Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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VIBRATORY MEASUREMENT TRANSDUCER
The invention relates to a vibration-type measurement pickup for
measuring a flowable medium, especially a gas, liquid, powder or other
flowable
substance, conveyed in a pipeline.
In the technology of process measurements and automation, physical
parameters, such as e.g. mass flow rate, density and/or viscosity, of a medium
flowing in a pipeline are often measured using inline measuring devices, which
include a vibratory measurement pickup, through which the medium flows, and a
measurement and operating circuit connected thereto, for effecting reaction
forces in
the medium, such as e.g. Coriolis forces corresponding to the mass flow rate,
inertial
forces corresponding to the density of the medium and/or frictional forces
corresponding to the viscosity of the medium, etc., and for producing, derived
from
these forces, measurement signals respectively representing mass flow rate,
density
and viscosity.
Such measurement pickups, especially those in the form of Coriolis
mass flow meters or Coriolis mass flow/density meters, are described in detail
e.g. in
WO-A 04/099735, WO-A 04/038341, WO-A 03/076879, WO-A 03/027616,
WO-A 03/021202, WO-A 01/33174, WO-A 00/57141, WO-A 98/07009, US Patent
Nos. 6,807,866, 6,711,958, 6,666,098, 6,308,580, 6,092,429, 5,796,011,
5,301,557,
4,876,898, EP-A 553 939, EP-A 1 001 254, EP-A 12 48 084, EP-A 1 448 956, or
EP-A 1 421 349. For conveying the medium flowing at least at times, the
measurement pickups include at least one pickup tube, which is secured
appropriately to a usually thicker-walled, especially tubular and/or beam-
like, support
cylinder or in a support frame. Additionally, the aforementioned measurement
pickups have a second pickup tube, which likewise vibrates, at least at times,
and is
mechanically coupled with the first pickup tube at least via two, especially,
however,
four, coupling elements, also named node plates or couplers, with at least the
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first pickup tube being constructed as a first measuring tube
communicating with the pipeline and serving for conveying the
medium to be measured. For producing the above-mentioned
reaction forces, the two pickup tubes are caused to vibrate
during operation, driven by a usually electrodynamic exciter
arrangement, with the two pickup tubes usually executing bending
oscillations, at least at times, about an imaginary oscillation
axis essentially parallel to a longitudinal axis of the
measurement pickup. For detecting vibrations of the pickup tube,
especially inlet and outlet end vibrations, and for producing at
least one oscillation measurement signal representing such, such
measurement pickups additionally include a sensor arrangement
reacting to movements, and thus also to mechanical oscillations,
of the pickup tube.
During operation, the above-described, internal oscillation
system of the measurement pickup, formed by the at least one
pickup tube, the medium conveyed at least instantaneously
therein, as well as at least partly by the exciter arrangement
and the sensor arrangement, is excited by means of the
electromechanical exciter arrangement at least at times in a
wanted oscillation mode to execute mechanical oscillations at at
least one dominating, wanted oscillation frequency. These
oscillations in the so-called wanted oscillation mode are
usually, at least partly, in the form of lateral oscillations,
especially when the measurement pickup is used as a Coriolis mass
flow and/or density meter. Usually chosen as the wanted
oscillation frequency in such cases is a natural, instantaneous,
resonance frequency of the internal oscillation system, which, in
turn, depends both on the size, shape and material of the pickup
tube and also on an instantaneous density of the medium; if
necessary, the wanted oscillation frequency can also be
significantly influenced by an instantaneous viscosity of the
medium. Due to fluctuating density of the medium to be measured
and/or due to medium changes occurring during operation, the
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wanted oscillation frequency during operation of the measurement
pickup is naturally changeable at least within a calibrated and,
thus, predetermined, wanted frequency band, which,
correspondingly, has a predetermined lower, and a predetermined
upper, limit frequency. The internal oscillation system of the
measurement pickup formed in common by the at least one pickup
tube, together with the exciter and sensor arrangements, is,
additionally, usually accommodated by a housing having the
support frame, or support cylinder, as integral component, with
the housing being mechanically coupled to the pipeline via an
inlet end and an outlet end and likewise exhibiting a plurality
of natural oscillation modes. Suitable pickup housings for
vibratory measurement pickups are described, for example, in WO-A
03/076879, WO-A 03/021202, WO-A 01/65213, WO-A 00/57141, US
Patent Nos. 6,776,052, 6,711,958, 6,044,715, 5,301,557, or EP-A 1
001 254.
Progress in the field of vibratory measurement pickups has, in
the meantime, reached a level where modern measurement pickups of
the described kind can be applied in practice for almost all
purposes in the technology of flow measurements and can satisfy
the highest requirements existing in such field. Thus, such
measurement pickups can be applied to measure mass flow rates of
only a few g/h (grams per hour) up to some t/h (tonnes per hour),
and pressures of up to 100 bar for liquids, or even over 300 bar
for gases. The accuracy of measurement achieved in such
applications lies, usually, at about 99.9% of the actual value,
or even above, i.e. a measurement error of about 0.1%, while a
lower limit of the guaranteed measurement range can lie quite
well at about 1% of the end value of the measurement range. On
the basis of the high bandwidth, measurement pickups of the
described kind can be offered, depending on application, also
with nominal diameters, as measured at the flange, lying between
1 mm and 250 mm, or even beyond.
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Investigations on vibratory measurement pickups having two,
mutually parallel, curved pickup tubes, such as are described
e.g. in US-B 6,711,958 or US-B 6,308,580, have shown, however,
that, despite a largely symmetrical construction with reference
to an imaginary central plane of the measurement pickup extending
between the two curved central tube segments of the pickup tubes,
alternating imbalances can be produced in significant measure in
the rhythm of the wanted oscillation frequency and, consequently,
associated disturbance oscillations can be coupled out into the
connected pipeline. Proving to be especially harmful, in this
regard, for the required, high measurement accuracy are those
disturbance oscillations which act in the direction of that
principal axis of inertia of the measurement pickup - in the
following designated the vertical axis - which lies in the
aforementioned, imaginary central axis of the measurement pickup
and extends essentially perpendicular to the axis of the
oscillations. To diminish such disturbance oscillations,
especially those directed transversely to the oscillation axis,
it is proposed both in EP-A 12 48 084 and in WO-A 04/099735 to
apply a cantilever-like balance-element to a curved, central,
middle tube segment of each of the two pickup tubes. The effect
of such balance elements lies essentially in their ability to
generate acceleration forces directed counter to the acceleration
forces produced by the vibrating pickup tubes and directed, in
the above sense, vertically to the oscillation axis, so that
these forces partially cancel one another. Further
investigations have, moreover, shown that, in the case of
measurement pickups of the described type, especially those with
V-shaped or trapezoidally bent, pickup tubes and/or with pickup
tubes whose tube diameters amount to 80 mm or more, besides such
forces coming mainly from the acceleration of moved masses, to an
increasing degree, also clamping forces can also lead to
significant imbalances in the measurement pickup, such as are
dependent on an asymmetric deformation of the pickup housing
stemming from an instantaneous deflection of the pickup tubes.
