Abstrict A weir is placed across a pipe section and an electromagnetic flow
meter with multiple electrodes is located upstream of the weir.
The liquid level and velocity of fluid in the pipe section are evaluated
by the electromagnetic flow meter to determine flow rate.
Claims What is claimed:
1. A device to measure the flow of fluid containing electrical
charges, said device comprising:
a generally horizontal pipe section having an electrically insulated
inner surface and through which fluid flows;
magnet means for generating a magnetic field which extends diametrically
of said pipe section;
electrode means responsive to shifts in charges in said fluid which
flows through said pipe section and the level of said fluid which
flows through said pipe section for sensing the flowrate of said
fluid which flows through said pipe section.
a weir positioned downstream of said electrode means and extending
across said pipe section for stemming the flow of said fluid which
flows through said pipe section;
and evaluation circuit means responsive to said electrode means
and calibrated by the characteristics of said weir which affect
the flow of said fluid which flows through said pipe section for
developing an indication of the flowrate of said fluid which flows
through said pipe section.
2. A device according to claim 1 wherein said weir has a cross-section
which decreases towards the bottom of said weir.
3. A device according to claim 1 wherein said evaluation circuit
means include:
(a) signal processing and storage means responsive to said electrode
means for storing first signals representative of shifts in charges
in said fluid which flows through said pipe section,
(b) fluid level measuring means responsive to said electrode means
for developing second signals representative of the height of said
fluid which flows through said pipe section, and
(c) means responsive to said first and said second signals for
developing said indication of flowrate of said fluid which flows
through said pipe section.
4. A device according to claim 3 wherein:
(a) said electrode means include a plurality of pairs of electrodes
positioned at selected heights, and
(b) said fluid level measuring means include a plurality of detector
circuits, one associated with each pair of said electrodes, which
develop said second signals representative of the height of said
fluid which flows through said pipe section.
5. A device according to claim 2 wherein said evaluation circuit
means include:
(a) signal processing and storage means responsive to said electrode
means for storing first signals representative of shifts in charges
in said fluid which flows through said pipe section,
(b) fluid level measuring means responsive to said electrode means
for developing second signals representative of the height of said
fluid which flows through said pipe section, and
(c) means responsive to said first and said second signals for
developing said indication of flowrate of said fluid which flows
through said pipe section.
6. A device according to claim 5 wherein:
(a) said electrode means include a plurality of pairs of electrodes
positioned at selected heights, and
(b) said fluid level measuring means include a plurality of detector
circuits, one associated with each pair of said electrodes, which
develop said second signals representative of the height of said
fluid which flows through said pipe section.
7. Device to measure the flow of fluids containing electrical charges
with an essentially horizontal pipe section in which the fluid flows
and which is at least electrically insulating on its inner side,
with a magnet arrangement which generates a magnetic filed essentially
diametrically in the pipe section, with an electrode arrangement
which responds to a shift of the charges in the fluid which flows
perpendicularly through the magnetic field, and with an evaluation
circuit controlled by the electrode arrangement which produces an
output signal corresponding to the fluid flowrate and which also
takes into account the level of the fluid, further including a weir
located downstream of the electrode arrangement in the pipe section
and extending across the pipe section to stem the flow and wherein
the evaluation circuit is calibrated taking into consideration the
dimensions of the weir.
8. Device in accordance with claim 7 wherein said weir has a decreasing
cross-section for flow towards its bottom.
9. Device in accordance with claim 8 wherein:
(a) said electrode arrangement contains electrodes located at various
heights, and
(b) said evaluation circuit contains:
(i) a detector circuit that makes a measurement approximating the
level of the fluid in the pipe section, and
(ii) an output correcting circuit responsive to said detector circuit.
Description BACKGROUND OF THE INVENTION
The present invention relates to a device to measure the flow of
fluids containing electrical charges and which has (1) an essentially
horizontal pipe section in which the fluid flows and which is at
least electrically insulating on its inner side, (2) a magnet arrangement
which generates a magnetic field essentially diametrically in the
pipe section, (3) an electrode arrangement which responds to a shift
of the charges in the fluid which flows perpendicularly through
the magnetic field, and (4) an evaluation circuit controlled by
the electrode arrangement which produces an output signal corresponding
to the fluid flowrate and which also takes into account the level
of the fluid.
Devices of this kind are known from German Patent Applications
P 31 26 965 and P 40 10 727 and from the European Patent Application
90 106 783.
