JPH0560687A - Infrared analyzer - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to an infrared analyzer used in the field of industrial measurement, and does not require a standard cell for reference, which has always been necessary, and is capable of measuring various gas concentrations. The purpose is to perform simultaneous measurement with one pyroelectric linear array sensor. [Structure] The light from an infrared light source 11 is guided to a measurement gas cell 14, the light output from the cell is condensed and separated, and detected by a pyroelectric linear array detection element 18. The reference level was measured by 3.7 μm light with low gas absorption and good atmospheric transmittance, and the signal output was obtained corresponding to the gas concentration of CO ₂ , CO, and NO ₂ introduced into the gas cell. By taking the difference, it is possible to measure many kinds of gas concentrations at the same time without using a reference standard cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an industrial measuring field such as environmental measurement and pollution gas measurement, and an infrared analyzer used for remote sensing on a global scale.

[0002]

2. Description of the Related Art In recent years, infrared analyzers have been widely used for measuring pollution gas and automobile exhaust gas. In addition, it is about to be used for remote sensing of the global environment mounted on artificial satellites.

A conventional infrared analyzer will be described below. FIG. 4 shows the configuration of a conventional infrared analyzer. In FIG. 4, 1 is an infrared light source. 2 is a chopper blade. 3 is a motor which rotates the chopper blades of 2 at a constant speed. 4 is a gas cell for measurement. 5 is a transparent window material for the gas cell of 4. Reference numeral 6 is a reference standard cell, which is generally filled with dry nitrogen gas. 7 is the same transparent window material as 6. Reference numeral 8 is an infrared interference filter that matches the absorption wavelength of the gas to be measured, and 9 is an infrared sensor that detects infrared light of that wavelength.

The operation of the infrared analyzer having the above structure will be described below. First, when the infrared ray from the infrared light source 1 is passed through the gas layer having a certain concentration introduced into the measuring gas cell 4, the intensity I of the infrared ray having the specific wavelength after passing through the layer follows Lambert-Beer's law.

[0005]

[Equation 1]

Here, I _{0 is} the intensity of incident light k (λ); the absorption coefficient of light of wavelength (λ) c is the gas concentration x is the thickness of the gas layer. When the concentration is low, k (λ) cx << 1, so

[0007]

[Equation 2]

The change amount ΔI of infrared rays is expressed as

[0009]

[Equation 3]

Therefore, ΔI is proportional to the gas concentration x.
Usually, there are few devices having a light dispersion device such as a prism or a grating, and generally infrared rays in all wavelength regions emitted from a light source are used for measurement. Therefore, non-dispersive infrared gas analyzer (NDIR; Non Dispersive Infra-Red gasanal)
yzer: Non Dispersive Infra Red Gas
Analyzer) is called. NDIR is also divided into positive filter type and negative filter type depending on the type of detector used. The positive filter type is the case where the detector is wavelength dependent, and the negative filter type is the case where the detector is not wavelength dependent. In the latter case, an infrared interference filter is used to give selectivity to a specific wavelength. The infrared interference filter 8 shown in FIG. 4 is adapted to a specific gas absorption line,
For CO ₂ , for example, a narrow band filter centering on 4.3 μm is used. In this case, the intensity I ₀ of the infrared incident light at the zero density level is required. To obtain this I ₀ , a reference standard cell filled with dry nitrogen, which generally does not absorb, is provided. This cell is installed side by side with the measuring cell, the infrared light that passes through both cells is alternately turned on and off by the chopper, and the light that passes through both cells is combined to produce an output when the gas concentration in the measuring cell is zero. This is a difference output method that is set to zero.

Further, a method capable of simultaneously measuring the spectrum of a wide range of low-energy infrared rays is disclosed in JP-A-59-1.
The contents are described in Japanese Patent No. 93341. Also in this case,
It is necessary to take the standard level, and basically the same as the standard cell for reference is required.

[0012]

However, in the above-mentioned conventional structure, a reference standard cell for taking a reference or a reference corresponding thereto is necessary, and the difference in conditions between the two cells causes an error. Had challenges.

The present invention solves the above-mentioned problems of the prior art, and provides an infrared analyzer which does not require a reference standard cell and can simultaneously measure the concentrations of various kinds of gases with one one-dimensional infrared sensor. With the goal.

[0014]

In order to achieve this object, the present invention selects a wavelength that does not absorb gas among infrared wavelengths and uses the output of that wavelength as a reference. Therefore, the standard cell for reference is not provided and the standard is obtained only by the measurement cell.

