Abstrict A mass flow meter for flowing media that works on the Coriolis
Principle includes a line inlet, at least one Coriolis line carrying
the flowing medium, at least one line outlet, at least one oscillator,
influencing the Coriolis line, at least one oscillating transducer
detecting Coriolis forces and/or Coriolis oscillations based on
Coriolis forces and a meter housing. The Coriolis line is connected
to the carrier system and the line inlet and the line outlet are
connected between the carrier systems and the housing. The flow
meter is largely "oscillation self-sufficient" because
the carrier system has a natural frequency that is substantially
greater than the Coriolis lines natural line frequency and the Coriolis
natural frequency. Also, the natural frequency of the flow meter
as a whole is substantially smaller than the carrier-system natural
frequency.
Claims I claim:
1. A mass flow meter for flowing media that works on the Coriolis
Principle with a meter housing, a line inlet, at least one Coriolis
line carrying a flowing medium, a line outlet at least one oscillator
acting on the Coriolis line, at least one oscillation transducer
detecting Coriolis forces and/or Coriolis oscillations based on
Coriolis forces and a carrier system, wherein the line inlet, the
Coriolis line and the line outlet are connected to the carrier system,
the Coriolis line is supported by the carrier system and the carrier
system is supported within the housing by the line inlet and the
line outlet characterized by the fact that the carrier system's
natural frequency is substantially greater than the Coriolis line
natural line frequency and the Coriolis natural frequency as well
as the flow meter natural frequency, the flow meter natural frequency
being equal to the natural frequency of the structural unit comprised
of the line inlet, the carrier system and the line outlet.
2. The mass flow meter according to claim 1 wherein said carrier-system
natural frequency is many times greater than said Coriolis line
natural line frequency and said Coriolis natural frequency.
3. The mass flow meter according to claim 2 wherein said Coriolis
line natural line frequency and said Coriolis natural frequency
are around 100 to 150 Hz and said carrier-system natural frequency
is around 2000 Hz.
4. The mass flow meter according to claim 2 wherein said flow
meter has a natural frequency which is substantially smaller than
the carrier-system natural frequency.
5. The mass flow meter according to claim 3 wherein the flow meter
has a natural frequency which is substantially smaller than the
carrier-system natural frequency.
6. The mass flow meter according to claim 1 wherein said flow
meter has a natural frequency which is many times smaller than said
carrier-system natural frequency.
7. The mass flow meter according to claim 6 wherein said Coriolis
line natural line frequency and said Coriolis natural frequency
are around 100 to 150 Hz and said natural frequency of the flow
meter is around 20 Hz.
8. The mass flow meter according to claim 1 wherein the line inlet
(1) and the line outlet (3) are straight pipes having thin walls.
9. The mass flow meter according to claim 1 wherein the line inlet
(1) and the line outlet (3) are curved pipes.
10. The mass flow meter according to claim 1 and further including
a housing (5) and spring means (6) hanging the carrier system (4)
from said housing (5).
11. The mass flow meter according to claim 1 and further including
a housing (5) and spring means (6) resiliently supporting the carrier
system (4) in said housing (5).
12. The mass flow meter according to claim 10 and further including
a housing (5) and spring means (6') attached to said housing (5)
and supporting the carrier system (4) in said housing (5).
13. The mass flow meter according to claim 3 wherein said Coriolis
line natural line frequency and said Coriolis natural frequency
are around 120 to 140 Hz.
14. The mass flow meter according to claim 7 wherein said Coriolis
line natural line frequency and said Coriolis natural frequency
are around 120 to 140 Hz.
Description FIELD OF THE INVENTION
This invention concerns a mass flow meter for flowing media that
works on the Coriolis Principle, with a pipe inlet, with at least
one Coriolis line carrying the flowing medium, with one pipe outlet,
with at least one oscillator acting on the Coriolis line and with
at least one oscillation transducer that detects 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, 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 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
522 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, there is a basic difference between those instruments
whose Coriolis line is designed as a straight pipe and others whose
Coriolis line is designed as a--single or multiple--curved pipe
and as a pipe loop. For the mass flow meters in question, there
is also a difference between those that have only one Coriolis line
and those that have two Coriolis lines; in designs with two Coriolis
lines, they may be connected in series or in parallel to one another,
according to the flow technology. All these different flow meter
embodiments have advantages and disadvantages.
The embodiments of mass flow meters in which the Coriolis line
is designed as a straight pipe and in which Coriolis lines are designed
as straight pipes are simple to produce as far as their mechanical
constructions are concerned and consequently cost relatively little.
