Note: Descriptions are shown in the official language in which they were submitted.
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Measuring Transducer of Vibration-type
Field of the Invention
The invention relates to a measuring transducer of
vibration-type, especially one for use in a Coriolis mass
flow meter.
Background of the Invention
For determining a mass flow of a medium flowing in a
pipeline, especially a liquid or other fluid, often such
measuring devices are used which, by means of a measuring
transducer of vibration-type and a control and evaluation
electronics connected thereto, effect in the fluid Coriolis
forces and, derived from these forces, produce a measurement
signal representing mass flow.
Such measuring transducers, especially also their use in
Coriolis mass flow meters, have been known already for a
long time and are in industrial use. Thus e.g. EP-A 11 30
367, US-A 2005/0139015, US-B 6,666,098, US-B 6,477,902, US-B
64 15 668, US-B 63 08 580, US-A 5,705,754, US-A 5,549,009 or
US-A 5,287,754 describe Coriolis mass flow meters having, in
each case, a measuring transducer of vibration-type, which
measuring transducer reacts to a mass flow of a medium
flowing in a pipeline and includes a transducer housing as
well as an internal part arranged in the transducer housing.
The internal part includes: At least one curved measuring
tube vibrating during operation, at least at times, and
serving for conveying the medium; as well as a
counteroscillator affixed on the inlet end to the measuring
tube for forming a first coupling zone and at the outlet end
to the measuring tube for forming a second coupling zone.
The counteroscillator essentially rests during operation, or
it oscillates essentially equally- oppositely to the
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measuring tube, thus with equal frequency and opposite
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phase. The internal part is additionally held oscillatably in the transducer
housing,
at least by means of two connecting tube pieces, via which the measuring tube
communicates with the pipeline during operation.
Curved, e.g. U, V or Q shaped, vibrating measuring tubes can, as is known,
when
excited to bending oscillations according to a first eigenoscillation form,
effect
Coriolis forces in the medium flowing therethrough. Selected as a first
eigenoscillation form of the measuring tube in the case of such measuring
transducers is usually that eigenoscillation form wherein the measuring tube
moves in the manner of a pendulum at a lowest natural resonance frequency
about an imaginary longitudinal axis of the measuring transducer in the manner
of a cantilever clamped at one end. The Coriolis forces produced in this way
in
the medium flowing therethrough lead, in turn, thereto, that the excited
pendulum-like, cantilever oscillations of the so-called wanted mode are
superimposed with bending oscillations according to at least one second
eigenoscillation form of equal frequency. In the case of measuring transducers
of the described kind, these cantilever oscillations compelled by Coriolis
forces
correspond to the so-called Coriolis mode, usually that eigenoscillation form
at
which the measuring tube also executes rotary oscillations about an imaginary
vertical axis perpendicular to the longitudinal axis. Due to the superimposing
of
wanted and Coriolis modes, the oscillations of the measuring tube registered
by
means of the sensor arrangement at the inlet and outlet ends exhibit a
measurable phase difference as a function also of the mass flow.
Frequently, the measuring tubes of such measuring transducers, e.g. installed
in
Coriolis mass flow meters, are excited during operation to an instantaneous
resonance frequency of the first eigenoscillation form, especially at an
oscillation
amplitude regulated, or controlled, to a constant level. Since this resonance
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frequency, especially also, depends on the instantaneous density of the fluid,
it is
possible, e.g. in the case of usual commercially available Coriolis mass flow
meters, also to measure, besides the mass flow, also the density of flowing
fluids.
An advantage of a curved tube shape is that e.g. thermally related changes in
length, especially also in the case of the use of measuring tubes having a
high
coefficient of thermal expansion, cause practically no, or only very small,
mechanical stresses in the measuring tube itself and/or in the connected
pipeline.
A further advantage of curved measuring tubes is, however, to be seen in the
fact
that the measuring tube can be made relatively long and consequently a high
sensitivity of the measuring tube can be achieved for the mass flow to be
measured at a relatively short installed length and at relatively low exciter
energy.
These circumstances make it possible also to manufacture the measuring tube
of materials of high coefficient of thermal expansion and/or high modulus of
elasticity, i.e. materials such as e.g. stainless steel. In comparison
thereto, in the
case of measuring transducers of vibration-type having straight measuring
tubes,
the measuring tube is usually made of a material having at least a lower
coefficient of thermal expansion and, as required, also a lower modulus of
elasticity than stainless steel, in order to prevent axial stresses and
achieve a
sufficient sensitivity of measurement. Consequently, for this case, measuring
tubes are preferably of titanium or zirconium, which are, however, on the
basis of
the higher cost of material and the usually also higher processing expense,
much
more expensive than those of stainless steel. Additionally, a measuring
transducer with a single measuring tube has, as is known, compared to one with
two measuring tubes flowed through in parallel, the additional great advantage
that distributor pieces serving for the connecting of the measuring tubes with
the
pipeline are not necessary. Such distributor pieces are on the one hand
complicated to manufacture and on the other hand also represent flow bodies
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having a marked inclination for the formation of accretions or for plugging.
Due to the mostly rather narrow band width of counteroscillators in the wanted
mode, measuring transducers with a single curved measuring tube have,
however, often for applications where density of the medium fluctuates over a
wide range, especially also in comparison to such measuring transducers with
two parallel measuring tubes, the disadvantage that, as a result of the
imbalance
of the internal part fluctuating with the density, the zero point of the
measuring
transducer and consequently also the measuring accuracy of the respective
inline
measuring device can equally fluctuate significantly and as, a result, can be
correspondingly decreased. This is a result of, among other things, that also
by
means of the usually single counteroscillator, transverse forces can only be
incompletely neutralized and, therefore, only incompletely kept away from the
connected pipeline. Such transverse forces are induced in the measuring
transducer due to alternating ended, lateral movements of the single measuring
tube conveying the medium and are rather broadbanded as a result of strongly
fluctuating medium densities, in comparison to the counterforces arising on
the
basis of the counteroscillator. The residual transverse forces can, in turn,
lead to
the fact that the above mentioned, internal part, moving, as a whole, in the
manner of a pendulum about the longitudinal axis of the measuring transducer,
begins also to oscillate laterally. These lateral oscillations of the internal
part
produce, correspondingly, also an additional elastic deformation of the
connecting tube piece and can in this way effect also undesirable vibrations
in the
connected pipeline. Moreover, on the basis of such lateral oscillations of the
internal part, it is also possible to provoke also cantilever oscillations in
the
measuring tube through which the fluid is not flowing. These are very similar
to
the Coriolis mode and, in any event, however, of equal frequency and
consequently practically indistinguishable from the Coriolis mode, which, in
turn,
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would make the measuring signal representing the actual mass flow unusable.
This arises also in the case of measuring transducers which are implemented
according, for example, to the principle proposed in US-A 5,705,754 or US-A
5,287,754. In the case of measuring transducers described there, the
transverse
forces produced by, or on the part of, the vibrating, single measuring tube
and
which are rather mid or high frequency oscillatory forces, are attempted to be
kept
away from the pipeline by means of a single counteroscillator, which is rather
heavy in comparison to the measuring tube and in any event is tuned to a
higher
frequency in comparison to the measuring tube, and, as required, by means of a
relatively soft coupling of the measuring tube to the pipeline, thus,
essentially by
means of a mechanical low pass. Unfortunately, in this case, however, the mass
of the counteroscillator required for achieving a sufficiently robust damping
of the
transverse forces rises more than proportionately with the nominal diameter of
the measuring tube. This represents a great disadvantage for such measuring
tubes of high nominal diameter, since a use of such components of high mass
means, namely, always an increased cost of assembly, both in the manufacture,
as well as also in the case of the installing of the measuring device into the
pipeline. Moreover, in this case, it is only possible to assure, at great
complexity,
that the smallest eigenfrequency of the measuring transducer which, yes, also
does become always lower with increasing mass, lies, after as before, very far
from the likewise low eigenfrequencies of the connected pipeline.
Consequently,
a use of such a measuring transducer in industrially usable, inline measuring
devices of the described kind, for example, Coriolis mass flow measuring
devices,
has long been rather limited to relatively low measuring-tube nominal
diameters
up to about 10 mm. Measuring transducers of the above described kind are
moreover also sold on the part of the assignee itself under the mark
"PROMASS",
series designation "A", for a nominal diameter range of 1-4 mm and have proven
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themselves there, especially also in the case of applications with very low
flow
rates and/or high pressure.
