U.S. patent application number 14/930754 was filed with the patent office on 2017-03-16 for moisture and volatiles analyzer.
This patent application is currently assigned to CEM Corporation. The applicant listed for this patent is CEM Corporation. Invention is credited to David Deese, William Jennings, Joseph Lambert.
Application Number | 20170074766 14/930754 |
Document ID | / |
Family ID | 56896416 |
Filed Date | 2017-03-16 |
United States Patent
Application |
20170074766 |
Kind Code |
A1 |
Lambert; Joseph ; et
al. |
March 16, 2017 |
MOISTURE AND VOLATILES ANALYZER
Abstract
A volatile content analysis instrument is disclosed that
includes a cavity and a microwave source positioned to produce and
direct microwaves into the cavity at frequencies other than
infrared frequencies. A balance is included with at least the
balance pan (or platform) in the cavity. An infrared source is
positioned to produce and direct infrared radiation into the cavity
at frequencies other than the microwave frequencies produced by the
microwave source. A lens is positioned between the infrared source
and the balance pan for more efficiently directing infrared
radiation to a sample on the balance pan. The lens has dimensions
that preclude microwaves of the frequencies produced by the source
and directed into the cavity from leaving the cavity.
Inventors: |
Lambert; Joseph; (Charlotte,
NC) ; Deese; David; (Indian Trail, NC) ;
Jennings; William; (Wingate, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CEM Corporation |
Matthews |
NC |
US |
|
|
Assignee: |
CEM Corporation
Matthews
NC
|
Family ID: |
56896416 |
Appl. No.: |
14/930754 |
Filed: |
November 3, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62217375 |
Sep 11, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01J 5/10 20130101; H05B
2206/046 20130101; G01N 5/045 20130101; H05B 6/6464 20130101; H05B
6/76 20130101; H05B 6/6482 20130101; H05B 6/645 20130101; H05B 6/64
20130101 |
International
Class: |
G01N 5/04 20060101
G01N005/04; G01J 5/10 20060101 G01J005/10; H05B 6/64 20060101
H05B006/64 |
Claims
1. A volatile content analysis instrument comprising: a cavity; a
balance with at least the balance pan in said cavity; an infrared
source that is positioned to direct infrared radiation into said
cavity; a lens between said infrared source and said balance pan
for more efficiently directing infrared radiation to a sample on
said balance pan.
2. An instrument according to claim 1 wherein said lens comprises a
reflective collimator positioned between said infrared source and
said balance pan.
3. An instrument according to claim 2 wherein: said instrument
includes a microwave source that produces and directs microwave
radiation into said cavity at frequencies other than the infrared
frequencies produced by said infrared source; and said collimator
is a metal opening having dimensions that preclude the microwave
frequencies produced by said microwave source from leaving said
cavity through said collimator opening.
4. An instrument according to claim 3 further comprising an
infrared temperature detector positioned to target a sample on said
balance pan.
5. An instrument according to claim 4 further comprising a
processor in communication with said infrared source, said
microwave source, and said temperature detector, for moderating the
application of radiation to a sample in response to the detected
temperature.
6. A volatile content analysis instrument comprising: a cavity; a
microwave source positioned to produce and direct microwaves into
said cavity at frequencies other than infrared frequencies; a
balance with at least the balance pan in the cavity; an infrared
source that is positioned to produce and direct infrared radiation
into said cavity at frequencies other than the microwave
frequencies produced by said microwave source; a lens between said
infrared source and said balance pan for more efficiently directing
infrared radiation to a sample on said balance pan; and said lens
having dimensions that preclude microwaves of the frequencies
produced by said source and directed into said cavity from leaving
said cavity.
7. An instrument according to claim 6 further comprising an
infrared temperature detector positioned to target a sample on said
balance pan.
8. An instrument according to claim 7 further comprising a
processor in communication with said infrared source, said
microwave source, and said temperature detector, for moderating the
application of radiation to a sample in response to the detected
temperature.
9. An instrument according to claim 6 wherein said lens is a metal
opening having dimensions that preclude microwaves produced by said
microwave source from leaving said cavity through said lens.
