JP2010276539A - Device and method for measuring concentration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device with a simple structure for measuring concentration, which can reduce measuring errors of photodetector's sensitivity caused by a change in temperature. <P>SOLUTION: The device for measuring concentration includes a light source 3 for irradiating a sample 4 with first light 3A1 and second light 3A2 containing light having an intrinsic absorption wavelength λ1 and a non-absorption wavelength λ2, a first photodetector 13 and a second photodetector 15 with first emitting light 3C1 and second emitting light 3C2 that have passed through a sample 4, a second optical attenuator 7 provided between the sample 4 and the optical detector 15, and a second optical attenuator controller 21. The photo-electric conversion sections 45 of the first photodetector 13 and the second photodetector 15 are based on a same photoelectric conversion principle and made of a same material, and the second optical attenuator 21 controls the luminous transmittance of the second optical attenuator 7 to bring the intensity of second emitting light 3E2 entering in the second photodetector 15 close to the strength of first emitting light 3E1 entering in the first photodetector 13. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  FIG. 8 of Patent Document 1 below describes a gas concentration measuring device that uses one light receiving element (photodetector). The apparatus includes a light source, a chamber for storing a gas sample, a bandpass filter that selectively transmits light having a specific absorption wavelength of a measurement target gas in the gas sample, a pyroelectric element as one light receiving element, It has. In this apparatus, the pulsed light emitted from the light source travels through the gas sample in the chamber and is emitted out of the chamber. The pulsed light emitted out of the chamber enters the pyroelectric element after passing through the band-pass filter. Light having a wavelength near the intrinsic absorption wavelength of the measurement target gas in the pulsed light is absorbed by the measurement target gas at a rate corresponding to the concentration of the measurement target gas in the gas sample when traveling in the gas sample. The light intensity of the pulsed light incident on the pyroelectric element changes corresponding to the concentration of the measurement target gas. For this reason, the concentration of the measurement target gas in the gas sample can be calculated from the light intensity of the pulsed light incident on the pyroelectric element.

  1 and 9 of Patent Document 1 below describe a gas concentration measuring device that uses two light receiving elements (photodetectors). These apparatuses include a light source, a chamber for storing a gas sample, a first bandpass filter that selectively transmits light having a wavelength near the intrinsic absorption wavelength of a measurement target gas in the gas sample, and a gas sample. A second bandpass filter that selectively transmits light having a wavelength in the vicinity of a wavelength that is not substantially absorbed by the various gases (non-absorption wavelength), a first pyroelectric element as two light receiving elements, and a second Two pyroelectric elements are provided.

  In these apparatuses, the pulsed light emitted from the light source travels through the gas sample in the chamber and is emitted out of the chamber from the two light emission surfaces (end surfaces) of the chamber. The pulsed light emitted from one light emitting surface of the chamber passes through the first bandpass filter and then enters the first pyroelectric element. The pulsed light emitted from the other light emitting surface of the chamber passes through the second bandpass filter and then enters the second pyroelectric element. The light intensity of the pulsed light incident on the first pyroelectric element changes in accordance with the concentration of the gas to be measured, as in the gas concentration measuring device using one light receiving element (photodetector) described above. To do. On the other hand, the light intensity of the pulsed light incident on the second pyroelectric element does not depend on the concentration of the measurement target gas in the gas sample.

  In the gas concentration measuring apparatus shown in FIG. 1 of Patent Document 1 below, the intensity of the emitted light from the light source is feedback-controlled so that the output value (measured value) of the second pyroelectric element approaches the set reference value. Thus, the intensity fluctuation of the emitted light from the light source is suppressed, and the concentration of the measurement target gas is calculated based on the output value (measured value) of the first pyroelectric element.

  Moreover, in the gas concentration measuring apparatus described in FIG. 9 of Patent Document 1 below, the ratio between the output value of the first pyroelectric element and the output value of the second pyroelectric element, that is, after passing through the gas sample The gas to be measured in a gas sample is calculated by calculating the ratio of the intensity of light having a wavelength near the intrinsic absorption wavelength of the gas to be measured and the intensity of light having a wavelength near the non-absorption wavelength. The concentration of is calculated.

Japanese Patent Laid-Open No. 8-128956

  In the gas concentration measuring apparatus using one photodetector as described in FIG. 8 of the above-mentioned Patent Document 1, if the intensity of the emitted light from the light source fluctuates due to deterioration of the light source, the concentration of the gas to be measured Regardless, the intensity of the light incident on the light receiving element fluctuates, and an error occurs in the measured value of the concentration of the measurement target gas.

  On the other hand, in the gas concentration measurement apparatus using two photodetectors as described in FIGS. 1 and 9 of the above-mentioned Patent Document 1, the measurement target gas caused by fluctuations in the intensity of the emitted light from the light source The error of the measured value can be reduced to some extent. Specifically, in the gas concentration measuring apparatus as described in FIG. 1 of the above-mentioned Patent Document 1, the fluctuation of the intensity of the emitted light from the light source is suppressed based on the output value of the second pyroelectric element. Therefore, it is possible to reduce to some extent errors in measured values caused by fluctuations in the intensity of light emitted from the light source.

  Further, in the gas concentration measuring apparatus as described in FIG. 9 of Patent Document 1, the intensity of light having a wavelength near the intrinsic absorption wavelength and the intensity of light having a wavelength near the non-absorption wavelength of the measurement target gas. Is used to calculate the concentration of the measurement target gas in the gas sample. When the intensity of the light emitted from the light source fluctuates, the intensity of light incident on the first photodetector and the intensity of light incident on the second photodetector fluctuate at substantially the same rate. Can be offset to some extent between the output fluctuation of the first photodetector and the output fluctuation of the second photodetector due to the intensity fluctuation of the emitted light of the light source. As a result, it is possible to reduce to some extent errors in measured values caused by fluctuations in the intensity of light emitted from the light source.

  However, the sensitivity of the photodetector (correlation between light intensity and output) has temperature dependence. That is, when the temperature of the photoelectric conversion unit in the photodetector fluctuates, the output value of the photodetector fluctuates regardless of the intensity of incident light. Therefore, in the gas concentration measuring apparatus as described in FIG. 1 of Patent Document 1, when the temperature of the photoelectric conversion unit of the first pyroelectric element changes during the measurement, the sensitivity of the first pyroelectric element. In addition to causing an error in the measurement value of the measurement target gas due to the change in the gas, the measurement error due to the fluctuation in the intensity of the light source due to the change in the sensitivity of the second pyroelectric element is appropriately reduced. Therefore, it is difficult to accurately measure the concentration of the measurement target gas.

  Moreover, in the gas concentration measuring apparatus using two photodetectors as described in FIG. 9 of Patent Document 1, the output value of the first pyroelectric element and the output value of the second pyroelectric element Since the concentration of the measurement target gas in the gas sample is calculated on the basis of the ratio of the above, the temperature dependence of the sensitivity of the first and second photodetectors cancels each other to some extent, It is considered that the measurement error due to the temperature dependence of sensitivity is suppressed to some extent.

  However, the intensity of light incident on the first photodetector and the intensity of light incident on the second photodetector are usually different from each other. Specifically, since the light incident on the first photodetector has a wavelength near the intrinsic absorption wavelength of the measurement target gas, it is absorbed to some extent by the measurement target gas and has a relatively low intensity. On the other hand, since the light incident on the second photodetector has a wavelength near the non-absorption wavelength, the light is not substantially absorbed by various gases in the gas sample, and the intensity is relatively high. Therefore, the temperature of the photoelectric conversion unit of the first photodetector and the temperature of the photoelectric conversion unit of the second photodetector during measurement are usually different from each other. Thus, when the temperature of the photoelectric conversion unit of the first photodetector and the temperature of the photoelectric conversion unit of the second photodetector are different from each other, the sensitivity of the first photodetector and the second photodetector are changed. The sensitivity of fluctuates at different rates. Therefore, even if the concentration of the measurement target gas in the gas sample is calculated based on the ratio between the output value of the first photodetector and the output value of the second photodetector, the first and second photodetectors are calculated. Because the temperature dependence of the sensitivity cannot be sufficiently offset each other, an error occurs in the measured value of the measurement target gas.

  In order to solve the problem of the temperature dependence of the sensitivity of the photodetector as described above, the temperature dependence of the sensitivity of the first photodetector and the second photodetector is measured in advance, and the first It is conceivable to provide the gas concentration measuring device with a temperature measuring device for measuring the temperatures of the photoelectric conversion unit of the photodetector and the photoelectric conversion unit of the second photodetector. Based on the temperature dependence of the temperature of the first photodetector and the second photodetector measured by the temperature measuring instrument, and the sensitivity of the sensitivity of the first photodetector and the second photodetector, By correcting the output values of the photodetector and the second photodetector, temperature compensation of the photodetector can be performed.

  However, if the temperature compensation of the photodetector is performed by such a method, the configuration of the gas concentration measuring apparatus becomes complicated, and the temperature of the sensitivity of the first and second photodetectors measured in advance is also measured. If there is an error in the dependency, it leads to a measurement error of the concentration of the measurement target gas, so that it is difficult to accurately measure the concentration of the measurement target gas.

  For the reasons described above, it is difficult for the conventional gas concentration measuring apparatus to sufficiently reduce the measurement error due to the temperature change in the sensitivity of the photodetector.

  The present invention has been made in view of such problems, and has a simple configuration, a concentration measuring apparatus capable of reducing measurement errors caused by temperature changes in the sensitivity of the photodetector, and a simple configuration. An object of the present invention is to provide a concentration measurement method capable of reducing a measurement error due to a temperature change in the sensitivity of a photodetector.

