CA2131865C - Optical sensing apparatus for remotely measuring exhaust gas composition of moving motor vehicles - Google Patents
Optical sensing apparatus for remotely measuring exhaust gas composition of moving motor vehicles Download PDFInfo
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Abstract
A light source (12) radiates an infrared beam (14) through the exhaust plume (22) of a motor vehicle (20) which passes in front of the source (12). A photosensor unit (18) includes a plurality of photodetectors (42,44,-46,48) which are spaced closely adjacent to each other and simultaneously sense the beam (14) after it propagates through the plume (22). An optical beam homogenizes or integrator (36) disposed between the plume (22) and the photosensor unit (18) causes the light incident on the photodetectors (42,44,46,48) to have uniform intensity.
The photodetectors (42,44,46,48) are sensitive to different wavelengths corresponding to spectral absorption peaks of constituents of the composition of the plume (22), including carbon monoxide (CO), carbon dioxide (CO2) and hydrocarbon (HC). A computer (24) computes the composition of the plume (22) as the percentages of the constituents based on the sensed transmittances of the respective wavelengths through the plume (22). A video camera (26) produces a video image of the vehicle license plate (28), and a combiner (24,32) causes the video image to be displayed on a video monitor (30) and recorded on a video recorder (32) together with the plume composition data.
The photodetectors (42,44,46,48) are sensitive to different wavelengths corresponding to spectral absorption peaks of constituents of the composition of the plume (22), including carbon monoxide (CO), carbon dioxide (CO2) and hydrocarbon (HC). A computer (24) computes the composition of the plume (22) as the percentages of the constituents based on the sensed transmittances of the respective wavelengths through the plume (22). A video camera (26) produces a video image of the vehicle license plate (28), and a combiner (24,32) causes the video image to be displayed on a video monitor (30) and recorded on a video recorder (32) together with the plume composition data.
Description
2~3 ~e65 OPTICAL SENSING APPARATUS FOR REMOTELY MEASURING EXHAUST GAS
COMPOSITION OF MOVING MOTOR VEHICLES
BACKGROUND OF 'rHE INVENTION
Field of the Invention The present invention generally relates to the monitoring of e:nvirona~ental pollution, and more specifical ly to an aptic<~1 sensing apparatus for remotely monitoring the exhaust gas composition of moving motor vehicles and emissions from industrial and other sources.
Description of the Related Art Environmental pollution is a serious problem which is especially acute in urban areas. A major cause of this pollution is exhaust emissions from automotive vehicles.
Official ;standards have been set for regulating the allowable amounts oi: pollutant species in automobile exhausts, and in some areas, periodic inspections or "smog checks" are required to ensure that vehicles meet these standards.
However, 'there are still large numbers of vehicles operating on public highways which fail to comply with the standards. It has also been determined that a dispropor tionately large amount of pollution is generated by a relatively small number of vehicles.
Highly polluting vehicles can operate even in areas in which periodic emission inspections are required. Some 2~3 ~e65 older vehicles and special types of vehicles are exempt from inspections.
Anti-pollution devices which are required equipment on newer vehicles accomplish their intended purpose of reducing pollution in the vehicle exhaust to within prescribed levels. However, it is perceived by some vehicle owners that antipollution equipment reduces engine performance.
For this reason, unscrupulous vehicle owners with mechanical ex~>ertise can perform whatever servicing is necessary to place their vehicles in condition to pass required inspections, and subsequently remove anti-pollu tion devices a:nd/or retune the vehicles with an attendant increase in pollutant emissions for normal use.
An anti-pollution program which depends entirely on mandatory periodic inspections performed at fixed facili-ties is therefore inadequate. It is necessary to identify vehicles which. are actually operating in violation of prescribed emi:asion standards, and either require them to be placed in conformance with the standards or be removed from operation..
A system for remote sensing of automotive exhaust emissions is described in an article entitled "ANALYTICAL
APPROACH - IR :Long-Path Photometry: A remote Sensing Tool for Automotive Emissions", by G. Bishop et al, in Analyti-cal Chemistry 7.989, 6:L, 617A. An infrared beam is trans-mitted through the exhaust plume of an automotive vehicle to a sensor unit which includes a beam splitter which spl its the beam into .a carbon dioxide ( C02) channel and a carbon monoxide: (CO) channel.
The beam i.n the COZ channel passes through a bandpass filter which isolates the spectral absorption region of carbon dioxide and is incident on a photovoltaic detector.
The beam in the CO channel passes through a rotating gas filter wheel, cne-half' of which contains a CO and hydrogen 2t3 ~8s~
COMPOSITION OF MOVING MOTOR VEHICLES
BACKGROUND OF 'rHE INVENTION
Field of the Invention The present invention generally relates to the monitoring of e:nvirona~ental pollution, and more specifical ly to an aptic<~1 sensing apparatus for remotely monitoring the exhaust gas composition of moving motor vehicles and emissions from industrial and other sources.
Description of the Related Art Environmental pollution is a serious problem which is especially acute in urban areas. A major cause of this pollution is exhaust emissions from automotive vehicles.
Official ;standards have been set for regulating the allowable amounts oi: pollutant species in automobile exhausts, and in some areas, periodic inspections or "smog checks" are required to ensure that vehicles meet these standards.
However, 'there are still large numbers of vehicles operating on public highways which fail to comply with the standards. It has also been determined that a dispropor tionately large amount of pollution is generated by a relatively small number of vehicles.
Highly polluting vehicles can operate even in areas in which periodic emission inspections are required. Some 2~3 ~e65 older vehicles and special types of vehicles are exempt from inspections.
Anti-pollution devices which are required equipment on newer vehicles accomplish their intended purpose of reducing pollution in the vehicle exhaust to within prescribed levels. However, it is perceived by some vehicle owners that antipollution equipment reduces engine performance.
For this reason, unscrupulous vehicle owners with mechanical ex~>ertise can perform whatever servicing is necessary to place their vehicles in condition to pass required inspections, and subsequently remove anti-pollu tion devices a:nd/or retune the vehicles with an attendant increase in pollutant emissions for normal use.
An anti-pollution program which depends entirely on mandatory periodic inspections performed at fixed facili-ties is therefore inadequate. It is necessary to identify vehicles which. are actually operating in violation of prescribed emi:asion standards, and either require them to be placed in conformance with the standards or be removed from operation..
A system for remote sensing of automotive exhaust emissions is described in an article entitled "ANALYTICAL
APPROACH - IR :Long-Path Photometry: A remote Sensing Tool for Automotive Emissions", by G. Bishop et al, in Analyti-cal Chemistry 7.989, 6:L, 617A. An infrared beam is trans-mitted through the exhaust plume of an automotive vehicle to a sensor unit which includes a beam splitter which spl its the beam into .a carbon dioxide ( C02) channel and a carbon monoxide: (CO) channel.
The beam i.n the COZ channel passes through a bandpass filter which isolates the spectral absorption region of carbon dioxide and is incident on a photovoltaic detector.
The beam in the CO channel passes through a rotating gas filter wheel, cne-half' of which contains a CO and hydrogen 2t3 ~8s~
(H2) mixture, a.nd the other half of which contains nitrogen (NZ) . From the filter wheel, the beam in the CO channel passes through another bandpass filter which isolates the spectral absorption region of carbon monoxide and is incident on another photovoltaic detector.
The outpui~ signals of the detectors vary in accordance with the transmittance of the vehicle exhaust plume at the respective wavelengths, and thereby the concentrations of CO and C02 in the plume. The CO/H2 portion of the filter l0 wheel provides a reference output, whereas the NZ portion provides a carbon monoxide output.
Baseline sensor outputs are obtained with no vehicle passing through the beam, and with the beam blocked by a vehicle prior to sensing of the plume. These values are used as referenceslfor calibrating the outputs of the detectors when the plume is actually sensed. The detector outputs, which. correspond to the transmittances at the respective wavelengths, are then processed in accordance with predetermined functions to determine the relative percentages of COz and CO in the vehicle exhaust plume.
