JPH056864B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field This invention relates to an infrared gas analyzer, and more specifically, a non-dispersive infrared gas analyzer that measures gas concentration based on the strength of infrared absorption of gas molecules in the infrared region. Regarding.

(B) Prior art In general, an infrared gas analyzer is equipped with an infrared transmission cell for measurement (hereinafter referred to as the measurement cell) and an infrared transmission cell for comparison (hereinafter referred to as the comparison cell), and the infrared rays of both cells are A gas-filled detector (Numatake detector) uses a condenser microphone or micro flow sensor to detect the difference in the amount of transmitted light.
It is detected as a pressure difference.

Conventional measurement methods using the above detector include a negative filter method and a positive filter method.

In the optical system of this negative filter method, as shown in FIG. 7, infrared rays from a pair of light source elements 1, 1 are transmitted through an infrared transmitting cell 2 filled with an inert gas such as nitrogen gas and a gas to be measured, respectively. The infrared transmitting cell (3, hereinafter referred to as gas cell) is transmitted through the infrared transmission cell (3, hereinafter referred to as gas cell), and further transmitted through the measurement cell 4 and comparison cell 5 through which the measurement gas flows.
The infrared light is incident on two infrared absorption chambers 8 and 9 separated by a capacitor film 7. Note that 10 is a chopper and 11 is a chopper drive motor.

In this method, when infrared rays are incident on both infrared absorption chambers 8 and 9, the pressure inside both infrared absorption chambers 8 and 9 changes, and the infrared rays enter the capacitor film 7 after passing through the measurement cell 4. Curve it to the 8th side. As a result, the capacitor capacity of the detector 6 changes, and the concentration of the component to be measured in the measurement gas is measured.

8 and 9 are diagrams showing the curved state of the capacitor film 7 due to the rotation of the chopper 10, and graphs showing changes in the capacitor capacitance of the detector 6. FIG.

When the concentration of the measurement gas is measured by the above method, absorption of the infrared rays of the components to be measured and interference components in the measurement gas occurs in the infrared absorption chamber 8 into which the infrared rays after passing through the measurement cell 4 are incident. On the other hand, in the other infrared absorption chamber 9, most of the component to be measured in the measurement gas is absorbed by the gas cell 3, so that a small amount of the component to be measured and the interference component are absorbed. At this time, if the absorption amount of the interference component is made to be approximately the same as the absorption amount of the other infrared absorption chambers 8, measurement without interference can be performed.

However, in this case, slight absorption of the component to be measured in the measurement gas occurs even in the infrared absorption chamber 9 into which the infrared rays after passing through the comparative cell 5 enter, so that the absorption of the measurement target component in the measurement gas in another infrared absorption chamber 8 occurs. Absorption of the component to be measured is canceled. As a result, in the negative filter method, the output of the detector 6 becomes 30 to 40% smaller than in the positive filter method. Therefore, the negative filter method has the disadvantage that when the concentration of the component to be measured in the measurement gas becomes lower than a limit value, the concentration cannot be measured. Furthermore, when compensating for interference, if the lengths of the measurement cell 4 and the comparison cell 5 are made the same, the compensation for interference becomes large and the interference may become negative. Therefore, it was necessary to design an optical system for the negative filter method in consideration of this point.

This invention was made in view of the above circumstances,
One of the main objectives is to configure a negative filter condenser microphone to have twice the output of a conventional condenser microphone, and to detect the concentration of the target component in the measurement gas with high sensitivity even when the concentration is low. Another main purpose is to configure the length of the comparison cell to be the length that optimizes interference compensation regardless of the length of the measurement cell. The objective is to make it possible to create a small optical system.

(c) Structure This invention is an infrared gas analyzer, which includes a pair of light sources that emit infrared rays in opposition, an infrared transmitting cell provided on the optical path between the two light sources, and a connection to the infrared transmitting cell. The infrared transmitting cell is equipped with an infrared detector and an infrared detector, and the infrared transmitting cell is provided with a measurement gas introduction part and a measurement gas discharge part. A pair of infrared absorption chambers filled with a reflector driving means for rotating a double-sided reflector so that the infrared rays from both light sources can be alternately incident on the absorption chamber; and a reflector drive means provided in the connecting part for detecting the pressure difference between the two infrared absorption chambers to be measured in the measurement gas. and a detection means for outputting a component concentration measurement signal.

In other words, in the present invention, when the reflector is rotated by the reflector drive means when measuring the concentration of the component to be measured in the measurement gas, infrared rays are alternately incident on both infrared absorption chambers, and both infrared rays are thereby generated. It is configured so that the pressure difference in the absorption chamber is detected by a detection means.

(E) Embodiments The present invention will be described in detail below based on embodiments shown in FIGS. 1 to 5. Note that this invention is not limited to this.

In FIG. 1, the infrared gas analyzer 12 includes a pair of light sources 13, 13 that emit infrared rays in opposite directions, and an optical path 14 between the two light sources 13, 13 from one light source 13 side to the other light source 13 side. It mainly consists of a measurement cell 15, an infrared detector 16, a comparison cell 17, and a gas cell 18 filled with a measurement gas, which are arranged in series in this order.

The measurement cell 15 and the comparison cell 17 are made of cylindrical infrared transmitting cells, and the cylindrical walls thereof are provided with measurement gas introduction sections 19 and 20 and measurement gas discharge sections 21 and 22, respectively.

