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The present invention relates generally to the identification of unknown
materials and pertains, more specifically, to non-destructive testing
devices and methods used for identifying given unknown materials utilizing
information obtained from thermoelectric junctions established between the
testing devices and the unknown materials.
Thermoelectric instruments and methods for testing materials have been in
use for some time now in identifying unknown materials by making use of
the well-known thermocouple principle to obtain data which enables
identification of a particular unknown material. Basically, these
instruments and methods form a junction between a known material and the
unknown material, heat the junction, and measure the voltage generated at
the junction. Since the voltage is a function of the materials and the
temperature at the junction and will differ from material to material, the
thermoelectric voltage may be used to identify the particular unknown
material in the junction. Unfortunately, however, the differences in the
thermoelectric voltage from one unknown material to another, when placed
in a heated junction with any one particular known material, very often
are not of sufficient magnitude to enable easy discrimination, and hence
accurate identification, of one unknown material over another. This is
true particularly among the wide variety of currently available alloys,
many of which tend to exhibit very similar thermoelectric voltages with
any one selected known material.
It is an object of the present invention to provide a thermoelectric
testing device and method which will identify unknown materials more
positively and with greater accuracy than previous devices and methods.
Another object of the invention is to provide a thermoelectric testing
device and method which will identify a wider variety of unknown materials
with accuracy.
Still another object of the invention is to provide a thermoelectric
testing device and method which will identify more accurately different
unknown materials having very similar thermoelectric properties when
placed in a thermoelectric junction with a particular known material.
Yet another object of the invention is to provide a thermoelectric testing
device and method which are easy to use in attaining more accurate and
positive results in the identification of a variety of unknown materials.
The above objects, as well as still further objects and advantages, are
attained by the present invention which may be described briefly as a
non-destructive testing device and method for identifying a given unknown
material utilizing information obtained from a plurality of thermoelectric
junctions established between the testing device and the unknown material,
the testing device and method providing a plurality of thermoelectric
junction-forming test elements, each test element having a known
characteristic selected to be different from the corresponding selected
known characteristics of the other test elements such that thermoelectric
junctions established between the test elements and the given unknown
material will produce different thermoelectric information for each
junction, test means for and the step of presenting each test element to
the given unknown material and establishing the thermoelectric junctions,
and information means for and the step of receiving the thermoelectric
information from each thermoelectric junction and providing identifying
data pertaining to the given unknown material based upon the
thermoelectric information received from the thermoelectric junctions.
The invention will be more fully understood, while still further objects
and advantages will become apparent, in the following detailed description
of a preferred embodiment of the invention illustrated in the accompanying
drawing, in which:
FIG. 1 is a block diagram illustrating a system in which the device and
method of the invention is operated;
FIG. 2 is a longitudinal cross-sectional view of the probe assembly of the
device, taken along line 2--2 of FIG. 3;
FIG. 3 is a partially cut-away bottom plan view of the probe assembly of
FIG. 2;
FIG. 4 is a schematic diagram of a portion of the probe coupled to the
system of FIG. 1;
FIG. 5 is a graphical representation of typical data obtained from the
device; and
FIG. 6 is an alternate graphical representation of the data shown in FIG. 5
.
Referring now to the drawing, and especially to FIG. 1 thereof, a block
diagram 10 illustrates a system in which a testing device 12 operates, all
in accordance with the present invention. Block diagram 10 illustrates
diagrammatically the manner in which a probe assembly 14 is associated
with a test specimen 16 of unknown material to obtain thermoelectric
information which then is processed to provide data for the identification
of the unknown material of test specimen 16.
Turning now to FIGS. 2 and 3, as well as to FIG. 1, probe assembly 14 is
seen to include an elongate probe housing 18 having a contact end 20 and
an opposite remote end 22. A retainer ring 24 is secured to the contact
end 20 by threaded fasteners 26 and holds a contact block 28 in place at
the contact end 20 of the probe housing 18. A plurality of test elements
shown in the form of test rods 30 extend through corresponding guide holes
31 in contact block 28, each test rod 30 including a terminal end 32 which
serves to contact the test specimen 16. An electrically powered heater 34
heats contact block 28 which, in turn, heats the test rods 30 to provide
the elevated temperature required at the junction between the terminal end
32 of each test rod 30 and the test specimen 16. A temperature sensing
element in the form of a thermistor 36 is placed within contact block 28
and is coupled to a temperature control 38 (see FIG. 1) for controlling
the temperature of the contact block 28 and of the test rods 30.
At the remote end 22 of probe housing 18, a cap 40 encloses the junctions
42 made between the test rods 30 and the conductors 44 of a control cable
46 which connects the probe assembly 14 with the remainder of the system.