In contrast, in the case of measuring transducers shown in US-B 6,666,098, US-
B
6,477,902, or US-A 5,549,009, the two, here essentially straight, connecting
tube
pieces are so oriented with respect to one another, as well as with respect to
an
imaginary longitudinal axis of the measuring tube, that the internal part,
formed by
means of the measuring tube and counteroscillator, as well as the oscillation
exciters and oscillation sensors correspondingly applied thereto, can move,
during operation, in a pendulum-like manner about the longitudinal axis. In
other
words, the entire internal part can execute pendulum oscillations during
operation
about the longitudinal axis L, conditioned on the, especially, density-
dependent
imbalances between measuring tube 10 and counteroscillator 20, which,
depending on the way in which the imbalance shows itself, are of equal phase
with the cantilever oscillations of the measuring tube 10 or of the
counteroscillator
20. In such case, the torsional stiffnesses of the connecting tube pieces are
preferably so tuned to one another and to the internal part carried by the
two, that
the internal part is suspended essentially rotationally softly about the
longitudinal
axis.
This is achieved, for example, in the case of US-B 6,666,098, in such a manner
that the torsional stiffness of the connecting tube pieces is so dimensioned
that
a respective eigenfrequency of a torsional oscillator inherently formed on the
inlet
end and on the outlet end by means of the respective connecting tube pieces
and
associated terminal mass fractions of the internal part which can be
considered
as essentially rigid and stable in form and oscillating about the longitudinal
axis
rotationally, lies in each case in the region of the oscillation frequency of
the
measuring tube oscillating in the wanted mode. Additionally, at least in the
case
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of the measuring transducer proposed in the case of US-B 6,666,098, measuring
tube and counteroscillator are so tuned to one another that they oscillate at
least
in the wanted mode with approximately equal resonance frequency. Measuring
transducers of the described kind are, furthermore, also sold by the assignee
itself under the mark "PROMASS", series designation "H", for a nominal
diameter
range of 8-50 mm and have proven themselves there, especially also in the case
of applications exhibiting a variable density of the medium to a considerable
degree during operation. The pendulum-like movement of the internal part is,
in
this way, especially developed, or at least favored, such that both a
measuring-tube center of mass spaced from the imaginary longitudinal axis, as
well as also a center of mass of the counteroscillator spaced from the
imaginary
longitudinal axis, lie in a common region of the measuring transducer spanned
by
the imaginary longitudinal axis and the measuring tube. However,
investigations
have in the meantime shown that the zero point of measuring transducers of the
named kind can be subject, at very low mass flow rates and media deviating as
to
density considerably from the calibrated reference density, after, as before,
to
considerable fluctuations. Experimental investigations on measuring
transducers
configured according to US-B 6,666,098, for which, as proposed, a relatively
heavy counteroscillator has been used, have, it is true, led to the
recognition that,
in this way, there is quite a certain improvement of the null point stability
and, as
a result, an improvement of the measuring accuracy of inline measuring devices
of the described kind, but, however, this has been achieved only to an
unsatisfactory degree. In any case, in the configurations proposed in US-B
6,666,098, a significant improvement of the measuring accuracy is essentially
achievable only in the face of having to accept the already discussed
disadvantages as discussed with reference to US-A 5,705,754 or US-A
5,287,754.
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As disadvantageous for possible improvements of the dynamic
oscillatory characteristics in the case of the measuring
transducers disclosed in US-B 6,666,098 has been the more
complicated structure of the internal part. This,
especially, because it involves a number of additional,
separate components serving at added masses. These are
complex, both in their manufacture and in their subsequent
assembly. And, they serve, in such case, essentially only
as simple mass for adjusting mass and/or mass distribution
of the internal part.
Summary
An object of some embodiments of the invention, therefore,
is to improve the mechanical structure of measuring
transducers of the described kind toward the goal that their
internal part can be constructed of comparatively few
separate components and, as a result, can exhibit a low
complexity. In spite of this, it should be enabled that the
measurement pickup is, on the one hand, dynamically well
balanced over a wide range of densities of the medium and,
on the other hand, is, in spite of this, as in comparison to
the measuring transducers proposed in US-A 5,705,754 or US-A
5,287,754, of lower mass. Especially in such case, the
compensating principle proposed in US-B 6,666,098, with the
terminal, inherent torsional oscillators tuned essentially
to the wanted frequency of the measuring tube and
counteroscillator tuned to the wanted frequency, can be
effectively applied after as before.
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According to one aspect of the present invention, there is
provided a measuring transducer of vibration type for a medium
flowing in a pipeline, said measuring transducer comprising: a
transducer housing; and an internal part arranged in the
transducer housing, said internal part including at least a
curved measuring tube serving for the conveying of the medium
and vibrating, at least at times, during operation, and a
counteroscillator affixed externally to the measuring tube
with the forming of a first coupling zone on an inlet-side of
the measuring tube and a second coupling zone on an
outlet-side of the measuring tube and said internal part being
mounted oscillatably in the transducer housing, at least by
means of two connecting tube pieces via which the measuring
tube communicates during operation with the pipeline, and
which are so oriented with respect to one another, as well as
with respect to an imaginary longitudinal axis of the
measuring transducer, that the internal part can move, during
operation, with pendulum-like motion about said longitudinal
axis wherein the counteroscillator is formed by means of at
least two counteroscillator plates, of which a first
counteroscillator plate is arranged on a left side of the
measuring tube and a second counteroscillator plate is
arranged on a right side of the measuring tube; wherein each
of the at least two counteroscillator plates shows an outer,
lateral surface, of which a first edge is formed by a
contour-providing edge distal with respect to the longitudinal
axis, and a second edge is formed by a contour-providing edge
proximal with respect to the longitudinal axis, and wherein
each of the at least two counteroscillator plates is so
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embodied and so placed in the measuring transducer that both
the distal, and the proximal, contour-providing edge of each
of the at least two counteroscillator plates shows, at least
in a middle-section region of the counteroscillator, a
separation from the longitudinal axis different from zero, and
that, at least in the region of a middle section of the
counteroscillator, a local plate height is, in each case,
smaller than, in each case, in the region of the two coupling
zones, wherein the local plate height thereat, in each case,
corresponds to a smallest separation between the distal and
proximal contour-providing edges of each of the at least two
counteroscillator plates.
In a first embodiment of the invention, it is provided that
the counteroscillator is formed by means of counteroscillator
plates arranged laterally to the measuring tube and that each
of the at least two counteroscillator plates has a curved
centroidal line imaginarily extending between a contour line
distal with respect to the longitudinal axis and a contour
line proximal with respect to the longitudinal axis. In a
further development of this embodiment of the invention, it is
provided that the counteroscillator is formed by means of
counteroscillator plates arranged laterally to the measuring
tube and that the centroidal line of each of the at least two
counteroscillator plates has a concave extent with reference
to the longitudinal axis, at least in the region of a middle
section. In another further development of this embodiment of
the invention, it is provided that the counteroscillator is
formed by means of counteroscillator plates arranged laterally
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to the measuring tube and that the centroidal line of each of the at least two
counteroscillator plates has, in each case, a convex extent with reference to
the
longitudinal axis, at least in the region of the coupling zones. Further, it
is
provided that the centroidal line of each of the at least two
counteroscillator plates
is formed essentially with U, or V, shape, at least in the region of a middle
section
of the counteroscillator, and/or that the centroidal line of each of the at
least two
counteroscillator plates extends essentially parallel to a measuring tube
centroidal line extending imaginarily within its lumen.
In a second embodiment of the invention, it is provided that the
counteroscillator
is formed by means of counteroscillator plates arranged laterally to the
measuring
tube and that each of the at least two counteroscillator plates has an
external,
lateral surface, of which a first edge is formed by an edge providing a
contour
distal with respect to the longitudinal axis and a second edge is formed by an
edge providing a contour proximal with reference to the longitudinal axis. In
a
further development of this embodiment of the invention, it is provided that
each
of the at least two counteroscillator plates is so formed and placed in the
measuring transducer that both the distal, as well as the proximal,
contour-providing edges of each of the at least two counteroscillator plates
has a
separation from the longitudinal axis different from zero, at least in a
middle
section of the counteroscillator. In such case, each of the at least two
counteroscillator plates can be so formed that, at least in the region of the
middle
section of the counteroscillator, a local plate height is smaller than, in
each case,
in the region of the two coupling zones, wherein the local plate height
thereat is,
in each case, a smallest distance between the distal, and the proximal,
contour-providing edges of each of the at least two counteroscillator plates.
