Note: Descriptions are shown in the official language in which they were submitted.
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Description
ACOUSTIC TRANSDUCER COMPONENTS
This is a divisional application of Canadian Application Serial No.
2,220,557.
1. Field of the Invention
The present invention relates to a damping element and a
waveguide suspension device for elongated waveguides in magnetostrictive
displacement or distance measuring transducers and circuits used for such
devices, and more particularly to modularly constructed magnetostrictive
transducers having damping elements, waveguide suspension and modular
construction including for displacement or distance measuring and using a
local
buffer circuit.
2. Description of the Art
Magnetostrictive transducers having elongated waveguides that
carry torsional strain waves induced in the waveguide when current pulses are
applied along the waveguide through a magnetic field are well known in the
art. A
typical linear distance measuring device using a movable magnet that interacts
with the waveguide when current pulses are provided along the waveguide is
shown in U.S. Patent No. 3,898,555.
Devices of the prior art of the sort shown in U.S. Patent No.
3,898,555 also have the sensor element embedded into the protective housing
which also houses the electronics to at least generate the pulse and provide
certain mounting means associated with the device for the customer.
U.S. Patent No. 5,313,160 teaches a modular design in which the
sensor and electronic assembly can be removed from the application package. In
the application package is the outer housing which is used by the customer for
mounting an attachment of the sensor and electronics assembly with the end
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device whose position is to be measured. None of the prior art teaches
excluding
all of the electronics except a local buffer circuit.
Sensor designs of the past have required delicate handling until the
fabrication of the total unit, including outer housing and electronics, has
been
completed. Prior art also utilizes difficult to produce and expensive methods
to
suspend the waveguide and to prevent the reflection of the desired sonic
strain
wave. Prior high performance waveguide suspension systems utilize thin
elastomer spacer discs which are individually positioned along the entire
length of
the waveguide. Installation of the discs is a time consuming, usually manual
operation. The best performing damping devices in use utilize molded rubber
elements with a central hole. These are difficult to mold and time consuming
to
apply.
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Further damping devices for waveguide are illustrated in U.S. Patent No.
3,898,555,
to prevent reflected sonic strain waves at both the remote end of the
waveguide and the
mounted end of the waveguide. These devices generally are soft rubber pads
that are
clamped about the waveguide to absorb sonic strain wave energy to minimize
reflections
of the generated pulse and reduce interference of the reflections with the
sonic strain-
wave signals to be sensed. The damping devices and the arrangement for
anchoring the
waveguide at a remote end may take up a substantial length at the end remote
from the
pick-up element of a sonic waveguide for prior art of this sort, as discussed
in U.S. Patent
No. 3,898,555. Where liquid levels, for example, are being sensed by the
transducers.
it is desirable to have the waveguide operable and active as close to the
bottom of the
tank as possible, thereby minimizing the length of the waveguide support at
its remote
end from the pick-up element. including the length of the separate damping
device at
such end, and at the mounted end of the waveguide. where the pick-up element
is
mounted.
In addition, in the prior art, the mass density of the damping material may be
quite
important to provide a mechanical impedance such that the sonic strain wave
energy can
be transferred into the damping device and dissipated. The coupling of the
waveguide
to the damping device must also be effective. The dissipation of the sonic
strain wave
energy by the damping medium has been thought in the prior an to provide the
damping.
It Is also known in the art to use gum type damping media because of the
ability
to attenuate or damp vibration but such materials harden at temperatures which
are near
the freezing point of water and become extremely soft at temperatures well
below 200
degrees Fahrenheit. The same is true for epoxy or urethane elastomers, and
such large
changes in characteristics change the "front" and reflection and the "extreme"
end
reflection characteristics drastically with temperature.
It is also known in the art to use silicone rubber dampers of two different
durometers and/or different loading pressure against the waveguide. Lower
pressure and
lower durometer silicone rubber has been utilized to minimize front end
reflection (input
end) while higher durometer silicone rubber in conjunction with greater
clamping
pressures has been utilized to provide damping at the remote or termination
end. This
use of silicone rubber was believed to be a compromise as a damping medium
because
of its NO resilience, which leads to the need for long damping sections.
Silicone rubber
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does have good stability over a wide temperature range which is an important
benefit for
damping materials.
The need for an effective damp material is especially evident when the
transducer
uses what is known as recirculation mode sensing. In the recirculation mode,
each time
the sensor receives a sonic strain wave signal, a new current pulse is sent,
and this leads
to a high frequency of sonic strain wave pulses and a build up of noise as a
result of
reflections. If effective damping is not provided, "noiW build-up reduces the
usefulness
of the sensing technique, especially since the sonic strain wave signal is
known in the
prior art to be of low amplitude. Thus. in the prior art, it was ideal for the
damp material
to be capable of being kept short, along with the end mounting structure for
the
waveguide, to have good coupling to the waveguide itself, and to have the
ability to
dissipate energy, the total of which is not well achieved in the prior art.
For other
approaches raising signal strength, see U.S. Patent 4,852,873, to use the
phase shifted
reflection from the end of the waveguide to reinforce the primary signal.
An alternate methodology for damping is set out in U.S. Patent No. 4,858,332.
This patent teaches an improved damping method. The damping device comprises a
highly viscous, flowable material that adheres to and couples to the
waveguide. and
which can have mass density changing additions, such as metallic powder, to
vary the
mass density along its length. The damping material is held against the
waveguide with
a suitable housing which can be loaded against the waveguide with pressure as
selected.
While such a method is effective, it is difficult to produce.
Also in the prior art, two half pieces (flat sheets) of rubber have been used
to
enclose a waveguide with a metal clamp to retain them around the waveguide and
apply
pressure to the waveguide at the input side, but this is fairly expensive.