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Figs. 1 and 2 are two schematic sketches for explaining the
oscillatory motion in the case of a measurement pickup of the
described kind having two curved, mutually parallel, pickup
tubes, which are mechanically coupled together at the inlet and
outlet ends via, in each case, two coupling elements. The pickup
tubes are shown here schematically in simplified form and shown
cut free at the ends, thus free of the pickup housing which
otherwise holds them, so that they can, therefore, oscillate
virtually at their ends. As already mentioned, the two pickup
tubes oscillate, during operation, relative to one another, and,
indeed, in a way such that they deflect laterally (X-direction)
practically over their entire lengths. The amplitudes of these
deflections may differ from one another. The predominant part of
the oscillations and of the associated forces is thus both
perpendicular to the oscillation axis (Z-direction) and to the
mentioned vertical axis (Y-direction) of the measurement pickup,
wherein, at least for the case that both pickup tubes are flowed
through at the same time by the medium, the component of the one
pickup tube essentially cancels the corresponding component of
the other pickup tube. A smaller component of the forces caused
by the oscillations acts also in the direction of the vertical
axis (Y-direction). The oscillatory motion of the pickup tubes
is, in spite of the coupling elements, transmitted through to the
- here free - ends, with also the coupling elements being
slightly deformed (Fig. 2). The middles of the coupling elements
move in such case also in the direction of the vertical axis,
while the "free" ends of the pickup tubes move oppositely in the
direction of the vertical axis. This movement of the ends of the
pickup tubes leads in the installed and fixed state inversely to
forces in the securing pickup housing, for example in the
possible, connected distributor pieces, and, thus, also to
deformations of the pickup housing.
A possibility for reducing such undesired forces in the mounting,
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which, for example, can vary a calibrated zero point of the measurement
pickup,
would, for example, be correspondingly to increase a stiffness of the pickup
housing
resisting the aforementioned deformations of the pickup housing by increasing
its wall
thickness. However, a special problem connected with such a measure is that,
in the
case of measurement pickups of large nominal diameter, the installed mass is
already very high. For measurement pickups of nominal diameter far in excess
of
150 mm, including flanges possibly attached thereto, the installed mass can
lie easily
at about 500 kg. Thus, in the case of measurement pickups of large nominal
diameter, the possibilities for sufficient stiffening of the pickup housing by
increased
material thicknesses must be considered as very limited, at least for the
desired
application of proven materials, especially stainless steel.
Proceeding from the above-related state of the art, some embodiments
of the invention may provide vibratory measurement pickups which, especially
while
largely retaining already established and proven forms of construction, also
with large
nominal diameters in excess of 150 mm, exhibit as high a measurement accuracy
as
possible, thus of 99.8% or more, and thus a measurement error of less than
0.02%.
According to one particular aspect of the invention, there is provided a
measurement transducer of vibration-type for measuring a flowable medium,
conveyed in a pipeline, said measurement transducer comprising: a transducer
housing, which is mechanically coupled with the pipeline via an inlet end and
an
outlet end; at least one first flow tube held in an oscillatable manner in
said
transducer housing and vibrating at least at times, and a second flow tube
mechanically coupled with said at least one first flow tube and likewise
vibrating at
least at times, each of said first and second flow tubes executing during
operation, at
least at times, bending oscillations about an imaginary oscillation axis
parallel to a
longitudinal axis of the measurement transducer, and at least one of said
first and
second flow tubes being embodied as a measuring tube communicating with the
pipeline and serving to convey the medium to be measured; each of the two flow
tubes including an at least sectionally curved central, middle tube segment,
each of
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the two flow tubes including at its inlet end a straight inlet tube segment
extending
parallel to the imaginary oscillation axis, each inlet tube segment
communicates with
the middle tube segment of the respective flow tube via an inlet-end, curved,
intermediate tube segment, and each of the two flow tubes including at an
outlet end
a straight outlet tube segment extending parallel to the imaginary oscillation
axis and
each outlet tube segment communicates with the middle tube segment of the
respective flow tube via an outlet-end, curved, intermediate tube segment; an
electromechanical exciter arrangement acting on at least one of the flow tubes
for
producing and/or maintaining mechanical oscillations of the at least one flow
tube; a
sensor arrangement reacting to movements at least of said at least one first
flow
tube, for producing at least one oscillation measurement signal representing
oscillations of said at least one first flow tube; and at least three coupling
elements
connecting the first and the second flow tubes together at their inlet ends,
as well as
at least three coupling elements connecting the first and the second flow
tubes
together at their outlet ends wherein: at least one first and at least one
second
coupling element of said at least three coupling elements, connecting the two
flow
tubes on the inlet end with one another, are each affixed to the inlet-end,
intermediate tube segments of the first and second flow tubes; and at least
one first
and at least one second coupling element of said at least three coupling
elements,
connecting the two flow tubes on the outlet end with one another, are each
affixed to
the outlet-end, intermediate tube segments of the first and second flow tubes,
and at
least one, third coupling element of the coupling elements connecting the two
flow
tubes together on the inlet end is fixed to each of the inlet-end tube
segments of the
first and second flow tubes and wherein at least one, third coupling element
of the
coupling elements connecting the two flow tubes together on the outlet end is
fixed to
each of the outlet-end tube segments of the first and second flow tubes.
