Abstrict A Coriolis effect mass flow meter having a brace bar of improved
flexibility which reduces the stress concentration in a brace bar
as well as in areas of meter's flow tubes proximate the brace bar
and flow tubes of the flow meter. A brace bar means is disclosed
that has a void in an area between its holes that receive the flow
tubes. This void increases the flexibility of the brace bar and
shifts the concentration of operational and manufacturing induced
stresses away from the braze joints between the brace bar and the
flow tubes. The stresses are reduced and shifted away from the flow
tubes to an area within the brace bar that is less critical to the
overall life and reliability of the flow tubes. Meter sensitivity
is improved due to enhanced flexibility of the present invention's
brace bar in response to the motion induced by the Coriolis effect.
Additional embodiments are disclosed which also provide increased
flexibility of the brace bar while maintaining required rigidity
to resist undesirable independent motion of the flow tubes.
Claims We claim:
1. In a Coriolis effect flow meter:
a pair of flow tubes having open ends attached to a manifold;
brace bar means having flat planar surfaces perpendicular to the
longitudinal axis of each of said flow tubes and further having
edge surfaces perpendicular to said planar surfaces;
a first end portion of said brace bar means having a first one
of said edge surfaces attached to an exterior circumferential surface
of a first one of said flow tubes; and
a second end portion of said brace bar means having a second one
of said edge surfaces attached to an exterior circumferential surface
of a second one of said flow tubes; and
drive means for vibrating said flow tubes out of phase with respect
to each other about axes perpendicular to said flow tubes and extending
through said brace bar means in a plane parallel to said planar
surfaces;
said brace bar means being spaced apart from said manifold and
providing a pivot point for out-of-phase vibrations of said flow
tubes;
a center portion of said brace bar means intermediate said first
end portion and said second end portion with said center portion
having a length greater than the distance between said first flow
tube and said second flow tube;
said center portion further having greater flexibility than said
first and second end portions for providing stress reduction in
the potion of said flow tubes proximate said brace bar means.
2. The Coriolis effect flow meter of claim 1 wherein said center
portion of said brace bar means includes a void.
3. The Coriolis effect flow meter of claim 1 wherein said center
portion of said brace bar means includes an area defined by a screen.
4. The Coriolis effect flow meter of claim 1 wherein said center
portion of said brace bar means includes an area having a thickness
substantially less than the thickness of said first and second end
portions.
5. The Coriolis effect flow meter of claim 1 wherein said center
portion of said brace bar means comprises at least one elongated
member interconnecting said first flow tube and said second flow
tube.
6. The Coriolis effect flow meter of claim 1 wherein said center
portion of said brace bar means includes a pair of side rails extending
between said first and second end portions;
each of said end portions comprising an annular ring comprising
a plurality of quadrants;
a first and a second one of said quadrants being connected to one
of said flow tubes by said edge surfaces and further being connected
to an end of one of said rails;
a third and a fourth one of said quadrants being connected to only
said flow tube by said edge surfaces.
7. The Coriolis effect flow meter of claim 1 wherein: said flow
tubes are substantially U-shaped.
8. The Coriolis effect flow meter of claim 1 wherein each of said
end portions of said brace bar means comprises a ring of material
that encircles said flow tubes with said center portion of said
brace bar means comprising a void.
9. The Coriolis effect flow meter of claim 1 wherein each of said
end portions of said brace bar means comprises a ring of material
that encircles said flow tubes with said center portion of said
brace bar means comprising a screen material.
10. The Coriolis effect flow meter of claim 1 wherein each of said
end portions of said brace bar means comprises a ring of material
that encircles said flow tubes with said center portion of said
brace bar means being of material substantially thinner than the
material comprising said end portions.
11. The Coriolis effect flow meter of claim 1 wherein each of said
end portions of said brace bar means comprises a ring of material
comprising a plurality of quadrants that encircle a different one
of said flow tubes with the material comprising a first and a second
quadrant being substantially narrower than the material comprising
a third and a fourth quadrant.
12. The Coriolis effect flow meter of claim 1 wherein said brace
bar means comprises a top rail and a bottom rail each of which extends
between said first portion and said second portion;
semi-circular end portions on each of said rails;
said semi-circular end portions each defining approximately a quadrant
of the circumference of one of said flow tubes and being affixed
by said edge surfaces to said flow tubes so as to leave approximately
one half of said circumferential surfaces of each of said flow tubes
free from attachment to said edge surfaces of said end portions.
13. In a Coriolis effect flow meter;
a pair of flow tubes having ends attached to a manifold:
a brace bar means having flat planar surfaces perpendicular to
the longitudinal axis of each of said flow tubes and further having
edge surfaces perpendicular to said planar surfaces;
said brace bar means being spaced apart from said manifold for
providing a pivot point for out-of-phase vibrations of said flow
tubes about an axis parallel to said planar surfaces;
a first end portion of said brace bar means attached by one of
said edge surfaces to a first one of said flow tubes;
a second end portion of said brace bar means attached by a second
one of said edge surfaces to a second one of said flow tubes; and
a center portion of said brace bar means intermediate said first
end portion and said second end portion with said center portion
having substantially greater flexibility than said first and second
end portions; said center portion being effective for reducing the
stress concentration in portions of said flow tubes proximate said
brace bar;
said center portion having a length greater than the distance between
said first flow tube and said second flow tube.
14. The Coriolis effect flow meter of claim 13 wherein said center
portion of said brace bar means includes a void.
