Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~,91~09
ULq'RASONIC TRANSDUCER
TECIINICAL FIELD
The present invention relates to a method for
measuring and/or monitoring the amount of material which
has been removed Erom a member through wear, machining,
etc., and more particularly to an ultrasonic piezoelectric
transducer for measuring and/or monitoring the amount of
material which has been removed from a member and other
physical properties oE the member in-situ.
BACKGROUND ART
Various approaches have been devised for detecting,
monitoring and measuring the amount of wear which has
occurred to a wear member. For example, in the area of
rotating equipment, a number of electrical devices are
available to detect and monitor bearing wear. These
devices are hased upon a number oE detection techniques.
Thus, wear detection might depend upon the completion of
an electrical circuit ~hrough the bearing when there is
excessive bearing wear, or it might depend upon the gen-
eration of a voltage if the shaft ro-tates eccentrically,
or it might depend upon the detection of an abnormal tem-
perature rise of the bearing. Each of these approaches
has some inherent disadvantages with respect to accuracy
and does no-t measure actual bearing wear, bearing wall
thickness or the amount of material which has been removed
from the bearing, i.e., each approach is responsive -to
bearing wear but does not measure quantitatively the
amount of wear that has occurred, the wall thickness
~ ~91~Og
remaining or the amount of material which has been
removed.
Other approaches have been devised to measure the
thickness of a workpiece or wear member, and by measuring
such thickness, the amount of wear which has occurred can
be calculated. These approaches have numerous commercial
and/or industrial applications, however, their use for
measuring the thickness of or wear which has occurred to
a work surface in-situ is cost prohibitive. In addition,
these approaches typically utilize devices fabricated
from materials which limit their applications to an operat-
ing environment having a temperature of normally less than
75C, and cause the resulting readings to be dependent upon
the temperature of the operating environment. It has also
been found that the materials utilized for these devices
cannot withstand severe operating environments which further
limits the applications in which they can be used. Thus,
these devices and measurement techniques are not usable
for measuring and/or monitoring the t}-ickness of or wear
which has occurred to work surfaces, such as a sleeve bear-
ing, in an elevated temperature operating environment such
as might exist in ro-tating equipment. This inability to
measure and/or monitor wear in-situ can result in costly
machine downtime to inspect the condition of -the bearings.
~lternatively, this inability can result in unnecessary
damage to the rotating equipment due to bearing failure
which was not promptly detected.
Because of the foregoing, lt has become desirable to
develop a device which can be utilized to measure and/or
monitor in-situ the thickness of, the amount of wear which
has occurred to, and the amount of material which has been
removed from a member such as sleeve or thrust bearings,
09
brake discs or pads, clutch plates and sealing members. Ideally, the
resulting device could also be used for measuring other physical properties
of the member, in-situ.
SUMMARY OF THE INVENTION
The present invention provides an ultrasonic piezoelectric
transducer that can be mounted within the wall of a wear member, such as a
sleeve or thrust bearing, brake disc or pad, clutch plate or sealing device,~
so that measurements of wall thickness, the amount of material which has
been removed through wear, and other physical properties can be made in-
situ.
Specifically, the invention relates to an ultrasonic transducerdevice for measuring the thickness of a member comprising a piezoelectric
element, means for biasing the piezoelectric element against a surface of
the member whose thickness is to be measured, and a thickness reference
member interposed between the biasing means and the piezoelectric element.
The thickness reference member operatively contacts the piezoelectric
element and applies a substantially uniform force thereto. The
pie~oelectric element has a pair of faces, one of the pair of faces being in
direct contact with a surface of the member whose thickness is to be
measured and the other of the pair of faces being compressed by the
thickness reference member.
