JP2009257808A - Infrared gas analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared gas analyzer which is made compact, low priced, and maintenence-free by omitting a movable mechanism such as a motor. <P>SOLUTION: An infrared gas analyzer comprises an infrared light source which is electrically directly-modulated and driven in a blinking manner, a first gas chamber which is filled with a measurement gas and into which an output light from the infrared light source is input, a correlation cell having a second gas chamber which is filled with a reference gas that does not absorb an infrared light, and into which the output light from the infrared light source is input, a measurement cell into which a gas to be measured is introduced, a band path filter having a transmissive band which is a little broader than an infrared light absorption band of the measurement gas, and an infrared light detector for detecting the infrared light which passes through the band path filter, wherein the infrared light source and the correletaion cell are provided at one end of the measurement cell, the infrared light detector is provided at the other end of the measurement cell, and the band path filter is provided at either end of the measurement cell. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an infrared gas analyzer, and more particularly, to a gas analyzer that measures the concentration of gas components such as in the atmosphere using infrared rays, omitting a movable mechanism.

FIG. 6 is a block diagram showing an example of a conventional gas concentration measuring apparatus, showing an example using a gas correlation method.
The output light of the infrared light source 1 enters the infrared detector 6 through the chopper 2 → the gas correlation cell 3 → the band pass filter 4 → the measurement cell 5.

FIG. 7 is a perspective view showing a specific example of the chopper 2 and the gas correlation cell 3 of FIG. The chopper 2 is formed in a disk shape, and the light transmitting portions 2a and the light shielding portions 2b are alternately provided along the circumferential direction. The gas correlation cell 3 is formed in a cylindrical shape, and the inside is partitioned into a measurement gas chamber 3a and a reference gas chamber 3b. The measurement gas chamber 3a is filled with, for example, CO ₂ gas, which is a gas to be measured, at a high concentration, and the reference gas chamber 3b is filled with, for example, N ₂ gas as a gas that does not absorb infrared light.

In FIG. 6 again, the chopper 2 and the gas correlation cell 3 are rotationally driven by the motor 6. The measurement cell 5 is provided with an inlet 5a and an outlet 5b for sample gas. For example, atmospheric gas containing CO ₂ is introduced into the inlet 5a as a sample gas, and is continuously exhausted from the outlet 5b.

  The bandpass filter 4 allows only the light in the infrared region slightly wider than the infrared absorption band of the measurement gas among the output light of the infrared light source 1 that has passed through the chopper 2 and the gas correlation cell 3 to pass through the measurement cell 5. Make it incident. Part of the infrared light incident on the measurement cell 5 is absorbed by the measurement gas introduced into the measurement cell 5 and is incident on the infrared light detector 6. The infrared light detector 6 is composed of an element having sensitivity to infrared light, such as a PbSe element, and detects the light intensity of the incident infrared light. The infrared light detector 6 is temperature controlled by a thermostat (not shown) so that the light intensity of the infrared light can be detected stably.

Japanese Patent No. 3424364 JP 2001-221737 A

  However, such a conventional infrared gas analyzer has to rotate and drive the chopper 2 and the gas correlation cell 3 with a motor 6 in order to modulate (chop) infrared rays, and is small, low cost, and does not require maintenance. There is a problem that it is difficult to make it (free).

  The present invention solves the above-described problems, and an object thereof is to provide an infrared gas analyzer that realizes a small size, low cost, and maintenance-free by omitting a movable mechanism such as a motor. It is.

In order to achieve the above object, in claim 1 of the present invention, an infrared light source that is directly modulated and driven to blink, and a measurement gas filled with output light from the infrared light source are incident. A correlation cell having a first gas chamber and a second gas chamber filled with a reference gas that does not absorb infrared light and into which the output light of the infrared light source is incident; a measurement cell into which a gas to be measured is introduced; A bandpass filter having a transmission band slightly wider than the infrared absorption band of the measurement gas, and an infrared light detector for detecting infrared light transmitted through the bandpass filter,
One end of the measurement cell is provided with the infrared light source and a correlation cell, the other end of the measurement cell is provided with the infrared light detector, and the bandpass filter is provided at one end of the measurement cell. It is characterized by being provided in.

