JPH1048135A - Infrared gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To the eliminate the need for span gas and prevent measurement from being interrupted by calibration. SOLUTION: A gas filter wheel 20 including gas filters (a), (c) filled with inert gas which does not absorb infrared rays and a gas filter (b) filled with measured component gas is provided between a light source 10 and a sample cell 2. When the gas filters (a), (b) are in a light path, zero gas flows to the sample cell 2, while sample gas flows to the sample cell 2 when the gas filter (c) is in the light path. As a result, when the gas filter (a) is in the light path, a zero-point signal is obtained as a signal from a detector 16, when the gas filter (b) is in the light path, a span-point signal is obtained, and when the gas filter (c) is in the light path, a measurement signal is obtained respectively. These signals are obtained per rotation of the gas filter wheel 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for process control relating to gas concentration in the environment of chemical factories and steelworks, flue gas analysis of boilers and combustion furnaces, monitoring of air pollution, measurement of automobile exhaust gas, etc. The present invention relates to an infrared gas analyzer that continuously measures the concentration of a specific component in a gas or vapor by utilizing a unique infrared absorption effect.

[0002]

2. Description of the Related Art FIG. 1 schematically shows a conventional infrared gas analyzer. (A) is a configuration diagram, and (B) is a plan view showing a sector portion thereof. Sample cell 2 that transmits infrared light
The sample gas and a reference gas having no absorption for infrared rays are supplied by switching through a three-way valve 8 from a gas inlet 4 and exhausted from a gas outlet 6. 10 is an infrared light source,
A sector 12 is provided between the light source 10 and the sample cell 2 for intermittently intermitting infrared light incident on the sample cell. Sector 1
2 has a notch as shown in FIG.
To intermittently interrupt the infrared light incident on the sample cell 2. Reference numeral 16 denotes an infrared detector which detects infrared light transmitted through the sample cell 2.

In this gas analyzer, a zero point is compensated by flowing a reference gas (zero gas) and a sample gas alternately through a sample cell 2. However, since the span point (sensitivity) is not compensated, it is necessary to periodically supply a span gas (standard gas) to calibrate the sensitivity.

[0004]

When the sensitivity is calibrated by periodically flowing a span gas as in a conventional apparatus, an expensive span gas is required. In addition, there is a problem that measurement is not performed during calibration (measurement cannot be performed). It is an object of the present invention to eliminate the need for span gas and prevent measurement from being interrupted for calibration.

[0005]

According to the present invention, there is provided a first transmitting portion comprising a gas filter filled with a predetermined concentration of a measuring component gas, and a second and a third transmitting portion having no absorption for infrared rays. A gas filter wheel that rotates and intermittently intercepts infrared light incident on the sample cell by rotating the respective transmission sections sequentially across the optical path between the light source and the sample cell is provided. The first of the wheels,
The second transmission portion traverses the optical path of the infrared light incident on the sample cell, and the third transmission portion of the gas filter wheel enters the sample cell with the sample gas supplied to the sample cell. The switching of the switching valve and the rotation of the gas filter wheel are synchronized so that the concentration of the component in the sample gas is calculated from the detection value of the infrared detector by the infrared light transmitted through each transmission part of the gas filter wheel. I do.

When the first transmitting portion enters the optical path, a reference gas is flowing through the sample cell, and a simulated span point due to a predetermined concentration of the measurement component gas filled in the gas filter of the first transmitting portion. The output is obtained. When the second transmission section enters the optical path, the reference gas is still flowing through the sample cell, and an output at the zero point is obtained. When the third transmission section enters the optical path, the sample gas is flowing through the sample cell, and an output by the sample gas is obtained. By calculating these outputs,
Not only the zero point but also the span point can always be compensated for measurement. Therefore, highly accurate measurement can be performed without performing sensitivity calibration using a standard gas periodically.

[0007]

FIG. 2 schematically shows an embodiment. FIGS. 3A and 3B show a gas filter wheel of which, FIG. 3A is a plan view, and FIG.
It is sectional drawing in the X 'line position. The same parts as those in FIG. 1 are denoted by the same reference numerals. A sample gas and a reference gas (zero gas) are switched from a gas inlet 4 to a sample cell 2 through which infrared light is transmitted by a three-way valve 8, and exhausted from a gas outlet 6. In order to interrupt the infrared light incident on the sample cell between the infrared light source 10 and the sample cell 2, the sector 12 shown in FIG.
Instead, a gas filter wheel 20 is provided.

As shown in FIG. 3, the gas filter wheel 20 has three gas filters a, b, and c as transmission portions whose both surfaces are sealed by an infrared transmission window 22 made of CaF ₂ or the like.
The gas filters a, b, and c are sequentially arranged so as to cross the optical path between the light source 10 and the sample cell 2 by the rotation of the gas filter wheel 20.
The gas filters a and c are filled with an inert gas such as nitrogen which does not absorb infrared rays, and the gas filter b is filled with a measurement component gas diluted with an inert gas such as nitrogen which does not absorb infrared rays. The measurement component gas concentration of the gas filter b is determined such that the same absorption amount as the infrared absorption amount when the measurement component gas of the full-scale concentration of the measurement range flows through the sample cell 2 is obtained by the gas filter b. ing. The gas filters a, b, and c correspond to the second, first, and third transmission units, respectively. Although not shown, a controller is provided to synchronize the switching of the three-way valve 8 and the rotation of the gas filter wheel 20.

