Abstrict A mass flow meter for flowing media that works on the Coriolis
Principle has at least one essentially straight Coriolis pipeline
carrying the flowing medium, with at least one oscillator acting
on the Coriolis pipeline and with at least one transducer detecting
Coriolis forces and/or Coriolis oscillations based on Coriolis forces.
Measuring errors or mechanical damage due to temperature fluctuations
and outside forces and torques are minimized or eliminated by providing
a compensation cylinder, and arranging the Coriolis pipeline inside
the compensation cylinder.
Claims We claim:
1. A mass flow meter for flowing media that works on the Coriolis
Principle, with at least one basically straight Coriolis tube having
opposite ends and carrying the flowing medium, at least one oscillator
acting on the Coriolis tube, at least one transducer detecting Coriolis
forces or Coriolis oscillations based on Coriolis forces and a support
tube having opposite ends, the Coriolis tube being inside the support
tube, and the Coriolis tube and the support tube being connected
to one another so as to prevent relative axial movement, the improvement
wherein the Coriolis tube (1) and the support tube (6) are made
of materials with substantially the same coefficients of thermal
expansion.
2. The mass flow meter according to claim 1 wherein the Coriolis
tube (1) and the support tube (6) are of materials with relatively
low coefficients of thermal expansion.
3. The mass flow meter according to claim 2 wherein the Coriolis
tube (1) is of titanium or a titanium alloy.
4. The mass flow meter according to claim 2 or 3 wherein the support
tube (6) is of a material selected from the group consisting of
unalloyed steel, ferritic stainless steel or a nickel alloy.
5. The mass flow meter according to claim 1 wherein first connecting
rings (7) connect the Coriolis tube and support tube ends to one
another so as to prevent relative axial movement, and further including
an outer tube (8) preferably of stainless steel and having opposite
ends, the structural unit consisting of the Coriolis tube (1), the
support tube (6) and said first connecting rings (7) being arranged
inside the outer tube (8).
6. The mass flow meter according to claim 5 further including second
connecting rings (9) connected to the ends of the outer tube (8),
a connecting flange (10) on the outside of each of said second connecting
rings (9), means for connecting each connecting flange (10) to the
corresponding second connecting ring (9), and connecting tubes (11)
having corresponding first ends connected to the opposite ends of
the Coriolis tube (1) and corresponding second ends extending through
the respective second connecting rings (9) into the respective connecting
flanges (10).
7. The mass flow meter according to claim 6 wherein the Coriolis
tube (1) and the connecting tubes (11) constitute a single length
of tubing.
8. The mass flow meter according to claim 7 further including a
reinforcing tube (12) housing each connecting tube (11).
9. The mass flow meter according to claim 8 wherein the connecting
tubes (11) are arranged under tension inside the respective reinforcing
tubes (12).
10. The mass flow meter according to claim 9 further including
soldering the connecting tubes (11) to the respective reinforcing
tubes (12), said soldering being vacuum hard nickel alloy soldering
with a soldering temperature of about 1000.degree. C.
11. The mass flow meter according to claims 6 wherein said connecting
tubes (11) are corrugated.
12. The mass flow meter according to claim 8 wherein the connecting
tubes (11) are movable axially within the respective reinforcing
tubes (12) and the connecting flanges (10).
13. The mass flow meter according to claim 12 further including
sealing means (13) on said second ends of the connecting tubes (11).
14. The mass flow meter according to claim 13 wherein said sealing
means (13) are O-rings.
15. The mass flow meter according to claim 13 wherein the sealing
means ( 13 ) are semicircular in cross section, are composed of
polytetrafluorenthylene and are spring loaded.
16. The mass flow meter according to claims 6 wherein the connecting
tubes (11) are curved.
17. The mass flow meter according to claim 16 wherein said opposite
ends (14) of the Coriolis tube (1) are curved.