15. The Coriolis effect flow meter of claim 13 wherein said center
portion of said brace bar means includes an area defined by a screen.
16. The Coriolis effect flow meter of claim 13 wherein said center
portion of said brace bar means includes an area having a thickness
substantially less than the thickness of said first and second end
portions.
17. The Coriolis effect flow meter of claim 13 wherein said center
portion of said brace bar means includes a pair of side rails extending
between said first and second ends portions;
each of said end portions comprising an annular ring having a plurality
of quadrants;
a first and second one of said quadrants being connected by said
edges surfaces to one of said flow tube and to an end of one of
said rails;
a third and a fourth one of said quadrants being connected by said
edges surfaces to only said flow tube.
18. The Coriolis effect flow meter of claim 13 wherein each of
said end portions of said brace bar means comprises a ring of material
that attachably encircles said flow tubes with said center portion
of said brace bar means comprising a void.
19. The Coriolis effect flow meter of claim 13 wherein each of
said end portions of said brace bar means comprises a ring of material
that attachably encircles said flow tubes with said center portion
of said brace bar means comprising screen material.
20. The Coriolis effect flow meter of claim 13 wherein each of
said end portions of said brace bar means comprises a ring of material
that attachably encircles said flow tubes with said center portion
of said brace bar means being substantially thinner than the material
comprising said end portions.
21. The Coriolis effect flow meter of claim 13 wherein each of
said end portions of said brace bar means comprises a ring of material
having quadrants that attachably encircle said flow tubes with the
material comprising a first and a second quadrant being substantially
narrower than the material comprising third and fourth quadrants.
22. The Coriolis effect flow meter of claim 13 wherein said brace
bar means comprises a top rail and a bottom rail each of which extends
between said flow tubes;
said end portions comprising semi-circular end portions on each
of said rails;
said semi-circular end portions each defining approximately a quadrant
of the circumference of one of said flow tubes and being affixed
by said edge surfaces to said flow tubes so as to leave approximately
one-half of said circumferential surface each of said flow tubes
free from attachment to said edges surfaces of said end portions.
23. The Coriolis effect flow meter of claim 13 wherein said center
portion of said brace bar means comprises at least one elongated
member interconnecting said first flow tube and said second flow
tube.
24. The Coriolis effect flow meter of claim 13 wherein:
said center portion of said brace bar means comprises a single
rail member connected at its ends to said first and second end portions
of said brace bar; and wherein:
said first and second end portions of said brace bar each comprises;
an upper end portion and a lower end portion each connected to
an end of said rail member;
an arcuate terminus on each of said end portions adapted for attachment
to a mating arcuate outer surface of said flow tubes; and
a space between said flow tubes and said upper and lower end portion
intermediate said arcuate terminus and the juncture of said end
portions with said rail member.
25. In a Coriolis effect flow meter:
a pair of flow tubes having ends attached to manifold means;
brace bar means having flat planar surfaces perpendicular to the
longitudinal axis of each of said flow tubes and edges surfaces
perpendicular to said planar surfaces;
a first end portion of said brace bar means having a first hole
for attachably receiving a first one of said flow tubes at a position
spaced apart from said manifold means;
a second end portion of said brace bar means having a second opening
for attachably receiving a second one of said flow tubes at said
position spaced apart from said manifold means; and
drive means for vibrating said flow tubes out of phase with respect
to each other about axes perpendicular to said flow tubes and extending
a surface parallel to said planar surfaces of said brace bar means;
said brace bar means being a picot point for said out-of-phase
vibrations of said flow tubes;
a center portion of said brace bar means intermediate said first
end portion and said second end portion with said center portion
having greater flexibility than said first and second end portions
for reducing operational stresses on said brace bar means and on
said flow tubes as said flow tubes are vibrated as well as for reducing
stresses applied to said brace bar means and said flow tubes when
said ends of said flow tubes are affixed sequentially, one at a
time, to said manifold means during the manufacture of said meter;
said center portion of said brace bar means having a length greater
than the distance between said first flow tube and said second flow
tube.
Description FIELD OF THE INVENTION
The present invention relates to a Coriolis effect mass flow meter.
The invention further relates to a method and apparatus for reducing
stress in flow tubes of the Coriolis effect meter. More specifically,
the present invention relates to a Coriolis flow meter having brace
bars which reduce stress the in flow tube areas adjacent the brace
bars.
PROBLEM
It is known to use Coriolis effect mass flow meters to measure
mass flow and other information for materials flowing through a
conduit. As disclosed in the art, such as in U.S. Pat. Nos. 4491025
(to J. E. Smith, et al., of Jan. 1 1985 and U.S. Pat No. Re. 31450
to J. E. Smith of Feb. 11 1982 these flow meters have one or more
flow tubes of straight or curved configuration. Each flow tube configuration
in a Coriolis mass flowmeter has a set of natural vibration modes,
which may be of a simple bending, torsional or coupled type. Fluid
flows into the flowmeter from the adjacent pipeline on the inlet
side, is directed to the flow tube or tubes, and exits the flowmeter
through the outlet side of the flowmeter. The natural vibration
modes of the vibrating, fluid filled system are defined in part
by the combined mass of the flow tubes and the fluid within the
flow tubes. Each flow conduit is driven to oscillate at resonance
in one of these natural modes.
