Note: Descriptions are shown in the official language in which they were submitted.
_ 203399~3
REMOTE SENSOR DEVICE FOR MONITORING
MOTOR VEHICL~ EXHAUST SYSTEMS
Backqround of the Invention
Field of the Invention
The present invention relates to the monitoring and
detection of vehicle emitted pollutants. The invention has
particular application to monitoring the exhaust emissions of
motor vehicles under actual operating conditions.
Description of the Prior Art
Detecting and limiting environmental pollution has
become an area of the utmost importance to industrialized
societies. Substantial effort and resources have been
committed to detecting and curbing sources of industrial
pollution in all forms. One of the major contributors to air
pollution is the internal combustion engine which is used to
power motor vehicles. It is highly desirable to measure
exhaust emissions from a vehicle under actual operating
conditions and not in a static situation such as while idling
at low RPM. Dynamic testing under actual operating conditions
not only provides a more accurate indication of pollutant
emissions, but also makes vehicle tampering for the purpose of
circumventing the pollution test equipment virtually
impossible.
Pollution monitoring systems for remotely measuring
vehicle emissions have been proposed. U.S. Patent No.
4,924,095 discloses a remote gas analyzer for motor vehicle
exhaust emission surveillance in which a planar array of gas
~ 939 9~
analyzer beams intersects substantially an entire cross-
sectional segment of the exhaust gas plume in order to
determine the volume concentration of first gas pollutants in
the exhaust of a motor vehicle passing the array. These first
pollutants have a relatively high and more easily detectable
concentration. A second, multi-spectral gas analyzer beam
intersects the exhaust to determine the change in concentration
of the less prevalent pollutants with respect to ambient, and
also determines the change in concentration of the first
pollutants. The gas analyzer beams transit the exhaust gas
plume in a first path and are then reflected back through the
plume in a second path by a matrix array of retro-reflectors.
Another approach for analyzing vehicle emissions is
disclosed in U.S. Patent No. 5,210,702 , issued 11th May,
1993 , for remote detecting, measuring and
recording of NOX, CO, CO2, HC and H2O levels from the exhaust of
moving motor vehicles. An optical mechanism splits an infrared
(IR) beam into two to four components, and devices are
positioned for receiving each of the IR components and
generating two to four signals indicative of, for example, CO,
CO2, HC and H2O. An IR source and the receiving mechanism are
aligned on opposite sides of a roadway and a visual recording
device is positioned for visually recording the vehicle and
test results. The IR beam makes a single pass across the
roadway through the vehicle's exhaust plume between the IR
source and detector. A polygon-shaped rotating mirror reflects
60298-328
~ ~ ~ 3 ~ 9 ~
the IR beam after passing through the vehicle's exhaust plume
onto a plurality of detectors, each adapted to measure the
concentration of a respective pollutant.
Even when monitoring vehicle exhaust emissions under
actual operating conditions, operating limitations of the gas
analyzer introduce measurement inaccuracies. For example,
typical IR detectors are highly temperature sensitive and
exhibit reduced resistivity with decreasing temperature. An IR
detector typically provides a maximum output at -70~C. Thermo-
electric coolers capable of reducing the temperature of a
detector 21~C below ambient are used to improve detector
signal-to-noise (S/N) ratio. By running the coolers at maximum
power, the detected signal level may be increased. Some prior
art gas analyzers utilize a number of manually adjustable
potentiometers to improve the S/N ratio by tuning the detector
circuit for operation at a given temperature. However,
variations in temperature during operation require additional
potentiometer adjustments which renders this approach
cumbersome because of the large number of required manual
adjustments and the typical range and rate of temperature
fluctuation. In addition, the latent heat absorbed by metal
components adjacent to the beam detector when the beam is
~n~ 60298-328
~ Q ~
~._
incident upon the detector gives rise to differential heating and
cooling rates which also reduce measurement accuracy. Finally,
prior art approaches have suffered from difficulty in aligning
the optical components on opposite sides of the roadway which
also limits the accuracy and sensitivity of the gas analyzer
measurements.
Summary of the Invention
It is a general object of the invention to provide an
improved vehicle emissions monitoring apparatus for roadside use
which avoids the disadvantages of prior approaches while afford-
ing additional structural and operating advantages.