In one embodiment the invention provides a measurement pickup of
vibration-type for measuring a flowable medium, especially a gas, liquid,
powder or
other flowable substance, conveyed in a pipeline, including:
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- a pickup housing, which is mechanically coupled with the pipeline via
an inlet end and an outlet end;
- at least one first pickup tube held in an oscillatable manner in the
pickup housing and vibrating at least at times, and a second pickup tube
mechanically coupled with the first pickup tube and likewise vibrating at
least at
times;
-- with the first pickup tube and the second pickup tube
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executing during operation, at least at times, bending
oscillations each about an imaginary oscillation axis
extending essentially parallel to a longitudinal axis of the
measurement pickup, and
-- with at least the first pickup tube being embodied as a first
measuring tube communicating with the pipeline and serving to
convey the medium to be measured;
an electromechanical, especially electrodynamic, exciter
arrangement acting on at least one of the pickup tubes for
producing and/or maintaining mechanical oscillations of the at
least one pickup tube;
- a sensor arrangement reacting to movements at least of the
first pickup tube, especially to bending oscillations, for
producing at least one oscillation measurement signal
representing oscillations of the first pickup tube; as well as
- at least three coupling elements, especially plate-shaped
coupling elements, connecting the first and second pickup tubes
together at their inlet ends, as well as at least three
coupling elements, especially plate-shaped coupling elements,
connecting the first and second pickup tubes together at their
outlet ends.
Additionally, the invention includes that the measurement pickup
for measuring a flowable medium conveyed in a pipeline has a
caliber of greater than 150 mm, especially of 250 mm or more,
and/or is for measuring a mass flow rate of a medium flowing
through a pipeline in amounts at least at times greater than 900
t/h, especially, at least at times, more than 1200 t/h.
According to a first embodiment of the measurement pickup of the
invention, the two pickup tubes oscillate during operation with
phases essentially opposite to one another.
In a second embodiment of the measurement pickup of the
invention, each of the two pickup tubes has an at least
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sectionally curved, especially essentially U-, V- or trapezoid-
shaped, central, middle tube segment.
A third embodiment of the measurement pickup of the invention
provides that the inlet-end coupling elements and the outlet-end
coupling elements are so arranged and fixed on the two pickup
tubes that those clamping forces produced by the vibrating pickup
tubes within the pickup housing are minimized, which act
predominantly in the direction of that principal axis of inertia
of the measurement pickup, that runs essentially perpendicular to
the longitudinal axis and lies essentially in an imaginary
central plane of the measurement pickup extending between the two
curved middle tube segments of the pickup tubes.
According to a fourth embodiment of the measurement pickup of the
invention, each of the two pickup tubes has at an inlet end a
straight inlet tube segment extending essentially parallel to the
imaginary oscillation axis. The inlet tube segment communicates
with its middle tube segment via an inlet-end, curved,
intermediate tube segment. In turn, each of the two pickup tubes
has at an outlet end a straight outlet tube segment extending
essentially parallel to the imaginary oscillation axis. The
outlet tube segment communicates with its middle tube segment via
an outlet-end, curved, intermediate tube segment.
[In a fifth embodiment of the measurement pickup of the
invention, there are at least one first and at least one second
coupling element of the coupling elements connecting the two
pickup tubes on the inlet end with one another, which coupling
elements are each affixed to the inlet-end, intermediate tube
segments of the first and second pickup tubes, and there are at
least one first and at least one second coupling element of the
coupling elements connecting the two pickup tubes on the outlet
end with one another, which coupling elements are each affixed to
the outlet-end, intermediate tube segments of the first and
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second pickup tubes.
A sixth embodiment of the measurement pickup of the invention
provides that at least one, third coupling element of the
coupling elements connecting the two pickup tubes together on the
inlet end is fixed to the inlet-end tube segment of the first and
second pickup tubes and that at least one, third coupling element
of the coupling elements connecting the two pickup tubes together
on the outlet end is fixed to the outlet-end tube segment of the
first and second pickup tubes.
According to a seventh embodiment of the measurement pickup of
the invention, the first pickup tube runs essentially parallel to
the second pickup tube.
In an eighth embodiment of the measurement pickup of the
invention, the first measurement pickup tube is essentially
constructed identically to the second measurement pickup tube.
A ninth embodiment of the measurement pickup of the invention
includes, additionally, a first distributor piece connecting the
first and second pickup tubes together at the inlet end, as well
as a second distributor piece connecting the first and second
pickup tubes together at the outlet end, with the second pickup
tube likewise being constructed as a second measuring tube
serving for the conveying of the medium to be measured and for
communicating with the pipeline. According to a further
development of this embodiment of the invention, each of the two
distributor pieces has a mass of more than 10 kg, especially more
than 20 kg.
According to a tenth embodiment of the measurement pickup of the
invention, the pickup housing includes a support element,
especially one of steel, to which the at least one pickup tube is
mechanically connected at its inlet and outlet ends. In a
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further development of this embodiment of the invention, the support element
is
constructed in the form of support cylinder, especially a tubular support
cylinder,
which is at least partially laterally open. The support cylinder is connected
with the at
least one pickup tube such that its at least one, curved tube segment
protrudes
laterally out of the support cylinder. According to another embodiment of this
further
development of the invention, the support element has a mass of at least 70
kg,
especially more than 140 kg, and/or a length of at least 1000 mm, especially
of more
than 1200 mm.
In an eleventh embodiment of the measurement pickup of the invention,
each of the pickup tubes, as well as the pickup housing, is made, at least in
part, of
steel, especially stainless steel.
A twelfth embodiment of the measurement pickup of the invention
provides that each of the pickup tubes has a mass of at least 10 kg,
especially of
greater than 25 kg.
According to a thirteenth embodiment of the measurement pickup of the
invention, each of the pickup tubes has an inner diameter of at least 80 mm,
especially greater than 100 mm.
In a fourteenth embodiment of the measurement pickup of the
invention, each of the pickup tubes has a cross section whose area moment of
inertia
is greater than 2 x 104 mm4, especially greater than 4 x 106 mm4.
In a fifteenth embodiment of the measurement pickup of the invention,
each of the pickup tubes has a cross section whose section modulus resisting
bending is greater than 106 mm4, especially greater than 2 x 106 mm4.
According to a sixteenth embodiment of the measurement pickup of the
invention, each of the pickup tubes has a stretched length of
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at least 1000 mm, especially greater than 1500 mm.
A seventeenth embodiment of the measurement pickup of the
invention provides that each of the middle tube segments of the
two pickup tubes has an essentially V-shape and each of the
middle tube segments of the two pickup tubes has a peak with an
included angle smaller than 150 , especially smaller than 120 .