The prior art has deficiencies in that the electronics are included within the
waveguide suspension device, an expensive means for waveguide suspension is
utilized
and the prior art does not disclose the relationship between the waveguide
suspension
mechanism and the damping mechanism. The prior art also has deficiencies by
not
closely coupling the mode converter (any device that converts mechanical
energy to
electrical energy or electrical energy to mechanical energy) to the input
pulse source
while utilizing the reflected energy at the input and of the device from the
end of the tape
component of a mode converter-
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It is also known in the prior art to use a coil for a mode converter having a
high
number of windings such as above 2400 windings and a coil for the mode
converter that
is a pickup coil with a low number of windings.
U.S. Patent 4,952,873 also discloses a waveguide mounting block supporting a
waveguide at the mounting end to provide a reflection point for the sonic
waves. The
block is precisely positioned a distance from the signal sensor that is
travelled by the
sonic wave during one-half of the signal lobe time period so that the
reflected wave
becomes an additive signal to the incoming sonic wave. Others in the prior art
have
chosen the length of the waveguide without a mounting block to accomplish the
same
purpose.
For general background information, see "Ultrasonic Level, Temperature and
Density Sensor" by S.G. Rogers and G.N. Miller, IEEE Transactions on Nuclear
Science,
Vol. NS-29, No. 1, February 1982.
It is an object of the present invention to produce a waveguide suspension
mechanism and damping mechanism which are easy to produce and assemble.
It is a further object of the present invention to facilitate packaging
options based
on a removable, interchangeable sensor element.
It is an additional object of the present invention to provide a robust sensor
element suitable for customers to incorporate into their products.
It is an object of the present invention to produce a local buffer circuit
that permits
closer coupling of a tape and coil mode converter arrangement for a
magnetostrictive
transducer.
It is a further object of the present invention to produce a local buffer
circuit that
is small and included within the sensor shielding while having the signal
generator outside
the sensor shielding.
Summery of the lnven#io t
The present invention relates to a remote end structure for an elongated
member,
such as a waveguide used with a magnetostrictive displacement or distance
measuring
transducer, that adequately prevents reflected waves, such as torsional or
longitudinal =
strain waves, and does not take up a substantial length at the remote end.
Thus, for
example, the waveguide is operable and active close to the end of the
elongated
member, while the remote and structure prevents reflection of sonic strain
waves that are
transmitted along the waveguide.
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The suspension is accomplished first by restriction of the elongated member
movement, as wall as shielding it from external sonic energy. In this manner,
shock and
vibration stimuli which can cause erroneous responses are also eliminated.
This is
accomplished by surrounding the elongated member, such as the waveguide. with
a
5 suspension element or sleeve sized such that the waveguide is in loose
contact with it,
yet the sleeve does not allow excessive lateral movement. The fiber used to
make the
sleeve is a fine, hard material, or a combination of materials such as ceramic
or metal or
polymer or glass. The sleeve may also be a composite tubing of different
material layers.
The tubing may be a composite rubberized glass fiber tube construction. An
enclosure
may also fit over the sleeve. Thus, the elongated member, such as the
waveguide, is
cushioned in the enclosure. The actual damping is achieved by a damping
element
sapped over the end of the waveguide. The damping element is similar to the
suspension element but sized to provide optimum damping. The end facing the
transducer head is cut at about a 45 angle in order to more properly match
impedance
with the elongated member, such as the waveguide.
The suspension is further accomplished by terminating the waveguide at a
bracket
which is used to hold the waveguide and the return conductor in spaced
relationship to
a pick-up coil and magnet and to permit attachment of the waveguide to a tape
inserted
into the pick-coil.
The electronics for pulse signal generation for transmission along the
waveguide
is not included in the electronics of the modularly constructed
magnetostrictive
transducer. The device electronics includes the fundamental signal.
The present invention also relates to a local buffer circuit for use with
remote end
structures for an elongated member, such as a waveguide used with a
magnetostrictive
displacement or distance measuring transducer, that adequately prevents
reflected waves
such as torsional or- longitudinal strain waves, at the remote end and does
not take up
a substantial length at the remote end, wherein the local buffer circuit
dampens the effect
of the signal at the input end and lessens the noise introduced to the mode
converter if
the mode converter includes a pickup coil with a high number of windings, such
as 400
to 2500 turns. Thus, for example, the mode converter is located at the input
end of the
elongated member and operable and active close to the end of the elongated
member,
while the remote and structure prevents reflection of sonic strain waves that
are
transmitted along the waveguide. The local buffer circuit protects the mode
converter
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from saturation by the received signal to help recovery of the pickup coil for
the
next signal by limiting the amount of energy delivered from the coil. Diodes
in the
local buffer circuit or a set of transistors are connected in parallel to the
pickup coil
and act to clip the peaks of the received signal and limit the energy induced
in the
pickup coil which results from the interrogation pulse. Thus, the position
magnet
(not shown here but described in U.S. Patent 3,898,555) may more closely
approach the head of the transducer.
Typically, the mode converter includes a pickup coil mounted
coaxially about a tape. The local buffer circuit is incorporated directly
after the
pickup coil. The local buffer circuit includes an emitter amplifier in
parallel with the
pickup coil so that the impedance of the pickup coil can be lowered by several
orders of magnitude in this manner. If the mode converter is shielded, such as
by
a housing, the buffer would be included inside of the shield or housing and
the
signal generator for the magnetostrictive device, i.e., the circuit that
drives the
waveguide, would be outside the shield. The use of a local buffer circuit
reduces
the sensitivity to electronic noise, maintains the signal integrity and
enables the
signal to be transmitted over long distance.
The electronics for pulse signal generation for transmission along
the waveguide is not included in the electronics of the magnetostrictive
transducer. The device electronics includes the fundamental signal and the
local
buffer circuit.
