U.S. patent application number 15/759158 was filed with the patent office on 2018-10-18 for gas detector with normalized response and improved sensitivity.
This patent application is currently assigned to Honeywell International Inc.. The applicant listed for this patent is Honeywell International Inc.. Invention is credited to James Allen Cox, Bernard Fritz, Terry Marta, Antony Phillips, Rodney Watts.
Application Number | 20180299369 15/759158 |
Document ID | / |
Family ID | 56940423 |
Filed Date | 2018-10-18 |
United States Patent
Application |
20180299369 |
Kind Code |
A1 |
Marta; Terry ; et
al. |
October 18, 2018 |
GAS DETECTOR WITH NORMALIZED RESPONSE AND IMPROVED SENSITIVITY
Abstract
A non-dispersive photoacoustic gas detector comprises an
infrared light source, a closed chamber, a gas sample disposed
within the closed chamber, and an acoustic sensor in fluid
communication with the dosed chamber. The dosed chamber comprises
at least one window that is substantially transparent to infrared
light from the infrared light source, and the gas sample comprises
a gas or a mixture of at least two gases.
Inventors: |
Marta; Terry; (White Bear
Lake, MN) ; Cox; James Allen; (Monument, CO) ;
Fritz; Bernard; (Eagan, MN) ; Phillips; Antony;
(Poole, GB) ; Watts; Rodney; (Wimborne,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Honeywell International Inc. |
Morris Plains |
NJ |
US |
|
|
Assignee: |
Honeywell International
Inc.
|
Family ID: |
56940423 |
Appl. No.: |
15/759158 |
Filed: |
September 7, 2016 |
PCT Filed: |
September 7, 2016 |
PCT NO: |
PCT/US2016/050455 |
371 Date: |
March 9, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62216929 |
Sep 10, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2021/1704 20130101;
G01N 2291/02809 20130101; G01N 2291/021 20130101; G01N 29/4427
20130101; G01N 21/1702 20130101; G01N 29/2425 20130101; G01N
21/3504 20130101; G01N 29/4436 20130101; G01N 21/37 20130101 |
International
Class: |
G01N 21/17 20060101
G01N021/17; G01N 21/37 20060101 G01N021/37; G01N 21/3504 20060101
G01N021/3504 |
Claims
1-15. (canceled)
16. A non-dispersive photoacoustic gas detector comprising: an
infrared light source; a closed chamber, wherein the closed chamber
comprises at least one window that is substantially transparent to
infrared light from the infrared light source, wherein the closed
chamber is spaced apart from the infrared light source, and wherein
the closed chamber is substantially sealed; a gas sample contained
within the closed chamber, wherein the gas sample comprises a
concentration configured to produce an acoustic response having a
large magnitude that is detectable in a high noise environment
based on an input radiation intensity; and an acoustic sensor in
communication with the closed chamber configured to detect any
acoustic response produced by pressure changes within the closed
chamber.
17. The non-dispersive photoacoustic gas detector of claim 16,
further comprising a second closed chamber and a reference gas
contained within the second closed chamber, wherein the reference
gas configured to absorb over a different wavelength than the gas
sample.
18. The non-dispersive photoacoustic gas detector of claim 16,
further comprising a light path disposed between the infrared light
source and the at least one window.
19. The non-dispersive photoacoustic gas detector of claim 18,
further comprising a sample chamber disposed between the infrared
light source and the closed chamber, wherein the light path passes
through the sample chamber.
20. The non-dispersive photoacoustic gas detector of claim 18,
further comprising a processor in signal communication with the
acoustic sensor, wherein the processor is configured to convert a
signal output from the acoustic sensor into a concentration of gas
in the light path based on a decrease in the signal output when the
gas is present in the light path.
21. The non-dispersive photoacoustic gas detector of claim 16,
further comprising a membrane disposed between an interior of the
closed chamber and the acoustic sensor, wherein the acoustic sensor
is in communication with the interior of the closed chamber through
the membrane.
22. The non-dispersive photoacoustic gas detector of claim 16,
wherein the at least one window comprises a lens configured to
focus the infrared light from the infrared light source into an
interior of the closed chamber.
23. The non-dispersive photoacoustic gas detector of claim 16,
wherein an inner surface of the closed chamber comprises a mirrored
surface.
24. The non-dispersive photoacoustic gas detector of claim 16,
wherein the at least one window comprises a material configured to
filter at least a portion of the infrared light from the infrared
light source.
25. The non-dispersive photoacoustic gas detector of claim 16,
wherein the at least one window comprises a thickness configured to
filter at least a portion of the infrared light from the infrared
light source.
26. A method of detecting a gas comprising: passing infrared light
through a light path, wherein the light path comprises one or more
target gases; absorbing, by the one or more target gases, at least
a portion of the infrared light in the light path; passing the
infrared light into a closed chamber after passing the infrared
light through the light path, wherein the closed chamber comprises
at least one window that is substantially transparent to the
infrared light, and wherein the closed chamber comprises a gas
sample; generating an acoustic signal within the closed chamber in
response to passing the infrared light into the closed chamber,
wherein the acoustic signal decreases in response to an increased
concentration of the one or more target gases in the light path;
detecting the acoustic signal; and converting the acoustic signal
into a response.
27. The method of claim 26, wherein the response comprises a
concentration of the one or more target gases in the light
path.
28. The method of claim 26, wherein the response comprises a
normalized response, wherein the normalized response comprises an
explosion level measurement, a flammability level measurement, a
toxicity level measurement, calorific value measurement, or any
combination thereof.
29. The method of claim 26, wherein the gas sample comprises
methane and ethane, wherein the one or more target gases comprise
at least one component of natural gas, and wherein the response
comprises an explosion level measurement.
30. The method of claim 26, wherein the gas sample comprises
trifluoromethane, difluoromethane, cyclopropane, methyl ether,
1,1,1,2-tetrafluoroethane, or any combination thereof, wherein the
one or more target gases comprise at least one component of a
solvent, and wherein the response comprises an explosion level.
31. A non-dispersive photoacoustic gas detector comprising: an
infrared light source; a closed chamber, wherein the closed chamber
comprises at least one window that is substantially transparent to
infrared light from the infrared light source; a gas sample
disposed within the closed chamber, wherein the gas sample
comprises a mixture of at least two gases, and wherein the gas
sample comprises a concentration configured to produce an acoustic
response based on an input radiation intensity; and an acoustic
sensor in fluid communication with the closed chamber.
32. The non-dispersive photoacoustic gas detector of claim 31,
further comprising a light path disposed between the infrared light
source and the at least one window, wherein one or more target
gases are present in the light path.
33. The non-dispersive photoacoustic gas detector of claim 31,
wherein the gas sample comprises methane, ethane, ethylene, or any
combination thereof.
34. The non-dispersive photoacoustic gas detector of claim 31,
further comprising a processor in signal communication with the
acoustic sensor, wherein the processor is configured to convert a
signal output from the acoustic sensor into a normalized response
to a concentration of the one or more target gases present in the
light path, wherein the normalized response comprises at least one
of an explosion level measurement, a flammability level
measurement, a toxicity level measurement, calorific value
measurement, or any combination thereof.
35. The non-dispersive photoacoustic gas detector of claim 31,
further comprising at least one acoustic sensor configured to
detect ambient noise or background noise.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 62/216,929, filed on Sep. 10, 2015 and
entitled "Gas Detector with Normalized Response and Improved
Sensitivity," which is incorporated herein by reference in its
entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable.
BACKGROUND
[0004] Photoacoustic measurement is based on the tendency of
molecules in a gas, when exposed to certain wavelengths of radiant
energy (e.g. infrared light), to absorb the energy and reach higher
levels of molecular vibration and rotation, thereby reaching a
higher temperature and pressure within a measurement cell. When the
radiant energy striking a gas is amplitude modulated at a known
frequency, the resulting fluctuations in energy available for
absorption produce corresponding temperature and pressure
fluctuations in the gas, which can be measured as an acoustic
signal. The amplitude of the acoustic signal is proportional to the
intensity of the radiation and the concentration value of the
absorbing gas. Such devices can be used to measure small
concentration values of gases in a sample.
SUMMARY
[0005] In an embodiment, a non-dispersive photoacoustic gas
detector comprises an infrared light source, a closed chamber, and
an acoustic sensor in fluid communication with the closed chamber.
The closed chamber comprises at least one window that is
substantially transparent to infrared light from the infrared light
source, and the closed chamber is spaced apart from the infrared
light source. The closed chamber is substantially sealed.
[0006] In an embodiment, a non-dispersive photoacoustic gas
detector comprises an infrared light source, a closed chamber, a
gas sample disposed within the closed chamber, and an acoustic
sensor in fluid communication with the closed chamber. The closed
chamber comprises at least one window that is substantially
transparent to infrared light from the infrared light source, and
the gas sample can comprise a gas or a mixture of at least two
gases.
[0007] In an embodiment, a method of detecting a gas comprises
passing infrared light through a light path, where the light path
comprises one or more target gases, absorbing, by the one or more
target gases, at least a portion of the infrared light in the light
path, passing the infrared light into a closed chamber that
contains a gas sample after passing the infrared light through the
light path, generating an acoustic signal within the closed chamber
in response to passing the infrared light into the closed chamber,
detecting the acoustic signal, and converting the acoustic signal
into a response. The closed chamber comprises at least one window
that is substantially transparent to the infrared light, and the
acoustic signal decreases in response to an increased concentration
of the one or more target gases in the light path.
