Abstrict The invention concerns a magnetically inductive flow meter for
flowing media with a tube consisting of ceramic material and used
as a measurement line, a magnet to produce a magnetic field running
at least essentially perpendicular to the tube axis, at least two
measuring electrodes arranged preferably perpendicular to the tube
axis and preferably perpendicular to the direction of the magnetic
field and at least two screening or shielding electrodes shielding
the measuring electrodes from outer electrical fields, wherein the
measuring electrodes and the screening or shielding electrodes are
placed outside the tube. The shielded magnetically inductive flow
meter is characterized in that there is a layer consisting of a
ceramic material surrounding the tube, that the measuring electrodes
are arranged essentially inside the layer and especially on the
border between the layer and the tube, and that the screening or
shielding electrodes inside the layer, especially on the border
between the layer and the tube and especially on the outer surface
of the layer are arranged so that the screening or shielding electrodes
shield the measuring electrodes from the outside.
Claims What is claimed is:
1. A magnetically inductive flow meter for flowing media of the
type including a tube (1) made of ceramic material used as a measuring
line, a magnet to produce a magnetic field extending perpendicular
to the axis of the tube, at least two measuring electrodes (2 3)
arranged perpendicular to the tube axis and perpendicular to the
direction of the magnetic field and, at least one shielding electrode
(4 5) shielding the measuring electrodes (2 3) from outside electrical
fields and a layer (6) of ceramic material surrounding the tube
(1), wherein the measuring electrodes (2 3) and said at least one
shielding electrode (4 5) are placed outside the tube and the measuring
electrodes (2 3) are arranged inside the layer (6) or on the border
between the layer (6) and the tube (1) and wherein at least one
flexible LTCC ceramic film or foil (7 8), each having a surface
and sinterable at low temperature, forms the layer (6) and the measuring
electrodes (2) and said at least one shielding electrodes (4 5)
is arranged on the surface of, or within said at least one LTCC
ceramic film or foil (7 8).
2. The flow meter according to claim 1 wherein parts of the measuring
electrodes (2 3) and part of said at least one shielding electrode
(4 5) is arranged, on the border between the LTCC ceramic film
or foil (7) and the tube (1) and/or on the outside of said at least
one LTCC ceramic film or foil (7), whereby there are throughplatings
or contacts (9 10) running through said at least one LTCC ceramic
film or foil (7).
3. The flow meter according to claim 1 with at least outer and
inner LTCC ceramic films or foils (7 8) wherein on the border between
the outer and inner LTCC ceramic films or foils (7 8) and/or on
the outside of the outer LTCC ceramic film or foil (8), parts of
the measuring electrodes (2 3) and parts of the said at least one
shielding electrode (4 5) are arranged, whereby there are throughplatings
or contacts (9 10) running through the outer LTCC ceramic film
or foil (8).
4. The flow meter according to claim 1 wherein the measuring electrodes
(2 3) are each designed to have a contact surface (11 12) on the
outer surface of the layer (6).
5. The flow meter according to claim 1 wherein the measuring electrodes
each has a contact surface and said at least one shielding electrode
(4 5) forms a continuous surface, except in an area around a said
contact surface (11 12).
6. The flow meter according to any one of claims 1 to 5 wherein
the layer (6) has a further LTCC ceramic film or foil (13) arranged
on the outside.
7. The flow meter according to claim 6 wherein the further LTCC
ceramic film (13) has another shielding electrode (14) and said
another shielding electrode (14) surrounds said at least one shielding
electrode (4 5).
8. The flow meter according to claim 7 wherein said at least one
shielding electrode (4 5) is guided electrically with the measuring
electrode (2 3) and said another shielding electrode (14) is connected
to a fixed reference potential and is preferably grounded.
9. The flow meter according to any one of claims 1 to 5 wherein
for each measuring electrode (2 3), there is a preamplifier and
conductor and resistor tracks necessary for building the preamplifier
in the further LTCC ceramic film or foil (13) which preamplifier,
conductor and resistor tracks are produced with LTCC technology.
10. The flow meter according to claim 6 wherein a conductive connector
extends from each measuring electrode (2 3) and preferably the
shielding necessary for that conductive connector, is produced in
the further LTCC ceramic film or foil (13) with LTCC technology.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a magnetically inductive flow meter for
flowing media with: a tube that is made of a ceramic material and
used as a measuring line; a magnet for producing a magnetic field
that runs at least essentially perpendicular to the axis of the
tube, with at least two measurement electrodes arranged preferably
perpendicular to the tube axis and preferably perpendicular to the
direction of the magnetic field; and at least two shielding or screening
electrodes that shield the measurement electrodes from outside electrical
fields, wherein the measurement electrodes and the shielding or
screening electrodes are placed outside the tube.