According to one aspect of the present invention, there is provided a
waveguide suspension for use with a waveguide and a return wire having an end
remote from the electronics connected to the waveguide, comprising: a
suspension sleeve, said suspension sleeve having an inner tubular,
nonconducting layer coaxial with and surrounding the waveguide; and an outer
tubular layer having means for maintaining the shape of said inner tubular
layer;
said suspension sleeve extending over a length of the waveguide.
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Description of the Drawings
For a further understanding of the nature and objects of the present
invention, reference should be had to the following figures in which like
parts are
given like reference numerals:
Fig. 1 depicts a side elevated view of the complete sensing element
assembly;
Fig. 2a is a cross-sectional view of the sensing element assembly of
the preferred embodiment of the present invention of Fig. 1 taken along
section
lines 2-2 of Fig. 1 showing a portion of the waveguide and surrounding sleeves
showing the damping element at the end of the waveguide;
Fig. 2b is the same cross-section view of Fig. 2a, but showing a first
alternative of using a tuning wire between the damping element and the
waveguide;
Fig. 2c is the same cross-sectional view as Fig. 2a, but shows a
second alternative of external tube crimped over the damping element;
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Fig. 2d is the same cross-sectional view of Fig. 2a, but shows a third
alternative
of the return conductor in a different position and with an external tube
crimped over the
damping element;
Fig. 3 depicts an elevated end view of the housing.which shows the connector;
Fig. 4 is a cross-sectional view of the sensing element assembly of the
preferred
embodiment of the present invention of Fig. 1 taken along section. lines 4-4
of Fig. I
showing the cross-section of the housing and a portion of the wavegulde and
surrounding sleeves but not showing the damping mechanism;
Fig. 5 is a plan view of the bracket of the preferred embodiment of the
present
invention:
Fig. 6 is a plan view of the bracket cover of the preferred embodiment of the
present invention;
Fig. 7 is a first profile view of the bracket of the preferred embodiment of
the
present invention;
Fig. 8 is a first profile view of the bracket cover of the preferred
embodiment of the
present invention;
Fig. 9 is a second profile view of the bracket of the. preferred embodiment of
the
present invention showing it Juxtaposed with the bracket cover of the
preferred
embodiment of the present invention;
Fig. 10 is a third profile view of the bracket of the preferred embodiment of
the
present invention showing the bracket cover juxtaposed;
Fig. 11 is a view in profile of the end opposite to the end of Figs. 9 and 10
of the
bracket of the preferred embodiment of the present invention showing the
bracket cover
juxtaposed to it;
Fig. 12 is a different side view of the profile of the bracket of the
preferred
embodiment of the present invention;
Fig. 13 illustrates a cross sectional view of a sensor assembly using the
transducer
of the preferred embodiment of the present invention;
Fig. 14 is the preferred embodiment of the local buffer circuit of the present
invention;
Fig. 15 is an alternate embodiment of the local : buffer circuit of the
present
invention; and
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Fig. IS illustrates a cross-sectional view of the sensing element assembly of
an
alternate embodiment of the present invention of Fig. 1 taken along section
lines 2-2 of
Fig. 1 showing a portion of the wavegulde and surrounding partial sleeves and
showing
the damping element at the and of the waveguide.
petafled Description of the Preferred and Altemate E i nts
A transducer or sensing element assembly, which may be any transducer,
including those of the prior art such as that shown in U.S. Patent No.
3,898,555 or any
other transducer presently on the market or may be introduced in the future,
for purposes
of the damping element, Is shown indicated at 25 in Figure 1. Transducer 25
may be
used for measuring displacements and/or distances or other measurements, and
the
damping device of the present invention will be applicable to any of them. The
type of
transducer that may be used for the present invention, should not be
considered to be
limited by the disclosure of the damping element used with. the transducer.
Further.
except for mechanical construction indicating. a preferred mechanical mounting
of the
waveguida, the general type of transducer should not be deemed to be limited
by the
disclosure of the waveguide suspension and except for the local buffer circuit
should not
be deemed to limit a mode converter used with a waveguide.. The transducer
should not
be deemed to be limited to any particular type of electronics used with the
waveguide
except for the local buffer circuit. Additionally, the general type and nature
of a
transducer in electrically producing the return pulse and interfacing through
the return
pulse with any electronics of a buyer or user of the device should not be
deemed to be
limited by the disclosure except for the mechanical construction: shown for
the preferred
embodiment and the printed circuit board containing the local buffer circuit.
The transducer 25 includes an elongated waveguide assembly enclosed in an
enclosure tube 3. Enclosure tube .3 and the waveguide assembly are
mechanically
supported at one and by a housing 17 through an end flange 19. The waveguide
assembly includes the outer enclosure tube 3 surrounding a coaxial elongated
interior
waveguide 4 (Fig. 2). Whenever "Fig. 2" is referenced in this specification,
it means any
of the embodiments of Figures 2a-2d. A current is passed through the waveguide
4 and
returns through a return conductor 1 electrically connected to the waveguide
4. Typically.
a magnet (not shown) is mounted over the waveguideassembly and enclosure tube
3
by being placed over and coaxial with enclosure tube 3. The magnet interacts
with the
current pulse as more completely described in U.S. Patent 3,898,555. Upon the
strain
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wave pulse returning to the housing 17 after passing through the waveguide 4
and return
conductor 1, the placement of waveguide 4 and return conductor 1 being more
completely described below, a suitable mode converter (partially shown) of any
type
known or to be known in the art provides an electrical signal through
connector 21 to any
electronic circuit connected to it, such as electronic circuit. 26.