  In order to solve the above-described problem, a concentration measuring apparatus according to the present invention is a concentration measuring apparatus that measures the concentration of a measurement target substance contained in a sample, and uses first emitted light including light of a first wavelength as a sample. A first light source for irradiating, a second light source for irradiating second emitted light including light of the second wavelength, and a first light intensity signal output so that the first emitted light transmitted through the sample is incident thereon. A first photodetector, a second photodetector that outputs an intensity signal of light provided so that the second emitted light is incident, and the sample and the second light so that the second emitted light that has passed through the sample is incident. A second optical attenuator that is provided between the detector and has a variable light transmittance; a second light attenuator control unit that controls the light transmittance of the second light attenuator; and a calculation that calculates the concentration of the measurement target substance. A light absorption rate by the measurement target substance of the first wavelength light is the second wave The photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector are based on the same photoelectric conversion principle and are made of the same material. The second optical attenuator control unit determines the intensity of the second outgoing light incident on the second photodetector based on the output value of the first photodetector and the output value of the second photodetector. The light transmittance of the second light attenuator is controlled so as to approach the intensity of the first outgoing light incident on the light, and the calculation unit calculates the concentration of the measurement target substance based on the light transmittance of the second light attenuator.

  In the concentration measuring apparatus according to the present invention, the second optical attenuator in the case where the intensity of the second emitted light incident on the second photodetector is equal to the intensity of the first emitted light incident on the first photodetector. The light transmittance is the second output incident on the second photodetector when the intensity of the first emitted light incident on the first photodetector is virtually 100% of the light transmittance of the second optical attenuator. It is proportional to the value divided by the intensity of light. And since the light absorption rate by the measurement target substance of the light of the first wavelength is higher than the light absorption rate by the measurement target substance of the light of the second wavelength, the light transmittance of the second optical attenuator is virtually 100%. In this case, the intensity of the first outgoing light incident on the first photodetector and the intensity of the second outgoing light incident on the second photodetector change at different rates corresponding to the concentration of the measurement target substance. To do. Therefore, the light transmittance of the second optical attenuator becomes a value corresponding to the concentration of the substance to be measured in the sample, and the concentration of the substance to be measured in the sample can be calculated from the light transmittance of the second optical attenuator. .

  Furthermore, in the concentration measuring apparatus according to the present invention, the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector are based on the same photoelectric conversion principle and are made of the same material. The temperature dependency of the photoelectric conversion unit on the sensitivity of the photodetector (correlation between light intensity and output) and the temperature dependency of the photoelectric conversion unit on the sensitivity of the second photodetector are substantially the same. In the concentration measurement apparatus according to the present invention, the second light attenuator causes the intensity of the second emitted light incident on the second photodetector to approach the intensity of the first emitted light incident on the first photodetector. Therefore, the temperature of the photoelectric conversion unit of the first photodetector during measurement and the temperature of the photoelectric conversion unit of the second photodetector are controlled to be substantially equal. Thereby, the rate of change in the sensitivity of the first photodetector during measurement and the rate of change in the sensitivity of the second photodetector are substantially equal. Therefore, the ratio of the error of the output value of the first photodetector and the error of the output value of the second photodetector due to the temperature change of the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector. Are substantially equal.

  Therefore, a value obtained by dividing the intensity of the first emitted light incident on the first photodetector by the intensity of the second emitted light incident on the second photodetector (that is, the intensity of the first emitted light and the second emitted light). In the intensity ratio), these errors cancel each other. Thereby, even if the temperature of the photoelectric conversion part of a 1st photodetector and the photoelectric conversion part of a 2nd photodetector changes, the influence on control of the light transmittance of a 2nd optical attenuator is reduced. As a result, according to the concentration measuring apparatus according to the present invention, without providing a temperature measuring device for measuring the temperatures of the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector, respectively, Since temperature compensation can be performed, the configuration is simplified. Further, as described above, since the temperature compensation of these photodetectors is performed by bringing the input / output values of the first photodetector and the second photodetector closer, the temperature dependence of the sensitivity of these photodetectors is reduced. There is no need to measure in advance. Therefore, there is no measurement error in the concentration of the measurement target gas due to the measurement error when measuring the temperature dependence of these photodetectors in advance. Therefore, the concentration measuring apparatus according to the present invention has a simple configuration and can reduce a measurement error due to a temperature change in the sensitivity of the photodetector.

  Furthermore, it is preferable that the first wavelength is an intrinsic absorption wavelength of the substance to be measured, and the second wavelength is a non-absorption wavelength different from each intrinsic absorption wavelength of each substance contained in the sample. As a result, the intensity of the first emitted light incident on the first photodetector changes more greatly corresponding to the concentration of the substance to be measured, and the intensity of the second emitted light incident on the second photodetector is measured. It becomes almost independent of the concentration of the target substance. As a result, since the rate of change of the light transmittance of the second optical attenuator with respect to the change in concentration of the measurement target substance becomes larger, the concentration of the measurement target substance can be measured with higher accuracy.

  Furthermore, it is preferable that the calculation unit calculates the concentration of the measurement target substance as a ratio of the measurement target substance to the entire sample. Thereby, the density | concentration of the measuring object substance as a ratio of the measuring object substance with respect to the whole sample can be measured.

  The sample further includes a reference material, the second outgoing light is transmitted through the sample before entering the second photodetector, and the light absorption rate of the second wavelength light by the reference material is the first Preferably, the calculation unit calculates the concentration of the measurement target substance as a ratio of the measurement target substance to the total of the measurement target substance and the reference substance.

  Thus, the ratio of the absorption rate of the first wavelength light by the measurement target substance to the absorption rate of the first wavelength light by the reference substance, and the absorption ratio of the second wavelength light by the measurement target substance and the reference substance The concentration of the measurement target substance as the ratio of the measurement target substance to the total of the measurement target substance and the reference substance can be calculated from the ratio of the absorption rate of the second wavelength light.

  Furthermore, in the concentration measurement apparatus according to the present invention, the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector are preferably the same. Thereby, the ratio of the error of the output value of the first photodetector due to the temperature change of the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector and the output value of the second photodetector. The error ratio is a closer value. As a result, it is possible to further reduce the measurement error due to the temperature change of the sensitivity of the photodetector.

  Furthermore, in the concentration measuring apparatus according to the present invention, the first light source and the second light source are preferably one light source. Thereby, when the light emission intensity of the light source changes, the intensity of the first emitted light and the intensity of the second emitted light change at the same rate. Therefore, a value obtained by dividing the intensity of the first emitted light incident on the first photodetector by the intensity of the second emitted light incident on the second photodetector (that is, the intensity of the first emitted light and the second emitted light). In the intensity ratio), these intensity changes cancel each other, so that the influence on the control of the light transmittance of the second optical attenuator is reduced. As a result, it is possible to reduce measurement errors caused by changes in the light emission intensity of the light source.

  Further, the concentration measuring apparatus according to the present invention is provided between the sample and the first photodetector so that the first outgoing light transmitted through the sample is incident, includes the first wavelength in a pass band, A first band pass filter that does not include two wavelengths in the pass band and a second output light that has passed through the sample are provided between the sample and the second photodetector so that the second wavelength is in the pass band. It is preferable to further include a second band pass filter that includes the first wavelength in the pass band.

  As a result, light having a wavelength near the intrinsic absorption wavelength is preferentially incident on the first photodetector, and light having a wavelength near the non-absorption wavelength is blocked by the first bandpass filter. Light having a wavelength near the non-absorption wavelength is preferentially incident on the two photodetectors, and light having a wavelength near the intrinsic absorption wavelength is blocked by the second bandpass filter. Therefore, the influence of light having a wavelength near the non-absorption wavelength on the output value of the first photodetector can be reduced, and light having a wavelength near the intrinsic absorption wavelength is given to the output value of the second photodetector. The influence can be reduced. As a result, the concentration of the measurement target gas can be measured with higher accuracy.

  Furthermore, in the concentration measuring apparatus according to the present invention, it is preferable that the sample is gaseous and the substance to be measured is gas. Thereby, it becomes possible to measure the density | concentration of the specific kind of gas in a gaseous sample with the density | concentration measuring apparatus which concerns on this invention.

  Further, the concentration measuring apparatus according to the present invention is provided between the sample and the first photodetector so that the first outgoing light transmitted through the sample is incident, and the first optical attenuator having variable light transmittance, It is preferable to further include a first optical attenuator control unit that controls the light transmittance of the first optical attenuator. Thereby, when the emitted light intensity of a light source changes, the influence of the change can be reduced with a 1st optical attenuator.

  Furthermore, in the concentration measuring apparatus according to the present invention, the second optical attenuator is preferably a liquid crystal optical shutter. As a result, the optical system can be simplified and the number of mechanical movable parts is reduced, so that the concentration measuring apparatus is inexpensive and has a low maintenance frequency.

  Furthermore, in the concentration measuring apparatus according to the present invention, it is preferable that the first photodetector and the second photodetector are each a thermal photodetector. Thereby, since the wavelength dependence of the first photodetector and the second photodetector is low, the difference between the intrinsic absorption wavelength and the non-absorption wavelength can be set large. For this reason, the influence of light having a wavelength near the non-absorption wavelength on the output value of the first photodetector can be further reduced, and light having a wavelength near the intrinsic absorption wavelength becomes the output value of the second photodetector. The influence exerted can be further reduced. As a result, the concentration of the measurement target substance can be measured with higher accuracy.