In one embodiment, the transducer, which is an integral part of
the member in which it is mounted, includes an outer sleeve which is
threadedly received in a blind bore within the wear member, a piezoelectric
element which is positioned within the blind bore, and spacer means
interposed between the end of the outer sleeve and the piezoelectric
MU.S/lcm
.~ ,
element. The spacer means and the end of the outer sleeve have
complementary configurations permitting the spacer means to align itself
within the end of the outer sleeve and apply a substantially uniform
compressive force to the piezoelectric element. The application of such a
substantially uniform compressive force causes a firm, electrical and
acoustical contact to be formed between the piezoelectric element and the
bottom of the blind bore which insures a highly accurate measurement of the
wall thiclcness between the bottom of the blind bore and the inner surface of
the wear member. For example', it has been found experimentally that this
transducer can measure the wall thickness of and/or the amount of material
which has been removed from the wall of a bronze bearing easily up to 300F
with a repeatability in the sub-micron range
- 3a -
MLS/lcm
ns
--4--
utilizing s-tate-of-the-art electronics. The transducers
can also be located in a pre-determined arrangement around
the periphery of the wear member so that wear and/or
material removed can be measured and/or monitored around
the periphery thereof. In addition, it has been found
that other physicaL properties such as strain resulting
from stress being applied to the wear member can be moni-
tored with the transducer. lt has also been found that
the transducer can be utilized to determine local tempera-
tures within the wear member and, in the case of rotating
machinery, the relative vibration and alignment between
the shaft and the member can be measured and/or monitored
with the transducer. It has been further found that if
ball bearings are being utilized, each ball exhibits
specific pressure characteristics which change due to wear
or Eracture, and that these pressure characteristics can
be measured and/or monitored with the transducer.
In an alternate embodiment oE the invention, a mount-
ing ring is provided to position one or more transducers
against the outer surface of the wear member. In this em-
bodiment, the piezoelectric elements contact the outer
surface of the wear member and the total thickness of the
wear member is measured.
In still another alternate embodiment oE the inven-
tion, the blind bores within the wear member are replaced
with through bores -to xeduce production costs. ~ transducer
assembly is received with:in each of the through bores so
that its end is flush wi-th the inner surface of the wear
member. In this embodiment, the end of the transducer
assembly is actually an integral part of the wear surface
and the thickness of the end of the transducer assembly
is being measured.
~91~09
--5--
Regardless of the embodiment utilized, a separate
transducer may be placed in the same environment as the
other transducers for use as a relevant time reference.
Two embodiments of relevant time references are disclosed.
BRIEF DESCRIPTION OF THE DR~WINGS
Figure l is a partial cross-sectional view of an
ultrasonic piezoelectric transducer embodying the inven-
tion of this disclosure and installed in a wear member.
Figure 2 is a partial cross-sectional view of a plur-
ality of ultrasonic piezoelectric transducers embodying
the invention of this disclosure and installed in and
around the periphery of a wear member, such as a sleeve
bearing.
Figure 3 is a partial cross-sectional view of a mount-
ing ring for retaining one or more ultrasonic piezoelectric
transducers against the outer surface of a wear member,
such as a sleeve bearing or a ball bearing.
Figure 4 is a partial cross-sectional view oE an alter-
nate embodiment oE an ultrasonic piezoelectric transducerembodying the invention oE this disclosure and installed in
a wear member.
Figure 5 is similar to Figure 4 in that it is a partial
cross-sectiona:L view of an ultrasonic piezoelectr;c trans-
ducer used as a relevant time reEerence.
Figure 6 is a partial cross-sectional view of another
embodiment of an ultrasonic piezoelectric transducer installed
in a wear member and used as a relevant time reference.
Figure 7 illustrates an interrogating pulse to and a
return "echo" from an ultrasonic piezoelectric transducer
embodying the invention of this disclosure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings where the illus-trations
are for the purpose of describing the preferred embodiment
of the present invention and are not intended to limit the
9~o~
invention hereto, Figure 1 is a cross-sectional view of the
transducer 10 installed in a wear member 12, such as a
sleeve or thrust bearing, clutch plate, brake disc or pad,
sealing member, valve or the like, in order to measure and/
or monitor the thickness of, -the amount of wear which has
occurred to, and the amount of material which has been
removed from the wear member. The transducer lO is com-
prised of an outer sleeve 14, an aligning and electri-
cally insulating spacer 16 received within the end ofthe outer sleeve, and a piezoelectric element 18.