The invention provides apparatus for monitoring
pollutant concentration in an exhaust plume of a vehicle travel-
ing on a roadway by directing an infrared (IR) beam through said
exhaust plume, said apparatus comprising: IR beam source means
disposed on a first side of the roadway for detecting an emitted
IR beam through the exhaust plume of a vehicle; lateral transfer
reflecting means including first and second spaced, generally
planar, mirrors disposed on a second, opposed side of the roadway
for receiving a redirecting said emitted IR beam as a reflected
IR beam across the roadway in a second, opposed direction,
wherein said reflected IR beam is displaced from said emitted IR
beam, and wherein said first and second mirrors form an integral
structure; IR detection means disposed on said first side of the
roadway adjacent said IR beam source means for receiving said
reflected IR beam and determining the pollutant concentration in
60298-328
'~
~ ~ Q 3 9 ~ 8
the vehicle's exhaust plume; and further including a laser beam
source and detector disposed adjacent said IR beam source and
said IR detection means for directing a laser beam across the
roadway onto said lateral transfer reflecting means and for
detecting alignment of said lateral transfer reflecting means
with said IR beam source and said IR detection means, and wherein
said lateral transfer reflecting means further includes a
generally planar panel coupled to and disposed intermediate said
first and second mirrors for use as a target for said laser beam.
The invention also provides apparatus for detecting
alignment of optical components in an infrared absorption spectro-
scopy system for use in measuring the concentration of pollutants
in a moving motor vehicle exhaust plume, wherein an infrared (IR)
beam is directed across a roadway through said exhaust plume and
interacts with pollutants therein, said apparatus comprising: a
laser for producing an alignment beam and arranged on one side of
the roadway; a reflector for reflecting the IR beam and the
alignment beam and being arranged on a side of the roadway
opposite said one side; detector means arranged on said one side
of the roadway and proximate said laser for receiving the align-
ment beam after transit across the roadway and reflection back
by said reflector for providing an analog signal representing the
amplitude of the received alignment beam; analog-to-digital (A/D)
converting means for transforming said analog signal to a digital
signal comprised of a series of pulses, wherein a pulse
60298-328
'~'
2 ~ 9 8
'_
repetition frequency (PRF) of said digital signal represents the
amplitude of the received alignment beam; and indicator means
coupled to said (A/D) converting means and responsive to said
digital signal for turning on and off at said PRF and providing
a pulsed output signal representing the amplitude of the received
alignment beam, wherein the PRF of said pulsed output signal
increases as the optical components including said reflector and
detector means are more precisely al-igned and, wherein said A/D
converting means increases said PRF so as to provide a continuous
digital signal when the amplitude of the received alignment beam
exceeds a predetermined signal level resulting in a continuous
output signal by said indicator means representing alignment of
the optical components.
The invention consists of certain novel features and a
combination of parts hereinafter fully described, illustrated in
the accompanying drawings, and particularly pointed out in the
appended claims, it being understood that various changes
5a
60298-328
' d~; ~
2~9399~
in the details may be made without departing from the spirit,
or sacrificing any of the advantages, of the present invention.
Brief Description of the Drawinqs
For the purpose of facilitating an understanding of
the invention there is illustrated in the accompanying drawings
a preferred embodiment thereof, from an inspection of which,
when considered in connection with the following description,
the invention, its construction and operation, and many of its
advantages should be readily understood and appreciated.
FIG. 1 is a simplified schematic diagram of a remote
sensor device for monitoring motor vehicle exhaust emissions in
accordance with the present invention;
FIG. 2 is a combined schematic and block diagram of
the remote sensor device for monitoring motor vehicle exhaust
emissions of FIG. 1;
FIG. 3 is a plan view of the detector optics used in
the remote sensor device for monitoring motor vehicle exhaust
emissions of FIG. 1;
FIG. 4 is a side elevation view of the detector
optics arrangement shown in FIG. 3;
FIG. 5 is a simplified schematic diagram of an
arrangement for aligning beam source optics in the remote
sensor device of the present invention during manufacture;
FIG. 6 is a combined schematic and block diagram of
an IR detector circuit used in the remote sensor device of the
present invention;
. ..