  In order to solve the above-described problem, a concentration measurement method according to the present invention is a concentration measurement method for measuring the concentration of a measurement target substance contained in a sample, and includes a first emitted light including light of a first wavelength. A step of irradiating the sample; a step of causing the first outgoing light transmitted through the sample to enter a first photodetector that outputs an intensity signal of the light; and a second outgoing light including light of the second wavelength. Irradiating to pass through a second optical attenuator having a variable rate, and causing the second light output light after passing through the second optical attenuator to enter a second photodetector that outputs a light intensity signal; A second optical attenuator control step for controlling the light transmittance of the second optical attenuator, and a calculation step for calculating the concentration of the measurement target substance. Higher than the light absorptance of the two-wavelength light to be measured, The photoelectric conversion unit of the detector and the photoelectric conversion unit of the second photodetector are based on the same photoelectric conversion principle and are made of the same material. In the second optical attenuator control step, the output value of the first photodetector And the second light so that the intensity of the second emitted light incident on the second photodetector is close to the intensity of the first emitted light incident on the first photodetector based on the output value of the second photodetector. The light transmittance of the attenuator is controlled, and in the calculation step, the concentration of the substance to be measured is calculated based on the light transmittance of the second light attenuator.

  In the concentration measurement method according to the present invention, the second optical attenuator in the case where the intensity of the second outgoing light incident on the second photodetector is equal to the intensity of the first outgoing light incident on the first photodetector. The light transmittance is the second output incident on the second photodetector when the intensity of the first emitted light incident on the first photodetector is virtually 100% of the light transmittance of the second optical attenuator. It is proportional to the value divided by the intensity of light. And since the light absorption rate by the measurement target substance of the light of the first wavelength is higher than the light absorption rate by the measurement target substance of the light of the second wavelength, the light transmittance of the second optical attenuator is virtually 100%. In this case, the intensity of the first outgoing light incident on the first photodetector and the intensity of the second outgoing light incident on the second photodetector change at different rates corresponding to the concentration of the measurement target substance. To do. Therefore, the light transmittance of the second optical attenuator becomes a value corresponding to the concentration of the measurement target substance in the sample, and the concentration of the measurement target substance in the sample can be calculated from the light transmittance of the second optical attenuator. .

  Furthermore, in the concentration measurement method according to the present invention, the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector are based on the same photoelectric conversion principle and are made of the same material. The temperature dependency of the photoelectric conversion unit on the sensitivity of the photodetector (correlation between light intensity and output) and the temperature dependency of the photoelectric conversion unit on the sensitivity of the second photodetector are substantially the same. In the concentration measurement method according to the present invention, the second optical attenuator is arranged such that the intensity of the second outgoing light incident on the second photodetector approaches the intensity of the first outgoing light incident on the first photodetector. Therefore, the temperature of the photoelectric conversion unit of the first photodetector and the temperature of the photoelectric conversion unit of the second photodetector during measurement are controlled to be substantially equal. Thereby, the rate of change in the sensitivity of the first photodetector during measurement and the rate of change in the sensitivity of the second photodetector are substantially equal. Therefore, the ratio of the error of the output value of the first photodetector and the error of the output value of the second photodetector due to the temperature change of the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector. Are substantially equal.

  Therefore, a value obtained by dividing the intensity of the first emitted light incident on the first photodetector by the intensity of the second emitted light incident on the second photodetector (that is, the intensity of the first emitted light and the second emitted light). In the intensity ratio), these errors cancel each other. Thereby, even if the temperature of the photoelectric conversion part of a 1st photodetector and the photoelectric conversion part of a 2nd photodetector changes, the influence on control of the light transmittance of a 2nd optical attenuator is reduced. As a result, according to the concentration measurement method of the present invention, the photodetector can be used without using a temperature measuring device that measures the temperatures of the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector, respectively. Therefore, the configuration is simplified. Further, as described above, since the temperature compensation of these photodetectors is performed by bringing the input / output values of the first photodetector and the second photodetector closer, the temperature dependence of the sensitivity of these photodetectors is reduced. There is no need to measure in advance. Therefore, there is no measurement error in the concentration of the measurement target gas due to the measurement error when measuring the temperature dependence of these photodetectors in advance. Therefore, according to the concentration measurement method of the present invention, it is possible to reduce measurement errors due to temperature changes in the sensitivity of the photodetector with a simple configuration.

  According to the present invention, the configuration is simple, and the concentration measuring device capable of reducing the measurement error due to the temperature change of the sensitivity of the photodetector and the temperature change of the sensitivity of the photodetector with a simple configuration are provided. A concentration measurement method capable of reducing the measurement error is provided.

FIG. 1 is a configuration diagram of a gas concentration measuring apparatus according to the first embodiment. FIG. 2 is a diagram showing the wavelength distribution of the light intensity of the first emitted light and the second emitted light immediately after being emitted from the light source. FIG. 3A is a diagram showing a wavelength distribution of the light intensity of the first outgoing light after passing through the first bandpass filter, and FIG. 3B is a second view after passing through the second bandpass filter. It is a figure which shows wavelength distribution of the light intensity of an emitted light. FIG. 4 is a schematic cross-sectional view showing the configuration of the first photodetector and the second photodetector. FIG. 5 is a configuration diagram of a gas concentration measuring apparatus according to the second embodiment. FIG. 6 is a configuration diagram of a gas concentration measuring apparatus according to the third embodiment. FIG. 7A is a diagram showing the wavelength distribution of the light intensity of the first emitted light immediately after being emitted from the light source 31, and FIG. 7B is the light intensity of the second emitted light immediately after being emitted from the light source 33. It is a figure which shows wavelength distribution. FIG. 8 is a configuration diagram of a pulse oximeter according to the fourth embodiment.

  Hereinafter, a concentration measuring apparatus according to an embodiment will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used for the same elements when possible. In addition, the dimensional ratios in the components in the drawings and between the components are arbitrary for easy viewing of the drawings.

(First embodiment)
First, a gas concentration measuring device and a gas concentration measuring method will be described as a concentration measuring device and a concentration measuring method according to the first embodiment.

  FIG. 1 is a configuration diagram of a gas concentration measuring apparatus according to the present embodiment. As shown in FIG. 1, the gas concentration measuring apparatus 1 of the present embodiment includes a light source 3, a sample container 5 that stores a gaseous sample 4, a second optical attenuator 7, a first bandpass filter 9, A second bandpass filter 11, a first photodetector 13, a second photodetector 15, a second optical attenuator control unit 21, and a calculation unit 23 are provided.

  The light source 3 irradiates the sample container 5 with the first outgoing light 3A1 and the second outgoing light 3A2. In the present embodiment, the first emitted light 3A1 and the second emitted light 3A2 are light having the same wavelength distribution and intensity distribution emitted from the same light source 3. That is, in the present embodiment, the light source 3 serves as both the first light source and the second light source. As the light source 3, for example, a halogen lamp, a xenon lamp, a tungsten lamp, a white lamp, a fluorescent lamp, a mercury lamp, sunlight, an LED, a heater, a laser, or the like can be used.

  FIG. 2 is a diagram showing the wavelength distribution of the light intensity of the first emitted light and the second emitted light immediately after being emitted from the light source. As shown in FIG. 2, the first outgoing light 3A1 and the second outgoing light 3A2 are both the intrinsic absorption wavelength λ1 of the substance to be measured contained in the sample 4, and the intrinsic absorption wavelengths of the substances contained in the sample 4. It includes light of different non-absorption wavelengths λ2. That is, in the present embodiment, the first wavelength is the intrinsic absorption wavelength λ1, and the second wavelength is the non-absorption wavelength λ2. The light source 3 may emit the first emitted light 3A1 and the second emitted light 3A2 having constant intensity in time, or the first emitted light 3A1 and the second emitted light as pulsed light emitted every predetermined period. 3A2 may be emitted.

  When the light source 3 serves as both the first light source and the second light source as in the present embodiment, the intensity of the light having the intrinsic absorption wavelength λ1 in each of the first emitted light 3A1 and the second emitted light 3A2 The intensity of light having the non-absorption wavelength λ2 is preferably the same as shown in FIG. 2, for example, the intensity difference is preferably within 5%. This is because the photoelectric conversion unit 45 of the first photodetector 13 by the first emitted light 3E1 can be used without greatly adjusting the intensity of the second emitted light 3E2 incident on the second photodetector 15 by the second optical attenuator 7. This is because it is easy to control the temperature rise degree of the second and third photoelectric detectors 45 of the second photodetector 15 by the second emitted light 3E2 to the same extent. As a result, the measurement accuracy of the concentration of the substance to be measured is improved.

  Note that, in each of the first outgoing light 3A1 and the second outgoing light 3A2, the intensity of the light of the intrinsic absorption wavelength λ1 and the intensity of the light of the non-absorption wavelength λ2 are greatly different (for example, the intensity difference is 5% or more) ) Before the concentration measurement, the light transmittance of the second optical attenuator 7 is set so that the output values of the first photodetector 13 and the second photodetector 15 when there is no substance to be measured become substantially the same value. It is preferable to set the initial state. Thereby, measurement accuracy can be improved. The second optical attenuator as described above, regardless of the difference between the intensity of the intrinsic absorption wavelength λ1 and the intensity of the non-absorption wavelength λ2 in each of the first emission light 3A1 and the second emission light 3A2. The initial state of the light transmittance of 7 can be set. Further, in each of the first outgoing light 3A1 and the second outgoing light 3A2, it is preferable that the intensity of the light having the non-absorption wavelength λ2 is greater than or equal to the intensity of the light having the intrinsic absorption wavelength λ1. . This is because the initial state of the light transmittance of the second optical attenuator 7 as described above can be easily set.