  The infrared gas analyzer according to claim 1, wherein one infrared light source is provided, and the output light is incident on the first gas chamber and the second gas chamber of the correlation cell in common. Two infrared light detectors are provided to individually detect the infrared light that has passed through these gas chambers.

  According to a third aspect of the present invention, in the infrared gas analyzer according to the first aspect, the two infrared light sources are provided, and the respective output lights are individually incident on the first gas chamber and the second gas chamber of the correlation cell. One infrared light detector is provided to commonly detect infrared light that has passed through these gas chambers.

  By eliminating movable mechanisms such as motors, maintenance-free, downsizing, and low cost can be realized.

  Further, by using a gas correlation method that is not easily influenced by interference components, and combining an infrared light source that can be directly electrically modulated and has a small change with time, and a correlation cell, the influence of the interference gas can be almost eliminated.

  Furthermore, since a direct modulation infrared light source that can emit light with an electric voltage that can be directly electrically modulated and does not change with time is used, there is no change in the amount of light with time, two infrared light sources and one infrared detector. In this case, since the sensor output is obtained by calculating each output signal, the change with time of the element and the ambient temperature fluctuation can be removed differentially.

  Hereinafter, the infrared gas analyzer of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the infrared gas analyzer of the present invention.

In FIG. 1, the light source unit 11 is provided with two infrared light sources 11a and 11b having the same light emission characteristics. These infrared light sources 11a and 11b are direct modulation infrared light sources that can emit infrared rays with a driving voltage that can be directly electrically modulated and do not change with time, and are alternately driven to blink. The output light from one infrared light source 11a is incident on a measurement gas chamber 12a filled with a high concentration of, for example, CO ₂ gas, which is a measurement gas, as the measurement gas of the correlation cell 12, and the output light from the other infrared light source 11b. Enters the reference gas chamber 12b filled with, for example, N ₂ gas as a reference gas that does not absorb the infrared light of the correlation cell 12. The light source unit 11 and the correlation cell 12 are provided at one end of a measurement cell 13 formed in a cylindrical shape into which a gas to be measured is introduced.

The measurement cell 13 is provided with an inlet 13a and an outlet 13b for sample gas. For example, atmospheric gas containing CO ₂ is introduced into the inlet 13a as a sample gas, and is continuously exhausted from the outlet 13b. In some cases, a sample gas passed through a sampling device or the like that removes dust with a filter or removes moisture that absorbs infrared light with a perm pure dryer may be introduced. A band pass filter 14 and an infrared light detector 15 are provided at the other end of the measurement cell 13. The band-pass filter 14 has a characteristic of allowing infrared light in a band slightly wider than the infrared absorption band of the measurement gas to pass. As the infrared light detector 15, a thermopile, a pyroelectric element, a quantum element, or the like is used.

The operation of FIG. 1 will be described.
Since the infrared light IRa of the infrared light source 11a that has passed through the measurement gas chamber 12a filled with the measurement gas of the correlation cell 12 absorbs almost the characteristic absorption band of the measurement gas in the sample gas, the measurement cell 13 There is almost no change in the amount of light due to the concentration of the measurement gas inside. On the other hand, the amount of light of the infrared light IRb of the infrared light source 11b transmitted through the reference gas chamber 12b filled with the reference gas changes according to the concentration of the measurement gas in the sample gas in the measurement cell 13.

The operation of FIG. 1 will be described using the measurement principle diagram of the gas correlation method of FIG.
(A) shows the transmission characteristics of infrared light IRb as measurement light output from the infrared light source 11b and transmitted through the reference gas chamber 12b filled with N ₂ gas as the reference gas. The measurement light that has passed through the bandpass filter 14 is incident on the infrared light detector 15 only in the infrared transmission band of the bandpass filter 14.