2~93998
FIG. 7 is a combined block and schematic diagram of a
digital timing and analog integration sampling circuit for use
in the IR detector of the present invention;
FIG. 8 is a schematic diagram of the analog portion
of the sampling circuit of FIG. 7;
FIGS. 9a and 9b are respectively graphic
illustrations of the variation of received IR signal amplitude
and the integration of the received IR signal by IR signal
processing circuitry in the remote sensor device over time; and
FIG. 10 is a simplified flow chart illustrating the
steps carried out by IR signal detection circuitry for
providing an audio and/or video signal for optical alignment of
the remote sensor device.
Description of the Preferred Embodiment
Referring to FIG. 1, there is shown a simplified
schematic diagram of a motor vehicle exhaust emission
monitoring system 10 in accordance with the principles of the
present invention. The exhaust emission monitoring system 10
is designed for non-intrusive measurement of vehicular emission
by generating and monitoring an IR beam emitted and reflected
approximately 10-18 inches above a roadway. Gasoline powered
vehicles drive through the beam and their exhaust "interferes"
with the transmission of the IR beam and appropriate detectors
measure and calculate the CO, HC and CO2 vehicular emissions
and provide a digitized video picture of the rear of the
vehicle including its license plate.
2~ .. 399 8
With reference to FIG. 1 as well as to FIG. 2, which
is a simplified plan view in schematic and block diagram form
of the exhaust emission monitoring system 10, a motor vehicle
30 travelling along a roadway 26 passes between a gas analyzer
12 and a lateral transfer mirror (LTM) 14 disposed on opposing
sides of the roadway. Gas analyzer 12 includes a source optics
module 16 and a detector optics module 18. The source and
detector optics modules 16, 18 include a laser for aligning the
source and detector optics with the LTM 14 prior to use. The
source optics module 16 includes an IR source for emitting an
IR beam which is 6 inches in diameter in a particular
embodiment. The IR source emits an IR beam 22 across roadway
26 and onto a first reflecting surface 14a of the LTM 14. LTM
14 is disposed in and supported by a housing 20. The incident
IR beam 22 is reflected from the LTM's first reflecting surface
14a onto a second reflecting surface 14b. The second
reflecting surface 14b directs the reflected IR beam 24 back
across the roadway 26 and onto the detector optics module 18 of
the gas analyzer 12. As vehicle 30 travels along roadway 26,
the IR beam is interrupted by the vehicle's chassis and is then
transmitted through the vehicle's exhaust emission plume 28
which trails the vehicle. At the-~same time, a video camera 32
connected to the gas analyzer 12 via a cable 34 takes a
photograph of the aft portion of vehicle 30 including its
license plate 30a. This provides an operator of the exhaust
emission monitoring system 10 with a permanent record of the
9 9 8
identity of the vehicle and the exhaust emission being
monitored. The gas analyzer 12 further includes an operator's
control/display panel 58 including an arrangement of control
elements and displays.
Video camera 32 in one embodiment is of the digital
type to provide a digitized still image video picture of the
vehicle's license plate 30a as the IR beam is directed through
its exhaust plume 28. The digital image may then be stored on
a disc file 35 in digital form for use by computers and
computerized equipment.
Disposed intermediate and coupled to the first and
second reflecting surfaces 14a, 14b of the LTM 14 is a third
generally planar panel 14c. The two reflectors 14a, 14b and
the planar panel 14c disposed therebetween form an integral
structure to facilitate alignment of incident and reflected IR
beams 22, 24 with source and detector optics modules 16, 18.
Planar panel 14c is comprised of milled aluminum in one
embodiment and may be used as a target for laser beam 15 for
aligning the source and detector optics modules with the LTM
14. The laser ~eam source and detector 17 is thus used in
combination with planar panel 14c of the LTM 14 for gross
alignment of the optical elements~of the motor vehicle exhaust
emission monitoring system 10.