The outer sleeve 14 is typically fabricated Erom
round tubing, such as brass tubing or the like, which has
threads 20 formed adjacent to one end thereof. Typically,
the tubing material has the same or similar thermal expan-
sion properties as that of the wear member 12 to maintain
a firm contact therewith. This firm contac-t is provided
by the threads 20 which engage complementary threads pro-
vided in the wear memher 12, as hereinafter described. The
threads 20 also permit the adjustment of the outer sleeve
14 within the wear member 12 to optimize the operation of
the transducer 10 as later discussed. It should be noted
that other approaches are possible for the adjus-table
attachment oE the outer sleeve 14 to the wear melTIber 12,
such as a bracket arrangement (not shown) that is adjust-
able with respect to the wear member 12 and which retains
the sleeve 14. The end 22 oE the outer sleeve 14 has an
indentation provided therein forming a surface 24
connecting the end 22 oE the sleeve 14 with the inner
circumferential wall 26 of the sleeve. This indentation
may have a curved configuration, such as semispherical or
parabolic, or it may have a conical configuration which is
preferred to permit alignment oE the spacer 16 therein.
~9~09
--7--
The aligning and electrically insulating spacer 16 is
fabricated from a ceramic or ceramic-like material that is
capable of sustaining high temperatures and high pressures.
For example, pyrolytic boronitride or another ceramic-like
material can be used for the spacer 16 ! The particular
ceramic or ceramic like material utilized for the spacer
16 is selected to properly compensate for the thermal expan-
sion properties of the other components comprising the trans-
ducer 10 and the wear member 12 so that the spacer 16 will
maintain a substantially uniform compressive force on the
piezoe:Lectric element 18 over a broad operating temperature
range. The spacer 16 typically has a conical configuration
that is complementary to that of the indentation formed in
the end 22 of the outer sleeve 14. The spacer 16 is re-
ceived within the indentation so that the outer surface 28
defining its conicaL configuration contacts the surface 24
formed by the indentation. The use of conical surEaces 24,
28 formed on the outer sleeve 14 and the spacer 16, re-
spectively permits the alignment of the spacer 16 within
the outer sleeve 14 through elastic deformation of the
spacer 16 and the indenta-tion Eormed in the end 22 of the
outer sleeve 14. In contrast, selE-alignment of -the spacer
16 within the outer sleeve 14 can be achieved by using a
semi-spherical or parabolic configuration Eor the surfaces
24, 28 formed on the end 22 of the outer sleeve 14 and the
spacer 16, respectively. It should be noted that regardless
oE the shape of the complementary configurations used for
the spacer 16 and the indentation in the end 22 of the outer
sleeve 14, a precise fit of the spacer 16 within the in-
dentation is not necessary since any variations in size or
shape will be compensated for by the elastic deformation
of the spacer 16 and the indentation and/or by the self-
alignment of the complementary curved surfaces. The
alignment of the spacer 16 within the outer sleeve 14,
~;~9~309
whether by elastic deformation of the spacer 16 and the
indentation in the end 22 of the outer sleeve 14 or by
self-alignment through complementary curved surfaces, is
necessary to ensure the application of a uniform compressive
force on the piezoelectric element 18. Such a substantially
uniform compressive force also minimizes the possibility of
damaging the piezoelectric element 18 through the applica-
tion of a nonuniEorm compressive force thereto. Even
though both of the foregoing approaches apply a substantially
uniform compressive force to the piezoelectric element 18,
it has been found that the use of an appropriate conical
configuration for -the spacer 16 and the indentation in the
end 22 of the outer sleeve 14 is easier to implement and
may result in a subs-tantially higher absorption and obliter-
ation of spurious echoes from the primary ultrasonic signal
than if complementary curved configurations are used for
the spacer 16 and the indentati.on in the end 22 of the outer
sLeeve 14. Thus, the use of a conical configuration for
the spacer 16 and the end 22 of the outer sleeve 14 generally
results in a higher signal to noise ratio than if comple-
mentary curved configurations are used for same. In
summary, the spacer 16 is necessary in -this structure in
order to provide a substantia:lly uniform compressive force
to the piezoelectric element 18 and to absorb and
ob.literate spurious echoes. r~egard.less of the configuration
utilized for the spacer 16, an aperture 30 is formed there-
through. This aperture is sufficiently large to permit the
passage of an electric conductor therethrough.