[0008] In an embodiment, a non-dispersive photoacoustic gas
detector comprises an infrared light source, a first closed chamber
having a plurality of windows that are substantially transparent to
infrared light from the infrared light source, a second closed
chamber having at least one window that is substantially
transparent to infrared light from the infrared light source, a
first acoustic sensor in fluid communication with the first closed
chamber, and a second acoustic sensor in fluid communication with
the second closed chamber. The first closed chamber is arranged in
series with the second closed chamber between the infrared light
source and the second closed chamber.
[0009] In an embodiment, a non-dispersive photoacoustic gas
detector comprises an infrared light source, a plurality of closed
chambers arranged in series with respect to a light path from the
infrared light source, and a plurality of acoustic sensors. Each
acoustic sensor of the plurality of acoustic sensors is associated
with a corresponding closed chamber of the plurality of closed
chambers, and each acoustic sensor is in fluid communication with
the corresponding closed chamber. A first closed chamber of the
plurality of closed chambers comprises a first sample gas, and a
second closed chamber of the plurality of closed chambers comprises
a second sample gas. The second sample gas has a different
composition than the first sample gas, and the plurality of closed
chambers comprises a transparent pathway through the plurality of
closed chambers.
[0010] In an embodiment, a method of detecting a gas comprises
passing infrared light through a light path that comprises one or
more target gases, absorbing, by the one or more target gases, at
least a portion of the infrared light in the light path, passing
the infrared light into a first closed chamber after passing the
infrared light through the light path, generating a first acoustic
signal within the first closed chamber in response to passing the
infrared light into the first closed chamber, passing the infrared
light through the first closed chamber into a second closed
chamber, generating a second acoustic signal within the second
closed chamber in response to passing the infrared light into the
second closed chamber, detecting the first acoustic signal and the
second acoustic signal, and converting the first acoustic signal
and the second acoustic signal into a response. The first closed
chamber comprises a plurality of windows that are substantially
transparent to the infrared light, and the first closed chamber
comprises a first gas sample. The second closed chamber comprises
at least one window that is substantially transparent to the
infrared light.
[0011] These and other features will be more clearly understood
from the following detailed description taken in conjunction with
the accompanying drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a more complete understanding of the present disclosure,
reference is now made to the following brief description, taken in
connection with the accompanying drawings and detailed description,
wherein like reference numerals represent like parts.
[0013] FIG. 1 schematically illustrates a photoacoustic sensor
according to an embodiment.
[0014] FIG. 2 schematically illustrates another photoacoustic
sensor according to an embodiment.
[0015] FIG. 3 schematically illustrates still another photoacoustic
sensor according to an embodiment.
DETAILED DESCRIPTION
[0016] It should be understood at the outset that although
illustrative implementations of one or more embodiments are
illustrated below, the disclosed systems and methods may be
implemented using any number of techniques, whether currently known
or not yet in existence. The disclosure should in no way be limited
to the illustrative implementations, drawings, and techniques
illustrated below, but may be modified within the scope of the
appended claims along with their full scope of equivalents.
[0017] The following brief definition of terms shall apply
throughout the application:
[0018] The term "comprising" means including but not limited to,
and should be interpreted in the manner it is typically used in the
patent context;
[0019] The phrases "in one embodiment," "according to one
embodiment," and the like generally mean that the particular
feature, structure, or characteristic following the phrase may be
included in at least one embodiment of the present invention, and
may be included in more than one embodiment of the present
invention (importantly, such phrases do not necessarily refer to
the same embodiment);
[0020] If the specification describes something as "exemplary" or
an "example," it should be understood that refers to a
non-exclusive example;
[0021] The terms "about" or "approximately" or the like, when used
with a number, may mean that specific number, or alternatively, a
range in proximity to the specific number, as understood by persons
of skill in the art field; and
[0022] If the specification states a component or feature "may,"
"can," "could," "should," "would," "preferably," "possibly,"
"typically," "optionally," "for example," "often," or "might" (or
other such language) be included or have a characteristic, that
particular component or feature is not required to be included or
to have the characteristic. Such component or feature may be
optionally included in some embodiments, or it may be excluded.
[0023] Disclosed herein are improved photoacoustic sensors and
methods of detecting one or more gases. The photoacoustic effect
has been used to irradiate a gas sample to produce an acoustic
response based on the absorption of a portion of the radiation to
produce heat and a corresponding pressure response. At low gas
concentrations, the acoustic response can be minimal, which may
require a sensitive acoustic sensor to detect the acoustic signal.
When the sensors are used in certain environments, noise from the
environment can mask the actual acoustic response. For example, an
industrial setting may include various mechanical equipment that
can create noise issues. While the noise may not occur at the same
frequency as the modulated light, and therefore the acoustic
response, the magnitude of the noise may be sufficient to create an
unacceptably low signal to noise ratio, which may make detection of
the presence of the gas difficult.
[0024] The present system does not rely on an acoustic response
from a target gas in the environment. Rather, a closed chamber or
cell is used to retain a gas sample. Radiation incident upon the
closed chamber may produce an acoustic response that can be
detected by an acoustic sensor. The concentration of the gas sample
can be carefully controlled within the closed and sealed chamber,
thereby producing an acoustic response having a relatively large
acoustic magnitude. When no gases that absorb radiation in the same
wavelength ranges are present between a source of the radiation and
the closed chamber, the acoustic response may be at or near peak.
When a target gas having an absorption profile similar to the gas
in the closed chamber is present between the source of the
radiation and the closed chamber, a portion of the radiation will
be absorbed prior to the radiation reaching the closed chamber. The
target gas then acts as a filter for the radiation, which results
in a decreased acoustic response for the gas in the closed chamber.
The decreased acoustic response can be detected by the acoustic
sensor and converted into a gas concentration in the light path
between the source of the radiation and the closed chamber.
[0025] This process can be used to determine a number of responses
including a concentration of one or more components present in the
light path. It has also been discovered that when a gas or gas
mixture is selected for use in the closed chamber, an overall or
normalized response to a plurality of gases can be detected. The
normalized response may include a measurement of a gas that is not
present the closed chamber. For example, a mixture of methane and
ethane can be used to detect the presence of not only methane and
ethane, but also of a wide range of hydrocarbons. The normalized
response may be useful in determining overall measurements such as
levels relative to flammability limits, toxicity exposures,
calorific value, and the like.
[0026] The photoacoustic sensor disclosed herein can also include a
plurality of closed chambers arranged in series where the radiation
passes through a first closed chamber, then through a second closed
chamber, etc. The ability to have multiple closed chambers in
series can allow for individual target gas concentrations to be
determined based on the acoustic response in different closed
chambers. Multiple normalized responses or a normalized response in
addition to one or more gas concentrations can also be
determined.
[0027] In some embodiments, one or more of the plurality of cells
can be used with a reference gas. The reference gas may absorb over
a different wavelength range than the other sample gases, and may
also have different absorption characteristics than a gas present
in the light path. The reference gas can then be used to provide an
indication of environmental effects on the acoustic response in the
other closed chambers. For example, the reference signal can be
used to determine any drop in the intensity of the radiation
output, any loss of intensity due to fouling of the detector (e.g.,
a fogged or dirty window, etc.), or any substances in the light
path that may affect the intensity of the radiation (e.g., dust,
water vapor, etc.). The reference chamber can also be used to
ensure that radiation is being received. If the reference chamber
does not produce an acoustic response, then an indication that the
radiation is not present may be generated. This may help ensure
that the system is operating. In comparison, a zero response in a
prior system may simply be interpreted as a lack of the presence of
a target gas when in fact the light source is not working. Thus,
the system disclosed herein may provide several advantages and
improvements in the field of gas detection.
[0028] FIG. 1 schematically illustrates an embodiment of a
photoacoustic sensor 100. The photoacoustic sensor 100 comprises a
light source 102 producing radiation 103, a light path 104, a
closed chamber 106, and an acoustic sensor 108 in fluid and/or
pressure communication with the interior of the closed chamber 106.
A window 105 can be used to allow light to pass into the closed
chamber 106. The photoacoustic sensor 100 can also include, in some
embodiments, a control system including a processor 110, a memory
112, a power source 114, and a display/output device 116 that can
be used to control the various elements of the system and/or
process the outputs (e.g., an acoustic signal generated by the
acoustic sensor 108.
[0029] The light source 102 serves to provide a source of modulated
light through the light path 104 and into the dosed chamber 106.
The efficiency at which a gas absorbs radiant energy can vary with
the radiation frequency of the energy. Energy absorption by a
particular gas over a frequency spectrum typically includes narrow
bands or lines of high absorptivity, spaced apart from one another
by frequency bands of much lower absorptivity. Each gas has a
unique absorptivity spectrum, which may be referred to as an
absorption profile. Accordingly, the light source 102 can be
selected to produce a frequency band or range encompassing the
absorption profile or lines of the gas of interest. In some
embodiments, a plurality of gases of interest can be radiated at
the same time, and the resulting frequency band of the light can be
selected to provide a suitable amount of radiation 103 at the
desired frequency to produce a measureable output signal across the
plurality of gases.
[0030] In an embodiment, the light source 102 can emit narrow or
broadband electromagnetic radiation in the infrared region. In an
embodiment, the light source 102 can include an incandescent lamp,
a black-body radiation source, or another emitter of
electromagnetic radiation in the infrared spectrum. In some
embodiments, the light source 102 can be a light emitting diode
(LED), an array of LEDs, a laser, a laser diode, or the like. In an
embodiment, the light source 102 can produce a broadband radiation
in the infrared range. In some embodiments, an optional filter can
be used with the light source 102 or the closed chamber 106 to
select a specific wavelength range from the radiation 103 produced
by the light source 102, as described in more detail herein.