Referring to FIG. 3, there is shown a plan view of
the detector optics module 18 within the gas analyzer 12. A
side elevation view of the detector optics module 18 is shown
209~8
in FIG. 4. As shown in the figures, the reflected IR beam 24
is directed into the detector optics module 18 and onto a
concave primary focusing mirror 38. The primary focusing
mirror 38 reflects the IR beam 24 downward and onto a multi-
sided rotating mirror 36. As shown in FIG. 3, rotating mirror
36 is rotationally displaced in a counter-clockwise direction
and reflects the IR beam in a sequential manner onto first,
second, third and fourth concave secondary mirrors 40, 42, 44
and 46. The concave secondary mirrors 40, 42, 44 and 46 are
arranged in a semi-circular, horizontally aligned, spaced array
for focusing the IR beam onto respective IR detectors. Thus,
the first, second, third and fourth concave secondary mirrors
40, 42, 44 and 46 respectively reflect and focus the IR beam
onto a CO detector 48, a HC detector 50, a C02 detector 52 and
a reference detector 54. IR beam 24 is reflected onto each of
the concave secondary mirrors in a sequential manner, beginning
with the fourth mirror 46 and ending with the first mirror 40.
In an actual embodiment, the detector optics module 18 is
designed to receive an IR beam 24 on the order of 4 inches
square and to concentrate "pulses" of that light on the
detectors. This is accomplished in an actual embodiment by
means of a 3 inch primary concave mirror 38, a 12,000 RPM
rotating mirror 36 comprised of a 12 faceted polygon and driven
by a motor 37, and four 38 mm concave secondary mirrors 40, 42,
44 and 46. This provides a pulse frequency of the IR beam on
each detector of 2,400 pulses per second. Each of the
2~93g~
detectors is comprised of lead sulfide or lead selenide in a
preferred embodiment. The IR beam is thus sequentially
directed onto the fourth, third, second and first flat
secondary mirrors 46, 44, 42 and 40 in this order. Drive motor
37 provides an output signal /OPTO representing the speed of
rotation of the spinning mirror 36. The /OPTO signal is
provided to a digital timing and integration sampling circuit
described below for high speed sampling of the detected IR
signal.
Referring to FIG. 5, there is shown a simplified
schematic diagram of an arrangement for aligning the source
optics and detector optics during manufacture. A laser beam
generator 64 is mounted to the detector base 56. Laser beam 66
is directed onto a source mirror 68 within the beam source
optics 60. Source mirror 68 reflects the laser beam 66 onto an
IR source 70. The IR source 70 and source mirror 68 are
mounted to a source optics platform 72. Laser 64 is positioned
at the same elevation above the detector base 56 as the
previously described primary focusing mirror 38 shown in FIG.
4. If the beam source optics 60 are aligned correctly, laser
beam 66 will strike the IR source 70 midway between its top and
bottom portions and halfway along~its length. The IR source 70
as well as source mirror 68 may be translationally displaced
and/or rotated for proper alignment of the beam source optics
60 with laser beam 66. With the beam source optics 60 properly
aligned, an IR beam emitted by IR source 70 and reflected by
20~3998
source mirror 68 will be incident upon the primary focusing
mirror 38 within the detector optics module 18 for focusing on
the various IR detectors as described above.
Referring to FIG. 6, there is shown a combined block
and schematic diagram of an IR detector 80 used in the remote
sensor device of the present invention. The IR detector 80
includes a C0 detector circuit 82, an HC detector circuit 84, a
CO2 detector circuit 86, and a reference detector circuit 88.
Details of the CO and HC detector circuits 82, 84 are shown in
the figure, with the Co2 and reference detector circuits 86, 88
shown simply as blocks, it being understood that all of the
detector circuits have essentially the same composition and
operate in the same manner. The C0 and HC detector circuits
82, 84 share a common computer controlled potentiometer 110 and
operate in essentially the same manner, with details of the
operation of only the CO detector circuit set forth herein for
simplicity. The Co2 and reference detector circuits 86, 88
similarly share a common computer controlled potentiometer,
which is not shown in the figure for simplicity.