Junctions 42 are supported in a terminal board 48 mounted by means of
sleeves 19 of insulating material within an upper block 50 which is heated
by an electrically powered heater 52 to raise the temperature of junctions
42 above ambient temperature. A second temperature sensing element in the
form of a second thermistor 54 is placed within the upper block 50 and is
coupled to temperature control 38 for controlling the temperature of upper
block 50 and the junctions 42. By setting the temperature of junctions 42
at some level above ambient temperature, but far below the temperature set
at the contact block 28 and the terminal ends 32 of test rods 30, the
thermoelectric voltages generated at junctions 42 remain stable and known
so that accuracy is assured in any measurement of thermoelectric voltages
at the terminal ends 32 of test rods 30.
The test rods 30 themselves are coated with a very thin coating of
dielectric material, such as a thin coating of Teflon, in order to isolate
the test rods 30 from the contact block 28 and the upper block 50, as well
as from one another. The coating is thin enough to enable appropriate
heating of the test rods 30.
In order to assure repeatable accuracy among the thermoelectric voltages
measured at each thermoelectric junction between a terminal end 32 of a
test rod 30 and the test specimen 16, the pressures with which the test
rods 30 are urged into contact with the test specimen 16 are essentially
equalized by means of a torsion spring provided by a loop 60 placed in
each test rod 30. Each loop 60 biases a corresponding test rod 30
longitudinally toward the test specimen 30 and is confined against lateral
movement by being contained within a corresponding individual guide
chamber 62 and each test rod 30 is anchored, as by the use of a set screw
64 threaded through a collar portion 66 of an anchor block 68 secured to
the probe housing 18. The dimensions of each loop 60 are selected so that
the pressures at the terminal ends 32 of the test rods 30 are equalized
when the probe assembly 14 is urged against test specimen 16.
As best seen in FIG. 3, the preferred arrangement of the test rods 30
places the test rods in a circular array, with each test rod located on
the circumference of a circle. In the illustrated embodiment there are
shown eight test rods 30 to by used for obtaining thermoelectric
information from eight corresponding thermoelectric junctions; however, a
number other than eight may be employed. In order to assure that the
terminal ends 32 of all eight of the test rods 30 are placed in
appropriate contact with test specimen 16, probe assembly 14 includes a
plurality of contact-sensing elements shown in the form of contact rods 70
each having essentially the same configuration as the test rods 30.
Contact rods 70 are interspersed within the circular array of test rods 30
so that when contact is made between all of the contact rods 70 and the
test specimen 16, each of the test rods 30 also will be in contact with
the test specimen 16. Thus, contact rods 70 do not participate in
producing thermoelectric information, but are so located within the array
of test rods 30 as to assure that all of the test rods are in appropriate
contact with the test specimen 16 before thermoelectric voltage are
measured. To this end, contact rods 70 are placed ninety degrees apart in
the circular array of test rods 30 and contact rods 70.
The operation of contact rods 70 in connection with the circular array is
shown schematically in FIG. 4. The eight test rods are seen at 30-1, 30-2,
30-3, 30-4, 30-5, 30-6 30-7 and 30-8. The four contact rods are shown at
70-1, 70-2, 70-3 and 70-4. The contact rods 70 are fabricated of a
material which is not necessarily thermoelectrically active, but which
will produce an output when in contact with the test specimen 16. A
suitable material is brass, although other materials are available which
will perform the same function. When the contact end 20 of probe assembly
14 is placed against the test specimen 16, the output from each contact
rod 70 is directed to a start test gate 72. Start test gate 72 is an AND
gate and will provide a start test signal at the output thereof only when
an input is received essentially simultaneously from all four of the
contact rods 70. Since it would be highly unlikely that all four contact
rods 70 will produce an output simultaneously without all eight of the
test rods 30 being in contact with the test specimen 16, the aforesaid
arrangement assures that thermoelectric information is not obtained until
all of the thermoelectric junctions are made properly, with essentially
equalized pressure, for accuracy of measurement.