[0031] The radiation 103 from the light source 102 can be modulated
to provide the acoustic response in the closed chamber 106. Various
types of modulators can be used. In an embodiment, the light source
102 can be modulated and/or the radiation 103 can be mechanically
or electrically modulated after being produced by the light source
102. For example, a controller can control the power signal to the
light source 102 to produce a modulated radiation output. The
radiation 103 can also be modulated after being produced by the
light source 102, including the use of modulation mechanisms such
as mechanical choppers (e.g., a rotating disc with passages
therethrough, a rotating mirror, etc.), interference gratings or
filters, interferometers, or the like. In some embodiments, optical
modulators can also be used to modulate the radiation 103 from the
light source 102 including, but not limited to, acousto-optic
modulation, electro-optic modulation, magneto-optic modulation, and
the like.
[0032] The radiation 103 can be modulated at a frequency that
allows the acoustic signal to be detected, and the detection limits
of the acoustic sensor along with any background noise can be taken
into consideration when selecting the modulation rate. The
radiation 103 can be modulated at a frequency of at least about 1
Hz, or at least about 10 Hz, though in some embodiments, the
radiation 103 can be modulated at a lower frequency. In some
embodiments, the radiation 103 may be modulated at higher
frequencies in order to decrease the sensitivity of the
photoacoustic sensor 100 to acoustical background noise. In an
embodiment, the radiation 103 may be modulated at a frequency
between 10 Hz and 100 kHz.
[0033] The radiation 103 produced by the light source 102 may
travel to the closed chamber 106 through a light path 104. As the
radiation 103 travels through the light path 104, any gases present
that absorb radiation at a frequency present in the radiation may
absorb a portion of the radiation 103 and act as a filter for the
radiation 103 reaching the closed chamber 106. The amount of
radiation 103 absorbed may depend on the amount of the gas present
in the light path 104, the length of the light path 104, the type
of gas, the frequency range of the radiation present, and the
absorption characteristics of the gas.
[0034] In some embodiments, the light path 104 may be an open
pathway that is not enclosed. This embodiment may be useful for the
detection of components present in atmospheric gases and/or within
the interior of vessels or other enclosures where the components
may normally be found. For example, a light source 102 can be
placed separate from the closed chamber 106 with only atmospheric
gases present between the light source 102 and the closed chamber
106.
[0035] In some embodiments, the light path 104 may comprise a
waveguide to allow the radiation 103 to pass from the light source
102 to the closed chamber 106. The waveguide can comprise an
optional enclosure or chamber. The enclosure can include a closed
pipe, conduit, or other vessel. The interior of the enclosure can
be polished to retain the radiation 103 within the enclosure and
guide the radiation 103 to the closed chamber 106. The enclosure
can have any suitable cross-sectional shape and can be formed of a
material suitable for use with the gases of interest. In some
embodiments, the enclosure can be formed from a metal (e.g.,
stainless steel, copper, aluminum, etc.), a polymeric material, a
ceramic or glass, or the like. The enclosure may have a length
selected to allow a sufficient amount of absorption by a target
gas. When very low concentrations are expected, the light path 104
may be longer than when moderate to high concentrations are
expected. In an embodiment, the light path 104 may have a length
between about 5 mm and about 10 m. For example, path lengths for
point measurements may be between about 10 cm and about 50 cm. Path
lengths for use in ducts can be less than about 0.5 m for small
ducts, between about 0.5 m and about 1 m for medium ducts, and
between about 1 m and about 10 m for larger ducts. In some
embodiments, path lengths longer than 10 m (e.g., up to about 100
m) may be possible when wave guides are used to focus the radiation
and/or focused beams of radiation are used across such
distances.
[0036] In some embodiments, the waveguide can comprise a portion
used to guide the radiation 103 from the light source 102. For
example, a glass or other solid portion (e.g., optical elements
such as lenses, reflectors, focusing elements, and the like) can be
used to guide the radiation into alignment with an ambient gas.
[0037] The use of an enclosure or chamber may allow the gases
within the enclosure to be isolated from the atmosphere, which may
be useful for toxic gases or other substances confined to enclosed
spaces. Fluid conduits can be coupled to the enclosure to provide
fluid communication between the interior of the enclosure and
another source of the gas being measured. For example, the
enclosure may be in fluid communication with a gas pipeline, a tank
interior, a closed system loop, or the like to allow for the
detection of one or more components without the need for the gases
to be exposed to the environment or for the light source 102 or
closed chamber 106 to be placed within the system.
[0038] In still other embodiments, the light path 104 may include
the optional enclosure and be in fluid communication with the gases
present adjacent to the photoacoustic sensor 100. In this
embodiment, an opening, aperture, porous membrane, or other
permeable opening may be associated with the enclosure to allow the
gases adjacent the enclosure to enter into the light path 104
between the light source 102 and the closed chamber 106.
[0039] The closed chamber 106 serves to retain a sample of a gas or
gas mixture of interest and allow the sample to be irradiated by
the radiation 103 that passes through the light path 104. In an
embodiment, the closed chamber 106 can comprise a window 105 that
allows the radiation 103 to pass into the interior of the closed
chamber 106. The closed chamber 106, along with the acoustic sensor
108, may be substantially sealed so that the sample of gas remains
within the closed chamber 106 and is not exchanged with any
external gasses or fluids.
[0040] The closed chamber 106 comprises a wall structure that can
include a generally rectilinear shape such as a cube, or
alternatively, a cylinder, or any other suitable shape. The
dimensions of the closed chamber 106 can vary and may be selected
to provide a predetermined volume or size. In an embodiment, the
closed chamber 106 can have dimensions (e.g., length, width,
diameter, and/or height) between about 1 mm and about 50 mm, though
one or more of the dimensions can be larger than 50 mm in some
instances. The closed chamber 106 may define a closed interior
space having a volume of between about 0.001 in.sup.3 to about 1
in.sup.3, or between about 0.005 in.sup.3 to about 0.5 in.sup.3,
though larger or smaller interior volumes may also be suitable.
[0041] The closed chamber 106 can be constructed of various
materials that are suitable for containing the sample within the
interior of the closed chamber 106. In an embodiment, the outer
wall may comprise a metal, such as aluminum, stainless steel,
copper, brass, or the like. In some embodiments, the outer wall may
comprise a plastic, or polymer, such as methacrylate. The outer
walls can also be formed of a ceramic or glass. The wall thickness
can be selected to provide a suitable structural support and
pressure containment. In some embodiments, the walls of the closed
chamber 106 can be constructed of a transparent material including
polymers, ceramics, glass, or the like, where the material may be
transparent to at least infrared radiation. This may reduce any
heating effects associated with the walls when radiation is
incident upon the walls.
[0042] In some embodiments, at least a portion of the wall or
interior surface of the closed chamber 106 can be mirrored. The
mirrored finish can serve to reflect light back into the interior
of the closed chamber 106 to provide an increased absorption and
acoustic response from the gas or mixture of gases in the closed
chamber 106. The mirrored finish can be on any portion of the
closed chamber 106. For example, a mirror finish (e.g., an
evaporated metal layer, etc.) can be formed on an external surface
of the wall of the closed chamber 106 where the wall is constructed
of a transparent material. In some embodiments, an internal metal
surface can be polished to produce a mirrored finish. In still
other embodiments, a mirror finish can be formed on one or more
portions of the interior surface of the closed chamber 106.
[0043] In an embodiment, a rear portion of the closed chamber 106
can comprise a mirrored surface. The mirrored surface may be
configured to direct the radiation 103 from the light source 102
back through the closed chamber 106 to the light source 102 and/or
a position near the light source 102. A corresponding mirror can be
placed at the light source 102 and/or near the light source 102 to
then reflect the radiation 103 back through the light path 104 to
the closed chamber 106. This arrangement may be useful in
increasing the effective path length along which the radiation 103
passes, which can be used to improve the detection limits of the
photoacoustic sensor 100 for small concentrations of the gas(es) of
interest.
[0044] In some embodiments, the walls can be formed, at least
partially, of a transparent material such as a glass or a polymer
that is transparent to infrared radiation in the wavelength of
interest while being impermeable to fluids (e.g., impermeable to
gasses and liquids). In some embodiments, at least a portion of a
wall section can be provided with a narrowed portion to allow the
portion of the wall to serve as the window 105 and improve
transmission of the radiant energy into the interior of the closed
chamber 106.
[0045] A closed chamber 106 that is constructed of a transparent
material such as a polymeric material may provide several
advantages. First, the material of the closed chamber 106 can react
to the radiation 103 in the same manner as the gas and cause
localized warming in response to the radiation. A transparent
material may allow the radiation 103 to pass through the walls
rather than being converted into heat. In addition, the transparent
materials may have a greater compliance and have a reduced
transmittance of any ambient sound signals better than metals. This
may serve to shield signal noise from interfering with the acoustic
signal generated within the gas sample.
[0046] The window 105 comprises an opening through a wall section
to allow the radiation 103 to pass into the interior of the closed
chamber 106. In an embodiment, the window 105 can comprise an
insert into an opening formed in the wall of the closed chamber.
The window 105 can be sealingly engaged with the opening in order
to prevent the escape of the sample or the entry of any external
gases into the closed chamber 106. The window 105 can be formed
from various materials so long as the material is at least
partially transparent to infrared radiation. In an embodiment, the
window 105 can comprise a glass. Other suitable materials can
include fused quartz (e.g., a UV fused quartz), germanium,
sapphire, silicon, or the like.