The C0 detector circuit 82 is energized by a DC power
supply 138 which includes a DC-to-DC converter 139 and a field
effect transistor (FET) 140. Res~istor 90 in series with-a 50
VDC input biases the Co detector element 128. Capacitor 92 DC
isolates the signal. The CO detector circuit 82 further
includes an CO detector element 128 whose resistivity changes
with temperature. Thus, as the temperature of the CO detector
12
~ ~S~399~
element 128 decreases, its resistance decreases. C0 detector
element 128 includes a lead salt detector element 128a, a
thermistor 128b to provide a measure of the temperature of the
detector element, and a thermoelectric cooler 128c for reducing
the temperature of the detector element. Signal ground is
provided to one input of a differential amplifier 94, with the
output of the C0 detector element 128 provided to its other
input. Also coupled to the input of differential amplifier 94
are jumper terminals 96 which allow for reducing large input
signal levels to the Co detector circuit 82. By connecting a
shunt (not shown) across jumper terminals 96 the output from C0
detector circuit 82 may be reduced to compensate for a large
input signal level. A capacitor 102 coupled to differential
amplifier 94 provides an offset compensation to prevent high
frequency signals such as RF noise from causing the amplifier
to oscillate. The combination of capacitor 104 and resistor
106 along with capacitor 100 and resistor 98 provides for high
frequency filtering and gain control of the output of
differential amplifier 94. These filter networks provide for
high frequency roll-off and reduce the sensitivity of the CO
detector circuit 82 to frequencies generally above 50 kHz. The
filtered output of differential~ amplifier 94 i8 provided
through resistor 108 to the computer controlled potentiometer
110 .
Potentiometer 110 includes a resistor ladder network
comprised of 256 resistors and functions as a dual computer
, .. ~ .
2 ~ 9 8
controlled potentiometer in that it also operates with the HC
detector circuit 84. Resistor 108 and clamping diodes 112 and
114 maintain the input to potentiometer 110 between plus and
minus five volts so that the output of the potentiometer does
not exceed predetermined limits. The output of potentiometer
llO is provided to a differential amplifier 116, the output of
which is fed back to the potentiometer for gain control. With
256 resistors in potentiometer 110, the gain of differential
amplifier 116 may be controlled in a step-wise fashion over
plus or minus 128 increments. With the gain of differential
amplifier 116 controlled ~y potentiometer 110, the output of
the differential amplifier is provided to analog sampling
circuitry described below.
IR detector 80 further includes an analog multiplexer
126 having an input pin 13Ob. Input pin 13Ob is coupled to an
output pin 130a of the Co detector element 128 for providing
the analog multiplexer 126 with an indication of the
temperature of operation of the IR detector element. Analog
multiplexer 126 is also coupled to the DC power supply 138 via
a voltage feedback (VFB) line 134. The 50 VDC output from
power supply 138 is divided down by the combination of a
capacitor 145 and resistors 141 and 143 to provide 1.2 VDC on
the VFB line 134 to the analog multiplexer 126. Analog
multiplexer 126 verifies that power supply 138 is operating at
50 VDC. Input pin 132 of analog multiplexer 126 receives a
/OPTO signal from the rotating mirror's drlve motor 37 (FIG. 4)
2~}~3~98
representing the speed of rotation of mirror 36 which signal is
further provided to computer 118 via amplifier 136.
Analog multiplexer 126 provides analog output signals
representing IR detector operating temperature via a voltage
follower amplifier 136 to a computer 118. Computer 118 in a
preferred embodiment is an 80186 microprocessor-based computer.
In response to the signal representing the temperature of the
Co detector element 128 and in accordance with temperature
calibration coefficients stored in computer 118, the computer
provides a controlled output via an I2C bus 123 to an I2C chip
120. The I2C chip 120 serves as an interface between computer
118 and potentiometer 110 and first and second electrically
erasable read only memories ("EEPROMs") 122 and 124, described
below. Pins 110a and llla coupled to the I2C chip 120 are
further coupled to input pins 110b and lllb, respectively, of
potentiometer 110. The control input provided from computer
118 via the I2C chip 120 controls, among other things, the
setting of potentiometer 110. In this manner, the amplitude of
the output signal from CO detector circuit 82 representing the
detected IR beam is controlled via computer 118 in accordance
with the operating temperature of the detector circuit's CO
detector element 128. The output~from the I2C chip 120 allows
for up and down toggling of the computer controlled
potentiometers within each of the respective detector circuits.