  As shown in FIG. 1, the sample container 5 is a box-shaped member that houses the sample 4 therein. The sample container 5 has one light incident part 5A provided on one end face of the sample container 5 and two light emitting parts 5B and 5C provided on the other end face of the sample container 5. The light incident part 5A preferably has a function of transmitting the first outgoing light 3A1 and the second outgoing light 3A2, but may be an opening.

The sample 4 can be, for example, a gaseous atmosphere. The substance to be measured can be, for example, carbon dioxide (CO ₂ ) gas, carbon monoxide (CO) gas, hydrocarbon (HC) gas, or the like. The intrinsic absorption wavelength λ1 (see FIG. 2) is 4 in order when the measurement target substance is carbon dioxide (CO ₂ ) gas, carbon monoxide (CO) gas, and hydrocarbon (HC) gas, respectively. 3 μm, 4.7 μm, and 3.4 μm. The non-absorption wavelength λ2 (see FIG. 2) is a wavelength different from each intrinsic absorption wavelength of each substance in the sample 4 including the measurement target substance. When the measurement target substance is carbon dioxide (CO ₂ ) gas, monoxide is oxidized. In the case of carbon (CO) gas and hydrocarbon (HC) gas, it can be set to, for example, 3.9 μm.

  Here, when the light source 3 serves as the first light source and the second light source as in the present embodiment, the intrinsic absorption wavelength λ1 and the non-absorption wavelength λ2 are close to each other (for example, the intrinsic absorption wavelength λ1 and the non-absorption wavelength). and the wavelength of the first outgoing light 3E1 immediately before entering the first photodetector 13 and the wavelength of the second outgoing light 3E2 immediately before entering the second photodetector 15 are different from each other. Are preferably not overlapped with each other. Generally, the light emitted from the light source has different light intensity depending on the wavelength, but if the wavelength difference between the intrinsic absorption wavelength λ1 and the non-absorption wavelength λ2 is small, the intrinsic absorption in the first emission light 3E1 and the second emission light 3E2 The intensities of the light of wavelength λ1 and the light of non-absorption wavelength λ2 are approximately the same. In addition, if the wavelength of the first outgoing light 3E1 and the wavelength of the second outgoing light 3E2 do not overlap with each other, the temperature rise of the photoelectric conversion unit 45 of the first photodetector 13 by the first outgoing light 3E1, It becomes easy to control the degree of temperature rise of the photoelectric conversion unit 45 of the second photodetector 15 by the second emitted light 3E2 to the same extent. Note that the wavelength of the first outgoing light 3E1 and the wavelength of the second outgoing light 3E2 do not overlap with each other because the wavelength range defining the half width of the wavelength with respect to the intensity peak of the first outgoing light 3E1 and the second outgoing light 3E2 This means that the wavelength range defining the half width of the wavelength with respect to the intensity peak does not overlap each other.

  The first emitted light 3A1 and the second emitted light 3A2 emitted from the light source 3 pass through the light incident part 5A and reach the sample 4. That is, the light source 3 irradiates the sample 4 with the first outgoing light 3A1 and the second outgoing light 3A2. The first outgoing light 3A1 and the second outgoing light 3A2 that have reached the sample 4 are the first outgoing light 3B1 and the second outgoing light 3B2, respectively, from the light incident part 5A to the light outgoing part 5B, and the light incident part 5A. To the light emitting part 5C. When the first outgoing light 3B1 and the second outgoing light 3B2 travel through the sample container 5, light having a wavelength near the intrinsic absorption wavelength is absorbed among the first outgoing light 3B1 and the second outgoing light 3B2. The amount of light absorbed at this time is proportional to the distance (optical path length) that the first outgoing light 3B1 and the second outgoing light 3B2 travel through the sample container 5 and the concentration of the measurement target substance in the sample 4.

  The light emitting part 5B and the light emitting part 5C are preferably those having a function of transmitting the first emitted light 3B1 and the second emitted light 3B2 as in the light incident part 5A, but may be openings. .

  The first emitted light 3B1 that has reached the light emitting part 5B passes through the light emitting part 5B and travels from the light emitting part 5B to the first bandpass filter 9 as the first emitted light 3C1. The second emitted light 3B2 that has reached the light emitting part 5C passes through the light emitting part 5C and travels from the light emitting part 5C to the second optical attenuator 7 as the second emitted light 3C2.

  The first bandpass filter 9 is an optical bandpass filter that includes the intrinsic absorption wavelength λ1 in its passband and does not include the non-absorption wavelength λ2 in its passband. A part of the first outgoing light 3C1 that has reached the first bandpass filter 9 passes through the first bandpass filter 9 and becomes the first outgoing light 3E1 from the first bandpass filter 9 to the first photodetector 13. It progresses to.

  FIG. 3A is a diagram showing the wavelength distribution of the light intensity of the first outgoing light after passing through the first bandpass filter. As shown in FIG. 3A, the first outgoing light 3E1 after passing through the first bandpass filter 9 has only a component having a wavelength in the vicinity of the intrinsic absorption wavelength λ1. That is, of the first outgoing light 3 </ b> C <b> 1, light having a wavelength near the intrinsic absorption wavelength λ <b> 1 passes through the first bandpass filter 9, and light having other wavelengths is blocked by the first bandpass filter 9.

  Further, as shown in FIG. 1, the second optical attenuator 7 has a function of blocking a part of the second outgoing light 3C2. The second optical attenuator 7 has a variable light transmittance. The light transmittance of the second optical attenuator 7 is controlled by the second optical attenuator control unit 21 so as to approach a predetermined condition, as will be described in detail later. Part of the second outgoing light 3C2 passes through the second optical attenuator 7 and travels from the second optical attenuator 7 to the second bandpass filter 11 as the second outgoing light 3D2.

  As the second optical attenuator 7, for example, an optical attenuator using an optical attenuation element having an optical attenuation function or an optical shutter can be used. Examples of the light attenuating element having a light attenuating function include a light attenuating filter such as an ND (Neutral Density) filter, a Faraday rotator, and an optical fiber. When an optical attenuation filter is used as the optical attenuation element, the light transmittance can be changed by moving the position of the optical attenuation filter relative to the optical axis. When a Faraday rotator is used as the light attenuating element, the light transmittance can be changed by changing the rotation angle of the Faraday rotator. When an optical fiber is used as the light attenuating element, the bending loss of the optical fiber depends on the radius of curvature, so that the light transmittance can be changed by changing the radius of curvature.

  Further, in the optical shutter, the light transmittance can be changed between two predetermined values (for example, 100% and 0%). Then, by periodically changing the light transmittance of the optical shutter by, for example, pulse width modulation control (Pulse Width Modulation control, PMW control), the light transmittance when temporally averaged can be set to a predetermined value. it can. In this case, the light transmittance can be changed by changing the pulse interval or the like during PMW control.

  Examples of the optical shutter include a mechanical shutter and a liquid crystal optical shutter. The liquid crystal optical shutter has a liquid crystal whose orientation can be changed by applying a voltage, and the light transmittance changes according to the orientation of the liquid crystal.

  As the second optical attenuator 7, it is preferable to use a liquid crystal optical shutter. This is because the optical system can be simplified and the number of mechanical movable parts is reduced, so that the cost can be reduced and the maintenance frequency can be reduced.

  The second bandpass filter 11 is an optical bandpass filter that includes the non-absorption wavelength λ2 in its passband and does not include the intrinsic absorption wavelength λ1 in its passband. Part of the second emitted light 3D2 that has reached the second bandpass filter 11 passes through the second bandpass filter 11 and becomes the second emitted light 3E2 from the second bandpass filter 11 to the second photodetector 15. It progresses to.

  FIG. 3B is a diagram showing the wavelength distribution of the light intensity of the second outgoing light after passing through the second bandpass filter. As shown in FIG. 3B, the second outgoing light 3E2 after passing through the second bandpass filter 11 has only a component having a wavelength near the non-absorption wavelength λ2. That is, in the second outgoing light 3D2, light having a wavelength near the non-absorption wavelength λ2 passes through the second bandpass filter 11, and light having other wavelengths is blocked by the second bandpass filter 11.

  The first photodetector 13 outputs an intensity signal of the first emitted light 3E1 incident on the first photodetector 13, and the second photodetector 15 outputs the second emitted light incident on the second photodetector 15. 3E2 intensity signal is output. In the present embodiment, the first photodetector 13 and the second photodetector 15 are the same photodetector. FIG. 4 is a schematic cross-sectional view showing the configuration of the first photodetector and the second photodetector. As shown in FIG. 4, the first photodetector 13 (second photodetector 15) includes a case body 41 in which an opening 41A is formed in a wall, a window 43 provided in the opening 41A, And a photoelectric conversion unit 45 provided in the case body 41 so as to face the window 43.

  The window 43 is made of a material having a high light transmittance, and light outside the measurement target enters the case body 41 through the window 43 and enters the photoelectric conversion unit 45. The photoelectric conversion unit 45 outputs a voltage signal corresponding to the amount of received light between the pair of output wirings 13A and 13B (15A and 15B).

  As the first photodetector 13 and the second photodetector 15, for example, thermopile, thermistor, bolometer, thermal type photodetection element such as pyroelectric element, quantum type such as photodiode, photoconductive cell, phototube, etc. A photodetection element can be used.