For example, the inner surfaces of each pipe can be processed easily,
e.g., polished. Also, their pressure loss is low. They are disadvantaged
in that at a certain structural length, their natural frequency
is relatively high. Embodiments of the mass flow meters in which
the Coriolis line(s) is/are designed as a curved pipe(s) have disadvantages
where the embodiments with straight pipe(s) have advantages; but
their advantage is that at a certain structural length, their natural
frequency is relatively low.
Mass flow meters that work on the Coriolis Principle have an oscillating
system or one capable of oscillating. The Coriolis line has a natural
line frequency and an oscillator oscillates the line at a selected
driving frequency. Usually, the oscillator oscillates at the natural
line frequency, i.e., the Coriolis line is excited by the oscillator
at an oscillation frequency that corresponds to the natural frequency
for the Coriolis line. The Coriolis natural frequency should be
the oscillation frequency preferably excited by the Coriolis force.
The fact that mass flow meters that work on the Coriolis Principle
represent an oscillating system or one capable of oscillating leads
to the fact that, on one hand, the oscillations are transferred
to the line into which the mass flow meter is inserted, and that,
on the other hand, oscillations in the line in which the mass flow
meter is inserted are transferred to the mass flow meter and distort
the measurement results; naturally neither one of these effects
is desired.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an improved
mass flow meter that works on the Coriolis Principle.
Another object is to provide a flow meter of this type which is
decoupled oscillation-wise from the fluid line into which the flow
meter is inserted.
Other objects will, in part, be obvious and will, in part, appear
hereinafter. The invention accordingly comprises the features of
construction, combination of elements and arrangement of parts which
will be exemplified in the following detailed description, and the
scope of the invention will be indicated in the claims.
The invention seeks to provide a mass flow meter that works on
the Coriolis Principle that is largely "oscillation self-sufficient".
By this we mean that, on one hand, the meter's own oscillations
are, in practice, not transferred to the line into which the mass
flow meter is inserted and that, on the other hand, oscillations
in the line into which the mass flow meter is inserted are, in practice,
not transferred to the mass flow meter's own measuring system.
The mass flow meter according to the invention, which meets these
criteria, is now characterized first and foremost by the fact that:
the Coriolis line is connected to a carrier system which is, in
turn, connected by the line inlet and outlet to the outer connections
of the flow meter by which the Coriolis line is coupled to the line
in which the flow meter is inserted; the carrier system has a natural
frequency that is substantially greater than the natural line frequency
of the Coriolis line and the Coriolis natural frequency, and the
natural frequency of the carrier system is substantially greater
than the natural frequency of the flow meter as a whole.
According to the invention, "natural-frequency-based decouplings"
are thus virtually put into practice. The carrier system of this
invention, which goes between the inherent measuring system and
the outer connections of the mass flow meter of the invention, depending
on the natural line frequency, is decoupled, on one hand, from the
inherent measuring system by the fact that the carrier system's
natural frequency is substantially greater than the Coriolis line's
natural frequency and the Coriolis natural frequency, and, on the
other hand, from the outer connections of the mass flow meter of
the invention by the fact that the meter's total natural frequency
is substantially smaller than the natural frequency of the carrier
system.
Taken separately now, there are various ways of building and improving
on the mass flow meter, which will be explained below only as examples.
The theory behind the invention is that the natural frequency of
the carrier system is substantially greater than the Coriolis line's
natural frequency and the Coriolis natural frequency and that the
natural frequency of the flow meter is substantially smaller than
the natural line frequency of the carrier system. This allows the
natural frequency of the carrier system to be many times greater
than the natural line frequency of the Coriolis line and the Coriolis
natural frequency, and the natural frequency of the meter as a whole
to be many times smaller than the natural frequency of the carrier
system.
In mass flow meters like the one in question, the Coriolis line's
natural line frequency and the Coriolis natural frequency are generally
around 100 to 150 Hz, preferably 120 to 140 Hz. It is advisable
to set the natural frequency of the carrier system at around 2000
Hz and the natural frequency of the flow meter at around 20 Hz.
Then, the natural frequency of the meter is not only substantially
smaller than the natural frequency of the carrier system, but it
is also many times smaller than the natural line frequency of the
Coriolis line and the Coriolis natural frequency.
It will be apparent from the foregoing that the mass flow meter
according to the invention has a carrier system as an added component
compared to mass flow meters prior to the invention. This carrier
system causes some static stress on the line inlet and line outlet.