2. Description of The Related Art
The flow meter previously described is known from DE-A-33 37 151
from which this invention comes. In that flow meter, the measurement
electrodes and the screening or shielding electrodes are placed
galvanically on the surface of the ceramic tube. Because of this
placement, the measurement electrode can only be shielded from the
side. Now in order to make screening or shielding possible radially
to the outside, DE-A-33 37 151 proposed attaching a ceramic supporting
body in the area of the measurement electrode from the outside.
This ceramic supporting body has screening or shielding electrodes
on the surfaces that form the outer surface of the whole arrangement
after the supporting body is placed on the tube and are also applied
galvanically. In order to produce a tight connection between the
ceramic supporting body and the tube with the measurement electrodes
and the screening or shielding electrodes, the screening or shielding
electrode placed on the ceramic supporting body is soldered to the
screening or shielding electrode placed on the tube. The electrical
signal that is produced by the measurement electrode is taken to
the outside by a contact pin that runs through a hole in the ceramic
supporting body. Provision is also made for the components of the
preamplifier to connect directly to the screening or shielding electrodes
arranged on the ceramic supporting body and the contact pin, which
are, in turn, shielded by a screening or shielding box or cup attached
to the supporting body from the outside.
The flow meter known from DE-A-33 37 151 now has various disadvantages.
For one thing, it takes a large number of operational steps to produce
the screening or shielding for the measurement electrodes. For this,
the measurement electrodes and screening or shielding electrodes
are first applied galvanically to the tube.
The ceramic supporting bodies are produced in a separate operation,
and the screening or shielding electrodes are then placed on them
by galvanization. Finally, the ceramic supporting body must be attached
to the tube by soldering the screening or shielding electrodes on
the tube on the outer edge of the contact surface to the screening
or shielding electrodes on the supporting body. So it takes many
operational steps to produce this arrangement of measurement and
screening or shielding electrodes.
Another disadvantage of the known flow meter is that flaws can
occur in the shielding of the measurement electrode, if the solder
points are damaged by shaking, for example, and so holes can occur
in the shielding. Another disadvantage of this flow meter is that
having the ceramic supporting body and the screening or shielding
box or cup attached to it makes the whole flow meter very high,
and it cannot be designed compactly.
Another magnetically inductive flow meter known from DE-A-43 03
402 measures the flow speed of dielectric or electrically conductive
media with a contactless capacitive pick-up. Since both the measurement
electrodes and the screening or shielding electrodes are arranged
on the outer surface of the tube, the screening or shielding electrodes
can, because of this arrangement, only shield the measurement electrodes
laterally, so that other measures are necessary to shield them radially
to the outside. For this, DE-A-43 03 402 specifies that shielding
covers insulated from the measurement electrodes and connected conductively
to the screening or shielding electrodes be arranged on the tube
from the outside. These box-shaped shielding covers are soldered
onto the screening or shielding electrodes. To further process the
voltage signals produced by the measurement electrodes, signal lines
are soldered onto the measurement electrodes, and these signal lines
lead to the outside for further processing of the electrical signals.
The magnetically inductive flow meter known from DE-A-43 03 402
has various disadvantages. For one thing, it is only possible to
place metal electrodes and shieldings on the ceramic tube in one
layer, directly on the surface of the measuring tube. Because of
this, it is not possible with the flow meter already described and
known from the state of the art, to shield the measuring electrodes
from the outside with shieldings placed on the ceramic tube. Therefore,
an expensive box-shaped shielding cover is necessary that must be
soldered to the screening or shielding electrodes. This is a disadvantage
because in producing the flow meter, a separate processing operation
is necessary to produce such a shielding or screening. Moreover,
soldering the screening or shielding cover to the screening or shielding
electrode is expensive, on the one hand, and accident-prone, on
the other, since the solder points are damaged by vibration, so
that cracks or even fractures occur and the shielding can be defective.
The journal "Markt & Technik-Wochenzeitung fur Elektronik"[Market
and Technology Weekly for Electronics], Issue 23 of Jun. 3 1994
page 36 describes the use of flexible ceramic films or foils sintered
at low temperature in thick-film or layer technology to make complex
multi-layer circuits. In this known LTCC (Low Temperature Cofired
Ceramic) technology, unfired LTCC films or foils are mechanically
structured, printed in thick-film or layer technology, laminated
and then sintered at high temperature, which then produces a multilayer
ceramic.