10. An instrument according to claim 6 wherein said lens comprises
a plurality of adjoining cells, open at both ends and oriented in a
wall of said cavity with the open ends of each said cell generally
aligned along a light path defined from said infrared source to
said balance pan; and with the interior walls of said cells having
a surface that is sufficiently specular to reflect electromagnetic
radiation in the infrared frequencies produced by said infrared
source.
11. An instrument according to claim 10 wherein said plurality of
adjoining cells are formed of metal.
12. An instrument according to claim 10 wherein said cells have a
length-to-opening ratio sufficient to attenuate the microwave
frequencies generated by said source and propagated into said
cavity.
13. An instrument according to claim 6 further comprising an
infrared reflector positioned to direct infrared radiation from
said source to said lens.
14. A method of loss-on-drying content measurement comprising:
collimating infrared radiation towards a volatile-containing
sample; and concurrently propagating microwave frequencies to the
same sample.
15. A method according to claim 14 further comprising attenuating
the microwave frequencies at a collimator that collimates the
infrared radiation.
16. A method according to claim 14 further comprising collimating
the infrared radiation through a microwave attenuator that is sized
proportionately to attenuate the concurrently propagated microwave
frequencies.
17. A method according to claim 14 further comprising measuring the
infrared radiation produced by a heated sample.
18. A method according to claim 17 further comprising adjusting a
factor selected from the group consisting of the collimated
infrared radiation, the propagated microwaves, and combinations
thereof, in response to the measured infrared radiation from the
heated sample.
19. A method according to claim 14 further comprising: weighing the
sample before the collimating and microwave propagation steps; and
weighing the sample during the collimating and microwave
propagation steps.
20. A method according to claim 14 further comprising: weighing the
sample before the collimating and microwave propagation steps; and
weighing the sample when the sample is dry.
21. A combined infrared collimator and microwave attenuator
comprising: a plurality of adjoining cells, open at both ends and
oriented with the open ends of each said cell generally aligned
substantially parallel to one another; wherein the interior walls
of said cells have surfaces that are sufficiently specular to
reflect electromagnetic radiation in the infrared frequencies; and
wherein said cells have a length-to-opening ratio sufficient to
attenuate electromagnetic radiation within the microwave
frequencies.
22. A combined infrared collimator and microwave attenuator
according to claim 21 wherein: said interior wall surfaces will
reflect infrared radiation having wavelengths between about 3
microns and 1 millimeter; and; said cells will attenuate microwave
radiation having wavelengths between about 1 millimeter and 1
meter.
23. A combined infrared collimator and microwave attenuator
according to claim 22 wherein said cells are formed of metal.
Description
BACKGROUND
[0001] The present invention relates to instrumentation for
conducting loss-on-drying analysis of moisture and volatile content
for a wide variety of materials.
[0002] Measuring the moisture content, or the volatile content, or
both of materials is a necessary, valuable, frequent, and
repetitive task in many circumstances.
[0003] For example, in a manufacturing setting, the measurement of
sample volatile content may be an important step in a quality
control procedure. If the time for conducting the analysis is long,
then poor quality samples may not be detected for several hours or
days. In this circumstance, the manufacturing facility may have
continued producing the lower quality product throughout the time
necessary for conducting the test. Accordingly, a large quantity of
poor quality material may have been produced before the quality
problem was discovered. Such a delay often leads to cost overruns
and manufacturing delays, as the poor quality product may require
disposal and the manufacturing process must begin again.
[0004] In its simplest form, determining volatile or moisture
content consists of weighing a representative sample of material,
drying the material, then re-weighing the material to ascertain the
losses on drying and, consequently, the initial volatile content of
the sample. Convective, hot-air ovens, which are often used for
this task, can be relatively slow to bring the sample to "oven-dry"
equilibrium. Such devices can also be expensive to operate as they
inefficiently consume energy. These problems lessen the utility of
hot-air devices for volatile analysis.
