Abstrict The invention concerns a mass flow meter for flowing media that
works on the Coriolis Principle, with at least one Coriolis line
carrying the flowing medium, at least one oscillator exciting the
Coriolis line, at least two transducers detecting Coriolis vibrations
based on Coriolis forces and a control unit controlling the oscillator
and evaluating the measurement signals from the transducers, wherein
the oscillator excites the Coriolis line with an excitation power
and wherein a generator is provided that supplies the excitation
power to the oscillator. The mass flow meter is characterized by
the fact that the excitation power of the generator can be adjusted
during operation, so that the amplitudes of the excitation oscillation
of the Coriolis line can be adjusted to the most optimal value possible.
Claims What is claimed is:
1. A method of measuring the mass flow of a flowing medium in a
Coriolis line comprising the steps of:
installing the Coriolis line in a pipeline system having certain
initial environmental conditions;
exciting the Coriolis line with a measured excitation power;
adjusting the excitation power so that the Coriolis line vibrates
with a predetermined vibration amplitude;
displaying the excitation power during operation of the flow meter,
and
using the displayed excitation power value as a measure for the
installation quality of the mass flow meter to minimize the coupling
of vibrations between the Coriolis line and the pipeline system
in which it is installed.
2. The method defined in claim 1 including the step of changing
one or more of said parameters to minimize the displayed excitation
power value and thereby optimize the mass flow measurement.
3. The method defined in claim 1 including the step of providing
a warning signal when the displayed excitation power value exceeds
a predetermined maximum value.
4. The method defined in claim 1 wherein said adjusting is done
manually.
5. The method defined in claim 1 wherein said adjusting is done
automatically while maintaining the predetermined vibration amplitude
constant during operation of the flow meter.
6. A method of measuring mass flow of a flowing medium using a
mass flow meter of the type that works on the Coriolis principle
and includes at least one Coriolis line carrying the flowing medium,
at least one oscillator exciting the Coriolis line, at least two
transducers detecting Coriolis vibrations based on Coriolis forces
and a control unit controlling the oscillator and evaluating the
measurement signals of the transducers and wherein the oscillator
excites the Coriolis line with an excitation power and wherein a
generator supplies adjustable excitation power to the oscillator
during operation of the flow meter, said method including the steps
of
installing the Coriolis line in a pipeline system having certain
initial environmental conditions;
measuring and displaying the excitation power during operation
of the flow meter, and
using the displayed excitation power value as a measure for the
installation quality of the mass flow meter to minimize the coupling
of vibrations between the Coriolis line and the pipeline system
in which it is installed.
7. The method defined in claim 6 including the step of adjusting
the exciting of the Coriolis line so that the Coriolis line vibrates
with a predetermined vibration amplitude.
8. The method defined in claim 7 including the step of changing
one or more of said parameters to minimize the displayed excitation
power value.
9. The method defined in claim 7 including the step of providing
a warning signal if the displayed excitation power value exceeds
a predetermined maximum value.
10. The method defined in claim 6 including the step of, while
holding the amplitude of the excitation oscillation at a desired
value, influencing the excitation power of the generator as a correcting
variable for the flow meter.
11. A mass flow meter for a flowing medium that works on the Coriolis
Principle, said flow meter having an installation quality and comprising
at least one Coriolis line carrying the flowing medium;
at least one oscillator exciting the Coriolis line into vibration
upon receiving excitation power;
a generator supplying adjustable excitation power to the oscillator;
at least two transducers detecting Coriolis vibrations based on
Coriolis forces and producing measurement signals indicative thereof;
means for evaluating said measurement signals;
means for measuring and displaying the excitation power during
operation of the flow meter so that the displayed excitation power
value can be used as a measure for the installation quality of the
mass flow meter in order to minimize coupling of vibrations between
the Coriolis line and a pipeline system.