SUMMARY OF THE INVENTION
The purpose of this invention is to design and develop the magnetically
inductive flow meter for flowing media known from the state of the
art in such a way that the measurement electrodes and the screening
or shielding electrodes can be placed outside the tube more easily
with respect to production and reliably.
The invention does this by having a layer of ceramic material surrounding
the tube, arranging the measuring electrodes essentially inside
the layer and arranging the screening or shielding electrodes both
inside the layer and on the outer surface of the layer so that the
measuring electrodes are shielded from the outside. In such a layer
it is also possible to arrange the surfaces of the measuring electrodes
and the screening or shielding electrodes at different distances
from the surface of the tube, so that the measuring electrodes can
be shielded both radially to the outside and also peripherally to
the side.
Because such extensive shielding is possible by putting or having
the layer with the measuring electrodes and screening or shielding
electrodes built or integrated, there are various advantages. For
one thing, the whole measuring electrode and screening or shielding
electrode arrangement can be produced in one operational step, so
that the soldering of extra screening electrodes known from the
state of the art is avoided. For another thing, the layer surrounding
the tube is not very thick, so that the size of the flow meter is
increased only slightly by that layer.
In one especially preferred embodiment of this invention, the flexible
LTCC ceramic film or foil sinterable at high temperature described
above are now used to build the layer surrounding the tube. Thus,
the advantages of using this LTCC ceramic film or foils are carried
over in a special way to building magnetically inductive flow meters.
Before being placed on the tube, the unfired LTCC ceramic films
or foils are provided with a conductive layer in an appropriate
way, so that the arrangement of measuring electrodes and screening
or shielding electrodes described above is produced if, for example,
two of these LTCC ceramic films or foils are placed on the tube
one over the other. It is also an advantage that the measuring electrodes
and screening or shielding electrodes formed in this way are arranged
between the LTCC ceramic films or foils, hence on their border as
well as on the outer surface of the outside LTCC ceramic film or
foil. Then, in the subsequent sintering operation, a multilayer
ceramic forming the layer surrounding the tube is created into which
the arrangement of measuring and screening electrodes is built or
integrated. By using LTCC technology to produce the magnetically
inductive flow meters according to the invention, it is thus possible
in a very advantageous way, to simplify the production process greatly
and at the same time position the measuring and screening or shielding
electrodes very precisely.
In another advantageous embodiment of this invention, the lines
and resistor tracks necessary for the preamplifiers for each measuring
electrode in the layer are produced using LTCC technology. This
allows extremely short tracks, and the electrical signals produced
by the measuring electrodes can be reliably preprocessed, so to
speak, on site. The components necessary for making the preamplifier
can thus be installed directly on the layer, hence, so to speak,
directly on the tube used as a measuring line. Thus, the cover of
the tube itself becomes a support for electronic components. Now
if the conductive connection between each measuring electrode and
its assigned preamplifier is produced using LTCC technology, all
of the advantages already indicated for the whole system, consisting
of measuring and screening or shielding electrodes and preamplifiers,
are exploited.
Another advantage of the design of the flow meter according to
the invention lies in the fact that the disturbing microphonical
effects known from using thick-film or foil technology are excluded.
Disturbances from microphonical effects are caused by split or crack
formation, i.e., very fine hollow spaces between electrode surface
and dielectrics and/or slight relative movements of the electrode
connections against the magnetic and/or electrical field of the
exciter layout of the flow meter, which make it practically impossible
to measure the volume flow on the basis of the small size of the
measurement signal. On the other hand, as described above, if LTCC
technology is used, solid ceramic structures are produced by the
sintering operation, which make the split or crack build-up leading
to microphonical effects and relative movements of the electrode
connections impossible.