[0005] Drying certain substances using microwave energy to
determine volatile or moisture content is generally convenient and
precise. The term "microwaves" refers to that portion of the
electromagnetic spectrum between about 300 and 300,000 megahertz
(MHz) with wavelengths of between about one millimeter (1 mm) and
one meter (1 m). These are, of course, arbitrary boundaries, but
help quantify microwaves as falling below the frequencies of
infrared (IR) radiation and above those referred to as radio
frequencies. Similarly, given the well-established inverse
relationship between frequency and wavelength, microwaves have
longer wavelengths than infrared radiation, but shorter than radio
frequency wavelengths. Additionally, a microwave instrument
incorporating a micro-processor can monitor the drying curve
(weight loss vs. time) of a sample and can predict the final dried
weight (and thus the original moisture content) based on an initial
portion of the drying curve. Such analyses may be conducted in
about one to three minutes for samples that contain free water.
[0006] More importantly, microwave drying to measure moisture
content is usually faster than equivalent hot-air methods.
Microwaves are, however, selective in their interaction with
materials, a characteristic that potentially leads to non-uniform
heating of different samples and associated problems. Stated
differently, the rapid manner in which microwaves tend to interact
with certain materials, which is an obvious advantage in some
circumstances, can cause secondary heating of other materials that
is disadvantageous (at least for volatile or moisture measurement
purposes).
[0007] Additionally, microwaves interact with materials in a
fashion known as "coupling," i.e., the response of the materials
("the load") to the microwave radiation. Some materials do not
couple well with microwave energy, making drying or other volatile
removal techniques difficult or imprecise. Other materials couple
well when their moisture content, or content of other
microwave-responsive materials (e.g., alcohols and other polar
solvents), is high. As they dry under the influence of microwaves,
however, they couple less and less effectively; i.e., the load
changes. As a result, the effect of the microwaves on the sample
becomes less satisfactory and more difficult to control. In turn,
the sample can tend to burn rather than dry, or degrade in some
other undesired fashion. Both circumstances, of course, tend to
produce unsatisfactory results.
[0008] As another factor, volatiles, such as "loose" water (i.e.,
not bound to any compound or crystal) respond quickly to microwave
radiation, but "bound" water (i.e., water of hydration in compounds
such as sodium carbonate monohydrate, Na.sub.2CO.sub.3.H.sub.2O)
and nonpolar volatiles (e.g., low molecular weight hydrocarbons and
related compounds) are typically unresponsive to microwave
radiation. Instead, such bound water or other volatiles must be
driven off thermally; i.e., by heat conducted from the
surroundings.
[0009] Thus, microwaves can help remove bound water from a sample
when the sample contains other materials that are responsive to
microwaves. In such cases, the secondary heat generated in (or by)
the microwave-responsive materials can help release bound water.
The nature of microwave radiation is such, however, that not all
such materials or surroundings may be heated when exposed to
microwaves. Thus, loss-on-drying measurements using microwaves are
typically less satisfactory for determining bound water than are
more conventional heating methods.
[0010] In order to take advantage of the speed of microwave
coupling for samples that do not readily absorb or couple with
microwaves, techniques have been incorporated in which a sample is
placed on a material that absorbs microwaves and becomes heated in
response to those microwaves (often referred to as a susceptor).
U.S. Pat. No. 4,681,996 is an example of one such technique. As set
forth therein, the goal is for the thermally-responsive material to
conductively heat the sample to release the bound water.
Theoretically, a truly synergistic effect should be obtained
because the thermally heated material heats the sample to remove
bound water while the free water responds to, and is removed by,
the direct effect of the microwaves.
[0011] Susceptor techniques, however, are less successful in actual
practice. As one disadvantage, the necessary susceptors are often
self-limiting in temperature response to microwaves, and thus
different compositions are required to obtain different desired
temperatures.
[0012] As another disadvantage, the predictability of a susceptor's
temperature response can be erratic. As known to those familiar
with content analysis, certain standardized drying tests are based
upon heating a sample to, and maintaining the sample at, a
specified temperature for a specified time. The weight loss under
such conditions provides useful and desired information, provided
the test is run under the specified conditions. Thus, absent such
temperature control, microwave techniques may be less attractive
for such standardized protocols.