This system is capable of sensing the exhaust gas composition of moving vehicles, and can be used to identify polluting vehicles fo:r enforcement purposes. However, it suffers from cs~rtain drawbacks.
Precise alignment: is required to ensure that the beams in the two paths are incident on the detectors in an identical manner. A small misalignment error can seriously degrade the measurement accuracy. The two photovoltaic detectors are remote from each other, and require separate cooling units for temperature regulation. A small differ-ence in temperature, as well as small mismatches in other characteristic; of the detectors, can also seriously degrade the measurement accuracy.
The rotating filter wheel is a mechanical unit which is expensive and prone to mechanical malfunction. The 2~3 1865 concentrations of tree gasses in the filter must be maintained at precise values in order to obtain accurate measurements. The system is also difficult to expand for sensing of additional. pollutant species, since each new channel will require ;mother beam splitter, detector, etc.
and involve the problems described above.
SUMMARY OF THE INVENTION
In accordance with the present invention, a light source radiate~~ an in:Erared beam through the exhaust plume of a motor vehicle which passes in front of the source. A
photosensor unit inc:Ludes a plurality of photodetectors which are spaced closely adjacent to each other and simultaneously sense the beam after it propagates through the plume.
The photodetectors- are sensitive to different wavelengths corresponding to spectral absorption peaks of constituents o:E the composition of the plume, including carbon monoxide (CO), carbon dioxide (COz) and hydrocarbon (HC) . A comput:er computes the composition of the plume as percentages of the constituents based on the sensed transmittances of the respective wavelengths through the plume .
An optical beam homogenizer disposed between the plume and the photosensor causes the light incident on the photodetectors to hava_ uniform intensity. A video camera produces a video image' of the vehicle license plate, and a combiner cause; the: v:Ldeo image to be displayed on a video monitor and rec:orde>.d on a video recorder together with the plume composition data.
According to one' aspect of the invention there is provided a sensing apparatus for sensing a composition of an exhaust plume of a motor vehicle, comprising a light source for radiat:inc3 light including a plurality of predetermined wavelengths through said plume; a chopper positioned bel~ween said source and said plume for 2~3 1865 4a alternating blocking and passing said light; a photosensor for simultaneously sensing alternating blocking and passing said light; a photosensor for simultaneously sensing alternating bl~~cked or passed radiation levels at said predetermined wavelengths for said light passing through said plume; and a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.
According to another aspect of the invention there is provided a sensing apparatus for sensing a composition of fluid, comprising a light source for radiating light including a plurality of predetermined wavelengths through said fluid; a chopper positioned between said source and said plume for alternating blocking and passing said light;
a photosensor for simultaneously sensing alternating blocked or passed radiation levels at said predetermined wavelengths for said :Light passing through said fluid; and a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.
Although especially suitable for vehicle emission sensing, the present invention can also be utilized for sensing the composition of fluids (gasses and liquids) in a variety of diagnostic and regulatory applications, such as industrial and waste-site chemical pollution monitoring.
2~.318G~
The present invention overcomes the drawbacks of the prior art system discussed above. The photodetectors are spaced closely adjacent to each other in a single detector head which is cooled by a single cooling unit and uniformly 5 illuminated by the light beam through the beam homogenizer after propagation through the vehicle exhaust plume.
The present system does not include a rotating filter wheel or simil<~r moving parts, or a beam splitter or other components which require critical alignment. The invention is therefore inexpensive to manufacture on a commercial production ba~:is, and suitable for mass deployment for regulatory and other purposes.
The photodetectors are integrally fabricated on a single substrate to enable isothermal operation and minimize cross-talk. This enables the characteristics of the photodetect:ors to be precisely matched, with a substan-tial increase :Ln measurement accuracy and reliability over the prior art.
These and other features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which like reference numerals refer to like parts.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified pictorial view of an optical sensing apparatus for' remotely measuring the exhaust gas composition of moving motor vehicles in accordance with the present invent:ion;
FIG. 2 is a block diagram of the present apparatus;
FIG. 3 is a block diagram illustrating a photodetector assembly of ths; appar<~tus;
FIG. 4 is a flowchart illustratina the oneratinn of the apparatus;
FIGS. 5 to 9 are ;simplified sectional views illustrat-2'~3 18 65 ing alternativ~a embodiments of the photodetector assembly;
FIG. 10 i;~ a simplified elevational view illustrating the photodetec;tor assembly in combination with a beam homogenizes;
FIG. 11 is a plan view of the beam homogenizes;
FIG. 12 is a fragmentary sectional view of the beam homogenizes il:Lustrated at enlarged scale;
FIG. 13 is a graph illustrating the relationship between optical transmittance and gas composition in accordance with the invention;
FIG. 14 is a graph illustrating the relationship between carbon dioxide concentration and carbon monoxide concentration as sensed by the apparatus; and FIG. 15 is a diagram illustrating a data display of the apparatus.
DETAILED DESCRIPTION OF THE INVENTION
An optical sensing apparatus for remotely measuring exhaust gas c:ompasii:ion of moving motor vehicles is illustrated in FIGs. 1. and 2 and designated as 10. A light source 12 radiates a collimated beam 14 of infrared light across a road :L6 to a photosensor unit 18. As an automo-tive vehicle 20 drives along the road 16, the body of the vehicle 20 and subsequently an exhaust gas plume 22 of the vehicle 20 pass through the beam 14.
The apparatus 10 further includes a computer 24 which receives and operates on electrical output signals from the photosensor unit 1.8, a video camera 26 for producing a video image of the rear end of the vehicle 20 including its license plate 28, a video display unit or monitor 30 for displaying the video image from the camera 26 and data from the computer 2~E, and a video recorder 32 for recording the image and data. The computer 24 includes a conventional frame grabber 'not shawn) for storing individual frames of video from the camera 26.
~
2t3 1865 As illustrated in FIG. 2, the photosensor unit 18 includes a mechanical or optical chopper 34 which alternat-ingly blocks and unblocks the light beam 14 at, for example, 200 times per second. An optical homogenizer or beam integrator 36 homogenizes the beam 14 so that its intensity is 'uniform throughout it cross-section. The homogenized beam 14 is incident on a detector head 38 which is regulated to a predetermined temperature by a cooler 40.
The apparatus l0 measures the composition of the plume 22 in terms of the relative proportions of the constituents C02, CO and HC. However, the invention is not so limited, and the conce:ntratians of other constituents such as nitrogen oxide (NOX), formaldehyde, particulate matter, etc. can simil<~rly be measured.
As illustrated in FIG. 3, the detector head 38 includes a ph.otodetector assembly 41 consisting of a reference photodetector 42, a carbon dioxide (COZ) photode-tector 44 , a carbon monoxide ( CO ) photodetector 4 6 and a hydrocarbon (H:C) photodetector 48 which are integrally fabricated on a common substrate 50.
One end o:E each of the photodetectors 42, 44, 46 and 48 is connected to a reference voltage Vbias . The other ends of the photodetectors 42, 44, 46 and 48 are connected to the non-inverting inputs of operational amplifiers 51, 52, 54 and 56 :respectively, the inverting inputs of which are grounded. The output voltages of the amplifiers 51, 52, 54 and 56 are amplified vertions of the outputs of the photodetectors 42, 44, 46 and 48 respectively. The substrate 50 i:~ maintained at ground potential.
As will be: described in detail below, the photodetec-tors 44, 46 and 48 include optical bandpass filters which pass only wavelengths of light which correspond to spectral absorption peaks of the respective constituents of the exhaust gas plume 22 which are to be sensed, and the photodetector 9:2 includes an optical bandpass filter which v 213 1$ fi5 passes only wavelengths of light where no spectral absorp tion peaks occur in the exhaust gas plume 22. The infrared light beam 14 produced by the light source 12 includes all wavelengths of light to be sensed by the photodetectors 42, 44, 46 and 48.