(B) shows the transmission characteristics of the measurement light that has passed through the reference gas chamber 12 b filled with N ₂ gas as the reference gas and has further passed through the measurement cell 13. When, for example, CO ₂ is present as a measurement gas inside the measurement cell 13, infrared light is absorbed according to the concentration of the measurement gas CO ₂ . In the band pass filter 14, the infrared light IRb from which the absorption of the measurement gas CO ₂ is subtracted is incident on the infrared light detector 15 by passing through a band slightly wider than the infrared absorption band of the measurement gas.

(C) shows the transmission characteristics of infrared light IRa as reference light that is output from the infrared light source 11a and passes through the measurement gas chamber 12a filled with high-concentration CO ₂ as the measurement gas. The reference light transmitted through the bandpass filter 14 passes through a band slightly wider than the infrared transmission band of the measurement gas CO ₂ in the bandpass filter 14, so that the infrared light IRa from which the absorption of the measurement gas CO ₂ has been subtracted. The light enters the infrared light detector 15.

(D) shows the transmission characteristics of the reference light that has passed through the measurement gas chamber 12a filled with high-concentration CO ₂ as the measurement gas and has further passed through the measurement cell 13. As is clear from the transmission characteristics of (D), infrared light IRb is detected by infrared light IRb, in which, for example, CO ₂ exists as a measurement gas in the measurement cell 13 and the amount of light hardly changes even if its concentration changes. Is incident on the vessel 15.

The amount of infrared light IRa and IRb output from the infrared light sources 11a and 11b and transmitted through the correlation cell 12 and the measurement cell 13 is detected by the infrared light detector 15, and based on the obtained signal, a gas correlation method has been conventionally used. The predetermined calculation being performed is performed to determine the concentration of the measurement gas, for example, CO ₂ .

FIG. 3 is a diagram for explaining the principle of interference gas compensation in the gas correlation method.
Infrared gas analyzers are generally affected by interference by being absorbed by a gas other than the measurement gas. For example, when the measurement gas is CO ₂ and the gas other than the measurement gas is CO, it can be considered as in FIG.
(A) shows the transmission characteristics of infrared light IRb as measurement light output from the infrared light source 11b and transmitted through the reference gas chamber 12b filled with N ₂ gas as the reference gas. Only the infrared transmission band of the bandpass filter 14 is incident on the infrared light detector 15 when the measurement light transmitted through the bandpass filter 14 is absorbed. If gas CO other than the measurement gas exists in the measurement cell 13, the measurement light is absorbed by the CO. As a result, the waveform is slightly cut.

(B) shows the transmission characteristics of the measurement light that has passed through the reference gas chamber 12 b filled with N ₂ gas as the reference gas and has further passed through the measurement cell 13. When, for example, CO ₂ is present as a measurement gas inside the measurement cell 13, infrared light is absorbed according to the concentration of the measurement gas CO ₂ . In the band pass filter 14, the infrared light IRb from which the absorption of the measurement gas CO ₂ and the gas CO other than the measurement gas is subtracted by passing through a band slightly wider than the infrared absorption band of the measurement gas is used as the infrared light detector. 15 is incident.

(C) shows the transmission characteristics of infrared light IRa as reference light that is output from the infrared light source 11a and passes through the measurement gas chamber 12a filled with high-concentration CO ₂ as the measurement gas. The reference light transmitted through the bandpass filter 14 passes through a band slightly wider than the infrared transmission band of the measurement gas CO ₂ in the bandpass filter 14, so that the infrared light IRa from which the absorption of the measurement gas CO ₂ has been subtracted. Although it is incident on the infrared light detector 15, if a gas CO other than the measurement gas is present in the measurement cell 13, the absorption by the CO occurs, and the waveform is slightly cut off.

(D) shows the transmission characteristics of the reference light that has passed through the measurement gas chamber 12a filled with high-concentration CO ₂ as the measurement gas and has further passed through the measurement cell 13. As is clear from the transmission characteristics of (D), infrared light IRb is detected by infrared light IRb, in which, for example, CO ₂ exists as a measurement gas in the measurement cell 13 and the amount of light hardly changes even if its concentration changes. Although it is incident on the vessel 15, if a gas CO other than the measurement gas exists in the measurement cell 13, the absorption by the CO occurs, so that the waveform is slightly cut.