The wear member 12 is provided with a blind bore 36
therein. The blind bore 36 is located so as to be substan-
tially perpendicular to -the cuter and inner surfaces 38, 40,
` ~9~09
respectively of the member 12. If the member 12 is a
sleeve bearing, the blind bore 36 is directed radially
inwardly so as to be normal to the inner surface 40 of the
member 12. The blind bore 36 is of a predetermined depth
and has a substantially flat surface 42 at the bottom there-
of. The distance between the flat surface 42 and the inner
surface 40 of the member 12 is the distance to be measured
and/or monitored. The blind bore 36 may also have threads
44 formed therein which terminate adjacent to the bottom
thereof.
The piezoelectric element 18 is a standard state-of~
the-art device and typically has a round disc-like shape.
The element 18 can be formed from commercially available
piezoelectric transducer material, such as PZT-511 available
from Vernitron, Inc. of sedford, Ohio. The size of the
element 18 is a function of the overall size of the trans-
ducer 10, however, an element having a diameter of 0.080
inch and a thickness of .003 inch has been tested experi-
mentally with excelLent results. The diameter of the ele-
ment 18 is slightly less than the diameter of -the blind bore
36 provided in the wear member 12. The element L8 is respon-
sive to a short voltage pulse, such as a 200 volt DC pulse
of 10 nanosecond duration, and converts khe voltage pulse
into a pressure pulse which is applied to the surEace of tlle
material whose thickness is to be measured and/or monitored.
Similarly, the piezoelectric element 18 converts the "echo"
return pressure pulse from the opposite surface of the
material whose thickness is being monitored into a voltage
pulse for measuremen-t purposes. The substantially uniform
compressive force applied to the piezoelectric element 18
by the spacer 16 ensures that the element 18 is firmly
~91~09
--10--
"seated" within the blind bore 36 for the proper trans-
mission of the voltage pulse into the element 18 and the
reception of the reflected "echo" pulse by the element.
Tn order to assemble the transducer lD, the piezoelectric
element 18 is received within the blind bore 36 and positioned
so that one side 46 thereof contacts the flat surface 42 at
the bottom of the blind bore 36. Inasmuch as the diameter
of the element 18 is only slightly less than the diameter
of the blind bore 36, the center of the element 18 and the
center of the flat surface 42 at the bottom of the blind bore
36 will substantlally coincide, however, such coincidence is
not necessary for the proper operation of the transducer
10. The other side 48 of the pi.ezoelectric element 18 may
be electrically connected to an electrical conductor 50. The
elec-trical conductor 50 is received through the aperture 30
provided in the spacer 16, and the spacer 16 is received in
the blind bore 30 so that its base 32 contacts the side 48 of
the piezoelectric element 18 which is mechanically and elec~
trically connected to the electrical conductor 50. The threads
20 on the outer sleeve 14 are coated with an adhesive, such
as Loctite, and the s.Leeve 14 .is threadedly advancecl into the
wear member 12 until the conical surface 24 provided on its
end 22 engages the outer surface 28 of the spacer 16. Fur-
ther advancement of the outer sleever 14 into the wear mem-
ber 12 causes the elastic deformation of the spacer 16 and
the indentati.on in the end 22 of the outer sleeve 14, and
the application of a substantially uniform compressive force
by the base 32 of the spacer 16 to the side 48 of the piezo-
electric element 18. If complementary curved configurations,such as semispherical or parabolic, are used for the spacer
16 and the indentation in the end 22 of the outer sleeve
14, the spacer 16 will self-align itself within the
~L~9~309
indentation in the end 22 of the outer sleeve 14 so that
its base 32 will apply a substantially uniform compres-
sive force to the side 48 of the piezoelectric element 18.