12. A mass flow meter for flowing media that works on the Coriolis
Principle and has an installation quality, with at least one Coriolis
line carrying the flowing medium, at least one oscillator exciting
the Coriolis line, at least two transducers detecting Coriolis vibrations
based on Coriolis forces and a control unit controlling the oscillator
and evaluating the measurement signals of the transducers wherein
the oscillator excites the Coriolis line with an excitation power
and wherein a generator supplies adjustable excitation power to
the oscillator during operation of the flow meter, characterized
by the fact that the flow meter includes a display element that
displays the measured excitation power as a measure for the installation
quality of the mass flow meter.
13. The mass flow meter according to claim 12 characterized by
the fact that in the control unit, there is a controller holding
the amplitude of the excitation oscillation as a control variable
at a desired value, and the controller influences the excitation
power of the generator as a correcting variable of the control circuit.
14. The mass flow meter according to claim 13 characterized by
the fact that the average of the amplitudes of the measured signals
is fed to the controller as an actual value.
15. The mass flow meter according to claim 13 characterized by
the fact that the sum of the amplitudes of the measured signals
is fed to the controller as an actual value.
16. The mass flow meter according to any one of claims 13 to 15
characterized by the fact that the controller influences the average
over time of the excitation power supplied by the generator.
17. The mass flow meter according to claim 16 characterized by
the fact that the generator supplies pulse-width-controlled power
pulses to the oscillator.
18. The mass flow meter according to any one of claims 12 to 15
characterized by the fact that the control unit has a threshold
comparator that gives a warning signal via a warning-display element
when a predetermined maximum excitation power is exceeded.
Description The invention concerns a mass flow meter for flowing media that
works on the Coriolis Principle, with at least one Coriolis line
carrying the flowing medium, at least one oscillator exciting the
Coriolis line, at least two transducers detecting Coriolis oscillations
based on Coriolis forces and one control unit controlling the oscillator
and evaluating the measurement signals of the transducer, wherein
the oscillator excites the Coriolis line with an excitation power
and wherein an excitation generator supplying the excitation power
to the oscillator is provided.
BACKGROUND OF THE INVENTION
Mass flow meters for flowing media that work on the Coriolis Principle
are known in various embodiments and are being used to an increasing
extent.
One significant variable that is the same for all known mass flow
meters is the amplitude of the excitation oscillation of the Coriolis
line. In contrast to the frequency of the excitation oscillation
of the Coriolis line, this amplitude does not enter into the first
order in the measurement result for the mass flow by the mass flow
meter, but into a higher order, caused by nonlinear effects in the
deformation of the Coriolis line during the excitation oscillation.
These higher-order effects are especially important to the precision
required today of a relative measurement accuracy smaller than 0.1%
with a mass flow value of 10% to 100% of the nominal flow for mass
flow meters that work on the Coriolis principle.
The amplitude of the excitation oscillation of the Coriolis line
is dependent on plurality of factors. They are, first of all, the
properties of the system capable of vibrating in the form of the
Coriolis line, its direct surroundings and the contents of the Coriolis
line, hence the flowing medium, per se, and secondly, the excitation
power supplied to the Coriolis line by the oscillator, and lastly
the coupling of the oscillating system to the outer environment,
hence to the surrounding system of pipes. Of these influencing factors,
the first two are relatively simple to control, since they are predetermined
or known. The coupling of the oscillating system's "mass flow
meter" to the surrounding system of pipes is, first of all,
not known in advance, and secondly is almost incapable of being
predetermined. The decisive factors influencing this coupling are,
for example, the diameter and wall strength of the adjacent pipelines
and the distance between the connection of the mass flow meter to
the adjacent pipeline and the next supporting points of the adjacent
pipelines. Depending on how the Coriolis line of the mass flow meter
is coupled to the adjacent pipelines, a great deal of the excitation
power exerted on the Coriolis line for the excitation oscillation
is lost and disappears in the adjacent pipeline system.