Further, it is provided that each of the at least two counteroscillator plates
is so
formed that it has in the region of the middle section of the
counteroscillator a
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smallest plate height and/or that the plate height of each of the at least two
counteroscillator plates decreases, in each case, starting from a coupling
zone
and proceeding to the middle section of the counteroscillator, especially
monotonically or continuously.
In a third embodiment of the invention it is provided that the
counteroscillator is
formed by means of counteroscillator plates arranged laterally to the
measuring
tube and that each of the at least two counteroscillator plates has a bow, or
hanger, contour.
In a fourth embodiment of the invention, it is provided that the
counteroscillator is
formed by means of counteroscillator plates arranged laterally to the
measuring
tube and that each of the at least two plates forming the counteroscillator is
arranged essentially parallel to the measuring tube.
In a fifth embodiment of the invention, it is provided that measuring tube and
counteroscillator are so formed and so oriented with respect to one another
that
both a measuring tube center of mass spaced from the imaginary longitudinal
axis and also a counteroscillator center of mass spaced from the imaginary
longitudinal axis lie in a common region of the measuring transducer spanned
by
the imaginary longitudinal axis and the measuring tube. Furthermore, measuring
tube and counteroscillator are so formed and so oriented with respect to one
another that the centerof mass of the measuring tube is additionally farther
from
the longitudinal axis than the center of mass of the counteroscillator. In a
further
development of this embodiment of the invention, it is provided that each of
the
aforementioned centers of mass has a separation from the imaginary
longitudinal
axis greater than 10% of a greatest separation between measuring tube and
imaginary longitudinal axis and/or smaller than 90% of a greatest separation
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between measuring tube and imaginary longitudinal axis. In another further
devcelopment of this embodiment of the invention, it is provided that each of
the
aforementioned centers of mass has a separation from the imaginary
longitudinal
axis which is greater than 30 mm and/or that a ratio of the separation of each
of
the aforementioned centers of mass to a diameter of the measuring tube is, in
each case, greater than one. Especially, the ratio of the separation of each
of the
aforementioned centers of mass to a diameter of the measuring tube can be
kept,
in each case, greater than two and smaller than ten.
In a sixth embodiment of the invention, it is provided that a diameter of the
measuring tube is greater than 1 mm and smaller than 100 mm.
In a seventh embodiment of the invention, it is provided that the longitudinal
axis
of the measuring tube imaginarily connects the two coupling zones together.
In a eighth embodiment of the invention, it is provided that the
counteroscillator
has a mass which is greater than a mass of the measuring tube. In a further
development of this embodiment of the invention, it is provided that a ratio
of the
mass of the counteroscillator to the mass of the measuring tube is greater
than
two.
In an ninth embodiment of the invention, it is provided that the measuring
tube is
essentially provided in U, or V, form.
In a tenth embodiment of the invention, it is provided that the measuring tube
and
counteroscillator are connected mechanically together on the inlet side by
means
of at least a first coupler and on the outlet side by means of at least a
second
coupler.
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In an eleventh embodiment of the invention, it is provided that the connecting
tube
ieces have essentially straight tube segments. In a further development of
this
embodiment of the invention, it is provided that the connecting tube pieces
are so
oriented with respect to one another that the tube segments extend essentially
parallel to the imaginary longitudinal axis. In such case, the connecting tube
pieces can be so oriented with respect to one another that the essentially
straight
tube pieces align essentially with one another and/or with the imaginary
longitudinal axis.
In a twelfth embodiment of the invention, it is provided that the measuring
tube
executes during operation, at least at times, bending oscillations relative to
the
counteroscillator and rellative to the longitudinal axis.
In a thirteenth embodiment of the invention, it is provided that measuring
tube and
counteroscillator execute, during operation, at least at times, and at least
in part,
bending oscillations of equal frequency, about the longitudinal axis.
According to
a further development of this embodiment of the invention, it is additionally
provided that these are such bending oscillations about the longitudinal axis
which are, at least in part, out of phase with one another, especially
essentially of
opposite phase.
In a fourteenth embodiment of the invention, it is provided that the internal
part
held oscillatably in the housing of the transducer has a natural lateral
oscillation
mode in which it oscillates during operation in accordance with deformations
of
the two connecting tube pieces, at least at times, relative to the transducer
housing and laterally about the longitudinal axis.
In a fifteenth embodiment of the invention, it is provided that the internal
part held
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oscillatably in the transducer housing has an oscillation mode in the manner
of a
pendulum in which it moves during operation in accordance with deformations of
the two connecting tube pieces, at least at times, about the imaginary
longitudinal
axis with a pendulum-like motion. According to a further development of this
embodiment of the invention, it is further provided that at least one natural
eigenfrequency of the pendulum-like oscillation mode is smaller than a lowest
oscillation frequency with which the measuring tube instantaneously vibrates
and/or that at least an instantaneous natural eigenfrequency of the
oscillation
mode in the manner of a pendulum is always smaller than an instantaneous
lowest natural eigenfrequency of the measuring tube.
In a sixteenth embodiment of the invention, it is provided that the internal
part held
oscillatably in the transducer housing has both an oscillation mode in the
manner
of a pendulum in which it moves in a pendulum-like manner during operation in
accordance with deformations of the two connecting tube pieces, at least at
times,
about the imaginary longitudinal axis and also a natural lateral oscillation
mode in
which it, during operation, oscillates in accordance with deformations of the
two
connecting tube pieces, at least at times, relative to the transducer housing
and
laterally about the longitudinal axis and that the lateral oscillation mode of
the
internal part has a lowest eigenfrequency which is greater than a lowest
eigenfrequency of the pendulum-like oscillation mode of the internal part. In
a
further development of this embodiment of the invention, it is further
provided that
a ratio of the lowest eigenfrequency of the lateral oscillation mode of the
internal
part to the lowest eigenfrequency of the pendulum-like oscillatory mode of the
internal part is greater than 1.2 and/or that a ratio of the lowest
eigenfrequency of
the lateral oscillation mode of the internal part to the lowest eigenfrequency
of the
pendulum-like oscillatory mode of the internal part is smaller than 10.
Especially,
the aforementioned ratio of the lowest eigenfrequency of the lateral
oscillation
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mode of the internal part to the lowest eigenfrequency of the pendulum-like
oscillation mode of the internal part can in such case be maintained greater
than
1.5 and smaller than 5.
In a seventeenth embodiment of the invention, it is provided that the internal
part
held oscillatably in the transducer housing has a pendulum-like oscillation
mode
in which it moves in the manner of a pendulum during operation in accordance
with deformations of the two connecting tube pieces, at least at times, about
the
imaginary longitudinal axis and that at least one natural eigenfrequency of
the
pendulum-like oscillation mode of the internal part is smaller than a lowest
oscillation frequency with which the measuring tube instantaneously vibrates
and/or that at least one instantaneous natural eigenfrequency of the
pendulum-like oscillatory mode of the internal part is always smaller than an
instantaneous lowest natural eigenfrequency of the measuring tube. In a
further
development of this embodiment of the invention, it is provided that a ratio
of the
lowest eigenfrequency of the measuring tube to the lowest eigenfrequency of
the
pendulum-like oscillatory mode of the internal part is greater than 3 and/or
is
smaller than 20. Especially, the ratio of the lowest eigenfrequency of the
measuring tube to the lowest eigenfrequency of the pendulum-like oscillatory
mode of the internal part can be in such case greater than 5 and smaller than
10.
In an eighteenth embodiment of the measuring transducer of the invention, such
further includes an exciter mechanism for causing measuring tube and
counteroscillator to vibrate.
