Abstrict A mass flow meter for flow media which works on the Coriolis Principle,
has a straight Coriolis pipe carrying the flow medium, an oscillator
acting on the Coriolis pipe and two transducers detecting Coriolis
forces and/or Coriolis oscillations based on Coriolis forces. The
Coriolis pipe also carries mass bodies and is arranged inside of
a housing or compensation cylinder. The mass flow meter improves
the measurement result that can be obtained by increasing the stiffness
of the Coriolis pipe for the excitation mode, preferably by including
a reinforcing spring which acts on Coriolis pipe to increase the
pipe stiffness for the excitation mode.
Claims We claim:
1. A mass flow meter for flow media that works on the Coriolis
Principle, with at least one basically straight Coriolis pipe carrying
the flow medium, at least one oscillator acting on the Coriolis
pipe, at least one transducer detecting Coriolis forces and/or Coriolis
oscillations based on Coriolis forces and stiffness increasing means
including at least one reinforcing leaf spring (6) acting in the
middle of the Coriolis pipe (1) that increases the stiffness of
the Coriolis pipe for the excitation mode, the improvement wherein
said spring is generally U-shaped with a bar (7) and two legs (89)
connected to opposite ends of the bar, there being at least one
flange (10 11) on the ends of the legs (89) remote from the bar
(7), said Coriolis pipe (1) is situated inside a housing (5) and
the spring (6) is attached by said bar (7) to the Coriolis pipe
(1) and is attached by said at least one flange (1011) to the housing
(5).
Description FIELD OF THE INVENTION
The invention concerns a mass flow meter for flow media that works
on the Coriolis Principle, with at least one basically straight
Coriolis pipe carrying the flow medium, at least one oscillator
acting on the Coriolis pipe and at least one transducer that detects
Coriolis forces and/or Coriolis oscillations based on Coriolis forces.
BACKGROUND OF THE INVENTION
Mass flow meters for flow media that work on the Coriolis Principle
are well known in various embodiments (see, for example, German
Disclosure Documents 26 29 833 28 22 087 28 33 0379 29 38 498
30 07 361 33 29 544 34 43 234 35 03 841 35 05 166 35 26 2977
37 07 777 39 16 285 39 28 839 40 16 907 41 24 295 and 41 24
296 European Patent Disclosure Documents 0 083 144 0 109 218
0 119 638 0 196 150 0 210 308 2 212 782 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.
Mass flow meter 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 curved--with
single or multiple pipes--and as pipe loops. The mass flow meters
in question are also divided into those with only one Coriolis pipe
and those with two; in designs with two, they may be in series or
in parallel fluidically.
Embodiments of mass flow meters in which the Coriolis pipe or pipes
are designed to be straight are simple in mechanical design and
consequently can be produced at relatively low cost. Also, the inner
surfaces of the pipes are easy to work on , for example, to polish.
They also have low pressure losses. The disadvantage is that at
a certain construction or layout length, their natural frequency
is relatively high. Embodiments of mass flow meters whose pipe or
pipes are designed to be curved have disadvantages whereas those
with a straight pipe or pipes have advantages; but their advantage
is that at a certain construction length, their natural frequency
is relatively low.
In a mass flow meter that works on the Coriolis Principle and has
at least one basically straight Coriolis pipe, at a certain construction
length, a relatively low natural frequency can be created, and at
a certain natural Frequency, a relatively short construction length
can be created, by having an oscillator that acts on the Coriolis
pipe via a pendulum arm (see pending U.S. patent application Ser.
No. 07/736400 filed Jul. 26 1991 claiming priority from German
application P40 23 989.6 of Jul. 28 1990). While the oscillator
acts directly on the Coriolis pipe and thus excites the Coriolis
pipe, at least almost exclusively, to bending oscillations in the
commonly known mass flow meters with at least one basically straight
Coriolis pipe, in the mass flow meter just described, where the
oscillator acts on the Coriolis pipe via a pendulum arm, the Coriolis
pipe is excited to torsion and bending oscillations. The point is
that the natural frequency relevant for bending oscillations can
be influenced, without influencing the length, the mass and/or the
stiffness of the Coriolis pipe, namely by the pendulum arm, i.e.,
by the mass of the pendulum arm and by the distance between the
longitudinal axis of the Coriolis pipe and the point where the oscillator
acts on the pendulum arm. The aforesaid pending application discloses
designs and advancements of the mass flow meter just described.
To prevent repetition, therefore, reference will be made expressly
to the content of U.S. patent application Ser. No. 07/736400 which
is hereby incorporated herein by reference.
Incidentally, in the mass flow meters that work on the Coriolis
Principle that are known from the previous publications and have
at least one basically straight Coriolis pipe, it is true that the
Coriolis oscillations have a relatively low amplitude, so that only
a very low measured value can be obtained. This is because of the
relatively high stiffness of the straight Coriolis pipe, both in
the excited mode and in the Coriolis mode.