[0015]

According to the present invention, with the above configuration, a reference signal is obtained by using a wavelength without gas absorption, and the difference between the reference signal and the measurement signal is taken out to eliminate the cause of error when two cells are used and always stabilize. You can know the gas concentration.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an infrared analyzer according to an embodiment of the present invention. In FIG. 1, 11 is an infrared light source,
12 is a chopper blade, and 13 is a motor for rotating the 12 chopper blades. Reference numeral 14 is a gas cell, and 15 is an infrared transmission window material of the gas cell. Reference numeral 16 is a condensing system that collects the light that has passed through the gas cell, 17 is a spectroscope that disperses the condensed light, and 18 is a pyroelectric linear array detection element that can detect the separated infrared light for each wavelength.

The principle of the infrared analyzer constructed as described above will be described with reference to the infrared spectrum shown in FIG. First, gases such as CO ₂ , CO, NO, and SO ₂ that affect the environment have absorption in the infrared wavelength range of 4 to 8 μm. The absorption wavelength position and absorption coefficient of each gas are shown in (Table 1).

[0019]

[Table 1]

As is clear from this (Table 1), C
O ₂ , CO, NO and SO ₂ are 4.3 μm and 4.7 μm, respectively
It has central absorption bands at m, 5.3 μm, and 7.4 μm. Further, as shown in FIG. 3, the infrared transmission characteristics of the atmosphere are largely influenced by water, but the 3 to 5 μm band and the 8 to 12 μm band are known to be the windows of the atmosphere and transmit infrared rays well. . For example, in the range of 3.5 to 3.8 μm, the effect of gas absorption is small, and the atmospheric transmittance is good. In the present embodiment, the spectroscope 17 is a 3.5 μm to 7 μm band spectroscope so that the above three kinds of gases (CO ₂ , CO, NO) can be detected. The pyroelectric linear array detection element had a 16-element configuration (pitch 0.4 mm). In this case, since the element at the extreme end corresponds to the 3.5 to 3.8 μm band, the signal output of this element is used as a reference to obtain the output corresponding to the gas concentration by taking the difference from the signal output of other elements. I was able to.

As described above, according to this embodiment, by using only the measuring gas cell and providing the combination of the infrared spectroscope and the pyroelectric linear array detecting element, the gas absorption is small and the atmospheric transmittance is good. The signal output in the band of 0.7 μm can be used as a reference, and various kinds of gas concentrations can be simultaneously measured without using a reference standard cell.

[0022]

As described above, according to the present invention, by providing a combination of an infrared spectroscope and a pyroelectric linear array detection element, it is possible to simultaneously measure various kinds of gas concentrations without using a reference standard cell. It is possible to realize an excellent infrared analyzer that can be used.

[Brief description of drawings]

FIG. 1 is a block diagram of an infrared analyzer according to an embodiment of the present invention.

FIG. 2 is a gas absorption pattern diagram showing absorption characteristics of a target gas of the infrared analyzer in the same Example.

FIG. 3 is an atmospheric absorption characteristic diagram of the infrared analyzer in the same example.

FIG. 4 is a block connection diagram of a conventional infrared analyzer.

[Explanation of symbols]

 1 infrared light source 2 chopper blade 3 motor 4 measurement gas cell 5 transmission window material 6 reference standard cell 7 transmission window material 8 infrared interference filter 9 infrared sensor 11 infrared light source 12 chopper blade 13 motor 14 gas cell 15 infrared transmission Window material 16 Condensing system 17 Spectroscope 18 Pyroelectric linear array detector

Claims (4)

[Claims] 1. An infrared light source, a chopper for connecting and disconnecting infrared light, a gas cell for flowing a gas to be measured, and a light condensing system for condensing infrared light absorbed by the gas to be measured. Consists of a spectroscope that separates infrared light by wavelength and a linear array element that detects the separated infrared light, and has a mechanism that uses a signal output of a wavelength without gas absorption as a reference without using a reference standard cell. Infrared analyzer. 2. A wavelength range of 3.5-3.
The infrared analyzer according to claim 1, wherein the infrared analyzer has a thickness of 8 μm. 3. An infrared analyzer according to claim 1, wherein a circuit for outputting the difference between the output of the element corresponding to the wavelength used as the reference signal and the other element is incorporated. 4. The infrared analyzer according to claim 1, wherein a pyroelectric sensor is used for the linear array element.