[0013] As another disadvantage, the susceptor may tend to heat the
sample unevenly. For example, in many circumstances, the portion of
the sample in direct contact with the susceptor may become warmer
than portions of the sample that are not in such direct contact.
Such uneven temperatures may lead to incomplete removal of bound
moisture as well as inaccurate loss-on-drying analyses.
[0014] Bound water may be removed in some circumstances by applying
infrared radiation to a sample. Infrared radiation succeeds in
driving off bound water (as well as any free water) by raising the
temperature of the sample to an extent that overcomes the
activation energy of the water-molecule bond. Infrared drying is
also faster than oven drying for many samples. Nevertheless,
infrared radiation tends to heat moisture-containing samples
relatively slowly as compared to microwaves. Furthermore, infrared
radiation typically heats the surface (or near surface) of the
material following which the heat conducts inwardly; and typically
takes time to do so. Infrared radiation will, however, heat almost
all materials to some extent, and thus it offers advantages for
materials that do not couple with microwaves.
[0015] Merely using two devices (e.g., one microwave and one
infrared) to remove the two types of volatiles does not provide a
satisfactory solution to the problem because moving the sample
between devices typically results in at least some cooling, some
loss of time (efficiency), the potential to regain moisture (under
principles of physical and chemical equilibrium), and an increase
in the experimental uncertainty (accuracy and precision) of the
resulting measurement. Furthermore, if a sample is moved from a
first balance in a microwave cavity to a second (separate) balance
exposed to infrared radiation, the tare on the first balance would
be meaningless with respect to the use of the second balance.
[0016] U.S. Pat. No. 7,581,876 addresses a number of these issues
successfully. As set forth herein, the present invention further
increases both heating efficiency and accuracy of temperature
measurement.
SUMMARY
[0017] In a first aspect, the invention is a volatile content
analysis instrument that includes a cavity and a balance with at
least the balance pan (or platform) in the cavity. An infrared
source is positioned to direct infrared radiation into the cavity,
with a lens between said infrared source and said balance pan for
more efficiently directing infrared radiation to a sample on said
balance pan.
[0018] The term "lens" is used herein in the sense of an item or
device that directs or focuses radiation, including frequencies
(wavelengths) other than visible light, such as infrared or
microwave radiation. The reflective collimator described and
claimed herein falls within this dictionary definition.
[0019] In another aspect, the invention is a volatile content
analysis instrument that includes a cavity and a microwave source
positioned to produce and direct microwaves into the cavity at
frequencies other than infrared frequencies. A balance is included
with at least the balance pan (or platform) in the cavity. An
infrared source is positioned to produce and direct infrared
radiation into the cavity at frequencies other than the microwave
frequencies produced by the microwave source. A lens is positioned
between the infrared source and the balance pan for more
efficiently directing infrared radiation to a sample on the balance
pan. The lens has dimensions that preclude microwaves of the
frequencies produced by the source and directed into the cavity
from leaving the cavity.
[0020] In another aspect, the invention is a method of
loss-on-drying content measurement. In this aspect the invention
includes the steps of collimating infrared radiation towards a
volatile-containing sample, and concurrently propagating microwave
frequencies to the same sample.
[0021] In yet another aspect, the invention is combined infrared
collimator and microwave attenuator. The collimator is formed of a
plurality of adjoining cells, open at both ends and oriented with
the open ends of each cell generally aligned substantially parallel
to one another. The interior walls of the cells have surfaces that
are sufficiently specular to reflect electromagnetic radiation in
the infrared frequencies; the cells have a length-to-opening ratio
sufficient to attenuate electromagnetic radiation within the
microwave frequencies.
[0022] The foregoing and other objects and advantages of the
invention and the manner in which the same are accomplished will
become clearer based on the followed detailed description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a front elevational view of an instrument
according to the invention.
[0024] FIG. 2 is a front perspective view of the instrument of FIG.