Regardless of the shape of the spacer 16 and the indentation
in the end 22 of the outer sleeve 14, the outer sleeve 14
is threadedly advanced~into the wear member 12 by manually
rotating the outer sleeve 14 until a snug fit exists be-
tween the indentation provided in its end 22 and the outer
surface 28 of the spacer 16, and between the base 32 of
the spacer 16 and the side 48 of the piezoelectric element
18. In order to ensure that such a snug fit exists, the
foregoing advancement of the outer sleeve 14 into the wear
member 12 is monitored by a pulser-receiver device and an
oscilloscope (all not shown). With this apparatus a sequence
of short voltage pulses is applied by the pulser to the
transducer 10 while the ou-ter sleeve 14 is being threadedl.y
advanced into the wear member 12 so that the sleeve 14 can
be rotationally adjusted until the optimum return "echo"
pulse, shown on the oscilloscope, is received by the
receiver. In this manner, a snug fit between the .Eore-
go.ing components is assured and the transducer 10 and the
wear member 12 are"mabah~d"to provide the optimum return
"echo" pulse with respect to shape, amplitude and signal to
noise ratio. This snug Eit is retained through the use oE
the aforementioned adhesive, such as Loctite, on the threads
of the outer sleeve 14, thus preventing any :Eurther movement
of the outer sleeve 14 with respect to the wear member 12.
In essence, the transducer 10 becomes permanently affixed
to and an integral part of the wear member 12, and the snug
fit between the indentation in -the end 22 of the outer
sleeve 14 and the outer surface 28 of the spacer 16 is main-
tained throughout the life of the device.
~9~09
-12-
Since the piezoelectric element 18 is somewhat deLorma-
ble under a compressive force, the application of a sub-
stantially uniform compressive force thereto results in a
firm, optimum electrical and acoustical contact between
the side 46 of the element 18 and the flat surface 42 at
the bottom of the blind bore 36. By providing such a firm,
optimum electrical and acoustical contact with the flat
surface 42 of the blind bore 36, any signals emanating from
the piezoelectric element 18 will be properly directed
toward the inner surface 40 of the wear member 12 to be
measured and/or monitored, and the wear member 12 will
provide the proper electrical ground for the system. Thus,
the surfaces 24, 28 compensate for deviations in manufac-
turing tolerances in the components involved, and thepossibility that the blind bore 36 may not be positioned
exactly normal to the inner surface 40 of the wear member
12. Botll of these conditions could result in the piezo-
electric element 18 not firmly contacting the flat sur-
face 42 of the blind bore 36 which, in turn, coul.d resultin inaccurate measurements and/or system malEunctions.
~fter the transducer 10 has been assembled and installed
in the wear member 12, the area 52 enclosed by the inner
circumferential wa.L.L 26 o.E the outer s.Leeve 1~ and con-
taining the electrica.L conductor 50 may be filled wi.th adense insulating and dampening mate.rial such as epoxy, e.g.,
Duro epoxy, loaded with tungsten for application temperatures
less than 400F. or a loaded ceramic adhesive for tempera-
tures in excess of 400F. This electric insulation mater-
ial and the spacer 16 preferably match the acoustical im-
pedance of the piezoelectric element 18 and help suppress
spurious echoes from interfering with the primary pulse.
~?,9~()9
The wear member 12 may have a configuration that is
either flat, such as a brake disc, c1utch plate, face type
seal or thrust type bearing, or circular, such as a sleeve
bearing or ring type seal. In any case, a plurality of
transducers can be utilized to measure and/or monitor wear
at various locations on the wear member 12. If a sleeve
bearing is utilized, the p:lurality of transducers 10 can
be placed within the outer bearing wall and around the
periphery of the bearing, as shown in Figure 2. In this
manner, the thickness oE, the amount of wear which has
occurred to, and the amount of material which has been re-
moved from the bearing can be measured and/or monitored at
various locations around -the periphery thereof. Thus, by
lS placing the transducer 10 within one or more blind bores
36 within the bearing, wear can be measured and/or monitored
in situ, eliminating costly periodic machine downtime to
inspect the condition of the bearing. Machine downtime
would only occur when a transducer indicates that sufficient
wear has occurred to justify the replacement of the bearing.
