U.S. patent application number 09/752449 was filed with the patent office on 2001-05-10 for multiple gain portable near-infrared analyzer.
This patent application is currently assigned to Zeltex, Inc.. Invention is credited to Rosenthal, Todd C., Wrenn, Stuart W..
Application Number | 20010000910 09/752449 |
Document ID | / |
Family ID | 26721899 |
Filed Date | 2001-05-10 |
United States Patent
Application |
20010000910 |
Kind Code |
A1 |
Rosenthal, Todd C. ; et
al. |
May 10, 2001 |
Multiple gain portable near-infrared analyzer
Abstract
A multiple-gain, hand-held, near-infrared grain analyzer
analyzes, e.g., protein content of grain by infrared transmittance
and interactance (transflectance) has at least two gain values. A
first gain value is used when calibrating the analyzer with an
empty analysis chamber (empty except for the presence of air), and
a second, higher gain value is used when, analyzinq grain
samples.
Inventors: |
Rosenthal, Todd C.;
(Hagerstown, MD) ; Wrenn, Stuart W.; (Frederick,
MD) |
Correspondence
Address: |
ROTHWELL, FIGG, ERNST & MANBECK, P.C.
555 13TH STREET, N.W.
SUITE 701, EAST TOWER
WASHINGTON
DC
20004
US
|
Assignee: |
Zeltex, Inc.
130 Western Parkway
Hagerstown
MD
|
Family ID: |
26721899 |
Appl. No.: |
09/752449 |
Filed: |
January 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09752449 |
Jan 3, 2001 |
|
|
|
09061893 |
Apr 17, 1998 |
|
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60044703 |
Apr 18, 1997 |
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Current U.S.
Class: |
250/341.5 ;
250/341.1 |
Current CPC
Class: |
G01N 21/359 20130101;
G01N 21/3563 20130101 |
Class at
Publication: |
250/341.5 ;
250/341.1 |
International
Class: |
G01N 021/59 |
Claims
We claim:
1. A multiple gain, hard-held analyzer, said analyzer comprising:
an analyzer body configured to receeve in a sample-receiving
portion thereof a sample to be analyzed; a source which emits
electromagnetic radiation at a desired wavelength, said source
positioned with respect to said sample-receiving portion to emit
radiation through a sample received in said sample-receiving
portion; an electromagnetic radiation receptor positioned such that
electromagnetic radiation emitted by said source and passing
through a sample received in said sample-receving portion strikes
said receptor, said receptor causing a first signal to be produced
which is proportional to the intensity of electromagnetic radiation
striking said receptor, said analyzer being configured such that
said first signal is selectively amplified by a gain factor
selected from a plurality of available gain factors to produce a
second signal; and means for analyzing said second signal to
determine a parameter of interest of a sample received in said
sample-receiving portion; wherein said analyzer is of a size and
weight which permit said analyzer to be carried by hand and
transported from one location to another for non-laboratory-bound
field use.
2. The analyzer of claim 1, wherein said analyzer is configured to
be calibrated with said sample-receiving portion empty except for
ambient air present therein, said first signal being amplified by a
first gain factor when said analyzer is being calibrated and said
first signal being amplified by a second gain factor when a sample
is received in said sample-receiving portion and is being analyzed,
said second gain factor being larger than said first gain
factor.
3. The analyzer of claim 2, wherein said second gain factor is of a
magnitude sufficient to permit said analyzer to be used to analyze
a sample of grain packed within a cuvette and disposed, in said
cuvette, in said sample-receiving portion.
4. The analyzer of claim 3, wherein said second gain factor is
approximately forty times said first gain factor.
5. The analyzer of claim 1, wherein said source emits near-infrared
radiation.
6. The analyzer of claim 1, wherein said sample-receiving portion
is configured with at least one axis of symmetry such that a
cuvette, used to hold a sample to be analyzed and configured to fit
precisely within said sample-receiving portion, can fit within said
sample-receiving portion with more than one orientation; and
wherein said source and said receptor are offset relative to said
axis of symmetry whereby electromagnetic radiation can be caused to
pass through multiple portions of a sample to be analyzed by
positioning said cuvette in said sample-receiving portion with two
or more orientations.
