JPH0429399Y2 - - Google Patents

Description

[Detailed description of the invention] Purpose of the invention [Field of industrial application] The invention relates to a gas analyzer for analyzing the concentration of exhaust gas from internal combustion engines, and in particular, to perform span calibration and calibration without using span gas. This article relates to a gas analyzer that uses infrared analysis that can perform

[Prior Art] Gas analyzers that use infrared analysis, such as analyzers for exhaust gas from automobile internal combustion engines, mainly use a sample cell into which the sample gas to be analyzed flows, and the concentration of gases such as carbon monoxide contained therein. A comparison cell filled with a comparison gas that is zero or a constant gas, a light source that irradiates each of these two cells with infrared rays, a chopper that intermits the infrared light that passes through the gas in these cells, and an intermittent of these two cells. It consists of a detector that compares the two signals and produces an output signal of gas concentration. When attempting to analyze the concentration of a sample gas using this type of exhaust gas analyzer, the relationship between the gas concentration and the output of the detector is calibrated in advance using multiple types of cylinder gases with known concentrations. It was necessary to create a calibration curve in advance, and it was also necessary to perform span calibration every time the exhaust gas concentration was analyzed. This calibration and span calibration requires many types of cylinder gases, and a large amount of man-hours are spent on managing these cylinder gases.

To solve this problem, instead of using cylinder gas during span calibration and calibration, a filter with the same infrared absorption rate as cylinder gas of known concentration is installed in the infrared light path to adjust the amount of infrared light. is being carried out.

The applicant has already improved some of the drawbacks of the above-mentioned conventional technology in Japanese Patent Application No. 60-230099. However, the following problems still remain to be solved.
In other words, the conventional filter-based span calibration or calibration uses an optical filter, so it is expensive, it is not easy to adjust the light attenuation rate, and it is difficult to obtain a desired light attenuation rate. In addition, there were problems with accuracy, such as the light attenuation rate changing when the surface of the optical filter became scratched or dirty.

[Problem to be solved by the invention] To solve this problem, the amount of infrared rays can be adjusted by providing multiple areas with different opening densities of through holes on a plate material that does not transmit infrared rays, that is, a light shielding plate, and then using the light shielding plate. It may be supported rotatably and rotated around the center of rotation so that infrared rays are applied to each area. However, at this time, even if the amount of infrared light applied to each area of the light shielding plate is constant, the total area of the through holes within the range to which infrared light is applied is not constant.
It is not possible to keep the amount of infrared light output constant. In other words, due to a slight shift in the resting position of the light shielding plate, the total area of the through holes within the range of infrared rays will change, and the amount of infrared light that is output will change. Preventing this shift requires precise adjustment, which requires extremely high precision equipment.

Structure of the invention Therefore, the present invention aims to solve the above problems and adopts the following structure.

[Means for solving the problem] In other words, the gist of the present invention is to allow one side of the infrared rays generated from the light source to be passed through and absorbed by the sample gas, and to allow the other side to be passed through and absorbed by a comparison gas with a zero concentration or a constant concentration. In a gas analyzer that analyzes the concentration of gas by detecting the energy difference between these two infrared light paths with a detector, a light-shielding plate that is made of a plate that does not transmit infrared rays and has multiple regions with different opening densities of through holes is rotated. By freely supporting the light shielding plate, each of the regions is provided so as to be able to advance freely in the infrared light path, and the shape of the through hole of each of the regions is formed in an arc shape centered on the rotation center of the light shielding plate. This gas analyzer is characterized by:

[Function] The gas analyzer of the present invention reduces the energy of infrared rays during span calibration or calibration by using a light-shielding plate that is made of a plate material that does not allow infrared rays to pass through and has multiple regions with different opening densities of through holes. There is. When this light-shielding plate is placed in the infrared light path, the infrared rays that are irradiated to areas without through holes will be completely blocked by the plate material, and will not reach the detector. All of the infrared rays irradiated to a certain part of the body reach the detector. In this way, the perforated light-shielding plate has a light-blocking effect similar to the light-reducing effect of an optical filter. Further, in the case of the light shielding plate used in the present invention, it is rotatably supported, and the through holes in each region having different opening densities are formed in an arc shape centered on the rotation center. Therefore, the aperture density can be easily changed by rotating this light shielding plate around the rotation center and switching the area.Moreover, the shape of the through hole is an arc centered around the rotation center. Therefore, a slight shift in the resting position of the light-shielding plate does not affect the total area of the through-hole within the range of infrared rays. In other words, a predetermined light shielding rate can be easily maintained without requiring precise adjustment.