The passbands of the filters of the COZ photodetector 44, the CO phot.odetect:or 46 and the HC photodetector 48 are preferably centered on 4.2, 4.6 and 3.3 micrometers respectively, although the invention is not so limited.
The passband for the reference photodetector 42 is prefera bly centered on 3.8 micrometers, which does not correspond to an absorption peak of any of the constituents of the plume 22 being sensed, and is substantially unaffected by propagation through them, although the invention is not so limited.
The reference photodetector 42 is provided to compen-sate the photod.etectors 44, 46 and 48 for variations caused by fluctuation of the output of the light source 12, particulate matter in the form of road dust and exhaust particles in the plume 22, and other factors which affect the light beam 14 as incident on the photodetectors. In other words, the photodetector 42 produces a baseline output which :is independent of the constituents being measured.
The outputs of the amplifiers 52, 54 and 56, are normalized (i.e. divided) by the output of the amplifier 51. The result:ing normalized voltages depend only on the effects of the constituents in the plume 22.
It will be: noted that the invention is not limited to dividing the reference signal into the constituent signals.
The constituent: signals can be referenced to the baseline using other methods.
The outputa of the amplifiers 51, 52, 54 and 56 are analog signals which are suitably processed in an analog signal processor 58 and converted to digital form by an 2'~3 i8fi5 analog-to-digii:al converter 60. The processor 58 prefera-bly level-shifts the signals such that they are automati-cally centered between two limit values.
The operation of the apparatus 10 is illustrated in the flowchart of FIG. 4. The apparatus 10 is suitable for either attended or unattended operation. The monitor 30 is optional for unattended operation, once the other compo nents have been set up and calibrated.
The apparatus 10 waits for a vehicle 20 to pass through the beam 14. This is indicated by a sharp drop in the amplitudes of the output signals of the photodetectors 42, 44, 46 and 48 when the vehicle 20 blocks the beam 14.
This generates a trigger which initiates measurement of the concentration of the vehicle exhaust plume 22.
The signal amplitudes will increase sharply when the rear end of the vehicle 20 clears the beam 14. This indicates that the beam 14 is unblocked and is propagating through the exhaust plume 22 of the vehicle 20.
The processor 58 integrates the output signals from the detector head 38 during the intervals the photodetec tors 42, 44, 46 and 48 are unblocked by the chopper 34, and processes the signals and feeds them to the computer 24 during the intearvals the photodetectors 42, 44, 46 and 48 are blocked by the chopper 34. In this manner, the outputs of the photodetectors 42, 44, 46 and 48 are periodically sampled and processed.
The computer 24 computes the composition of the plume 22 in terms of the percentages or concentrations of the constituents CC~2, CO and HC based on the amplitudes of the signals from the photodetectors 44, 46 and 48, and displays this data together with the video from the camera 26 on the monitor 30 as illustrated in FIG. 1. This operation is performed for a predetermined length of time, for example one-half second, which is sufficient for the apparatus 10 to produce an a:ccuratE~ measurement.
The computer then determines if the composition is within specified regulatory tolerances. If so, the apparatus 10 resets and waits for the next vehicle. If not, indicating that the vehicle 20 is producing excessive 5 pollution, the computer 24 grabs a frame of video including the license pl<~te 28 of the vehicle 20 from the camera 26, superimposes the concentration data on the video frame, and stores the combined video and data frame in a mass storage device such as a hard drive.
10 The data c:an be retrieved at a later time for enforce-ment use, such as sending a notice of violation to the owner of the vehicle. It is also within the scope of the invention to store a combined video and data frame for every vehicle which passes through the beam 14 , rather than just polluting vehicles, for applications such as generat-ing a database: of exhaust gas composition for different types and make:a of vehicles.
The photodetector assembly 41 is illustrated in FIG.
5. The photodetectors 42, 44, 46 and 48 include photosen sitive elements 62, 64, 66 and 68 which are integrally fabricated on a substrate 70. The elements 62, 64, 66 and 68 are preferably photoconductive and formed of mercury cadmium telluride (HgCdTe or HCT), whereas the substrate 70 is cadmium zinc: telluride (CdZnTe).
However, the invention is not so limited, and the photodetectors 42, 44, 46 and 48 can be fabricated using other group II-VI material systems such as mercury zinc telluride (HgZnTe), lead salts or group III-V materials.
The photosensitive elements 62, 64, 66 and 68 can also be photovoltaic rather than photoconductive.
The photosensitive elements 62, 64, 66 and 68 are optically isolated from each other by an opaque material 72 such as alumina to minimize optical cross-talk. Optical filters 74, 76, 78 and 80 having passbands centered on 3.8, 4.2, 4.6 and 3.3 micrometers respectively are formed on a 2~3 1865 transparent substrate 70 and adhered to the elements 62, 64, 66 and 68 respectively by an optically transparent adhesive 84. The substrate 70 is typically formed of germanium (Ge), whereas the filters 74, 76, 78 and 80 are formed as dielectric stacks including multiple layers of zinc sulfide (~~nS) .
The elements 62, 64, 66 and 68 are approximately 1 x 1 millimeter in size, although the invention is not so limited, which is large enough to accommodate the filters 74, 76, 78 and 80, but small enough to achieve a high signal-to-noise ratio. The integral design of the photode-tector assembly 41 ensures that the photodetectors 42, 44, 46 and 48 operate isothermally, thereby eliminating inaccuracies resulting from temperature differences. The assembly 41 is regulated to a temperature of approximately 200°K by the cooler 40.
FIG. 6 illustrates a modified photodetector assembly 41', in which like elements are designated by the same reference numerals used in FIG. 5, and corresponding but modified elements are designated by the same reference numerals primed. The assembly 41' differs from the assembly 41 in that the substrate 82 is removed after filters 74', T6', 78' and 80' have been adhered to the elements 62, 64, 66 and 68 and opaque material 72 by the adhesive 84.
FIG. 7 illustrates another modified photodetector assembly 41" in which like elements are designated by the same reference numerals used in FIG. 5, and corresponding but modified elements are designated by the same reference numerals double: primed. The assembly 41" differs from the assembly 41 in that the substrate 82 and adhesive 84 are omitted, and l:ilters 74", 76", 78" and 80" are formed directly on thE~ photosensitive elements 62, 64, 66 and 68 respectively.
FIG. 8 :illustrates an alternative photodetector arrangement for practicing the invention, with the filters not shown for simplicity of description. The individual photodetectors are interchangeable, and will be described collectively.
A photodei:ector assembly 90 includes a substrate 92.
Reflector layers 94 of a suitable material such as gold are formed on the ~~ubstrate 90. Photosensitive elements 96 of HCT or other suitable material which are optically trans-parent to the wavelengths they are intended to detect are adhered to the reflector layers 94 by optically transparent adhesive 98. The lateral areas between the elements 96 and reflector layers 94 are filled with opaque material 100.
Light incident on the photosensitive elements 96, after passing through the plume 22, passes through the elements 96 and is reflected back into the elements 96 by the respective reflector layers 94. This "double pass"
minimizes optical cross-talk between the elements 96, and increases the light detecting efficiency thereof.
FIG. 9 illustrates another alternative photodetector assembly 102 t:or practicing the invention, including a substrate 104 or an optically transparent material such as CdZnTe. Photosensitive elements 106 of HCT or other suitable optically transparent material are formed on the substrate 104. The lateral spaces between the elements 106 are filled with an opaque material 108. An anti-reflection coating 110 is formed on the back side of the substrate 104, and an absorbing layer 112 having high optical absorption efficiency is formed on the coating 110. The coating 110 and. layer 112 are typically formed of ZnS2.
Light from the beam 14 which is incident on the photosensitive elements 106 passes through the elements 106, substrate 104 and coating 110 and is absorbed by the absorbing layer 112. The coating 110 prevents light from being reflected from the layer 112 back to the elements 106. This arrangement also enables efficient photodetec-2~3 18fi5 tion with low optical cross-talk.