[0047] In an embodiment, the window 105 can have a shape designed
to direct the radiation 103 into the closed chamber 106. Since the
window 105 is transparent, the window 105 can form a lens to direct
the radiation 103 into the closed chamber 106. The window 105 can
comprise a converging lens configured to direct the radiation 103
passing through the light path 104 into the closed chamber 106. The
power of the lens can be selected depending on the desired focus
point within the closed chamber 106 or past the closed chamber 106.
In some embodiments, two or more windows 105 can be used to shape
and/or direct the radiation 103 into a desired beam.
[0048] The window material and/or thickness can be selected to have
some filtering properties for the radiation. While an optional
filter element can also be used, the window may be selected to
provide a desired degree of filtering without the need for an
additional filter. For example, the window material may be selected
to filter infrared wavelengths in the region absorbed by water
and/or carbon dioxide, both of which can cause interference with
the resulting acoustic signal. As a specific example, a window
material comprising fused UV quartz may serve as a filter for
blocking transmission of infrared waves in the range of 2.6 .mu.m
to 2.9 .mu.m, which corresponds to the approximate absorption
wavelengths of water and carbon dioxide. The amount of filtering
can be based on the thickness of the window, and both the selection
of the window material and the thickness can determine the amount
of filtering provided by the window (e.g., the amount of absorption
of wavelengths corresponding to water and carbon dioxide). As a
result, the window material may serve as a filter without the need
for any additional, optional filters.
[0049] An optional filter can be provided in the light path 104 to
select a desired portion of the radiation spectrum to pass into the
closed chamber 106. The filter can be placed adjacent to the light
source 102 and/or adjacent to the closed chamber 106, or at any
point in between the light source 102 and the closed chamber 106.
In an embodiment, the filter can be placed adjacent to the window
105, and in some embodiments, may be coupled to or deposited on a
surface of the window 105.
[0050] The optional filter can be made of a material that is
selectively transparent to infrared radiation in a desired
wavelength range. The selectively can be chosen based on the
absorption profile of a particular target gas or gasses. For
example, a filter may transmit the radiant energy only within a
somewhat narrowed waveband or frequency bandwidth. The transmission
frequency through the filter can be chosen to broadly coincide with
the strongest absorption bands of each gas to be detected.
[0051] The acoustic sensor 108 is in fluid communication with the
interior of the closed chamber 106 and serves to detect pressure
changes resulting in an acoustic signal originating within the
dosed chamber 106. The pressure changes within the closed chamber
106 are caused by gases absorbing the radiant energy of specific
wavelengths of the radiation 103 and changing temperature as a
result. The resulting temperature fluctuations in the gas
correspond to the modulation frequency of the radiation 103 from
the light source 102. The temperature changes result in pressure
changes within the closed chamber 106 that can be detected with the
acoustic sensor 108. Any suitable acoustic sensor or transducer can
be used. In some embodiments, the acoustic sensor 108 can include a
microphone, a pressure transducer (e.g., a piezoelectric
transducer, an electrostatic transducer, a flow based transducer,
an optical transducer, an electrically sensitive element, etc.).
The acoustic sensor 108 may be capable of detecting an acoustic
signal in the frequency range corresponding to the modulation
frequency of the radiation from the light source 102. In an
embodiment, the acoustic sensor can comprise a microphone. In some
embodiments, the acoustic sensor may comprise a piezoelectric
material.
[0052] The acoustic sensor 108 can be positioned to detect the
pressure changes within the closed chamber 106. In some
embodiments, the acoustic sensor 108 can be in a separate component
from the closed chamber. 106 and can be fluidly coupled to the
closed chamber 106 by an aperture or other opening. The combination
of the acoustic sensor 108, the aperture, and the interior of the
closed chamber 106 may form a closed chamber or cell that is
substantially sealed. In some embodiments, a flexible, impermeable
membrane can be disposed between the interior of the closed chamber
106 and the acoustic sensor 108 to allow for the transmission of
the pressure signal between the closed chamber 106 and the acoustic
sensor 108 while preventing the sample gas or gasses from directly
contacting the acoustic sensor 108.
[0053] While shown in FIG. 1 as having the acoustic sensor 108 in a
separate chamber, the acoustic sensor 108 can be placed directly
within the closed chamber 106 and/or form a portion of a wall of
the closed chamber 106. Signal lines can be used to provide a
connection between the acoustic sensor 108 and the processor 110,
memory 112, and power source 114.
[0054] In some embodiments, a plurality of acoustic sensors can be
associated with the photoacoustic sensor 100. For example, a
plurality of acoustic sensors 108 can be positioned to detect
pressure changes within the closed chamber 106. The use of multiple
acoustic sensors may provide redundancy in the event of an acoustic
sensor failure, error reduction through the use of combined signal
analysis, and/or noise cancellation across the cell. In some
embodiments, an additional acoustic sensor 108 can be associated
with the photoacoustic sensor 100 in order to detect ambient and/or
background noise. The ambient noise detector can be sealed from the
closed chamber 106 to detect ambient signals rather than a signal
generated within the closed cell 106. The resulting ambient and/or
background signal can be used to correct the output signal from the
acoustic sensor 108 detecting a signal from the photoacoustic
sensor 100 to account for noise, etc.
[0055] In some embodiments, additional and optional sensors can be
used with the system to provide environmental data that can be used
in correcting a detected signal. In some embodiments, the
photoacoustic sensor 100 can be used to determine a concentration
value of a target component in the light path 104. The term
"concentration value" is used herein to denote a measured signal
corresponding to the number of gas molecules in the light path 104.
The concentration value may depend on the gas concentration in the
light path 104, which can vary with changes in ambient temperature
and ambient pressure. For example, the approximate elevation of the
photoacoustic sensor 100 affects the pressure of the target gases
in the light path when the light path contains atmospheric gases.
In order to correct the concentration values for temperature and
pressure variations, a temperature and/or pressure sensor may also
be present. The temperature and/or pressure sensors may be in
signal communication with the processor 110 and the resulting
measured value or values can be used to correct the calculated
concentration value. Any suitable temperature sensor (e.g., a
thermocouple, etc.) and/or pressure sensor can be used with the
system. 100561 In some embodiments, a light sensor such as a
photodiode can be used to ensure that the light source 102 is
generating radiation. The photodiode can be placed behind the light
source 102 (e.g., in a position with light incident upon the
photodiode), within the light path 104, within the closed chamber
106, and/or behind the closed chamber 106 to provide an indication
of the presence of the radiation 103, and in some embodiments, an
intensity of the radiation 103. The light sensor may provide a
safety check to ensure that the radiation 103 is present, and may
also be used to correct the output values from the acoustic sensor
108 based on the detected intensity.
[0056] A processor 110 can receive and convert the signals from the
acoustic sensor 108 into a response such as a concentration value
of a component within the light path 104. The processor 110 can be
in signal communication through a wired and/or wireless connection
with the light source 102 along with the acoustic sensor 108. The
processor 110 can include circuitry for controlling the modulation
of the light source 102, as well as circuitry for receiving and
processing signals from the acoustic sensor 108, and optionally, a
temperature sensor, a pressure sensor, and/or one or more
photodiodes
[0057] In an embodiment, the processor 110 may comprise a
microcontroller. As used herein, the term "processor" can refer to
any type of computational circuit, such as but not limited to a
microprocessor, a microcontroller, a complex instruction set
computing (CISC) microprocessor, a reduced instruction set
computing (RISC) microprocessor, a very long instruction word
(VLIW) microprocessor, a graphics processor, a digital signal
processor (DSP), or any other type of processor or processing
circuit.
[0058] The memory 112 is used by the processor circuitry during
operation, and may include random access memory (RAM), one or more
hard drives, and/or one or more drives that handle removable media.
The memory 112 can include a non-transitory memory for retaining a
control and/or processing program that can execute upon the
processor 110.
[0059] The output or display device 116 can be used to indicate the
presence and respective concentration values of the particular
gases within the light path 104. The display device 116 may
comprise any suitable output device, including a video terminal,
LED indicator, analog gauge, printer, or other peripheral device.
Generally, the display device 116 may indicate concentration
measurements of a particular gas in terms of parts per million
(ppm) and/or partial pressure. The display devices 116 may also be
used to indicate the modulation frequency of the radiation 103. In
some embodiments, the display device 116 can be used to present
alarms or other warning conditions if a concentration value or
level is above a threshold.
[0060] The power source 114 can provide power to the light source
102, acoustic sensor 108, temperature sensor, pressure sensor,
photodiode, processor 110, memory 112, and display device 116. In
an embodiment, the power source 114 may comprise a battery, such as
a rechargeable lithium-ion battery. In an alternative embodiment,
power source 116 may comprise an alternating current (AC)
adaptor.
[0061] The processor 110 can transform the signal using various
algorithms to identify the one or more gases within the light path
104 and a concentration corresponding to each of those gases.
Specifically, the processor 110 may contain a file providing a base
acoustic response measurement when no gas is present in the light
path 104. The base acoustic response may be considered an upper
response level. When a gas is present in the light path 104, the
gas may absorb along one or more lines in the frequency range
available in the radiation spectrum. The absorption may filter the
radiation signal reaching the dosed chamber 106. A decrease in the
output signal of the sample gas within the chamber may result from
the absorption of the gas in the light path 104. The degree of the
decrease in the signal output within the closed chamber 106 can be
correlated to the concentration of the target gas present in the
light path, and the processor 110 may utilize a correlation,
optionally along with the ambient pressure and temperature and/or
the radiation intensity, to determine a concentration value of the
target gas in the light path 104.
