TECHNICAL FIELD
The present disclosure relates generally to a non-dispersive infrared gas
sensor and more particularly relates to a non-dispersive infrared gas sensor with a
reflective diffuser therein to promote scattering so as to reduce overall mechanical
sensitivity.
BACKGROUND OF THE INVENTION
Gas sensors such as a non-dispersive infrared ("NDIR") gas sensor may
measure gas concentrations based upon infrared absorption. Specifically, NDIR gas
sensors measure the gas concentrations based on unique absorption characteristics
specific to each gas at certain wavelengths. In other words, different gases have clearly
defined absorption characteristics. The NDIR gas sensors may include an infrared source
and an infrared detector. The infrared source may be modulated and the measured signal
may be correlated to the gas concentrations. A waveguide may be used as the gas sample
chamber between the source and the detector. The internal surface of the waveguide
typically is smooth and reflective so as to minimize the scattering of the infrared light
therein. The waveguide surface thus may provide near specular reflections so as to
maximize the signal received at the detector.
Although the smooth surface providing nearly specular reflections may
minimize scattering and maximize the signal, a gas sensor using such a surface also may
be sensitive to mechanical changes. For example, temperature changes may have an
impact on the components and, hence, the reliability of the signal. As a result, known
attempts to increase overall gas sensor stability have involved the use of precision
components and/or bum in periods so as to stabilize the electronics therein. These
techniques, however, generally may be expensive and/or time consuming.
There is thus a desire for an improved gas sensor such as a NDIR gas
sensor. Such an improved NDIR gas sensor may provide overall mechanical stability for
a more homogeneous signal without requiring the use of expensive components or
modifications.
SUMMARY OF THE INVENTION
The present application and the resultant patent thus provide a nondispersive
infrared gas sensor. The non-dispersive infrared gas sensor may include an
infrared source, an infrared detector, and a waveguide extending about the infrared source
and the infrared detector. The waveguide may include a reflective diffuser thereon.
I The present application and the resultant patent further provide a method
of measuring a concentration of a gas in a chamber. The method may include the steps of
pulsing an infrared signal into the chamber, scattering the infrared signal off of a
reflective diffuser, receiving the scattered infrared signal at an infrared detector, and
determining the intensity of the scattered infrared signal.
The present application and the resultant patent hrther provide a nondispersive
infrared gas sensor. The non-dispersive infrared gas sensor may include an
infrared source, an infrared detector, and a waveguide extending about the infrared source
and the infrared detector. The waveguide may include a reflective diffuser with a
textured surface and a reflective coating thereon.
These and other features and improvements of the present application and
the resultant patent will become apparent to one of ordinary skill in the art upon review of
the following detailed description when taken in conjunction with the several drawings
and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram of an NDIR gas sensor.
Fig. 2 is a schematic diagram of an NDIR gas sensor as may be described
herein.
Fig. 3 is a side cross-sectional view of a reflective diffuser as may be used
with the NDIR sensor of Fig. 2.
Fig. 4 is an alternative embodiment of a reflective diffuser as may be used
with the NDIR sensor of Fig. 2.
Fig. 5 is an alternative embodiment of an NDIR sensor.
Fig. 6 is an alternative embodiment of an NDIR sensor.
Fig. 7 is an alternative embodiment of an NDIR sensor.
DETAILED DESCRIPTION
Referring now to the drawings, in which like numerals refer to like
elements throughout the several views, Fig. 1 shows a typical NDIR gas sensor.
Generally described, the NDIR gas sensor 10 may include an infrared source 15 and an
infrared detector 20. More than one infrared detector 20 may be used. The infrared
source 15 and the infrared detector 20 may be positioned on a printed circuit board 25.
The infrared source 15 and the infrared detector 20 may be in communication via a
microprocessor 30. Various types of amplifiers, filters, and other components also may
be used.
The NDIR sensor 10 may be enclosed by a waveguide 35. The waveguide
35 may define a chamber 40 extending fiom and enclosing in part the infrared source 15
to the infrared detector 20. The waveguide 35 may include one or more internal
reflective surfaces 45. The reflective surfaces 45 typically may be smooth and may
provide near specular reflection so as to minimize scattering of the light therein. The
waveguide 35 may be made from thermoplastic, metal, rubber, composite materials, and
the like. If the waveguide 35 is made out of thermoplastics, for example, the injection
mold for the waveguide 35 may be highly polished about the reflective surfaces 45. The
reflective surfaces 45 then may receive a plate or coating 50. The plate or coating 50
may be a metal surface so as to produce a near specular reflective surface 55.
