US3727050A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Gas analyzer
Assignee: OCA APPLIED OPTICS Inc A CORP OF
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Filing: 1971-09-20
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Granted: 1973-04-10
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Expires: 1991-09-20
Abstract
Abstract A gas analyzer for determining the presence and proportional amount of gases of interest in a sample, such as a sample of automobile exhaust gas, utilizes a very thin cell having a window in one side to admit chopped radiation, such as infrared radiation of a wavelength coinciding with an absorption band of the gas of interest. Heat absorbed from the applied radiation by a gas component of interest increases its temperature and hence increases the pressure of the sample. This pressure increase is measured to determine the proportional amount of a gas of interest present by means of the modulated output of a lowfrequency microphone associated with the cell. The thickness of the cell is from about 0.1 mm. to about 4 mm.; with a cell this thin the heat loss to the window and to the back wall is so rapid that a slow chopping rate can be applied such that absorption of radiation by the gas of interest approaches a steady state during the sample illuminating portion of the chopping cycle. The measured concentration is thus independent of small variations in the chopping rate. Even a very small quantity of a gas of interest is measured rapidly and accurately. Specificity is facilitated by initially reducing the pressure of the sample in the cell to a fraction of an atmosphere, for example, one tenth. When the pressure is thus reduced, a method is provided for selecting a new cell thickness or chopping rate such that there is little loss in sensitivity at the reduced pressure. This invention relates to gas analyzers for analyzing gas mixtures, and is of the general type in which absorption of radiation by a component of interest is detected and measured as means for determining the presence of such component and measuring the proportional amount present. In particular the invention is an analyzer which is particularly adapted for rapidly and accurately detecting and measuring very low concentrations of gases of interest which may be present in the mixture. The gas analyzer of this invention is simple to operate and economical to manufacture. It is, for example, particularly suited for quick, on the spot analysis of automobile exhaust gases for reliably and inexpensively checking compliance with air pollution control standards for automobile exhaust emissions.
Inventors
- 👤 E Kerr
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 22:36
CPC Classifications
G; G01; G01N; G01N21/00; G01N21/17; G01N21/25; G01N21/31; G01N21/35; G01N21/37; G01N21/01; G01N21/03; G01N21/05; G01N21/1702; G01N2021/0346
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
321 words
A gas analyzer for determining the proportional amount of a gas of interest in a sample comprising a thin cell having an inlet and an outlet for a gas sample, means for at least partially closing the inlet, means for at least partially closing the outlet, said cell having a window in one side wall for admitting radiation of wavelength coinciding with the absorption band of a gas of interest, the area of said window being the major portion of the area of said side wall, the interior diameter of the cell being substantially greater than the interior thickness of the cell from the window to the opposite side wall, said thickness being from about 0.1 mm. to about 4 mm., a source of radiation of a wavelength coinciding with an absorption band of said gas of interest positioned for applying radiation through said window to a sample gas in the cell, the size and position of the radiation source in relation to the area of the window being such that radiation from the source passes into the cell over the major portion of the area of the window, cyclic means for blocking the passage of radiation into the cell from the source during a portion of each cycle thereof, and means responsive to a change in the physical conditions of sample gas in the cell due to absorption of radiation by said gas of interest as means for determining the proportion of said gas of interest in the sample, the frequency of said cyclic means being selectable with regard to the expected thermal conductivity, temperature, and pressure of the sample gas in order that the changes in temperature and pressure of the sample gas due to absorption of said radiation by said gas of interest in the cell at least nearly reach a steady state in the portion of each cycle thereof during which said radiation passes into the cell.
Claim 2
Dependent Claim
321 words
A gas analyzer for determining the proportional amount of a gas of interest in a sample comprising a thin cell having an inlet and an outlet for a gas sample, means for at least partially closing the inlet, means for at least partially closing the outlet, said cell having a window in one side wall for admitting radiation of wavelength coinciding with the absorption band of a gas of interest, the area of said window being the major portion of the area of said side wall, the interior diameter of the cell being substantially greater than the interior thickness of the cell from the window to the opposite side wall, said thickness being from about 0.1 mm. to about 4 mm., a source of radiation of a wavelength coinciding with an absorption band of said gas of interest positioned for applying radiation through said window to a sample gas in the cell, the size and position of the radiation source in relation to the area of the window being such that radiation from the source passes into the cell over the major portion of the area of the window, cyclic means for blocking the passage of radiation into the cell from the source during a portion of each cycle thereof, and means responsive to a change in the physical conditions of sample gas in the cell due to absorption of radiation by said gas of interest as means for determining the proportion of said gas of interest in the sample, the frequency of said cyclic means being selectable with regard to the expected thermal conductivity, temperature, and pressure of the sample gas in order that the changes in temperature and pressure of the sample gas due to absorption of said radiation by said gas of interest in the cell at least nearly reach a steady state in the portion of each cycle thereof during which said radiation passes into the cell.
