Abstrict A magnetic-inductive flow meter, includes a pipe section for carrying
fluid flowing in a given direction, insulation in the form of a
ceramic tube disposed loosely inside of the pipe section, magnet
coils disposed on the outside of the pipe section for producing
a magnetic field in the pipe section perpendicular to the given
flow direction, at least two electrodes disposed inside the pipe,
holding pieces wedged against the ceramic tube for securing the
ceramic tube against rotation, and leads connected to the electrodes
and disposed inside the ceramic tube, the leads being extended through
the pipe section beyond an end of the ceramic tube.
Claims I claim:
1. Magnetic-inductive flow meter, comprising a pipe section for
carrying fluid flowing in a given direction, insulation in the form
of a ceramic tube disposed loosely inside of said pipe section,
magnet coils disposed on the outside of said pipe section for producing
a magnetic field in said pipe section perpendicular to the given
flow direction, at least two electrodes disposed inside said pipe,
holding pieces wedged against said ceramic tube for securing said
ceramic tube against rotation, and leads connected to said electrodes
and disposed inside said ceramic tube, said leads being extended
through said pipe section beyond an end of said ceramic tube.
2. Flow meter according to claim 1 including a ceramic jacket
insulating said leads in vicinity of said ceramic tube, said leads
including a transition section at the end of said ceramic tube,
and mineral-insulated jacketed measuring conductors adjacent said
transition section, said measuring conductors being tightly welded
to said pipe section where said leads are extended through said
pipe section.
3. Flow meter according to claim 1 wherein said magnet coils are
highly temperature-resistant coils.
Description The invention relates to a magnetic-inductive flow meter for high
temperatures and poorly electrically conducting liquids. Magnetic-inductive
flow meters have been used in engineering for a long time. Due to
Lorenz forces, a magnetic field oriented perpendicularly to a flowing
liquid causes a voltage to be built up in the flowing liquid which
is perpendicular to the direction of the magnetic field and to the
direction of the flow. For a given magnetic field, this voltage
is proportional to the volumetric flow of the liquid. It is conventional
to measure this voltage by means of electrodes and to construct
flow meters according to this system.
In a brochure of the firm Fischer and Porter GmbH, Gottingen (Cat.
1.2 1982), newer flow meters based on this principle are described.
In order to avoid electrochemical processes, these flow meters are
not operated with a constant magnetic field, but instead with a-c
current or pulsating d-c current. In the case of poorly electrically
conducting liquids, a further problem must be considered. A metallic
pipeline would short the voltage produced in the liquid and make
a measurement impossible. Therefore, magnetic-inductive flow meters
for poorly electrically conducting liquids must have a section of
pipe which is electrically insulated on the inside in vicinity of
the magnetic field. The electrodes must also be brought through
the wall of the pipe section in an insulated manner and through
the insulation into the interior, where they come into contact with
the liquid. The above-mentioned brochure discloses flow meters for
poorly electrically conductive liquids which operate in accordance
with this principle and are covered on the inside thereof with rubber,
plastic or ceramic. However, this structure has an upper limit with
respect to the maximum measurement material temperature, which is
in the range of 180.degree. C. For higher temperatures, it has not
been possible heretofore to satisfactorily solve the problems which
result from lack of temperature stability of the lining or different
coefficients of expansion of the pipe section and the lining, as
well as from the tight feedthrough of the electrode leads.
It is accordingly an object of the invention to provide a magnetic-inductive
flow meter for high temperatures, which overcomes the hereinafore-mentioned
disadvantages of the heretofore-known devices of this general type,
which can be used at substantially higher temperatures, and which
is suitable for poorly electrically conducting liquids.
With the foregoing and other objects in view there is provided,
in accordance with the invention, a magnetic-inductive flow meter,
comprising a pipe section for carrying fluid flowing in a given
direction, insulation in the form of a ceramic tube disposed loosely
inside of the pipe section, i.e. with a little play, magnet coils
disposed on the outside of the pipe section for producing a magnetic
field in the pipe section perpendicular to the given flow direction,
at least two electrodes disposed inside the pipe, holding pieces
wedged against the ceramic tube for securing the ceramic tube against
rotation, and leads connected to the electrodes and disposed inside
the ceramic tube, the leads being extended through the wall of the
pipe section beyond an end of the ceramic tube.