When there is no flow through the flowmeter, all points along the
flow tube oscillate with identical phase due to an applied driver
force. As fluid begins to flow, Coriolis accelerations cause each
point along the flow tube to have a different phase. The phase on
the inlet side of the flow tube lags the driver, while the phase
on the outlet side leads the driver. Sensors can be placed on the
flow tube to produce sinusoidal signals representative of the motion
of the flow tube. The phase difference between two sensor signals
is proportional to the mass flow rate of fluid through the flow
tube. A complicating factor in this measurement is that the density
of typical process fluids varies. Changes in density cause the frequencies
of the natural modes to vary. Since the flowmeter's control system
maintains resonance, the oscillation frequency varies in response.
Mass flow rate in this situation is proportional to the ratio of
phase difference and oscillation frequency.
U.S. Pat. No. Re. 31450 discloses a Coriolis flowmeter that avoided
the need of measuring both phase difference and oscillation frequency.
Phase difference is determined by measuring the time delay between
level crossings of the two sinusoidal signals. When this method
is used, the variations in the oscillation frequency cancel, and
mass flow rate is proportional to the measured time delay. This
measurement method is hereinafter referred to as a time delay measurement.
It is known to drive pairs of flow tubes of Coriolis meters so
that they vibrate 180 degrees out of phase with respect to one another
at a natural mode of vibration or at a harmonic of that natural
frequency. These driven vibrations are termed "out-of-phase"
vibrations. The pair of tubes in a Coriolis meter also has a natural
mode of vibration in which the tubes move in phase with each other.
These are called in-phase vibrations. In-phase vibrations are of
no use in Coriolis meters but can be excited under certain conditions
such as by the vibration of the pipeline in which the meter is mounted,
or by pressure pulsations in the fluid. If the Coriolis meter does
not have a brace bar, the in-phase and out-of-phase vibrations will
have essentially the same pivot points and hence nearly identical
frequencies. The amplitudes of these in-phase vibrations are added
to the out-of-phase vibrations. This combination of vibrations is
undesirable since it can result in a beat frequency between the
two modes, and it complicates the computation of mass flow by requiring
compensation for the effects due to the in-phase vibration of the
flow tubes. An additional problem is that, without a brace bar,
both types of vibrations (in-phase and out-of-phase) cause the flow
tubes to pivot about an axis through the weld joint that attaches
the flow tubes to the manifold of the Coriolis meter. In time, the
stresses caused by the sum of the in-phase and out-of-phase vibrations
can weaken and eventually break the welded joints.
Brace bars are used on Coriolis meters to overcome these problems.
Brace bars are typically affixed to the two flow tubes at a point
between the driver location on the flow tubes and the welded joint
that affixes the flow tubes to the manifold. A separate brace bar
is affixed to the flow tubes at both the inlet and outlet sides
of the tubes to fix the positions of the flow tubes with respect
to one another. This bracing of the flow tubes solves the problems
discussed above. The brace bar defines a new pivot axis for the
out-of-phase vibrations of the flow tubes. This shifts the axis
of out-of-phase vibrations away from the welded joint and raises
the frequency of the out-of-phase driven vibrations from that of
the in-phase vibrations. The desired frequency separation of the
in-phase versus out-of-phase vibration is achieved by selecting
an appropriate position for the brace bars. This simplifies a determination
of mass flow since complexities resulting from the additive effects
of the in-phase and out-of-phase vibrations of the flow tubes are
no longer significant.
However, the use of brace bars creates high stresses in the portions
of the flow tubes that are adjacent the braze joints that bond the
flow tubes to the brace bar. These stresses can cause a premature
failure of the brace bar or the flow tubes. These stresses, to some
extent, are a result of the process used in affixing the flow tubes
to the meter manifold. In the manufacture of particularly large
flow meters, it is often desirable to braze the brace bars to the
flow tubes before welding the flow tubes to the manifold. The flow
tube ends are then welded one at time to the manifold. An end of
a first flow tube is welded to the manifold, and then the corresponding
end of the second of the flow tube is welded to the manifold. Each
tube shrinks in length during the welding process. This shrinkage
bends the brace bar and induces stress in the brace bar and the
flow tube areas where the brace bar is brazed to the flow tubes.
For example, the flow tubes are positioned as a pair with their
ends abutting the portions of the manifold to which the flow tubes
are to be attached. At this time, the brace bar is unstressed since
the ends of the flow tubes evenly abut the manifold. However, during
the welding of the first flow tube, it shrinks in length considerably,
such as 1/32nd of an inch. This shrinkage bends the brace bar downward
at one end and stresses the brace bar beyond its yield point so
that the brace
bar assumes a new, permanently bent, position. Next, when the second
flow tube is welded, the second tube shrinks in length, bends the
brace bar in the other direction and again stresses the brace bar
beyond its yield point. This stressing of the brace bar beyond its
yield points causes corresponding stress in the flow tubes to which
the brace bar is attached. All of these residual stresses are added
to the normal operating stresses subsequently described as the meter
enters commercial use. As a result, the stressed elements may fail
prematurely and shorten the life of the meter.
The driven out-of-phase vibrations also create stress in the flow
tube areas proximate the brace bars. In normal operation the flow
tubes act like end loaded cantilever beams in that their stresses
are greatest at their fixed ends (the brace bar). In this locale,
the stresses are greatest in the tube elements which are furthest
from the tubes' neutral bending axes. This is the same location
where the manufacturing residual stresses are at their greatest.