The beam :integrator 36, which is illustrated in FIGs.
10, 11 and 12, homogenizes the beam 14 after propagation through the plume 22 such that the optical intensity or energy is substantially uniform throughout the cross section of the homogenized beam 14 which is incident on the photodetector assembly 41. This ensures that the same homogenized or averaged scene is sensed by the photodetec tors 42, 44, S66 and 48, and substantially increases the accuracy of measurement.
The beam integrator 36 preferably includes a plano-convex lens 120. A rectangular array of flat facets 122 are formed in .a convex surface 124 of the lens 120. The facets 122 refract segments of light from respective portions of the incident beam 14 toward a central axis 126, such that the refracted light segments are superimposed with each other on the photodetector assembly 41.
The superimposed. image which is incident on the assembly 41 consists of the homogenized or averaged images refracted from the facets 122, and thereby the average intensity of i~he beam 14. Further illustrated is an optional converging lens 128 for reducing the size of the homogenized image on the photodetector assembly 41.
The principles of the beam integrator 36 are disclosed in U.S. PatentlJo. 4,195,913, entitled "OPTICAL INTEGRATION
WITH SCREW SUP1?ORTS", issued April 1, 1980 to D. Dourte.
A beam integrator 36 suitable for practicing the invention is commercially available from Spawr Optical Research, Inc.
of Corona, CA, the assignee of the Dourte patent.
The configuration of the beam integrator 36 suitable for practicing the invention is not limited to the multi-faceted design illustrated in FIGS. 10 to 12. If the requirements are not so critical, the beam integrator 36 can be embodied, for example, by a converging or diverging lens which prooluces a de-focussed image of the beam 14 on the photodetector assembly 41. The beam integrator 36 can also be embodied using a reflective, rather than a refrac-tive implementation as disclosed by Dourte.
The concentrations of CO2, CO and HC as functions of the transmittances of the respective wavelengths of light as sensed by the photodetectors 42, 44, 46 and 48 are computed in a manner similar to that disclosed in the above referenced article to Bishop. The transmittance varies with constituent concentration in a non-linear manner as illustrated in FIG. 13.
The illustrated curves for C02 and CO were obtained experimentally over an absorption pathlength of 203 millimeters, a:nd can be used as reference for computation and field calibration of the apparatus 10. A similar curve (not shown) exists for HC.
The C02 and CO constituents in the plume 22 disperse at the same rate. Fox this reason, the ratio of CO vs COZ is independent of the actual concentrations and the pathlength which vary over time, and can be measured directly. This ratio is in itself a useful indicator of the pollutant composition of the exhaust plume 22. A similar ratio is obtained for Hc: vs CO;,.
Since the plume progressively decays after emission from the tailpipe of the vehicle 20, the concentrations of the constituenia COZ and CO will vary with time. However, their ratio wi7:1 remain substantially constant. The CO vs COZ ratio can be expressed as the slope of a line 130 which can be computed. by, for example, linear regression analysis of the individual data samples obtained over the sampling interval.
The parameters which are sensed directly by the apparatus 10 a:re concentration-pathlength products of the constituents. The pathlengths vary with time and are indeterminate. For this reason, the actual concentrations of the constituents cannot be measured directly.
However, 'the composition of the plume 22 in terms of percentage constituent concentrations is often required for regulatory purposes. This can be calculated with suffi-cient accuracy for practical use using the stoichiometric 5 chemical relationships of the combustion process. A
preferred example of such a computation for practicing the present invention is as follows.
The constituent concentrations in a nominal absorption pathlength of 10 centimeters is calculated using curves 10 such as illustrated in FIG. 13. Calibration is performed periodically as field conditions vary using a standard source gas with known concentrations of CO, HC and COZ.
This standard source gas is released into the beam 14, and transmitta~nces Tao, TH~ and T~o2 are measured as a 15 function of time during the dispersion of the gas. The concentration-pathlength product for the CO contained in the gas is determined from the measured transmittance Tao.
The measurement of concentration-pathlength product is determined repeatedly during the dispersion of the gas released into t:he beam.
For each measurement of the concentration-pathlength product for CO, the concentration-pathlength product for HC
and C02 is determined based on the measured concentration-pathlength product of CO and the known ratios of HC/CO and COz/Co in the standard source gas.
From the measured transmittances THE and T~oz. and the concentration-pathlength products determined for HC and COZ, the relationships between transmittance and pathlength-products (such as those shown in FIG. 13), can be quickly determined for HC and COZ. This is particularly important for COZ because it is a component in ambient air, hence, the relationship between concentration-pathlength product and transmittance will vary as a function of the distance between the light source 12 and the photosensor unit 18.
For measurements of CO/COZ and HC/COZ in the exhaust plume of a moving vehicle, the transmittances Tco, Tic and Tcoz are measured directly and concentration-pathlength products for C~O, COZ and HC are determined from the rela-tionships shown in FIG. 13 that result from the calibra-tions described above. Absolute tailpipe concentrations of CO, HC and C02 are then calculated using the following formulas.
%COZ = 42/' (2 .79 + 2Sco - 0. 37SHC) %CO = %CO;; x Sco %HC = %CO;; X SHc Derivation of %C02 is based on stoichiometric chemical balance in the combustion process using a "nominal fuel"
having a carbon vs hydrogen ratio of 1.8.
For norma:L operation, the concentrations %CO, %COZ and %HC are displayed on the monitor 30 together with the video image of the license plate 28 of the vehicle 20 as illus trated in FIG. 1 and stored as frames by the video recorder 32.
FIG. 15 illustrates an expanded data screen which can be displayed on the monitor 30 if more information is required. The display of FIG. 15 includes the concentra-tions %CO, %C0~2 and %HC as a function of time (with 200 equivalent to one second at a sampling rate of 200 sam-ples/second) and the ratios CO vs COZ and HC vs C02 in addition to t:he peak-to-peak voltage outputs of the photodetectors 42, 44, 46 and 48, and the slopes, inter-cepts and standard deviations of the calculated CO vs COZ
and HC vs COZ ratios.
While sevE~ral illustrative embodiments of the inven tion have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art, without departing from the spirit and scope of the invention. Accordingly, it is intended that the present invention not be limited solely to the specifically described illustrative embodiments. Various modifications 2t3 18fi5 l~
are contemplated and can be made without departing from the spirit and scope of the invention as defined by the appended cl a ims~ .
The outpui~ signals of the detectors vary in accordance with the transmittance of the vehicle exhaust plume at the respective wavelengths, and thereby the concentrations of CO and C02 in the plume. The CO/H2 portion of the filter l0 wheel provides a reference output, whereas the NZ portion provides a carbon monoxide output.
Baseline sensor outputs are obtained with no vehicle passing through the beam, and with the beam blocked by a vehicle prior to sensing of the plume. These values are used as referenceslfor calibrating the outputs of the detectors when the plume is actually sensed. The detector outputs, which. correspond to the transmittances at the respective wavelengths, are then processed in accordance with predetermined functions to determine the relative percentages of COz and CO in the vehicle exhaust plume.
This system is capable of sensing the exhaust gas composition of moving vehicles, and can be used to identify polluting vehicles fo:r enforcement purposes. However, it suffers from cs~rtain drawbacks.
Precise alignment: is required to ensure that the beams in the two paths are incident on the detectors in an identical manner. A small misalignment error can seriously degrade the measurement accuracy. The two photovoltaic detectors are remote from each other, and require separate cooling units for temperature regulation. A small differ-ence in temperature, as well as small mismatches in other characteristic; of the detectors, can also seriously degrade the measurement accuracy.
The rotating filter wheel is a mechanical unit which is expensive and prone to mechanical malfunction. The 2~3 1865 concentrations of tree gasses in the filter must be maintained at precise values in order to obtain accurate measurements. The system is also difficult to expand for sensing of additional. pollutant species, since each new channel will require ;mother beam splitter, detector, etc.
and involve the problems described above.