  The photoelectric conversion principle of the thermopile photoelectric conversion unit 45 is based on the thermoelectromotive force effect, and the photoelectric conversion principle of the thermistor and bolometer photoelectric conversion unit 45 is based on the thermocouple effect. The principle is based on the pyroelectric effect. The photoelectric conversion principle of the photoelectric conversion unit 45 of the photodiode is based on the photovoltaic effect, and the photoelectric conversion principle of the photoelectric conversion unit 45 of the photoconductive cell is based on the photoconductive effect. The conversion principle is based on the photoelectron emission effect. In the present embodiment, since the first photodetector 13 and the second photodetector 15 are the same photodetector, the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit of the second photodetector 15. 45 is based on the same photoelectric conversion principle, is made of the same material, and has the same shape.

  The thermopile photoelectric conversion unit 45 is a thermocouple, the thermistor and bolometer photoelectric conversion unit 45 is a resistor whose electrical resistivity changes with temperature change, and the pyroelectric element photoelectric conversion unit 45 has a pyroelectric effect. A pyroelectric body made of a material having The photoelectric conversion unit 45 of the photodiode is a semiconductor unit having a pn junction or a pin junction, the photoelectric conversion unit 45 of the photoconductive cell is a semiconductor unit having a photoconductive effect, and the photoelectric conversion unit 45 of the photoelectric tube is a photocathode. It is the metal part which has the photoelectric effect which comprises.

  Moreover, it is preferable that each of the first photodetector 13 and the second photodetector 15 is a thermal photodetector. Thereby, since the wavelength dependence of the first photodetector 13 and the second photodetector 15 is lowered, the difference between the intrinsic absorption wavelength λ1 and the non-absorption wavelength λ2 can be set large (see FIG. 2). ). Therefore, the influence of light having a wavelength near the non-absorption wavelength λ2 on the output value of the first photodetector 13 can be reduced, and light having a wavelength near the intrinsic absorption wavelength λ1 can be reduced. The influence on the output value can be further reduced. As a result, the concentration of the measurement target substance can be measured with higher accuracy.

  Further, as shown in FIG. 1, the output wiring 13A and the output wiring 15A are connected to the second optical attenuator control unit 21, and the output wiring 13B and the output wiring 15B are grounded. As a result, the first photodetector 13 outputs a voltage signal corresponding to the magnitude of the first outgoing light 3E1 to the second optical attenuator controller 21, and the second photodetector 15 gives the magnitude of the second outgoing light 3E2. A voltage signal corresponding to the voltage is output to the second optical attenuator control unit 21.

  Based on the output value of the first photodetector 13 and the output value of the second photodetector 15, the second optical attenuator control unit 21 determines the intensity of the second emitted light 3E2 incident on the second photodetector 15. The light transmittance of the second optical attenuator 7 is controlled so as to approach the intensity of the first outgoing light 3E1 incident on the first photodetector 13. For example, when the output value of the second photodetector 15 is larger than the output value of the first photodetector 13, the second optical attenuator control unit 21 reduces the light transmittance of the second optical attenuator 7, When the output value of the second light detector 15 is smaller than the output value of the first light detector 13, the light transmittance of the second light attenuator 7 is increased by the second light attenuator control unit 21. When the light source 3 emits pulsed light at every predetermined period, the light transmittance of the second optical attenuator 7 is controlled by the second optical attenuator control unit 21 so as to be synchronized with the period. As described above, in the present embodiment, the second optical attenuator control unit 21 transmits light from the second optical attenuator 7 based on the output value of the first optical detector 13 and the output value of the second optical detector 15. Control the rate in a feedback way. In addition, when the light source 3 emits pulsed light for every predetermined period, it is preferable to make the drive period of the 2nd optical attenuator 7 shorter than the light emission period of pulsed light. This is because the light transmittance of the second optical attenuator 7 can be finely controlled with respect to the unit light emission pulse, so that the transmittance of the second optical attenuator 7 can be accurately controlled.

  In the present embodiment, the second optical attenuator control unit 21 includes an output value comparison unit 17 connected to the first photodetector 13 and the second photodetector 15, an output value comparison unit 17, and the second optical attenuator 7. And a servo control unit 19 connected to. The output value comparison means 17 is connected to the output wiring 13A and the output wiring 15A, and outputs a voltage signal corresponding to the difference between the output value of the first photodetector 13 and the output value of the second photodetector 15 to the servo controller. 19 output. The servo control unit 19 controls the light transmittance of the second optical attenuator 7 according to the voltage signal from the output value comparison unit 17. Specifically, the servo control unit 19 controls the light transmittance of the second optical attenuator 7 so that the difference between the output value of the first photodetector 13 and the output value of the second photodetector 15 approaches zero. As a result, the intensity of the second emitted light 3E2 incident on the second photodetector 15 is made closer to the intensity of the first emitted light 3E1 incident on the first photodetector 13.

  As the output value comparison means 17, it is preferable to use an operational operational amplifier, for example, as shown in FIG. Further, as the output value comparison means 17, a subtractor or a divider can be used.

  The calculation unit 23 is connected to the servo control unit 19 in this embodiment. The calculation unit 23 calculates the concentration of the measurement target substance as a ratio of the measurement target substance to the entire sample 4 based on the light transmittance of the second optical attenuator 7.

  In the gas concentration measuring apparatus 1 according to this embodiment as described above, the intensity of the second emitted light 3E2 incident on the second photodetector 15 is the intensity of the first emitted light 3E1 incident on the first photodetector 13. The light transmittance of the second optical attenuator 7 when it is equal to the intensity is 100% of the intensity of the first outgoing light 3E1 incident on the first photodetector 13, virtually the light transmittance of the second optical attenuator 7. Is proportional to the value divided by the intensity of the second outgoing light 3E2 incident on the second photodetector 15. Since the light absorptance of the light having the intrinsic absorption wavelength λ1 by the measurement target substance is higher than the light absorption ratio by the measurement target substance of the light having the non-absorption wavelength λ2, the light transmittance of the second optical attenuator 7 is virtually set. In the case of 100%, the intensity of the first outgoing light 3E1 incident on the first optical detector 13 and the intensity of the second outgoing light 3E2 incident on the second optical detector 15 depend on the concentration of the measurement target substance. Correspondingly vary at different rates. Therefore, the light transmittance of the second optical attenuator 7 becomes a value corresponding to the concentration of the substance to be measured in the sample 4, and the concentration of the substance to be measured in the sample 4 is calculated from the light transmittance of the second optical attenuator 7. can do.

  For example, in the present embodiment, a calculation unit is obtained from the integrated value of the control amount of the second optical attenuator 7 light transmittance at a certain reference time and the light transmittance of the second optical attenuator 7 by the servo control unit 19 after the reference time. 23, the light transmittance of the second optical attenuator 7 can be calculated. Based on the calculated light transmittance of the second optical attenuator 7, the concentration of the measurement target substance in the sample 4 can be calculated by the calculation unit 23. In addition, the calculation unit 23 does not use the integrated value of the control amount by the servo control unit 19 and calculates the measurement target substance in the sample 4 from the light transmittance of the second optical attenuator 7 at the time of calculating the concentration of the measurement target substance. May be calculated.

  Furthermore, in the gas concentration measuring apparatus 1 according to this embodiment as described above, the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 are based on the same photoelectric conversion principle. And based on the same material (see FIG. 4), the temperature dependence of the photoelectric conversion unit 45 of the sensitivity (correlation between light intensity and output) of the first photodetector 13 and the second photodetector 15 The temperature dependence of the sensitivity of the photoelectric conversion unit 45 is substantially the same. In the gas concentration measurement apparatus 1 according to the present embodiment, the second light attenuator 7 causes the intensity of the second emitted light 3E2 incident on the second photodetector 15 to be incident on the first photodetector 13. Since it is controlled so as to approach the intensity of the first outgoing light 3E1, the temperature of the photoelectric conversion unit 45 of the first photodetector 13 and the temperature of the photoelectric conversion unit 45 of the second photodetector 15 during measurement are substantially equal. It is controlled to become. Thereby, the rate of change in sensitivity of the first photodetector 13 and the rate of change in sensitivity of the second photodetector 15 during measurement are substantially equal. Therefore, the ratio of the error of the output value of the first photodetector 13 due to the temperature change of the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 and the second photodetector. The rate of error of the 15 output values is substantially equal.

  Therefore, a value obtained by dividing the intensity of the first emitted light 3E1 incident on the first photodetector 13 by the intensity of the second emitted light 3E2 incident on the second photodetector 15 (that is, the intensity of the first emitted light 3E1). And the intensity of the second outgoing light 3E2), these errors cancel each other. Thereby, even if the temperature of the photoelectric conversion part 45 of the 1st photodetector 13 and the temperature of the photoelectric conversion part 45 of the 2nd photodetector 15 changes, the influence on control of the light transmittance of the 2nd optical attenuator 7 is reduced. Is done. As a result, according to the gas concentration measuring apparatus 1 according to the present embodiment, the temperature measuring device that measures the temperatures of the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 respectively. Since the temperature compensation of the first photodetector 13 and the second photodetector 15 can be performed without providing them, the configuration becomes simple. Further, as described above, since the temperature compensation of these photodetectors is performed by bringing the input / output values of the first photodetector 13 and the second photodetector 15 close to each other, the sensitivity of these photodetectors depends on the temperature. There is no need to measure the sex beforehand. Therefore, there is no measurement error in the concentration of the measurement target gas due to the measurement error when measuring the temperature dependence of these photodetectors in advance. Therefore, the gas concentration measuring apparatus 1 according to the present embodiment has a simple configuration and can reduce measurement errors caused by temperature changes in the sensitivity of the first photodetector 13 and the second photodetector 15. is there.