7. A miethod of analyzing a sample, said method comprising:
providing an analyzer which is of a size and weight which permit
said analyzer to be carried by hand and transported from one
location to another for non-laboratory-bound field use, said
analyzer comprising: an analyzer body configured to receive in a
sample-receiving portion thereof a sample to be analyzed; a source
which emits electromagnetic radiation at a desired wavelength, said
source positioned with respect to said sample-receiving portion to
emit rudiation through a sample received in said sample-receiving
portion; and an electromagnetic radiation receptor positioned such
that electromagnetic radiation emitted by said source and passing
through a sample received in said sample-receiving portion strikes
said receptor, said receptor causing a first signal to be produced
which is proportional to the intensity of electromagnetic radiation
striking said receptor; passing electromagnetic radiation from said
source through said sample-receiving portion with said
sample-receiving portion empty, except for the presence of ambient
air therein, such that said first signal is produced having a first
first signal value; amplifying said first signal by a first gain
factor to produce a second signal having a first second signal
value; calibrating said analyzer by analyzing said second signal;
disposing a sample to be analyzed in said sample-receiving portion
and passing electromagnetic radiation from said source through said
sample to be analyzed such that said first signal is produced
having a second first signal value; amplifying said first signal by
a second gain factor to produce said second signal having a second
second signal value, said second gain factor being larger than said
first gain factor; and analyzing said second signal to determine a
parameter of interest of said sample.
Description
FIELD OF THE INVENTION
1. The invention relates to near-infrared analyzers which operate
on the principle of transmittance and interactance (transflectance)
and, in particular, to such analyzers which are portable.
BACKGROUND OF THE INVENTION
2. Near-infrared analyzers are relatively well-known and are used
to analyze such diverse properties as the octane content of
gasoline, the moisture content of cheese, and the oil/protein
content of grain. They operate by passing near-infrared light into
a sample that is to be tested and measuring the intensity of
selected frequencies of the light that either passes through the
sample or that is reflected bask from the sample.
3. With relatively translucent materials such as gasoline, most of
the light is able to pass through the sample. Therefore, relatively
little amplification of the signal generated by the photodetector
is needed. For such materials, the analyzer may be calibrated
before testing of the sample simply by performing an analysis run
on the empty test chamber. With other, relatively opaque materials
such as grain or other food products, however, much of the light is
absorbed or blocked by the material. Accordingly, when testing the
material, it is necessary to amplify by greater amounts the
photodetector signal to be abie to extract the information used to
analyze the content of the sample.
4. For portable or hand-held near-infrared analyzers configured to
analyze grain or other relatively opaque samples, it has been
customary to provide a sealed calibration standard having known
parameters of interest for each type of grain or other material
that is to be analyzed. The calibration standard is inserted into
the analyzer first and a calibrating analysis run is performed on
the standard. After the analyzer has been calibrated, the
calibration standard is renoved and the sample to be tested is
inserted into the analyzer and analyzed.
5. Because the transmisivity of the calibration standard and the
test sample are relatively the sane, the photodetector signal
generated when analyzing the test sample is not amplified any more
than the photodetector signal generated when analyzing the
calibration standard is. In other words, the analyzer operates at a
single gain. This has been standard procedure for the past several
years because it was believed that a dual gain portable analyzer
was impractical. This is because noise in the signal -- which tends
to be present in the photodetector signal to a far greater extent
in a hand-held unit than in a larger, better shielded laboratory or
table-top unit -- becomes amplified as well, and it had been
believed that such noise amplification would make analysis of the
signal unreliable.
6. Using calibration standards to calibrate the analyzer using the
calibration standard is not ideal, however. This is because the
standards tend to get soiled or smeared with debris as they are
handled, and this can taint the calibration or otherwise degrade
instrument performance. Additionally, the standards constitute
extra equipment that can be lost and which needs to be carried with
the analyzer. Accordingly, a portable, hand-held, near-infrared
analyzer for analyzing grain or other relatively opaque material
that does not need calibrating standards to operate -- i.e., one
which can calibrate itself using an empty chamber -- is
desirable.