To guarantee that the mass flow meter is sufficiently precise,
the amplitude of the excitation oscillation of the Coriolis line
must not fall short of a minimum amplitude, since otherwise the
transducer no longer supplies signals that can be analyzed. To guarantee
this minimum amplitude of the excitation oscillation of the Coriolis
line in the overwhelming number of ways of mounting the mass flow
meter in a pipeline system, the excitation power predetermined during
the process of producing the known flow meters is relatively large,
so that on one hand, under optimal mounting conditions, the amplitude
of the excitation oscillation of the Coriolis line is clearly above
the minimum amplitude, but on the other hand, when the mounting
of the mass flow meter is not optimal, sufficient amplitude of the
excitation vibration of the Coriolis line is guaranteed. Here the
problem is that the greater the amplitude of the excitation oscillation
of the Coriolis line, the more higher-order sources of error are
present.
The problem solved by the invention is, therefor, based on designing
and developing the known mass flow meter so that the amplitude of
the excitation oscillation of the Coriolis line measured on the
environmental factors always assumes as optimal a value as possible.
SUMMARY OF THE INVENTION
The mass flow meter of the invention, in which the problem presented
above is solved, is characterized by the fact that the excitation
power of the generator supplying the excitation power can be adjusted
during operation. The measure in the invention guarantees that regardless
of the process for producing the mass flow meter, during the operation
of the mass flow meter, an optimal value for the amplitude of the
excitation oscillation of the Coriolis line can be obtained manually
or automatically. For example, when the mass flow meter is mounted
in the optimal position within a pipeline system, it can be guaranteed
that the amplitude of the excitation oscillation of the Coriolis
line actually corresponds only to the minimum amplitude necessary
for optimal operation of the transducer. This guarantees that the
higher-order measurement errors that occur at a high amplitude of
the excitation oscillation of the Coriolis line are minimized and
thus precision is clearly increased when the mass flow is determined.
There are many ways of designing and developing the mass flow meter
of the invention. For this, please refer, on one hand, the patent
claims and, on the other hand, to the description of an embodiment
of the invention with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
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 schematic drawing of a preferred
embodiment of a mass flow meter according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The drawing figure is a schematic representation of a preferred
embodiment of a mass flow meter for flowing media that works on
the Coriolis Principle. This mass flow meter has a Coriolis line
1 conveying the flowing medium, an oscillator 2 exciting the Coriolis
line 1 two transducers 34 detecting Coriolis oscillations based
on Coriolis forces and a control unit 5 that controls the oscillator
2 and evaluates the measurement signals of the transducers 34.
Here it should be noted that it is conceivable to dispense with
one of the transducers 34 and instead of the signals from said
one transducer 3 or 4 transmit the signals from the oscillator
2 to the control unit 5 for evaluation. In the mass flow meter in
the invention, the oscillator 2 excites the Coriolis line 1 with
an excitation power, wherein there is a generator 6 in the control
unit 5 that supplies the excitation power to the oscillator 2. As
with the known mass flow meters, the measured signals of the transducers
3 4 are fed to a phase-difference detector 7 in the control unit
5 which determines the phase difference between the measured signals
from the transducers 3 4 in proportion to the mass flow through
the Coriolis line 1.
According to the invention, the mass flow meter is characterized
by the fact that the excitation power of the generator 6 can be
adjusted during operation of the flow meter.
According to a first alternative, the mass flow meter of the invention
is designed so that the excitation power of the generator 6 can
be adjusted by an operator via an activating or control element
accessed from the outside as shown by the phantom arrow. This guarantees
that an operator, using the activating element accessed from the
outside, can raise the excitation power until the mass flow meter
supplies reproducible values or, during a calibration process, supplies
the corresponding measured value for a predetermined mass flow.
This guarantees that the excitation oscillation of the Coriolis
line 1 does not have an unnecessarily high amplitude.