According to an eighteenth embodiment of the measurement pickup
of the invention, an internal oscillation system of the
measurement pickup is formed by the two pickup tubes, the medium
at least instantaneously conveyed therein, and at least in part
by the exciter arrangement and the sensor arrangement, and the
internal oscillation system, driven by the exciter arrangement,
executes during operation of the measurement pickup, at least at
times, mechanical oscillations, especially in the form of lateral
oscillations, with at least one wanted oscillation frequency,
which depends both on the size, shape and material of the pickup
tube and on an instantaneous density of the medium, and which is
changeable during operation of the measurement pickup, within a
predetermined wanted frequency band having upper and lower limit
frequencies. In a further development of this embodiment of the
invention, a total mass of the internal oscillation system
amounts to at least 70 kg, and especially during operation, at
least at times, to more than 90 kg.
In a nineteenth embodiment of the measurement pickup of the
invention, an external oscillation system of the measurement
pickup is formed by the pickup housing and at least by the
distributor pieces, while an internal oscillation system of the
measurement pickup is formed by the two pickup tubes, the medium
at least instantaneously conveyed therein and at least in part by
the exciter arrangement and the sensor arrangement, and the
internal oscillation system, driven by the exciter arrangement,
executes during operation of the measurement pickup, at least at
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times, mechanical oscillations, especially in the form of lateral
oscillations, having at
least one wanted oscillation frequency, which depends both on the size, shape
and
material of the pickup tube and on an instantaneous density of the medium, and
which is changeable during operation of the measurement pickup within a
predetermined wanted frequency band having lower and upper limit frequencies.
According to a further development of this embodiment of the invention, a
total mass
of the external oscillation system amounts to at least 200 kg, especially to
more than
300 kg. In another further development of this embodiment of the invention, a
mass
ratio of a total mass of the external oscillation system to a total mass of
the internal
oscillation system is, during operation, at least at times, especially,
however,
continuously, smaller than 3, especially smaller than 2.5.
According to a twentieth embodiment of the measurement pickup of the
invention, an installed mass to nominal diameter ratio of an installed mass of
the total
measurement pickup to a nominal diameter of the measurement pickup, which
corresponds to a caliber of the pipeline in whose course the measurement
pickup is
to be installed, amounts to at least 1.5, especially more than 2. In a twenty-
first
embodiment of the measurement pickup of the invention, the installed mass of
the
total measurement pickup is greater than 200 kg, especially greater than 400
kg.
Some embodiments of the invention may suppress the disturbance
oscillations produced by means of the at least six coupling elements possibly
in the
end regions of the vibrating pickup tubes, especially in the region of the
intermediate
segments, especially disturbance oscillations acting in the direction of the
vertical
axis of the measurement pickup. The invention is based here on the surprising
discovery that through the use of at least 2 x 3 coupling elements and their
arrangement each in the region of the intermediate segments, as compared to
conventional measurement pickups with 2 x 2 coupling elements, an effective
direction especially of oscillation-based deformations in the pickup housing,
or of
clamping forces arising in the distributor pieces, can be rotated into a
direction less
damaging for the measurements and, at the same time, at least the disturbance
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oscillations otherwise acting in the direction of the vertical axis can also
be
considerably minimized. Thus, the at least three coupling elements mounted on
the
pickup tubes at the inlet end and the at least three coupling elements mounted
on the
pickup tubes at the outlet end act, from a practical point of view, as
mechanical
polarization filters, which are so constructed that at least disturbance
oscillations
acting in the direction of the vertical axis of the measurement pickup are
suppressed
or even eliminated.
An advantage of some embodiments of the invention might be, among
other things, that, compared to conventional measurement pickups with four
coupling
elements, already the use of two additional coupling elements and, thus, in
comparison to conventional measurement pickups, without great additional
effort, a
large, and, in the best case, even an almost complete, canceling of the most
disturbing clamping forces, especially those acting in the direction of the
vertical axis
of the measurement pickup, can be realized. Thus, a further advantage could be
seen in the fact that such leads to a possibility for realizing vibration-type
measurement pickups even at large nominal diameters of over 150 mm, especially
at
nominal diameters of greater than 200 mm, which are both economically
reasonable
and also have an installed mass which is manageable. A further advantage could
be
that, at the same time, already established and proven construction forms,
especially
with respect to the pickup tubes, can also largely be retained.
A measurement pickup as disclosed herein consequently, could also be
suitable for the measurement of flowable media, which are
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conveyed in a pipeline having a caliber of greater than 150 mm,
especially of 250 mm or above. Moreover, the measurement pickup
is also suited for the measurement of mass flow rates, which are,
at least at times, greater than 900 t/h, especially, at least at
times, more than 1200 t/h, such as can arise e.g. in the case of
applications for measuring oil, natural gas or other
petrochemical substances.
The invention will now be explained in greater detail on the
basis of examples of embodiments and the figures of the drawing.
Functionally equal parts are provided in the separate figures
with the same reference characters, which, however, are repeated
in subsequent figures only when such appears helpful.
Figs. 1, 2 are schematic sketches of different side views
for explaining the oscillatory motion of
conventional measurement pickups,
Figs. 3a, b show different side views of an inline measuring
device serving, for example, as a Coriolis mass
flow/density and/or as a viscosity measuring
device, and
Figs. 4 to 6 show, in different, partially sectioned side
views, details of a vibration-type measurement
pickup suited for an inline measuring device as
shown in Figs. 3a, b.
Figs. 3a, b show an inline measuring device 1, especially one
constructed as a Coriolis mass flow and/or density measuring
device, serving, for example, for registering a mass flow rate m
of a medium flowing in a pipeline (not shown) and for mapping
such into a mass flow rate, measured value Xm instantaneously
representing this mass flow rate. The medium can be practically
any flowable substance, for example a powder, a liquid, a gas, a
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vapor, or the like. Alternatively, or in supplementation, the
inline measuring device 1 can also be used, if desired, to
measure a density p and/or a viscosity r) of the medium. In
particular, the measurement pickup is provided for measuring
media such as oil, natural gas or other petrochemical substances,
which flow in a pipeline having a caliber of greater than 150 mm,
especially a caliber of 250 mm or greater, and/or which exhibit,
at least at times, a mass flow rate of greater than 900 t/h,
especially greater than 1200 t/h.