AlternativeLy, rather than placing a plurality of
transducers 10 within the blind bores provided in the outer
bearing wall, a mounting attachment 54, such as a ring as
shown in Figure 3, can be used to retain the transducers
10 in a radially spaced apart relationship. In such an
arrangement, the mounting attachment 52 is slipped over
the sleeve bearing 56 and the piezoelectric elements 18
firmly contact the outer surEace of the bearing wall.
9~9
-14-
Thus, no blind bores, which could damage the bearing or
aEfect its performance, are required in the bearing wall.
The foregoing is particularly important in the case of ball
bearings. In the arrangement shown in Figure 3, the radius
of the curvature of the bearing 56 is substantially greater
than the diameter of each piezoelec-tric element 18. Since
a substantial compressive force is being applied to each
element 18 by its associated spacer 16, it has been found
10 that sufficient surface contact exists between each ele-
ment 18 and the outer surface of the bearing 56 to produce
very accurate distortionless measurements of wall thick-
ness. Thus, by using this apparatus, the thickness of, the
amount of wear which has occurred to, the rate of wear of,
15 and the amount of material which has been removed from the
bearing wall can be measured and/or monitored at various
locations on the bearing. From the foregoing, it is
apparent that the mounting attachment 54 can also be used to
measure the wall thickness or the overall thickness of a
20 non-wear cylindrical member, such as a machine member, by
sLipping the mounting attachment 54 over the non-wear member
and positioning the piezoeLectric elements 18 so that they
Eirmly contact the outer surface of the non-wear member at
specific locations thereon. Thus, the transducer 10 can be
25 utilized for precision in-process gauging or in-process
measuring of strain.
In addition -to being able to measure and/or monitor the
thickness of, the amount of wear which has occurred to,
and the amount of ma-teria:L which has been removed from a wear
30 member in-situ, the construction of the transducer 10 pro-
vides another advantage in that no buffer element is re-
quired between the piezoelectric element 18 and the wall
whose thickness is being measured and/or monitored, i.e.,
~9~309
the distance between the flat surface 42 of the blind bore
36 and the inner surface 40 of the wear member 12. Typi-
cally, in prior art devices such a buffer element is re-
quired for mechanical support, impedance matching and seal-
ing of the transducer, however, its use greatly attenuates
and degrades the primary pulses produced by the trans-
ducer and the reflected "echo" pulses received by -the trans-
ducer. Inasmuch as the transducer 10 requires no buffer
element, such signal attenuation and degradation does not
occur. In addition, because of the absence of a buffer
element, a firm electrical and acoustical contact can be
made by the piezoelectric element 18 directly to the wall
whose thickness is being measured and/or monitored, and
the resulting measurements have a much higher degree of
accuracy than those resulting from prior art devices. For
example, measurements with a repeatability in the sub-
micron range utilizing state-of-the-art electronics have
been achieved. And lastly, due to the inherent simplicity
of the structure of the transducer, it is substantially
less costly to produce than the prior art devices.
In an alternate embodiment oE the inventiorl, as shown
in Figure 4, the blind bore 36 in the wear member 12 is
replaced with a through bore 60 connecting the outer and
inner surfaces 38, 40 of the member 12. Tlle through bore
60 may have threads 62 formed -therein. A transducer 64
comprising an outer sleeve 14, a spacer 16, and a piezo-
electric element 18 is received within a blind bore 66 in
a wear reference member 68 which may have threads 70 formed
on the outer surface thereof. The wear reference member 68
is received within the through bore 60 so that its end 72 is
substantially flush with the inner surface 40 of the wear
member 12. The inner surface 40 of the wear member 12 is
then machined to ensure that the end 72 of the wear reference
~9~09
-16-
member 68 is flush with the inner surface 40. It should be
noted that the material utilized for the wear reference
member 68 may be the same as or may be different from the
material comprising the wear member 12 inasmuch as only the
-thickness of the end oE the reference member 68 is being
monitored and/or measured. The operation of this embodi-
ment is similar to the previous embodiment utilizing a
bLind bore, however, it is easier and less costly to produce.
