According to the gas measuring method of the present invention, it is possible to realize power saving and higher measurement accuracy.

FIG. 5 is a block diagram for explaining Example 2 of the gas measuring device of the present invention. In the gas measurement device 200 of Example 2, the measurement target gas (GAS in FIG. 5) indicates CO ₂ , the reference numeral 50 indicates an optical filter, and the other reference numerals are the same as those in FIG. In other words, since the content of the second embodiment is limited to some conditions of the first embodiment, the description of the first embodiment is applied to the second embodiment as it is, and a description specific to the second embodiment is added.

<Optical filter>
By inserting the optical filter 50 in the optical path 32 between the light source 10 and the infrared detection element 20, it is possible to determine the gas concentration with higher accuracy. The optical filter 50 preferably includes an absorption wavelength band and a non-absorption wavelength band in a continuous wavelength band having a transmittance of 50% or more of the maximum transmittance.
The optical filter 50 used in the gas measuring apparatus 200 of the second embodiment has a transmittance of 100% at a wavelength of 3.8 μm to 4.4 μm and a transmittance of 0% for other wavelengths. It is.

<Light source>
The infrared rays output from the light source 10 output infrared rays depending on the light source temperature in accordance with Planck's radiation law. The emission spectrum of infrared rays emitted from the light source 10 is controlled by the control unit 60 so as to continuously change.
<Control unit>
The controller 60 controls the emission spectrum of the light source 10 to change continuously based on the temperature of the light source 10 changing continuously. In addition, the control method regarding the continuous change of an emission spectrum is not limited to this, Other control methods may be used.

<Infrared emission spectrum according to Planck's radiation law>
FIG. 6 is a diagram of an infrared emission spectrum shown for each temperature of the light source. The emission spectrum follows Planck's radiation law at each temperature of the light source 10. FIG. 7 is an enlarged view in the vicinity of a wavelength of 3.8 μm to 4.4 μm in the emission spectrum of FIG. In the following description of the embodiments, the wavelength band of 3.8 μm to 4.0 μm is λ1, the wavelength band of 4.0 μm to 4.2 μm is λ2, and the wavelength band of 4.2 μm to 4.4 μm is λ3. Called.

FIG. 8 is a diagram showing the amount of infrared rays incident on the infrared detection element at a light source temperature of 1200 ° C. and a CO ₂ concentration of 3000 ppm. In the wavelength band λ1, since infrared absorption by CO ₂ does not occur, the output is substantially the same as the output when the CO ₂ concentration is 0 ppm. In the wavelength band λ2, since infrared absorption by CO ₂ is slightly generated, the output is slightly reduced compared with the output in the case where the CO ₂ concentration is 0 ppm. In the wavelength range [lambda] 3, since the infrared absorption by CO ₂ frequently occur, as compared with the output for the CO ₂ concentration 0 ppm, significantly output decreases.
Here, assuming that the output from each wavelength band λi infrared detection element at a CO ₂ concentration of 0 ppm and temperature T ° C. is I _{λ1 (T),} and the absorption coefficient of each wavelength band λi at the CO ₂ concentration c is λi (c), CO ₂ concentration cppm, temperature T ° C. Output I (T, c) from the infrared detection element is expressed by the following equation (2).

<Calculation unit>
The calculation executed by the calculation unit 40 is the same as in the first embodiment. In the light emission output acquisition step (S20), the output from the infrared detection element 20 is acquired a plurality of times within the period of continuous change in the emission spectrum of the infrared light emitted from the light source 10, and the output group I _{all (T, C )} The transmittance A _{λi (c)} is derived from the following equation (2) regarding the output group I _{all (T, C)} .