1 opened to illustrate the cavity portion and the balance pan.
[0025] FIG. 3 is a rear perspective view of the opened instrument
of FIG. 2.
[0026] FIG. 4 is a side elevational view of an instrument according
to the present invention.
[0027] FIG. 5 is a side elevational view corresponding to FIG. 4,
but with the instrument open.
[0028] FIG. 6 is a rear elevational view of the instrument in the
closed orientation.
[0029] FIG. 7 is a partial cross-sectional, partial perspective
view of the interior of the instrument.
[0030] FIG. 8 is a partial perspective, partial cross-sectional
view oriented perpendicularly to FIG. 7 of an instrument according
to the invention.
[0031] FIG. 9 is a direct cross-sectional view of the instrument
perpendicular to FIG. 12.
[0032] FIG. 10 is an enlarged view of a portion of the interior of
the instrument illustrating the infrared sensor temperature.
[0033] FIG. 11 is a segregated enlarged view of the collimator
according to the invention.
[0034] FIG. 12 is a cross-sectional view taken perpendicularly to
the cross-section of FIG. 9.
DETAILED DESCRIPTION
[0035] FIG. 1 is a perspective view of an instrument according to
the present invention and broadly designated at 20. FIG. 1
illustrates an upper housing 21, a lower housing 22, and an
input/output control 23 shown in the form of a touch screen. A
latch 24 is part of the upper housing 21 and, as described further
herein, permits access to the infrared lamps of this illustrated
embodiment.
[0036] FIG. 2 illustrates the instrument 20 in partial perspective
view with the housing opened on the hinges 18 to show portions of
the interior. In particular, FIG. 2 illustrates the cavity 25 in
the form of its upper specially shaped chamber 26 and the cavity
floor 27. The instrument 20 includes a balance, more details of
which will be described with respect to other drawings, but that
has at least the balance pan 30 in the cavity 25 just above the
cavity floor 27.
[0037] FIG. 3 is a rear elevational view of the instrument 20
illustrating the upper housing in the open position. FIG. 3
illustrates a number of items in common with other figures
including the upper housing 21- and the lower housing 22. FIG. 3
also illustrates a plurality of network connections 46, and a
plurality of pedestal feet 15 upon which the lower housing 22 and
the remainder of the instrument 20 rest. FIG. 3 also illustrates
that an on-off switch 16 can be positioned at the rear of the
instrument 20 along with the plug 17 for a power cord.
[0038] The network connectors can be selected by those of skill in
this art without undue experimentation, but the instrument and
processor are in most cases consistent with Ethernet connections,
or 802.11 wireless transmissions ("WiFi") or short range radio
frequency connections for which the 2.4 gigahertz standard
("Bluetooth") is widely accepted and used. Again, the choices are
exemplary rather than limiting.
[0039] FIG. 3 also illustrates an exhaust elbow 28 that is
connected to the cavity 25 illustrated in other drawings and which
is used to draw volatile gases and water vapor from the cavity
during the heating process.
[0040] FIG. 4 is a side elevational view of the instrument 20
illustrating a number of the same items as FIGS. 1-3 and that
additionally illustrates the vents 29 as well as a printer 38
adjacent the vents 29. The printer has a door 39 that flips down so
that paper rolls can be added as desired or necessary.
[0041] FIG. 5 has the same orientation as FIG. 4, but showing the
instrument in the open position. FIG. 5 accordingly illustrates the
balance pan 30, and the cavity floor 27.
[0042] FIG. 6 is a rear elevational view of the instrument 20 that
illustrates the same items as FIG. 3, but with the instrument in
the closed position.
[0043] Although the use of a cavity is primarily expected for
microwave techniques, the use of the cavity with infrared radiation
also has advantages independent of the use of microwaves. As one
advantage, the cavity provides a defined thermal environment for
the sample and thus raises the heating efficiency. As another
advantage, when the cavity is made of a material that reflects
infrared radiation (such as metal, which is typical), the cavity
likewise enhances the overall heating efficiency. As yet another
advantage, when using a sensitive balance for which even small air
currents can give a false or inaccurate reading, such as described
in commonly assigned U.S. Pat. No. 6,521,876, the cavity provides a
shield against exterior air movement and again increases the
accuracy and precision of the weighing step and thus increases the
overall efficiency.