The structure of the circuit 26 is dependent on the use of transducer 25, and
will
work with the wavegulde suspension sleeve 2 and modular construction elements
of the
present invention despite disparities in structure. The structure of circuit
26 should not
be considered as limiting the invention. Thus, no particular mechanism for the
arrangement of the element 26 or any conditioning of the signal to circuit 26
is shown to
be preferred to emphasize generality except the local buffer circuit 95 shown
in Figure
14 or Figure 15. Further, it should be understood that the waveguide
suspension sleeve
2 mechanism of the present Invention is applicable to any transducer 25 and
waveguide
4 of the type for measuring displacement and/or distance and/or other
measurement
using the magnetostrictive or other principles, such as piezoelectric or such
as generally
shown in U.S. Patent 3,898,555, but is dependent for modular assembly to some
extent
on the mechanical arrangement of elements in housing 17. Thus, for example, a
particular mechanism for the arrangement of the elements in the housing 17 Is
shown to
be preferred for mounting, but otherwise should not limit generality. The
mechanism
other than mounting may be of any sort, including such as those shown in U.S.
Patent
3,898,555 or others known in the art or still to be thought of in the art or
that are in
design in the art. For this same reason, the type of magnet used and the type
of
application used is also not shown. and may be any application. Finally,
because there
is some need to show the interaction between the damping element 6 (Fig. 2)
and the
!5 waveguide suspension sleeve 2 and other portions of transducer 25 at the
remote portion
of the waveguide assembly, a preferred embodiment for an enclosure tube 3
(Fig. 2),
discussed below, with the waveguide suspension sleeve 2 and damping element 6
is
shown. This should not be considered as limiting but only illustrative, the
waveguide
suspension sleeve 2 being capable of use with any type of waveguide assembly
as set
0 out above.
The remote end portion of enclosure tube 3. remote from housing 17, is shown
in cross-section in Fig. 2 and ends with an end plug 20. An inert gas may be
introduced
in enclosure tube 3 to further promote isolation and sealing. End plug 20 acts
to stop
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fluid and other materials from entering enclosure tube 3. The end of the
waveguide
assembly having end plug 20, is normally the and which would be at the bottom
of a
tank, if transducer 25 is being used for determining the level of liquid in a
tank, or at the
pnd of the displacement if the transducer 25 were used to measure distance. As
5 discussed in the Background, it is desired to make the dead zone, or non-
signal
producing zone, adjacent to the and plug 20 as short as possible and yet
accomplish the
purpose of dampening the sonic strain wave signal to prevent reflected strain
waves from
interfering with the desired return strain wave signal that represents
distance or level,
such as discussed in U.S. Patent 3,898,555.
'10 As shown in Pig. 2, a waveguide 4 is enclosed through concentrically
layered
enclosure mechanisms, including a suspension sleeve 2 and enclosure tube 3.
The
suspension sleeve 2 comprises a tubular braided sleeve, or elastorner sleeve,
or
composite sleeve, of a geometry having the characteristics of restricting the
lateral
movement of the waveguide 4 and insulating the waveguide 4 from vibration and
external
sonic noise yet not contacting the waveguide 4 so much as to damp the sonic
strain
wave signal generated by the interaction of the electric current and external
magnet.
Suspension sleeve 2 is coaxial with and surrounds the waveguide 4 for
substantially its
entire length, or at least a major portion thereof. Suspension sleeve 2 is
shown mounted
within and coaxial for substantially the entire length of waveguide 4, or at
least a major
portion thereof. with outer enclosure tube 3.
The inner diameter of the suspension sleeve 2 must be. small enough to limit
the
movement of the waveguide 4 yet large enough so that it does not hold, grab,
constrict
or otherwise compress the waveguide 4. If suspension sleeve.2 compresses,
holds,
grabs or constricts the waveguide 4. attenuation of the sonic strain wave
signal along
waveguide 4 will occur. The Wiedemann Effect does not promote a large sonic
strain
wave signal in the prior art, making it difficult to differentiate it from
noise produced by
other mechanisms. Accordingly, signal attenuation is known in the prior art to
be a
phenomenon to be avoided.
The outer diameter of suspension sleeve 2 must be large enough to restrict
lateral
movement of suspension sleeve 2 within enclosure tube 3, yet small enough to
fit easily
within the inner diameter of the enclosure tube 3, together with the return
conductor 1 as
will be discussed below. Also, it may be possible to have the suspension
sleeve 2
present without requiring the restriction of an enclosure tube 3, and the use
of an
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enclosure tube 3 should not be considered limiting to the invention or even to
the
wavegulde suspension. Overall, the waveguide 4 must be suspended in a manner
that
cushions it from shock and vibration stimuli so that associated erroneous
responses are
eliminated.
Suspension sleeve 2 includes an inner layer 27 and an outer layer 29. The
fiber
that makes up inner layer 27 of suspension sleeve 2 is non conducting and may
be a
fine, hard material, or a combination of materials such as ceramic or glass or
metal or.
polymer. The strand count and weave configuration of such fiber are typically
from eight
to sixteen strands in diamond, regular, hercules or other weave pattern. Such
strand.
count and weave configuration enable the suspension sleeve 2 to act as a
cushion
between the waveguide 4 and the enclosure tube 3. Interior to the inner layer
27 and
exterior to the waveguide 4, there is clearance 28 such that the inner layer
27 is loosely
fitting around waveguide 4. The outer layer 29 of suspension sleeve 2 helps to
maintain
the shape of the inner layer 27, and isolate it from the enclosure tube 3. The
outer layer
29 is typically a softer material, such as a silicone rubber, and is a second
layer of inner
layer 27.
Suspension sleeve 2 ends at its remote side at end 31 facing toward the end
plug
20. Juxtaposed with the end 31 of the suspension sleeve 2 Is damping element
6.
Damping element 6 is slipped over the end of the waveguide 4 and is coaxial
with
waveguide 4 and generally cylindrical in shape, as is suspension sleeve 2.