SUMMARY OF THE INVENTION
7. The present invention bucks the conventional wisdom and provides
a near-infrared analyzer having two or more gain values associated
with the photodetector signal. This allows the analyzer to be
calibrated on an empty test chamber using a first, low gain value,
and then the sample to be tested using a high gain value. Gain
switching is effected by altering the resistance in the feedback
path around the op-amp used to anplify the photodetector
signal.
DESCRIPTION OF THE DRAWINGS
8. An embodiment of the invention will now be described in detail
in conjunction with the following drawings, in which
9. FIG. 1 is a perspective view showing a hand-held near-infrared
analyzer and a sample-containing cuvette;
10. FIG. 2 is a schematic diagram showing the relationship between
the electrical and optical components of the analyzer shown in FIG.
1:
11. FIG. 3 is a schematic diagram showing components of the
detector board shown in FIG. 2, which is configured to provide two
different photodetector signal gain values;
12. FIG. 4 is a schematic diagram showing components of the
connector board shown in FIG. 2;
13. FIG. 4A is a more detailed schematic diagram showing components
of the gain-switching circuit located on the connector board shown
in FIGS. 2 and 4; and
14. FIG. 5 is a schematic diagram showing components of a detector
board that is configured to provide three different photodetector
signal gain values.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
15. A portable, hand-held, near-infrared analyzer 10 is shown in
FIG. 1. The analyzer has a main body portion 12 in which most of
the electronics are housed and a sample-receiving portion 14. The
body portion 12 has a keypad 16 that is used to control operation
of the analyzer; a display window 18 that displays user prompts and
results; and, optionally, a printer mechanism 20 such as a tape
printer. The main, body portion 12 also has an on/off switch 22; a
battery compartment 24; and an A/C adapter port 26.
16. The test chamber 30 constitutes a rectangular cavity in the
sample-receiving portion 14. An array of near-infrared emitting
diodes is housed in the sample-receiving portion 14, positioned to
emit near-infrared light of various wavelengths from light port 32
located in one wall of the chamber. A photodetector (not visible in
FIG. 1) is located directly opposite to the light port 32 in the
wall of the test chamber 30 across from the light port 32. It will
be noted that, for purposes explained below, the light port 32 (and
hence the photodetector) is not centered laterally but, rather, is
closer to one end of the test chamber than the other.
17. An opaque lid 34 -- preferably black -- is pivotally attached
to the sample-receiving portion 14, e.g., by means of hinge 36. The
sample-receiving portion 14 and the lid 34 are constructed such
that when the lid is closed, the test chamber 30 is entirely sealed
from ambient light.
18. As further shown in FIG. 1, the sample of material, e.g.,
grain, is loaded into a generally rectangular cuvette 40. The
cuvette has an upper opening 42, which may or may not be sealed,
and a pair of transparent panels 44 on opposite sides which allow
light omitted from the light port 32 to pass through the sample to
the photodetector.
19. The electronic components and test configuration of the
near-infrared analyzer 10 are shown schematically in FIG. 2.
20. The near-infrared emitting diodes are assembled together to
for, the source array 50, which illuminates the grain sample
contained within the cuvette 40. The rhotodetector (not shown in
FIG. 2), which is located on detector board 52, detects light
passing through the sample and sends a signal along signal line 54,
through conne-tor board 56, and to a microprocessor (not shown)
located on microprocessor board 58. In addition to the
photodetector signal the microprocessor receives signals indicating
the temperature of the detector board and the sample these signals
are transmitted to the connector board along signal lines 60 and
62, respectively, and then to the microprocessor.
21. Components of the detector board are shown in greater detail in
FIG. 3. The photodetector 70 is a silicon photodiode, e.g., a
Hamamatsu S1337 photodiode, the output current of which is
proportional to the intensity or the light impinging on it. The
photodetector is connected across pins 2 and 3 (negative and
positive, respectively) of op-amp 72 which is, for example, a
Harris 3160T op-amp. The output voltage of the op-amp (at pin 6) is
measured by the microprocessor as the detector signal.