[0044] When microwaves are also used in the instrument, the cavity
provides the desired shielding against undesired propagation of
microwaves outside of the instrument, and some cavity designs help
support a single mode of microwave radiation for one or more of the
frequencies generated by the source. Nevertheless, a cavity that is
closed to radiation entering or leaving for microwave purposes is
as a result usually opaque to visible or infrared frequencies, and
some opening must be provided for visible or infrared frequencies
in a dual source instrument.
[0045] FIG. 7 is a partial cross-sectional, partial perspective
view of the instrument 20 according to the invention. FIG. 7
illustrates the same items as in FIG. 1 and FIG. 2, but with
additional interior detail. It will be understood by the skilled
person that much of the interior detail is straightforward and need
not be described in detail herein other than as the parts fit
together in an exterior housing of a particular size and shape.
That said, a pair of infrared lamps 54 (FIG. 9) are positioned near
the top of the upper housing 21 and are covered with an infrared
reflector 31 typically (although not necessarily) formed of metal
and typically having a highly reflective surface. Of these
characteristics, the reflective surface and the ability to be in
close proximity to the infrared lamps 54 is functionally most
important, and other materials such as ceramics or engineering
polymers can potentially be incorporated provided they can
withstand the ambient heat generated by the lamps and otherwise do
not interfere with the function of the lamps, or any other portions
or operations of the instrument.
[0046] A lens illustrated as the honeycomb shaped collimator 32 is
positioned in an upper wall of the cavity 25 between the lamps 54
and the balance pan 30. The lens 32 serves to direct infrared
radiation more efficiently at (or to) the balance pan 30 position
rather than simply flooding the cavity with infrared radiation.
Focusing the infrared radiation in this manner has at least several
benefits, including but not necessarily limited to, heating the
sample more efficiently (and thus using less energy) and minimizing
or eliminating any interference when temperature control is carried
out using an infrared thermal sensor (e.g., 59; FIG. 9).
[0047] To repeat a salient point, the term "lens" is used herein in
the sense of an item or device that directs or focuses radiation,
including frequencies (wavelengths) other than visible light, such
as infrared or microwave radiation. The reflective collimator
described and claimed herein falls within this dictionary
definition.
[0048] FIG. 7 also illustrates the microwave source 33 which in the
illustrated embodiment is a magnetron, but which (depending upon
costs and other factors) could include a klystron or an IMPATT
diode. An antenna 34 projects microwaves into the waveguide 35 and
from the waveguide 35 into the cavity 25. The power supply 36
provides power to the microwave source 33 and these portions of the
instrument 20 are cooled as necessary by one or more fans 40, 41. A
switching power supply (e.g., commonly assigned U.S. Pat. No.
6,288,379) can offer additional precision and control.
[0049] As some additional details, FIG. 7 illustrates that the
balance pan 30 is in the form of an open framework that will
support a rigid or semi rigid sample pan; i.e., the balance pan
itself does not need to be a solid planar object. The balance pan
30 is supported by a shaft 42.
[0050] In most embodiments, including this illustrated embodiment,
the balance 44 is a load cell of the strain gauge type, although
this is illustrative rather than limiting of the invention. A
mechanical scale is acceptable assuming that it is accurate,
precise, reliable, and properly calibrated and maintained. The
method of operation can involve either the use of a weight
balancing mechanism or the detection of the force developed by
mechanical levers.
[0051] A processor and its associated electronics are illustrated
at 45. The processor is in communication with the balance, the
infrared source 54, the microwave source 33 the temperature sensor
55, and the input and output control 23. The electronics for the
touch screen input control 23 are illustrated at 47. FIG. 7 also
shows reinforcing structures throughout the instrument such as the
supporting structure floor 53 under the instrument, the grid 50
below the touch screen 23, and the grid 51 above the power supply
36. A plurality of radiating fins 52 on the magnetron 33 help to
reduce heat accumulation as do the heat sink fins 57 (FIG. 8) near
the infrared lamps 54.