  Moreover, since the gas concentration measuring apparatus 1 according to the present embodiment can reduce the measurement error as described above, the first outgoing light 3B1 and the second outgoing light 3B2 travel through the sample container 5. Even if the distance (optical path length) is short, the concentration of the substance to be measured can be measured. Therefore, according to the gas concentration measuring apparatus 1 according to the present embodiment, it is possible to reduce the size of the entire apparatus.

  Furthermore, in the gas concentration measuring apparatus 1 according to this embodiment as described above, the first wavelength is the intrinsic absorption wavelength λ1 of the measurement target substance, and the second wavelength is the non-absorption wavelength λ2. As a result, the intensity of the first outgoing light 3E1 incident on the first photodetector 13 changes more greatly corresponding to the concentration of the substance to be measured, and the second outgoing light 3E2 incident on the second photodetector 15 changes. The intensity becomes almost independent of the concentration of the substance to be measured. As a result, the change rate of the light transmittance of the second optical attenuator 7 with respect to the change in the concentration of the measurement target substance becomes larger, so that the concentration of the measurement target substance can be measured with higher accuracy.

  Furthermore, in the gas concentration measuring apparatus 1 according to the present embodiment, as described above, the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 are the same (FIG. 2). reference). Thereby, the ratio of the error of the output value of the first photodetector 13 caused by the temperature change of the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 and the second light detection. The ratio of the error of the output value of the device 15 is even closer. As a result, it is possible to further reduce the measurement error due to the temperature change of the sensitivity of the first photodetector 13 and the second photodetector 15.

  Furthermore, in the gas concentration measuring apparatus 1 according to the present embodiment, as described above, the light source 3 serves as both the first light source and the second light source (see FIG. 1). Thereby, when the light emission intensity of the light source 3 changes, the intensity of the first emitted light 3A1 and the intensity of the second emitted light 3A2 change at the same rate. Therefore, a value obtained by dividing the intensity of the first emitted light 3E1 incident on the first photodetector 13 by the intensity of the second emitted light 3E2 incident on the second photodetector 15 (that is, the intensity of the first emitted light 3E1). And the intensity ratio of the second emitted light 3E2), these intensity changes cancel each other, so that the influence on the control of the light transmittance of the second optical attenuator is reduced. As a result, it is possible to reduce measurement errors caused by changes in the light emission intensity of the light source 3.

  Furthermore, the gas concentration measuring apparatus 1 according to the present embodiment is provided between the sample 4 and the first photodetector 13 so that the first outgoing light 3C1 transmitted through the sample 4 is incident as described above. The sample so that the first bandpass filter 9 including the intrinsic absorption wavelength λ1 of the target substance in the passband and not including the non-absorption wavelength λ2 in the passband and the second emission light 3C2 and 3D2 transmitted through the sample 4 are incident. 4 and the second photodetector 15, and further includes a second bandpass filter 11 that includes the non-absorption wavelength λ2 in the passband and does not include the intrinsic absorption wavelength λ1 in the passband. (See FIG. 1).

  As a result, light having a wavelength near the intrinsic absorption wavelength λ1 is preferentially incident on the first photodetector 13, and light having a wavelength near the non-absorption wavelength λ2 is received by the first bandpass filter 9. The light having a wavelength near the non-absorption wavelength λ2 is preferentially incident on the second photodetector 15, and light having a wavelength near the intrinsic absorption wavelength λ1 is received by the second bandpass filter 11. Blocked. Therefore, the influence of light having a wavelength near the non-absorption wavelength λ2 on the output value of the first photodetector 13 can be reduced, and light having a wavelength near the intrinsic absorption wavelength λ1 can be reduced. The influence on the output value can be reduced. As a result, the concentration of the measurement target gas can be measured with higher accuracy.

  In addition, as in the case of the present embodiment, in each of the first outgoing light 3A1 and the second outgoing light 3A2, the intensity of the light having the intrinsic absorption wavelength λ1 and the intensity of the light having the non-absorption wavelength λ2 are as shown in FIG. For example, when the intensity difference is within 5%, it is particularly preferable that the gas concentration measurement apparatus 1 includes the first bandpass filter 9 and the second bandpass filter 11. This is because the temperature rise degree of the photoelectric conversion unit 45 of the first photodetector 13 by the first outgoing light 3E1 and the temperature rise degree of the photoelectric conversion unit 45 of the second photodetector 15 by the second outgoing light 3E2 are the same. This is because it becomes easy to control to the extent. As a result, the measurement accuracy of the concentration of the substance to be measured is improved. Note that the gas concentration measuring apparatus 1 can measure the concentration of the measurement target gas even if it does not include the first band-pass filter 9 and the second band-pass filter 11.

  Further, in the concentration measuring method according to the present embodiment as described above, the intensity of the second emitted light 3E2 incident on the second photodetector 15 is the intensity of the first emitted light 3E1 incident on the first photodetector 13. The light transmittance of the second optical attenuator 7 when it is equal to the intensity is 100% of the intensity of the first outgoing light 3E1 incident on the first photodetector 13, virtually the light transmittance of the second optical attenuator 7. Is proportional to the value divided by the intensity of the second outgoing light 3E2 incident on the second photodetector 15. Since the light absorption rate of the first wavelength light by the measurement target substance is higher than the light absorption rate of the second wavelength light measurement target substance, the light transmittance of the second optical attenuator 7 is virtually 100%. In this case, the intensity of the first emitted light 3E1 incident on the first photodetector 13 and the intensity of the second emitted light 3E2 incident on the second photodetector 15 correspond to the concentration of the measurement target substance. Vary at different rates. Therefore, the light transmittance of the second optical attenuator 7 becomes a value corresponding to the concentration of the substance to be measured in the sample 4, and the concentration of the substance to be measured in the sample 4 is calculated from the light transmittance of the second optical attenuator 7. can do.

  Furthermore, in the concentration measurement method according to the present embodiment, the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 are based on the same photoelectric conversion principle and from the same material. Therefore, the temperature dependency of the photoelectric conversion unit 45 on the sensitivity (correlation between the light intensity and the output) of the first photodetector 13 and the temperature dependency of the sensitivity of the second photodetector 15 on the photoelectric conversion unit 45 are , Become substantially the same. In the concentration measurement method according to the present embodiment, the intensity of the second emitted light 3E2 incident on the second photodetector 15 approaches the intensity of the first emitted light 3E1 incident on the first photodetector 13. In addition, since the light transmittance of the second optical attenuator 7 is controlled, the temperature of the photoelectric conversion unit 45 of the first photodetector 13 and the temperature of the photoelectric conversion unit 45 of the second photodetector 15 during the measurement are approximately Controlled to be equal. Thereby, the rate of change in sensitivity of the first photodetector 13 and the rate of change in sensitivity of the second photodetector 15 during measurement are substantially equal. Therefore, the ratio of the error of the output value of the first photodetector 13 due to the temperature change of the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 and the second photodetector. The rate of error of the 15 output values is substantially equal.

  Therefore, a value obtained by dividing the intensity of the first emitted light 3E1 incident on the first photodetector 13 by the intensity of the second emitted light 3E2 incident on the second photodetector 15 (that is, the intensity of the first emitted light 3E1). And the intensity of the second outgoing light 3E2), these errors cancel each other. Thereby, even if the temperature of the photoelectric conversion part 45 of the 1st photodetector 13 and the temperature of the photoelectric conversion part 45 of the 2nd photodetector 15 changes, the influence on control of the light transmittance of the 2nd optical attenuator 7 is reduced. Is done. As a result, according to the concentration measurement method according to the present embodiment, the temperature measuring device that measures the temperatures of the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 is used. Since the temperature compensation of the photodetector can be performed without any problems, the configuration is simplified. Further, as described above, since the temperature compensation of these photodetectors is performed by bringing the input / output values of the first photodetector 13 and the second photodetector 15 close to each other, the sensitivity of these photodetectors depends on the temperature. There is no need to measure the sex beforehand. Therefore, there is no measurement error in the concentration of the measurement target gas due to the measurement error when measuring the temperature dependence of these photodetectors in advance. Therefore, according to the concentration measurement method according to the present embodiment, it is possible to reduce a measurement error due to a temperature change in the sensitivity of the photodetector with a simple configuration.

(Second Embodiment)
Next, as a concentration measuring apparatus and a concentration measuring method according to the second embodiment, a gas concentration measuring apparatus and a gas concentration measuring method of a different aspect from the first embodiment will be described.

  FIG. 5 is a configuration diagram of the gas concentration measuring apparatus of the present embodiment. As shown in FIG. 5, the gas concentration measurement device 1 a of the present embodiment further includes a first optical attenuator 27 and a first optical attenuator control unit 29, and the gas concentration measurement of the first embodiment described above. Different from the device 1.

  The first optical attenuator 27 is provided between the sample 4 and the first bandpass filter 9 so that the first outgoing light 3C1 transmitted through the sample 4 is incident thereon. The first optical attenuator 27 has a function of blocking a part of the first outgoing light 3C1 that has passed through the sample 4. The first outgoing light 3C1 that has passed through the sample 4 is partially blocked by the first optical attenuator 27 and then travels from the first optical attenuator 27 to the first bandpass filter 9 as the first outgoing light 3D1.