Now, in order to reduce or eliminate this stress, another theory
behind the invention is that the carrier system may hang on carrier
springs attached to the meter housing and/or may be supported on
supporting springs attached to the meter housing. The carrier springs
and/or supporting springs must be sized so that the natural frequency
of the meter as a whole which is the natural frequency of the entire
moving unit (i.e., line inlet-carrier system (with Coriolis line,
oscillator(s), oscillating transducer(s), carrier springs and/or
support springs)-line outlet) is substantially smaller than the
natural line frequency of the Coriolis line and the Coriolis natural
frequency; preferably, the natural frequency of the meter is at
least three times smaller than the natural line frequency of the
Coriolis line and the Coriolis natural frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained below using drawings that show
only exemplary embodiments, wherein:
FIG. 1 is a top view, with parts in section, of a first embodiment
of a mass flow meter according to the invention;
FIG. 2 is a side view, with parts in section, of a second embodiment
of a mass flow meter according to the invention, and
FIG. 3 is a view similar to FIG. 1 of the mass flow meter pictured
in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The mass flow meters for flowing media, shown only schematically
in the drawings figures, work on the Coriolis Principle. The basic
design of each consists of a line inlet 1 a Coriolis line or flow
tube 2 carrying the flowing medium, a line outlet 3 at least one
oscillator, shown in phantom at 2a, acting on the Coriolis line
2 and at least one oscillation transducer or sensor, shown in phantom
at 2b, detecting Coriolis forces and/or Coriolis oscillations based
on Coriolis forces.
According to the invention, there is a carrier system 4 shown
in the form of a generally rectangular frame. The opposite ends
of Coriolis line 2 are connected to the carrier system 4 at coupling
block 7 and at block 8 respectively. The line inlet 1 and the line
outlet 3 are also connected at their corresponding inner ends to
the carrier system 4 at blocks 7 and 8 respectivefully, and communicate
with line 2. In fact, as shown in the FIG. 1 meter embodiment, line
outlet 3 may be an extension of Coriolis line 2 and line inlet 1
may be a separate pipe.
Each mass flow meter according to the invention also includes a
meter housing 5. The meter housing 5 thus contains a unit made up
of the line inlet 1 the carrier system 4 (including everything
supported by that system) and the line outlet 3. The corresponding
outer ends of inlet 1 and outlet 3 are connected to pipe fittings
10 and 12 respectively, mounted to the end walls of housing 5 and
by which the flow meter may be inserted into a flow line.
According to the invention, the natural frequency of the carrier
system, i.e., without the Coriolis line 2 and the oscillator(s)
2a and transducer(s) 2b, is made substantially greater than the
natural line frequency of the Coriolis line 2 and the Coriolis natural
frequency, i.e., the frequency of the oscillation induced in line
2 by oscillator(s) 2a. Also, the natural frequency of the flow meter
as a whole, i.e., that of the whole unit inside housing 5 including
line inlet 1 carrier system 4 (with line 2 oscillator(s) 2a, transducer(s)
2b) and line outlet 3 is made substantially smaller than the natural
frequency of the carrier system.
The natural line frequency of the Coriolis line is influenced mainly
by the length and mass of the line as well as by the elastic modulus
of the line material. The natural frequency of the carrier system
is influenced mostly by the geometry and mass of the carrier system
and the elastic modulus of the carrier material. The natural frequency
of the meter is influenced primarily by the mass of the carrier
system and the geometry and elasticity of the line inlet 1 and line
outlet 3. The flow meter may be given a low natural frequency advantageously
by designing the line inlet 1 and the line outlet 3 as straight
pipe with relatively thin walls or, as will be described presently,
as curved pipe.
For the mass flow meters of the invention, shown only schematically
in the figures, the Coriolis line natural line frequency and the
Coriolis natural frequency are preferably 120 to 140 Hz, the carrier-system
natural frequency is preferably around 2000 Hz and the natural frequency
of the meter is preferably around 20 Hz.
The mass flow meter embodiment according to the invention shown
in FIGS. 2 and 3 is different from the FIG. 1 embodiment in that
the line inlet 1 and line outlet 3 are formed as curved pipes. Also,
the carrier system 4 is hung on carrier springs 6 attached to the
top wall of meter housing 5. Alternatively or additionally, springs
may support the system 4 from below as shown at 6' in FIG. 2. The
springs largely eliminate, or at least sharply reduce, static stresses
on the line inlet 1 and the line outlet 3 due to the carrier system
4.
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 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 be
interpreted as illustrative and not a limiting sense.
It should also be understood that the following claims are intended
to cover all of the generic and specific features of the invention
described herein.
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