(Where I _{all (T, c)} represents the output group (I _{all (T, C)} ) of the infrared detection element (20) at a light source temperature T [° C.] and a gas concentration c, and A _{λi (c)} represents gas Infrared transmittance of the wavelength band λi at the concentration c, I _{λi (T)} indicates the output of the infrared detection element (20) for the infrared of the wavelength band λi at a gas concentration of zero and temperature T [° C.], n is infrared (An integer greater than or equal to 2 is shown by the number which divides | segments the range of the infrared spectrum which injects into a detection element (20).)
When applied to the second embodiment, n = 3, T = 1000, 1100, and 1200 ° C.
And the output of the infrared detection element in each of the temperature of a light source is 1000 degreeC, 1100 degreeC, and 1200 degreeC is represented by following formula (3)-(5), respectively.

If at least the condition number of the light source temperature used for the calculation and n are the same, the transmittance A _λi corresponding to the CO ₂ concentration can be obtained by solving the inverse matrix. That is, in the above example, the number of output groups (I _{all (T, C)} ) is equal to n, and the inverse matrix of the output group (I _{all (T, C)} ) represented by the equation (2) is solved. To derive infrared transmittance A _{λi (c)} in each wavelength band λi.
Then, since the number of acquired output groups is equal to n in the equation (2), the light source temperatures of the output groups represented by the above equation (2) are three, and n is 3, the inverse matrix is solved. Thus, the transmittance A _λi in each wavelength band can be obtained.
The above equations (3) to (5) can be expressed by the following determinant (6).

  Here, the above equation (6) is replaced with the following equation (7).

  Therefore, the coefficient A to be obtained can be expressed as the following formula (8).

  The method for obtaining the inverse matrix shown in the following equation (9) may be any of a method using LU decomposition, a sweep-out method, and a method using a cofactor.

In order to further improve the accuracy, the number of output groups (I _{all (T, C)} ) is n or more, and a minimum of two from the output group (I _{all (T, C)} ) represented by the above formula (2). It is preferable to derive infrared transmittance A _{λi (c)} in each wavelength band λi by using multiplication.
That is, the number of acquired output groups I _{all (T, C)} is n or more, and simultaneous measurement may be performed using measurement data of light source temperatures higher than n, and regression analysis may be performed. Here, according to the equation (7), the transmittance A _{λi (c)} in each wavelength band is calculated using the least square method. The least square method is a method for obtaining the transmittance A _{λi (c)} in each wavelength band so as to minimize the sum of squares of errors in a single regression equation, and is described below using a pseudo inverse matrix shown in the following equation (10). It can be calculated by equation (11).

From the transmittance A _λi in each wavelength band derived in this way, the concentration of CO ₂ gas in the space can be determined. As the density determination method, the calculation processes (1) and (2) described in the first embodiment are executed.
(1) The transmittance A _{λi (α)} at a desired concentration α is stored as a threshold, and the concentration of the CO ₂ gas in the space is equal to or greater than the threshold by comparing the threshold and the derived transmittance A _λi. An arithmetic process for determining whether or not.
(2) A calculation process in which the transmittance at each concentration is stored, and the CO ₂ concentration in the space is quantitatively determined by comparing these values with the derived transmittance Aλi.

In the transmittance A _{λi (c)} of the second embodiment, a calculation for _{obtaining the} ratio of the transmittance A _{λref (c)} of the wavelength band λ _ref without gas absorption to the transmittance of other wavelength bands is used as a reference parameter. You may do it. Specifically, it is used that each output from the infrared detection element is represented by the following formula (12) instead of the above formula (2). Thereby, the gas concentration is determined by deriving A _{λ1 (c)} / A _{λref (c)} , A _{λ2 (c)} / A _{λref (c)} , A _{λ3 (c)} / A _{λref (c)} , respectively. It is a method to do.

According to this method, even when the value of I _{all (T, c)} fluctuates due to the deterioration of the light source 10 over time or the influence of the deposits on the optical filter 50, the gas is maintained with high determination accuracy. It is possible to perform density determination.
The gas concentration determination operation when this method is employed will be described under the conditions limited in the second embodiment. That is, the measurement target gas is CO ₂ and the light source 10 uses a tungsten filament bulb. Due to the continuous change in the temperature of the light source 10, infrared light whose emission spectrum continuously changes is emitted from the light source 10. The optical filter 50 is under the condition that a band-pass filter having an infrared transmittance of 100% for wavelengths from 3.8 μm to 4.4 μm and a transmittance of 0% for other wavelengths is used.