[0052] FIG. 8 is another partial perspective, partial
cross-sectional view of the instrument 20. FIG. 8 illustrates many
of the same items as FIGS. 1-3, but is particularly illustrative of
the reflector 31, the infrared source shown as a pair of infrared
lamps 54, and the temperature sensor illustrated as the infrared
detector 55. As FIG. 8 illustrates, the detector 55 focuses on the
sample pan 30, and thus on a sample during use. The infrared
detector 55 is in communication with the processor 45 so that the
temperature of the sample on the pan 30 can be taken into
consideration as drying proceeds. FIG. 8 also illustrates an on-off
switch 56 located near the rear of the lower housing 22.
[0053] FIG. 9 is a cross-sectional view generally perpendicular to
the longitudinal view of FIG. 12. FIG. 9 includes many of the same
elements as the previous drawings, but also illustrates details of
the infrared lamps 54, the infrared reflector 31, a plurality of
heat sink fins 57, and portions of the infrared detector 55, which
in turn is illustrated in greater detail in FIG. 10. The portions
of the infrared detector 55 illustrated in FIG. 9 include a mount
60 and a collar 61. FIG. 9 also broadly illustrates portions of the
lamp electronics 62, and portions of the processor and balance
electronics 63.
[0054] For reasons well understood to those familiar with this art,
the infrared temperature detector 55 is positioned to target a
sample on the balance pan 30. In particular, the nature of the
detector and the distance from the detector to the source (in this
case a heated sample) help increase the efficiency and precision of
the results from such detectors, and these factors are likewise
well understood in the art.
[0055] The processor 45 is in communication with the infrared
source lamps 54, the microwave source 33, and the temperature
detector 55, so that the application of radiation (infrared or
microwave or both) to a sample can be moderated in response to the
detected temperature. Such temperature detection and response
provides precise control over the sample heating, and helps keep
the temperature within a range that drives off moisture and other
volatiles without creating undesired decomposition that would
produce inaccurate results based on the measured weight change of
that sample.
[0056] FIG. 10 is a cutaway perspective view taken generally along
the segment 10-10 in FIG. 9. FIG. 10 illustrates the infrared
detector 55 in more detail, particularly the collar 61 and a mirror
64 that directs infrared radiation from the cavity 25 to reflect
into the detector diode (not shown) within its housing 65.
[0057] FIG. 11 is a segregated perspective view of the collimator
32 according to the present invention. In the illustrated
embodiment, which has been found to be advantageous, the collimator
is formed of a frame 66 and a plurality of smaller hexagonally
shaped open cells 67 within the perimeter defined by the collar 66.
Because the collimator serves two functions, it is engineered and
proportionately sized to meet both functions. As a first function,
the collimator re-directs (or more closely directs) infrared
radiation from the lamps 54 and the reflector 31 to the portion of
the cavity 25 at which the sample will be positioned. In the
illustrated embodiment, this position is predominantly defined by
the balance pan 30.
[0058] Therefore, the size of the cells 67 (length and width),
their surface, and the material from which they are made, all must
be consistent with their infrared radiation related function.
[0059] As a concurrent function, however, the collimator must
preclude microwave energy having frequencies produced by the source
33 from leaving the cavity 25. Therefore, the size and material of
the cells 67 must meet that function as well. The function is
referred to as attenuation, and an item with such a function is
informally referred to as a choke. In order to serve as a choke,
the length (longer dimension) of the opening structure must exceed
the diameter (or open area) of the structure by a defined
proportional amount. The use and sizing of such attenuators is well
understood in the art and need not be discussed herein in detail
other than to note that an attenuator in the form of a cylinder
should have a diameter smaller than the propagated wavelength
(.lamda.) and a length that is at least one-fourth of the
propagated wavelength.