The problems described above are solved by the provision that the
insulation is no longer a layer which is firmly connected to the
inside of the pipe section, but as a whole, a ceramic tube is inserted
into the pipe section with a little play and is wedged to the pipe
section in such a way as to be secured against rotation. Since there
is no firm connection between the pipe section and the ceramic tube,
breaks and damage to the insulation cannot occur, even in the case
of different thermal expansion. In addition, feedthroughs in the
ceramic tube are dispensed with entirely and instead, the leads
of the electrodes are installed on the inside of the ceramic tube
up to the end of the tube and are only then brought through the
wall of the pipe section. Since it is not a problem to bring lines
through a metallic wall, the risks mentioned above are avoided in
this manner.
A basic feature of this new structure is the insight that penetration
of liquid between the ceramic tube and the wall of the pipe section
has no adverse affect on the measurement. The decisive factor is
to only ensure that no short circuit can occur by way of the pipe
wall at the point of the induced voltage.
In accordance with another feature of the invention, there is provided
a ceramic jacket insulating the leads in vicinity of the ceramic
tube, the leads including a transition section at the end of the
ceramic tube, and mineral-insulated jacketed measuring conductors
adjacent the transition section from the transition system on, the
measuring conductors being tightly welded to the wall of the pipe
section where the leads are extended through the pipe section. The
use of mineral-insulated jacketed measurement conductors is particularly
advantageous because it is relatively easy to make tight feed-throughs
with jacketed measurement conductors through metal walls. However,
this type of insulation cannot be used in the interior of the ceramic
tube, since at that location the metallic jacket would again cause
the short-circuit currents which are to be avoided by the structure
of the invention.
In the interior of the ceramic tube, small ceramic tubes or a ceramic
compound are therefore used for insulating the electrode leads.
In accordance with a concomitant feature of the invention, the
magnet coils are highly temperature-resistant coils. This permits
the formation of a compact structure of the flow meter without the
need for cooling the coils separately or for placing them distant
from the pipeline. Highly temperature-resistant coils have heretofore
been used in electromagnetic induction pumps, for instance.
Other features which are considered as characteristic for the invention
are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied
in a magnetic-inductive flow meter for high temperatures, it is
nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein
without departing from the spirit of the invention and within the
scope and range of equivalents of the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be
best understood from the following description of specific embodiments
when read in connection with the accompanying drawings, in which:
FIG. 1 is a longitudinal-sectional view of a flow meter according
to the invention;
FIG. 2 is a cross-sectional view taken along the line II--II of
FIG. 1 in the direction of the arrows; and
FIG. 3 is a fragmentary cross-sectional view taken along the line
III--III of FIG. 1 in the direction of the arrows.
Referring now to the figures of the drawing in detail and first
particularly to FIG. 1 thereof, there is seen a section of pipe
1 which is provided at both ends thereof with flanges 2. A ceramic
tube 3 is placed quasi loosely in the interior of the pipe section
1. This ceramic tube 3 is wedged at the ends thereof by slightly
conical holding pieces 4 and 5 which are welded in, and it is fastened
so as to be secure against rotation by meshing engagement with the
holding piece 4. The holding pieces 5 are non-rotational, symmetrical
parts, but they support the ceramic tube 3 in such a way as to leave
space for the installation of lines between them. Electrodes 6 are
disposed in the interior of the ceramic tube 3. The electrodes 6
have leads which are installed along the inside of the ceramic tube
3. The leads have a first piece 7 which is insulated by means of
a small ceramic tube up to a transition 8 at the end of the ceramic
tube 3. After the transition 8 the leads are continued in mineral-insulated
jacketed measuring conductors 9. These jacketed measuring conductors
are tightly welded by welds 10 at feed-throughs passing through
the wall of the pipe section 1. The position of coils 11 is indicated
by broken lines in FIG. 1 and is seen more clearly in FIG. 2. These
coils are accomodated in a housing 13 fastened to the pipe section
1. A terminal box 12 for accomodating the electrical terminals is
likewise fastened to the pipe section.
FIG. 2 shows a section through a flow meter according to the invention,
taken along the line II--II in FIG. 1. The highly temperature-resistant
coils 11 and the magnet cores are disposed and protected in the
housing 13 on both sides of the pipe section 1. Materials with a
high Curie point are used as the magnet laminations.
FIG. 3 shows a section through FIG. 1 taken along the line III--III.
The holding pieces 5 which are of conical shape, are welded to
the pipe section 1 and secure the ceramic tube 3 in its position.
Space remains between the holding pieces 5 for installing the jacketed
measuring conductors 9 which are brought through the tube wall in
vicinity of the holding pieces 5 and are welded to the tube wall
at welds 10.
The foregoing is a description corresponding in substance to German
Application No. P 32 44 473.7 dated Dec. 1 1982 the International
priority of which is being claimed for the instant application,
and which is hereby made part of this application. Any material
discrepancies between the foregoing specification and the aforementioned
German application are to be resolved in favor of the latter. |