  The first optical attenuator 27 is connected to the first optical attenuator control unit 29. The light transmittance of the first optical attenuator 27 is variable, and the light transmittance is controlled by the first optical attenuator control unit 29. The first optical attenuator 27 can be an optical attenuator similar to the second optical attenuator 7. The calculation unit 23 is connected to the first optical attenuator control unit 29. The calculation unit 23 calculates the concentration of the measurement target substance in the sample 4 in consideration of the light transmittance of the first optical attenuator 27.

  According to the gas concentration measuring apparatus 1a of this embodiment, when the light emission intensity of the light source 3 changes, the influence of the change can be reduced by the first optical attenuator 27. Specifically, for example, the intensity of the second emitted light 3E2 when the light transmittance of the second optical attenuator 7 is set to 100% is periodically measured by the second photodetector 15, etc. Intensity fluctuations due to changes in emission intensity over time are measured. And when the emitted light intensity of the light source 3 falls, the light transmittance of the 1st optical attenuator 27 can be increased, and the intensity fluctuation | variation of 1st emitted light 3D1 can be suppressed.

  Note that, in each of the first outgoing light 3A1 and the second outgoing light 3A2, the intensity of the light of the intrinsic absorption wavelength λ1 and the intensity of the light of the non-absorption wavelength λ2 are greatly different (for example, the intensity difference is 5% or more) ), Before the concentration measurement, the second optical attenuator 7 and / or the second optical attenuator 7 and / or the second optical attenuator 7 so that the output values of the first photodetector 13 and the second photodetector 15 when there is no substance to be measured become substantially the same value. It is preferable to set the initial state of the light transmittance of the one light attenuator 27. Thereby, measurement accuracy can be improved. The second optical attenuator as described above, regardless of the difference between the intensity of the intrinsic absorption wavelength λ1 and the intensity of the non-absorption wavelength λ2 in each of the first emission light 3A1 and the second emission light 3A2. 7 and / or the initial state of the light transmittance of the first optical attenuator 27 can be set.

  The first optical attenuator 27 may be provided between the first bandpass filter 9 and the first photodetector 13.

(Third embodiment)
Next, as a concentration measuring apparatus and a concentration measuring method according to the third embodiment, a gas concentration measuring apparatus and a gas concentration measuring method which are different from the first and second embodiments will be described.

  FIG. 6 is a configuration diagram of the gas concentration measuring apparatus of the present embodiment. As shown in FIG. 6, the gas concentration measuring device 1b of the present embodiment is provided with two light sources (a light source 31 and a light source 33) instead of the light source 31 (see FIG. 1). This is different from the gas concentration measuring apparatus 1 of FIG.

  The light source 31 of the present embodiment emits the first emitted light 31A. The first outgoing light 31A passes through the light incident part 5A and travels from the light incident part 5A to the light outgoing part 5B as the first outgoing light 31B. The first emitted light 31B that has passed through the light emitting unit 5B travels from the light emitting unit 5B to the first bandpass filter 9 as the first emitted light 31C. The first outgoing light 31C that has passed through the first bandpass filter 9 travels from the first bandpass filter 9 to the first photodetector 13 as the first outgoing light 31E.

  The light source 33 of the present embodiment emits the second emitted light 33A. The second emitted light 33A passes through the light incident part 5A and travels from the light incident part 5A to the light emitting part 5C as the second emitted light 33B. The second emitted light 33B that has passed through the light emitting part 5C travels from the light emitting part 5B to the second optical attenuator 7 as the second emitted light 33C. The second outgoing light 33C that has passed through the second optical attenuator 7 travels from the second optical attenuator 7 to the second bandpass filter 11 as the second outgoing light 33D. The second emitted light 33D that has passed through the second bandpass filter 11 travels from the second bandpass filter 11 to the second photodetector 15 as the second emitted light 33E.

  As the light source 31 and the light source 33, LED, a laser, etc. can be used, for example.

  FIG. 7A is a diagram showing the wavelength distribution of the light intensity of the first emitted light immediately after being emitted from the light source 31. As shown in FIG. 7A, in the present embodiment, the first outgoing light 31A has only a wavelength component near the intrinsic absorption wavelength λ1, and does not have a wavelength component near the non-absorption wavelength λ2.

  FIG. 7B is a diagram illustrating the wavelength distribution of the light intensity of the second emitted light immediately after being emitted from the light source 33. As shown in FIG. 7B, in the present embodiment, the second outgoing light 33A has only a wavelength component near the non-absorption wavelength λ2, and does not have a wavelength component near the intrinsic absorption wavelength λ1.

  In the gas concentration measuring apparatus 1b of the present embodiment, as described above, the first outgoing light 31A has no wavelength component near the non-absorption wavelength λ2, and the second outgoing light 33A has a wavelength near the intrinsic absorption wavelength λ1. Is not included. That is, the gas concentration measuring device 1b includes two light sources (the light source 31 and the light source 33), and the light source 31 emits the first emission light 3A1 having only a component having a wavelength near the intrinsic absorption wavelength λ1, A part of the first emitted light 3E1 is made incident on the first photodetector 13, and the light source 33 emits the second emitted light 3A2 having only a component having a wavelength near the non-absorption wavelength λ2, and is a part thereof. The second outgoing light 3E2 is incident on the second photodetector 15. Therefore, the gas concentration measuring device 1b may not include the first bandpass filter 9 and / or the second bandpass filter 11. In this case, it is preferable that the first outgoing light 3A1 and the second outgoing light 3A2 have substantially the same half width.

  The light source 31 may have a component having a wavelength near the non-absorption wavelength λ2. In that case, the gas concentration measuring device 1b preferably includes a first bandpass filter 9. Similarly, the light source 33 may have a component having a wavelength near the intrinsic absorption wavelength λ1. In that case, it is preferable that the gas concentration measuring apparatus 1b includes the second band-pass filter 11.

  When the gas concentration measuring device 1 b includes two light sources (light source 31 and light source 33) as in the present embodiment, the intensity of the first emitted light 31 </ b> A immediately after emission from the light source 31 and immediately after emission from the light source 33. The intensity of the second emitted light 33A is preferably the same as shown in FIG. 7, for example, the intensity difference is preferably within 5%. This is because the photoelectric conversion unit 45 of the first photodetector 13 by the first emitted light 31E can be used without greatly adjusting the intensity of the second emitted light 33E incident on the second photodetector 15 by the second optical attenuator 7. This is because it is easy to control the temperature rise degree of the second and the photoelectric conversion unit 45 of the second photodetector 15 by the second emitted light 33E to the same degree. As a result, the measurement accuracy of the concentration of the substance to be measured is improved.

  When the intensity of the first emitted light 31A immediately after emission from the light source 31 and the intensity of the second emitted light 33A immediately after emission from the light source 33 are significantly different (for example, when the intensity difference is 5% or more), before the concentration measurement is performed. In addition, the initial state of the light transmittance of the second optical attenuator 7 is set so that the output values of the first optical detector 13 and the second optical detector 15 when there is no measurement target substance are substantially the same value. Is preferred. Thereby, measurement accuracy can be improved. It should be noted that the light transmittance of the second optical attenuator 7 as described above is independent of the magnitude of the difference in intensity between the first emitted light 31A immediately after emission from the light source 31 and the second emitted light 33A immediately after emission from the light source 33. The initial state can be set. Further, the intensity of the second emitted light 33A immediately after being emitted from the light source 33 is greater than the intensity of the first emitted light 31A immediately after being emitted from the light source 31, or is equal to the intensity of the first emitted light 31A immediately after being emitted from the light source 31. Preferably there is. This is because the initial state of the light transmittance of the second optical attenuator 7 as described above can be easily set.

  Here, as in the case of the present embodiment, when the gas concentration measuring device 1 b includes two light sources (the light source 31 and the light source 33), the wavelength of the first emitted light 31 </ b> A immediately after being emitted from the light source 31 and the light emitted from the light source 33. It is preferable that the wavelength of the 2nd emitted light 33A just after does not overlap with each other. If the wavelength of the first emitted light 31A and the wavelength of the second emitted light 33A do not overlap with each other, the temperature rise of the photoelectric conversion unit 45 of the first photodetector 13 by the first emitted light 31E, and the second emitted light It becomes easy to control the degree of temperature rise of the photoelectric conversion unit 45 of the second photodetector 15 by 33E to the same extent. Note that the wavelength of the first emitted light 31A and the wavelength of the second emitted light 33A do not overlap with each other because the wavelength range defining the half width of the wavelength with respect to the intensity peak of the first emitted light 31A and the second emitted light 33A This means that the wavelength range defining the half width of the wavelength with respect to the intensity peak does not overlap each other.

  In the first to third embodiments, the second light attenuator 7 is not irradiated on the sample 4 with the second emitted light 3A2 (or the second emitted light 33A) emitted from the light source 3 (or the light source 33). It may be incident.

(Fourth embodiment)
Next, as a concentration measuring apparatus and a concentration measuring method according to the fourth embodiment, a concentration measuring method using a pulse oximeter and a pulse oximeter will be described.

  FIG. 8 is a configuration diagram of the pulse oximeter of the present embodiment. As shown in FIG. 8, the pulse oximeter 1 c of this embodiment is different from the gas concentration measurement apparatus 1 of the first embodiment described above in that it does not include the sample container 5 that stores the sample 4.

  The pulse oximeter 1c is a device for measuring arterial oxygen saturation percutaneously. As shown in FIG. 8, when the pulse oximeter 1c is used, the body tissue 51, the body tissue 51, and the body tissue 51 are located in the interior of the sample container 5 of the gas concentration measuring device 1a according to the first embodiment. A blood vessel 53 through which blood 55 flows is disposed. The body tissue 51, the blood vessel 53, and the blood 55 become the sample 4a.