However. the
damping element 6 is not loose fitting over the waveguide 4, but is more
constrictive over
waveguide 4 in order to provide damping. Thus, as shown in Figs. 2a and 2b,
the inner
layer 27 of damping element 6 snugly fits about waveguide 4. Further. the
outer layer 29
of damping element 6 while usually of softer elastomer materials, such as
silicone rubber.
does not normally contact enclosure tube 3, as does outer layer 29 of
suspension sleeve
2, but instead is sized to control the amount of and to exert pressure on the
inner layer
27 which in turn exerts pressure on the waveguide 4. Thus, a space is left
between the
outer layer 29 of damping element 6 and the inner surface of enclosure tube 3.
In addition,' a tuning wire 5 (see Fig. 2b) of a diameter ranging from .005
inches
to .016 inches may be used to act as a wedge, thereby controlling the pressure
of inner
layer 27 on the waveguide 4. The tuning wire 5 is adjacent to waveguide 4 and
extends
substantially along and is enclosed by inner layer 27 of damping element 6. It
is used
to change the acoustic impedance of the damping element 6 but to do so
gradually so
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that the sonic strain wave signal is dampened gradually along the distance of
the
wavegulde 4 enclosed by damping element 6. In this way, no reflection will
occur from
sudden changes in impedance, but instead damping of the sonic strain wave
amplitude
along the damping element 6 will occur. It should be noted that the tuning
wire 6 while
only shown in Fig. 2b may be used with any of the configurations of Figs. 2a -
2d and
may be used in any other kind of damping element for the purposes set out
above.
Further, because damping element 6 is used to provide optimum damping of the
sonic strain wave pulse traveling in the waveguide 4, and because proper
acoustic
matching of the waveguide 4 and the damping element 8 is determined by the
pressure
exerted on the waveguide 4 by the inner layer 27, there are other mechanisms
besides
the tuning wire 5 that can be used. As shown in Figs. 2c and 2d, a damping
element 6
for use over a broad temperature range could be used, comprising a short
braided
sleeve 8 of the sort of inner layer 27, but with such braided sleeve 8
inserted into a
coaxial, larger diameter metal sleeve 9. This assembly of sleeves 8, 9 is
slipped onto the
end of the waveguide 4. The metal sleeve 9 may then be crimped such that the
braided
sleeve 8 contacts the waveguide 4 with sufficient pressure to provide the
required
damping action.
Thus, as seen through Figs. 2a - 2d, damping may occur through the pressure of
outer layer 29 or through the tuning wire 5 trapped in inner layer 27 or
through the
crimping of metal sleeve 9 or by any other mechanism that applies the
appropriate
pressure to control the impedance matching along a predetermined length of the
damping element 6 as determined by experiment.
The and 32 of damping element 6 facing end 31 of suspension sleeve 2 is
preferably cut between a 40 and 50 angle and preferably about a 45 angle in
order to
properly match its impedance at that of the waveguide 4.
An additional way to minimize end reflections from the damping element 6 is to
place another damping sleeve 33 of dissimilar material or size or pressure in
front of
damping element 6 (toward the suspension sleeve 2). Damping sleeve 33 should
be
designed to have a closer acoustic impedance match to the waveguide 4. That
is, it
should have less pressure, or smaller outer diameter, or lower mass density
than
damping element 6, or if it is an elastomer. it should have a low durometer,
such that the
front and reflection is minimized. Damping sleeve 33 includes a face 34 facing
toward
face 32 of damping element 6. Face 34 normally has a plane substantially
perpendicular
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to the longitudinal axis of the waveguide 4. it should be noted that damping
sleeve 33
may be used with any of the damping elements 6 of Figures 2a, 2b, 2c and 2d.
and the
depiction showing it only in Figure 2a should not limit its generality.
Further, the
orientation of face 34 will not change if damping sleeve 33 Is used with the
damping
sleeves 6 of Figures 2b, 2c or 2d, each of which has a slanted face 32. The
face 34 will
continue to have a plane substantially perpendicular to the longitudinal axis
of the
wavegulde 4. Generally, this damping sleeve 33 does not damp as efficiently as
the
damping element 6, but it will damp the reflection from the damping element 6,
thereby
lowering the overall sonic energy leaving the damping system, damping element
6 acting
as the primary damp and damping sleeve 33 acting as a secondary damp.
Still another method of minimizing the front end reflection coming from the
damping element 6 is to expand the inside diameter of the damping element 6 at
the front
end. The end facing suspension sleeve - 2. This can be accomplished by
inserting a
flaring tool in such front end of the damping element 6 just prior to placing
it on the
waveguide 4.
Still another method for minimizing the front end reflection coming from
damping
element 6 is to remove material from the outside diameter on such front end of
damping
element 6. This removal region should be in the range .of-Ø125" to O.5` as
measured
from such front end of damping element 6. This can be accomplished, for
example, by
~Cl using a set of wire strippers to remove part of the elastomer that
overlaps the braid.
The return conductor t must pass over damping element.6 as shown in Figs. 2a,
2b and 2d, or through damping element 6 as in Fig. 2c. In Fig. 2c, the return
conductor
t is insulated (as it may be in all other cases) and can also act in a manner
similar to the
tuning wire 5 of Fig. 2b. In all events, the return conductor 1 must then be
attached to
5 the tip of the waveguide 4 using solder or a crimp ring 7. and must be
electrically
connected to form the rest of the circuit to support the current pulse which
begins in
housing 17 and flows through waveguide 4 to return through return conductor 1,
which
may be arranged as discussed in U.S. Patent 3.898.555 or any other way known
or to
be known in the an.
3 The pressure applied by the inner layer 27 may be substantially uniform, but
may
also be nonuniform with less pressure on the side facing the housing 17 and
more
pressure on the side facing the end plug 20 to shorten the length of the
damping element
6 for a given damping effectiveness while preventing reflection.
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14
Alternately, the return conductor 1 may be braided into suspension sleeve 2 or
enclosure tube 3 may be conductive and the return conductor I may be connected
electrically to enclosure tube 3. Otherwise, in assembly, the return conductor
1 and
suspension sleeve 2 are inserted into enclosure tube 3. The waveguide 4 is
then pulled
into the suspension sleeve 2 because suspension sleeve 2 is sized such that
the
waveguide 4 is in loose contact with it but does not allow excessive lateral
movement.