Finally, it should also be pointed out that the magnetically inductive
flow meter already described is very reliable up to very high temperatures
and that if the line and resistor tracks for making the preamplifiers
are produced by LTCC technology, there is good temperature coupling
between the two preamplifiers, which improves the temperature synchronization
advantageously.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention will be explained in greater detail below using
an exemplary embodiment and referring to the drawings wherein:
FIG. 1 shows a cross-section through the tube of a first embodiment
of a flow meter according to the invention,
FIG. 2 shows a cross-section through the tube of a second embodiment
of the flow meter of the invention,
FIG. 3 is a top view of the tube of the FIG. 1 embodiment,
FIG. 4 is a cross section through the tube of a third embodiment
of a flow meter according to the invention, and
FIG. 5 shows a cross section through the tube of a fourth embodiment
of a flow meter according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a cross-section of the tube 1 made of ceramic material
and used as a measuring line. The use of ceramic as a material for
the tube 1 is advantageous if the liquids or media are aggressive,
for example, highly corrosive or at high temperatures. A magnetic
field running essentially perpendicular to the tube axis is produced
by a magnet, not shown in the drawing; FIG. 1 shows the magnetic
field schematically with arrows. Because of this magnetic field
and the speed of the charged particles present in the medium, the
medium is deflected from its track perpendicular to the tube axis
and perpendicular to the direction of the magnetic field due to
the Lorenz force. In this way, particles with different charges
are separated from one another, so that a charge polarization and
hence an electrical field is formed in the flowing medium.
This electrical field can be measured by measuring electrodes 2
and 3 arranged preferably near the flowing medium perpendicular
to the tube axis and preferably perpendicular to the direction of
the magnetic field. In the magnetically inductive flow meter according
to the invention, the measuring electrodes 2 and 3 are not in direct
contact with the flowing medium, but are arranged outside the tube.
The voltage values measured at the measuring electrodes 2 and 3
have only a low amplitude, so that it is necessary to shield the
measuring electrodes 2 and 3 well from outside electrical fields.
For this, at least two screening or shielding electrodes 4 and 5
that shield the measuring electrodes 2 and 3 are provided and arranged
outside the tube 1.
According to the invention, a layer 6 made of a ceramic material
is now provided that surrounds the tube 1. In this layer 6 the
measuring electrodes 2 and 3 are essentially arranged in the inside
of, that means in, the layer 6. But it is also possible to arrange
the measuring electrodes 2 and 3 on the inner surface of the layer
6 so that they are on the border between the tube 1 and the layer
6. Moreover, the screening or shielding electrodes 4 and 5 are also
arranged in the layer 6 whereby the screening electrodes 4 and
5 are both arranged partially inside the layer 6 and also on the
border between the layer 6 and the tube 1 or on the outer surface
of the layer 6. This arrangement of the measuring electrodes 2 and
3 and the screening or shielding electrodes 4 and 5 shields the
measuring electrodes 2 3 almost completely from the outside.
In another preferred way, the layer 6 is made of at least one flexible
LTCC ceramic film or foil 7 8 sinterable at low temperature. In
this way, the advantages associated with using this ceramic film
or foil already mentioned are carried over to the production of
flow meters.
In the first embodiment the layer 6 is mater according to the invention
shown in FIG. 1 the layer 6 is made essentially from LTCC ceramic
film or foil 7. The LTCC ceramic film or foil 7 has flat metal coatings,
which are arranged so that after the LTCC ceramic film or foil 7
is placed on the tube 1 these metal surfaces form the measuring
electrodes 2 and 3 as well as the screening or shielding electrodes
4 and 5. On one hand, parts of the measuring electrodes 2 and 3
and parts of the screening or shielding electrodes 4 and 5 are arranged,
on one hand, between the tube 1 and the LTCC ceramic film or foil
7 hence on their border, and, on the other hand, on the outside
of the LTCC ceramic film or foil 7. Now in order to produce a conductive
connection from the inner parts of the measuring electrodes 2 and
3 and the screening or shielding electrodes 4 and 5 with parts of
the measuring electrodes 2 and 3 and screening or shielding electrodes
4 and 5 arranged on the outer surface of the LTCC ceramic film or
foil 7 the LTCC ceramic film or foil 7 has throughplating or contacts
9 at appropriate places for the measuring electrodes 2 and 3 and
throughplatings or contacts 10 for the screening or shielding electrodes
4 and 5.
In the second embodiment shown in FIG. 2 the layer 6 is composed
of two LTCC ceramic films or foils 7 and 8. The LTCC ceramic films
or foils 7 and 8 have flat metal coatings that are arranged so that
after the LTCC ceramic films or foils 7 and 8 are placed on the
tube 1 these metal surfaces form the measuring electrodes 2 and
3 and the screening or shielding electrodes 4 and 5. Here, parts
of the measuring electrodes 2 and 3 and parts of the screening electrodes
4 and 5 are arranged, on one hand, between the LTCC ceramic films
or foils 7 and 8 hence on their borders, and, on the other hand,
on the outside of the outer LTCC ceramic film or foil 8. Since the
layer 6 is made of LTCC ceramic films or foils 7 and 8 lying one
over the other, the parts of the measuring electrodes 2 and 3 and
the screening or shielding electrodes 4 and 5 lying inside the layer
6 are at a fixed defined distance from the tube 1 in the layer 6.