In all the mass flow meters in question that work on the Coriolis
Principle and have at least one basically straight Coriolis pipe,
problems can also result from the fact that undesirable, i.e., interfering,
oscillations can occur at frequencies that are relatively close
to the frequencies of the desired oscillations, i.e., oscillations
in the excitation mode and in the Coriolis mode.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to improve the mass
flow meter on which the invention is based in terms of the measurement
results that can be obtained.
Another object is to provide a mass flow meter which minimizes
the effects of interfering oscillations of the meter's flow pipe.
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 mass flow meter of the invention, which reaches the aforesaid
objectives is characterized first and foremost by the fact that
the stiffness of the Coriolis pipe is high in the excitation mode,
especially due to the fact that the Coriolis pipe has a reinforcing
spring that increases its stiffness for the excitation mode. Preferably,
there is only one reinforcing spring, and it is in the middle of
the Coriolis pipe. According to the invention, the stiffness of
the Coriolis pipe is high for the excitation mode, without nominally
influencing the stiffness of the Coriolis pipe for the Coriolis
mode. This can ensure that the frequency of the oscillations in
the excitation mode contrasts with the frequency of the undesired,
i.e., interfering, oscillations sharply enough so that the influence
of such interfering oscillations in thus largely suppressed.
Now, there are various ways of designing and developing the mass
flow meter according to the invention. In this connection, please
refer to the embodiments that will be described along with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the nature and objects of the invention,
reference should be had to the following detailed description taken
in connection with the accompanying drawings, in which:
FIG. 1 shows schematically a section through one part of a preferred
embodiment of a mass flow meter according to the invention;
FIG. 2 is a sectional view of the mass flow meter taken along line
II--II of FIG. 1 and
FIG. 3 is an enlarged isometric view of the reinforcing spring
incorporated into the mass flow meter in FIGS. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The mass flow meter for flow media according to the invention is
one that works on the Coriolis Principle. Consequently, the mass
flow meter according to the invention has at least one straight
Coriolis pipe 1 that carries the flow medium, an oscillator 2 acting
on the Coriolis pipe 1 by way of a mounting block on the pipe and
two transducers 3 detecting Coriolis forces and/or Coriolis oscillations
based on Coriolis forces. FIG. 1 also shows that the Coriolis pipe
1 has mass bodies 4 through whose mass and arrangement along the
pipe, the natural frequency of the Coriolis pipe 1 can be influenced
within certain limits, as is well known by the skilled artisan.
FIGS. 1 and 2 show that the Coriolis pipe 1 is arranged within
a housing or compensation cylinder 5. Other details on the significance
of the housing or compensation cylinder 5 and components that go
with the mass flow meter--connecting rings, receiving cylinder,
connecting flanges, connecting pipes, reinforcing cylinder--cannot
be inferred from the figures. For them, please refer to pending
U.S. patent application Ser. No. 07/917517 filed Jul. 21 1992
whose contents are expressly incorporated herein by reference.
When oscillator 2 is energized, it oscillates pipe 1 in an oscillation
mode, i.e., laterally in FIG. 2. When fluid flows through pipe 1
the pipe is caused to oscillate in a Coriolis mode as is well known,
for example, from U.S. Pat. Nos. 3329019; 4632858 and 4680974
whose contents are incorporated by reference herein.
Those oscillations are detected by transducers 3 which produce
corresponding electrical signals which are processed in well known
ways to provide an indication of a characteristic such as mass flow
or density of a medium flowing through pipe 2.
According to the invention, as FIGS. 1 and 2 show, the Coriolis
pipe 2 has a reinforcing spring 6 to increase its stiffness for
the excitation mode. Preferably, although not necessarily, reinforcing
spring 6 acts in the middle of the Coriolis pipe 1. The theory behind
the invention thus leads to an increase in the stiffness of the
Coriolis pipe 1 for the excitation mode, without the stiffness of
the Coriolis pipe 1 being thereby influenced for the Coriolis mode.
The step taken in the invention now ensures that the frequency of
the oscillations of the Coriolis pipe 1 in the excitation mode contrasts
with the frequency of the undesired, i.e., interfering, oscillations
sharply enough so that the influence of such interfering oscillations
is therefore largely suppressed in the flow meter output.
The reinforcing spring 6 provided according to the invention can
be designed in different ways. In the illustrated embodiment, the
reinforcing spring 6 as FIG. 3 especially shows, is designed as
a leaf spring, U-shaped with a bar 7 attached to the mounting block
and two legs 8 9 and on each end of the legs 8 9 remote from
the bar, there are attachment flanges 10 11 facing out secured
to housing 5.
As already described above, the illustrated embodiment of a mass
flow meter according to the invention is one in which the Coriolis
pipe 1 is inside a housing or compensation cylinder 5. The reinforcing
spring 6 is then between the Coriolis pipe 1 and the housing or
compensation cylinder 5. The bar 7 of the reinforcing spring 6 is
attached to the Coriolis pipe, and its attachment flanges 10 11
are attached to the housing or compensation cylinder.
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 construction
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 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
herein described.
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