Further, the damping element 6 is then slipped over the waveguide 4.
Further, a series of short suspension sleeves 2 may be located along the
length
of waveguide 4, instead of a single continuous suspension sleeve 2, as shown
in Fig. 16,
although this is an alternate embodiment and believed to be more difficult to
construct.
In such a series, care should be taken in the spacing to decouple or otherwise
suppress
external or internal mechanical noise.
Return conductor 1, suspension sleeve 2, enclosure tube 3 and waveguide 4 are
supported in housing 17 by a bracket 10 (Figure 4) preferably made of plastic.
The
details of the bracket 10 are shown in Figs. 5-12. Bracket 10 includes a base
60, the
outer diameter of base 60 being substantially equal to the inner diameter of
the main
enclosure 62 of housing 17. Base 60 includes two flanges 64.66 located on
either side
of a recess portion 68 of base 60. This arrangement permits a groove 70 (Fig.
4) to be
present between the two flanges 64, 68. A seal ring 16 is located inside
groove 70
seatingly engaging the sidewalls 72, 74 of flanges 64, 66, respectively, and
the outward
facing wall 76 of recess 68, as shown in Figure 4. As used above, the word
"diameter"
does not imply a circular shape. As best seen in Figure 4 and from the shape
of flanges
64, 86, the interior 62 of housing 17 is more rectangular in shape with two
curved
opposing sides. Thus, with the shape and sizing of flanges 64. 66, seal ring
16 also
?5 contacts the interior sidewall surface 78 of the main enclosure 62 of
housing 17.
Therefore, seal ring 16 acts to seal wiring and connectors interior in housing
17 to surface
80 of flange 66 (Figure 4 and Figure 9).
The end of housing 17 is closed by flange 19. An opening 82 is formed in
flange
19 and sized to permit enclosure tube 3 to snugly fit through opening 82 and
extend into
0 an opening 84 formed in flanges 64, 66 and recess portion 68 of base 60
which is coaxial
with opening 82 and of the same size as opening 82. Base 60 also includes a
second
opening 86 formed adjacent to flange 66 and coaxial with opening 84 but of
smaller
diameter than opening 84, thereby forming a shoulder 88 between openings 84,
86
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against which abuts end 90 of the combination of suspension sleeve 2 and
enclosure
tube 3.
Bracket 10 further includes an extension 91 that extends beyond base 60 toward
the and surface _ 92 of enclosure or housing 17. Extension 91 includes an
intermediate
5 opening 94 spaced between opening 86 and the end surface 96 of bracket 10
and end
98 of bracket 10. Opening 94 is coaxial with openings 84, 86. Opening 94 is
also
partially formed by bracket cover 14 (Fig. 8). In forming such opening 94, a
lateral
opening 100 is formed by the clearance between bracket 10 and a notch 61 in
bracket
cover 14. Opening 100 connects the interior between opening 94 and opening 86
with
10 a channel 30, formed in bracket cover 14.
With the combination of suspension sleeve 2 and enclosure tube 3 abutting or
otherwise terminating at shoulder 88. both the return conductor I and the
waveguide 4
extend from end 90 into the space interior to housing 17. Return conductor 1
is caused
to pass through openng 100 and into tunnel 30 with a spec alignment described
15 below. Waveguide 4 continues coaxial with opening 94 and is anchored by a
wavegulde
anchor 11, preferably made of brass. Waveguide anchor 11 has a cylindrical
shaped
lower end 101 of diameter sufficient to fit into opening 94. A larger
substantially
rectangular cap 103 forms the top of waveguide anchor 11 with shoulder 105
formed
therebetween. Shoulder 105 rests on surfaces 102. 104 which form the upper or
inner
facing surface of opening 94. Another opening 55 is provided in extension 91
whose axis
is at right angles to the axis of openings 84, 86, 94 (Figure 10). The
identical opening 55
is formed in the other side of the extension 91 as shown in Figure 7. The
waveguide
anchor 11 is sized such that in its seated position with surface 105 in
contact with
surfaces 102, 104, anchor 11 does not extend over opening 55. Wavegulde anchor
11
further includes a central opening 106 coaxial with the axis of suspension
sleeve 2 and
waveguide 4. Opening 106 is sized to permit the insertion. of waveguide 4
through it.
Cylindrical shaped elements 108, 110 extend from surface 98 and face toward
the
and 92 of housing 17. The upper surface 114 of cylindrical member 110 is
substantially
coplanar with the end surfaces 96 and act as supports for a printed circuit
board 12
mounted near end 92. Cylindrical shaped elements 108 extend from surfaces 96
and
engage reciprocally located features (not shown) in circuit board 12 to locate
and align
circuit board 12. Printed circuit board 12 i5 equipped with a series of
openings 116. 118
and two not shown to permit return conductor 1 to pass through opening 116 and
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16
waveguide 4 to pass through opening 118 and two additional leads from a pickup
coil
13 yet to be discussed through the local buffer circuit yet to be discussed.
In addition,
printed circuit board 12 has openings 120 that permit leads 50 to pass from
connector
21 through printed circuit board 12. Thus, return conductor 1, waveguide 4, a
dummy
lead 50 and leads 35 of pickup coil 13 (yet to be discussed) through the local
buffer
circuit yet to be discussed all pass through printed circuit board 12 and are
electrically
connected by printed circuit board 12 with electrical connector 21 as five
leads 50 (Fig.
3). Connector 21 physically rests on printed circuit board 12 and extends from
it through
an opening 122 formed in the end 92 of housing 17 to make connector 21
available to.
customers or users as shown in Figure 3. Housing 17 is closed by flange 19
which may
also include extensions 124 having openings 126 therethrough for mounting
housing 17
In the customer's or user's device.