22. As noted above, the temperature of the photodetector (as well
as the temperature of the sample) is measured and fed to the
microprocessor. This is accomplished using thermistor 74 which is,
for example, a Betatherm 10K3D409.
23. To this extent, the detector board components are as known in
the art. With respect to the op-aup feedback path, however, it is
modified to provide dual gain on the photodetector signal (op-amp
output at pin 6) Specifically, the feedback path has a pair of
resistors R1 and R2 arranged in parallel, with R1 having a
signifcantly greater resistance than R2. For example, R1 is
preferably 1000 megohms and R2 is preferably 25 megohms.
24. Switch 76 is located between the resistors R1 and R2 and is
provided by means of a reed relay. The switch is normally closed,
in which case almost all the current in the feedback path flows
through R2 (path of least resistance) and just a small amount flows
through R1. When current flows through coil 78, on the other hand,
the switch 76 is opened. This forces all the current to flow
through R1 and the gain on the photodetector signal is increased by
a factor of approximately 40 (1,000.div.25). (Diode 80, arranged in
parallel with the coil, protects the driver circuit from the
voltage spike created when the field of the relay coil
collapses.)
25. The circuitry also includes capacitors C1-C4, as well as a
guard ring 82 surrounding high-impedance points on both sides of
the circuit board. Capacitors C1 and C2 are integrating capacitors
for noise reduction, if needed. Capacitors C3 and C4 are provided
to bypass noise from the power lines VA.sup.+and VA.sup.-to
ground.
26. The switch 76 is controlled by a gain-switching circuit 90,
preferably located on the connector board 56 as shown in FIGS. 4
and 4A. The other components on the connector board are generally
known in the field.
27. As shown in greater detail in FIG. 4A, the gain-switching
circuit consists of a photocoupler 82, which is, for example, a
4N35 photocoupler, and a transistor 84, e.g., a 2N4400 transistor.
When a high gain signal is issued by tne microprocessor, the
transistor 84 turns on, allowing current to flow through LED 36
which is embedded in the photocoupler chip 82. Light emitted by the
LED 86 causes the embedded photoresistor 88 to turn on, thereby
allowing current to flow to the coil 78 of the reed relay, which is
indicated schematically in dashed lines. As noted above, this
causes the switch 76 (FIG. 3) to open, thereby amplifying the
photodetector signal by a gain factor of about 40.
28. In operation, the analyzer 10 is turned on and initialized with
an empty test chamber 30. In other words, the lid 34 is closed with
no sample in the test chamber, and a calibrating analysis of the
empty test chamber is conducted.
29. After the analyzer has been calibrated, the microprocessor
issues a high gain signal which causes the switch 76 to open,
thereby increasing the photodetector signal gain. The cuvette 40
containing the sample is placed in the test chamber 30, the lid 34
is closed, and an analysis of the sample is performed using methods
that are known in the art.
30. As is customary, two different sample analyses and their
results are averaged. With prior art analyzers, in which the optics
(light port 32 and photodetector 70) are laterally centered with
respect to the length of the test chamber, it is necessary to
discard the contents of the curvette and fill it with another
sample to avoid analyzing the exact same portions of the sample --
albeit from opposite sides -- which would skew the average
value.
31. As noted above, however, the optics of the present analyzer are
laterally shifted along the lenqth of the test chamber; in other
words, they are not centered. Therefore, rather than discarding the
contents of the cuvette and refilling it, it is only necessary to
rotate the cuvette by 180.degree. and replace it in the test
chamber. The sample is then analyzed once again -- this time by
passing the near-infrared light through a different portion of the
sample -- and the results are averaged.
32. Finally, it will be appreciated that the dual-gain principle of
the present invention can be extended to provide three or even more
different gain values. A configuration having three resistors R3,
R4, and R5 in the feedback path and reed relay switches 76 between
the three resistors is shown in FIG. 5. The switches are both
normally closed, which provides a first gain value. By opening the
switch between R4 and R5, then the switch between R3 and R4, two
additional gain values are obtained.
33. Other embodiments are deemed to be within the scope of the
following claims:
* * * * *