[0062] Thus, the present system relies upon a decrease in the
output signal to determine an increase in the presence of a target
gas in the light path. The concentration determination may be
advantageous by providing a high signal to noise ratio at low
concentration values. In contrast to systems relying on an acoustic
response at low concentrations, the noise level from various
sources including ambient acoustic signals may not significantly
interfere with the concentration determination. Further, the length
of the light path 104 can be configured to provide a desired level
of sensitivity wherein a long light path may provide a greater
sensitivity to lower concentration values.
[0063] The photoacoustic sensor 100 can be used to detect a gas in
an environment. The detection process can begin with the light
source 102 producing a radiation 103 that can be modulated and
passing the radiation 103 through a light path 104. The light path
104 can comprise one or more target gases whose concentration is
being measured. The one or more target gases can absorb at least a
portion of the radiation 103. For example, the target gas in the
light path 104 can absorb radiation 103 at certain frequencies. The
remaining radiation 103 having the portion of the energy absorbed
can pass to the closed chamber 106 through the window 105.
[0064] The interaction of the remaining radiation 103 with the
sample gas in the closed chamber 106 can cause temperature changes,
and corresponding pressure changes, within the closed chamber 106
that correspond to the modulation frequency of the radiation 103.
The pressure changes results in an acoustic signal being generated
within the closed chamber 106, and the acoustic signal can be
detected with the acoustic sensor 108. The acoustic signal can be
converted into a response upon being sent to the processor 110. in
an embodiment, the response can comprise a concentration value of
the target gas in the light path 104. For example, the processor
110 may then be used to perform calculations on the electrical
signal produced by the acoustic sensor 108, which allows for the
determination of the presence and concentration of one or more
gases in the light path 104. In some embodiments, various
additional inputs can be used in the determination of the
concentration value including a temperature input, an ambient
pressure input, an intensity measurement of the radiation 103, or
the like.
[0065] In an embodiment, a single sample gas may be present in the
closed chamber 106 alone or in combination with a carrier gas. The
optional carrier gas may not absorb at the same frequency as the
sample gas or may not substantially absorb infrared radiation. As a
result, the carrier gas may not contribute to the acoustic response
within the closed chamber 106. The use of the carrier gas may allow
the concentration of the sample gas within the closed chamber 106
to be controlled to produce a desired acoustic response based on an
input radiation intensity. The carrier gas can also be used to
control the pressure within the closed chamber 106, which may be
useful for controlling leaks and the partial pressure of the sample
gas or gasses present n the closed chamber 106.
[0066] The use of a single sample gas may allow the presence of the
same gas to be detected in the light path 104. For example, the use
of methane in the closed chamber 106 may be used to detect the
presence of methane in the light path 104 based on a decrease in
the detected acoustic signal generated within the closed chamber
106. In this embodiment, the gas sample within the closed chamber
may allow for a concentration value of the same gas in the light
path 104 to be determined.
[0067] In some embodiments, a single gas or a mixture of sample
gases can be present in the closed chamber 106, which can he used
to produce a normalized response to a mixture of gases in the light
path 104. In general, various gases may have similar absorption
characteristics based on a similarity of internal bonds and
structures. For example, a mixture of light hydrocarbons such as
methane, ethane, propane, and butane, may exhibit some overlapping
absorption characteristics when present in a mixture. A mixture of
a plurality of sample gases that are selected to have absorption
ranges that overlap with the gases that can be present in the light
path can be used to provide an overall indicator of the presence of
the gas.
[0068] As used herein a "normalized response" refers to an
indication of a level of the gas in the light path without
providing a direct indication of the individual concentration of
each gas in the light path. The normalized response may also
contain an indication of the presence of a gas that is not present
in the sample in the closed chamber 106. This type of response may
be useful in several areas including determining a presence of one
or more gases relative to an explosion limit, an exposure
threshold, a toxicity threshold, or any combination thereof. The
explosion limit, which can also be referred to as a flammability
limit, refers to the range of concentrations of a flammable mixture
in air that will combust. The explosion limit has both an upper
concentration limit (e.g., an upper explosion limit) and a lower
concentration limit (e.g., a lower explosion limit or LEL). Outside
of this concentration range, the flammable mixture will not combust
in the air. The LEL can be monitored to prevent a concentration of
flammable gases from accumulating and potentially leading to an
explosive condition. The exact threshold for the LEL varies from
jurisdiction to jurisdiction, but the LEL thresholds generally
represent a fraction of the LEL that is allowable before an alarm
should be triggered.
[0069] In an embodiment, the photoacoustic sensor 100 can be used
to produce a normalized response that is indicative of the LEL of
various flammable mixtures. Different sample gases can be selected
to produce the acoustic response in the closed chamber 106 to
indicate an overall concentration of flammable components in the
light path 104, without being specific to one or more flammable
components. The choice of the gas or mixture of gases can be based
on the ability of the gas or mixture of gases to remain a gas over
the operating temperature range (e.g., having a boiling point below
about -40.degree. C., etc.), the absorption of wavelengths of
radiation in a range that overlaps with the gases of interest
(e.g., absorbs radiation in the wavelengths from about 3.2 .mu.m to
about 3.6 .mu.m), the ability of the gas or mixture of gases to
avoid absorption in a range corresponding to potential interfering
compounds (e.g., avoids CO.sub.2 absorption between about 4.2 .mu.m
and about 4.35 .mu.m), and/or the relative toxicity of the gas or
mixture of gases to provide for safe handling and use of the
device. In some embodiments, the selection and/or concentration of
the gas or mixture of gases can be based on the desired sensitivity
and geometry of the gas detector and the length of the light path
104.
[0070] In some embodiments, the concentration of flammable
components in the light path can be correlated to an LEL using a
mixture of gases in the sample chamber comprising methane,
ethylene, ethane, propane, difluoromethane, chlorofluoromethane,
chlorodifluoromethane, trifluoromethane, propene, propylene,
tetrafluoroethylene, pentafluoroethane, trifluorotheylene,
1,1,1,-trifluoroethane, methyl fluoride, cyclopropane, other
hydrocarbon gases, or any combination thereof The mixtures can
include any suitable mixture ratios including those based on
chamber length, cell length, carrier gas composition, sample gas
composition, and the like. In an embodiment, the sample gas in the
closed chamber 106 can comprise a mixture of methane and ethane at
a ratio of between about 4:1 and about 1:1. In another embodiment,
the sample gas in the closed chamber 106 can comprise a mixture of
methane and ethylene at a ratio of between about 6:1 and about 1:1.
In yet another embodiment, the sample gas in the closed chamber 106
can comprise a mixture of methane and trifluoromethane at a ratio
of between about 3:1 and about 1:3. In still another embodiment,
the sample gas in the closed chamber 106 can comprise a mixture of
methane having a concentration between about 20% and about 40% and
ethane having a concentration between about 10% and about 30%, with
the balance being an inert gas (e.g., a mixture of about 30%
methane and about 18% ethane for use with a 40 mm light path 104).
In some embodiments, the closed chamber 106 can comprise
cyclopropane (e.g., 100% cyclopropane) for use in detecting one or
more components of a solvent. In some embodiments, the sample gas
in the closed chamber 106 can comprise a mixture of
trifluoromethane and an inert gas.
[0071] Each of the sample gas mixture may be useful for determining
a normalized response of flammable gases in the light path 104
relative to an LEL threshold. Various flammable gases can include,
but are not limited to, ethanol, ethyl acetate, toluene, methyl
ethyl ketone, isopropanol, acetone, n-hexane, n-heptane,
cyclohexanon, butanol, o-xylene, p-xylene, methanol, dimethyl
ether, benzene, butyl acetate, 1-methoxy-2-propanol, ethoxy
propanol, methyl glycol, tetrahydrofuran, dimethylformamide, propyl
acetate, methyl isobutyl ketone, methane, ethane, propane, butane,
pentane, C6+ hydrocarbons, and any combination thereof.
[0072] In order to determine the concentration of the flammable
gases relative to the applicable LEL threshold, the output of the
photoacoustic sensor 100 can be determined over a range of gas
concentrations for one or more flammable components using a mixture
of gases as described above in the closed chamber 106. A
correlation between the percentage of the LEL and the concentration
of the flammable gas in the light path can be developed and used
with the output acoustic signal from the acoustic sensor 108 to
determine a flammability level relative to the LEL. The use of a
plurality of sample gases in the closed chamber 106 to produce the
normalized response over a broad range of flammable components in
the light path represents an advantage relative to the need to
determine each gas concentration individually and can be more
accurate than past flammability detectors.
[0073] The use of a sample gas or a plurality of gases in the
sample gas mixture within the closed chamber 106 has also been
shown to be applicable to other normalized responses. For example,
mixtures of sample gases can be used to determine an exposure level
to various hydrocarbons, an exposure level relative to a toxicity
threshold, or the like. As with the specific examples listed
herein, a correlation between the sample gas mixture and the
expected gases within the light path 104 (e.g., aromatic
hydrocarbons, refrigerants, solvents, carbon monoxide, carbon
dioxide, etc.) can be tested and measured, and the sample gas
mixture can then be used with closed chamber 106 to provide a
normalized response over a range of target gases within the light
path 104.
[0074] In an embodiment, a sample gas or a plurality of gases can
be used in the sample gas mixture within the closed chamber 106 to
obtain a normalized response for a calorific value of a gas sample.