With any of the foregoing embodiments, it might be
desired to compensate for the temperature and pressure of
the environment and the strains existing on the transducer.
Such compensation can be accomplished by usi.ng a time refer-
ence transducer 80, as shown in Figure 5~ The structure of
thi.s t.ransducer 80 is similar to transducer 10, in that it
i.s comprised of an outer sleeve 14, a spacer 16, and a piezo-
electric element 18, however, the foregoing components are
received in a b.Lind bore 82 provided in a reference member
84, which is similar to wear reEerence member 68. The
material utilized for the reference member 84 is the same
as or similar to the material for the wear member L2 if a
blind bore 36 is utilized in the member 12, or the same as
or similar to the material for the wear reEerence member
68 i.f a through bore 60 is provided in the wear member 12.
The assembly of the transducer 80 and the reference member
84 i.s placed within the same temperature, pressure or
material environment as the other transducers 10, though
not necessarily contacting the wear member 12. By moni-
toring the measurements of the reEerence distance, produced
by the transducer 80, the measurements produced by the
transducer 10 can be adjusted to compensate for possible
measurement variations caused by opera-ting environment
changes.
~9~09
-17-
Another embodiment of a reference transducer 90 is
shown in Figure 6. The structure of this transducer is also
similar to the transducer 80 in that it is comprised of an
outer sleeve 14, a spacer 16, a piezoelectric element 18,
and an electrical conductor 50, however, the foregoing
components are received in a blind bore 36 provided in the
wear member 12. The electrical conductor 50 is attached to
a disc-shaped electrical connector 92 which is interposed
].0 between the base 32 of spacer 16 and the top surface 94
of a reference acoustical member 96 having a cylindrical
configuration. The bottom surface 98 of the reference
acoustical member 96 firmly contacts the other side 48 of
the piezoelectric element 18. The diameters of the disc-
shaped electrical connector 92 and the reference acoustical
member 96 are similar and are slightly less than the dia-
meter of the blind bore 36 permitting the easy insertion
therein. The reference acoustical member 96 is formed from
the same material as, or similar material to, the material
comprising the wear member 12. ~ cylindrical recess 100 is
provided in the top surface 94 of the reference acoustical
member 96 and is concentric with the center of the refer-
ence member 96 leaving the area between the diameter of the
recess 100 and the outer diameter of the reference member
96 in contact with the bottom surEace of the electrical
connector 92. ~ low impedance acoustical material 102 may
be provided in the recess 100 or the recess 1.00 may be left
empty in which case it would have approximately a zero im-
pedance. The low i.mpedance of the recess 100 provides a
relatively large reflection coefficient for any pressure wave
intercepted thereby. Such a relatively large reflection
coefficient is beneficial for the operation of this trans-
ducer 90 hereinafter described.
~;~9~E~09
-18-
Operationally, a short voltage pulse is applied to the
piezoelectric element 18 via the electrical conductor 50,
the electrical connector 92 and the reference acoustical
member 96. The piezoelectric element 18 converts the voltage
pulse into two pressure pulses which are transmitted in
opposite directions--one pressure pulse being transmitted
into the wear member via the one side 46 of the element 18
and the other pressure pulse being transmitted into the
reference acoustical member 96 via the other si~e 48 of the
element 18. The pressure pulse transmi-tted into the wear
member 12 is reflected by the inner surface 40 of the wear
member 12 back toward the one side 46 of the piezoelectric
element 18 and is intercepted by same. Similarly, the
pressure pulse transmitted into the reference acoustical
member 96 is reflected by the low impedance acoustical mater-
ial 102 in the recess 100 back toward the other side 48 of
the piezoelectric element 18 and is intercepted by same.