Specifically, such a near specular reflective surface 55 may maximize the signal received
at the infrared detector 20 by limiting scattering.
As described above, the infrared source 115 may pulse an infrared beam
within the chamber 40. The beam may reflect off of the reflective surfaces 45 of the
waveguide 35 and may be received by the infrared detector 20. The gas within the
chamber 40 absorbs radiation of a known wavelength and this absorption is a measure of
the concentration of the gas. Different gases have clearly defined absorption
characteristics. The infrared detector 20 thus delivers a signal proportional to the gas
concentration to the microprocessor 30. These signals then may be averaged. Other
components and other configurations may be used.
Fig. 2 shows a NDIR gas sensor 100 as may be described herein. Similar
to that described above, the NDIR gas sensor 100 may include an infrared source 110 and
an infrared detector 120. More than one infrared detector 120 may be used herein. The
infrared source 110 and the infrared detector 120 may be of conventional design. The
infrared source 110 and the infrared detector 120 may be positioned about a printed
circuit board 130 or other type of mechanical support andlor electronic connection. The
infrared source 110 and the infrared detector 120 may be in communication via a
microprocessor 140. The microprocessor 140 may be any type of programmable logic
device. Various types of filters, amplifiers, and the like also may be used herein. Other
components and other configurations may be used herein.
The NDIR gas sensor 100 also may include a waveguide 150. The
waveguide 150 may define a chamber 160 therein extending from the infrared source 1 10
to the infrared detector 120. The waveguide 150 may be made from thermoplastics,
metal, rubber, composite materials and the like. The waveguide 150 may have any size,
shape, or configuration.
The waveguide 150 may have one or more internal reflective surfaces 170
therein. In this example, a detector reflective surface 180 may be positioned above the
infrared detector 120. The reflective surface 170 may be in the form of a reflective
difhser 190 instead of the specular reflective surface 55 described above. As opposed to
such a smooth surface, the reflective diffuser 190 may include a non-specular or a
textured surface 200. As is shown in exaggerated form in Fig. 3, the textured surface 200
may include a random pattern 210. Further, the textured surface 200 also may include a
uniform or a precision pattern 220 as is shown in exaggerated form in Fig. 4. Any type of
textured surface 200 may be used herein. Holographic patterns also may be used herein.
Further, combinations of random patterns, precision patterns, holographic patterns, and
the like may be used together herein.
I If the waveguide 150 is injection molded thermoplastic component and the
like, the injection mold may provide the textured surface 200 as part of the mold. The
mold thus produces a textured component 230 with the textured surface 200. The surface
properties largely may be controlled by the nature of the mold. The textured component
230 then may be coated or plated with a reflective coat 240 to produce the reflective
diffuser 190. The reflective coating 240 may be metallic and the like. Many other
manufacturing techniques may be used herein. For example, existing components may
be textured via sandpaper and the like and then coated.
The textured surface 200 of the reflective diffuser 190 is generally
incorporated on a reflective surface 170 in the signal path where the majority of the
infrared energy must pass. As such, the detector reflective surface 180 is shown in Fig. 2
adjacent to the infrared detector 120. Alternatively, Fig. 5 shows a source reflective
surface 250 positioned above the infrared source 110. Multiple reflective surfaces 170
also may be used herein. Moreover, the printed circuit board 130 also may act as a
reflective surface 170. In Fig. 6, the printed circuit board 130 may have a printed circuit
board reflective surface 260. The printed circuit board reflective surface 260 may be
electroplated with, for example, an electroless nickel immersion gold ("ENIG") surface
270. Such an ENIG surface 270 may be sufficiently textured so as to act as a reflective
diffuser 190. Other types of surfaces 270 may be used. Other components and other
configurations may be used herein.
In use, the NDIR gas sensor 100 with the reflective diffuser 190 induces
scattering into the infrared signal pulses produced by the infrared source 110. Because
the reflective energy is being diffused, the signals being reflected off of the textured
surface 200 of the reflective diffuser 190 may have more of an average and homogeneous
signal intensity distribution. The reflective diffuser 190 thus reduces overall mechanical
sensitivity in the waveguide 50, the infrared source 110, and the infrared detector 120
such that the NDIR gas sensor 100 as a whole may have increased stability. The nature
of the textured surface 200 of the reflective diffuser 190 may be optimized for different
gases and intended uses.
