WO2011144343A1

WO2011144343A1 - Method for operating a magnetic flowmeter

Info

Publication number: WO2011144343A1
Application number: PCT/EP2011/002505
Authority: WO
Inventors: Daniel Schrag; Harald Grothey; Kai Hencken
Original assignee: Abb Technology Ag
Priority date: 2010-05-19
Filing date: 2011-05-19
Publication date: 2011-11-24
Also published as: DE102010020963A9; DE102010020963A1

Abstract

The invention relates to a method for operating a magnetic flowmeter according to the preamble of claim 1. The aim of the invention is to devise a magnetic flowmeter which allows, in addition to the filling level in the measuring tube to be measured, a selective distinction between sedimentation, foaming, and incorrect fitting position. According to the invention, the filling level is determined by carrying out two independent measurements by measuring at the same time two voltages between different electrode pairs.

Description

Method for operating a magnetic flow meter

The invention relates to a method for operating a magnetic

Flowmeter, according to the preamble of claim 1.

DE 196 37 716 C1 and DE 101 18 002 A1 B4-A disclose methods for operating flow-measuring devices, both for operation in partially filled tubes (first patent) and for diagnosing malfunctions by measuring impedance values (second patent), but only with completely filled tubes, in which a two-electrode system is used. However, this is not sufficient for selective determination and quantification of disturbances, which can occur in particular in partially filled pipes, but also in fully filled pipes.

The invention is therefore based on the object, in addition to the measurement of the level height in the measuring tube selective discrimination between

Sedimentation, foaming, to allow incorrect mounting position or to detect or correct the influence of these disturbances by improved measurements.

In a method of the generic type is the task

solved according to the invention by the characterizing features of claim 1.

Further embodiments and alternatives of the invention are in the following

Claims 2 to 10 specified.

CONFIRMATION COPY A first embodiment is designed such that the filling level is determined by carrying out two independent measurements by measuring two voltages between different pairs of electrodes at the same time or in succession (multiplexing mode) when supplied to other electrodes or to earth. Thus, the measurement result is independent of the conductivity of the medium to be measured.

In addition, it can be measured quickly, and preferably according to the 2-line principle, to additionally avoid lines.

For this purpose, the principle of multiplexing and current superposition is advantageously used. In this case, the (voltage or current) signal is fed via an electrode and the ground potential, and the voltage is measured via another electrode against ground potential. At the end, all four possible voltages (two voltage measurements on two electrodes with two signal feeds each) are evaluated together. See below, Figure 1.

It is also advantageous to use a multiplexing that is arranged as close as possible to the electrodes. So can with a smaller number of

Connections are made to an evaluation device. This leads to a

Reduction of cables or less effort for protective functions for

Intrinsic safety (ATEX).

A further alternative is that the filling level is determined by feeding two current signals to different electrodes or electrode combinations, and that the voltage ratios are determined at the two other electrodes, and from these impedance values are determined, and from this a fill level is determined. For this purpose, the 4-electrode arrangement is again important.

A further alternative is that a multiplicity of impedances is determined, and that from the impedance patterns it is concluded that there is sedimentation in the measuring tube. It is important that MORE be measured as two different impedances, which are set in relation to each other. For example, in one

Cross-section position electrodes are more low position, which are more sensitive in terms of conductivity at the bottom of the medium, and which are positioned higher in terms of conductivity of the medium in the midst of the flow itself. Both can be set well and gives meaningful results in terms of both sedimentation and sedimentation. In an embodiment, it is stated that in this way foaming and / or other inhomogeneities in the measuring medium are determined which are above the

Material flow itself are available. Here, the role of the electrodes with respect to the measurement of the disturbance reverses.

A further advantageous embodiment in the operating method is that a plurality of measurement responses are performed within a short time, so that at different results under the same conditions / at the same electrodes AUTOMATIC at least one further measurement is performed, so that a self-monitoring of the flow meter can be performed on this. Preferably, more than three measurements are performed. In this way, highly self-verifying parameters can be determined. That's how it works

Evaluation system independent of temporary faults.