The calorific value as used herein refers to the energy content of
a fuel and represents a measurement of the amount of heat produced
by the complete combustion of a specific quantity of the fuel. In
this embodiment, mixtures of sample gases can be used to determine
the calorific value of a gas (e.g., natural gas, etc.), for
example, passing through a pipeline. Existing gas metering uses
volumetric metering and customers can be billed for energy.
However, the meter only tends to measure volume while the natural
gas provider monitors and compensates for the varying aspects of
the natural gas (pressure, temperature, and energy content), which
can cause changes in the energy contained in a volume of the
natural gas. As with the other examples listed herein, a
correlation between the calorific value in various gas samples in
the light path 104 and a sample gas mixture can be tested and
measured, and the sample gas mixture can then be used with closed
chamber 106 to provide a normalized response over a range of
calorific values of a gas within the light path 104. Since it may
be expected that a natural gas or other gas containing substantial
amounts of hydrocarbons can absorb the radiation within the path
length, the overall length of the light path 104 can be set to
allow for the proper output signal strength in the closed cell.
[0075] In each of the normalized response determinations, the
resulting normalized response can be compared to a threshold. For
example, the normalized flammability limit can be output as a
percentage of the LEL. The resulting output can be compared to a
threshold percentage of the LEL, and an alarm or warning can be
generated if the normalized response exceeds the threshold. This
may allow for the monitoring of a condition that can be caused by a
large range of gases, any one or more of which may be present at
any given time. Thus, the photoacoustic sensor 100 with a plurality
of sample gases may simplify the monitoring process for these types
of conditions.
[0076] Another embodiment of a photoacoustic sensor 200 is
schematically illustrated in FIG. 2. The photoacoustic sensor 200
of FIG. 2 is similar in many aspects to the photoacoustic sensor
100 of FIG. 1, and similar components will not be discussed in
detail in the interest of brevity. In general, the photoacoustic
sensor 200 comprises a light source 102 producing radiation 103, a
light path 104, a first closed chamber 206, a first acoustic sensor
208 in fluid communication with the interior of the first closed
chamber 206, a second closed chamber 210, and a second acoustic
sensor 212 in fluid communication with the interior of the second
closed chamber 210. The light source 102, the light path 104, the
processor 110, the memory 112, the power source 114, and the
display device 116 can be the same or similar to the corresponding
components described with respect to FIG. 1.
[0077] The main difference between the photoacoustic sensor 200
shown in FIG. 2 and the photoacoustic sensor 100 shown in FIG. 1 is
the presence of a plurality of closed chambers 206, 210, each with
an associated acoustic sensor 208, 212, respectively. Each closed
chamber 206, 210 and the corresponding acoustic sensor 208, 212 may
be the same or similar to the acoustic sensor and closed chamber
described with respect to FIG. 1. In an embodiment, the closed
chambers 206, 210 can be constructed of a transparent material as
described above.
[0078] The multiple closed chambers 206, 210 can be arranged in a
number. of configurations. As shown in FIG. 2, the first dosed
chamber 206 may have a first window 105 disposed in a first wall.
The first window 105 may allow the radiation that passes through
the light path 104 to pass into the first closed chamber 206. A
second window 205 can be disposed in a second wall of the first
closed chamber 206, which may be a common wall between the first
closed chamber 206 and the second closed chamber 210. The second
window 205 may be sealingly engaged with the second wall to form a
seal between the first closed chamber 206 and the second closed
chamber 210. The housing forming the two closed chambers 206, 210
can be an integrated housing with an internal divider with the
second window 205. The volumes and shapes of each closed chamber
206, 210 can be the same or different. In an embodiment, the second
closed chamber 210 may have a different volume than the first
closed chamber 206.
[0079] The first window 105 and the second window 205 can be formed
from any of the materials described herein. In an embodiment, the
first window 105 and the second window 205 are formed from the same
material and may have approximately the same thickness. In order to
allow the radiation to pass through the first closed chamber 206
and into the second closed chamber 210, the first window 105 and
the second window 205 may be substantially aligned along a line
extending towards the light source 102. In some embodiments, the
first window 105, and the second window 205 can comprise different
materials, and one or more optional filters can be associated with
the first window 105 and/or the second window 205. For example, the
second window 205 may filter the radiation 103, or alternatively
have a separate filter for filtering the radiation 103, passing
through the first closed chamber 206 to provide a different
radiation spectrum for the radiation 103 passing into the second
closed chamber 210.
[0080] In an embodiment, one or more of the first window 105 and/or
the second window 205 can be formed as one or more lenses. For
example, the first window 105 can be formed as a converging lens to
gather and cause the radiation to converge into the first closed
chamber 206. The second window 205 can comprise a converging or
diverging lens. For example, the second window 205 may comprise a
diverging lens to produce a shaped beam from the converging
radiation passing through the first window 105. Any combination of
shaped windows can be used to provide the desired light beam shape
in the first closed chamber 206 and/or the second closed chamber
210.
[0081] In an embodiment, a mirrored surface can present n the first
closed chamber 206 and/or the second closed chamber 210. In sonic
embodiments, one or more of the windows 105, 205 can be replaced
with a mirror or mirrored surface to reflect at least a portion of
the radiation 103 back into the same closed chamber or other closed
chambers. The mirrored surface may also, in some embodiments,
reflect at least a portion of the radiation 103 back to the light
source 102 or a reflective surface near the light source 102 as
described in more detail above.
[0082] While shown as two closed chambers 206, 210 sharing a common
window 205, the two closed chambers 206, 210 can also be separate
closed chambers that are disposed adjacent to each other. In this
embodiment, the first closed chamber 206 could comprise two windows
opposite each other and aligned so that the light passing through
the light path 104 can pass into the first closed chamber 206,
through the interior and out of the closed cell on the opposite
side. The second closed chamber 210 could comprise a window aligned
with the two windows in the first closed chamber 206 so that
radiation 103 passing through the first closed chamber 206 could
pass into the second closed chamber 210. Any number of separate
closed chambers with the appropriate alignment of the windows could
be placed in series to allow the radiation to pass through the
closed chambers in series.
[0083] The use of a plurality of closed chambers 206, 210 may
provide for a number of different uses of the photoacoustic sensor
200. For example, the second closed chamber 210 can be used to hold
a reference gas and/or the second closed chamber 210 can be used to
hold a second sample gas for detecting different gases within the
light path 104. In an embodiment, the first closed chamber 206 can
retain a reference gas and the second closed chamber 210 can hold
the sample gas.
[0084] In an embodiment, the second dosed chamber 210 can be used
to hold a reference gas. A reference gas can include a gas that
absorbs a portion of the radiation 103 at a different frequency
than the sample gas within the first closed chamber 206. In some
embodiments, the reference gas may absorb radiation 103 at a
different frequency than an expected gas within the light path 104.
When the radiation 103 passes into the second closed chamber 210,
the reference gas may produce an acoustic response that corresponds
to the modulation frequency of the radiation 103. A suitable
reference gas or mixture of reference gases may be selected based
upon the sample gas or gasses present in the first closed chamber
206 as well as the expected gases present in the light path 104. In
an embodiment, the reference gas can comprise nitrous oxide (e.g.,
NO2), diborane, combinations thereof, or any other gas or
combination of gases that can produce an acoustic response at a
frequency other than the gases of interest.
[0085] The use of a gas that may not be affected by the presence of
any gases between the light source 102 and the second dosed chamber
210 may provide a reference acoustic signal that can be detected by
the second acoustic sensor 212. The reference signal may be used in
several ways. First, the reference signal may provide an indication
that radiation 103 is being produced by the light source 102.
Without such an indication, the photoacoustic sensor 200 may
provide a false indication as to the presence of a target gas.
[0086] The reference signal can also be used to provide a
correction for the acoustic signal detected in the first closed
chamber 206. The frequency range of the radiation 103 at which the
reference gas absorbs may not be absorbed or otherwise filtered
between the light source 102 and the second closed chamber 210. As
a result, the reference gas may produce an acoustic response that
is only affected by attenuation of the radiation 103 that is common
to both the reference gas and the sample gas in the first closed
chamber 206. For example, fogging of the first window 105 and/or
the second window 205, a reduction in the output intensity of the
light source 102, atmospheric attenuators such as dust, or the like
may result in a decrease in the radiation intensity reaching the
second closed chamber 210. Since these effects may be common to
both the first closed chamber 206 and the second closed chamber
210, the reference signal can be used to compensate the detected
signal from the first closed chamber 206 to produce a response with
an improved accuracy.
[0087] In some embodiments, the plurality of closed chambers 206,
210 can both comprise sample gases. The sample gas in the first
closed chamber 206 can be different than the sample gas in the
second closed chamber 210. The ability to use two different samples
that can each comprise one or more gases can allow for different
target gases to be detected in the light path 104. In an
embodiment, two different sample gases are retained in the two
closed chambers 206, 210, When the absorption characteristics of
the two sample gases do not overlap, or only overlap to a limited
degree, a concentration value of a corresponding target gas in the
light path 104 can be determined.
[0088] In an embodiment, when a target gas is present in the light
path 104 that is the same as the first sample gas or that has
similar absorption characteristics as the first sample gas, the
reduction in the acoustic response in the first closed chamber 206
can be processed to determine a concentration value of the target
gas in the light path. Similarly, when a second target gas is
present in the light path 104 that is the same as the second sample
gas or that has similar absorption characteristics as the second
sample gas, the reduction in the acoustic response in the second
closed chamber 206 can be processed to determine a concentration
value of the second target gas in the light path 104. When both the
first and second target gases are present in the light path at the
same time, a reduction in the acoustic response in the first closed
chamber 206 and the second closed chamber 210 can be used to
determine a concentration value of first and second target gases at
the same time. This may allow for individual concentration values
of a plurality of target gases in the light path 104 to be
determined simultaneously.