[Example] Next, an example of the present invention will be described. The present invention is not limited to these, but includes various embodiments without departing from the gist thereof.

FIG. 2 shows a longitudinal cross-sectional view of essential parts of a gas analyzer 1 which is a first embodiment of the present invention. A sample cell 3 and a comparison cell 4 are provided at opposite positions below a pair of light sources 1 and 2 that stably and continuously emit infrared rays. A sample gas 5 whose gas concentration is to be measured is introduced into the sample cell 3, and a contact portion between the sample gas 5 and infrared rays is formed to cause absorption of infrared rays by components in the sample gas 5. The comparison cell 4 is filled with zero gas or a gas at a constant concentration, and a constant amount of infrared rays is always passed therethrough to be compared with the amount of infrared rays passing through the sample cell 3. These sample cells 3 and comparison cells 4 are housed in a constant temperature bath 6 and heated and kept within a range of about 150°C to 200°C.

A metal light shielding plate 7 is rotatably provided on the lower surface of the sample cell 3. As shown in FIG. 1, this light shielding plate 7 is formed into a disk shape, and a black coating film for preventing diffuse reflection of infrared rays is formed on the surface. On the same circumference from the center point of this light shielding plate 7, there are six circular areas 7a, 7b, 7c, with different light shielding rates.
7d, 7e, and 7f are arranged. This area 7
Area 7 of a, 7b, 7c, 7d, 7e, 7f
A simply has a hole, but the other regions 7b, 7c, 7d, 7e, and 7f have a circular region with an arc-shaped band K centered around the rotation center. A through hole H is opened. The size of this through hole H differs from region to region, and
The sizes decrease in the order of 7d, 7e, and 7f. Since the widths of the arcuate bands K around the center of rotation are all the same, the areas 7b, 7c, 7d, 7e, 7f
The aperture density decreases in this order. Further, the diameters of the regions 7a to 7f are formed larger than the inner diameter of the infrared radiation opening 3a of the sample cell 3.
Pitch circles a to 7f are arranged so as to pass through the center of the infrared radiation opening 3a of the sample cell 3. Furthermore, fixed magnets are provided on the periphery of the light shielding plate 7 at positions aligned with the regions 7a to 7f.
Magnets 8a, 8b, 8c, 8d, 8e, and 8f are attached to determine the stop positions corresponding to 8 m. In this way, the light shielding plate 7
is rotationally driven by a motor 9, so that desired areas 7a to 7f can be placed in the infrared radiation aperture 3a.

A chopper 10 is provided below the light shielding plate 7 to convert the infrared rays that have passed through the sample cell 3 and comparison cell 4 into intermittent light, and this chopper 10 is rotated at a constant speed by a chopper motor 11. The infrared rays that have passed through the sample cell 3 and comparison cell 4 and have been turned into intermittent light by the chopper 9 reach left and right light receiving chambers 12a and 12b formed in the detector 12, respectively. A movable film 12c is formed between the light receiving chambers 12a and 12b of this detector 12,
A pressure difference corresponding to the difference in energy absorbed by the light receiving chambers 12a and 12b is generated, and the movable film 12c is displaced. This displacement is electrically detected, amplified by the preamplifier 13, and taken out as an output signal.

Next, the operation of this embodiment will be explained. It is assumed that the comparison cell 4 is filled with zero gas. When performing zero calibration of the gas analyzer, flow zero gas into the sample cell 3, and use the magnet 8a on the periphery of the light shielding plate 7 and the fixed magnet 8m to accurately align the infrared radiation opening 3a of the sample cell 3 with the area 7a. Align. In this state, infrared rays are incident on the detector 12 without being blocked, and zero calibration is performed correctly. Next, when performing span calibration, zero gas is flowed into the sample cell 3 in the same way as when performing zero calibration. Then, the motor 9 is driven to rotate the light shielding plate 7 to align the region 7f with the radiation opening 3a, and the span calibration of the calibration curve is performed with the region 7f of the light shielding plate 7 accurately matching the infrared light path. Note that it is necessary to check the output value for this region 7f in advance using span gas, and the output value at this time becomes the calibration value. If more accurate calibration or a new calibration curve is required, then the regions 7e, 7d, 7c, and 7b arranged on the light shielding plate 7 with different light shielding rates are sequentially inserted into the optical path and detected. The output value is determined by the device 12 and the average value of the calibration values is obtained, or a calibration curve as shown in FIG. 3 is created. At this time, zero gas is always allowed to flow through the sample cell 3.