In a nineteenth embodiment of the measuring transducer of the invention, such
further includes a sensor arrangement for registering oscillations, at least
of the
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measuring tube. In a further development of this embodiment of the invention,
it
is provided that the sensor arrangement for registering oscillations of the
measuring tube includes at least a first sensor arranged on the inlet side at
the
measuring tube, as well as a second sensor arranged on the inlet side at the
measuring tube. Additionally, it can be of advantage, when the sensor
arrangement for registering oscillations of the measuring tube includes,
further,
at least a third sensor arranged on the inlet side at the measuring tube, as
well as
a fourth sensor arranged on the outlet side at the measuring tube. This,
especially also then, when the first sensor is arranged opposite to the third
sensor
at the measuring tube, and the second sensor is arranged opposite to the
fourth
sensor at the measuring tube.
A basic idea of the invention is, especially also in contrast to the measuring
transducers disclosed in US-B 6,666,098, to construct the counteroscillator of
plates arranged laterally to the measuring tobe and, by a suitable shaping, to
enable a tuning of the counteroscillator to the wanted frequency of the
measuring
tube, as well as also enabling the masses, mass distributions and mass moments
of inertia required for the decoupling mechanism proposed in US-B 6,666,098.
Additionally, it is possible, especially due to the use of counteroscillator
plates
having, on the one hand, an essentially hanger-shaped contour, and, on the
other
hand, a plate height tapering in the direction toward the middle, to tune the
counteroscillator, and, as a result, also the internal part, very simply both
as
regards mass distributions and as well as also largely independently as
regards
the aforementioned eigenfrequencies. Moreover, it is possible, so, to
construct
the terminal, torsional oscillators as integral components of the internal
part
required for the decoupling mechanism and, in such case, to tune largely
independently of the aforementioned criteria.
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As a result, the principle of compensation proposed in US-B 6,666,098 can not
only be further put into practice, but also further improved, in the respect
that the
counteroscillator can be embodied not only somewhat heavier but also
especially
somewhat more bending, and twisting, stiffer. Further, it was possible already
at
a comparatively small increase in mass in the order of magnitude of about ten
percent to achieve an improvement of the sensitivity of more than 50% in
comparison with the above mentioned measuring transducer of type "PROMASS
H" and, as a result, also a corresponding improvement of the measurement
accuracy. Especially, it was possible, besides the improvement of the
density-dependent, zero point influenceability, even in the case of large
deviation
from the calibrated reference density of the measuring transducer, also to
detect
a considerable improvement of the accuracy of measurement of the inline
measuring device in the case of small flow rates.
The measuring transducer of the invention distinguishes itself furthermore by
the
fact that, in the use of a counteroscillator of the aforedescribed kind with
correspondingly higher mass, the two connecting tube pieces can, without more,
be kept correspondingly short, and, consequently, also an installed total
length of
the measuring transducer can be significantly decreased, while maintaining an
essentially constant, high quality of the dynamic oscillation decoupling.
Moreover,
the measuring transducer can be embodied, despite its short installed length,
after as before, relatively lightly.
In the following, the invention and further advantages will be explained on
the
basis of an example of an embodiment presented in the figures of the drawing.
Equal parts are provided in the figures with equal reference characters. In
case
conducive to overviewability, already mentioned reference characters are
omitted
in subsequent figures. The figures of the drawing show as follows:
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Figs. 1a, b in different side views, an inline measuring device for media
flowing
in pipelines;
Fig. 2 partially sectioned, in perspective view, a measuring transducer of
vibration-type suitable for an inline measuring device according to
Figs. 1 a, 1 b; and
Figs. 3 and 4 partially sectioned, in different side views, the measuring
transducer
of Fig. 2.
Shown in Figs. 1a, b is an inline measuring device, for example, one embodied
as a Coriolis mass flow measuring device, density measuring device, viscosity
measuring device, or the like, installable into a pipeline, for example, a
process
line of an industrial plant. The inline measuring device serves for measuring
and/or monitoring at least one parameter, for example, a mass flow, a density,
viscosity, etc., of a medium flowing in a pipeline. The inline measuring
device
includes, for such purpose, a measuring transducer of vibration-type, through
which, during operation, a medium to be measured flows. Figs. 2 and 3 show,
schematically, a corresponding example of an embodiment for such a measuring
transducer of vibration-type. The principle mechanical construction, and the
manner in which such operates, is, for the most part, quite comparable with
that
of the measuring transducer disclosed in US-B 6,666,098. The measuring
transducer serves for producing in a medium flowing therethrough mechanical
reaction forces, e.g. mass flow dependent, Coriolis forces, density dependent,
CA 02633527 2008-06-17
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inertial forces and/or viscosity dependent, frictional forces, which react
measurably, especially sensorially registerably, on the measuring transducer.
Derived from these reaction forces, it is possible, in the manner known to
those
skilled in the art, to measure e.g. a mass flow m, a density p and/or a
viscosity 1/
of the medium. The measuring transducer includes for such purpose a
transducer housing 100, as well as an internal part arranged in the transducer
housing 100 for actually effecting the physical-to-electrical converting of
the at
least one parameter to be measured.
1o For conveying the medium, the internal part includes a measuring tube 10,
here
a single, curved measuring tube 10, which is caused to vibrate during
operation
and, as a result, is repeatedly elastically deformed to execute oscillations
about
a static rest position. The measuring tube 10, and, as a result, also the
centroidal
line of the measuring tube 10, which connects the centres of mass (centroids)
of
the cross-sectional areas of measuring tube, extending imaginarily within the
lumen, can for, example, be embodied essentially in S2 or U shape, or, as
shown
in Fig. 2, essentially with a V shape. Since the measuring transducer should
be
usable for a multiplicity of different applications, especially in the field
of industrial
measurements and automation technology, it is further provided that the
measuring tube, depending on the application of the measuring transducer, has
a diameter lying in the range between about 1 mm and about 100 mm.
For minimizing disturbing influences acting on the measuring tube 10, as well
as
also for reducing oscillatory energy transferred from the measuring transducer
to
the connected pipeline, a counteroscillator 20 is additionally provided in the
measuring transducer. This is, as also shown in Fig. 2, arranged separated
laterally from the measuring tube 10 in the measuring transducer and affixed
to
the measuring tube 10 in each case with the forming of an inlet-side first
coupling
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zone 11#, basically defining an inlet end of the measuring tube 10, and with
the
formation of a second coupling zone 12# on the outlet-side, essentially
defining
an outlet end of the measuring tube 10. The counteroscillator 20, which in the
illustrated example of an embodiment is arranged extending essentially
parallel to
the measuring tube 10, especially also coaxially thereto, can also be
embodied,
for example, tubularly or also essentially with box shape. For the latter
case, the
counteroscillator 20 can be formed, as also illustrated in Fig. 2, for
example, by
means of plates arranged on the left and right sides of the measuring tube 10.
As can be seen from a comparison of Figs. 2 and 3, the counteroscillator 20 is
mounted by means of at least one inlet-side, first coupler 31 at the inlet end
11#
of the measuring tube 10 and by means of an outlet-side, second coupler 32,
especially a coupler 32 essentially identical to the coupler 31, at the outlet
end
12# of the measuring tube 10. Serving as couplers 31, 32 can, in such case, be
e.g. simple node plates, which are secured in corresponding manner on the
inlet-side and outlet-side, in each case, to the measuring tube 10 and to the
counteroscillator 20. Additionally, it is possible, as in the case of the
example of
an embodiment shown here, to have completely closed boxes formed in each
case on the inlet-side and outlet-side by means of node plates mutually
separated
from one another in the direction of the longitudinal axis together with
protruding
ends of the counteroscillator 20, or, as required, to have also partially open
frames, serve as coupler 31, respectively coupler 32.
For allowing the medium to be measured to flow through, the measuring tube 10
is additionally connected to the pipeline (not shown) supplying the medium,
and,
then, conveying it away, via a first connecting tube piece 11 opening on the
inlet-side in the region of the first coupling zone 11# and via a second
connecting
tube piece 12, especially one essentially identical to the first connecting
tube
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piece 11, opening on the outlet-side in the region of the second coupling zone
12#,
with each of the two connecting tube pieces 11, 12 having tube segments which
are essentially straight. Advantageously, the measuring tube 10 and the two
connecting tube pieces 11, 12 can be embodied as one piece, so that, for their
manufacture, e.g. a single tubular stock can be used. Instead of measuring
tube
10, inlet tube piece 11, and outlet tube piece 12, being formed by segments of
a
single, one-piece tube, these can, in case required, however, also be
manufactured by means of separate, subsequently joined, e.g. welded together,
stock, or pieces of stock. For manufacturing the measuring tube 10, it is
furthermore appropriate to use practically any of the materials usual for such
measuring transducers, e.g. steel, Hastelloy, titanium, zirconium, tantalum,
etc..
