Abstrict A mass flow meter for flow media which works primarily on the Coriolis
Principle has a pipe inlet, a straight pipe carrying the flow medium,
a pipe outlet, an oscillation generator operating on the pipe and
two transducers detecting preferably Coriolis forces and/or Coriolis
oscillations affecting Coriolis forces. The flow meter has a relatively
low natural frequency at a certain layout length or a relatively
short layout length at a certain natural frequency, and in this
way, the oscillation generator engages the pipe via an articulated
arm so that the conduit is excited to torsional and bending vibrations.
Claims We claim:
1. A Coriolis-type meter for flow media including
a basically straight pipe having inlet and outlet ends and a longitudinal
centerline;
means for supporting the ends of the pipe;
an arm connected at one end to the pipe intermediate the ends of
the pipe;
at least one oscillation generator contacting said arm at a selected
contact point thereon spaced from said one end of the arm for moving
said arm so as to simultaneously torsionally oscillate said pipe
about said centerline and bend said pipe in an oscillating manner,
and
at least one transducer responsive to movements of said pipe between
the ends thereof to produce electrical signals indicative of those
movements.
2. The meter according to claim 1 wherein the contact of said oscillator
generator to said arm is adjustable along the arm so as to vary
the distance between said axis and said contact point.
3. The meter according to claim 1 or 2 and further including a
natural frequency control mass adjustably positioned along said
arm away from the pipe axis.
4. The meter according to claims 1 or 2 and further including a
carrier arm having one end contacting the pipe and another end contacting
the transducer for coupling the movements of the pipe to the transducer.
5. The meter according the claims 1 or 2 wherein
the support means include a carrier system which prevents lateral
displacement and rotation about said axis of the pipe ends, and
the oscillation generator and the transducer are supported by the
carrier system.
6. A Coriolis-type meter for flow media comprising a basically
straight pipe having opposite ends and a longitudinal centerline;
means for supporting the ends of the pipe;
exciting means engaging said pipe intermediate the ends thereof
for applying an oscillating force to said pipe which simultaneously
torsionally oscillates said pipe about said centerline and bends
said pipe in an oscillating manner, and
transducer means contacting the pipe intermediate the ends of the
pipe and being responsive to the movements of the pipe to produce
electrical signals indicative of those movements.
7. The meter defined in claim 6 wherein the exciting means include
means for adjusting the torque applied to said pipe.
8. The meter defined in claim 6 and further including means for
adjusting the natural frequency of the torsional oscillation of
said pipe.
Description The invention concerns a mass flow meter for flow media that works
primarily on the Coriolis Principle, with a pipe inlet with at least
on basically straight pipe carrying the flow medium and a pipe outlet
with at least one oscillation generator exerting an effect on the
pipe, and at least one transducer that preferably detects Coriolis
forces and/or Coriolis vibrations affecting Coriolis forces.
BACKGROUND OF THE INVENTION
Various embodiments of mass flow meters for flow media that work
on the Coriolis Principle are known (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 Patent Disclosure Documents 0
083 144 0 109218 0 119 638 0 185 709 0 196 150 0 210 308 0
212 782 0 235 274 0 239 679 0 243 468 0 244 692 0 250 706
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 applied in practice.
Mass flow meters for flow media that work on the Coriolis Principle
are basically divided into those whose pipes are designed to be
straight, and those whose pipes are designed to be single or multi-curved,
and a pipe loop. Another differentiation is made between those in
question with only one pipe and those with two; in designs with
two, they may be fluidally in series or in parallel. All these embodiments
have advantages and disadvantages.
The mass flow meters in which the pipe/s is/are designed to be
straight are simple in mechanical design and consequently can be
produced at relatively low cost and the inner surfaces of the pipes
are easy to process, for example, to polish. They also have low
pressure losses. The disadvantage is that they have a relatively
high natural frequency at a certain layout length. The embodiments
of mass flow meters in which the pipe/s is/are designed to be curved
have disadvantages where those with a straight pipe or pipes have
advantages. But their advantage is that they have a relatively low
natural frequency at certain layout lengths.
SUMMARY OF THE INVENTION
The task of the invention is to provide a mass flow meter with
at least one basically straight pipe that has relatively low natural
frequency at a certain layout length or that can be built with a
relatively short layout length at a certain natural frequency.
The mass flow meter of the invention, which solves the task that
has been introduced and presented, is now first and foremost characterized
by the fact that the oscillation generator engages the pipe via
an articulated arm. While in known mass flow meters with at least
one basically straight pipe, the oscillation generator acts directly
on the pipe, thus exciting the pipe--at least almost exclusively--to
bending vibrations, the measures in the invention whereby the oscillation
generator engages the pipe via an articulated arm cause the pipe
to be excited to torsional vibrations and bending vibrations. The
main thing is that the natural frequency related to the torsional
vibrations is substantially smaller than the natural frequency related
to the bending vibrations and can be influenced, without influencing
the length, mass and/or stiffness of the pipe, namely via the articulated
arm, i.e., via the mass of the articulated arm and via the distance
between the longitudinal axis of the pipe and the mass of the articulated
arm.
Mass flow meters of the type in question generally operate in resonance.
On the one hand, this has the advantage that the excitation can
be produced with a minimum expenditure of energy. On the other hand,
operating in resonance is a precondition for determining the density
of the flow medium with this type of mass flow meter. Actually,
mass flow meters of the type in question are used both for determining
the flow of a mass and for determining the density of the flow media.