In this manner, the resistance of each resistance ladder
potentiometer may be precisely ad~usted in a stepwise manner
2~ 9~
for precisely controlling the output signal level of the
detector circuit representing the concentration of a particular
pollutant within a vehicle's exhaust plume. This ensures that
the output signals from each of the gas detector circuits 82,
84, 86 and 88 are precisely adjusted to compensate for
differences in the operating temperatures in the detector
elements in each of these circuits.
Computer 118 also provides outputs to the
aforementioned first and second EEPROMs 122 and 124. EEPROMs
122 and 124 store calibration coefficients for each of the
computer controlled potentiometers from computer 118. Thus, so
long as the detector circuits remain with EEPROM's 122 and 124
after calibration at the factory following manufacture, the
detector module may be removed from one remote detector system
and incorporated in another remote detector system, such as
during trouble shooting in the field, without requiring a
complicated and lengthy calibration procedure. The calibration
data stored in EEPROM's 122 and 124 includes specific gas
coefficients for each detector circuit.
Referring to FIG. 7, there is shown a combined block
and schematic diagram of a digital timing and analog
integration sampling circuit 152--for use in the IR detector
portion of the remote sensor device of the present invention.
Digital timing and analog integration sampling circuit 152
provides for high speed sampling of the detector outputs.
Prior approaches in IR gas analyzers incorporating a rotating
16
~ f ' ~ 9 ~
mirror arrangement provide for sampling of the gas with every
revolution of the rotating mirror. With the rotating mirror
typically spinning at a speed of 12,000 RPM, the gas is sampled
6000 times per minute. The present invention employing the
digital timing and analog integration sampling circuit 152 of
FIG. 7 allows for sampling of the gas with each pulse provided
by a respective flat of the rotating mirror. With the rotating
mirror having 12 flat sides, the digital timing and analog
integration sampling circuit 152 allows for sampling of the gas
at a rate of 12 times 12000 RPM, or 144000 times per minute.
In other words, each time an IR pulse from the rotating mirror
is incident upon the detectors, the received signal is analog-
to-digital converted to provide a digital representation of
each received IR pulse. This extremely high rate of gas
sampling minimizes the effect of noise variations in the
detectors and associated circuitry for more accurate analysis
of the composition of the gas. With reference to FIG. 7 as
well as to the pulse diagrams of FIG. 9a and 9b, the operation
of the digital timing and analog integration sampling circuit
152 will now be described.
Briefly, the digital timing and analog integration
sampling circuit 152 samples the detector's output in- the
absence of an IR beam incident upon the dëtector. The sampling
circuit then waits for a designated period of time as
determined by the speed of rotation of the rotating mirror, and
then again samples the detector and stores the sampled value on
'- 2G~9~998
a capacitor for integrating the IR pulse received by the
detector. The stored value is then analog-to-digital converted
to provide a digital representation of the concentration of a
pollutant in the vehicle's exhaust plume, which value i8 then
stored.
The digital timing and analog integration sampling
circuit 152 includes a programmable logic chip (PLC) 154 which
receives, among other signals, a clock input TOUT1 from a
master clock (not shown) and the optical pick-up output /OPTO
from the drive motor 37 of rotating mirror 36. The optical
pick-up signal /OPTO synchronizes operation of the digital
timing and analog integration sampling circuit 152 with the
high speed rotation of mirror 36, while the clock input TOUT1
synchronizes the digital timing and analog integration sampling
circuit with computer 118 and other portions of the remote
sensor device. Following receipt of the /OPTO input from the
rotating mirror's drive motor 37, the digital timing and analog
integration sampling circuit 152 counts a selected time
interval, following which the IR detector circuits sample the
received IR beam. The time at which the IR beam is sampled i5
determined by the speed of rotation of mirror 36. The /OPTO
signal is provided to a progra~mable logic chip 154 which
functions as a counter for initiating the countdown following
receipt of the /OPTO input signal. After a predetermined time
interval, PLC 154 provides an output to first and second
decoders 166 and 168 as well as to an analog multiplexer 156.
.
18
~- ~
. _ ~ . ....
-
2~93998
Decoders 166 and 168 provide timed store and clear inputs to an
analog sampling circuit 170 described in detail below. Also
provided to the analog sampling circuit ~70 is the
aforementioned outputs from the individual detector circuits
shown in FIG. 6 and described in detail above. The outputs
from the analog sampling circuit 170 representing the detected
IR signals are also provided to the analog multiplexer 156.