These stresses are additive to any manufacturing induced stresses,
as above described, so that the resulting total stress on the flow
tubes is the sum of the manufacturing induced stress and stresses
caused by the out-of-phase vibrations of the flow tubes. The magnitude
of stresses in the elements of a Coriolis flow meter is related
to the useful life of the meter. It is therefore important that
all possible efforts be taken to reduce these stresses and, in particular,
the stresses that are caused by the manufacturing processes used
during the fabrication of the Coriolis flow meter.
SOLUTION
The present invention solves the above problems and achieves an
advance in the art by providing a Coriolis meter brace bar that
reduces the manufacturing and operational stresses in the flow tubes
to which it is attached.
In order to explain the advantages of the present invention, it
is necessary to establish a Cartesian coordinate system for each
tube. The origins shall be at the intersections of each tube's centerline
with the plane of the flat top surface of the brace bar. The Z axes
shall be coincident with the flow tubes' longitudinal center line.
The common X axis shall be on the plane of the top surface of the
brace bar and intersect the Z axes of both flow tubes. The Y axes
shall be on the plane of the surface of the brace bar and perpendicular
to the Z and X axes.
The brace bar of the present invention has increased flexibility
so as to permit the tubes increased relative translation in the
Z axes and increased relative rotation about the Y axes.
Any brace bar must allow the meter's flow tubes to rotate independently
with minimal constraint about the Y axis while rigidly constraining
the flow tubes from translating independently in the X axis. This
is axiomatic given the purpose of the brace bar. Increased independence
of the Y axis rotation reduces stresses at the joints between the
flow tubes and the brace bars due to out of phase driven vibration.
Increased independence of the flow tubes to translate in the Z axis
reduces the manufacturing induced stresses arising from thermal
shrinkage due to the sequential welding of the flow tubes to the
meter manifold. As the first tube to be welded shrinks during the
welding process, the brace bar of the present invention is capable
of flexing without yielding. Thus, when the second tube is welded
and shrinks, the brace bar is returned to its undeformed state.
This reduces the overall stress in the flow tubes, in the brace
bars, and in the braze joints connecting the flow tubes to the brace
bars by reducing or eliminating the residual stresses. The increased
flexibility of the brace bars of the present invention decrease
the stress level as well as shift the stresses into the brace bars
and away from the joints between the flow tubes and the brace bars.
All of this improves reliability of the joints, the brace bars,
and lifetime of the flow tubes.
An additional benefit the brace bar of the present invention is
that its increased flexibility enhances meter sensitivity to facilitate
mass flow measurement at lower flow rates.
Various exemplary embodiments of a flexible brace bar of the present
invention are disclosed. In one embodiment, a void is formed in
the area of the brace bar between the flow tubes. A second embodiment
removes only a portion of the material in this area of the bar leaving
a "screen" of brace bar material. Another embodiment removes
most, but not all of the brace bar material in the area between
the flow tubes. In yet another embodiment, the brace bar is formed
by joining of separate pieces. All the disclosed embodiments share
the common advantage that the brace bar is more flexible in response
to independent motion of the flow tubes in Z axis translation and
to Y axis rotation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an exemplary Coriolis effect meter utilizing the brace
bars of the invention;
FIG. 2 shows a typical prior art brace bar;
FIG. 3 shows one possible embodiment of a brace bar of the present
invention with a void formed between the brace bar holes that receive
the flow tubes;
FIG. 4 shows a side on view of flow tubes and a brace bar in their
nominal rest position;
FIG. 5 shows a side on view of flow tubes and a brace bar flexed
outward by the out of phase vibration of the flow tubes;
FIG. 6 shows a side on view of flow tubes and a brace bar flexed
inward by the out of phase vibration phase of the flow tubes;
FIGS. 7 and 8 illustrate the stresses induced in the flow tubes
and brace bar by the manufacturing process; FIG. 9 shows a plot
of the stress concentrations in the brace bar of FIG. 2;
FIG. 10 shows a plot of the stress concentrations in the brace
bar of FIG. 3;
FIG. 11 shows a possible exemplary embodiment of the brace bar
of FIG. 10 with a void formed in the bar between the flow tube holes;
FIG. 12 shows a possible alternative embodiment of the brace bar
of FIG. 11 with a screen formed in the area between the tubes; FIG.
13 is a perspective view of another possible alternative exemplary
embodiment of the brace bar of FIG. 11;
FIG. 14 shows another possible embodiment of a brace bar of FIG.
3 formed by two separate sections of material;
FIG. 15 shows another possible embodiment of a Coriolis effect
meter utilizing the brace bars of the invention; and
FIG. 16 shows another possible embodiment of a brace bar.
DETAILED DESCRIPTION
A typical Coriolis effect mass flow meter 10 is illustrated in
FIG. 1 as having two cantilever mounted flow tubes 12 14 mounted
to a manifold body 30 so as to have substantially identical spring
constants and moments of inertia about their respective out of phase
bending axes W--W and W'--W'.
A drive coil and magnet 16 are mounted at a midpoint region between
the top portion 130 and 130' of flow tubes 12 14 to oscillate flow
tubes 12 14 out of phase about axes W--W and W'--W'. Left sensor
18 and right sensor 20 are mounted near the respective ends of the
top portion 135 136 and 135', 136 of flow tubes 12 14 to sense
the movement of flow tubes 12 14. This sensing may be done either
by measuring the movement of the ends 135 136 and 135', 136 of
the flow tubes 12 14 through their zero crossings or by measuring
the velocity of movement of the flow tubes. Flow tubes 12 and 14
have left side legs 131 and 131' and right side legs 134 and 134'.