18. The mass flow meter according to claim 16 or 17 wherein the
curved connecting tubes (11) have a larger diameter than the Coriolis
tube.
19. The mass flow meter according to claim 18 wherein said opposite
ends (14) of the Coriolis tube (1) have a larger diameter than the
remainder of the Coriolis tube (1).
Description FIELD OF THE INVENTION
The invention concerns a mass flow meter for flowing media, which
works on the Coriolis Principle, with at least one basically straight
Coriolis line carrying the flowing medium, with at least one oscillator
acting on the Coriolis line and with at least one transducer detecting
Coriolis forces and/or Coriolis oscillations based on Coriolis forces.
BACKGROUND OF THE INVENTION
Mass flow meters for flowing media that work on the Coriolis Principle
are known in various embodiments (see, for example, the German Disclosure
Documents 26 29 833 28 22 087 28 33 037 29 38 498 30 07 361
33 29 544 34 43 234 35 03 841 35 05 166 35 26 297 37 07 777
39 16 285 and 40 16 907 the European Disclosure Documents 0 083
144 0 109 218 0 119 638 0 196 150 0 210 308 0 212 782 0 235
274 0 239 679 0 243 468 0 244 692 0 271 605 0 275 367 and 0
282 552 as well as U.S. Pat. Nos. 4491009 4628744 and 4666421),
and are increasingly being used in practice.
In mass flow meters for flowing media that work on the Coriolis
Principle, a basic differentiation is made between those whose Coriolis
pipeline is designed basically straight, and those whose Coriolis
pipeline is designed to be shaped like a loop. A differentiation
is also made for the mass flow meter in question between those that
have only one Coriolis pipeline, on the one hand, and those that
have two Coriolis pipelines, on the other. Those that have two Coriolis
pipelines can have them in series or parallel to one another. All
forms of embodiment have advantages and disadvantages.
Embodiments of mass flow meters in which the Coriolis pipeline(s)
is/(are) designed to be straight are simple with respect to mechanical
design, and consequently can be produced at low cost. Their inner
surfaces are easy to work on--for example, to polish; they also
have low pressure-loss.
A disadvantage of mass flow meters that work on the Coriolis Principle
and whose Coriolis pipeline(s) is/(are) designed to be straight,
is that both thermally caused expansion and thermally caused stress,
plus outside forces and torques, can lead to measuring errors and
to mechanical damage--namely, stress cracks.
An objective of the invention is, therefore, to design and develop
the mass flow meter described at the beginning, in which the Coriolis
pipeline or pipelines is/are designed to be basically straight,
so that temperature fluctuations and outside forces and torques
do not lead to measuring errors or mechanical damage, or do so to
a lesser extent.
The invention accordingly comprises the features of construction,
combination of elements, and arrangement of parts which will be
exemplified in the construction hereinafter set forth, and the scope
of the invention will be indicated in the claims.
SUMMARY OF THE INVENTION
The mass flow meter according to the invention, from which the
task just derived and presented is solved, is now characterized
first and foremost by the fact that there is a compensation cylinder,
with the Coriolis pipeline being arranged inside of this compensation
cylinder. Preferably, the Coriolis pipeline and compensation cylinder
are connected to one another in a way that excludes relative axial
movement --namely, via two connecting rings connected to the ends
of the compensation cylinder.
The term "compensation cylinder" refers to a metallic
cylinder, preferably surrounding the Coriolis pipeline concentrically,
which compensates for temperature fluctuations and outside forces
and torques, and largely eliminates effects of such forces and torques.
The structural unit consisting of the Coriolis pipeline and the
compensation cylinder--because of the compensation cylinder and,
if need be, other measures to be described--is virtually "immune"
to temperature fluctuations and outside forces and torques.