The combination of analog multiplexer 156, an operational
amplifier 158 and an analog-to-digital (A/D) converter 160
convert the analog output of sampling circuit 170 to digital
form. The digital outputs of the A/D converter 160 are then
provided via buffers 162 and 164 to computer 118. Computer
118, in turn, provides a compensated, digital signal
representing the detected IR signal to the aforementioned
control/display panel 58 for display for a system operator.
The curve in FIG. 9a represents a series of pulses
received by each of the detectors in the IR detector circuit of
FIG. 6. The curve in FIG. 9b illustrates the integration of
the received pulses shown in FIG. 9a over time by the digital
timing and analog integration sampling circuit 152. With a
speed of rotation of 12000 RPM, the period of received IR
pulses i8 416 microseconds. T~e dlgital timing and analog
integration sampling circuit 152 shown în FIG. 7 integrates the
pulses received from each detector clrcuit as shown in FIG. 9b
and re-zeroes, or clears, the detector circuits after receipt
2~3~
of an IR pulse in preparation for receipt of the next IR pulse
as described below.
Referring to FIG. 8, there is shown in combined
schematic and block diagram form details of the analog sampling
circuit 170 of the digital timing and analog integration
sampling circuit 152 of FIG. 7. As shown in FIG. 8, the analog
sampling circuit 170 includes a CO analog sampling circuit 200,
an HC analog sampling circuit 202, a CO2 analog sampling
circuit 204, and a reference analog sampling circuit 206.
Details of only the cO analog sampling circuit 200 are shown in
the figure for simplicity, as the remaining analog sampling
circuits are similar in configuration and operation.
As shown in the upper portion of FIG. 8, two inputs
are provided to a differential amplifier 208 in the CO analog
sampling circuit 200 via respective voltage divider networks
comprised of resistors 207, 209 and 211, 213. One input to
differential amplifier 208 is the output from the CO detector
circuit 82 of ~IG. 6, while the other input is a reference
voltage VREF. Differential amplifier 208 operates as a voltage
follower and compensates for any power or grounding problems in
the input line. The output of differential amplifier 208 is
provided via the combination of a solid state switch 210 and
. .
grounded capacitor 212 to one input of an operational amplifier
220. A /CLR1 input is provided to the first solid state switch
210 as well as to a second solid state switch 222 from decoder
166 as shown in FIG. 7 for clearing these switches. Solid
2~33~9~
state switch 210 is closed in the absence of an IR input to the
detector, representing a zeroing of the detector. Thus, solid
state switch 210 is closed for a short period, typically 10-15
microseconds, allowing capacitor 212 to charge to a level
representing the detector voltage in the absence of an IR beam.
Switch 210 and capacitor 212 thus operate as a sample and hold
circuit, providing an input to operational amplifier 220
representing the absence of an IR input to the detector. The
charge of capacitor 216 is integrated via a resistor 214 and is
applied to one input of operational amplifier 218. Capacitor
216 is charged over time, such that when the charging pulse is
removed, the output of differential amplifier 218 is
essentially at the same level as the charge on capacitor 216.
The detected IR pulse has thus been integrated as represented
by the output of operational amplifiers 218 and 220 which
function as a differential common mode amplifier. The
integrated detected IR signal is provided from operational
amplifiers 218 and 220 to operational amplifier 224 via
respective networks comprised of resistors 228, 232 and 230,
234. The output of operational amplifier 224 is provided to
another sample and hold circuit comprised-of solid state switch
226 and grounded capacitor 236. The sample and hold circuit is
updated upon receipt by switch 226 of a /STORE input from the
aforementioned decoder 166 shown in FIG. 7. The output of the
sample and hold circuit comprised of solid state switch 226 and
capacitor 236 is provided to operational amplifier 238, the
2~53~98
output of which is low pass filtered by means of the
combination of resistors 240, 244 and 248 and capacitors 242,
246 and 250. The low pass filtered output of operational
amplifier 238 is provided to operational amplifier 252 and
thence to the analog multiplexer 156 in the digital timing and
analog integration sampling circuit 152 as shown in previously
described FIG. 7.