For measuring the medium, the inline measuring device includes a
vibration-type measurement pickup 10, through which the medium
flows during operation, as well as a measuring device electronics
20 (shown here only schematically in the form of a labeled block)
electrically connected with the measurement pickup 10.
Advantageously, the measuring device electronics 20 is designed
such that it can, during operation, exchange measurement and/or
other operational data with a measured value processing unit, for
example a programmable logic controller (PLC), a personal
computer and/or a work station superordinated thereto, via a data
transmission system, for example a field bus system.
Additionally, the measuring device electronics is designed such
that it can be fed from an external power supply, for example
even over the aforementioned field bus system. For the case that
the inline measuring device is to be coupled to a field bus or
other communication system, the measuring device electronics 20,
especially a programmable version thereof, additionally has a
corresponding communications interface for a data communications,
e.g. for transmitting measured data to the above-mentioned
programmable logic controller or a superordinated process control
system.
Figs. 3a, b, and 4 to 6 show in various types of drawings an
example of an embodiment of a measurement pickup 1 serving
especially as a Coriolis mass flow, density and/or viscosity
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pickup. As already mentioned, the measurement pickup 1 serves to
produce in a through-flowing medium mechanical reaction forces,
especially Coriolis forces dependent on mass flow rate, inertial
forces dependent on density of the medium and/or frictional
forces dependent on the viscosity of the medium, forces which
react measurably, that is registerably by sensor, on the
measurement pickup. Derived from these reaction forces
describing the medium, for example the mass flow rate, the
density and/or the viscosity of the medium can be measured by
means of evaluation processes correspondingly implemented in the
measuring device electronics in manner known to those skilled in
the art. The measurement pickup 1 is, in operation, inserted via
flanges 2, 3 into the course of a pipeline (not shown) flowed
through by a medium to be measured, especially a powdered,
liquid, gaseous or vaporous medium. Instead of flanges, the
measurement pickup 1 can also be connected to said pipeline by
other known means, such as e.g. triclamp, or screwed,
connections.
For conveying at least a portion of the medium to be measured,
the measurement pickup includes at least one pickup tube 4
serving as measuring tube and held oscillatably in a pickup
housing 10. In use, tube 4 communicates with the pipeline and,
driven by an electromechanical exciter arrangement 60, is caused
to vibrate, at least at times, in at least one oscillation mode
suited for determining the physical, measured, variable. Besides
the especially one-piece pickup tube 4, there is provided,
additionally, as shown in Figs. 5 and 6, a second pickup tube 5
in the measurement pickup. Tube 5, which is essentially
identical to tube 4, likewise communicates with the pipeline and
thus serves as second measuring tube of the measurement pickup.
During operation, tube 5 likewise executes mechanical
oscillations. The oscillations at least of the first pickup tube
are registered by a sensor arrangement reacting to its movements,
especially its bending oscillations, and are converted into an
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oscillation measurement signal svb representing the oscillations.
Thus, practically the entire internal oscillation system of the
measurement pickup 1, formed by the two pickup tubes 4, 5, the
medium at least instantaneously conveyed therein, and at least
partially by the exciter and sensor arrangements 60, 70, executes
during operation of the measurement pickup 1, at least at times,
mechanical oscillations with at least one wanted oscillation
frequency Fn with the mechanical oscillations being at least at
times, and/or at least partially, lateral oscillations,
especially bending oscillations. The wanted oscillation
frequency F, is, at the same time, in manner known to those
skilled in the art, dependent both on size, shape and material of
the two pickup tubes 4, 5 and also, especially, on an
instantaneous density of the medium, and, thus, during operation
of the measurement pickup, variable within a predetermined,
wanted frequency band AF, exhibiting upper and lower limit
frequencies. During operation of the measurement pickup, the
instantaneous wanted oscillation frequency F, of the internal
oscillation system is advantageously controlled and adjusted,
such that it corresponds essentially to an instantaneous, natural
eigenfrequency of the internal oscillation system.
The two, especially at least sectionally, mutually parallel
pickup tubes can, as indicated in Figs. 5 and 6 and shown, for
example, also in US-B 6,711,958, US-A 5,796,011, US-A 5,301,557,
be connected together by means of distributer pieces 11, 12 into
flow paths flowed through in parallel during operation; they can,
however, also, as shown e.g. in US-A 6,044,715, be connected
serially together on the basis of sequentially arranged flow
paths. It is, however, also possible, as, for instance, proposed
in US-B 6,666,098 or US-A 5,549,009, to use only one of the two
pickup tubes as measuring tube for the conveying of medium and
the other as a blind tube not conveying medium to be measured and
serving, instead, for the reduction of intrinsic imbalances in
the measurement pickup. According to an advantageous embodiment
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of the invention, each of the two pickup tubes 4, 5 has at least
one middle, tube segment 41, 51 bent at least sectionally in at
least one plane. The pickup tubes 4, 5 can, in this connection,
as shown in US-B 6,776,052, have a clearly U-shaped form, for
example, or, as proposed in US-B 6,802,224 or US-B 6,711,958 and
shown in Figs. 4 - 6, be given an essentially V-shape.
Furthermore, the pickup tubes can be bent only slightly, as
described e.g. in US-A 5,796,011, or, rather, rectangularly or
trapezoidally, as shown e.g. in WO-A 01/65213, US-B 6,308,580,
US-A 6,092,429, US-A 6,044,715. Suited as material for the
pickup tubes are, especially, steel, especially stainless steel,
titanium, zirconium or tantalum. Beyond this, however, the
material for the pickup tubes can be practically any material
usually used, or at least suited, therefor.
In the illustrated example of an embodiment, at least the middle
tube segments 41, 51 of the two pickup tubes 4, 5 are excited at
least partially during operation by the action of the
electromechanical exciter arrangement 60 at least partly affixed
thereto to execute cantilever-type vibrations, in which they are
laterally deflected out of the above-mentioned plane and
oscillate with essentially opposite phase relative to one
another. In doing this, the first and second pickup tubes
execute, at least at times during operation, bending oscillations
about an imaginary oscillation axis essentially parallel to a
longitudinal axis L of the measurement pickup. Said differently,
at least the middle tube segments 41, 51 are caused to oscillate
in a bending oscillation mode, in the manner of cantilevers
clamped at one end, or the tines of a tuning fork. In a further
development of the invention, each of the two central, middle
tube segments is curved in essentially V-shape or even
trapezoidally. In a further development of this embodiment of
the invention, each of the two pickup tubes 4, 5 includes,
additionally, on the inlet end a straight inlet tube segment
running essentially parallel to the imaginary oscillation axis.