Now, in order to produce a conductive connection from the parts
of the measuring electrodes 2 and 3 and the screening or shielding
electrodes 4 and 5 arranged on the outer surface of the LTCC ceramic
film or foil 8 to the parts of the measuring electrodes 2 and 3
and the screening or shielding electrodes 4 and 5 arranged inside-in
the same way described above-there is throughplatings or contacts
9 for the measuring electrodes 2 and 3 in the outer LTCC ceramic
film 8 at appropriate places, as well as throughplatings or contacts
10 for the screening or shielding electrodes 4 and 5.
In the examples of embodiments of the magnetically inductive flow
meter according to the invention shown in FIGS. 1 and 2 the measuring
electrodes 2 and 3 are connected conductively to contact surfaces
11 and 12 with throughplatings or contacts 9 at which the voltage
signals produced by the measuring electrodes 2 and 3 can be picked
up. The contact surface 11 can also be seen in the top view of the
magnetically inductive flow meter shown in FIG. 3. In this special
embodiment, the contact surface 11 is rectangular. As can also be
seen in FIG. 3 it is naturally necessary that the screening or
shielding electrodes 4 are recessed in a region around the contact
surface 11. In the other area, along the section including measuring
electrodes 2 and 3 on the outside of the tube, the screening or
shielding electrode 4 forms a continuous surface. Because of the
symmetric arrangement of both the measuring electrodes 2 and 3 and
the screening or shielding electrodes 4 and 5 the embodiment of
the screening or shielding electrode 4 shown is also true for the
screening or shielding electrode 5.
The two flow meter embodiments shown in FIGS. 1 and 2 can also
be surrounded, according to the invention, with another LTCC ceramic
film or foil 13 as is the case in the third and fourth embodiments
shown in FIGS. 4 and 5. This other LTCC ceramic film or foil 13
is mainly used for extra shielding. As shown in FIG. 5 the layer
6 in the fourth embodiment has another screening or shielding electrode
14 which preferably shields the screening or shielding electrodes
4 and 5 from the outside.
Finally, the shielding effect of the screening or shielding electrodes
4 5 and 13 can be further enhanced, on one hand, by having the
screening or shielding electrodes 4 and 5 guided electrically (bootstrap)
with the measuring electrodes 2 and 3 electrically and, on the other
hand, by having the screening or shielding electrode 14 connected
to a fixed reference potential, preferably the earth, so that it
is electrically conductive.
Since, as already described, the amplitude of the electrical signals
that are available at the measuring electrodes 2 and 3 is very
low, it is advantageous to amplify measuring signals with preamplifiers
before further processing; here it is an advantage if the signal
lines between the measuring electrodes 2 and 3 and their preamplifiers
are kept as short as possible.
For this, another embodiment of the magnetically inductive flow
meter in the invention is provided, to produce the conductor and
resistor tracks needed to make the preamplifiers in the layer 6
with LTCC technology. For this, corresponding structures are formed
on the LTCC ceramic films 7 and 8 before they are put on the tube
1 outside of the areas covered by the metal surfaces of the measuring
electrodes 2 and 3 and the screening or shielding electrodes 4 and
5. For this, extra LTCC ceramic film or foil 13 is preferably used,
when available.
In an especially advantageous way, a conductive connection from
each measuring electrode 2 and 3 to its respective preamplifier
is also produced in layer 6 preferably in the LTCC ceramic film
or foil 13 with LTCC technology; preferably the shielding necessary
for this conductive connection is made the same way. That way, after
sintering, a complex structure is produced in the layer 6 which
contains the arrangement of the measuring electrodes 2 and 3 and
the screening electrodes 4 and 5 and also the signal line and the
conductor and resistor tracks necessary for the design of the preamplifier.
Then the electronic components need only be arranged directly on
the layer 6 to receive preamplified measuring signals from the two
measuring electrodes 2 and 3.
In other words, a large part of the measurement system is built
into the tube 1 along with the layer 6 whereby the ceramic layer
6 is used as a "carrier plate" for the electronic components
of the preamplifier.
In all the embodiments shown in FIGS. 1 2 4 and 5 it is true
that the LTCC ceramic films or foils 7 8 and 13 are shown extra
thick in order to clarify the arrangement of the metal surfaces. |