The side legs converge downwardly toward each other and are affixed
to surfaces 120 and 120' of manifold elements 121 and 121'. Brace
bars 140R and 140L are brazed to the legs of flow tubes 12 14 and
serve to define the axes W--W and W'--W' about which the flow tubes
oscillate out of phase when driver 16 is energized over path 156.
The position of axes W--W and W--W' is determined by the placement
of brace bars 140R and 140L on flow tube side legs 131 131' and
134 134'.
Raising or lowering brace bars 140R and 140L along the legs alters
the frequency difference between in-phase vibrations of the flow
tubes 12 14 about axes Z--Z and Z'--Z' caused by ambient conditions
of the pipe to which the flow meter 10 is attached and the out-of-phase
vibrations of flow tubes 12 14 about axes W--W and W'--W'. The
use of brace bars 140R and 140L also reduces the stress on the welds
which join flow tube side legs 131 131', 134 134' to manifold
surfaces 120 and 120' due to out-of-phase vibrations. This results
from the fact that flow tubes 12 14 vibrate out of phase about
axes W--W and W'W' when a brace bar is used rather than about axes
Z--Z and Z'Z'.
Temperature detector 22 is mounted on side leg 131 of flow tube
14 to measure the flow tube's temperature and the approximate temperature
of the flowing fluid therein. This temperature information is used
to determine changes in the spring constant of the flow tubes. Driver
16 sensors 18 20 and temperature detector 22 are connected to
mass flow instrumentation 24 by paths 156 157 158 and 159. Mass
flow instrumentation 24 may include a microprocessor which processes
the signals received from sensors 18 20 and 22 to determine the
mass flow rate of the material flowing through flow meter 10 as
well as other measurements, such as material density and temperature.
Mass flow instrumentation 24 also applies a drive signal over path
156 to driver 16 to oscillate tubes 12 and 14 out-of-phase about
axes W--W and W'W'.
Manifold body 30 is formed of casting 150 150'. Casting elements
150 150' are attachable to a supply conduit and exit conduit (not
shown), by flanges 103 103'. Manifold body 30 diverts the material
flow from the supply conduit into flow tubes 12 14 and then back
into an exit conduit. When manifold flanges 103 and 103' are connected
via inlet end 104 and outlet end 104' to a conduit system (not shown),
carrying the process material to be measured, the material enters
manifold body 30 and manifold element 110 through an inlet orifice
(not shown) in flange 103 and is connected by a channel (not shown)
having a gradually changing cross-section in casting element 150
to flow tubes 12 14. The material is divided and routed by manifold
element 121 to the left legs 131 and 131' of flow tubes 14 and 12
respectively. The material then flows through the top tubes elements
130 130' and through the right side legs 134 and 134' and is recombined
into a single stream within flow tube manifold element 121'. The
fluid is thereafter routed to a channel (not shown) in exit casting
element 150' and then to exit manifold element 110'. Exit end 104'
is connected by flange 103' having bolt holes 102' to the conduit
system (not shown).
FIG. 2 depicts a typical prior art brace bar 200 used with the
meter of FIG. 1. Flow tubes 12 14 of FIG. 1 are inserted through
holes 201a and 201b of FIG. 2 and brace bar 200 is slid to the desired
position on flow tubes 12 14 to define the desired pivot axis W--W
and W'--W' (FIGS. 1) for out-of-phase vibrations of flow tubes 12
14. The flow tubes are then brazed to brace bar 200 and then their
ends are welded to manifold surfaces 120 120'.
Brace bar holes 201a and 201b provide rigid support for flow tubes
12 14 of FIG. 1 to hold them spaced apart while providing for the
limited twist and flex, of flow tubes 12 14 that is needed for
Coriolis flow measurements. Brace bar 200 is a pivot point that
provides substantial resistance to the out-of-phase flexing of flow
tubes 12 14. This is due to the fact that the brace bar of FIG.
2 is a solid piece of metal between holes 201a and 201b. In practice,
the brace bar shown in FIG. 2 may be 1/8 of an inch thick. It is
desired in operation to have the flow tubes 12 and 14 flex with
ease out of phase about the axes W--W and W'--W'. The prior art
brace bar of FIG. 2 is formed of solid metal between the areas defined
by the holes 201a and 201b and tends to resist any such flexing
of the flow tubes. These out of phase vibrations of the flow tubes
both generate stresses within the areas of the flow tubes adjacent
to brace bar and in the brace bar itself.
FIG. 3 depicts a brace bar 300 designed in accord with the present
invention. Brace bar 300 is representative of brace bars 140R and
140L of FIG. 1 and includes a void 303 and holes 301a and 301b for
receiving flow tubes 12 14. Void 303 increases the bending flexibility
of brace bar 300 as compared to brace bar 200 in FIG. 2. Only small
strips 302a, 302b of material on the sides of brace bar 300 need
to be flexed by the out-of-phase vibration of flow tubes 12 14
as opposed to the solid mass of material between flow tube holes
201a and 201b of brace bar 200 in FIG. 2. This enhanced flexibility
reduces and shifts the stresses generated by the manufacturing process,
as subsequently described, away from the braze joint of brace bar
300 and the flow tubes at flow tube holes 301a and 301b. It also
reduces the flow tube stresses caused by the out of phase vibration
of tubes 12 14. Various shapes may be utilized to form void 303.