As shown in FIGS. 2 and 3, the infrared detector 16 includes a pair of infrared absorption chambers 23, 23 filled with a measurement gas, a double-sided reflector (mirror) 24,
Mirror drive motor 25 and detection means 26 that detects the pressure difference between both infrared absorption chambers 23 and outputs a detection signal.
Both infrared absorption chambers 23 are provided with the optical path 14.
are installed facing each other in a direction perpendicular to the optical path 14, and are connected by a connecting portion 27 provided on the infrared detector 16 so as not to interrupt the optical path 14. On the other hand, the mirror 24 has its surface perpendicular to the optical path 14 and is rotatable toward both the infrared absorption chambers 23.
It is installed on 4. Further, the detection means 26
is composed of a capacitor microphone consisting of a metal thin film (capacitor film) 28 and a counter electrode 29. In addition, as the detection means 26, a micro flow sensor may be used.

Next, the operation of the analyzer 12 will be explained. In addition,
Measurement gases include carbon monoxide, dioxide ions,
Exhaust gas such as nitrogen monoxide is used.

First, the measurement gas is applied to the measurement cell 15 and comparison cell 1.
7 will be introduced. Next, when measuring the concentration of the component to be measured in the measurement gas, when the mirror drive motor 25 is operated to rotate the mirror 24, infrared rays are alternately incident on both the infrared absorption chambers 23. Therefore, a pressure difference is generated in both infrared absorption chambers 23, and as a result, the metal thin film 28 is bent alternately toward both infrared absorption chambers 23 as shown in FIG. A signal like the one shown is output. The concentration is then measured based on this output signal.

In this manner, the change in capacitance of the capacitor of the detection means 26 is twice that of the conventional method, allowing concentration measurement to be performed with high sensitivity. Further, since there is no need to provide a cell filled with inert gas between the measurement cell 15 and the light source 13, concentration measurement can be performed with higher sensitivity than in the past. Furthermore, since the length of the comparison cell can be set regardless of the length of the measurement cell, the influence of interference can be minimized, and even if only the length of the comparison cell is changed, extra space will be created in the analyzer. Therefore, the measured values are no longer affected by the gas surrounding the analyzer. As a result of the above, an infrared analyzer with an excellent S/N value can be obtained.

FIG. 6 is a diagram showing another embodiment, 13a, 13
a is a light source, 15a is a measurement cell, 23a, 23a are infrared absorption chambers, and 24a is a mirror. This example is constructed by omitting the comparative cell 17 and gas cell of the first example.

(F) Effects This invention is configured so that infrared rays from both light sources can be incident on both infrared absorbing chambers alternately, so that the output signal of the detection means can be doubled compared to the conventional one. Therefore, it is possible to measure the concentration of the component to be measured in the measurement gas with high sensitivity.

[Brief explanation of drawings]

Fig. 1 is a configuration explanatory diagram showing one embodiment of an infrared gas analyzer according to the present invention, Fig. 2 is a longitudinal sectional view of this detector, Fig. 3 is a sectional view taken along line A-A in Fig. The figure is an explanatory diagram of the curved state of this metal thin film, Figure 5 is a graph showing the output signal of the condenser microphone, Figure 6 is a diagram corresponding to Figure 1 of other embodiments, Figures 7, 8 and 8. Figure 9 shows the first conventional example.
FIG. 4 is a diagram corresponding to FIG. 4 and FIG. 5. 12...Infrared gas analyzer, 13...Light source, 1
4... Optical path, 15... Measurement cell (infrared transmission cell), 16... Infrared detector, 19... Measurement gas introduction section, 21... Measurement gas discharge section, 23... Infrared absorption chamber, 24... Mirror (Reflector), 25...
Mirror drive motor (reflector drive means), 26...
Detection means, 27...connection section.

Claims (1)

[Claims] 1. A device comprising: a pair of light sources that emit infrared rays in opposition; an infrared transmitting cell provided on an optical path between the two light sources; and an infrared detector connected to the infrared transmitting cell; An infrared transmission cell is provided with a measurement gas introduction part and a measurement gas discharge part, and an infrared detector is installed facing each other via an optical path, and a pair of infrared absorption chambers are filled with a measurement gas or a gas equivalent to this gas. , a connecting part that connects both infrared absorption chambers so as not to interrupt the optical path, a double-sided reflector that is rotatably installed on the optical path between both infrared absorption chambers, and an infrared ray from both light sources that enters both infrared absorption chambers. a reflector drive means for rotating the double-sided reflector so that the infrared rays can be incident alternately; and a detection device provided in the connecting portion for detecting the pressure difference between the two infrared absorption chambers and outputting a concentration measurement signal of the component to be measured in the measurement gas. An infrared analyzer consisting of means. 2. Claim 1 in which the detection means is a condenser microphone or a microflow sensor.
Infrared analyzer described in section. 3. On the optical path between the light source and the infrared detector on the infrared detector side, there is an infrared transmitting cell for comparison that is connected to the infrared detector and equipped with a measurement gas introduction part and a measurement gas discharge part, and an infrared transmission cell of this infrared transmission cell. 2. The infrared gas analyzer according to claim 1, further comprising an infrared transmission cell connected to the opposite side of the infrared detector and filled with a measurement gas or a gas equivalent to this gas.