As additionally shown in Figs. 2 and 3, the transducer housing 100, especially
one
which is bending- and torsion-stiff in comparison to measuring tube 10, is
affixed,
especially rigidly, to an inlet end of the inlet-side, connecting tube piece
11 distal
with reference to the first coupling zone #11, as well as to an outlet end of
the
outlet-side, connecting tube piece 12 distal with reference to the first
coupling
zone #11. Thus, as a result, the entire internal part is not only completely
encased by the transducer housing 100, but, as a result of its own mass and
the
resilience of both connecting tube pieces 11, 12, also held oscillatably in
the
transducer housing 100. Additionally to accommodating the internal part, the
transducer housing 100 can also serve for holding an electronics housing 200
of
the inline measuring device with measuring device electronics accommodated
therein. For the case in which the measuring transducer is to be mounted
releasably with the pipeline, additionally, a first flange 13 is formed on the
inlet-side, connecting tube piece 11 at an inlet end and a second flange 14 on
the
outlet-side, connecting piece 12 at an outlet end. The flanges 13, 14 can, in
such
case, as is quite usual for measuring transducers of the described kind, also
be
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integrated into the transducer housing 100, at least partially, on the ends
thereof.
In case required, the connecting tube pieces 11, 12 can also, however, be
connected directly with the pipeline, e.g. by means of welding or brazing.
During operation of the measuring transducer, the measuring tube 10, as usual
in
the case of such measuring transducers of vibration type, is so excited to
cantilever, or wagging, oscillations at an exciter frequency fexc that it
deflects in
essentially a natural, first eigenoscillation form in the so-called wanted
mode,
oscillating about the longitudinal axis L of the measuring transducer. As a
result
of this, thus, the measuring tube 10 executes during operation, at least at
times,
bending oscillations relative to counteroscillator 20 and longitudinal axis L.
At the
same time, also the counteroscillator 20 is excited to cantilever oscillations
and
indeed so such that it, at least in part, oscillates out of phase with,
especially
essentially with opposite phase to, the measuring tube 10 oscillating in the
wanted mode. Especially, measuring tube 10 and counteroscillator 20 are, in
such case, so excited that they execute during operation, at least at times
and at
least in part, bending oscillations of equal frequency but essentially
opposite
phase about the longitudinal axis L. The bending oscillations can, in such
case,
be so developed that they are of equal modal order and consequently, at least
in
the case of resting fluid, essentially of equal form. In other words,
measuring tube
10 and counteroscillator 20 move then in the manner of tuning fork tines
oscillating oppositely to one another. In a further embodiment of the
invention,
the exciter, or also wanted mode, frequency fexc is, in such case, so tuned
that it
corresponds, as much as possible, exactly to a natural eigenfrequency of the
measuring tube 10, especially a lowest natural eigenfrequency of the measuring
tube 10. In the case of an application of a measuring tube manufactured from
stainless steel with a nominal diameter of 29 mm, a wall thickness of about
1.5
mm, a stretched length of about 420 mm, and a bridge length of about 305 mm
CA 02633527 2008-06-17
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measured from inlet end #11 to outlet end 12#, the lowest resonance frequency
of the same would amount, for example, at a density of practically zero, e.g.
in the
case of a measuring tube filled completely with air, to about 490 Hz.
Advantageously, it is further provided that also a lowest natural
eigenfrequency
f2o of the counteroscillator 20 is about equal to the lowest natural
eigenfrequency
fro of the measuring tube and as a result also about equal to the exciter
frequency
fexc=
For producing mechanical oscillations of the measuring tube 10 and the
counteroscillator 20, the measuring tube further includes an exciter mechanism
40, especially an electrodynamic exciter mechanism. This serves for converting
an electric exciter energy EeXCi e.g. one having a controlled current and/or a
controlled voltage, fed, for example, by a control electronics (not shown) of
the
above mentioned Coriolis mass flow meter and accommodated in electronics
housing 200, into an exciter force feXC acting, e.g. in pulse or harmonic
form, on
the measuring tube 10 and deflecting this in the aforementioned manner.
Controls suitable for the adjusting of the exciter energy Eexc include the
control
electronics shown e.g. in US-A 4,777,833, US-A 4,801,897, US-A 4,879, 911 or
US-A 5,009,109. The exciter force feXC can, as usual for measuring transducers
of such type, be developed bidirectionally or unidirectionally and, in the
manner
known to those skilled in the art, be tuned e.g. by means of a current and/or
voltage control circuit with respect to its amplitude and e.g. by means of a
phase
locked loop with respect to its frequency. The exciter mechanism 40 can be
e.g.
a simple solenoid arrangement having a cylindrical exciter coil connected to
the
counteroscillator 20 and flowed-through during operation by a corresponding
exciter current and including a permanently magnetic armature plunging, at
least
at times, into the exciter coil and affixed externally, especially at the
halfway point
on the measuring tube 10. Additionally, e.g. also an electromagnet can serve
as
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the exciter mechanism 40.
For detecting oscillations of the measuring tube 10, the measuring transducer
additionally includes a sensor arrangement 50. Sensor arrangement 50 can be
practically any sensor arrangement usual for such measuring transducers for
registering the movements of the measuring tube 10, especially movements on
the inlet-side and on the outlet-side and converting such into corresponding
sensor signals. Thus, the sensor arrangement 50 can, e.g. in manner known to
those skilled in the art, be formed by means of a first sensor 51 arranged on
the
measuring tube 10 on the inlet-side and a second sensor 52 arranged on the
measuring tube 10 at the outlet-side. The sensors can be e.g. electrodynamic
velocity sensors relatively measuring the oscillations or, however, also
electrodynamic path sensors or acceleration sensors. Alternatively to or in
supplementation of the electrodynamic sensor arrangements, it is also possible
to
use, for detecting oscillations of the measuring tube 10, resistive or
piezoelectric
strain gauges or opto-electronic sensor arrangements. In case required,
additionally, in manner known to those skilled in the art, other sensors used
for
the measuring and/or operation of the measuring transducer, such as, e.g.
additional oscillation sensors arranged on the counteroscillator 20 and/or on
the
transducer housing 100 can be provided (compare in this regard also US-A
5,736,653) or, e.g. temperature sensors can be arranged on the measuring tube
10, on the counteroscillator 20 and/or on the transducer housing 100; compare
in
this connection also US-A 4,768,384 or WO-A 00/102816.
For further improving signal quality of the sensor signals delivered by the
sensor
arrangement and/or for obtaining additional oscillatory information, a further
development of the invention provides arranged at the measuring tube 10, in
addition to the two motion, or oscillation, sensors 51, 52, two additional
oscillation
CA 02633527 2008-06-17
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sensors 53, 54 reacting to movements of the measuring tube, so that, thus, the
sensor arrangement 50, as also shown schematically in Fig. 4, is composed of
at
least four such sensors. In such case, a third sensor 53 is placed likewise on
the
inlet-side on the measuring tube 10 and a fourth sensor 54 is placed likewise
on
the outlet-side on the measuring tube 10. According to an embodiment of this
further development of the invention, it is further provided that the third
sensor 53
is arranged in the region of the first sensor 51, especially on the oppositely
lying
side of the measuring tube 10, and the fourth sensor 54 is arranged in the
region
of the second sensor 52, especially on the oppositely lying side of the
measuring
tube 10. For the case illustrated in Fig. 4, wherein, in each case, the two
inlet-side
sensors 51, 53 and the two outlet-side sensors 52, 54 are arranged vis-a-vis,
thus
lying directly opposite one another and, as seen in the oscillation direction,
aligned with one another, it is possible, in this way, especially in the case
of serial
connecting of the two, in each case, oppositely lying sensors 51, 53,
respectively
52, 54, to achieve, through a comparatively small extra effort in the
implementing
of the sensor arrangement 50, among other things, a significant, advantageous
improvement in the signal-to-noise ratio for oscillation measurement signals
delivered thereby. For simplifying both the construction of the sensor
arrangement 50 and also the evaluation of the oscillation measurement signals
delivered thereby, according to a further embodiment, it is additionally
provided
that the oscillation sensors forming the sensor arrangement 50 are essentially
equal in structure.