Each shape shifts the stresses of manufacturing to different locations
in brace bar 300. An easy flexing of the flow tubes about these
axes contributes to an enhanced sensitivity for Coriolis motion
detection purposes.
FIG. 3 depicts the three axes for which brace bar rigidity and
flexibility are relevant: the Z axis 306 is perpendicular to the
plane of brace bar 300 and coincident with the longitudinal axis
of the side legs 131 134 of flow tubes 12 14 the X axis 304 is
on the plane of the top flat surface of brace bar 300 and intersects
both the center lines of flow tubes, and the Y axis 305 is on the
plane the top flat surface of brace bar 300 and perpendicular to
the X axis.
Brace bar 300 permits increased independence of translation of
the flow tubes in the Z axis and increased independent rotation
of the tubes in the Y axis as compared to brace bar 200 of FIG.
2. The increased independence of translation of the flow tubes in
the Z-axis reduces the manufacturing induced stresses. Increased
independence of the tubes' Y axis rotation reduces stresses in the
joints between the flow tubes and the brace bars during normal out
of phase vibration of the flow tubes. FIGS. 4-6 depict a brace bar
300 affixed by brazing to flow tubes 12 14. The ends of flow tubes
12 14 are, in turn, welded to surface 120 of manifold element 121.
As driver 16 (FIG. 1) vibrates flow tubes 12 14 out of phase, flow
tubes 12 14 alternately flex outwardly and inwardly from the pivot
point (axis W--W [FIG. 1]) where brace bar 200 is affixed to flow
tubes 12 14. FIG. 4 depicts the flow tubes at the center point
of such oscillations. FIG. 5 depicts the outward flex of tubes 12
14 due to these out-of-phase vibrations. FIG. 6 depicts the inward
flex of tubes 12 14. In FIG. 5 it can be seen that brace bar 300
flexes upward at its center as flow tubes 12 14 are driven outward.
In FIG. 6 brace bar 300 flexes downward at its center in response
to tubes 12 14 being driven inward. It is relatively difficult
to flex the prior art brace bar of FIG. 2 in the manner shown in
FIGS. 5 and 6 since forces required must be applied to the brace
bar by the flow tubes 12 and 14. These forces are relatively high
for brace bar 200 and cause stress in the areas of the flow tubes
adjacent the brace bar as well as in the brace bar itself.
Brace bar 300 has improved flexibility and bends more easily because
of its void 303 and its thin side rails 302a and 302b. This improved
flexibility reduces stress in both brace bar 300 and flow tubes
12 14 in the area of their braze joint with brace bar 300. A brace
bar such as 200 of FIG. 2 without the improved flexibility of the
present invention, resists these out-of-phase oscillations more
than does brace bar 300. This increases the stress in brace bar
200 and flow tubes 12 14. Such increased stress can weaken and
eventually destroy the brace bar, the flow tubes, or both.
Increased independence of the flow tubes to translate in the Z-axis
with the use of brace bar 300 reduces the manufacturing induced
stresses arising from thermal warpage and shrinkage due to sequential
welding process used to join the flow tubes to the manifold surfaces
120 120'. FIGS. 4 7 and 8 depict brace bar 300 affixed by brazing
to flow tubes 12 14. On large flow meters, flow tubes 12 14 are
welded sequentially at their ends to manifold surface 120 after
they are brazed to a brace bar. Each flow tube shrinks slightly
when it is welded to manifold element 120. In FIG. 4 flow tubes
12 14 are brazed to brace bar 300 and their ends abut manifold
surface 121 but are not yet welded. In FIG. 7 flow tube 12 is
welded to manifold 121 at joint 700. The welding process causes
flow tube 12 to shrink and bend brace bar 300 at its center downwardly
to accommodate the shrinkage of flow tube 12. In FIG. 8 flow tube
14 is next welded to manifold surface 120 at joint 700. The welding
process causes flow tube 14 to shrink slightly and bend brace bar
300 at its center back to a nearly nominal planar position. The
rigid brace bar 200 of FIG. 2 resists the bending forces due to
the shrinkage of flow tubes 12 and 14. Often, a brace bar 200 will
resist bending to the point of yielding at its brazed joint to flow
tubes 12 14 when the first flow tube is welded. This creates undesirable
residual stress. Once a first braze joint between brace bar 200
and flow tube 12 has yielded, the welding of the second flow tube
14 creates a second set of large stress at the braze joints of the
brace bar 200 and flow tubes 12 14 as the brace bar is sent back
to a planar position of FIG. 8. Brace bar 300 because of its improved
flexibility, does not yield after the first tube weld and is thus
returned to a stress free condition by the sequential welding process.
FIG. 9 is a graphical representation of the stresses at various
points on brace bar 200. The shaded areas 902a and 902b indicate
areas of high stress created by both the out-of-phase vibrations
and the manufacturing process described above. These high stress
shaded areas 902a and 902b also occur at the braze joint between
brace bar 200 and the flow tubes (not shown) inserted through flow
tube holes 201a and 201b. These stresses can weaken and eventually
destroy brace bar 200 the flow tubes 12 14 or both.