Inasmuch as the thickness of the reference acoustical member
96 varies independently of wear and is typically afEected
only by variations in temperature, the elapsed time between
the transmission of the initial pressure pulse and the re-
ceipt of the "echo" return pressure pulse can be determined
and utilized as a temperature reference parameter. Thus, in
essence, one pressure pulse "monitors" the thickness of the
wear member 12 and the other pressure pulse "monitors" the
thickness of the reference acoustical member 96 between the
top surface of the piezoelectric element 18 and the bottom
of the recess 100 containing the low impedance material 102.
sy "measuring" the latter thickness through elapsed pulse
travel time, compensation can be made for variations in the
thickness of the wear member 12 resulting from temperature
variations. In addition, through manipulation of the
`" ~?,9~309
-19-
resulting pulse travel time data, compensation can be made
for variations in the thickness of the wear member 12 re-
sulting from variations in the pressure to which the member
12 is subjected.
The advan-tage of interposing the piezoelectric element
18 between the reference acoustical member 96 and the por-
tion of the wear member 12 whose thickness is being monitored
or measured, and using the piezoelectric element 1~ to sim-
ultaneously transmit pressure pulses in opposite directionsis that signal degradation is minimized and a high signal-to~
noise ratio is maintained. For example, if the reference
acoustical member is located on the same side of the piezo-
electric element as the portion of the wear member whose
thickness is being monitored or measured, i.e., the reference
acoustical member is interposed between the piezoelectric
element and the "monitored or measured" portion of the wear
member, pressure pulses only in one direction are required.
Ilowever, each pressure pulse must pass through the reference
acoustical member, the portion of the wear member whose
thickness is being monitored or measured, and the i.nterface
therebetween. The end result is significant degradation and
attenuation oE the signal and substantial diEferences in the
amplitude of the "echo" return pulses f.rom the foregoing
i.nterface and the inner surface of the wear member. Such
signal degradation and differences in pulse amplitude re-
sults in inaccuracies in elapsed travel time measurements,
low signal-to-noise ratios, and inaccuracies in the "temper-
ature compensations" made for variations in the thickness
of the wear member.
~ s previously indicated, physical properties other than
the thickness of, the amount of wear which has occurred to,
and the amount of material which has been removed from the
wear member can be measured and/or monitored by the transducer
.. ~?g9~()9
-20-
10. For example, it has been found that strain due to
stress being applied to the wear member can be readily
monitored by one or more transducers mounted w.ithin or
attached to the wear member. By such monitoring, appro-
priate means can be taken to minimize and/or control such
stress within the wear member. It has also been found
that local temperature within the wear member can be de-
termlned with one or more transducers and, in the case of
rotating equipment, the relative vibration and alignment
between the shaft and the wear member can be measured
and/or monitored by the transducers. It has been further
found that if balL bearings are being utiliæed, the pres-
sure characteristics of each ba:Ll can be measured and/or
monitored by a transducer to determine ball wear or
fracture.
Another approach for obtaining temperature compensa-
tion when using the transducer 10 or for measuring tem-
perature of the wear member 12 with the transducer 10 is
shown in Figure 7 which illustrates an interrogating vol-
tage pulse which is applied to the transducer 10 and the
resulting return "echo" voltage pulse produced by the same
transducer. The return voltage pulse i.s defined by a first
zero crossing point corresponding to time t and a second
zero crossing point corresponding to time tL~ It has been
found experimentally, that the ratios tl, and thus tl-t,
t t
are relatively/independent of temperature and pressure
variations to which the transducer and the wear member
may be subject and these ratios remain substantially con-
stant unless wear has occurred. Even though the foregoing
ra-tios are relatively independent of temperature and pressure,
the time t and the time interval tl-t are each a function
~9~o~
of temperature and can be utilized to determine the temper-
ature of the transducer 10 or the wear member 12 at a par-
ticular location thereon. Alternatively, the -temperature
of the wear member 12 can be determined by using a reference
transducer 80, as in Figure 5, and the resulting tempera-
-ture can be substituted in the functional relationship
between temperature, pressure and the time interval tl-t
to determine pressure. Thus, the time interval tl-t can
be utilized to determine the temperature and/or the pres-
sure to which the transducer and/or wear meillber are being
subjected.
Certain modifications and improvements will occur to
those skilled in the art upon reading the foregoing. It
should be understood that all such modifications and improve-
ments have been deleted herein for the sake of conciseness
and readability, but are properly within the scope cf the
following claims.
