Multi-component gas analyzer having cassette-type light path...

Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

Reexamination Certificate

active

06661011

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a multi-component gas analyzer having cassette-type light path system, and more particularly, relates to a unified and systemized gas analyzer that can analyze multi-component gases at the same time without any movable parts.
BACKGROUND OF THE INVENTION
The health problems, affected by modern living environment of human being and caused by the air pollution resulted from industrialization and dense population, have called wide attention in all walk of life. There are problems of how to analyze and judge the air quality, to what extent of the air is polluted, what kinds of air components are noxious to the health of human being, what the percentage of noxious gas components contained in the air. These problems depend on reliable and precise apparatus to analyze and to measure. Owing to the regulations and air pollution policies imposed by the government at all levels, relatively high demands are requested on the indoor and outdoor air quality as well as on the single and multi-component gas analyzers for analyzing and measuring the exhaust gases of automobiles and motorcycles. In general, the mandate gas components needed to be analyzed and measured are carbon dioxide (CO
2
), hydrocarbon (HC), and carbon mono-oxide (CO) etc. There are many ways of analyzing and measuring the gas components among the many gas analyzers, and currently, a non-dispersive infrared (NDIR) spectrometry is considered to be the most popular one.
NDIR is an optical absorption method based on the spectral selected principle. Basically, each kind of gas has one or multiple different Infrared (IR) absorption characteristics. In other word, the IR absorbance for each gas having a specific wave-length relates directly to the concentration of the gas. This kind of IR absorbance principle for a gas is called Beer-Lambert Law. As shown in
FIG. 1
, the IR absorbance for a gas is proportional to the concentration and the length of light path of the gas and is shown by the following formula
A=K×C×L
Where
A=IR absorbance that takes the logarithm of the ratio of the light intensity of the original incident light to the light intensity after the light is absorbed;
K=the IR absorption coefficient of the gas;
C=the concentration of the gas;
L=the length of light path through which the gas absorbs the IR.
As shown in
FIG. 1
, while ideally, the absorbance of the gas to IR is linearly proportional to the concentration of the gas, in reality, there is always a discrepancy, thereby, a nonlinear relationship exist between them. Moreover, the higher the optical density, the higher the extent of the discrepancy will be. The optical density denotes the product (C×L) of the gas concentration C and the length of the light path L. To lower the discrepancy so as to improve the measuring accuracy of the system, the designer of the system needs to select an optimum optical density. In other word, a gas having relatively high concentration or high absorbance needs to select a gas analyzer with relatively short light path, and vice versa. Consequently, the design of a gas analyzer that is capable of measuring multi-gas requires that the gas analyzer can select to use a multiple of lengths of light path so as to extend the measurable dynamic range of the apparatus.
Moreover, the frequency range of a specific gas is a constant value, thereby, a specific filter corresponding to the frequency range is required in order to filter and select an IR of a single specific frequency. Thereafter, a sensor is used to sense the variation of the light intensity of the IR. There is also a design option to have a detector combining sensors with filters.
The first prior art quoted by the invention is a multi-channel gas sample chamber disclosed by the U.S. Pat. No. 5,222,389. As shown in
FIG. 2
, the characteristic of the first prior art is that a plurality of detectors
206
,
208
, and
210
are provided respectively at their detector ports
212
,
214
, and
216
on the circumference
202
of a long cylindrical hollow light tube. In addition, a detector
218
is also provided at the end of the light exit. These detectors are used for measuring the multi-gas in response to the above-mentioned principle, that is, a gas having relatively high absorbance to IR needs to select a gas analyzer with relatively short light path. On the contrary, a gas having relatively low absorbance to IR needs to select a gas analyzer with relatively long light path.
However, the first prior art is unable to substantially attain the expected effect for the following reasons:
1. The IR, denoted by arrow heads as shown in
FIG. 2
, received at the detector
206
208
and
210
that are provided on the circumference
202
of the light tube are incident lights at skew angles rather than at right angles. Since optimum effect of gas measuring can be obtained if the incident lights are at right angles, thereby, the incident IR lights at skew angle will affect the accuracy of the output frequency of the filters in the detectors.
2. Since the incident lights transmitted into the detectors are at skew angles, the intensity of the incident lights is attenuated, consequently, the output signal
oise ratio is lower.
The second prior art quoted by the invention is a multiple component gas analyzer disclosed by the U.S. Pat. No. 4,914,719. As shown in
FIG. 3
, the multiple component gas analyzer includes an IR source
300
that can generate light beam; an optical absorption chamber
302
; three beam splitter
304
,
306
,
308
; four detectors
310
,
312
,
314
,
316
; four filters
320
,
322
,
324
,
326
. The light beam transmits through the optical absorption chamber
302
, and is then guided into the splitters
320
,
322
,
324
,
326
to become split light beams that are reflected by the splitters
320
,
322
,
324
,
326
and are deflected to the detectors
310
,
312
,
314
,
316
. One of the light beams that transmits directly all the way through the series of splitters
320
322
,
324
,
326
hits into the detector
316
through the filter
326
. Each of the filters
320
,
322
,
324
, and
326
corresponds respectively to a specific distinctive frequency range.
However, the second prior art can not substantially attain the effect of extending the measurable dynamic range of the apparatus. Since the length of the optical absorption chamber
302
is the only length that is available, there are no multiple lengths of light path to be selected in order to match the different gas concentration. Here are some of the examples showing the resulting situations.
1. According to the Beer-Lambert Law, the absorption intensity of the gas to the IR will be rather high if a relatively long light path is employed by a relatively high concentration of gas. This will result in the fact that the absorption of the gas to the IR is apt to attain saturation which makes the light intensity measured by the sensor rather weak.
2. On the other hand, according to the Beer-Lambert Law, the absorption intensity of the gas to the IR will be rather low if a relatively short light path is employed by a relatively low concentration of gas. This will result in the fact that the absorption of the gas to the IR is little which makes the variation of the light intensity measured by the sensor is rather limited. Consequently, the detecting ability of the analyzer is relatively low,
3. The above-mentioned extreme cases will result in the fact that the concentration range that can be measured by the gas analyzer is limited. In other word, a gas analyzer having relatively short light path and is adequate for measuring gases having relatively high concentration will make the range of measuring gases having relatively low concentration become narrow. On the contrary, a gas analyzer having relatively long light path and is adequate for measuring gases having relatively low concentration will make the range of measuring gases having relatively high concentration become narrow too.
The third prior art quoted by

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Multi-component gas analyzer having cassette-type light path... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Multi-component gas analyzer having cassette-type light path..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-component gas analyzer having cassette-type light path... will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-3127629

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.