FIG. 10 shows a graphical representation of the same manufacturing
induced stresses in a brace bar 300 designed with a void 303 in
accord with the present invention. The shaded areas 1002a and 1002b
show that these manufacturing induced stress are moved away from
the brace bar's 300 area where the flow tubes are inserted through
flow tube holes 301a and 301b. These manufacturing stresses are
one tenth the magnitude of the stresses induced in a brace bar without
the void 200 of FIG. 9 and are no longer coincident with the stresses
due to out-of-phase bending. Moving these manufacturing induced
stress points 1002a and 1002b away from the braze joint between
brace bar 300 and the flow tubes 12 14 isolates the flow tubes
12 14 from these manufacturing induced stresses, lowers all the
stresses in the region, and improves the reliability of the flow
tubes and the brace bar 300 itself.
FIG. 11 depicts brace bar 1100 comprising another possible exemplary
embodiment of the invention. Flow tubes (not shown) are inserted
through flow tube holes 1101a and 1101b. Void 1102 is formed in
the area between these holes to increase the flexibility of brace
bar 1100 by removing rigid mass that is resistant to flexing between
flow tube holes 1101a and 1101b in a manner similar to that of void
303 in brace bar 300 of FIG. 3. Brace bar 1100 also has less material
than does the brace bar of FIG. 3 in its outer areas 1104a and 1104b.
The elimination of the material that would otherwise comprise areas
1104a and 1104b reduce the stresses on the outside of flow tubes
inserted into holes 1101a and 1101b by transferring the brace bar
forces to the tubes primarily near the flow tubes neutral bending
axes. Elimination of the mass of material reduces the stiffness
of the brace bar. This reduces stress in both the flow tubes and
brace bars by reducing the impedance to out-of-phase bending.
FIG. 12 shows a brace bar 1200 comprising another possible exemplary
embodiment of the present invention. Flow tubes (not shown) are
inserted through flow tube holes 1201a and 1201b. Rather than a
total void as depicted in FIG. 12 only a portion of the material
is removed from brace bar 1200 of FIG. 12 between flow tube hole
areas 1201a and 1201b. This leaves a porous screen area 1202 rather
than the void of 1102 of FIG. 1. Screen area 1202 increases the
flexibility of brace bar 1200 by removing some rigid mass that is
resistant to flexing between flow tube hole 1201a and 1201b. This
increases its flexibility of brace bar 1200 to bend in response
to Z axis translation and Y axis rotation of the flow tubes.
FIG. 13 shows a brace bar 1300 comprising another possible exemplary
embodiment of the present invention. Flow tubes (not shown) are
inserted through flow tube holes 1301a and 1301b. Rather than a
total void as depicted in FIG. 11 only a portion of the material
is removed from brace bar 1300 between flow tube holes 1301a and
1301b leaving a thin continuous flexible area 1302. The thin area
1302 has a small amount of material that has a lowered resistance
to bending and therefore increases the flexibility of brace bar
1400 due to the reduction in the material that must be flexed. This
provides stress reductions in both the flow tubes and the brace
bar for the same reasons already discussed in connection with the
brace bars of FIGS. 11 and 12.
FIG. 14 shows brace bar 1400 as comprising another possible exemplary
embodiment of the present invention. Brace bar 1400 is made of two
separate sections 1401a and 1401b. Sections 1401a and 1401b are
joined to flow tubes 12 14 (viewed from above as a cross-section)
at joints 1402. The two sections 1401a and 1401b are in substantially
the same plane perpendicular to flow tubes 12 14. This brace bar
construction provides added flexibility to brace bar 1400 which
enables it to bend in response to Z axis translation and Y axis
rotation of the flow tubes 12 14 while maintaining sufficient
rigidity to constrain independent X axis translation of flow tubes
12 14. The embodiment of FIG. 14 is advantageous in that it provides
for the total elimination of the brace bar material that would otherwise
be attached to the outboard sides of the flow tubes as viewed in
FIG. 14. When comparing the brace bars of FIG. 11 and 14 it can
be seen that the brace bar of FIG. 14 does not have the left side
areas 1106a and 1106b of FIG. 11 nor does it have the right side
areas 1107a and 1107b of the brace bar of FIG. 11. These left and
right side areas 1106a and 1106b and 1107a and 1107b provide no
useful function regarding the brace bar and its flexibility or with
respect to stress reduction in either the brace bar or the flow
tubes. Conversely, the provision of the brace bar of FIG. 14 which
does not have elements corresponding to 1106a and 1106b and 1107a
and 1107b, reduces impedance to motion of the material that is attached
to the flow tube areas proximate the brace bar. The impedance reduction
decreases the stress on the flow tube and thereby increases both
the life of the flow tube and the life of the brace bar.
FIG. 16 shows another possible exemplary embodiment of the invention
as comprising brace bar 1600 having a single rail section 1601 extending
between flow tubes 14 and 12. Rail 1601 is connected on its left
end to brace bar elements 1602 and 1603 and on its right end to
elements 1604 and 1605. The upper left end element 1602 is connected
by an arcuate portion 1607 to the upper portion of tube 14. The
lower left element 1603 is connected by its arcuate portion 1606
to the bottom of flow tube 14. In a similar manner, the right end
portions 1604 and 1605 are connected via their arcuate portions
1609 and 1608 respectively, to the upper and lower portions, respectively,
of flow tube 12.