When measuring the sample gas 5, the sample gas 5 is caused to flow into the sample cell 3, and the output value is determined by the detector 12 with the area 7a of the light shielding plate 7 precisely aligned with the optical path. The gas concentration of the sample gas 5 is determined using the Brasion curve. During this time, the sample cell 3 and comparison cell 4 are constantly heated and kept at about 150° C. to 200° C. in a constant temperature bath 6.

According to this embodiment, each region 7a to 7f of the light shielding plate for span calibration and calibration can be accurately inserted into the infrared light path without any positional deviation. Furthermore, since the shape of the through-hole in each region with different opening density is formed in an arc shape centered on the rotation center of the light-shielding plate 7, a slight deviation in the resting position of the light-shielding plate 7 will be caused by the infrared rays hitting it. Does not affect the total area of through holes within the range. In other words, a predetermined light shielding rate can be easily maintained. In addition, since infrared rays can reach the detector 12 without being affected by scratches or dust on the light-shielding plate 7, accurate measurements can be made without using cylinder gas, and span calibration and calibration curve creation are possible. can also be done accurately. Furthermore, since a metal plate is simply used as the light shielding plate 7, the thickness is 1 mm or less, for example, several tens of μm.
~ several hundred microns is sufficient to maintain its own shape in the device, and the sample cell 3 and detector 12
The gap between the two can be made extremely narrow. Therefore, compared to conventional filters, there is less variation in the light shielding rate due to diffused reflection of light. Further, since the light shielding rate is determined simply by the aperture ratio of the through hole H, the light shielding rate can be easily adjusted by cutting the opening edge. Furthermore, since the sample cell 3 and the comparison cell 4 are heated and kept warm, they can be prevented from being contaminated by gas, eliminating drift due to contamination, and allowing accurate gas analysis.

FIG. 4 is a longitudinal sectional view showing a second embodiment of the present invention. In this figure, the same or equivalent parts as in the first embodiment shown in FIG. 2 are denoted by the same reference numerals and the explanation thereof will be omitted. This embodiment is a case in which the present invention is applied to a cross-flow type infrared gas analyzer. In the case of a cross-flow type, two sample cells 15 are separated by a rotary valve 14 that rotates at a constant cycle.
A sample gas and a zero gas are alternately flowed through a and 15b, and the output difference is detected by the detector 12 by utilizing the modulation effect caused by the absorption of infrared rays by the sample gas itself. In this case as well, calibration, zero calibration, and span calibration are performed using the light shielding plate 16 without using calibration gas. As shown in FIG. 5, this light shielding plate 16 consists of support plates 16a, 16b, and 16c stacked in multiple stages so as to open in a fan shape, and includes an area 17.
a, 17b, 17c are the respective support plates 16a, 16
b, 16c (region 17c is not shown). The shape of the through hole in this region is an arc centered on the rotation center. The light shielding plate 16 is operated in conjunction with the rotary valve 14 by the motor 9, centering on the fan-shaped main part.
It is designed to rotate 180 degrees. This light shielding plate 1
A magnet 18 is provided at a position on the periphery of the magnet 6 that is aligned with the center of the areas 17a, 17b, and 17c, respectively.
a, 18b, 18c are provided, and are attracted by the fixed magnet 19 to form areas 17a, 17b, 1.
7c is configured so that the center thereof is located precisely at the center of the infrared light path. This area 17a, 17
b and 17c are regions that block light to an amount equivalent to the amount of infrared light that reaches the detector 12 without being absorbed by the span gas, and the amount of light blocked is calibrated in advance with a span gas of a known concentration.