Thus, there is an influence of interference between the reference light transmitted through the measurement gas chamber 12a filled with high concentration CO ₂ as the measurement gas and the measurement light transmitted through the reference gas chamber 12b filled with N ₂ gas as the reference gas. Since it becomes the same level, the calculated value of the infrared light detected in FIGS. 2B and 2D and the calculated value of the infrared light detected in FIGS. 3B and 3D are almost the same. Thus, it can be seen that it is hardly affected by interference.

  Further, for example, gas having a wide band such as water and having an influence on the base line can reduce the influence of the interference.

FIG. 4 is an explanatory diagram showing the relationship between the CO ₂ concentration and the output signal of the infrared light detector 15 and the calculation. For example, the infrared light detector 15 in the case where the CO ₂ concentration in the measurement cell 13 changes. The signal change is modeled. As shown in FIG. 1, by providing two infrared light sources 11a and 11b and one infrared light detector 15, the reference light transmitted through the measurement gas chamber 12a filled with high-concentration CO ₂ as the measurement gas. When the output signal A and the output signal B of the measurement light transmitted through the reference gas chamber 12b filled with N ₂ gas as the reference gas are alternately obtained, the output signal A does not change even if the CO ₂ concentration changes. In the output signal B, the CO ₂ concentration increases and the output signal changes small.

Further, when one infrared light source 11 and two infrared light detectors 15 are provided, the output signal A of the reference light transmitted through the measurement gas chamber 12a filled with high concentration CO ₂ as the measurement gas and The output signal B of the measurement light transmitted through the reference gas chamber 12b filled with N ₂ gas as the reference gas can be obtained at the same time. The sensor output Sout is obtained by calculating the output signal A and the output signal B, and the CO ₂ concentration Cc in the measurement cell 13 is obtained from the calibration curve obtained in advance, that is, the relationship between the CO ₂ concentration Cc and the sensor output Sout.

  When three infrared light sources 11 are provided, two types of components are detected, and when two infrared light sources 11 are provided, one type of component is detected. That is, when n infrared light sources 11 are provided, (n-1) types of components can be detected.

  In the embodiment of FIG. 1, the light source unit 11 and the correlation cell 12 are integrated and provided at one end of a measurement cell 13 formed into a cylindrical shape into which a gas to be measured is introduced, and a bandpass is provided at the other end of the measurement cell 13. Although an example in which the filter 14 and the infrared light detector 15 are integrally provided has been shown, the present invention is not limited to this combination, and the correlation cell 12 and the measurement cell 13 are interposed between the infrared light source 11 and the infrared light detector 15. And the band pass filter 14 may be combined, and may be combined as shown in FIGS. 5 that are the same as those in FIG. 1 are denoted by the same reference numerals.

  (A) Infrared light source 11 and correlation cell 12 are individually formed and provided at one end of measurement cell 13, and bandpass filter 14 and infrared light detector 15 are integrated at the other end of measurement cell 13. It is the provided structural example.

  (B) shows that the infrared light source 11, the correlation cell 12, and the band pass filter 14 are integrated and provided at one end of the measurement cell 13, and the infrared light detector 15 and infrared light provided at the other end of the measurement cell 13. This is a configuration example in which an infrared window material 16 having a high transmittance is integrated.

  (C) Infrared light source 11, correlation cell 12, and bandpass filter 14 are individually formed and provided at one end of measurement cell 13, and infrared light detector 15 provided at the other end of measurement cell 13. And an infrared window material 16 having a high infrared transmittance.

  Moreover, a plurality of gas components can be measured by increasing the combination of the infrared light source 11 and the correlation cell 12.