Since the measurement target gas is CO ₂ under the conditions limited in the second embodiment, infrared absorption by the gas does not occur in the wavelength band λ1 of 3.8 μm to 4.0 μm. When the infrared transmittance A _{λ1 (c)} in this wavelength band λ1 is A _{ref (c)} , the above equation (12) becomes the following equation (13).

This equation (13) is _converted into A _{λ1 (c)} / A _{λ1 (c)} , A _{λ2 (c)} / A _{λ1 ( )} using the inverse matrix or the least square method in the same manner as the above equations (3) to (5). _c) and A _{λ3 (c)} / A _{λ1 (c)} are derived, respectively, so that the gas concentration can be determined.
When a simulation was performed under the following conditions, a highly accurate determination result was obtained. That is, in the case where the gas concentration is 1000 ppm and the temperature of the light source 10 is 1240 ° C., 1460 ° C., and 1630 ° C., respectively, when an offset of 5% is added to the output I _{all (T, 1000 ppm)} of the infrared detection element, A _{λ1 (1000 ppm)} , A _{λ2 (1000 ppm), and} A _{λ3 (1000 ppm)} derived on the basis of the same value have an error of 5% with respect to the set value. On the other hand, A _{λ2 (1000 ppm)} / A _{λ1 (1000 ppm)} derived based on the above equation (13) is an error of 0.005% with respect to the set value, and A _{λ3 (1000 ppm)} / A _{λ1 (1000 ppm)} is It was confirmed that the error was suppressed to 0.0005%. That is, it has been confirmed that the determination result derived based on the above equation (13) has extremely high accuracy.
As described above, according to the present invention, it is possible to realize a gas measuring device that is simpler, easier to manufacture, and has high measurement accuracy, and a gas measuring method that supports power saving.

The present invention is a gas measurement in which an infrared signal emitted from a light source is displayed as a concentration of a measurement target gas by an electric signal output in accordance with the amount of infrared rays reaching the infrared detection element in an atmosphere of the measurement target gas introduced into an optical path. Regarding the apparatus and the gas measuring method, the gas measuring apparatus and the gas measuring method of the present invention acquire the output of the infrared detecting element a plurality of times within a period in which the emission spectrum of the infrared light emitted from the light source is continuously changing, Since the concentration of the measurement object gas is determined with extremely high accuracy based on the acquired output, it is suitable for determining the concentration of a gas typified by CO ₂ .

10 light source 20, 321, 322 infrared detection element,
30, 330 Measurement cells 31, 331 Internal space 40 Calculation unit 50, 351, 352 Optical filter 100, 200, 300 Gas measuring device

Claims (16)