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78639-32
Each of these inlet tube segments is in communication with the middle tube
segment
of its tube, via a curved, inlet-end, intermediate tube segment. Also, each of
the two
pickup tubes 4, 5 includes, additionally, on the outlet end a straight inlet
tube
segment running parallel to the imaginary oscillation axis. Each of these
outlet tube
segments is in communication with the middle tube segment of its tube, via a
curved,
outlet-end, intermediate tube segment. In another development of this
embodiment of
the invention, each of the middle tube segments exhibits a peak having an
included
angle smaller than 1500, especially smaller than 1200.
As already mentioned, the measurement pickup 1 is provided especially
also for measurements of high mass flow rates in a pipeline of large caliber.
Due to
this, a further embodiment of the measurement pickup 1 provides that at least
the
pickup tube 4 serving as measuring tube has an inner diameter measuring at
least 80
mm. Especially, at least the pickup tube 4 is constructed such that its inner
diameter
is greater than 100 mm, especially even greater than 110 mm. In a further
embodiment of the invention, the pickup tube 4 has, moreover, a cross section
whose
area moment of inertia is greater than 2 x 104 mm4, especially greater than
4 x 106 mm4 and/or whose section modulus resisting bending is greater than
106 mm4, especially greater than 2 x 106 mm4. Additionally, in another
embodiment
of the invention, the pickup tube 4 serving as measuring tube is designed such
that it
has a stretched length of at least 1000 mm, especially greater than 1500 mm.
Consequently, at least for the case that the pickup tube 4 is of steel, this
example
results in a mass of at least 10 kg, at least for a wall thickness of somewhat
over
1 mm. In a further embodiment of the invention, at least the pickup tube 4 is,
however, dimensioned such that, due to a relatively great wall thickness of
about 5
mm and/or a relatively large stretched length of about 2000 mm, it has a mass
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of more than 25 kg. It is also to be noted here, that the second
pickup tube 5, at least for the case that it likewise serves as
measuring tube, is arranged essentially parallel to the pickup
tube 4 and is constructed essentially identically to the first
pickup tube 4, and, thus, exhibits both the same physical
properties and the same geometric properties. Considering that,
as a consequence of the special dimensioning, each of the pickup
tubes 4, 5 weighs well over 10 kg, and, can, therefore, as is
clearly evident from the above measurements-data, exhibit a
capacity of 10 1 or more, then the internal oscillation system,
which includes the two pickup tubes 4, 5, can, at least when a
medium of high density is flowing therethrough, reach a total
mass of well over 50 kg. Especially in the case of use of pickup
tubes of relatively large inner diameter, wall thickness and
stretched length, the mass of the internal oscillation system
can, consequently, easily be greater than 70 kg, or, at least
when medium is flowing therethrough, more than 90 kg.
Besides the pickup housing 10 and the pickup tubes 4, 5 held
therein, the measurement pickup 1 includes an electromechanical,
especially electrodynamic, exciter arrangement 60 acting on the
at least one pickup tube 4 for producing and/or maintaining
mechanical oscillations. Furthermore, the measurement pickup
includes a sensor arrangement 70 reacting to mechanical
oscillations, for example bending oscillations, of the pickup
tube 4 for producing at least one oscillation measurement signal
svb representing oscillations of the pickup tube 4. At least the
two pickup tubes 4, 5, as well as components additionally fixed
thereon, such as e.g. part of the exciter arrangement 69 and part
of the sensor arrangement 70, thus comprise, for practical
purposes, an internal oscillation system of the measurement
pickup.
For producing and/or maintaining mechanical oscillations of at
least one pickup tube, the exciter arrangement 60 of the
CA 02590807 2007-06-12
illustrated example of an embodiment has at least one oscillation
exciter arranged on the two pickup tubes 4, 5, in each case in
the region of the peak, especially about, in each case, at the
middle, or halfway point, of the tube length. The oscillation
exciter can be, for example, one of the electrodynamic types,
thus an oscillation exciter realized by means of a magnet coil 62
fixed to the pickup tube 5 and an armature 61 correspondingly
fixed to the other pickup tube 4 and plunging into the coil 62.
For registering vibrations, at least of the one pickup tube 4,
and for producing the at least one oscillation measurement signal
svb representing oscillations of the pickup tube 4, there is, as
already mentioned, a sensor arrangement provided, by means of
which vibrations, especially vibrations at the inlet and outlet
ends, of the tube segment 41 can be signalized and fed for
further electronic processing, in the manner usual for such
measurement pickups. In the illustrated example of an
embodiment, the sensor arrangement includes, for this purpose, a
first oscillation sensor arranged on the pickup tubes at the
inlet ends, and a second oscillation sensor arranged on the
pickup tubes 4, 5 at the outlet ends. Especially, the second
oscillation sensor is essentially identical to, or built the same
as, the first oscillation sensor. The oscillation sensors can
likewise be of the electrodynamic type, thus each comprised of
magnet coils 72, 82 fixed to the sensor tube 5 and armatures 71,
81 fixed correspondingly on the other pickup tube 4 for plunging
in the magnet coils 72, 82. Beyond this, also other oscillation
sensors known to those skilled in the art, for example
optoelectronic oscillation sensors, can be used. For determining
the at least one physical, measured variable on the basis of the
at least one oscillation measurement signal svb, the exciter
arrangement 60 and the sensor arrangement 70 are additionally, as
is usual in the case of such measurement pickups, coupled in
suitable manner, for instance galvanically and/or
optoelectronically, to a measuring and operating circuit
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correspondingly provided in the measuring device electronics 20.