As shown in Figure 7, two additional openings 128, 130 are included in
extension
91 of bracket 10. The axis of each opening 128, 130 is perpendicular to the
axis of the
other openings discussed above. Opening 128 is larger than opening 130 and is
sized
to admit a pickup coil 13 (Fig. 4). Pickup coil 13 may be any type coil and is
shown
preferably with a high wire winding count, such as 400 to 2500 turns, and
preferably 1800
turns, instead of a low winding count of the prior art, but may be of any
design without
limiting the generality of the invention. The pickup coil 13 is shown in
Figure 4 as having
copper windings 40 mounted on a bobbin base 45. Two leads 35 extend from
pickup
coil 13 through printed circuit board 12 on which is located the local buffer
circuit where
they are electrically connected as discussed above. Pickup coil 13 is mounted
coaxially
about a tape 15 reciprocally mounted in an opening 132 in pickup coil 13. Tape
15
extends from substantially the end of bobbin 45 facing outward towards housing
17
through the pickup coil 13 and to the waveguide 4 where it is connected to
waveguide
4 by welding or other method of mechanical connection. -Tape 15 does extend
for a
length 15' beyond the end of the bobbin 45. This length .15' provides
constructive
interference to the signal. The signal is developed as a voltage. across the
coil 13- The
constructive interference is produced by the sonic wave continuing past the
coil 13,
reflecting from the end of tape 15, including all of the length 15', and
arriving back at coil
13 with such time delay as to produce an additive effect. This causes
constructive
interference for any type of tape 15 or circuitry with respect to the coil 13.
An anchor or
bracket for the end of tape 15 could alternately be used to set the length
15'. Tape 15
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17
is typically made of a ferromagnetic or magnetostrictive material and may be
of the same
material as the waveguide 4 but have a different metallurgical treatment.
Opening 128
is thus located in close proximity to channel 30 to place the pickup coil 13
in dose
proximity to return conductor 1, thereby permitting a reduction in energy of
the Input
pulse to waveguide 4.
As shown in Fig. 14, a local buffer circuit or amplifier comprising a local
buffer
ampfifier 24 and dipper 22, 23 is connected to pickup coil 13. The purpose of
the buffer
amplifier 24 is to isolate the pickup coil 13 from electrical, external
Interference and to
provide a low output impedance drive for connecting to remotely located
electronics 26
and may also be used to amplify the signal, although this is not preferred.
The local
buffer circuit is mounted dose to pickup coil 13 to lower capacitance. The
local buffer
circuit may incorporate some sort of signal limiting device or devices such as
diodes 22,
23 or transistor 36 in combination with amplifier 24 of Fig. 15 to limit the
amplifier 24
signals to nominal levels, particularly during a waveguide interrogation
pulse.
The local buffer circuit or amplifier of Figures 14 or 15 is incorporated
directly.after
the pickup coil 13 and would be included in the housing or shield 17. The
circuit that
drives the waveguide 4 would be outside housing or shield 17. For Figure 14,
two diodes
22,23 are connected in opposite directions parallel to pickup coil 13. One
side of pickup
coil 13 and one side of each of the diodes is then connected to the base of an
emitter
amplifier 24, the collector portion of which is connected to the other end of
pickup coil
13 and the diodes 22, 23. Signals from the pickup coil 13 are fed into emitter
amplifier
24 which reduces the electrical impedance of the pickup coil 13 by several
orders of
magnitude. The emitter of emitter amplifier 24 is the output in both
embodiments, and,
in use, the receiving circuit on a board 157 (Fig. 13) will use a pull-up
resistor (not
shown), as discussed in more detail below. The local buffer circuit is
included because
of the high number of turns of winding of the pickup coil .13. In the prior
art, there are
only a few turns in order to avoid noise and therefore only a few millivolts
of output signal
was developed. With a large number of turns, such as 400 to 2500 turns and
preferably
1800 turns for pickup coil 13 as discussed above, one can obtain a signal in
the
hundreds of millivolt range. However, pickup coil 13 with a large number of
turns has
high impedance and potential noise that may be introduced, between the pickup
coil 13
and the electronics 26 where the output signal is directed which is usually on
another
board 157 (Fig. 13), as discussed in more detail below, which may be two
inches or more
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18
away from the physical location of pickup coil 13. The local buffer circuit
lowers the high
impedance and therefore the noise that can be picked up by the leads 35.158
between
the pickup coil 13 and the electronics on board 157 (Fig. 13) that processes
the signal
from leads 35 via a cable 156 discussed in more detail below. Further, the
metal housing
17 in which both the pickup coil 13 and the local buffer circuit are located
enhances the
use of the new high impedance by blocking electrical noise, thereby producing
a high
signal level using low impedance external to the transducer.
The diodes 22, 23 act to clip or limit the peak of the signal, and hence the
energy
produced, in the pickup coil 13 which is generated by the signal received
through the
magnetostrictive device. This helps the recovery of the pickup coil 13 for the
next input
by limiting the amount of energy delivered from the pickup cod 13. Thus, the
position
magnet may more closely approach the head of the transducer 25.
The local buffer circuit of Fig. 15 is an alternate embodiment that uses two
PNP
transistors, one as an emitter follower buffer amplifier 24 and the other as
reverse dipper
diode 36_ Thus, instead of diodes 22, 23, to perform the peak clipping of the
signal, the
collector of transistor 36 is connected to the base of emitter amplifier 24
and the base of
transistor 36 is connected to the collector of emitter amplifier 24. The
emitter of transistor
36 is not connected to anything. The base to collector of transistor 36 is
used as a diode
which matches the base to collector junction of emitter amplifier 24 which
acts as the
reverse diode.