The construction of brace bar 1600 provides added flexibility which
enables the brace bar to bend in response to Z axis translations
and Y axis rotations of flow tubes 12 and 14 while maintaining sufficient
rigidity to constrain independent X axis translations of flow tubes
12 and 14. The voids 1610 and 1611 between the outer surface of
the flow tubes and the end portions of the brace bar move the stress
concentration, due to manufacturing into stresses as well as out-of-phase
vibrations, away from the portions of the brace bar and flow tubes
where the movement and flexing of these elements is the greatest
with respect to each other. The stresses in the embodiment of FIG.
16 are moved to the arcuate brazed joints bonding the flow tubes
12 and 14. These are the arcuate portions 1606 through 1609 of the
end portions of the brace bar. The relative motions of the flow
tubes and the brace bar with respect to each other are relatively
small at these arcuate sections so that the induced stresses do
not approach a level that can cause operational problems. The relatively
narrow single rail section 1601 is sufficiently flexible to permit
the Z axis translations associated with welding induced stresses
during manufacture. The single rail section 1601 together with the
end sections 1602 through 1605 are sufficiently flexible to accommodate
the out-of-phase vibrations of the flow tubes.
FIG. 15 shows an alternative embodiment of a Coriolis effect meter
utilizing the brace bars of the present invention. The meter 1210
of FIG. 15 is similar in many respects to the meter 10 of FIG. 1
and operates in the same manner utilizing the same principals to
derive mass flow information in response to the concurrence of a
driven out-of-phase vibration of flow tubes 1212 and 1214 together
with a flow of the material whose characteristics are to be measured
through flow tubes 1212 and 1214. The output information is supplied
over conductors 158 and 157 to mass flow electronics 24. A temperature
information signal applied to mass flow electronics 24 over path
159 and the mass flow electronics applies a drive signal over path
156 to driver 1280 which causes the two flow tubes to vibrate out
of phase with respect to each other about the axes W--W and W'--W'.
Since the Coriolis effect meter 1210 of FIG. 15 is similar in most
respects and in its principals of operation to the Coriolis effect
meter 10 of FIG. 1 the following is primarily directed to the manner
in which the Coriolis effect meter of FIG. 15 differs from that
in FIG. 1.
The Coriolis meter assembly 1510 includes a pair of manifolds 1510
and 1510'; tubular member 1550; a pair of parallel flow tubes 1514
and 1512; driver 1580; a pair of sensors 1520 and 1518 each of which
comprises a magnet B and coils A. Tubes 1512 and 1514 are substantially
U-shaped and have their ends attached to mounting blocks 1520 and
1520' which in turn are secured to respective manifold 1510 and
1510'.
With the side legs 1531 1531', 1534 and 1534' fixedly attached
to the tube mounting blocks 1520 and 1520' and these blocks, in
turn, fixedly attached to manifolds 1510 and 1510', a continuous
close fluid path is provided through the Coriolis meter assembly
1510. The right side legs are designated 1534 and 1534' while the
left side legs are designated 1531 and 1531'. The left and right
side brace bars 140L and 140R correspond identically to those shown
on FIG. 1 and serve the same purpose as the brace bars previously
described in the preceding figures. Specifically, the brace bars
shown on FIG. 15 have end portions attached to the two flow tubes
and a middle portion intermediate the two end portions with the
middle portion of the brace bar having substantially greater flexibility
than the material comprising the end portion of the brace bars.
The two flow tubes are driven to vibration in an out-of-phase manner
by driver 1580. These vibrations cause the tubes to pivot about
the axes W--W and W'--W' extending through the brace bars 140L and
140R. The flow tube assembly also vibrates in an in-phase mode about
the axes Z--Z and Z'--Z' in the same manner as previously described
in connection with the meter assembly of FIG. 1.
When meter 1510 is connected via inlet end 1501 and outlet end
1501', into a conduit system (not shown) which carries the fluid
whose characteristics are to be measured, fluid enters the meter
through an orifice end 1501 of manifold 1510 and is connected through
a passageway therein having a gradually changing cross-section to
mounting block 1520. There, the fluid is diverted and routed into
the two flow tubes 1512 and 1514. Upon exiting the flow tubes 1512
and 1514 the fluid is recombined in a single stream within mounting
block 1520' and is thereafter routed to manifold 1510'. Within manifold
1510' the fluid flows through a passageway having a similar gradually
changing cross-section to that of manifold 1510--as shown by dotted
lines 1505--to an orifice in outlet end 1501'. At end 1501', the
fluid reenters the conduit system. Tubular member 1550 does not
conduct any fluid. Instead, this member serves to axially align
manifolds 1510 and 1510' and maintain the spacing therebetween by
a predetermined amount so that these manifolds will readily receive
mounting blocks 1520 and 1520' and flow tubes 1512 and 1514.
The meter assembly of FIG. 15 is similar in all other respects
to the meter assembly of FIG. 1 and operates in the same manner
as previously described for the meter assembly of FIG. 1 to generate
mass flow and other information, as desired, for the material.
The specific meter structure shown in FIG. 15 devoid of the brace
bar 140R and 140L of the present invention, is shown in detail in
the U.S. Pat. No. 4843890 of Jul. 4 1989 to Allen L. Sampson
and Michael J. Zolock. Reference is hereby made to that patent for
further detailed information regarding the meter structure of FIG.
15. The disclosure of the Sampson-Zolock patent is hereby incorporated
by reference into the present specification to the same extend as
if fully set forth herein.
It is expressly understood that the claimed invention is not to
be limited to the description of the preferred embodiment but encompasses
other modifications and alterations within the scope and spirit
of the inventive concept. |