JPS6288943A - Exhaust gas analyzer - Google Patents

Abstract

PURPOSE:To perform accurate span calibration by providing plural dimming filters which differ in dimming rate on a sample-gas passing infrared-light optical path so that they move on and off the optical path freely and also providing a magnet which stops the dimming filter on the optical path. CONSTITUTION:A sample cell 3 and a comparison cell 4 are provided under light sources 1 and 2 which radiates infrared rays. Sample gas 5 is admitted into the cell 3 to form the contacting part between the gas 5 and infrared rays. The cell 3 is put in a thermostatic chamber 6. A dimming filter plate 7 is provided rotatably on the reverse surface of the cell 3, and this filter 7 has holes 7a at positions of the same radius and is provided with the filters 7b-7f which differ in dimming rate. Magnets 8a-8f which determine a stop position corresponding to a fixed magnet 8m are fitted at positions on the outer periphery of the filter plate 7 where the filters 7b-7f are matched. Thus, accurate span calibration is performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust gas analyzer that analyzes the concentration of exhaust gas from internal combustion engines, etc., and particularly relates to an infrared analyzer that can perform span calibration without using span gas. This article relates to an exhaust gas analyzer using the method.

[Prior art]

Exhaust gas analyzers that use infrared analysis mainly use
A sample cell into which the sample gas to be analyzed flows, a comparison cell filled with a comparison gas containing zero or constant gas concentration such as carbon monoxide, and these two cells are each irradiated with infrared rays. It consists of a light source, a chopper that intermittents the infrared light that has passed through the gas in these cells, and a detector that compares these two intermittent signals and outputs an output signal representing the gas concentration. When attempting to analyze the concentration of a sample gas using this type of exhaust gas analyzer, calibrate the relationship between the gas concentration and the output of the detector using multiple types of cylinder gases with known concentrations in advance. This so-called span calibration requires a wide variety of cylinder gases, and a large amount of man-hours are spent on managing these cylinder gases.

To solve this problem, we do not use cylinder gas when calibrating the span, but instead set the infrared light path in such a way that it matches the amount of infrared light that reaches the detector without being absorbed by the gas when cylinder gas of a known concentration is flowed. A light shielding plate is provided to adjust the amount of infrared light. However, according to the conventional span calibration using this shielding plate method,
Since the method for inserting the light shielding plates into the infrared light path was to slide one plate at a time, the insertion position would shift, making accurate span calibration impossible.Also, depending on the light shielding plate, the infrared rays would not be uniformly irradiated onto the detector, so it was difficult to calibrate. There was a problem that the tion curve became inaccurate.

Furthermore, it has been pointed out that the amount of infrared light changes due to dirt on the sample cell, causing problems in terms of accurate analysis.

[Problem that the invention seeks to solve]

As mentioned above, the present invention solves problems that occur during span calibration in conventional exhaust gas analyzers, such as misalignment of the insertion position of the light-shielding plate, non-uniformity of infrared irradiation, and staining of the sample cell. It is an object of the present invention to provide an exhaust gas analyzer using infrared rays that can solve the problem of calibration errors and perform accurate span calibration without using span gas.

[Means for solving problems]

In the present invention, one of the infrared rays generated from a light source is absorbed by a sample gas, and the other is absorbed by a comparison gas with zero concentration or a constant concentration, and the energy difference between these two infrared light paths is detected by a detector to determine the concentration of exhaust gas. In an exhaust gas analyzer that performs analysis, a plurality of neutral density filters with different attenuation rates are rotated by a motor in the infrared light path passing through the sample gas to attenuate the infrared light to the same amount of light as when a span gas is passed. A filter is disposed concentrically on a circular plate or on a plurality of support plates stacked on top of each other, and is provided so as to be able to freely advance into the infrared light path, and to ensure accurate stopping of the neutral density filter in the infrared light path. This exhaust gas analyzer is characterized by being equipped with a magnet, and the sample gas and comparison gas cells are housed in a thermostatic chamber to prevent the sample cells from becoming contaminated.