  In the pulse oximeter 1c of this embodiment, oxygenated hemoglobin in the blood 55 is used as a measurement target substance, and reduced hemoglobin in the blood 55 is used as a reference substance. The light absorption rate of oxyhemoglobin of light of the first wavelength is higher than the light absorption rate of oxyhemoglobin of light of the second wavelength, and the light absorption rate of deoxyhemoglobin of light of the second wavelength is The first wavelength and the second wavelength are determined so as to be higher than the light absorptance of the light having the wavelength by reduced hemoglobin. The first wavelength can be 940 nm, for example, and the second wavelength can be 660 nm, for example.

  In the present embodiment, the ratio between the absorption rate of light of the first wavelength by oxyhemoglobin and the absorption rate of light of the first wavelength by reduced hemoglobin, and the absorption rate of light of the second wavelength by oxyhemoglobin and the first absorption rate by reduced hemoglobin. Based on the ratio of the absorption rate of light of two wavelengths, the calculation unit 23 calculates the concentration of oxyhemoglobin as the ratio of oxyhemoglobin to the total of oxyhemoglobin and deoxyhemoglobin. In addition, the arterial oxygen saturation can be calculated from the oxyhemoglobin concentration thus calculated.

  In the present embodiment, reduced hemoglobin may be used as a measurement target substance, and oxygenated hemoglobin may be used as a reference substance. In this case, the calculation unit 23 calculates the concentration of reduced hemoglobin as the ratio of reduced hemoglobin to the total of oxidized hemoglobin and reduced hemoglobin.

  The present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above-described embodiments, the first photodetector 13 and the second photodetector 15 are the same photodetector (see FIGS. 1, 4, 5, 6, and 8). ) If the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 are based on the same photoelectric conversion principle and are made of the same material, the first photodetector 13 and the first photodetector 13 The two photodetectors 15 may not be the same photodetector. However, even in that case, it is preferable that the photoelectric conversion unit 45 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 are the same. As described above, the error in the output value of the first photodetector 13 due to the temperature change of the blood 55 of the first photodetector 13 and the photoelectric conversion unit 45 of the second photodetector 15 and the second photodetector 15. This is because the error ratio of the output value can be made closer.

  In the first embodiment, the second embodiment, and the third embodiment described above, the first wavelength is the intrinsic absorption wavelength λ1 of the measurement target substance, and the second wavelength is the intrinsic characteristic of each substance contained in the sample 4. Although the non-absorption wavelength is different from the absorption wavelength and the non-absorption wavelength λ2 (see FIG. 2), the light absorption rate of the first wavelength light by the measurement target substance is larger than the light absorption rate by the second wavelength light measurement target substance. It is sufficient that the first wavelength and the second wavelength are determined so as to be higher. In this case, an optical bandpass filter that includes the first wavelength in the passband and does not include the second wavelength in the passband is used as the first bandpass filter 9, and the second wavelength is used as the second bandpass filter 11. An optical bandpass filter that is included in the passband and does not include the first wavelength in the passband is used.

  Further, the pulse oximeter 1c in the above-described fourth embodiment may further include a first optical attenuator 27 as in the gas concentration measuring device 1a in the second embodiment (see FIG. 5). In addition, the pulse oximeter 1c in the fourth embodiment described above may include two light sources (a light source 31 and a light source 33) instead of the light source 31, similarly to the gas concentration measurement device 1b in the third embodiment. (See FIG. 6).

  Further, when there are two types of measurement target substances in the sample 4 (for example, two types of measurement target gases), the gas concentration measurement device of each of the above embodiments measures the first measurement target substance as described above. And a third light source, a fourth light source, a third photodetector, a fourth photodetector, and a third attenuator for measuring the second measurement target substance in the same manner as the first measurement target substance, and A third attenuator control unit may be further provided. In this case, the third light source irradiates the sample 4 with light including the intrinsic absorption wavelength of the second measurement target substance (a wavelength different from the intrinsic absorption wavelength λ1 of the first measurement target substance), and the fourth light source provides the sample 4 The sample 4 is irradiated with light including a non-absorption wavelength different from each intrinsic absorption wavelength of each substance therein. Some or all of the first to fourth light sources may be the same light source, or the first to fourth light sources may be separate light sources.

DESCRIPTION OF SYMBOLS 1 ... Concentration measuring device (gas concentration measuring device), 3 ... Light source (1st light source, 2nd light source), 3A1, 3B1, 3C1, 3D1, 3E1 ... 1st emitted light, 3A2, 3B2, 3C2, 3D2, 3E2 ... second outgoing light, 4 ... sample, 5 ... sample container, 7 ... second optical attenuator, 9 ... first bandpass filter, 11 ... 2nd band pass filter, 13 ... 1st photodetector, 15 ... Photodetector, 21 ... Optical attenuator control part, 23 ... Calculation part, (lambda) 1 ... 1st wavelength (Intrinsic absorption) Wavelength), λ2... Second wavelength (non-absorbing wavelength).

Claims (12)

A concentration measuring device for measuring the concentration of a measurement target substance contained in a sample,
A first light source that irradiates the sample with first emitted light including light of a first wavelength;
A second light source for irradiating second emitted light including light of a second wavelength;
A first photodetector for outputting an intensity signal of light provided so that the first outgoing light transmitted through the sample is incident;
A second photodetector for outputting an intensity signal of light provided so that the second emitted light is incident;
A second optical attenuator provided between the sample and the second photodetector so that the second emitted light transmitted through the sample is incident, and having a variable light transmittance;
A second optical attenuator control unit for controlling the light transmittance of the second optical attenuator;
A calculation unit for calculating the concentration of the measurement target substance;
With
The light absorption rate by the measurement target substance of the light of the first wavelength is higher than the light absorption rate by the measurement target substance of the light of the second wavelength,
The photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector are based on the same photoelectric conversion principle and are made of the same material,
The second optical attenuator control unit determines the intensity of the second emitted light incident on the second photodetector based on the output value of the first photodetector and the output value of the second photodetector. Controlling the light transmittance of the second optical attenuator so as to approach the intensity of the first outgoing light incident on the first photodetector;
The concentration unit is a concentration measurement device that calculates the concentration of the measurement target substance based on the light transmittance of the second optical attenuator. The first wavelength is an intrinsic absorption wavelength of the measurement target substance,
The concentration measurement apparatus according to claim 1, wherein the second wavelength is a non-absorption wavelength different from each intrinsic absorption wavelength of each substance contained in the sample.   The concentration measurement apparatus according to claim 1, wherein the calculation unit calculates a concentration of the measurement target substance as a ratio of the measurement target substance to the entire sample. The sample further comprises a reference material;
The second outgoing light passes through the sample before entering the second photodetector,
The light absorption rate of the second wavelength light by the reference material is higher than the light absorption rate of the first wavelength light by the reference material,
The concentration measurement apparatus according to claim 1, wherein the calculation unit calculates a concentration of the measurement target substance as a ratio of the measurement target substance to a total of the measurement target substance and the reference substance.   The concentration measuring apparatus according to claim 1, wherein the photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector are the same.   The concentration measuring apparatus according to claim 1, wherein the first light source and the second light source are one light source. Provided between the sample and the first photodetector so that the first emitted light that has passed through the sample is incident, includes the first wavelength in the pass band, and includes the second wavelength in the pass band No first bandpass filter, and
Provided between the sample and the second photodetector so that the second outgoing light transmitted through the sample is incident, includes the second wavelength in the pass band, and includes the first wavelength in the pass band No second bandpass filter, and
The concentration measuring apparatus according to claim 1, further comprising:   The concentration measurement apparatus according to claim 1, wherein the sample is gaseous, and the measurement target substance is gas. A first optical attenuator provided between the sample and the first photodetector so that the first emitted light transmitted through the sample is incident, and having a variable light transmittance;
A first optical attenuator control unit for controlling the light transmittance of the first optical attenuator;
The concentration measuring device according to any one of claims 1 to 8, further comprising:   The concentration measuring apparatus according to claim 1, wherein the second optical attenuator is a liquid crystal optical shutter.   The concentration measuring apparatus according to claim 1, wherein each of the first photodetector and the second photodetector is a thermal photodetector. A concentration measurement method for measuring the concentration of a measurement target substance contained in a sample,
Irradiating the sample with first emitted light including light of a first wavelength;
Making the first outgoing light transmitted through the sample enter a first photodetector that outputs a light intensity signal;
The second emitted light including the second wavelength light is irradiated so as to pass through the second optical attenuator having a variable light transmittance, and the second emitted light after passing through the second optical attenuator Incident on a second photodetector that outputs an intensity signal of
A second optical attenuator control step for controlling the light transmittance of the second optical attenuator;
A calculation step of calculating the concentration of the measurement target substance;
With
The light absorption rate by the measurement target substance of the light of the first wavelength is higher than the light absorption rate by the measurement target substance of the light of the second wavelength,
The photoelectric conversion unit of the first photodetector and the photoelectric conversion unit of the second photodetector are based on the same photoelectric conversion principle and are made of the same material,
In the second optical attenuator control step, the intensity of the second emitted light incident on the second photodetector is determined based on the output value of the first photodetector and the output value of the second photodetector. Controlling the light transmittance of the second optical attenuator so as to approach the intensity of the first outgoing light incident on the first photodetector;
In the calculating step, a concentration measuring method for calculating a concentration of the measurement target substance based on the light transmittance of the second optical attenuator.

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