Another embodiment is that four electrodes or, three and one ground are used, so that an upper top electrode is provided, and a lower opposite ground electrode or a ground outside the flowmeter, the other two electrodes in this symmetric left and are arranged distributed to the right of the top electrode, such that these oppositely disposed electrodes are used as standard measuring electrodes, and in each case opposing measurements on the left and the right electrode are performed. In this case, however, it can also be provided that the top electrode can also be controlled as a normal measuring electrode by switching over the control of the same. Thus, by a mode switching the top electrode in one case to a level electrode and in another case to a measuring electrode for signal feed or Messignalabnahme. In particular, a

Flow rate using the top electrode and one of the two

Side electrodes are determined. This can serve as a replacement for the actual measurement, or for verification. In addition, the conductivity in the left and right part of the measuring tube or in the entire measuring tube can be determined and thus closed inhomogeneities of the field or the flow medium.

Another embodiment is that the injected signal on Low frequency signal is, in the range of 1 mHz to 100 Hz. About this

Procedure, it is possible a definite distinction between typical frequency-dependent interference to more frequency-independent interference

make.

For example, corrosion effects are typically rather low frequency and are therefore much better detectable at such low frequencies, or selectable, so to distinguish from other disturbances. On the other hand, a frequency-based measurement is significantly less sensitive to disturbances, in particular of triboelectric effects in a measurement with DC voltages or currents.

Another embodiment is that a two-fold (redundant)

Electrode assembly arranged in the flow direction one behind the other and operated so that the two flow meters are operated synchronized signaling. If these two electrode arrangements are operated synchronized, interference is avoided. This can be in addition to the

Flow measurement of the medium through a correlation in time

Flow rate of a second medium, e.g. be determined by solids. This is important when the medium serves as a carrier of the second medium, or contains several phases, which have different speeds.

An embodiment of this is that a number of each 4 electrodes are arranged distributed on the circumference of the measuring tube in such a way that they on the

Edge line of a cross-sectional area, which is orthogonal to the flow direction, and that at least one further four-electrode arrangement is provided, which are arranged on a second, to the first cross-sectional area in the flow direction shifted cross-sectional area, and that are measured within a measuring tube at two staggered locations can.

One implementation for this is that a series of measurements are made over time, which is used to determine additional parameters. Due to the large number of measurements, or the measurements under certain conditions (fill level, flow rate), a much more accurate determination can be carried out. This is of particular interest for parameters related to the calibration of the flowmeter, eg the calibration of the electrode positions, a Determination of the mounting position (angle) but also a calibration of magnetic field deviations.

An embodiment of this is that a conductivity measurement of the medium can also be performed in partially filled pipes. Thus, one of the methods mentioned above can be used to determine the filling level. Alternatively, independent level measurements can be used (capacitive, ultrasonic, radar ...). From knowledge of the dependence of an impedance value on the filling level and the conductivity, a value for the conductivity can then be calculated. For Impendanzmessung one of the already determined

Impedances, but also a further impedance measurement can be used, e.g. a two- or four-electrode measurement.

One embodiment of this is that measurements of the voltages induced by the magnetic field and the medium flow at the two or more electrodes are combined with a measurement of the impedances. Thus, both the conductivity and the velocity distribution within the measuring tube can be closed, and e.g. in the case of sediments or foaming, these are detected more reliably or corrected.

Furthermore, it is stated that by using more than one

Evaluation unit and the controlled control of the measuring electrodes

Redundancy of the measurements can be achieved. So the two can

Evaluation units determine flow values one after the other and compare them. Failure of one of the two units would still lead to a reliable measurement.

