JPH07190930A - Gas analyzer - Google Patents

Abstract

PURPOSE:To provide a compact and inexpensive infrared gas analyzer in which a same component can be measured accurately from a low concentration region to a high concentration region using only one optical bench. CONSTITUTION:Two cells 1, 2 having different cell length are disposed in parallel between a light source 7 and a detector 11 and an optical chopper 10 is disposed on the optical path between the light source 7 and the detector 11. A sample gas S is fed constantly between the cells 1 and 2 and the light beam projected from the light source 7 toward the detector 11 is intercepted in the light path on the longer cell side 1 only at the time of measurement of high concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas analyzer such as a non-dispersion type infrared gas analyzer.

[0002]

2. Description of the Related Art A non-dispersive infrared gas analyzer uses Lambert-Beer's law as a basic principle. The intensity of light incident on a cell is I ₀ , the cell length (effective cell length) is l,
Assuming that the absorption coefficient determined by the measurement wavelength and the component to be measured is k and the concentration of the component to be measured is C, the intensity I of the light transmitted through the cell is expressed by the formula I = I ₀ e ^-kCl (1) It

Therefore, regarding the relationship between the concentration of the measurement target component and the output in this type of gas analyzer, as shown in FIG. 5, the curve A representing the output shows a larger curve as the concentration of the measurement target component increases. Therefore, due to the linearity of the output characteristics, there is a certain limit to high concentration measurement, and it is difficult to accurately measure the same component from the low concentration region of ppm level to the high concentration region of% level. is there.

Therefore, in order to accurately measure the same component from a low concentration region to a high concentration region, one method is as follows.
As shown in FIG. 6 (A), a long-cell optical bench BL for a low-concentration range having a cell having a relatively long cell length (hereinafter referred to as a long cell) and an apparatus for measuring a high-concentration region are the same. Both the short cell optical bench BS for the high concentration range, which is provided with a cell having a relatively short cell length (hereinafter referred to as a short cell) as shown in FIG.

In FIG. 6A and FIG. 6B, 61
Is an infrared light source, 62 is a detector, 63 is an optical chopper, and 64 is an optical filter. Further, 65 and 66 are sample cells into which the sample gas S is introduced and supplied, and the cell length of one sample cell 65 is longer than that of the other sample cell 66. 67 and 68 are sample cells 65 and 6
A reference cell such as zero gas is sealed in a comparison cell provided according to the length of 6.

As another method, as shown in FIG. 7, a short cell 73 and a long cell 74 are optically arranged in series between an infrared light source 71 and a detector 72, while two short sides Solenoid valves 75 and 76 are connected in series, and this three-way solenoid valve 7
When measuring the low concentration region by appropriately opening and closing 5, 76, the sample gas S is supplied only to the long cell 74, and the purge gas P such as zero gas that does not absorb infrared light is supplied to the short cell 73. On the contrary, in the case of measuring the high concentration region, the sample gas S is supplied only to the short cell 73, the purge gas P is supplied to the long cell 74, and only one cell is used for the measurement. There is something.

[0007]

However, in the configuration shown in FIG. 6, the two optical benches BL and B are used.
Since S is provided, there is an inconvenience that the size of the device is increased and the cost is increased.

Further, in the configuration shown in FIG.
Unlike the one shown in FIG. 6, the measurement can be performed by a single optical bench, and the configuration of the device is slightly downsized and the cost is improved a little, but there are the following disadvantages. It was That is, in the configuration of FIG. 7, when either the low-concentration region or the high-concentration region is being measured, the purge gas P must be supplied to the cells that are not used for the measurement, and the purge gas other than the sample gas S must be supplied. Will be required.

Further, for example, when switching from the measurement in the low concentration region to the measurement in the high concentration region, it is necessary to switch and supply the purge gas, but this switching requires a considerable time, and the range is switched instantaneously. There is an inconvenience that you cannot do it. This means that, for example, the so-called dilution measurement mode in which exhaust gas from an automobile is diluted and measured is switched to the so-called direct measurement mode in which exhaust gas is directly measured without being diluted, or conversely, the direct measurement mode is diluted in the dilution measurement mode. It means that it is not possible to respond instantly when switching to.

The present invention has been made in consideration of the above matters, and is an inexpensive and compact gas analyzer capable of measuring the same component widely and accurately from a low concentration region to a high concentration region by a single optical bench. Is intended to provide.

[0011]

In order to achieve the above object, the gas analyzer of the present invention provides two cells having different cell lengths in parallel between a light source and a detector, and detects from the light source. An optical chopper is installed in the optical path between the cell and the sample gas so that the sample gas always flows in both cells, and only when measuring high concentrations, the light from the light source to the detector is blocked in the optical path on the cell side where the cell length is long. It is configured.