For the case provided for operation, wherein the medium is flowing in the
pipeline
and, consequently, the mass flow m is different from zero, the measuring tube
10
vibrating in the above described manner induces in the through-flowing medium
also Coriolis forces. These in turn act on the measuring tube 10 and, so,
effect
an additional, sensorially registerable deformation of the same essentially
CA 02633527 2008-06-17
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according to a natural, second eigenoscillation form. An instantaneous feature
of
this so-called Coriolis mode superimposed with equal frequency on the excited,
wanted mode is, in such case, especially with respect to their amplitudes,
also
dependent on the instantaneous mass flow m. A second eigenoscillation form
can be, as usual in the case of measuring transducers with curved measuring
tube, e.g. the eigenoscillation form of the antisymmetric, twist mode, thus
that in
which the measuring tube 10 executes, as already mentioned, also rotational
oscillations about an imaginary vertical axis H directed perpendicular to the
longitudinal axis L and lying in a single plane of symmetry of the illustrated
measuring transducer.
For the quite usual and, as a result, to be expected case, that, during
operation,
the density of the medium flowing in the measuring tube, and, consequently
accompanying therewith, also the mass distribution in the internal part,
changes
considerably, the force equilibrium between the vibrating measuring tube 10
and
the counteroscillator 20, likewise vibrating in the above described manner, is
disturbed. When the transverse forces resulting therefrom, acting in the
internal
part at equal frequency with the oscillations of the measuring tube 10 cannot
be
compensated, the internal part suspended on the two connecting tube pieces 11,
12 is deflected laterally from an assigned, static, installed position. In
this way,
transverse forces can, at least in part, also act on the connected pipeline
via
connecting tube pieces 11, 12, by way of which the measuring tube 10
communicates, as already mentioned, during operation with the pipeline and
cause this, as well as also the inline measuring device as such, to
consequently
vibrate as such in undesired manner. Furthermore, such transverse forces can
also lead to the fact that the measuring tube 10 is, due to a, from
oscillatory
details point-of-view, non-uniform suspending of the internal part, or also of
the
entire measuring transducer, caused e.g. by practically unavoidable
CA 02633527 2008-06-17
FL0319-WO 27
manufacturing tolerances, excited additionally to disturbance oscillations of
equal
frequency, for example, additional cantilever oscillations according to the
second
eigenoscillation form, which then, especially due to the fact of the equal
oscillation
frequency, are no longer distinguishable practically sensorially from the
actual
Coriolis mode.
Besides the lateral disturbance oscillations, the internal part suspended in
the
transducer housing can additionally also execute pendulum-like oscillations
about the longitudinal axis L, wherein the coupling zones are rotated about
the
longitudinal axis and the connecting tube pieces 11, 12 are twisted. In
corresponding manner, also the two coupling zones and, consequently, also the
two couplers 31, 32 experience a corresponding torsional rotation about the
longitudinal axis L, i.e. also they oscillate and indeed, with respect to one
another,
in essentially opposite phase. In other words, the internal part oscillatably
held in
the transducer housing has a pendulum-like, oscillatory mode, in which it
moves
as a pendulum during operation, accompanied by deformations of the two
connecting tube pieces, at least at times, about the imaginary longitudinal
axis L.
In such case, the vibrating measuring tube 10 and the counteroscillator 20
additionally execute common pendulum-like movements about the longitudinal
axis L which are essentially of equal phase, at least at resting medium, to
one
another and to the cantilever oscillations of the counteroscillator 20,
provided that
a mass m20 of the counteroscillator 20 is smaller than an instantaneous total
mass of the measuring tube 10 conveying the medium. For the opposite case,
that the total mass of the measuring tube 10 conveying the medium is smaller
than the mass of the counteroscillator 20, these pendulum-like motions of the
internal part can be embodied with equal phase to the cantilever oscillations
of
the measuring tube 10.
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On the other hand, however, the internal part suspended oscillatably in the
transducer housing 100 has itself at least one lateral oscillation mode
determined
predominantly by the bending spring stiffness of the connecting tube pieces
11,
12, as well as its instantaneous total mass. In this lateral oscillation mode,
the
internal part would, accompanied by corresponding bending deformations of the
two connecting tube pieces 11, 12, oscillate in resonance, during operation,
relative to the transducer housing 100 and laterally about the longitudinal
axis L,
to the extent that it is correspondingly pushed against, to so excite it.
Equally, the
internal part also has at least one natural, pendulum-like, oscillatory mode,
determined primarily by the torsional spring stiffness of the connecting tube
pieces 11, 12, as well as an instantaneous total moment of inertia about the
longitudinal axis L, in which it moves, to the extent that it is
correspondingly
excited, in resonance as a pendulum during operation, accompanied by
corresponding deformations in the form of twisting of the two connecting tube
pieces about the imaginary longitudinal axis L.
Luckily, it is possible, as already discussed in US-B 6,666,098, to transform
also
the residual transverse forces affecting the lateral oscillation mode of the
internal
part by suitable tuning or matching of the connecting tube pieces 11, 12 and
the
internal part largely into much less critical pendulum-like oscillations of
the entire
internal part about the longitudinal axis L and as a result to largely prevent
the
otherwise damaging lateral oscillations of the internal part. For such
purpose, it is
necessary to adjust (by appropriate dimensioning of the two connecting tube
pieces 11, 12, as well as the two couplers 31, 32) only one natural
eigenfrequency,
f1, of the first torsional oscillator formed on the inlet-side by means of the
connecting tube piece 11 and the coupler 31, defining essentially the inlet-
side
coupling zone 11#, and one natural eigenfrequency, f2, of the second torsional
oscillator formed equally by means of the connecting tube piece 12 and the
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coupler 32, defining essentially the outlet-side coupling zone 11#, in such a
manner that the two eigenfrequencies, fl, f2, are about equal to the exciter
frequency, fexc, at which the measuring tube 10, at least predominantly,
oscillates;
compare in this connection also US-B 6,666,098. As a result of possible
pendulum-like oscillations of the internal part at the wanted frequency, fexc,
the
two aforementioned torsional oscillators are then caused to oscillate
torsionally
about the longitudinal axis L. For adjusting the eigenfrequencies, fl, f2, an
inlet-side mass moment of inertia (here essentially provided by means of the
inlet-side coupler 31) about the longitudinal axis L and a torsional stiffness
of the
associated connecting tube piece 11, as well as an outlet-side mass moment of
inertia (here provided essentially by means of the coupler 32) about the
longitudinal axis L and a torsional stiffness of the outlet-side connecting
tube
piece 12 are to be correspondingly tuned to one another. In the case of the
measuring transducer illustrated here, besides the node plates and the, in
each
case, terminally protruding, plate ends, also those tube segments extending
between the two respective node plates of the couplers 31, 32 are to be
appropriately taken into consideration in the sizing of the mass moment of
inertia
for the tuning of the inlet-side torsional eigenmode.
On the basis of a tuning of wanted mode and torsional eigenmode in the
described manner, it is achieved that the internal part which moves during
operation in the manner of a pendulum with equal frequency with the measuring
tube 10 oscillating at the exciter frequency fexCi practically exactly drives
the
inlet-side and outlet-side torsional oscillators in an intrinsic eigenmode.
For this
case, the two torsional oscillators, oscillating at their respective
eigenfrequencies,
fi, f2, and also compelled to have equal phase with the internal part, oppose
its
torsional oscillations with practically no, or only very small, counter
moments.