SUMMARY OF THE INVENTION
In accordance with the present invention, a light source radiate~~ an in:Erared beam through the exhaust plume of a motor vehicle which passes in front of the source. A
photosensor unit inc:Ludes a plurality of photodetectors which are spaced closely adjacent to each other and simultaneously sense the beam after it propagates through the plume.
The photodetectors- are sensitive to different wavelengths corresponding to spectral absorption peaks of constituents o:E the composition of the plume, including carbon monoxide (CO), carbon dioxide (COz) and hydrocarbon (HC) . A comput:er computes the composition of the plume as percentages of the constituents based on the sensed transmittances of the respective wavelengths through the plume .
An optical beam homogenizer disposed between the plume and the photosensor causes the light incident on the photodetectors to hava_ uniform intensity. A video camera produces a video image' of the vehicle license plate, and a combiner cause; the: v:Ldeo image to be displayed on a video monitor and rec:orde>.d on a video recorder together with the plume composition data.
According to one' aspect of the invention there is provided a sensing apparatus for sensing a composition of an exhaust plume of a motor vehicle, comprising a light source for radiat:inc3 light including a plurality of predetermined wavelengths through said plume; a chopper positioned bel~ween said source and said plume for 2~3 1865 4a alternating blocking and passing said light; a photosensor for simultaneously sensing alternating blocking and passing said light; a photosensor for simultaneously sensing alternating bl~~cked or passed radiation levels at said predetermined wavelengths for said light passing through said plume; and a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.
According to another aspect of the invention there is provided a sensing apparatus for sensing a composition of fluid, comprising a light source for radiating light including a plurality of predetermined wavelengths through said fluid; a chopper positioned between said source and said plume for alternating blocking and passing said light;
a photosensor for simultaneously sensing alternating blocked or passed radiation levels at said predetermined wavelengths for said :Light passing through said fluid; and a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.
Although especially suitable for vehicle emission sensing, the present invention can also be utilized for sensing the composition of fluids (gasses and liquids) in a variety of diagnostic and regulatory applications, such as industrial and waste-site chemical pollution monitoring.
2~.318G~
The present invention overcomes the drawbacks of the prior art system discussed above. The photodetectors are spaced closely adjacent to each other in a single detector head which is cooled by a single cooling unit and uniformly 5 illuminated by the light beam through the beam homogenizer after propagation through the vehicle exhaust plume.
The present system does not include a rotating filter wheel or simil<~r moving parts, or a beam splitter or other components which require critical alignment. The invention is therefore inexpensive to manufacture on a commercial production ba~:is, and suitable for mass deployment for regulatory and other purposes.
The photodetectors are integrally fabricated on a single substrate to enable isothermal operation and minimize cross-talk. This enables the characteristics of the photodetect:ors to be precisely matched, with a substan-tial increase :Ln measurement accuracy and reliability over the prior art.
These and other features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which like reference numerals refer to like parts.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified pictorial view of an optical sensing apparatus for' remotely measuring the exhaust gas composition of moving motor vehicles in accordance with the present invent:ion;
FIG. 2 is a block diagram of the present apparatus;
FIG. 3 is a block diagram illustrating a photodetector assembly of ths; appar<~tus;
FIG. 4 is a flowchart illustratina the oneratinn of the apparatus;
FIGS. 5 to 9 are ;simplified sectional views illustrat-2'~3 18 65 ing alternativ~a embodiments of the photodetector assembly;
FIG. 10 i;~ a simplified elevational view illustrating the photodetec;tor assembly in combination with a beam homogenizes;
FIG. 11 is a plan view of the beam homogenizes;
FIG. 12 is a fragmentary sectional view of the beam homogenizes il:Lustrated at enlarged scale;
FIG. 13 is a graph illustrating the relationship between optical transmittance and gas composition in accordance with the invention;
FIG. 14 is a graph illustrating the relationship between carbon dioxide concentration and carbon monoxide concentration as sensed by the apparatus; and FIG. 15 is a diagram illustrating a data display of the apparatus.
DETAILED DESCRIPTION OF THE INVENTION
An optical sensing apparatus for remotely measuring exhaust gas c:ompasii:ion of moving motor vehicles is illustrated in FIGs. 1. and 2 and designated as 10. A light source 12 radiates a collimated beam 14 of infrared light across a road :L6 to a photosensor unit 18. As an automo-tive vehicle 20 drives along the road 16, the body of the vehicle 20 and subsequently an exhaust gas plume 22 of the vehicle 20 pass through the beam 14.
The apparatus 10 further includes a computer 24 which receives and operates on electrical output signals from the photosensor unit 1.8, a video camera 26 for producing a video image of the rear end of the vehicle 20 including its license plate 28, a video display unit or monitor 30 for displaying the video image from the camera 26 and data from the computer 2~E, and a video recorder 32 for recording the image and data. The computer 24 includes a conventional frame grabber 'not shawn) for storing individual frames of video from the camera 26.
~
2t3 1865 As illustrated in FIG. 2, the photosensor unit 18 includes a mechanical or optical chopper 34 which alternat-ingly blocks and unblocks the light beam 14 at, for example, 200 times per second. An optical homogenizer or beam integrator 36 homogenizes the beam 14 so that its intensity is 'uniform throughout it cross-section. The homogenized beam 14 is incident on a detector head 38 which is regulated to a predetermined temperature by a cooler 40.
The apparatus l0 measures the composition of the plume 22 in terms of the relative proportions of the constituents C02, CO and HC. However, the invention is not so limited, and the conce:ntratians of other constituents such as nitrogen oxide (NOX), formaldehyde, particulate matter, etc. can simil<~rly be measured.
As illustrated in FIG. 3, the detector head 38 includes a ph.otodetector assembly 41 consisting of a reference photodetector 42, a carbon dioxide (COZ) photode-tector 44 , a carbon monoxide ( CO ) photodetector 4 6 and a hydrocarbon (H:C) photodetector 48 which are integrally fabricated on a common substrate 50.
One end o:E each of the photodetectors 42, 44, 46 and 48 is connected to a reference voltage Vbias . The other ends of the photodetectors 42, 44, 46 and 48 are connected to the non-inverting inputs of operational amplifiers 51, 52, 54 and 56 :respectively, the inverting inputs of which are grounded. The output voltages of the amplifiers 51, 52, 54 and 56 are amplified vertions of the outputs of the photodetectors 42, 44, 46 and 48 respectively. The substrate 50 i:~ maintained at ground potential.
As will be: described in detail below, the photodetec-tors 44, 46 and 48 include optical bandpass filters which pass only wavelengths of light which correspond to spectral absorption peaks of the respective constituents of the exhaust gas plume 22 which are to be sensed, and the photodetector 9:2 includes an optical bandpass filter which v 213 1$ fi5 passes only wavelengths of light where no spectral absorp tion peaks occur in the exhaust gas plume 22. The infrared light beam 14 produced by the light source 12 includes all wavelengths of light to be sensed by the photodetectors 42, 44, 46 and 48.
The passbands of the filters of the COZ photodetector 44, the CO phot.odetect:or 46 and the HC photodetector 48 are preferably centered on 4.2, 4.6 and 3.3 micrometers respectively, although the invention is not so limited.
The passband for the reference photodetector 42 is prefera bly centered on 3.8 micrometers, which does not correspond to an absorption peak of any of the constituents of the plume 22 being sensed, and is substantially unaffected by propagation through them, although the invention is not so limited.
The reference photodetector 42 is provided to compen-sate the photod.etectors 44, 46 and 48 for variations caused by fluctuation of the output of the light source 12, particulate matter in the form of road dust and exhaust particles in the plume 22, and other factors which affect the light beam 14 as incident on the photodetectors. In other words, the photodetector 42 produces a baseline output which :is independent of the constituents being measured.
The outputs of the amplifiers 52, 54 and 56, are normalized (i.e. divided) by the output of the amplifier 51. The result:ing normalized voltages depend only on the effects of the constituents in the plume 22.