[Effect]

According to the above configuration, span calibration of the exhaust gas analyzer can be performed without using span gas. In addition, since the filter can be placed in the correct position in the infrared light path, the detector can be uniformly irradiated with infrared rays, and the sample cell does not leak, making it possible to obtain an accurate concentration-output calibration curve. I can do it.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

(First Embodiment) FIG. 1 is a longitudinal sectional view showing a first embodiment of an exhaust gas analyzer according to 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 determined 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 are heated and kept at a temperature within the range of approximately 15°C to 200°C. A neutral density filter plate 7 is rotatably provided on the lower surface of the sample cell 3. This attenuation filter plate 7 is formed into a disk shape as shown in FIG. 2, and has a hole 7a and five filters 7b, 7ct7d with different attenuation rates concentrically arranged.
, 7 e17f are provided. Magnets 8a, 8b, 8c, and 8d are located on the outer periphery of the neutral density filter plate 7 at positions aligned with the holes 7a and the filters 7b to 7f, respectively, to determine the stop positions corresponding to the fixed magnets 8m.
, 8e, and 8f are attached.

The diameters of the holes 7a and the filters 7b to 7f are larger than the inner diameter of the infrared radiation opening 3a of the sample cell 3. The neutral density filter plate 7 is rotatably driven by a motor 9, and is arranged so that the pitch circles of the holes 7a and the filters 7b to 7f pass through the center of the infrared radiation opening 3a of the sample cell 3. ing. 10 is a chopper that converts the infrared rays that have passed through the sample cell 3 and comparison cell 4 into intermittent light; the chopper motor 11
is rotated at a constant speed by 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 membrane 12c is formed between the light receiving chambers 12a and 12b of this detector 12, and a pressure difference corresponding to the difference in energy absorbed by the light receiving chambers 12a and 12b is generated, causing displacement in the movable membrane 12c. give. This displacement is electrically detected and amplified by a preamplifier 13 to obtain 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 exhaust gas analyzer, zero gas is flowed into the sample cell 3 using the magnet 8a on the outer periphery of the neutral density filter plate 7 and the fixed magnet 8m.

The infrared radiation opening 3a of the sample cell 3 and the hole 7a are accurately aligned. In this state, the infrared light path is accurately incident on the detector 12, and zero calibration is performed correctly. When performing span calibration next, zero gas is flowed into the sample cell 3 in the same manner as when performing zero calibration. Then, span calibration is performed with the filter 7b of the neutral density filter plate 7 precisely aligned with the infrared light path. Note that the output value of this filter 7b must be confirmed in advance using span gas, and the output value at this time becomes the calibration value. Next, the filters 7c, 7d, 7e, and 7f arranged on the neutral density filter plate 7 with different extinction ratios are similarly inserted into the optical path one after another, and the output value is determined by the detector, and the calibration is performed as shown in FIG. Create a tion curve. At this time, sample cell 3
Always keep zero gas flowing through.

When measuring the sample gas 5, the sample gas 5 is flowed into the sample cell 3, and the output value is determined by the detector 12 with the hole 7a of the neutral density filter plate 7 precisely aligned with the optical path, as shown in FIG. The gas concentration of the sample gas 5 is determined using the calibration curve shown. During this time, sample cell 3
And the comparative cell 4 is always kept at 150' to 20' by the constant temperature bath 6.
It is heated and kept at around 0°C.

According to this embodiment, the filter for span calibration can be accurately inserted into the infrared light path without positional deviation.

Furthermore, since the infrared rays can reach the detector 12 uniformly, span calibration can be performed with high accuracy. Similarly, calibration curves can be created accurately without using cylinder gas. Furthermore, since sample cell 3 and comparison cell 4 are heated and kept warm,
It is possible to prevent gas contamination, eliminate drift due to contamination, and enable accurate exhaust gas analysis.

(Second example) 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. 1 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 infrared exhaust gas analyzer.

In the case of a cross-flow set, sample gas and zero gas are alternately flowed into two sample cells 15 and 16 by a rotary valve 14 that rotates at a constant cycle.

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, zero calibration and span calibration are performed using the neutral density filter plate 17 without using a calibration gas. As shown in FIG. 5, this neutral density filter plate 17 has filters 17a, 17b, and 17c provided on support plates stacked in multiple stages so as to open in a fan shape.

The attenuation filter plate 17 is rotated 180 degrees by the motor 9 about the fan-shaped latch in conjunction with the rotary valve 14. The filters l7a, ], 7b, on the outer periphery of this neutral density filter plate 17,
Magnets 18a, 18b, and L8c are provided at positions aligned with the center of L7c, respectively, and are attracted by the fixed magnet 19 so that the filters 17a, 17b, and 1
7c is configured so that its center is located precisely at the center of the infrared light path.