As described above, in connection with FIGS. 1 and 2, the contact block 28
is heated by heater 34 to heat test rods 30 so as to provide the heated
junctions between terminal ends 32 and test specimen 16. At the same time,
heater 52 heats upper block 50 to heat junctions 42. Temperature control
38 maintains the temperature of contact block 28 far higher than the
temperature of upper block 50. Typically the temperature of contact block
28 is maintained at about 300.degree. F., while the temperature of upper
block 50 is held at about 100.degree. F. Sufficient heat is transferred
from contact block 28 to the test rods 30 for providing the required
heated junctions by virtue of the relative dimensions of the contact block
28 and the test rods 30. Thus, by assuring that the guide holes 31 each
have a length far greater than the diameter of the corresponding test rod
30 passing through the guide hole, sufficient heat is transferred to the
test rods. By way of example, the diameter of each test rod may be about
0.020 to 0.030 inch, with a dielectric coating having a thickness of about
0.0005 inch, and the guide holes 31 have an inside diameter great enough
to provide about 0.001 inch clearance between a coated test rod and the
contact block. The length of each guide hole 31 is at least approximately
ten times the diameter of a test rod 30 so that adequate heat transfer is
assured. The dielectric coating on each test rod 30 does not extend over
the terminal end 32 so that direct contact is made between the material of
each test rod 30 and the test specimen 16.
The materials of the test rods 30 themselves may be chosen from among a
very wide variety of suitable materials. A sampling of some of the
materials which provide suitable results are: iron, copper, silicon
carbide, silver, nickel, titanium, gold, columbium (niobium), 410 SST,
Inconel 600, BeCu, 17-4Ph, 6Al-4V titanium, 90/10, 50Ni/50 Fe, 50Ni/50Cr,
302 SST and 70/30. Other materials will be apparent to those skilled in
the art of materials. For illustrative purposes, the following table sets
forth eight particular materials chosen for each of the eight test rods 30
and tabulates thermoelectric information in terms of thermoelectric
voltage obtained at each junction between the terminal end 32 of the
corresponding test rod 30 and each of two test specimens 16, the
thermoelectric junctions being heated to about 300.degree. F.:
______________________________________
TEST TEST ROD TEST SPECIMEN
ROD MATERIAL COPPER IRON/NICKEL
______________________________________
30-1 410 SST 7.3 mv 4.6 mv
30-2 302 SST 6.0 mv 4.5 mv
30-3 6Al-4V TITANIUM
5.5 mv 4.5 mv
30-4 70/30 2.4 mv 2.3 mv
30-5 17-4Ph 6.7 mv 4.6 mv
30-6 INCONEL 600 7.1 mv 5.1 mv
30-7 90/10 4.4 mv 2.9 mv
30-8 COPPER 6.1 mv 2.6 mv
______________________________________
The above data is plotted in FIGS. 5 and 6 wherein it becomes obvious that
the composite characteristics of the total data obtained for each test
specimen 16 are quite different, even though at least one point, namely,
the data obtained at test rod 30-4, is so similar for both test specimens
as to render accurate differentiation impractical. The plotted data
illustrates that not only are the measured absolute thermoelectric
voltages different for the various test rods used in conjunction with the
two test specimens, but the relative directions from point to point along
each plot also differ. The resulting data may be displayed in a number of
ways so that the composite characteristics more positively identify a
particular unknown material than any single piece of data. Thus, by
utilizing data obtained essentially simultaneously from a plurality of
different thermoelectric junctions, rather than from only one, an unknown
material is more accurately identified with increased ease.
Returning now to FIG. 1, the thermoelectric information obtained from the
probe assembly 14 is processed by testing device 12 to obtain the data
which will identify a particular test specimen 16 of unknown material.
Upon receiving a start test signal from start test gate 72, as explained
above in connection with FIG. 4, a central processing unit in the form of
a microprocessor 82 will operate to actuate an eight channel analog switch
84 to sequentially pass the thermoelectric information obtained from the
eight test rods 30 to analog signal amplifiers 86 and then to an
analog-to-digital converter 88 from which the digital information is
supplied to the microprocessor 82. The digital information then may be
stored in the system memory 90 and/or processed to provide data which will
serve to identify the particular material of the test sample 16. The data
may be displayed in any one of several available display devices, examples
being a digital display 92 which will display identifying digital
information, an analog display 94, such as a meter, or a graphic display
96 which can display data in forms such as those illustrated in FIGS. 5
and 6, as well as in other forms. In addition, an interface 98 is provided
for connection to various automation devices. Thus, the composite
characterictics drawn from several thermoelectric junctions are employed
to identify more precisely the particular unknown material, easily and
with accuracy. While there may be similarities in information provided by
establishing a thermoelectric junction between one known material and
different unknown materials, which similarities render it difficult to
distinguish one unknown material from another, information obtained from
junctions made between a plurality of known materials and the unknown
materials will provide a set of composite characteristics for each unknown
material, which sets of composite characteristics will be different enough
to distinguish one unknown material from another.
It is to be understood that the above detailed description of a preferred
embodiment of the invention is provided by way of example only. Various
details of design and construction may be modified without departing from
the true spirit and scope of the invention as set forth in the appended
claims.
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