It will be: noted that the invention is not limited to dividing the reference signal into the constituent signals.
The constituent: signals can be referenced to the baseline using other methods.
The outputa of the amplifiers 51, 52, 54 and 56 are analog signals which are suitably processed in an analog signal processor 58 and converted to digital form by an 2'~3 i8fi5 analog-to-digii:al converter 60. The processor 58 prefera-bly level-shifts the signals such that they are automati-cally centered between two limit values.
The operation of the apparatus 10 is illustrated in the flowchart of FIG. 4. The apparatus 10 is suitable for either attended or unattended operation. The monitor 30 is optional for unattended operation, once the other compo nents have been set up and calibrated.
The apparatus 10 waits for a vehicle 20 to pass through the beam 14. This is indicated by a sharp drop in the amplitudes of the output signals of the photodetectors 42, 44, 46 and 48 when the vehicle 20 blocks the beam 14.
This generates a trigger which initiates measurement of the concentration of the vehicle exhaust plume 22.
The signal amplitudes will increase sharply when the rear end of the vehicle 20 clears the beam 14. This indicates that the beam 14 is unblocked and is propagating through the exhaust plume 22 of the vehicle 20.
The processor 58 integrates the output signals from the detector head 38 during the intervals the photodetec tors 42, 44, 46 and 48 are unblocked by the chopper 34, and processes the signals and feeds them to the computer 24 during the intearvals the photodetectors 42, 44, 46 and 48 are blocked by the chopper 34. In this manner, the outputs of the photodetectors 42, 44, 46 and 48 are periodically sampled and processed.
The computer 24 computes the composition of the plume 22 in terms of the percentages or concentrations of the constituents CC~2, CO and HC based on the amplitudes of the signals from the photodetectors 44, 46 and 48, and displays this data together with the video from the camera 26 on the monitor 30 as illustrated in FIG. 1. This operation is performed for a predetermined length of time, for example one-half second, which is sufficient for the apparatus 10 to produce an a:ccuratE~ measurement.
The computer then determines if the composition is within specified regulatory tolerances. If so, the apparatus 10 resets and waits for the next vehicle. If not, indicating that the vehicle 20 is producing excessive 5 pollution, the computer 24 grabs a frame of video including the license pl<~te 28 of the vehicle 20 from the camera 26, superimposes the concentration data on the video frame, and stores the combined video and data frame in a mass storage device such as a hard drive.
10 The data c:an be retrieved at a later time for enforce-ment use, such as sending a notice of violation to the owner of the vehicle. It is also within the scope of the invention to store a combined video and data frame for every vehicle which passes through the beam 14 , rather than just polluting vehicles, for applications such as generat-ing a database: of exhaust gas composition for different types and make:a of vehicles.
The photodetector assembly 41 is illustrated in FIG.
5. The photodetectors 42, 44, 46 and 48 include photosen sitive elements 62, 64, 66 and 68 which are integrally fabricated on a substrate 70. The elements 62, 64, 66 and 68 are preferably photoconductive and formed of mercury cadmium telluride (HgCdTe or HCT), whereas the substrate 70 is cadmium zinc: telluride (CdZnTe).
However, the invention is not so limited, and the photodetectors 42, 44, 46 and 48 can be fabricated using other group II-VI material systems such as mercury zinc telluride (HgZnTe), lead salts or group III-V materials.
The photosensitive elements 62, 64, 66 and 68 can also be photovoltaic rather than photoconductive.
The photosensitive elements 62, 64, 66 and 68 are optically isolated from each other by an opaque material 72 such as alumina to minimize optical cross-talk. Optical filters 74, 76, 78 and 80 having passbands centered on 3.8, 4.2, 4.6 and 3.3 micrometers respectively are formed on a 2~3 1865 transparent substrate 70 and adhered to the elements 62, 64, 66 and 68 respectively by an optically transparent adhesive 84. The substrate 70 is typically formed of germanium (Ge), whereas the filters 74, 76, 78 and 80 are formed as dielectric stacks including multiple layers of zinc sulfide (~~nS) .
The elements 62, 64, 66 and 68 are approximately 1 x 1 millimeter in size, although the invention is not so limited, which is large enough to accommodate the filters 74, 76, 78 and 80, but small enough to achieve a high signal-to-noise ratio. The integral design of the photode-tector assembly 41 ensures that the photodetectors 42, 44, 46 and 48 operate isothermally, thereby eliminating inaccuracies resulting from temperature differences. The assembly 41 is regulated to a temperature of approximately 200°K by the cooler 40.
FIG. 6 illustrates a modified photodetector assembly 41', in which like elements are designated by the same reference numerals used in FIG. 5, and corresponding but modified elements are designated by the same reference numerals primed. The assembly 41' differs from the assembly 41 in that the substrate 82 is removed after filters 74', T6', 78' and 80' have been adhered to the elements 62, 64, 66 and 68 and opaque material 72 by the adhesive 84.
FIG. 7 illustrates another modified photodetector assembly 41" in which like elements are designated by the same reference numerals used in FIG. 5, and corresponding but modified elements are designated by the same reference numerals double: primed. The assembly 41" differs from the assembly 41 in that the substrate 82 and adhesive 84 are omitted, and l:ilters 74", 76", 78" and 80" are formed directly on thE~ photosensitive elements 62, 64, 66 and 68 respectively.
FIG. 8 :illustrates an alternative photodetector arrangement for practicing the invention, with the filters not shown for simplicity of description. The individual photodetectors are interchangeable, and will be described collectively.
A photodei:ector assembly 90 includes a substrate 92.
Reflector layers 94 of a suitable material such as gold are formed on the ~~ubstrate 90. Photosensitive elements 96 of HCT or other suitable material which are optically trans-parent to the wavelengths they are intended to detect are adhered to the reflector layers 94 by optically transparent adhesive 98. The lateral areas between the elements 96 and reflector layers 94 are filled with opaque material 100.
Light incident on the photosensitive elements 96, after passing through the plume 22, passes through the elements 96 and is reflected back into the elements 96 by the respective reflector layers 94. This "double pass"
minimizes optical cross-talk between the elements 96, and increases the light detecting efficiency thereof.
FIG. 9 illustrates another alternative photodetector assembly 102 t:or practicing the invention, including a substrate 104 or an optically transparent material such as CdZnTe. Photosensitive elements 106 of HCT or other suitable optically transparent material are formed on the substrate 104. The lateral spaces between the elements 106 are filled with an opaque material 108. An anti-reflection coating 110 is formed on the back side of the substrate 104, and an absorbing layer 112 having high optical absorption efficiency is formed on the coating 110. The coating 110 and. layer 112 are typically formed of ZnS2.
Light from the beam 14 which is incident on the photosensitive elements 106 passes through the elements 106, substrate 104 and coating 110 and is absorbed by the absorbing layer 112. The coating 110 prevents light from being reflected from the layer 112 back to the elements 106. This arrangement also enables efficient photodetec-2~3 18fi5 tion with low optical cross-talk.
The beam :integrator 36, which is illustrated in FIGs.
10, 11 and 12, homogenizes the beam 14 after propagation through the plume 22 such that the optical intensity or energy is substantially uniform throughout the cross section of the homogenized beam 14 which is incident on the photodetector assembly 41. This ensures that the same homogenized or averaged scene is sensed by the photodetec tors 42, 44, S66 and 48, and substantially increases the accuracy of measurement.
The beam integrator 36 preferably includes a plano-convex lens 120. A rectangular array of flat facets 122 are formed in .a convex surface 124 of the lens 120. The facets 122 refract segments of light from respective portions of the incident beam 14 toward a central axis 126, such that the refracted light segments are superimposed with each other on the photodetector assembly 41.
The superimposed. image which is incident on the assembly 41 consists of the homogenized or averaged images refracted from the facets 122, and thereby the average intensity of i~he beam 14. Further illustrated is an optional converging lens 128 for reducing the size of the homogenized image on the photodetector assembly 41.