[0089] In some embodiments, a plurality of closed chambers 206, 210
can be used to provide one or more normalized responses along with
a concentration value for a specific target gas. In this
embodiment, one of the closed chambers 206, 210 may comprise a
mixture of sample gases to provide a normalized response while
another closed chamber can contain a sample gas to provide an
individual concentration value of a target gas. The ability to
combine multiple closed chambers 206, 210 in series can then be
used to provide a variety of output responses according to the
needs of the sensor.
[0090] While illustrated in FIG. 2 as having two closed chambers
206, 210, any number of closed chambers can be arranged in series.
For example, 3, 4, 5, 6, or more closed chambers can be arranged in
series to enable the detection of a concentration value of one or
more components, one or more normalized responses, and/or the use
of a reference signal to ensure the operation of the sensor and/or
provide a correction signal.
[0091] While illustrated in FIG. 2 as being arranged in series, the
plurality of closed chambers 206, 210 can also be arranged in
parallel. For example, the cells can be stacked so that a single
light source 102 can be incident on each cell of the plurality of
closed chambers 206, 210 at the same time. The remaining components
may be the same or similar. An arrangement in parallel can allow
for sample gases that have overlapping absorption lines or ranges
to be used for the simultaneous detection of one or more target
gases. By arranging the closed chambers 206, 210 in parallel, the
absorption of the radiation 103 by a sample gas in one of the
closed chambers should not filter or prevent a sample gas in the
second closed chamber 210 from being used to detect a signal over
the absorption band. Further, in some embodiments, a plurality of
closed chambers can be arranged in both parallel and series with
multiple parallel rows of closed chambers having closed chambers
also arranged in series.
[0092] FIG. 3 schematically illustrates such an arrangement. In
this embodiment, three closed chambers 206, 210, 314 can be
arranged in series. This embodiment can be similar to the
embodiment illustrated in FIG. 1 and FIG. 2, and similar elements
will not be described in the interest of brevity. The main
distinction between the photoacoustic sensor 300 of FIG. 3 and the
previous photoacoustic sensors (e.g., sensor 100 and/or sensor 200)
is the presence of the third closed chamber 314. As described
herein, the three chambers can be formed with a single housing with
windows 105, 205, 305 separating the closed chambers 206, 210, 314
and/or one or more of the dosed chambers 206, 210, 314 can be a
separate closed chamber arranged along the light path 104. One or
more of the windows 105, 205, 305 can comprise a lens as described
herein. The acoustic sensors 208, 212, 316 can be used to detect
the acoustic response in the respective closed chambers 206, 210,
314.
[0093] In the embodiment shown in FIG. 3, the first closed chamber
206 and/or the second closed chamber 210 can be used in any of the
ways described with respect to the two closed chambers illustrated
in FIG. 2. The addition of the third closed chamber 314 may further
allow for the use of a reference gas to provide a reference signal
in addition to two concentration values for different target gases,
two normalized response values using a mixture of sample gases, or
a combination of a concentration value and a normalized response
value. In some embodiments, the third closed chamber 314 could be
used for a further concentration value determination or a
normalized response value determination. The addition of one or
more additional closed chambers could also provide additional
responses.
[0094] Referring to FIG. 2 and FIG. 3, the photoacoustic sensors
200, 300 can be used to detect a gas in a light path 104. The
detection process can occur by passing modulated radiation such as
infrared radiation through a light path 104. In an embodiment, the
radiation 103 can comprise a broad spectrum infrared radiation. The
light path 104 can be open or enclosed, depending on the
application. The light path 104 may comprise one or more target
gases whose presence is being detected. When the one or more target
gases are present, the target gases can absorb at least a portion
of the infrared light in the light path 104. The remaining
radiation 103 may comprise a spectrum having the intensity of the
radiation 103 as the absorption lines decreased.
[0095] The infrared light can then be passed into a first closed
chamber 206 through a first window 105. The window can be
substantially transparent to infrared light, though an optional
filter may be used to allow a selective range of frequencies or
wavelengths to pass into the first closed chamber 206. The first
closed chamber 206 can comprise a first sample of one or more
gases. The interaction of the remaining radiation 103 with the
first sample can generate an acoustic signal that can be detected
by a first acoustic sensor 208. The acoustic signal can be
generated in response to the absorption of a portion of the
remaining radiation 103 by the sample gas in the first closed
chamber 206. The resulting absorption may produce a temperature
variation and corresponding pressure variation that corresponds to
the modulation frequency of the radiation 103 passing through the
light path 104.
[0096] The radiation 103 that is not absorbed in the light path 104
and the first closed chamber 206 can then pass out of the first
closed chamber 206 and into a second dosed chamber 210. The
radiation 103 can pass through one or more windows between the
first closed chamber 206 and the second closed chamber 210, where
the window can be a common window that separates the two chambers
from each other. The second closed chamber 210 can comprise one or
more gases. The interaction of the remaining radiation 103 with the
one or more gases in the second closed chamber 210 can generate a
second acoustic signal that can be detected by a second acoustic
sensor 212. The second acoustic signal can be generated in response
to the absorption of a portion of the remaining radiation 103 by
the one or more gases in the second closed chamber 210. The
resulting absorption may produce a temperature variation and
corresponding pressure variation that corresponds to the modulation
frequency of the radiation 103 passing through the light path
104.
[0097] The outputs from the first acoustic sensor 208 and the
second acoustic sensor 212 can pass to a processor 110. The
processor 110 may use a correlation or comparison with a base level
response when no target gases are present in the light path 104 to
determine a reduction in the acoustic signals. The resulting
reduction in the acoustic signals can be used to determine a
response. Various corrections can be applied to the acoustic sensor
outputs include corrections for pressure and temperature.
[0098] The response can comprise a concentration of a first target
gas in the light path 104. When the first target gas is the same as
one of the gases in the first closed chamber 206 or the second
closed chamber 210, or has similar absorption characteristics to
one of the gases in the first closed chamber 206 or the second
closed chamber 210, the processor 110 can determine a concentration
value for the target gas. The response can also include a
concentration value for a second target gas in the light path 104.
When the second target gas is the same as one of the gases in the
first closed chamber 206 or the second closed chamber 210, or has
similar absorption characteristics to one of the gases in the first
closed chamber 206 or the second closed chamber 210, the processor
110 can determine a concentration value for the second target gas,
which can occur at the same time as the determination of the
concentration value for the first target gas.
[0099] In an embodiment, the one or more gases in the second closed
chamber 210 can comprise a reference gas. The reference gas may
have different absorption characteristics than the sample in the
first closed chamber 206, and the reference gas may have different
absorption characteristics than a gas expected to be present in the
light path 104. As a result, the reference gas may produce an
acoustic response that can be used to indicate interference from
the materials in the window, a filter, or a reduction in the output
of the light source producing the radiation. The response can then
be corrected based on the acoustic output from the reference gas in
the second closed chamber
EXAMPLES
[0100] The disclosure having been generally described, the
following example is given as particular embodiments of the
disclosure and to demonstrate the practice and advantages thereof.
It is understood that the example is given by way of illustration
and is not intended to limit the specification or the claims in any
manner. 1001021 To demonstrate the use of the photoacoustic sensor
as described herein, a filament bulb was used as a source with a
1000 nm wide filter in front to pass wavelengths in the .about.3-4
micron range. The source/filter combination was placed
approximately 40 mm away from the detector which was comprised of
two stacked closed chambers. The "sample" closed chamber contained
a mixture of methane (approx. 30% v/v) and ethane (approx. 18%
v/v)with a balance of an inert gas such as nitrogen. The
"reference" closed chamber contained (nitrous oxide) with an
absorption cross section within the 3-4 micron wavelength band, but
outside the absorption band for the hydrocarbons to be measured.
The deviation of response with 4.4% Methane (50% LEL UK) contained
within the path length (between the bulb and closed chambers)
produced a measured deviation response of about 15% (against an
N.sub.2 baseline--no gas).
[0101] It is expected that other hydrocarbon gases will provide a
similar deviation response. The results demonstrate the ability for
a single calibration using a gas mixture that can provide a
normalized response for a number of hydrocarbons.
[0102] Having described some systems and methods herein, various
embodiments can include, but are not limited to:
[0103] In a first embodiment, a non-dispersive photoacoustic gas
detector comprises: an infrared light source; a closed chamber,
wherein the closed chamber comprises at least one window that is
substantially transparent to infrared light from the infrared light
source, wherein the closed chamber is spaced apart from the
infrared light source, and wherein the closed chamber is
substantially sealed; and an acoustic sensor in communication with
the closed chamber.
[0104] A second embodiment can include the non-dispersive
photoacoustic gas detector of the first embodiment, further
comprising a gas sample disposed within the closed chamber.
[0105] A third embodiment can include the non-dispersive
photoacoustic gas detector of the first or second embodiment,
further comprising a light path disposed between the infrared light
source and the at least one window.
[0106] A fourth embodiment can include the non-dispersive
photoacoustic gas detector of the third embodiment, further
comprising a sample chamber disposed between the infrared light
source and the closed chamber, wherein the light path passes
through the sample chamber.