SUMMARY OF THE INVENTION
The present invention is based on the fact that the height of the
fluid in a weir is a measure of the flowrate as described in the
"Handbuch der Wassermessung" [handbook for water metering]
published by Verlag R. Oldenbourg, Munich-Vienna 1965 pages 178
to 182. Therefore, if the height of the fluid level in the weir
is determined by the electrode arrangement, a correction factor
can be established which can be used to improve the flowrate measurement.
An objective of the present invention is to provide a device which
will provide a particularly exact measurement of the fluid flowrate.
This objective is achieved by a weir located downstream of the
electrode arrangement in the pipe section to stem the flow with
the evaluation circuit calibrated to take into consideration the
dimensions of the weir.
In order to evaluate especially low fluid levels in the weir, the
weir has a decreasing flow cross section towards its bottom.
In a particular embodiment of the present invention which results
in an improvement of known evaluation circuits, the electrode arrangement
includes electrodes located at various heights, the evaluation circuit
includes a detector circuit that makes a measurement approximating
the level of the fluid in the pipe section, and a signal from the
detector circuit controls an output correcting circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows partially in perspective and partially schematically
the device, constructed in accordance with the present invention,
upstream of the weir
FIG. 2 shows an axial cross section through the device
FIG. 3 shows a cross section through the weir taken along line
III--III of FIG. 2
FIG. 4 shows the schematic arrangement of the evaluation circuit,
basically as it is described in the European Patent Application
90 106 783 however with improvements in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The figures show a pipe section 1 which has an electrically insulating
material on its inner surface and two electromagnets 2a, 2b for
the generation of a magnet field which passes through the pipe section
in an essentially diametrical direction. Also shown are two electrodes
3a, 3b, affected by the charge shift in the fluid, whose central
connecting axis X is essentially diametrical to the pipe section
1 and essentially perpendicular to the central connecting axis Y
of the two electromagnets 2a, 2b. The electromagnets 2a, 2b are
connected through off/reversing switches 4 5 to a supply device
13. By suitable changing of the switches, the electromagnets 2a,
2b can be connected in series, and, to alter the excitation of the
electromagnet 2a or the electromagnet 2b, an additional winding
can be provided on electromagnet 2a or electromagnet 2b, which can
be excited in a direction opposite to the excitation direction of
the main electromagnet. The electrodes 3a, 3b are connected to a
signal amplifier 6 whose output is connected to a signal switching
element 7. A timing circuit 11 switches, in synchronization with
the off/reversing switches 4 5 the output channels of the signal
switching element 7 which can be directed, for example, to a signal
memory 8 when the polarities of the electromagnets 2a, 2b are in
the same direction, to a signal memory 9 when the polarities of
the electromagnets 2a, 2b are in opposition, and to signal memory
10 when the electromagnets 2a, 2b are turned off. The signals stored
in the signal memories 8 9 10 are processed, using empirical parameters,
in the first correction circuit 12 so that the signal at the output
14 of the correction circuit 12 is essentially free of the distortions
of the flow profile in the pipe section 1 especially for deviations
from axisymmetry.
Below electrodes 3a, 3b are located two additional electrodes 3a',
3b' which also are affected by the charge shift in the fluid. The
central connecting axis X' of electrodes 3a', 3b' also is essentially
perpendicular to the pipe section 1 and essentially perpendicular
to the central connecting axis Y of the two electromagnets 2a, 2b.
The timing circuit 11 additionally controls the signal switching
element 7' which feeds the signal from the signal amplifier 6' which
is connected to the electrodes 3a', 3b' to the second signal memories
8', 9', 10', which correspond to signal memories 8 9 10 and the
various switch conditions of electromagnets 2a, 2b. The signals
stored in the signal memories 8', 9', 10' also are supplied to the
first correction circuit 12 to be processed, using empirical parameters,
to provide an output signal 14.
For partially full conditions in the pipe section 1 the first
correction circuit 12 provides an output signal 14 corresponding
to the partially full condition.
A partially full condition is indicated in FIG. 1 FIG. 2 and FIG.
3 by the level h designation. This partially full condition exists
upstream of the weir 20 which has a decreasing flow cross section
22 toward its bottom. Downstream of the weir 20 the level h decreases
as is shown by the level depiction 24.
The level upstream of the weir 20 is measured by the electrode
arrangement 3a, 3b, 3a', 3b'. A detector circuit 15a is connected
to electrodes 3a, 3b as shown in FIG. 4 and a detector circuit 15b
is connected to electrodes 3a', 3b'. The detector circuits 15a,
15b recognize even a partial utilization of the inner surface of
the pipe section 1 in the regions of the electrodes 3a, 3b or 3a',
3b' and provide corresponding output signals to a second correction
circuit 16 which takes into consideration the level in the weir
20 and thereby provides an improvement of the flow measurement signal.
|