The principles of the beam integrator 36 are disclosed in U.S. PatentlJo. 4,195,913, entitled "OPTICAL INTEGRATION
WITH SCREW SUP1?ORTS", issued April 1, 1980 to D. Dourte.
A beam integrator 36 suitable for practicing the invention is commercially available from Spawr Optical Research, Inc.
of Corona, CA, the assignee of the Dourte patent.
The configuration of the beam integrator 36 suitable for practicing the invention is not limited to the multi-faceted design illustrated in FIGS. 10 to 12. If the requirements are not so critical, the beam integrator 36 can be embodied, for example, by a converging or diverging lens which prooluces a de-focussed image of the beam 14 on the photodetector assembly 41. The beam integrator 36 can also be embodied using a reflective, rather than a refrac-tive implementation as disclosed by Dourte.
The concentrations of CO2, CO and HC as functions of the transmittances of the respective wavelengths of light as sensed by the photodetectors 42, 44, 46 and 48 are computed in a manner similar to that disclosed in the above referenced article to Bishop. The transmittance varies with constituent concentration in a non-linear manner as illustrated in FIG. 13.
The illustrated curves for C02 and CO were obtained experimentally over an absorption pathlength of 203 millimeters, a:nd can be used as reference for computation and field calibration of the apparatus 10. A similar curve (not shown) exists for HC.
The C02 and CO constituents in the plume 22 disperse at the same rate. Fox this reason, the ratio of CO vs COZ is independent of the actual concentrations and the pathlength which vary over time, and can be measured directly. This ratio is in itself a useful indicator of the pollutant composition of the exhaust plume 22. A similar ratio is obtained for Hc: vs CO;,.
Since the plume progressively decays after emission from the tailpipe of the vehicle 20, the concentrations of the constituenia COZ and CO will vary with time. However, their ratio wi7:1 remain substantially constant. The CO vs COZ ratio can be expressed as the slope of a line 130 which can be computed. by, for example, linear regression analysis of the individual data samples obtained over the sampling interval.
The parameters which are sensed directly by the apparatus 10 a:re concentration-pathlength products of the constituents. The pathlengths vary with time and are indeterminate. For this reason, the actual concentrations of the constituents cannot be measured directly.
However, 'the composition of the plume 22 in terms of percentage constituent concentrations is often required for regulatory purposes. This can be calculated with suffi-cient accuracy for practical use using the stoichiometric 5 chemical relationships of the combustion process. A
preferred example of such a computation for practicing the present invention is as follows.
The constituent concentrations in a nominal absorption pathlength of 10 centimeters is calculated using curves 10 such as illustrated in FIG. 13. Calibration is performed periodically as field conditions vary using a standard source gas with known concentrations of CO, HC and COZ.
This standard source gas is released into the beam 14, and transmitta~nces Tao, TH~ and T~o2 are measured as a 15 function of time during the dispersion of the gas. The concentration-pathlength product for the CO contained in the gas is determined from the measured transmittance Tao.
The measurement of concentration-pathlength product is determined repeatedly during the dispersion of the gas released into t:he beam.
For each measurement of the concentration-pathlength product for CO, the concentration-pathlength product for HC
and C02 is determined based on the measured concentration-pathlength product of CO and the known ratios of HC/CO and COz/Co in the standard source gas.
From the measured transmittances THE and T~oz. and the concentration-pathlength products determined for HC and COZ, the relationships between transmittance and pathlength-products (such as those shown in FIG. 13), can be quickly determined for HC and COZ. This is particularly important for COZ because it is a component in ambient air, hence, the relationship between concentration-pathlength product and transmittance will vary as a function of the distance between the light source 12 and the photosensor unit 18.
For measurements of CO/COZ and HC/COZ in the exhaust plume of a moving vehicle, the transmittances Tco, Tic and Tcoz are measured directly and concentration-pathlength products for C~O, COZ and HC are determined from the rela-tionships shown in FIG. 13 that result from the calibra-tions described above. Absolute tailpipe concentrations of CO, HC and C02 are then calculated using the following formulas.
%COZ = 42/' (2 .79 + 2Sco - 0. 37SHC) %CO = %CO;; x Sco %HC = %CO;; X SHc Derivation of %C02 is based on stoichiometric chemical balance in the combustion process using a "nominal fuel"
having a carbon vs hydrogen ratio of 1.8.
For norma:L operation, the concentrations %CO, %COZ and %HC are displayed on the monitor 30 together with the video image of the license plate 28 of the vehicle 20 as illus trated in FIG. 1 and stored as frames by the video recorder 32.
FIG. 15 illustrates an expanded data screen which can be displayed on the monitor 30 if more information is required. The display of FIG. 15 includes the concentra-tions %CO, %C0~2 and %HC as a function of time (with 200 equivalent to one second at a sampling rate of 200 sam-ples/second) and the ratios CO vs COZ and HC vs C02 in addition to t:he peak-to-peak voltage outputs of the photodetectors 42, 44, 46 and 48, and the slopes, inter-cepts and standard deviations of the calculated CO vs COZ
and HC vs COZ ratios.
While sevE~ral illustrative embodiments of the inven tion have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art, without departing from the spirit and scope of the invention. Accordingly, it is intended that the present invention not be limited solely to the specifically described illustrative embodiments. Various modifications 2t3 18fi5 l~
are contemplated and can be made without departing from the spirit and scope of the invention as defined by the appended cl a ims~ .
Claims (30)
1. A sensing apparatus for sensing a composition of an exhaust plume of a motor vehicle, comprising:
a light source for radiating light including a plurality of predetermined wavelengths through said plume;
a chopper positioned between said source and said plume for alternating blocking and passing said light;
a photosensor for simultaneously sensing alternating blocking and passing said light;
a photosensor for simultaneously sensing alternating blocked or passed radiation levels at said predetermined wavelengths for said light passing through said plume; and a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.
a light source for radiating light including a plurality of predetermined wavelengths through said plume;
a chopper positioned between said source and said plume for alternating blocking and passing said light;
a photosensor for simultaneously sensing alternating blocking and passing said light;
a photosensor for simultaneously sensing alternating blocked or passed radiation levels at said predetermined wavelengths for said light passing through said plume; and a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.
2. An apparatus as in claim 1, in which:
the photosensor comprises a plurality of photodetectors, each photodetector being sensitive to a band of wavelengths that includes on one of said predetermined wavelengths; and the photosensor is disposed such that said light from the light source is simultaneously incident on the photodetectors.
the photosensor comprises a plurality of photodetectors, each photodetector being sensitive to a band of wavelengths that includes on one of said predetermined wavelengths; and the photosensor is disposed such that said light from the light source is simultaneously incident on the photodetectors.
3. An apparatus as in claim 2, in which the photodetector further comprises light blocking members for optically isolating the photodetectors from each other.
4. An apparatus as in claim 2, in which the photodetector further comprises a substrate on which the photodetectors are substantially isothermally disposed.
5. An apparatus as in claim 4, in which the photosensor further comprises a temperature regulator for maintaining the substrate and photodetectors at a predetermined temperature.
6. An apparatus as in claim 2, in which each photodetector comprises:
a photosensitive element; and a filter disposed between said plume and the photosensitive element having a passband coinciding with said respective band of wavelengths.
a photosensitive element; and a filter disposed between said plume and the photosensitive element having a passband coinciding with said respective band of wavelengths.
7. An apparatus as in claim 2, in which each photodetector comprises:
a photosensitive element which absorbs light at said respective predetermined wavelength; and a reflector for reflecting light from the light source which has propagated through said plume and the photosensitive element back through the photosensitive element.
a photosensitive element which absorbs light at said respective predetermined wavelength; and a reflector for reflecting light from the light source which has propagated through said plume and the photosensitive element back through the photosensitive element.