Individually, there are now a great many ways of designing and
developing the mass flow meter according to the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the nature and objects of the invention
reference should be made to the following detailed description,
taken in connection with the accompanying drawings, in which:
FIG. 1 is a longitudinal section through an initial embodiment
of a mass flow meter according to the invention;
FIG. 2 is a similar view, on a larger scale, of a section of the
FIG. 1 flow meter;
FIG. 3 is a sectional view, on a still larger scale, taken along
the line III--III of FIG. 2;
FIG. 4 is a view similar to FIG. 3 showing a second embodiment
of a mass flow meter according to the invention;
FIG. 5 is a longitudinal section similar to FIG. 2 but on a larger
scale, through a section of a third embodiment of a mass flow meter
according to the invention;
FIG. 6 is a longitudinal section through a section of a fourth
embodiment of a mass flow meter according to the invention;
FIG. 7 is a longitudinal section through a fifth embodiment of
a mass flow meter according to the invention, and
FIG. 8 is a longitudinal section through a sixth embodiment of
a mass flow meter according to the invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The mass flow meter for flowing media according to the invention
is one that works on the Coriolis Principle. Consequently, it has
a straight Coriolis pipeline 1 carrying the flowing medium as shown
in FIGS. 1 to 6 or a basically straight Coriolis pipeline 1 as
seen in FIGS. 7 and 8. It also has an oscillator 2 acting on the
Coriolis pipeline 1 and 2 transducers 3 for detecting Coriolis forces
and/or Coriolis oscillations based on Coriolis forces. In the embodiment
shown specifically in FIG. 1 the oscillator 2 works with a pendulum
arm 4 provided on the Coriolis pipeline 1 as described in U.S. application
Ser. No. 07/736400 filed Jul. 26 1991 the contents of which
are hereby incorporated by reference herein. In addition, FIG. 1
shows that the Coriolis pipeline 1 also carries units of mass 5
through whose masses and arrangements the natural frequency of the
Coriolis pipeline 1 can be influenced within certain limits.
According to the invention, the flow meter also includes a compensation
cylinder 6 and the Coriolis pipeline 1 is arranged within the compensation
cylinder 6. The Coriolis pipeline 1 and compensation cylinder 6
are connected to one another in a way that excludes relative axial
movement, in all embodiments shown, via two connection rings 7 connected
to the ends of the compensation cylinder 6. The connecting rings
7 can be connected by welding or hard soldering to compensation
cylinder 6; it is also conceivable for the connecting rings to be
screwed onto the ends of the compensation cylinder. Preferably,
the connecting rings 7 are composed of the same substance as the
Coriolis pipeline 1. The Coriolis pipeline 1 is connected by welding
or by hard soldering to the connecting rings 7 preferably by vacuum
hard soldering e.g., nickel alloy with a soldering temperature of
about 1000.degree. C.
As stated above, the Coriolis pipeline I can be made virtually
"immune" to temperature fluctuations and to forces and
torques from the outside by means of the compensation cylinder 6
and, if necessary, by other measures. The Coriolis pipeline 1 may
be arranged under tension within cylinder 6. For this, the pipeline
may consist of a nickel alloy and the cylinder 6 may consist of
a nickel alloy, or unalloyed steel or ferritic stainless steel.
A supplemental measure for "immunizing" the Coriolis
pipeline 1 to temperature fluctuations and to outside forces and
torques consists of using materials with the same or almost the
same heat expansion coefficients for the Coriolis pipeline I and
the compensation cylinder 6 especially materials with relatively
low heat-expansion coefficients. From this standpoint, it is suggested
that titanium or a titanium alloy or a nickel alloy, especially
Hastelloy C4 be used for the Coriolis pipeline 1 and unalloyed
steel, e.g., A1S1 1018 ferritic stainless steel or the above nickel
alloy for the compensation cylinder 6.