[0012]

In the gas analyzer having the above structure, for example, when measuring a low concentration region, the optical paths of the long cell and the short cell are not shielded by the shutter, but in order to switch from this state to the measurement of the high concentration region, The optical path on the cell side is blocked by a shutter. This allows only the light rays that have passed through the short cells to enter the detector and obtain the desired detector output.

[0013]

FIG. 1 shows an infrared gas analyzer according to the first embodiment of the present invention. In this figure, reference numerals 1 and 2 denote long cells and short cells to which the sample gas S is introduced and supplied, which are arranged in parallel with each other. Although not shown in detail, both ends of the cells 1 and 2 are sealed with window materials made of an infrared permeable material, and the inlets 1a and 2a and outlet 1b of the sample gas S are introduced. 2b is provided, and the sample gas inlets 1a and 2a are respectively connected to flow paths 4 and 5 in which the other end of the sample gas flow path 3 connected to a sample gas source (not shown) is branched into two. ing.

Numeral 6 is a space cell for equalizing the cell lengths of the long cell 1 side and the short cell 2 side, which is a window material which is arranged optically in series with the short cell 2 and whose both ends are made of an infrared transmitting material. In addition to being sealed, zero gas such as nitrogen gas and argon gas that does not absorb infrared rays is sealed inside. The cell length ratio of the space cell 6 to the short cell 2 is preferably large, and is, for example, about 10 to 500.

Reference numeral 7 is a light source portion provided on one window side of the cells 1 and 2, and is formed by integrating two infrared light sources 8 and 9 for irradiating the cells 1 and 2, respectively. 10 is an optical chopper provided between the infrared light sources 8 and 9 and the cells 1 and 2, and
It is rotationally driven by a motor (not shown). Reference numeral 11 is a condenser microphone type detector provided on the other window side of the cells 1 and 6, and two light receiving chambers 12 and 13 thereof are arranged so as to correspond to the cells 1 and 6, respectively. 1
Reference numerals 4 and 15 denote optical filters provided immediately in front of the light receiving chambers 12 and 13, for example, when the measurement target component is CO ₂ , C
It is composed of a multilayer interference filter that passes only infrared light in the absorption wavelength band of O ₂ .

A shutter 16 is provided in front of the entrance window of the light receiving chamber 12 corresponding to the long cell 1.
The optical path on the side is blocked or opened. That is,
The shutter 16 is slidable in the direction of the arrow UV in the figure, and by appropriately moving in the direction of the arrow U, the light receiving chamber 12 exits the infrared light source 8 and passes through the long cell 1. Enters the light receiving chamber 12 and enters a light receiving state, and when the light receiving state moves from the light receiving state in the direction of the arrow V to the state shown in FIG. 1, the infrared light is blocked from entering the light receiving chamber 12, 12 is shielded from light.

Reference numeral 17 denotes a preamplifier provided on the output side of the condenser microphone type detector 11, the output side of which is connected to a signal processing section (not shown).

Next, a case will be described in which, for example, the CO ₂ concentration in the exhaust gas of an automobile is measured using the infrared gas analyzer configured as described above.

First, when the CO ₂ concentration in the sample gas S is relatively low and is at the ppm level, the shutter 16
Is moved in the direction of arrow U to bring the two light receiving chambers 12 and 13 of the condenser microphone type detector 11 into a light receiving state, and the infrared light sources 8 and 9 irradiate the cells 1 and 2,
The optical chopper 10 is rotated at an appropriate frequency. In this state, when the sample gas S is introduced into the cells 1 and 2 at the same timing, the condenser microphone type detector 11
Outputs an AC signal indicating the CO ₂ concentration. Then, this AC signal is sent to a signal processing unit (not shown) via the preamplifier 17 and subjected to predetermined signal processing,
The CO ₂ concentration at that time is displayed on a concentration indicator (not shown).

In this case, since the cell length ratio of the space cell 6 to the short cell 2 is large, and therefore the short cell 2 is considerably shorter than the long cell 1, the absorption amount of CO ₂ in the short cell 2 can be almost ignored. It plays the role of a so-called reference cell. This has the advantage of a so-called double beam (two light sources). That is, since the two optical paths can be balanced by optical adjustment or the like, the vibrating membrane of the condenser microphone type detector 11 can be brought into a substantially neutral state, and therefore,
The background can be made smaller than that of a single beam (one cell and one light source), and it is possible to suppress the influence of the background when the signal amount is small in the low concentration region, and highly accurate measurement can be performed.