8. An apparatus as in claim 2, further comprising a substrate on which the photodetectors are disposed and which is substantially transparent to said predetermined wavelengths, in which:
each photodetector comprises a photosensitive element which is substantially transparent to said respective predetermined wavelength;
and an absorber for absorbing light from the light source which has propagated through the plume, the photosensitive element and the substrate.
each photodetector comprises a photosensitive element which is substantially transparent to said respective predetermined wavelength;
and an absorber for absorbing light from the light source which has propagated through the plume, the photosensitive element and the substrate.
9. An apparatus as in claim 2, in which the photosensor further comprises an homogenizer disposed between said plume and the photosensor for causing said light to be incident on the photodetectors with substantially uniform intensity.
10. An apparatus as in claim 9, in which the light source radiates said light through said plume as a beam.
11. An apparatus as in claim 10, in which the homogenizer comprises a multifaceted optical beam integrator.
12. An apparatus as in claim 10, in which the homogenizer comprises an optical lens for defocussing said beam.
13. An apparatus as in claim 1, further comprising:
a video camera for producing a video image of the vehicle; and a combines for combining said video image from the camera with said composition from the computer.
a video camera for producing a video image of the vehicle; and a combines for combining said video image from the camera with said composition from the computer.
14. An apparatus as in claim 13, further comprising a video monitor for displaying said video image from the camera and said composition from the computer.
15. An apparatus as in claim 13, further comprising a video recorder for recording said video image from the camera and said composition from the computer.
16. An apparatus as in claim 15, in which the computer controls the video recorder to record said video image from the camera and said composition from the computer only if said composition is outside a predetermined range.
17. An apparatus as in claim 1, in which:
said predetermined wavelengths include spectral absorption peaks of predetermined constituents of said composition;
said predetermined wavelengths further include a predetermined reference wavelength which is not a spectral absorption peak of said predetermined constituents; and the computer computes said transmittances as ratios of transmittances of said predetermined wavelengths which are spectral absorption peaks of said predetermined constituents and a transmittance of said reference wavelength.
said predetermined wavelengths include spectral absorption peaks of predetermined constituents of said composition;
said predetermined wavelengths further include a predetermined reference wavelength which is not a spectral absorption peak of said predetermined constituents; and the computer computes said transmittances as ratios of transmittances of said predetermined wavelengths which are spectral absorption peaks of said predetermined constituents and a transmittance of said reference wavelength.
18. A sensing apparatus for sensing a composition of fluid, comprising:
a light source for radiating light including a plurality of predetermined wavelengths through said fluid;
a chopper positioned between said source and said plume for alternating blocking and passing said light;
a photosensor for simultaneously sensing alternating blocked or passed radiation levels at said predetermined wavelengths for said light passing through said fluid; and a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.
a light source for radiating light including a plurality of predetermined wavelengths through said fluid;
a chopper positioned between said source and said plume for alternating blocking and passing said light;
a photosensor for simultaneously sensing alternating blocked or passed radiation levels at said predetermined wavelengths for said light passing through said fluid; and a computer for computing transmittances of said predetermined wavelengths from respective differences between said blocked and passed radiation levels, and computing said composition as a predetermined function of said transmittances.
19. An apparatus as in claim 18, in which:
the photosensor comprises a plurality of photodetectors, each photodetector being sensitive to a band of wavelengths that includes only one of said predetermined wavelengths; and the photosensor is disposed such that said light form the light source is simultaneously incident on the photodetectors.
the photosensor comprises a plurality of photodetectors, each photodetector being sensitive to a band of wavelengths that includes only one of said predetermined wavelengths; and the photosensor is disposed such that said light form the light source is simultaneously incident on the photodetectors.
20. An apparatus as in claim 19, in which the photosensor further comprises light blocking members for optically isolating the photodetectors from each other.
21. An apparatus as in claim 19, in which the photosensor further comprises a substrate on which the photodetectors are substantially isothermally disposed.
22. An apparatus as in claim 21, in which the photosensor further comprises a temperature regulator for maintaining the substrate and photodetectors at a predetermined temperature.
23. An apparatus as in claim 19, in which each photodetector comprises:
a photosensitive element; and a filter disposed between said fluid and the photosensitive element having a passband coinciding with said respective band of wavelengths.
a photosensitive element; and a filter disposed between said fluid and the photosensitive element having a passband coinciding with said respective band of wavelengths.
24. An apparatus as in claim 19, in which each photodetector comprises:
a photosensitive element which absorbs light at said respective predetermined wavelength; and a reflector for reflecting light from the light source which has propagated through said fluid and the photosensitive element back through the photosensitive element.
a photosensitive element which absorbs light at said respective predetermined wavelength; and a reflector for reflecting light from the light source which has propagated through said fluid and the photosensitive element back through the photosensitive element.
25. An apparatus as in claim 19, further comprising a substrate on which the photodetectors are disposed and which is substantially transparent to said predetermined wavelengths, in which:
each photodetector comprises:
a photosensitive element which is substantially transparent to said respective predetermined wavelength;
and an absorber for absorbing light from the light source which has propagated through said fluid, the photosensitive element and the substrate.
each photodetector comprises:
a photosensitive element which is substantially transparent to said respective predetermined wavelength;
and an absorber for absorbing light from the light source which has propagated through said fluid, the photosensitive element and the substrate.
26. An apparatus as in claim 19, in which the photosensor further comprises a homogenizer disposed between said fluid and the photosensor for causing said light to be incident on the photodetectors with substantially uniform intensity.
27. An apparatus as in claim 26, in which the light source radiates said light through said fluid as a beam.
28. An apparatus as in claim 27, in which the homogenizer comprises a multifaceted optical beam integrator.
29. An apparatus as in claim 27, in which the homogenizer comprises an optical lens for defocussing said beam.
30. An apparatus as in claim 18, in which:
said predetermined wavelengths include spectral absorption peaks of predetermined constituents of said fluid;
said predetermined wavelengths further include a predetermined reference wavelength which is not a spectral absorption peak of said predetermined constituents; and the computer computes said transmittances as ratios of transmittances of said predetermined wavelengths which are spectral absorption peaks of said predetermined constituents and a transmittance of said reference wavelength.
said predetermined wavelengths include spectral absorption peaks of predetermined constituents of said fluid;
said predetermined wavelengths further include a predetermined reference wavelength which is not a spectral absorption peak of said predetermined constituents; and the computer computes said transmittances as ratios of transmittances of said predetermined wavelengths which are spectral absorption peaks of said predetermined constituents and a transmittance of said reference wavelength.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US11978893A | 1993-09-10 | 1993-09-10 | |
| US119,788 | 1993-09-10 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2131865A1 CA2131865A1 (en) | 1995-03-11 |
| CA2131865C true CA2131865C (en) | 2000-06-13 |
Family
ID=22386417
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2131865 Expired - Fee Related CA2131865C (en) | 1993-09-10 | 1994-09-12 | Optical sensing apparatus for remotely measuring exhaust gas composition of moving motor vehicles |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2131865C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105259304B (en) * | 2015-09-16 | 2017-04-12 | 张世达 | On-line monitoring system and method for pollutants in vehicle tail gas |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1930466A (en) | 2004-02-09 | 2007-03-14 | 环境系统产品控股公司 | Remote emissions sensing including calculation and calibration techniques compensating for temperature and pressure effects |
| MX2007002213A (en) * | 2004-08-25 | 2007-05-04 | Environmental Syst Prod | System and method for calibrating remote emissions sensing instruments. |
| WO2017202947A2 (en) | 2016-05-25 | 2017-11-30 | Phoenix Ip Bv I.O. | Method and system for determining the fuel consumptions actually resulting from the everyday operation of road vehicles, energy inputs and emissions |
-
1994
- 1994-09-12 CA CA 2131865 patent/CA2131865C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105259304B (en) * | 2015-09-16 | 2017-04-12 | 张世达 | On-line monitoring system and method for pollutants in vehicle tail gas |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2131865A1 (en) | 1995-03-11 |
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| EEER | Examination request | ||
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