[0060] Accordingly, the cells 67 are open at both ends and standing
alone are oriented with the open ends of each of the cells
generally aligned substantially parallel to one another. The
interior walls 68 of the cells 67 have surfaces that are
sufficiently specular to reflect electromagnetic radiation in the
infrared frequencies, and the cells 67 have the length-to-opening
ratio that is sufficient to attenuate electromagnetic radiation
within the microwave frequency range.
[0061] As examples of relevant infrared sources, quartz-halogen
lamps emit wavelengths predominately at about 3.5 microns (.mu.m)
and tungsten lamps at about 2.5 .mu.m. The detector 55 can be
selected or designed to offer the most sensitivity within a
particular range. In exemplary embodiments, the detector 55
measures radiation from the sample in the range of about 8-15
.mu.m. By virtue of this selection, the frequency (or corresponding
wavelength) of the infrared source differs from both the microwave
frequencies and from the infrared detector frequencies, thus
enhancing the accuracy and precision of the temperature measurement
and in turn of the feedback control.
[0062] Expressed in this manner, the interior wall surfaces 68 will
reflect infrared radiation having wavelengths of between about 1
microns (.mu.m) and 1 millimeter (mm) and the cells 67 will
attenuate microwave radiation having wavelengths between about 1 mm
and 1 meter. In most cases the combined collimator and attenuator
has cells formed of metal.
[0063] It will be noted, of course that for microwave attenuation
purposes, the cell walls 68 do not need to be specular, and that
for collimating purposes, the cells 67 do not need to meet the
microwave attenuation ratio. The combination of these functions
thus provides an unexpected benefit for both purposes that neither
an attenuator nor an infrared collimator would provide if standing
alone.
[0064] The instruments described herein are typically designed to
operate in the S band (2-4 gigahertz; 7.5-15 millimeters) based on
regulation of electromagnetic radiation in the United States and
elsewhere. Based upon that, in the illustrated embodiment, the
overall frame has dimensions of about 14 centimeters by about 12
centimeters, and the hexagonal openings are approximately 0.9
centimeters across and about 1 centimeter long. In one sense, if
the proportional requirements for infrared radiation and microwave
attenuation are met, different sizes can be selected based on
available space, the size and positioning of the lamps, and the
microwave frequencies being propagated into the cavity.
[0065] FIG. 12 is a full cross sectional view longitudinally
through the instrument and illustrates everything in FIG. 7 along
with several additional items. In particular, FIG. 12 illustrates a
microwave stirring blade 70 mounted on a small rotating shaft 71.
FIG. 12 also provides an excellent illustration of the shape of the
cavity 25 which can be the same or similar to the shape described
in commonly assigned U.S. Pat. No. 6,521,876, the contents of which
are incorporated entirely herein by reference.
[0066] In another aspect the invention includes a method of
loss-on-drying content measurement that collimates infrared
radiation towards a volatile-containing sample while concurrently
propagating microwave frequencies to the same sample. In the method
the microwaves are attenuated at a collimator that collimates the
infrared radiation used to dry the sample. Based on that, the
microwave attenuator has the proportional dimensions required to
attenuate the microwave frequencies being propagated.
[0067] As is fundamental to loss-on-drawing techniques, the method
further includes the steps of weighing the sample before starting
either of the collimating or microwave propagating steps, and
weighing is also carried out during the heating and microwave
steps. In this manner the sample can be dried to completion and
once a weighing step is carried out after completion, the
percentage of volatiles in the material can be easily
calculated.
[0068] As those familiar with microwave techniques are aware,
however, in many cases the loss of moisture and volatiles during
the heating process will rapidly assume an asymptotic curve from
which an end point (i.e., mathematically representative of a
totally dry sample) can be calculated once several (two or three
are often sufficient) measurements are taken during drying. The
processor included with the instrument can provide this function as
well; see, U.S. Pat. No. 4,457,632.
[0069] In the drawings and specification there has been set forth a
preferred embodiment of the invention, and although specific terms
have been employed, they are used in a generic and descriptive
sense only and not for purposes of limitation, the scope of the
invention being defined in the claims.
* * * * *