Next, when the CO ₂ concentration in the sample gas S is considerably high and is at the% level, the shutter 16 is set in the state as shown in FIG. 1 to correspond to the long cell 1 of the condenser microphone type detector 11. The light receiving chamber 12 is turned into a light blocking state, and only the light receiving chamber 13 corresponding to the short cell 2 is brought into a light receiving state. Then, by irradiating the cells 1 and 2 with the infrared light sources 8 and 9 and introducing the sample gas S into the cells 1 and 2 at the same timing while the optical chopper 10 is rotated at an appropriate frequency. , from the condenser microphone detector 11, is output AC signal representative of the CO ₂ concentration, as in the case described above, the CO ₂ concentration at that time is displayed on the concentration indicator.

In this case, since the short cell 2 is used, l in the above formula (1) becomes small, so that the high concentration region can be measured with high accuracy.

As will be understood from the above description, the sample gas S is supplied to both the long cell 1 and the short cell 2 in both the low concentration region measurement and the high concentration region measurement. In addition, the shutter 14 is moved in a predetermined direction only when measuring the high-density region, and the long cell 1
The light receiving chamber 13 corresponding to the optical path on the side is shielded, and the infrared light traveling from the infrared light source 8 to the light receiving chamber 13 is blocked. Therefore, when the CO ₂ concentration rises and suddenly rises to the% level for some reason in the mode where the low concentration region is being measured, the concentration indicator becomes so-called scale-over, and at this time, the range is changed and By performing the switching operation of the shutter 16, it is possible to instantaneously switch from the measurement in the low density region to the measurement in the high density region.

On the contrary to the above, even when the CO ₂ concentration is small and drops to the ppm level when measuring the high concentration region, the measurement from the high concentration region to the low concentration region is instantaneously performed in the same manner. Can be switched to.

That is, according to the present invention, when the output of the detector is being observed, even if the CO ₂ concentration greatly changes, it immediately follows this and switches the measurement mode to lower the measurement range. It is possible to switch from the high density region to the high density region or from the high density region to the low density region.

FIG. 2 shows an infrared gas analyzer according to the second embodiment of the present invention. In this embodiment, the light source unit 7 is a separate type light source in which the infrared light sources 8 and 9 are separated, and the optical chopper 10 is provided on the side of the cells 1 and 2 far from the infrared light sources 8 and 9. With this configuration, the space cell 6 can be omitted.

FIG. 3 shows an infrared gas analyzer according to the second embodiment of the present invention. In this embodiment, the long cell 1 and the short cell 2 are connected by the connection flow path 18 so that the sample gas S flows in the long cell 1 and the short cell 2 in series. According to this structure, the structure is remarkably simplified as compared with the conventional two-optical bench type. In addition,
The same thing as this embodiment can be applied to the configuration of FIG.

FIG. 4 shows an infrared gas analyzer according to the fourth embodiment of the present invention. In this embodiment, a solid-state detector such as a semiconductor detector is used as the detector. That is, in FIG. 4, 19 is a solid-state detector and 20 is a light guide block. The light guide block 20 guides infrared light that has passed through the long cell 1 and the short cell 2 so as to enter a single solid-state detector 19, and is a hollow body made of, for example, aluminum. The inner peripheral surface 20a is tapered from the cells 1 and 2 to the solid-state detector 19 and is mirror-finished. The shutter 16 is provided on the front surface of the light guide block 20 so as to block or open the optical path on the long cell 1 side.

The operation of the infrared gas analyzers of the above-mentioned second to fourth embodiments is the same as that of the first embodiment, so the explanation thereof will be omitted.

It goes without saying that the present invention can be applied not only to the infrared gas analyzer described above, but also to other gas analyzers such as an ultraviolet gas analyzer.

[0031]

As described above, according to the gas analyzer of the present invention, the same component can be widely and accurately measured from the low concentration region to the high concentration region by only one optical bench. Further, the structure is simplified, the size is reduced, and the manufacturing cost is significantly reduced. Also,
It is not necessary to flow purge gas or the like, and the running cost is reduced.

Further, in the gas analyzer of the present invention, even when the exhaust gas of an automobile is measured by diluting it, the exhaust gas is suddenly switched to a state where the exhaust gas is measured as it is. However, there is an excellent advantage that continuous measurement can be performed only by switching the range and switching the shutter position without interrupting the measurement.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the concentration of a measurement target component and the output in a gas analyzer.

FIG. 6 is a diagram for explaining a conventional technique.

FIG. 7 is a diagram for explaining a conventional technique.

[Explanation of symbols]

1, 2 ... Cell, 8, 9 ... Light source, 10 ... Optical chopper, 1
1, 19 ... Detector, S ... Sample gas.

Claims (1)

[Claims] 1. A cell having a different cell length between a light source and a detector.
Two cells are provided in parallel with each other, and an optical chopper is provided in the optical path between the light source and the detector so that the sample gas always flows in both cells. A gas analyzer characterized in that a light beam from a light source to a detector is blocked in the optical path.