The measurement and operating circuit, in turn, produces, on the
one hand, an exciter signal sx, correspondingly driving the
exciter arrangement 60 and controlled, for example, with respect
to an exciter current and/or an exciter voltage. On the other
hand, the measuring and operating circuit receives the at least
one oscillation measurement signal sõ, of the sensor arrangement
70 and generates therefrom desired measured values, which can
represent, for example, a mass flow rate, a density and/or a
viscosity of the medium being measured and which, if necessary,
can be displayed on location or, if necessary, further processed
at a higher level. The measuring device electronics 20,
including the measuring and operating circuit, can, for example,
be accommodated in a separate electronics housing 9, which is
arranged remotely from the measurement pickup or it can be
attached directly to the measurement pickup 1, for example
externally on the pickup housing 10, in which case a single,
compact device is formed. In the case of the example of an
embodiment illustrated here, a neck-like transition piece 8 is,
therefore, additionally mounted on the pickup housing to serve
for attachment of the electronics housing 9. In Figs. 4 to 6,
the transition piece 8 and the electronics housing 9 are,
however, omitted; only Fig. 6 shows a mounting surface 63,
recessed in a wall of the pickup housing 10, for the transition
piece 8. An electrical conduit 64 is arranged in the mounting
surface 63, by means of which electrical connections for the
exciter arrangement 60 and the sensor arrangement 70, as well as
possible other electrical components, such as e.g. pressure
and/or temperature sensors provided, if needed, in the
measurement pickup 1, can be made.
The pickup tubes 4, 5 of the measurement pickup, as well as the
exciter and sensor arrangements applied in each case thereto, are
practically completely encased by the pickup housing 10, as is
clear from the presentation provided by Figs. 3a, b and 5 and as
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is, in fact, usual for measurement pickups of such type. The
pickup housing serves, thus, not only as holder of the pickup
tubes 4, 5, but also, additionally, for protecting the internal
components of the measurement pickup 1, such as, for example, the
exciter and sensor arrangements, and, additionally, other
components placed therein, from external, environmental
influences, such as e.g. dust or water spray. Beyond this, the
pickup housing 10 can also additionally be embodied and
dimensioned such that, in the case of possible damage to the
pickup tube 4, e.g. by crack formation or bursting, escaping
medium is retained as completely as possible within the pickup
housing, up to a required maximum gage pressure. Possible
choices of material for the pickup housing, especially also the
housing cap 7, can include steels, such as structural steel or
stainless steel, or also other suitable high-strength materials.
In a further embodiment of the measurement pickup, the pickup
tube 4, especially an at least sectionally curved one, and the
pickup housing are made each of the same material, especially
steel or stainless steel, or at least materials which are similar
to one another, especially various types of steel. Additionally,
it is provided that the flanges are constructed as integral
components of the pickup housing, as, in fact, shown in Figs. 3a,
b and as is quite common with such measurement pickups, in order
to achieve as short an installation length as possible, coupled
with as high stability of the measurement pickup as possible;
equally, the possibly present distribution pieces 11, 12 can also
be integrated directly into the pickup housing.
In the case of the example of an embodiment shown here, the
pickup housing 10 includes a support element 6 (here illustrated
in the form of a laterally at least partially open, support
cylinder), which, as shown in Figs. 4 to 6, is mechanically
connected at the inlet and outlet ends with the at least one
pickup tube, such that the at least one, curved tube segment 41
extends laterally outwards. Additionally, the pickup housing
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includes a housing cap 7 arranged spaced from the curved middle
tube segments of the pickup tubes 4, 5 and fixed to the support
element 6, especially permanently and/or sealed against escape of
medium. In the case of the example of an embodiment illustrated
here, at least the pickup tube 4 is held in the, in this
instance, tubular support element 6 at the inlet and outlet ends,
such that the oscillatable middle tube segment 41, extending
through two cutouts 61, 62 of the support element, protrudes
laterally out of such and, consequently, into the housing cap 7
likewise fixed on the support element 6. It is to be noted, in
this context, that, instead of the essentially tubular support
element 6 illustrated here, also a, if need be, solid support
cylinder of some other suitable cross section can be used, for
example a support element more in the form of a beam.
Depending on which form and stretched length is actually chosen
for the pickup tubes 4, 5, the here essentially cylindrical
support element has a length essentially equal to, or somewhat
shorter than, the stretched length of the pickup tubes 4, 5. In
keeping with this and the above-mentioned dimensions of the
essentially identical pickup tubes 4, 5, the support element of
this embodiment of the measurement pickup has likewise a length
of at least about 1000 mm. Preferably, the cylindrical support
element is, however, realized with a length of over 1200 mm.
Furthermore, the support element has a mass of at least 70 kg,
especially in the case that it is made of steel. According to a
further embodiment of the measurement pickup, the support element
is, however, constructed and dimensioned such that its mass
amounts to more than 140 kg. Accordingly, the measurement pickup
of the invention is embodied and dimensioned such that a mass
ratio of a total mass of an outer oscillation system composed of
the pickup housing and the possibly present distributor pieces to
a total mass of the inner oscillation system can be, without
more, smaller than 3, especially equal to or less than 2.
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The housing cap 7 serving for the housing of the tube segments 41
includes, as indicated schematically in Figs. 3a, b, a channel-
shaped cap segment 10c, together with an essentially planar,
first lateral housing segment 10a and a second lateral housing
segment 10b essentially mirror-symmetrical to the first segment
10a. The form of the cap segment 10c corresponds, as clearly
evident from the combination of Figs. 3a and 3b, essentially to
that of a toroidal shell. Accordingly, the cap segment 10c has
an essentially circular-arc-shaped, preferably semicircularly
shaped, cross section of predeterminable radius r and, at least
virtually, an essentially circular-arc-shaped, first segment edge
10c' having a radius R significantly larger than the radius r, as
well as a second segment edge 10c" formed essentially identically
to the first segment edge. In case necessary, both the cross
section and the segment edge can be formed less than ideally
circular, thus slightly elliptically. As clearly evident from
the combination of Figs. 3a, b and 4, the lateral housing
segments 10a, 10b are each connected with, respectively, the
first and second segment edges 10c', 10c" of the cap segment 10c,
via a circular-arc-shaped, first segment edge 10a', respectively
10b', and, indeed, such that the lateral housing segments 10a,
10b are each arranged essentially aligned in a tangential plane
of the cap segment 10c and, consequently, toward a tangent which
can be constructed on the respective associated segment edges
10ca and 10cb. Stated differently, in each case between the cap
segment 10c and the housing segment 10a, and between the cap
segment 10c and the housing segment 10b, there is a largely
continuous, thus as smooth as possible, transition, so that, in
the case of allowable internal gage pressure, almost no, or only
very small, bending stresses are produced. Moreover, the housing
cap 7 is fixed via a third segment edge 10c' and a fourth segment
edge 10c" of the cap segment 10c, as well as via, in each case, a
second segment edge 10a", 10b" of the first and second lateral
housing segments 10a, 10b, to the support element 6, and, indeed,
CA 02590807 2007-06-12
such that the cap segment, and, thus, the housing segments 10c,
10a, 10b, remain, during operation, spaced from the at least one,
vibrating tube segment 4. For manufacture of the housing cap 7,
the segments 10c, 10a, 10b are each prefabricated separately and
subsequently joined together, especially welded together.