In the gas measuring device in which the concentration of the measurement target gas is displayed according to the amount of infrared rays that the infrared ray emitted from the light source reaches the infrared detection element in the atmosphere of the measurement target gas introduced into the optical path.
A measurement cell capable of introducing a gas to be measured into the internal space;
A calculation unit for determining the concentration of the measurement target gas in the internal space based on the output from the infrared detection element;
A control unit for controlling the light source and the calculation unit,
The light source is capable of simultaneously emitting both infrared light in an absorption wavelength band absorbed by the measurement target gas and infrared light in a non-absorption wavelength band that is not absorbed,
The control unit acquires the output of the infrared detection element a plurality of times within a period in which the emission spectrum of the infrared light emitted from the light source is continuously changing, and the concentration of the measurement target gas based on the acquired output A gas measuring apparatus that causes the calculation unit to execute a calculation for determination.   The gas measuring apparatus according to claim 1, wherein the control unit controls a continuous change in the emission spectrum based on a continuous change in an infrared peak emitted from the light source.   The gas measurement device according to claim 1, wherein the control unit controls a continuous change in the emission spectrum based on a continuous change in the temperature of the light source.   The controller controls a continuous change in the emission spectrum within a predetermined period after the light source is controlled to start lighting and within a predetermined period after the light source is controlled to be turned off. The gas measuring device according to claim 1, 2, or 3.   5. The gas measurement according to claim 1, wherein the calculation unit cancels an offset due to infrared radiation from other than the light source based on an output of an infrared detection element when the light source is not emitting light. apparatus. The gas measuring apparatus according to claim 1, wherein the measurement target gas is CO ₂ .   The optical filter further includes an optical filter interposed in an optical path between the light source and the infrared detection element, and the optical filter has a transmittance with respect to infrared rays in the absorption wavelength band and a non-absorption wavelength band of 50% of the maximum transmittance. 7. The gas measuring device according to claim 1, wherein the gas measuring device is included in a continuous wavelength band having the above transmittance.   The gas measurement according to any one of claims 1 to 7, wherein the control unit controls the timing of acquiring the output from the infrared detection element within a period in which the emission spectrum is continuously changing. apparatus.   The control unit controls the timing for acquiring the output from the infrared detecting element based on either the temperature of the light source or the elapsed time after the light source starts lighting and the elapsed time after the extinction control. The gas measuring device according to claim 8. In the gas measurement method in which the infrared light emitted from the light source is displayed as the concentration of the measurement target gas in accordance with the amount of infrared light that has reached the infrared detection element in the atmosphere of the measurement target gas introduced into the optical path.
A light emitting step of simultaneously emitting both infrared light of the absorption wavelength band and infrared light of the non-absorption wavelength band from the light source;
A light emission output acquisition step of obtaining an output group by acquiring the output from the infrared detection element a plurality of times during a continuous change in the emission spectrum of the infrared light emitted from the light source;
And a gas concentration calculation step of performing a calculation for determining the concentration of the measurement target gas based on the output group.   The gas measurement method according to claim 10, wherein the continuous change in the emission spectrum is due to a continuous change in the temperature of the light source. It further includes an output acquisition step when not emitting light that acquires an output of the infrared detection element acquired when the light source does not emit light,
The said gas concentration calculation process performs the said calculation based on the output of the infrared rays detection element acquired when the said light source is not light-emitted by the said light emission time output acquisition process, and the said output group. 11. The gas measuring method according to 11. The gas measurement method according to claim 10, 11 or 12, wherein the calculation is executed based on a transmittance A _{λi (c)} derived by the following equation (1) relating to the output group.

(Where I _{all (T, c)} represents the output group (I _{all (T, C)} ) of the infrared detection element at the light source temperature T [° C.] and the gas concentration c, and A _{λi (c)} represents the gas concentration c. Infrared transmittance of the wavelength band λi is shown, I _{λi (T)} indicates the output of the infrared detecting element for the infrared of the wavelength band λi at a gas concentration of zero and temperature T [° C.], and n is the infrared ray incident on the infrared detecting element (An integer greater than or equal to 2 is indicated by the number dividing the spectrum range.) The number of the output groups (I _{all (T, C)} ) is n or more, and the least square method is used from the output group (I _{all (T, C)} ) represented by the formula (1). The gas measurement method according to claim 13, wherein an infrared transmittance A _{λi (c)} in each wavelength band λi is derived. Each wavelength is obtained by solving the inverse matrix of the output group (I _{all (T, C)} ) represented by the formula (1) in which the number of the output groups (I _{all (T, C)} ) is equal to the n. 14. The gas measuring method according to claim 13, wherein infrared transmittance A _{λi (c)} in the band λi is derived. In the transmittance A _{λi (c)} , a calculation for _{obtaining a} ratio of the transmittance A _{λref (c)} of the wavelength band λ _ref without gas absorption to the transmittance of other wavelength bands is performed. The gas measuring method according to claim 13, wherein

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