Consequently, the internal part is so rotationally softly journaled during
operation
CA 02633527 2008-06-17
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that it can be considered as being practically completely decoupled as to
oscillations from the two connecting tube pieces 11, 12. On the basis of the
fact
that the internal part, despite a practically complete decoupling, moves as a
pendulum during operation about the longitudinal axis L and does not rotate,
then
also no total rotational impulse of the internal part can exist. Consequently,
however, also a lateral total impulse, almost directly dependent on the total
rotary
impulse, especially in the case of similar mass distributions in the measuring
tube
and the counteroscillator 20, and, consequently, also dependent therefrom,
lateral impulses, which can be transmitted from the internal part to the
outside,
10 are likewise both practically equal to zero. For the desired case, thus
that the
pendulum movement of the internal part occurs during operation in the range of
the respective instantaneous eigenfrequencies of the two torsional
oscillators, the
measuring tube can execute a pendulum-like motion, together with the
counteroscillator, practically free of transverse forces and torsional moments
about the longitudinal axis L. As a result, in the case of this balance, or
also
decoupling, mechanism, density dependent imbalances lead primarily to changes
of oscillation amplitudes solely of the pendulum-like oscillations of the
internal
part, however, in any case to negligibly small lateral displacements of the
same
out of the installed static position assigned to it. As a result of this, the
measuring
transducer can be dynamically balanced within a comparatively broad working
range, largely independently of the density n of the fluid and, so, its
sensitivity to
internally produced transverse forces can be significantly decreased.
In order, beyond this, to implement an as robust as possible decoupling of the
internal part of the measuring transducer also from disturbing in-couplings on
the
part of the measuring tube 10, especially also to assure that the internal
part itself
begins to oscillate in the manner of a pendulum as much as possible
exclusively
due to the acting decoupling mechanism and as much as possible not due to the
CA 02633527 2008-06-17
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excitings of other eigenresonances, a further embodiment of the invention
provides that at least one natural eigenfrequency of its pendulum-like
oscillation
mode is smaller than a lowest oscillation frequency with which the measuring
tube
is caused to vibrate instantaneously, for example, thus, the wanted frequency
5 fexc. For this, the internal part is additionally so embodied that at least
a lowest
instantaneous natural eigenfrequency of the pendulum-like oscillatory mode of
the internal part is always smaller than the instantaneously lowest natural
eigenfrequency of the measuring tube 10.
10 As a result of the fact that the decoupling mechanism implemented in the
proposed manner rests essentially on a more structural tuning of the
aforementioned torsional oscillators and the internal part, a tuning which
during
operation can practically not be changed from the exterior, naturally quite a
very
small detuning is to be expected on the basis of changing characteristics of
the
medium as compared to conventional measuring transducers without the above
described decoupling mechanism. These parameters relevant for the tuning can
be, besides the density, for example, the viscosity of the medium and/or its
temperature and, in accompaniment therewith, the temperature of the internal
part itself. In order also, for such cases, to be able to provide a measuring
transducer as well balanced as possible, a further embodiment of the invention
provides that the internal part is so sized that a natural eigenfrequency of
its
pendulum-like oscillatory mode is smaller than a lowest oscillation frequency
with
which the measuring tube 10 vibrates instantaneously or that at least an
instantaneous natural eigenfrequency of the pendulum-like oscillatory mode of
the internal part is always smaller than an instantaneously lowest natural
eigenfrequency of the measuring tube 10. It has been found in this case that a
ratio of the lowest eigenfrequency of the measuring tube 10 to the lowest
eigenfrequency of the pendulum-like oscillatory mode of the internal part
should
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be greater than 3 and, conversely, does not need to be greater than 20. It
has, in
this case, additionally been found that for most cases of application it can
be
sufficient that this ratio of the lowest eigenfrequency of the measuring tube
10 to
the lowest eigenfrequency of the pendulum-like oscillatory mode of the
internal
part is kept in a comparatively narrow working range about between 5 and 10.
According to a further embodiment of the invention, the internal part and the
two
connecting tube pieces 11, 12 are so tuned to one another that the lateral
oscillatory mode of the internal part exhibits a lowest eigenfrequency which
is
greater than a lowest eigenfrequency of the pendulum-like oscillatory mode of
the
internal part. Especially it is provided in such case, that the internal part
and the
two connecting tube pieces 11, 12 are so matched to one another that a ratio
of
the lowest eigenfrequency of the lateral oscillatory mode of the internal part
to the
lowest eigenfrequency of the pendulum-like oscillatory mode of the internal
part is
greater than 1.2. Additionally, it is provided that this ratio of the lowest
eigenfrequency of the lateral oscillatory mode of the internal part to the
lowest
eigenfrequency of the pendulum-like oscillatory mode of the internal part is
so
tuned that it is smaller than 10. It has additionally been found in such case
that,
for most cases of application, it can be sufficient to keep this ratio of the
lowest
eigenfrequency, fL, of the lateral oscillatory mode of the internal part to
the lowest
eigenfrequency, fp, of the pendulum-like oscillatory mode of the internal part
in a
relatively narrow working range between about 1.5 and 5.
According to a further embodiment of the invention, it is additionally
provided that
the two connecting tube pieces 11, 12 are so oriented with respect to one
another
as well as with respect to a longitudinal axis imaginarily connecting the two
coupling zones 11#, 12# that the internal part, accompanied by twistings of
the
two connecting tube pieces 11, 12, can move in the manner of a pendulum about
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the longitudinal axis L. For this purpose, the two connecting tube pieces 11,
12
are to be so directed with respect to one another that the essentially
straight tube
segments extend essentially parallel to the imaginary longitudinal axis L, as
well
as being essentially aligned to this and to one another. Since the two
connecting
tube pieces 11, 12 in the example of an embodiment illustrated here, are
embodied essentially straight over their entire length throughout, they are,
accordingly, directed essentially aligned entirely with one another, as well
as with
the imaginary longitudinal axis L. According to an embodiment of the
invention, it
is furthermore provided that, as a compromise between optimum spring action
and acceptable installed size of the measuring transducer, on the one hand, a
length of each of the connecting tube pieces 11, 12 corresponds in each case
at
most to 0.5 times a shortest separation between the two coupling zones 11#,
12#.
In order to be able to provide as compact a measuring transducer as possible,
each of the two connecting tube pieces 11, 12 has especially a length, which
is, in
each case, smaller than 0.4 times the shortest separation between the two
coupling zones.
For improving the above-described decoupling mechanism, the counteroscillator
20, in a further embodiment of the invention, is essentially made heavier than
the
measuring tube 10. Ina further development of this embodiment of the
invention,
in such case, a ratio of the mass, M20, of the counteroscillator 20 to a mass,
M10,
of the measuring tube 10 is made greater than two. Especially, measuring tube
10 and counteroscillator 20 are additionally so embodied that the latter has a
mass, M20, which is also greater than a mass of the measuring tube 10 filled
with
the medium to be measured. In order that the counteroscillator 20, in spite of
its
comparatively high mass, M20, has an eigenfrequency which lies about at the
eigenfrequency of the measuring tube excited in the wanted mode, or at least
in
its range, the counteroscillator 20 is additionally so embodied, at least in
the case
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of this embodiment of the invention, that it is, in corresponding manner, as
well,
bending-stiffer than the measuring tube 10.
For implementing the counteroscillator 20, especially one which is also more
heavily, equally, however, also more bending-stiffly embodied, and for
simplified
tuning of the same to the measuring tube 10 and/or the terminal torsional
oscillators in the described manner, it is additionally provided that the
counteroscillator 20 is at least partially formed by means of plates 21, 22
arranged laterally to the measuring tube 10. In the case of the example of an
embodiment shown here, the counteroscillator is formed by means of at least
two
curved counteroscillator plates 21, 22, of which a first counteroscillator
plate 21 is
located to the left of measuring tube 10 and a second counteroscillator plate
22 is
arranged to the right of the measuring tube 10. Each of the at least two,
here,
essentially formed bow-, or hanger-, like, counteroscillator plates 21, 22 has
an
outer lateral surface, of which a first edge is formed by an edge providing a
contour distal with reference to the longitudinal axis and a second edge is
formed
by an edge providing a contour proximal with reference to the longitudinal
axis. In
the example of an embodiment illustrated here, additionally, each of the at
least
two counteroscillator plates 21, 22 forming the counteroscillator 20 is
arranged
essentially parallel to the measuring tube 10. In a further embodiment of the
invention, each of the at least two counteroscillator plates 21, 22 is
furthermore
so embodied and so placed in the measuring transducer relative to the
measuring
tube 10 that both the distal, as well as also the proximal contour providing
edge
of each of the at least two counteroscillator plates 21, 22, at least in the
region of
a central section of the counteroscillator 20 has a separation from the
longitudinal
axis L different from zero.