Advantageously, in producing the housing cap 7, for example the
method for manufacturing a metal cap usable as housing cap 7
described in the already mentioned WO-A 03/021202 can be used, in
which such is formed by the welding of two cap halves of
essentially identical form, especially such cut out of a plate-
shaped stock, with an edge bead, especially a bead in the form of
a quarter torus. Additionally, the housing cap 7 can also be
e.g. deep drawn from a metal sheet of appropriate thickness.
In one embodiment of the measurement pickup, the housing cap 7 is
dimensioned such that it has a mass of at least 10 kg,
especially, however, of more than 20 kg, especially in the case
of steel as the material of the housing. Considering that the
support element can easily have a mass of 70 kg or more, a pickup
housing having a mass of at least 80 kg results, especially,
however, of more than 160 kg. However, for the above-mentioned
case that flanges and/or distributor pieces are provided in the
measurement pickup and these are, thus, also part of the external
oscillation system, a correspondingly higher mass is to be
estimated for the total mass of the external oscillation system
and to be appropriately considered in the tuning of the external
oscillation system to the internal oscillation system. At least
to this extent, the mass of the total external oscillation system
can easily amount to 200 kg or considerably more. Especially in
the case of applying pickup tubes having an inner diameter of
over 100 mm, the mass of the external oscillation system can be
far above 300 kg. In the example of an embodiment of the
measurement pickup 1 illustrated here, transport hook-in means
are provided at the inlet and outlet ends on the support element,
as shown schematically in Figs. 4 and 6, these serving as defined
26
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attachment points for possible installation-helping means, such
as e.g. appropriate cables or bands of lifting tools, in order
better to prevent any damaging of the possibly over 500 kg heavy
measurement pickup, for example due to inappropriate transport
and/or unsuitable choice of hook-in points. For minimizing
disturbance oscillations developed on the part of the external
oscillation system, especially on the part of the pickup housing,
additional, appropriate support elements can be fixed to the
pickup housing, such as are described e.g. in the not-pre-
published, German patent application DE 102004053883.2.
For tuning mechanical resonance frequencies of the internal
oscillation system, as well as for minimizing mechanical stresses
and/or vibrations caused by the vibrating tubes at the inlet or
outlet ends in the pickup housing, the two pickup tubes 4, 5 are
connected mechanically together on the inlet end by means of at
least three coupling elements 217a, 217b, 217c, as well as on the
outlet end by means of at least three coupling elements 218a,
218b, 218c.
In an embodiment of the invention, the coupling elements 217a,
217b, 217c, especially plate-shaped such elements, on the inlet
end, as well as the coupling elements 218a, 218b, 218c,
especially plate-shaped such elements, on the outlet end are
arranged and fixed on the two pickup tubes such that at least
those clamping forces produced within the pickup housing by the
vibrating pickup tubes 4, 5 are minimized, that act predominantly
in the direction of that principle axis of inertia H of the
measurement pickup, which runs essentially perpendicularly to the
oscillation axis and essentially lies in an imaginary middle
plane E of the measurement pickup lying between the two, curved
middle tube segments 41, 51 of the pickup tubes 4, 5, thus in the
direction of the vertical axis of the measurement pickup, as
already mentioned above. The six coupling elements 217a, 217b,
217c, 218a, 218b, 218c are, in such case, so arranged and
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oriented that a symmetry of the measurement pickup, existing with
reference to the vertical axis H as well as with reference to the
mentioned middle plane, is maintained, this effort towards
symmetry being evident without more from Fig. 4 and being usual
for measurement pickups of the described kind.
It has been found, surprisingly, in such case, that, be it by
their dimensioning and/or their positioning on the two pickup
tubes 4, 5, the wanted oscillation frequency F. of the internal
oscillation system can be still be influenced predominantly by
means of the coupling elements 217a, 218a nearest to the halfway
point of the pickup tubes, while the coupling elements 217c, 218c
farthest from the halfway point of the pickup tubes can be used
to optimize the clamping forces acting predominantly
perpendicularly to the vertical axis H (X-direction) and the
intermediate of three coupling elements at the inlet end and the
intermediate of the three coupling elements at the outlet end -
here, thus, the coupling elements 217b, 218b - can be used to
optimize clamping forces acting predominantly in the direction of
the vertical axis (Y-direction). Thus, for concrete measurement
pickups, the optimum positions of the at least six coupling
elements 217a, 217b, 217c, 218a, 218b, 218c can be found, once
the wanted frequency band AF, for the internal oscillation system
has been given, with very little effort experimentally and/or by
means of computer-aided calculations, especially also
simulations.
Also as a result of such investigations, a further embodiment of
the invention provides that at least a first and second coupling
element 217a, 217b of the coupling elements 217a, 217b, 217c
connecting the two pickup tubes 4, 5 together on the inlet end
are each fixed to the intermediate tube segments 43, 53 of the
first and second pickup tubes 4, 5 on the inlet end. Equally in
the case of this embodiment of the invention, at least a first
and second coupling element 218a, 218b of the coupling elements
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218a, 218b, 218c connecting the two pickup tubes 4, 5 together on
the outlet end are each fixed to the intermediate tube segments
45, 55 of the first and second pickup tubes 4, 5 on the outlet
end. In another embodiment of the invention, additionally, at
least a third coupling element 217c of the coupling elements
217a, 217b, 217c connecting the two pickup tubes 4, 5 together at
the inlet end is fixed to the inlet tube segment 42, 52 of the
first and second pickup tubes, and at least a third coupling
element 218c of the coupling elements 218a, 218b, 218c connecting
the two pickup tubes 4, 5 together at the inlet end is fixed to
the inlet tube segment 44, 54 of the first and second pickup
tubes 4, 5.
29