That is the reason that at the beginning it was called a "mass
flow meter for flow media that works primarily on the Coriolis Principle"
and "with at least one transducer preferably detecting Coriolis
forces and/or Coriolis vibrations affecting Coriolis forces."
(Because when the density of the flow medium is determined with
the mass flow meter in question, the mass flow meter naturally is
not working on the Coriolis Principle.)
Besides the advantage, already mentioned, of the mass flow meter
of the invention--low natural frequency despite short layout length--the
oscillation generator manages to act on the pipe via an articulated
arm, and the pipe is therefore--and primarily--excited to torsional
vibrations; thus with the mass flow meter of the invention, the
viscosity of the flow medium can also be determined. Thus, first
of all, we have a meter which
a) the mass flow of the flow medium can be determined via Coriolis
forces or Coriolis oscillations, resulting from the bending vibration,
b) the density of the flow medium can be determined via the natural
frequency of the bending vibration or alternatively to b)
c) the viscosity of the flow medium can be determined via the natural
frequency of the torsional vibration (or via the expenditure of
energy required for the torsional vibration).
Taken individually, there are now many possibilities for building
and developing the mass flow meter of the invention. In this connection,
consider the description of a preferred embodiment, in connection
with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the nature and objects of the invention,
reference should be made to the following description, taken in
connection with the accompanying drawings, in which:
FIG. 1 is a fragmentary perspective view of a measurement system
of a mass flow meter that works on the Coriolis Principle according
to the invention;
FIG. 2 is a similar view illustrating the operation of the FIG.
1 system, and
FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 to 3 show only the actual measurement system of a mass
flow meter for flow media that works on the Coriolis Principle.
Along with it are a straight pipe 1 having an inlet and an outlet
and carrying the flow medium, an oscillation generator 2 engaging
the pipe 1 and a transducer 3.
As the figures show, although the oscillation generator 2 does
not engage the pipe 1 directly, it does engage the pipe 1 via an
articulated arm 4. While in the known mass flow meters on which
the invention is based, the oscillation generator excites the pipe--at
least almost exclusively--to bending vibrations, the mass flow meter
in the invention acts on the oscillation generator 2 via an articulated
arm 4 so that the pipe 1 is excited to torsional vibrations and
bending vibrations. The natural frequency related to the torsional
vibrations is basically lower than the natural frequency related
to the bending vibrations and can be influenced without influencing
the length, the mass and/or the rigidity of the pipe 1.
Now, with reference to FIGS. 2 and 3 an embodiment of the mass
flow meter of the invention is conceivable in which the distance
A between the longitudinal axis LA of the pipe 1 and the contact
point S of the oscillation generator 2 on the articulated arm 4
can be adjusted; but this is not shown in detail in the figures.
In the mass flow meter of the invention, the natural frequency
related to the torsional vibrations can be influenced by the articulated
arm 4 i.e., via the mass of the articulated arm 4 and by the distance
A.sub.2 between the longitudinal axis LA of the pipe 1 and the mass
of the articulated arm 4 which have an effect on the natural frequency.
This can be done in the embodiment shown by giving the articulated
arm 4 a natural frequency control mass 5 that is adjustable in relation
to the distance A.sub.3 to the longitudinal axis LA of the pipe
1.
For the mass flow meter of the invention shown in the figures,
as well as for the known mass flow meters on which the invention
is based, it is true that both the oscillation generator 2 and the
transducer 3 each consist of a moving part 2a or 3a and a stationary
part 2b or 3b. The figures show embodiments of the mass flow meter
of the invention in which the moving part 3a of the transducer 3
is connected directly to the pipe 1. But it is also conceivable
to have a form of embodiment in which the moving part of the transducer
is likewise connected to the pipe via a carrier arm, in the same
way that the oscillation generator 2 engages the pipe 1 via an articulated
arm 4. This can be used particularly for thermal uncoupling between
the pipe 1 an the moving part 3a of the transducer 3.
Moreover, in the mass flow meter of the invention, a series of
measures can be taken that are described in German Disclosure Documents
39 16 285 and 40 18 907 but not shown in the figures. Hence, the
contents of German Disclosure Documents 39 16 285 (corresponding
to U.S. Pat. No. 5129263) and 40 16 907 are incorporated by reference
herein for the description of the mass flow meter of the invention.
Finally, the figures show one preferred embodiment of the mass
flow meter of the invention that has a torsion-proof, rigid carrier
system 6 with the stationary part 2b of the oscillation generator
2 and the stationary part 3b of the transducer 3 connected to the
carrier system 6.
The figures show the theory behind the invention in one form or
embodiment of a mass flow meter that has only one pipe 1. The theory
behind the invention can, however, be applied to mass flow meters
that have two pipes, wherein both pipes can be fluidally in series
or in parallel.
The figures show that the articulated arm 4 is excited around the
longitudinal axis LA of the pipe 1. But it is also conceivable to
have another embodiment in which the articulated arm is excited
to vibrations in the plane in which the longitudinal axis of the
pipe is found. Then, the articulated arm can be on both sides of
the pipe, and natural frequency control masses can be provided on
each side of the pipe.
In addition, the double-sided articulated arm can be engaged on
one side to the oscillation generator, and the natural frequency
control masses can be provided on the other.
The mass flow meter of the invention provides, for the first time,
a meter with which the mass flow of the flow medium can be determined
by Coriolis forces or Coriolis oscillations resulting from the bending
vibration, the density by the natural frequency of the bending vibration
and the viscosity by the natural frequency of the torsional vibration
(or by the expenditure of energy required for the torsional vibration).
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