The single transistor circuit with a limiting diode or transistor is the
preferred
method to provide minimum cost and size. Other embodiments are possible, and
may
utilize a multiple transistor circuit to provide amplification, impedance
matching, amplitude
control, or voltage regulation. Such circuits may also, or alternatively,
include operational
amplifiers and other integrated circuits to provide the improved performance,
but at
added cost.
The use of a local buffer circuit with housing or shield 17 reduces the
sensitivity
to electronic noise, maintains the signal integrity and enables the signal to
be transmitted
over long distance. The reduction of saturation because of the diodes 22. 23
or
transistors 24, 36 allows the return signals to be nearer to the mode
converter and to
have a very short response time after interrogation.
Opening 130 is sized to receive a bias magnet 18 or unmagnetized magnet
material which could be installed for later magnetization during the assembly
process.
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19
For assembly of the waveguide assembly into housing 17. the waveguide 4 is
placed Into the waveguide anchor 11 after suspension sleeve 2, waveguide 4 and
enclosure tube 3 had been inserted into the openings 82, 84 of flange 19 and
bracket 10.
After the waveguide 4 is inserted into anchor 11, it is connected to the
printed circuit
board 12. The suspension sleeve 2 and enclosure tube 3 are held in place in
the bracket
with adhesive or by suitable retaining elements not shown.
After the waveguide 4 is placed into the brass waveguide anchor i 1 and
connected to the printed circuit board 12, the pickup coil 13 is added. The
return
conductor 1 Is held in place while the bracket cover 14 is installed and then
the tape 15
10 is welded or otherwise mechanically connected onto the waveguide 4 using
openings 55_
It is not necessary to attach the tape in the sequence set out above and the
sequence
should not be considered as limiting for all the inventions disclosed. The
bias magnet
18 is then installed, or as indicated above unmagnetized - magnetic material
could have
been installed earlier and then magnetized. Finally seal ring 16 is placed
into groove 70
of bracket 10. Thereafter, the bracket 10 and the waveguide 4 and the flange
19 (f the
flange 19 is used) as an assembly is inserted into the housing 17. The housing
17 is
crimped and/or welded in place. Finally, the air inside the device is
displaced by a dry.
unreactive gas, and the end plug 20 is held in place with adhesive or other
means-
The distance and location of return conductor I with respect to waveguide 4
can
be adjusted in any appropriate manner to permit the magnetic fields induced in
these two
wires to cancel each other. "in addition, by properly routing return conductor
1 in the area
immediately adjacent the pick up coil 13, the ringing of the interrogation
pulse can be
reduced significantly, such as fifty percent or more. The size and magnetic
properties,
such as using copper of the sizes set out above for tuning wire 5 also have an
effect on
the ringing.
Transducer 25 is produced in one inch incremental lengths or some other
incremental length on the order of one-half inch to four inches. This is done
to reduce
the total number of unique lengths to which waveguide 4. suspension sleeve 2.
return
conductor 1. and enclosure tube 3 must be cut. This. reduces the cost and
complexity
of manufacturing transducer 25. yielding a more cost effective product.
Complete sensor
assemblies which utilize transducer 25 can be manufactured in any length or
incremental
length desired. This is accomplished by providing a mounting means for
transducer 25
within the complete sensor assembly which allows transducer 25 to be
positioned axially
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at any point within 1 /2 inch of its median position within the complete
sensor assembly.
A transducer 25, the length of which is within 1/2 inch of the length desired
for the
complete sensor assembly, can thus be positioned within the complete sensor
assembly
to provide precisely the sensing length desired.
5 Fig. 13 illustrates one possible implementation of the mounting means for
using
transducer 25 in one inch incremental lengths (or some other incremental
length on the
order of one-half inch to four inches) to produce sensor assemblies 158 in any
length
desired. Sensor assembly 158 includes an application housing 150 having an
endcap
155. Transducer 25 Is secured to application housing 150 using screw fasteners
152
10 passing through openings 126 of extensions 124 of mounting housing 17 or
other
suitable attachment means. When necessary to achieve a proper fit, a spacer
block 151
may be positioned between transducer 25 and application housing 150. Spacer
block
151 is utilized in a variety of thicknesses or is not used at all depending on
the sensing
length required of sensor assembly 158 and the standard length of the
enclosure tube
15 3 containing waveguide 4 supplied as part of transducer 25. Fasteners 152
are also used
in a variety of lengths to correspond to the thickness of spacer block 151.
Transducer
is shown in Fig. 13 In the middle of the range of movement possible within
endcap
155. Wire harness 156 carries signals and supply voltages. between transducer
25 and
customer or vendor supplied electronic circuit board 157. Wire harness 156 is
of
20 sufficient length and flexibility to allow transducer 25 to be secured
anywhere within the
allowed range of positions after being connected to electrical connector 21.
Electronic
circuit board 157 provides the interrogation and signal conditioning
circuitry, as known
in the art, necessary to communicate with the end user system and to provide
the
desired position feedback signals. A wire harness 153 is connected to the
electronic
25 circuit board 157 and carries signals and supply voltages between
electronic circuit board
157 and an external connector 154 attached to endcap 155. External connector
154
provides the physical means for connecting to the end user system (not shown).
Further, the transducer disclosed in this application may be fully
electrically
isolated or shielded including electrically shielded by housing 17 from all
devices in which
it is mounted by having mounting or spacer block 151 and screw fasteners 152
made of
nonconducting material and having an insulating material 200 between tube 3
and
external extension tube 202. All of the features of a particular preferred
embodiment of
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21
the waveguide assembly are not shown in the above disclosure In order to
emphasize
the generality of the disclosure.
Because many varying and different embodiments may be made within the scope
of the invention concept taught herein which may involve many modifications in
the
embodiments herein detailed in accordance with the descriptive requirements of
the law,
it is to be understood that the details herein are to be interpreted as
Illustrative and not
in a limiting sense.