[0107] A fifth embodiment can include the non-dispersive
photoacoustic gas detector of the third or fourth embodiment,
further comprising a processor n signal communication with the
acoustic sensor, wherein the processor is configured to convert a
signal output from the acoustic sensor into a concentration of gas
in the light path based on a decrease in the signal output when the
gas is present in the light path.
[0108] A sixth embodiment can include the non-dispersive
photoacoustic gas detector of any of the first to fifth
embodiments, wherein the infrared light source is configured to
produce a broad-spectrum infrared light.
[0109] A seventh embodiment can include the non-dispersive
photoacoustic gas detector of any of the first to sixth
embodiments, further comprising a membrane disposed between an
interior of the closed chamber and the acoustic sensor, wherein the
acoustic sensor is in communication with the interior of the closed
chamber through the membrane.
[0110] An eighth embodiment can include the non-dispersive
photoacoustic gas detector of any of the first to seventh
embodiments, wherein the at least one window comprises a lens
configured to focus the infrared light from the infrared light
source into an interior of the closed chamber.
[0111] A ninth embodiment can include the non-dispersive
photoacoustic gas detector of any of the first to eighth
embodiments, wherein an inner surface of the closed chamber
comprises a mirrored surface.
[0112] A tenth embodiment can include the non-dispersive
photoacoustic gas detector of any of the first to ninth
embodiments, wherein the at least one window comprises a material
configured to filter at least a portion of the infrared light from
the infrared light source.
[0113] An eleventh embodiment can include the non-dispersive
photoacoustic gas detector of any of the first to eleventh
embodiments, wherein the at least one window comprises a thickness
configured to filter at least a portion of the infrared light from
the infrared light source.
[0114] In a twelfth embodiment, a non-dispersive photoacoustic gas
detector comprises: an infrared light source; a dosed chamber,
wherein the closed chamber comprises at least one window that is
substantially transparent to infrared light from the infrared light
source; a gas sample disposed within the closed chamber, wherein
the gas sample comprises a gas or a mixture of at least two gases;
and an acoustic sensor in fluid communication with the closed
chamber.
[0115] A thirteenth embodiment can include the non-dispersive
photoacoustic gas detector of the twelfth embodiment, further
comprising a light path disposed between the infrared light source
and the at least one window, wherein one or more target gases are
present in the light path.
[0116] A fourteenth embodiment can include the non-dispersive
photoacoustic gas detector of the thirteenth embodiment, further
comprising a processor in signal communication with the acoustic
sensor, wherein the processor is configured to convert a signal
output from the acoustic sensor into a normalized response to a
concentration of the one or more target gases present in the light
path.
[0117] A fifteenth embodiment, can include the non-dispersive
photoacoustic gas detector of the fourteenth embodiment, wherein
the gas sample comprises methane, ethane, ethylene, or any
combination thereof.
[0118] A sixteenth embodiment can include the non-dispersive
photoacoustic gas detector of the fifteenth embodiment, wherein the
normalized response comprises at least one of an explosion level
measurement, a flammability level measurement, a toxicity level
measurement, calorific value measurement, or any combination
thereof.
[0119] A seventeenth embodiment can include the non-dispersive
photoacoustic gas detector any of the fourteenth to sixteenth
embodiments, wherein the gas sample comprises trifluoromethane.
[0120] An eighteenth embodiment can include the non-dispersive
photoacoustic gas detector of the seventeenth embodiment, wherein
the normalized response comprises a flammability level measurement,
a toxicity level measurement, calorific value measurement, or any
combination thereof.
[0121] A nineteenth embodiment can include the non-dispersive
photoacoustic gas detector of any of the twelfth to eighteenth
embodiments, wherein the gas sample comprises methane, ethane,
ethylene, propane, difluoromethane, chlorodifluoromethane,
trifluoromethane, propene, tetrafluoroethylene, pentafluoroethane,
trifluoroethylene, 1,1,1-trifluoroethane, methyl fluoride, or any
combination thereof.
[0122] In a twentieth embodiment, a method of detecting a gas
comprises: passing infrared light through a light path, wherein the
light path comprises one or more target gases; absorbing, by the
one or more target gases, at least a portion of the infrared light
in the light path; passing the infrared light into a closed chamber
after passing the infrared light through the light path, wherein
the closed chamber comprises at least one window that is
substantially transparent to the infrared light, and wherein the
closed chamber comprises a gas sample; generating an acoustic
signal within the closed chamber in response to passing the
infrared light into the closed chamber, wherein the acoustic signal
decreases in response to an increased concentration of the one or
more target gases in the light path; detecting the acoustic signal;
and converting the acoustic signal into a response.
[0123] A twenty first embodiment can include the method of the
twentieth embodiment, herein the response comprises a concentration
of the one or more target gases in the light path.
[0124] A twenty second embodiment can include the method of the
twentieth or twenty first embodiment, wherein the gas sample
comprises a plurality of sample gases.
[0125] A twenty third embodiment can include the method of the
twenty second embodiment, wherein the response comprises a
normalized response.
[0126] A twenty fourth embodiment can include the method of the
twenty third embodiment, wherein the normalized response comprises
an explosion level measurement, a flammability level measurement, a
toxicity level measurement, calorific value measurement, or any
combination thereof.
[0127] A twenty fifth embodiment can include the method of the
twenty second embodiment, Wherein the gas sample comprises methane
and ethane, wherein the one or more target gases comprise at least
one component of natural gas, and wherein the response comprises an
explosion level measurement.
[0128] A twenty sixth embodiment can include the method of the
twenty fifth embodiment, further comprising: comparing the
explosion level measurement to a lower explosion level threshold,
determining that the explosion level is above the lower explosion
level threshold, and generating an alarm in response to the
determining.
[0129] A twenty seventh embodiment can include the method of the
twenty second embodiment, Wherein the gas sample comprises
trifluoromethane, difluoromethane, cyclopropane, methyl ether,
1,1,1,2-tetrafluoroethane, or any combination thereof, wherein the
one or more target gases comprise at least one component of a
solvent, and wherein the response comprises an explosion level.
[0130] A twenty eighth embodiment can include the method of the
twenty seventh embodiment, wherein the gas sample further comprises
methane.
[0131] A twenty ninth embodiment can include the method of the
twenty seventh embodiment, further comprising: comparing the
explosion level to a lower explosion level threshold, determining
that the explosion level is above the lower explosion level
threshold, and generating an alarm in response to the
determining.
[0132] While various embodiments in accordance with the principles
disclosed herein have been shown and described above, modifications
thereof may be made by one skilled in the art without departing
from the spirit and the teachings of the disclosure. The
embodiments described herein are representative only and are not
intended to be limiting. Many variations, combinations, and
modifications are possible and are within the scope of the
disclosure. Alternative embodiments that result from combining,
integrating, and/or omitting features of the embodiment(s) are also
within the scope of the disclosure. Accordingly, the scope of
protection is not limited by the description set out above, but is
defined by the claims which follow, that scope including all
equivalents of the subject matter of the claims. Each and every
claim is incorporated as further disclosure into the specification
and the claims are embodiment(s) of the present invention(s).
Furthermore, any advantages and features described above may relate
to specific embodiments, but shall not limit the application of
such issued claims to processes and structures accomplishing any or
all of the above advantages or having any or all of the above
features.
[0133] Additionally, the section headings used herein are provided
for consistency with the suggestions under 37 C.F.R. 1.77 or to
otherwise provide organizational cues. These headings shall not
limit or characterize the invention(s) set out in any claims that
may issue from this disclosure. Specifically and by way of example,
although the headings might refer to a "Field," the claims should
not be limited by the language chosen under this heading to
describe the so-called field. Further, a description of a
technology in the "Background" is not to be construed as an
admission that certain technology is prior art to any invention(s)
in this disclosure. Neither is the "Summary" to be considered as a
limiting characterization of the invention(s) set forth in issued
claims. Furthermore, any reference in this disclosure to
"invention" in the singular should not be used to argue that there
is only a single point of novelty in this disclosure. Multiple
inventions may be set forth according to the limitations of the
multiple claims issuing from this disclosure, and such claims
accordingly define the invention(s), and their equivalents, that
are protected thereby. In all instances, the scope of the claims
shall be considered on their own merits in light of this
disclosure, but should not be constrained by the headings set forth
herein.
[0134] Use of broader terms such as comprises, includes, and having
should be understood to provide support for narrower terms such as
consisting of, consisting essentially of, and comprised
substantially of. Use of the term "optionally," "may," "might,"
"possibly," and the like with respect to any element of an
embodiment means that the element is not required, or
alternatively, the element is required, both alternatives being
within the scope of the embodiment(s). Also, references to examples
are merely provided for illustrative purposes, and are not intended
to be exclusive.
[0135] While several embodiments have been provided in the present
disclosure, it should be understood that the disclosed systems and
methods may be embodied in many other specific forms without
departing from the spirit or scope of the present disclosure. The
present examples are to be considered as illustrative and not
restrictive, and the intention is not to be limited to the details
given herein. For example, the various elements or components may
be combined or integrated in another system or certain features may
be omitted or not implemented.
[0136] Also, techniques, systems, subsystems, and methods described
and illustrated in the various embodiments as discrete or separate
may be combined or integrated with other systems, modules,
techniques, or methods without departing from the scope of the
present disclosure. Other items shown or discussed as directly
coupled or communicating with each other may be indirectly coupled
or communicating through some interface, device, or intermediate
component, whether electrically, mechanically, or otherwise. Other
examples of changes, substitutions, and alterations are
ascertainable by one skilled in the art and could be made without
departing from the spirit and scope disclosed herein.
* * * * *