As also illustrated in Figs. 2 and 3, furthermore, each of the at least two
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counteroscillator plates 21, 22 is so embodied that, at least in the region of
a
central section of the counteroscillator 20, a local plate height is in each
case
smaller than, in each case, in the region of the two coupling zones. The local
plate height corresponds in such case, in each case, to a smallest separation
which on a selected location of the corresponding counteroscillator plates is
measured between the distal and the proximal contour-providing edge of each of
the at least two counteroscillator plates 21, 22. According to a further
development of the invention, each of the at least two counteroscillator
plates 21,
22 has additionally, in the region of the central section of the
counteroscillator 20,
a smallest plate height. Further, it is provided that the plate height of each
of the
at least two counteroscillator plates 21, 22, in each case, decreases starting
from
a coupling zone and moving toward the central section of the counteroscillator
20.
In a further embodiment of the invention, each of the at least two plates 21,
22
forming the counteroscillator 20 has an essentially hanger-shaped contour or
silhouette. In corresponding manner, a centroidal line of each of the at least
two
counteroscillator plates 21, 22 imaginarily extending between a contour line
distal
with reference to the longitudinal axis L and a contour line proximal with
reference
to the longitudinal axis is likewise so-curved. As explained with respect to
the
measuring tube, the imaginary centroidal line of each of said plates connects
centroids of its respective cross-sectional areas. On the basis of the
hanger-shaped form of the counteroscillator 20, the centroidal line of each of
the
at least two counteroscillator plates 21, 22 has a concave curvature at least
in the
range of a central section with reference to the longitudinal axis and a
curvature
convex with reference to the longitudinal axis at least in the region of the
coupling
zones.
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Measuring tube 10 and counteroscillator 20 are, as already mentioned, as
required, to be so embodied that they, in the case of an external spatial form
as
similar as possible, also have equal, or at least mutually similar, mass
distributions. In a further embodiment of the invention, it is, therefore,
provided
that the plates 21, 22 forming the counteroscillator 20 and, as a result, also
the
counteroscillator 20 itself, have a curvature essentially comparable with, or
at
least similar to, that of the curved measuring tube. Equally, also the
centroidal
line of each of the at least two counteroscillator plates 21, 22 is
essentially equally
as curved, at least in the region of a middle section of the
counteroscillator, as is
the measuring tube 10. Accordingly, the counteroscillator plates 21, 22
forming
the counteroscillator 20 and consequently both the counteroscillator 20 as
well as
also the entire internal part, have, in the example of an embodiment shown
here,
essentially a U-shaped or V-shaped, curved silhouette. Equally, in this
example
of an embodiment, also the centroidal line of each of the at least two
counteroscillator plates 21, 22 is formed essentially U or V-shaped, at least
in the
region of a middle section of the counteroscillator 20 situated between the
two
coupling zones. In a further embodiment, the counteroscillator plates 21, 22
are
additionally so formed and so arranged with reference to the measuring tube 10
that the centroidal line of each of the at least two counteroscillator plates
21, 22
extends essentially parallel to the centroidal line of the measuring tube 10
extending imaginarily inside of its lumen.
By a combination of hanger-shaped contour of the counteroscillator 20, on the
one hand, and the plate height tapering toward the center, on the one hand,
the
counteroscillator 20, and, as a result, also the internal part, can be
adjusted very
simply both with respect to the mass distributions, especially the relative
positions
of the centers of mass, M10, M20, as well as also largely independently
thereof,
with respect to the above stated eigenfrequencies f2o, fL, fp. Beyond this,
also the
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decoupling mechanism implemented by means of the terminal torsional
oscillators can in this way be tuned largely independently of the
aforementioned
criteria, since, on the one hand, indeed, the protruding ends of the
counteroscillator plates together with the utilized node plates provide the
predominant contribution to the required mass moment of inertia, and, on the
other hand, however, their height can, in each case, be suitably selected
within
wide limits, essentially without influencing the above mentioned other
oscillatory
characteristics of the counteroscillator 20.
It has, further, been found, that, in the case of measuring transducers of the
described kine, especially also in the implementing of the above-described
decoupling mechanism, not only the rotationally soft, mechanical coupling of
the
internal part to the transducer housing and the connected pipeline is of
importance. Surprizingly, it also depends especially on assuring that, during
operation, those moments resulting from the motion of the vibrating measuring
tube are, as much as possible, in each case, introduced into the terminally
located coupling zones at the same angle of attack as are those moments
produced by the likewise vibrating counteroscillator. However, it has
additionally
been found that, as a result of fluctuating density of the medium, a quite
significant angle mismatch can arise between the angles of attack.
In order to hold this practically unavoidably fluctuating, angular mismatch as
much as possible within boundaries which can be handled for the desired
working
range, measuring tube 10 and counteroscillator 20 are, in the case of the
measuring transducer of the invention, so embodied and so oriented with
respect
to one another that both a center of mass, M10, of the measuring tube 10
spaced
from the imaginary longitudinal axis L, as well as also a center of mass, M20,
of the
counteroscillator 20 spaced from the imaginary longitudinal axis L, lie, as
shown
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schematically in Fig. 3, in a region of the measuring transducer spanned in
common by the imaginary longitudinal axis L and the measuring tube 10.
Moreover, measuring tube 10 and counteroscillator 20 are furthermore so
embodied and so oriented with respect to one another that, at least in the
rest
position, the center of mass, M10, of the measuring tube 10 is farther from
the
longitudinal axis L than the center of mass, M20, of the counteroscillator.
According to a further embodiment of the invention, it is additionally
provided that
each of the two aforementioned centers of mass, M10, M20, has a separation
from
the imaginary longitudinal axis which is greater than 10% of a greatest
separation
measurable between measuring tube 10 and the imaginary longitudinal axis L.
For an implementing of the measuring transducer with usual installation
measures, this would mean, practically, that each of the centers of mass, M10,
M20,
has a distance from the imaginary longitudinal axis L greater than 30 mm.
Additionally, it has been found that a ratio of the separation of each of the
centers
of mass, M10, M20, to the diameter of the measuring tube 10 should be, in each
case, greater than one, especially at least two. Additionally, it was possible
to
discover that it can be of advantage, when each of the centers of mass, M10,
M20,
has a separation from the imaginary longitudinal axis L which is smaller than
90%
of the greatest separation between measuring tube 10 and imaginary
longitudinal
axis L. According to a further embodiment of the invention, it is, therefore,
additionally provided, that the ratio of the separation of each of the centers
of
mass, M10, M20, to the diameter of the measuring tube 10 is in each case
greater
than 2 and smaller than 10.
By the displacement of the centers of mass in the aforementioned manner, the
working range of the measuring transducer can be markedly increased,
especially also in comparison to the disclosure of US-B 6,666,098, such that
an
angular mismatch between the two aforementioned angles of attack as a result
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of fluctuating medium density can be both negative as well as also positive,
and
consequently assumes absolute magnitudes only about half as large and, as a
result, is comparatively small. Consequently, also the density-dependent
zero-point influenceability of the measuring transducer can also be
significantly
decreased.
In order to enable an as simple as possible matching of the counteroscillator
20
to a mass or a mass distribution effective in the case of the actual measuring
tube
10, it is also possible to attach, especially releasably, to the
counteroscillator 20
additionally mass balancing elements 21 serving as discrete, added masses.
Alternatively or in supplementation, a corresponding mass distribution can be
realized over the counteroscillator 20 also by the forming of longitudinal or
annular grooves. A mass and/or mass distribution of the counteroscillator 20,
respectively the internal part, ultimately suited for the particular
application can,
without more, be initially determined e.g. by means of finite element
calculations
and/or by means of corresponding calibration measurements. The parameters
then to be selected in the case of a concrete measuring transducer for optimum
tuning of the inlet-side and outlet-side angles of attack, thus corresponding
masses, mass distributions, and/or mass moments of inertia of measuring tube
10 and counteroscillator 20 and geometric dimensions derived therefrom can be
determined, e.g. in the manner known per se to those skilled in the art, by
means
of finite element or other computer based, simulation calculations coupled
with
corresponding calibration measurements.
The measuring transducer of the invention is, due to its good dynamic
balancing,
especially suited for application in a Coriolis mass flow meter, a Coriolis
mass
flow/density meter, or in a Coriolis mass flow/density/viscosity meter, as
provided
for media with densities fluctuating significantly during operation.
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