Referring to FIGS. 1 and 2 another supplemental measure for "immunizing"
the Coriolis pipeline 1 against temperature fluctuations and outside
forces and torques consists of having an outer cylinder 8 preferably
made of stainless steel, and arranging the unit consisting of the
Coriolis pipeline 1 the compensation cylinder 6 and the connecting
rings 7 within the outer cylinder 8. As best seen in FIGS. 2 and
3 this embodiment is preferably also characterized by the fact
that the outer cylinder 8 has two connecting rings 9 on its opposite
ends, preferably made of stainless steel, a raised connecting flange
10 on the outside of the connecting rings 9 and connecting pipelines
11 connected to the Coriolis pipeline 1 by the connecting rings
9 in the connecting flanges 10. Preferably, the Coriolis pipeline
1 and the connecting pipelines 11 are designed in one piece; that
is, preferably a single length of pipeline extends all the way through
the flow meter.
It is also recommended that a reinforcing cylinder 12 e.g., of
Nylo 36 cover the connecting pipelines 11 to protect them, as shown.
For the reasons given above, it may be desirable to arrange the
connecting pipelines 11 under tension within the reinforcing cylinder
12. In this way, the connecting pipelines 11 can be connected to
the reinforcing cylinders 12 by hard soldering, preferably by vacuum
hard soldering and preferably with a nickel alloy solder at a soldering
temperature of around 1000.degree. C. This is shown by the heavy
black circle in FIG. 3.
As described above, one supplemental measure to "immunize"
the Coriolis pipeline I against temperature fluctuations and against
outside forces and torques can consist of choosing materials with
the same or almost the same heat-expansion coefficients for the
Coriolis pipeline 1 and the compensation cylinder 6 especially
materials with relatively low heat-expansion coefficients. In such
an embodiment of our mass flow meter, it is not necessary to connect
the connecting pipes 11 to the reinforcing cylinder 12. This is
shown in FIG. 4 by the absence of a heavy black circle between pipeline
11 and cylinder 12.
The primary measure of the invention, namely a structural unit
consisting of Coriolis pipeline 1 compensation cylinder 6 and connecting
rings 7 as already stated, means that the--Coriolis pipeline 1--essential
for measurement--is--more or less--"immune" to temperature
fluctuations and outside forces and torques. Immunizing measures
concerning the connecting pipelines 11 have already been described.
Another measure, shown in FIG. 5 is to design the walls of the
connecting pipelines 11 to be curved or wavy. This ensures that
the structural unit consisting of the Coriolis pipeline 1 the compensation
cylinder 6 and the connecting rings 7 can expand thermally within
certain limits without any impermissibly high stresses.
FIGS. 6 to 8 show embodiments of the mass flow meter according
to invention, in which impermissibly high stresses due to heat-related
expansion of the structural unit--consisting of the Coriolis pipeline
1 compensation cylinder 6 and connecting rings 7--is avoided in
ways other than those described in connection with FIG. 5.
In the embodiment only suggested in FIG. 6 the connecting pipelines
11 can move axially within the reinforcing cylinder 12 and the connection
flanges 10. Also, gaskets 13 are arranged on the ends of the connecting
pipelines 11 away from the Coriolis pipeline 1. While O-rings may
be used as the gaskets, for the embodiment shown in FIG. 6 each
gasket 13 is designed as a semicircular ring, e.g., of polytetrafluorethylene,
and acted on and held in place by a similarly shaped stainless steel
spring 13a.
In the flow meter embodiment depicted in FIG. 7 the connecting
pipelines 11 are curved, i.e., S-shaped, while in the embodiment
shown in FIG. 8 the ends 14 of the Coriolis line I are curved,
i.e., shaped like a quarter-circle, and the connecting pipelines
11 are also shaped like a quarter-circle. Also, as shown in FIG.
7 the curved connecting pipelines 11 may have a larger diameter
than the Coriolis pipeline I to reduce or eliminate the pressure-drop
caused by the curves. The line ends 14 may likewise be enlarged.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently attained
and, since certain changes may be made in the above constructions
without departing from the scope of the invention, it is intended
that all matter contained in the above description or shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
described herein. |