Next, the operation of this embodiment will be described. A sample gas or a reference gas is supplied to the sample cell 2 via the three-way valve 8. As shown in FIG. 4, when a gas filter a filled with an inert gas or a gas filter b filled with a gas containing a measurement component enters the optical path, zero gas as a reference gas flows through the sample cell 2. When the gas filter c enters the optical path, the rotation of the three-way valve 8 and the rotation of the gas filter wheel 20 are controlled synchronously so that the sample gas flows through the sample cell 2. As a result, a detection signal as shown in FIG. 5A is obtained as a signal from the detector 16 according to the types a, b, and c of the gas filters in the optical path.

FIG. 5B shows gas filters a, b, c.
It shows the type of detection signal obtained with respect to the type of gas flowing through the sample cell 2. That is, a signal at the zero point is obtained when the gas filter a enters the optical path, a signal at the span point when the gas filter b enters the optical path, and a measurement signal when the gas filter c enters the optical path.
These signals are obtained for each revolution of the gas filter wheel 20.

The signal at the zero point is RZ, and the signal at the span point is R
Assuming that S and the measurement signal are M, the concentration C of the sample gas is expressed as C = f ((RZ-M) / (RZ-RS)). CR. Here, f (x) is a function for linearizing the infrared absorption signal, and CR is the density of the range.

As described above, each time the gas filter wheel 20 makes one rotation, the zero point and the span point are compensated for with high accuracy. Actually, as an initial calibration of the gas filter b, a standard gas is caused to flow through the sample cell 2 to calibrate the gas filter b (correction of a deviation from a theoretical value), and its correction coefficient is stored. It is desirable to use it for correction.

[0013]

According to the present invention, there are provided a first transmitting portion comprising a gas filter filled with a predetermined concentration of a measuring component gas, and second and third transmitting portions having no absorption for infrared rays. A gas filter wheel that intermittently intercepts infrared light incident on the sample cell by sequentially traversing the optical path between the light source and the sample cell, wherein the first and second gas filter wheels are provided in a state where the reference gas is supplied to the sample cell. The second transmission portion traverses the optical path of the infrared light incident on the sample cell, and the third gas filter wheel is moved in a state where the sample gas is supplied to the sample cell.
The switching of the switching valve and the rotation of the gas filter wheel are synchronized so that the transmission part of the gas crosses the optical path of the infrared light incident on the sample cell, and the infrared light transmitted by each transmission part of the gas filter wheel is transmitted by the infrared light. Since the component concentration in the sample gas is calculated from the detection value of the detector, the periodic calibration with the standard gas is not required, and the measurement can be performed with high accuracy without any missing measurement.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional infrared gas analyzer.
(A) is an overall configuration diagram, and (B) is a plan view showing a sector portion thereof.

FIG. 2 is a configuration diagram schematically showing one embodiment.

FIGS. 3A and 3B are diagrams showing a gas filter wheel in the embodiment, wherein FIG. 3A is a plan view and FIG. 3B is a cross-sectional view taken along the line XX ′.

FIG. 4 is a timing chart showing the type (A) of gas in the sample cell and the opening degree (B) of the gas filter in the operation of the embodiment.

FIG. 5 is a diagram showing a signal obtained by a detector;
(A) is a waveform diagram, and (B) is a chart showing correspondence.

[Explanation of symbols]

 2 sample cell 4 gas inlet of sample cell 6 gas outlet 8 three-way valve of switching valve 10 light source 16 detector 20 gas filter wheel a, b, c, gas filter

Claims (1)

[Claims] 1. A sample cell having a gas inlet and a gas outlet and transmitting infrared light, and a sample gas provided at a gas inlet of the sample cell and switching between a sample gas and a reference gas having no absorption for infrared light are supplied to the sample cell. A first light transmitting portion comprising a gas filter filled with a predetermined concentration of a measurement component gas, a second light source having no absorption for infrared light,
A gas filter wheel having a third transmitting portion, intermittently intermitting infrared light incident on the sample cell by rotating and each transmitting portion sequentially traversing the optical path between the light source and the sample cell; An infrared detector for detecting external light, and first and second transmission portions of a gas filter wheel traversing the optical path of infrared light incident on the sample cell while a reference gas is supplied to the sample cell, And a controller for synchronizing the switching of the switching valve and the rotation of the gas filter wheel so that the third transmitting portion of the gas filter wheel crosses the optical path of the infrared light incident on the sample cell in a state where the gas is supplied to the sample cell. Calculating means for calculating a component concentration in the sample gas from a detection value of an infrared detector based on infrared light transmitted through each transmission portion of the gas filter wheel.