Specifically, the NDIR gas sensor 100 described herein uses the textured
surface 200 of the reflective diffuser 190 as a lambertian surface to induce scattering into
the signal. This scattering thus optically averages the signal. The signal reflected off the
reflective diffuser 190 has more of an average and homogeneous signal intensity
distribution because the reflective energy therein is diffused. The more homogeneous
signal intensity distribution thus results in reduced sensitivity to mechanical changes and
therefore an increase in overall stability. As opposed to sensors with the specular surface
55 intended to reduce scattering described above, the NDIR gas sensor 100 herein
purposefully induces such scattering for increased stability. Such an increase in stability
may permit tighter accuracy specifications with lower costs. Other components and other
configurations may be used herein.
The NDIR gas sensor 100 also may include multiple infrared detectors
120. In the example of Fig. 7, a first infrared detector 280 and a second infrared detector
290 may be used. Any number of infrared detectors 120 may be used herein. The
infrared detectors 280, 290 may be in physically separated different locations. The signal
reflected by the reflective diffuser 190 may result in similar energy presented to the
detectors 280, 290. The reflective diffuser 190 thus averages the signals to allow both
detectors 280, 290 to see similar intensity energy such that the sensor 100 may be less
sensitive to mechanical changes.
It should be apparent that the foregoing relates only to certain
embodiments of the present application and the resultant patent. Numerous changes and
modifications may be made herein by one of ordinary skill in the art without departing
from the general spirit and scope of the invention as defined by the following claims and
the equivalents thereof.
NON-DISPERSIVE INFRARED SENSOR WITH A REFLECTIVE DIFFUSER
NDIR gas sensor
infrared source
infrared detector
printed circuit board
microprocessor
waveguide
chamber
reflective surface
plate
near specular reflective surface
NDIR sensor
infrared source
infrared detector
printed circuit board
microprocessor
waveguide
chamber
reflective surfaces
detector reflective surface
reflective diffusor
textured surface
random pattern
precision pattern
textured component
reflective coating
source reflective surface
printed circuit board surface
ENIG surface
first infrared detector
second infrared detector

We claims:
1. A non-dispersive infrared gas sensor (loo), comprising:
an infrared source (1 10);
an infrared detector (120); and
a waveguide (150) extending about the infrared source and the infrared detector;
the waveguide comprising a reflective diffuser (190) thereon.
2. The non-dispersive infrared gas sensor (100) of claim 1, wherein the
waveguide defines a chamber (160).
3. The non-dispersive infrared gas sensor (100) of claim 1, wherein the
reflective diffuser comprises a textured surface (200).
4. The non-dispersive infrared gas sensor (100) of claim 3, wherein the
textured surface comprises a random pattern (2 10).
5. The non-dispersive infrared gas sensor (100) of claim 3, wherein the
textured surface comprises a precision pattern (220).
6. The non-dispersive infrared gas sensor (100) of claim 3, wherein the
reflective diffuser comprises a reflective coating (240) thereon.
7. The non-dispersive infrared gas sensor (100) of claim 1, wherein the
waveguide comprises a textured thermoplastic component (230) with a reflective metallic
coating (240) thereon.
8. The non-dispersive infrared gas sensor (100) of claim 1, wherein the
reflective diffuser comprises a detector reflective surface (1 80).
9. The non-dispersive infrared gas sensor (100) of claim 1, wherein the
reflective diffuser comprises a source reflective surface (250).
10. The non-dispersive infrared gas sensor (100) of claim 1, wherein the
reflective diffuser comprises a printed circuit board reflective surface (260).
1 1 . The non-dispersive infrared gas sensor (1 00) of claim 10, wherein the
printed circuit board reflective surface comprises an electroless nickel immersion gold
surface (270).
12. The non-dispersive infrared gas sensor (100) of claim 1, further
comprising a plurality of infrared detectors (120).
13. The non-dispersive infrared gas sensor (100) of claim 1, further
comprising a plurality of infrared detectors spaced apart from each other.
14. The non-dispersive infrared gas sensor (100) of claim 1, further
comprising a microprocessor (140) in communication with the infrared source and the
infrared detector.
15. A method of measuring a concentration of a gas in a chamber (160),
comprising:
pulsing an infrared signal into the chamber;
scattering the infrared signal off of a reflective diffuser (190);
receiving the scattered infrared signal at an infrared detector (120); and
determining the intensity of the scattered infrared signal.