This filter 17a is a filter that attenuates the light amount to the same amount as the amount of infrared light that is absorbed by the span gas and reaches the infrared detector 12, and the amount of attenuation is calibrated in advance using the span gas having a known concentration.

Next, the operation of this embodiment will be explained. At the time of zero calibration and when sample a1 is set, filters 17a and 17b are used.

17c is removed from the two infrared light paths, and light sources 1,
The infrared rays from 2 are guided to the detector 12 without being attenuated. On the other hand, during span calibration, the sample cell 15,
16 is in a zero gas state, and the filter 17a is a dark filter plate 1 driven by a motor 9 synchronized with the rotary valve 14.
By the rotation of 7 and the attraction of magnets 18a and 19,
They are correctly inserted alternately into the infrared light paths of sample cells 15 and 16. Therefore, the infrared rays from light sources 1 and 2 are filtered by the filter 1.
After the light is attenuated to the same amount of light as when the span gas was flowed through 7a, it is guided to the detector 12. In this case, during sample measurement, the sample gas flows through both of the two sample cells 15° and 16, and the dirty state between the cells is the same, so there is no zero drift due to cell dirt. A constant temperature bath is not required. Other effects are the same as in the first embodiment6. In this embodiment, the case where three filters 17a, 17b, and 17c are provided on the neutral density filter plate 17 has been described, but the A predetermined light attenuation rate can be obtained by combining a plurality of filters with different light rates and advancing them into the infrared light path.Furthermore, in the first and second embodiments, five and three light density filters are provided. I explained the case.

Naturally, the number of neutral density filters is not limited to these.

Furthermore, in this embodiment, an example in which two infrared light sources are provided has been described, but as shown in FIG. It is also possible to arrange the neutral density filter on a fan-shaped support plate, for example, as shown in FIG. , 27 can be passed through and absorbed, similar effects can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, in an exhaust gas analyzer using a non-dispersive double beam infrared analysis method, a plurality of sensors having different attenuation rates are installed in the infrared light path after passing through the sample gas before the detector. Since a neutral density filter plate provided with a filter is provided, accurate span calibration can be performed without using a calibration gas.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing an embodiment of the exhaust gas analyzer according to the present invention, FIG. 2 is a plan view showing the neutral density filter plate of FIG. 1, and FIG. A graph showing an example of a calibration curve. FIG. 4 is a schematic vertical sectional view showing another embodiment of the present invention, and FIG.
The figure includes an ilZ diagram showing the neutral density filter section in Figure 4.
FIG. 6 and FIG. 7 are diagrams showing other embodiments. 1.2...Light source 3.4. ．． 15. 26, 27.28... Sample cell 5... Sample gas 6... Constant temperature chamber 7.17.29... Neutral density filter support plates 7b, 7c,
7d, 7e, 7f, 16a, 16b, 16c
...Night filter 8.18, 19.30...Magnet 12...Detector 9...Motor 20...Reflection mirror

Claims (4)

[Claims] (1) One of the infrared rays generated from the light source is passed through and absorbed by a sample gas, the other is passed through and absorbed by a comparison gas with zero concentration or a constant concentration, and the energy difference between these two infrared light paths is detected by a detector, and the exhaust gas In an exhaust gas analyzer that analyzes the concentration of the infrared rays, a plurality of neutral density filters with different attenuation rates are installed in the infrared light path passing through the sample gas to attenuate the infrared rays to the same amount of light as when a span gas is passed through the infrared rays. An exhaust gas analyzer, characterized in that a magnet is provided so as to be freely advanced into the optical path and to ensure accurate stopping of the neutral density filter in the infrared optical path. (2) The exhaust gas analyzer according to claim 1, wherein the neutral density filter is arranged concentrically on a disc driven by a motor. (3) A plurality of the attenuation filters are disposed on a stacked support plate, and one or more attenuation filters are advanced into the infrared light path to obtain a predetermined attenuation rate. An exhaust gas analyzer according to claim 1. (4) The exhaust gas analyzer according to any one of claims 1 to 3, wherein the sample gas and comparison gas cells are housed in a thermostatic chamber.