  1 and 5 show from left to right the infrared light source 11 → correlation cell 12 → measurement cell 13 → bandpass filter 14 → infrared light detector 15 or infrared light source 11 → correlation cell 12 → bandpass. The filter 14 → the measurement cell 13 → the infrared window material 16 → the infrared light detector 15 are configured in this order. From the right to the left, the infrared light source 11 → the correlation cell 12 → the measurement cell 13 → the bandpass filter 14 → red. The external light detector 15 or infrared light source 11 → correlation cell 12 → bandpass filter 14 → measurement cell 13 → infrared window material 16 → infrared light detector 15 may be configured in this order.

  As is clear from these embodiments, since the correlation cell 12 is fixed, a movable mechanism such as a motor can be omitted and maintenance-free can be achieved. Since the number of parts can be reduced by omitting a movable mechanism such as a motor, downsizing and cost reduction can be realized.

  Further, by using an optical system in which an infrared light source 11 that can be directly electrically modulated and does not change with time and a fixed correlation cell 12 and a gas correlation method that is not easily affected by interference components are used, interference is prevented. The effect of gas can be almost eliminated.

  In addition, since the infrared light source 11 that can be electrically directly modulated and emits infrared light with a drive voltage that does not change with time, the change in the amount of light with time can be eliminated.

  Further, when the measurement cell 13 is structured to be multiple-reflected, the infrared light source 11 and the infrared light detector 15 can be arranged on the same substrate, so that the size can be reduced with high accuracy. Can do.

  Further, two infrared light sources 11 and one infrared light detector 15 are provided, and an output signal A of the reference light transmitted through the measurement gas chamber 12a filled with the measurement gas and a reference gas filled with the reference gas. By calculating the output signal B of the measurement light that has passed through the chamber 12b and obtaining the sensor output Sout, it is possible to differentially remove changes in the elements over time and ambient temperature fluctuations.

  In each of the above-described embodiments, an example in which the measurement cell is formed in a cylindrical shape has been described. However, the measurement cell is not limited to a cylindrical shape, and may be formed in an appropriate shape depending on the application.

  As described above, according to the present invention, a rotating mechanism such as a motor can be omitted, and an infrared gas analyzer that is small, inexpensive, and free of maintenance can be realized.

It is a block diagram which shows one Example of this invention. This is the measurement principle of the gas correlation method used in the present invention. It is principle explanatory drawing of interference gas compensation in the gas correlation method used by this invention. The CO ₂ concentration and the infrared light detector 15 output signal and calculating the relationship of the present invention; FIG. It is a block diagram which shows the other Example of this invention. It is a block diagram which shows an example of the conventional gas concentration measuring apparatus. It is a perspective view which shows the specific example of the chopper 2 and the gas correlation cell 3 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Light source part 12 Correlation cell 13 Measurement cell 14 Band pass filter 15 Infrared light detector 16 Infrared window material

Claims (3)

An infrared light source that is electrically directly modulated and driven to blink, a first gas chamber that is filled with a measurement gas and into which the output light of the infrared light source is incident, and a reference gas that does not absorb infrared light is filled with the red light source. A correlation cell having a second gas chamber into which output light of an external light source is incident, a measurement cell into which a gas to be measured is introduced, a bandpass filter having a transmission band slightly wider than the infrared absorption band of the measurement gas, It has an infrared light detector that detects infrared rays that pass through this bandpass filter,
One end of the measurement cell is provided with the infrared light source and a correlation cell, the other end of the measurement cell is provided with the infrared light detector, and the bandpass filter is provided at one end of the measurement cell. An infrared gas analyzer characterized by being provided in   One infrared light source is provided, and its output light is incident on the first gas chamber and the second gas chamber of the correlation cell in common, and two infrared light detectors are provided, and these gas chambers are provided. The infrared gas analyzer according to claim 1, wherein infrared light that has passed through is individually detected.   Two infrared light sources are provided, and each output light is individually incident on the first gas chamber and the second gas chamber of the correlation cell, and one infrared light detector is provided for these gases. The infrared gas analyzer according to claim 1, wherein infrared light passing through the chamber is commonly detected.

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