One especially preferred flow meter embodiment shown in the drawing
figure incorporates a control unit 5 which has a controller 8 that
keeps the amplitude of the excitation oscillation as a control variable
at a desired value and influences the excitation power of the generator
6 as a correcting variable of the control circuit. This guarantees
a constant amplitude of the excitation oscillation of the Coriolis
line 1 regardless of all potential factors. If the desired value
for the amplitude of the excitation oscillation of the Coriolis
line 1 corresponds to the minimum amplitude to be evaluated optimally
by the transducers 3 4 this guarantees that the measurement precision
for the mass flow is constantly high.
Another design variant is the example of the embodiment shown of
a mass flow meter according to the invention wherein the average
of the amplitude of the measurement signals detected by an amplitude
detector 9 is fed to the controller 8 as an actual value. Feeding
the average of the amplitudes of the measured signals to the controller
8 as an actual value increases the accuracy of the measurement.
As an alternative to the design described above of the preferred
embodiment, there is a version wherein the sum of the amplitude
of the measured signals is fed to the controller 8 as an actual
value. This is a simplification over the previous design, since
the amplitudes of the measured signals do not have to be determined
independently of one another and then the mean taken, but rather
the amplitude of the measured signals added together only has to
be found once.
Alternatively, the amplitude of at least one measured signal can
be determined directly from the measured signal itself, i.e., by
comparing the measured signals at various points in time, or indirectly
from an average of the measured signal over time. The last alternative
for finding the amplitude of the measured signal can be used, for
example, by integrating the absolute value of any measured signal
in a predetermined interval of time.
Since in the preferred embodiment, the generator 6 does not have
to supply excitation power to the oscillator 2 continually, the
mass flow meter of the invention is preferably designed so that
the controller 8 influences the average of the excitation power
supplied by the excitation generator 6 over time.
One especially preferred design is the embodiment shown in the
figure of a mass flow meter according to the invention wherein the
excitation generator 6 supplies conventionally produced pulse-width-controlled
power pulses to the oscillator 2. This guarantees that the influence
of the excitation power is very simple.
Another especially advantageous design is an embodiment of a mass
flow meter according to the invention wherein there is a display
element 10 that displays the excitation power as a measure for the
installation quality of the mass flow meter. Both in the case of
manual adjustment of the excitation power of the generator 6 by
an operator and also in the case of automatic control of the amplitude
of the excitation oscillation, the excitation power necessary for
highly precise operation of the mass flow meter is a measurement
of the installation quality: if the excitation power is relative
low for example, so the coupling of the mass flow meter to the surrounding
system of pipes is also low. Displaying the excitation power necessary
for highly precise operation has a special advantage, because the
coupling of the mass flow meter to the surrounding system of pipes
in known mass flow meters influences the amplitude of the excitation
oscillation of the Coriolis line 1 and because a higher coupling
is also responsible for a higher scatter of oscillations present
in the adjacent pipeline system into the mass flow meter, and this
scatter can substantially influence the measurements of the phase
difference between the measurement signals of the transducers 34.
Thus, if the display element 10 shows a high excitation power,
this is an indication to the operator that the installation should
be optimized in order to maintain a measurement precision that complies
with the specifications for the mass flow meter. In the preferred
embodiment shown in the figure, the display element 10 is used for
displaying the mass flow, which comes from the phase difference
determined in the phase-difference detector 7 besides showing the
excitation power. Of course, a separate display element can also
be provided to show the excitation power.
In conclusion, the preferred embodiment shown of a mass flow meter
according to the invention can be improved by providing a threshold
comparator 12 that gives a warning signal via a warning display
element 11 when a predetermined maximum excitation power is exceeded
in the control unit 5. This threshold comparator 12 and warning
display element 11 signal the operator that the excitation power
is in a range that shows that the installation of the mass flow
meter should be optimized. The warning display element 11 can, of
course, alternatively be built into the display element 10.
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 drawing 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. |