Next, the operation of this embodiment will be explained. At the time of zero calibration and sample measurement, areas 17a, 17b, 1
7c is removed from the two infrared light paths, and the infrared light from the light sources 1 and 2 is guided to the detector 12 without being blocked. On the other hand, when creating a calibration curve or calibrating span, sample cell 1
5a and 15b are in a zero gas state, and regions 17a and 15b are in a zero gas state.
Either one of 17b and 17c is rotary valve 1
By rotation of the light shielding plate 16 by the motor 9 synchronized with the sample cell 4 and suction between the magnet 19 and any one of the magnets 18a, 18b, and 18c, the samples are inserted correctly and alternately into the infrared light paths of the sample cells 15a and 15b. . Therefore, the infrared rays from the light sources 1 and 2 are guided to the detector 12 after being blocked by one of the regions 17a, 17b, and 17c to the same amount of light as when the span gas was flowing. In this case, when measuring the sample, two sample cells 15a, 1
Since the sample gas flows through both of the cells 5b and the contamination conditions between the cells are the same, there is no zero drift due to contamination of the cells, so a constant temperature bath for preventing contamination of the cells is not required. Other effects are similar to those of the first embodiment.

In this embodiment, the case where three regions are provided on the light shielding plate 16 has been described, but within the measurement concentration range, a plurality of regions selected from the regions 17a, 17b, and 17c are combined to form a light beam in the infrared light path. It is possible to obtain four or more desired light shielding rates by advancing the light shielding ratio.

Further, in the first and second embodiments, the cases where five and three light shielding regions are provided have been described, but the number of light shielding regions is not limited thereto.

Furthermore, in this embodiment, an example in which two infrared light sources are provided has been described, but it is also possible to form two or more infrared light paths with one light source by using a reflecting mirror, and furthermore, it is possible to form two or more infrared light paths. A similar effect can be obtained by providing a region above the sample cell so that it can freely advance so that the infrared rays that have been blocked pass through and are absorbed by the sample cell.

The light shielding plates used in each of the above embodiments are usually made of metal. For example, commonly used metals and alloys such as stainless steel, aluminum alloy, copper alloy, etc. are used. Other materials that block infrared rays, such as tough ceramic plates such as alumina, zirconia, and silicon nitride, can be used.

Furthermore, methods for forming through holes in a light shielding plate include etching, wire cutting, electrical discharge machining, laser machining, plasma machining, etc. for metals, and for ceramics, in addition to these methods, In this state, a through hole of a desired shape can be formed by punching or the like.

Effects of the Invention In the present invention, the light shielding rate is adjusted by the opening density of the through holes, so the structure is extremely simple and the cost is lower than that of an optical filter. Moreover, since the through-hole is formed in an arc shape centered on the rotation center of the light shielding plate, the aperture density can be easily adjusted by supporting the light shielding plate at this rotation center, rotating it, and switching the area. can be changed, and
Since the shape of the through hole is an arc centered on the rotation center, a slight shift in the resting position of the light shielding plate does not affect the total area of the through hole within the range of infrared rays. In this way, a predetermined light shielding rate can be easily maintained.

[Brief explanation of the drawing]

FIG. 1 is a front view showing an example of the light shielding plate of the present invention;
Fig. 2 is a longitudinal cross-sectional view showing the first embodiment of the gas analyzer according to the present invention, Fig. 3 is a graph showing an example of the calibration curve obtained by this embodiment, and Fig. 4 is a graph showing the first embodiment of the gas analyzer according to the present invention. FIG. 5 is a longitudinal sectional view showing a second embodiment of the gas analyzer, and FIG. 5 is a front view showing the light shielding plate portion of FIG. 4. 1, 2... Light source, 3, 15a, 15b... Sample cell, 4... Comparison cell, 7, 16... Light shielding plate, 12... Detector, H... Through hole.

Claims (1)

[Claim for Utility Model Registration] One of the infrared rays generated from a light source is passed through and absorbed by a sample gas, the other is passed through and absorbed by a comparison gas of zero concentration or a constant concentration, and the energy difference between these two infrared light paths is detected by a detector. In a gas analyzer that detects and analyzes the concentration of gas, a light-shielding plate having a plurality of regions with different opening densities of through-holes is supported on a plate material that does not transmit infrared rays so as to be rotatable. A gas analyzer characterized in that each region is provided so as to be freely advanced, and the through hole in each region is formed in an arc shape centered on the center of rotation of the light shielding plate.