C0 analog sampling circuit 200 operates to sample
each detector circuit for a detected IR input, temporarily
store a detected IR input and then provide the IR input to
computer 118 for processing and storage. Each of these
operations is performed in a precisely timed manner determined
by the rotational speed of spinning mirror 36. The output of
the detector is sampled a predetermined time interval following
detection of the absence of the IR beam on the detector, where
the predetermined time interval is determined by the rotational
speed of the spinning mirror.
Referring to FIG. 10, there is shown a flow chart of
the operations carried out primarily by computer 118 in the
remote sensor device for providing either an audio or optical
signal for precisely aligning the optical elements in the
source and detector modules optics 16 and 18 with the LTM 14.
At step 144 an analog IR signal is detected such as by the CO
detector circuit 82 which is provided to the analog sampling
circuit 170 shown in FIG. 8. The output of the analog sampling
circuit 170 is provided to the analog multiplexer 156 which in
~ 2~S3g98
combination with operational amplifier 158 and A/D converter
160 converts the analog IR signal to digital form, with a count
N representing signal amplitude as shown in step 146. The
digitized detected IR signal is then provided to computer 118
which at step 148 determines whether the count N is greater
than 3000 but less than 9500. In the present invention,
twenty-four A/D conversions are used to sample the detector
signal and to detect a count range of from 0 to 2048 counts.
The maximum number of counts with twenty-four A/D conversions
per detector is 49,152 divided by 5, or 9820. The number of
counts is divided by 5 to provide an arbitrary maximum count of
lO,ooo. A full scale count is arbitrarily set at 8500, with a
3000 count establishing the low end of the detection of an IR
signal. Computer 118 therefore at step 148 compares the number
of counts in the detected IR signal with, the low end limit of
3000 and the upper end limit of 9500. If the number of counts
is less than 3000 or greater than 9500, an audio beeper 174
and/or a light source 176 coupled to the computer is turned
off, indicating absence of a received IR signal. If at step
148 it is determined that the count of the detected IR signal
is between 3000 and 9500, the program stored in computer 118
branches to step 150 and pulses~the audio beeper 174 and/or
light source 176 with a signal count N. The operator of the
remote sensor device then adjusts the optical components of the
system, such as the lateral transfer mirror, to increase the
'' -
i 9 ~
count, or pulse rate, of the audio and/or light signals until
the beat frequency is maximized.
From the foregoing, it can be seen that there has
been provided apparatus for detecting and measuring relative
concentrations of pollutants such as HC, CO and C02 in the ex-
haust emissions of a passing vehicle. The apparatus employs an
IR beam directed twice through the vehicle's exhaust plume
using a combination IR source and detector module on one side
of the roadway and a lateral transfer mirror on the other side
of the roadway. The lateral transfer mirror provides a fixed,
precisely defined horizontal displacement between the emitted
and reflected beams which permits close spacing between the
source and detector optics such as in a single module. The
lateral transfer mirror includes two transversely oriented
reflectors rigidly coupled by an intermediate aluminum panel
which provides an integral structure which facilitates optical
alignment of the apparatus. Compensation for temperature
variation in the temperature-sensitive IR detectors as well as
for a range of vehicle operating conditions is provided by an
adjustable, computer-controlled potentiometer in each of the
pollutant gas detector-circuits. T~e IR detector module
includes a high speed, rotating mirror arrangement- for
sequentially directing the reflected IR beam in a pulsed manner
onto a plurality of spaced detector elements, each adapted for
detecting a specific pollutant. The IR beam is sampled with
each IR pulse provided to the detectors at a rate greater than
24
.
2~9399~
the speed of rotation of the mirror which nominally operates at
12,000 RPM. This high speed sampling rate is used to calibrate
each detector circuit at a high rate to minimize circuit drift
and other sources of measurement inaccuracy. A pulsed output
representing the detected IR signal is provided to an audio
beeper and/or a visible light which are pulsed so as to
indicate the strength of the received IR signal. The optical
elements of the source and detector optics are adjusted until
the audio beeper and/or light source provide a maximized beep
and/or light pulse frequency.