Claim 3
Dependent Claim
35 words
The gas analyzer of claim 1 in which said means responsive to a change in the physical conditions of sample gas in the cell is means for measuring change in the pressure of the sample.
Claim 4
Dependent Claim
24 words
The gas analyzer of claim 2 including means for reducing the pressure of a sample gas in the cell to less than an atmosphere.
Claim 5
Dependent Claim
25 words
The gas analyzer of claim 1 in which the ratio of the interior diameter of the cell to its interior thickness is greater than 3.
Claim 6
Dependent Claim
18 words
The gas analyzer of claim 4 in which said interior thickness of the cell is about 2 mm.
Claim 7
Dependent Claim
35 words
The gas analyzer of claim 1 which includes a narrow band-pass filter between said radiation source and the cell for passing only a radiation wavelength coinciding with an absorption band of said gas of interest.
Claim 8
Dependent Claim
16 words
The gas analyzer of claim 6 in which said source is a source of infrared radiation.
Claim 9
Dependent Claim
77 words
The gas analyzer of claim 1 in which the inlet and thE outlet of the cell each includes capillary leak means for reducing the inlet and outlet flow to an amount such that changes in temperature and pressure due to absorption of said radiation by sample gas in the cell at least nearly reach a steady state during that portion of one cycle of the cyclic radiation blocking means during which said radiation passes into the cell.
Claim 10
Dependent Claim
112 words
The gas analyzer of claim 1 in which said means for determining the proportion of a gas of interest in a sample in the cell comprises a capacitance microphone which includes a capacitor formed by two electrically conductive surfaces defining walls of a compartment and being movable relative to each by changes in the pressure of a gas in the compartment so as to effect a proportional change of capacitance, said compartment being connected to the cell to produce a change in capacitance in proportion to changes in the pressure of the sample gas in the cell, means to sense said change in capacitance, and means to measure such change in capacitance.
Claim 11
Dependent Claim
27 words
The gas analyzer of claim 1 in which the interior surface of the cell side wall opposite the window is a reflective surface for reflecting said radiation.
Claim 12
Dependent Claim
223 words
The gas analyzer of claim 1 including a capacitance microphone connected for determining the proportion of a gas of interest in a sample in the cell, said capacitance microphone comprising a chamber separated into a first and a second compartment by a flexible electrically conductive membrane and a pair of capacitor plates respectively in the compartments, inlet means for introducing a sample gas into the first compartment, said first compartment having a closable gas outlet, conduit means between the second compartment and the interior of the cell for sample gas in the cell to flow into the second compartment and for a change in pressure in gas in the cell to be communicated to gas in the second compartment within the portion of one cycle of said cyclic means during which said radiation passes into the cell, means for initially equalizing the gas pressure in the first compartment with the gas pressure in the cell and in the second compartment before application of said radiation to gas within the cell, means connected to sense the changes of capacity respectively of said capacitor plates and said membrane by deflection of the membrane, means connected to sum said changes of capacity, means connected to produce electrical signals proportional to the sum of said changes of capacity, and means to measure the value of said signals.
Claim 13
Dependent Claim
177 words
The gas analyzer of claim 11 in which said means for initially equalizing the gas pressure in the first compartment with the gas pressure in the cell and in the second compartment comprises a capillary leak connection between the interior of the cell and the second compartment, the time constant of said capillary leak being relatively long in comparison with the time of the portion of a cycle of said cyclic means during which said radiation passes into the cell. 13. The gas analyzer of claim 11 including an oscillator connected to apply a modulated electric signal to said flexible membrane, a summing amplifier connected to said capacitor plates for summing the changes of capacity respectively of the capacitor plates and the membrane and for producing output signals proportional to such sum, a first synchronous demodulator connected to receive the modulated signal from the oscillator and the output signals from the summing amplifier for producing output signals proportional to the sum of said changes in capacity, and means for measuring the output signals of the synchronous demodulator.
Claim 14
Dependent Claim
82 words
The gas analyzer of claim 13 in which said means for measuring the synchronous demodulator output signals comprises means producing cyclic output electric signals in timed correspondence with the cyclic operation of said cyclic radiation-blocking means, a second demodulator connected to receive said cyclic output signals and the output signals from said first demodulator for smOothing out and accentuating the output signals from the first demodulator, and a meter connected to measure said smoothed out and accentuated signals from the second demodulator.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-04-09 | 1976-10-09 | 1977-04-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-04-09 | 1980-10-09 | 1981-04-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-04-09 | 1984-10-09 | 1985-04-10 | $7700.00 | Window Closed / Lapsed |