Furthermore, it is stated that a large number of data are stored in an adaptive data field, that specific patterns for filling height determination, foaming in the flowing measuring medium, sedimentation and conductive deposits on the inner circumferential surface of the measuring tube are applied, and patterns of values on filling levels and / or foaming in the medium and / or sedimentation and / or conductive deposits on the inner surface of the measuring tube is closed. With the measuring electrode arrangement indicated above, it is therefore possible to switch between the different operating modes, or to switch back and forth.

For each specific measurement task, i. Disturbances such as level, foam, particles, sedimentation, etc. can be provided a separate data field, so that with the switching of the electrodes and a switching of the evaluation algorithms takes place.

This leads to a highly sensitive, selective and because of

Self-calibration capabilities to a much more robust flow measurement system.

FIG. 1 shows schematically the cross section through the measuring tube.

Here, four individual measurements are carried out, measurement 1 to 4.

An electrode is used to supply a current and an electrode measures one

Tension. This allows an impedance determination for any

Electrode combination can be achieved with only two test leads.

The impedances are then evaluated as follows as a whole:

FIG. 2 shows how filling level determination for voltage measurements on unloaded electrodes can be carried out by combining two current injection patterns even with four electrodes

FIG. 3 shows the optimization by the evaluation of more than two

Voltage values or differences. A first possibility is to calculate more than two resistances / impedances or to determine from the measurements: R1 = U1 / I, R2 = U2 / I, R3 = U3 / I

From these three, a fill level is determined by an optimization method. The following formal context applies here:

h = argmin _{fci (i0} T [Ä _; - a ₀ Si (h)] ² i

The curves also show the error range when measured with two impedance values (dashed) and three values (solid). FIG. 4 shows a possibility of how the mounting position can be determined by combining the measurement over a longer time:

- Example of angle determination (angle a) from the asymmetry of the two

Resistors R1 (U1) and R2 (U2)

- Combination of measurements over time (a as a function of time as a plot).

5 shows the detection of "flow disturbances." In addition to the sedimentation detection, an extension to the detection of conductive deposits and the formation of foam on the surface are shown.

Further down in Figure 6, the measurement of the conductivity in a partially filled tube is shown schematically. By a Füllhöhenbestimmung (here represented by a radar system) and an impedance measurement (left figure) and the known dependence of the impedance of the filling level (right figure) at a

Reference conductivity can be deduced on the conductivity of the medium.

Claims

claims:

1. A method for operating a magnetic flow meter in which electrodes are distributed over the measuring tube circumference, via which a flow rate is determined by means of a magnetic field,

characterized,

In the distributed electrodes signals are fed and measured and measured by the permutation of respective pairs of electrodes impedance and / or voltages and that the filling level is determined by performing two or more independent measurements.

2. Method for operating a magnetic flow meter, in which electrodes are distributed over the measuring tube circumference, by means of which a flow rate is determined by means of a magnetic field,

characterized,

that the fill level is determined by feeding at least two current signals to different electrodes, and that the voltages are determined at the at least two other electrodes, and from these in turn impedances are determined, and from this a fill level is determined.

3. A method of operating a magnetic flow meter in which electrodes are distributed over the measuring tube circumference, by means of which a flow rate is determined by means of a magnetic field,

characterized,

In the distributed electrodes signals are fed and measured and measured by the permutation of respective electrode pairs impedances and / or voltages and that a plurality of impedances are determined, and that is concluded from the impedance patterns on sedimentation, electrode coatings, conductive coatings or foam in the measuring tube.

4. A method of operating a magnetic flow meter in which electrodes are distributed over the measuring tube circumference, by means of which a flow rate is determined by means of a magnetic field,

characterized, In the distributed electrodes signals are fed and measured and measured by the permutation of respective pairs of electrodes impedance and / or voltages and that a plurality of

Repeated measurements are carried out within a short time, so that at different results under the same conditions / at the same electrodes AUTOMATIC at least one further measurement is performed, so that a self-monitoring of the flow meter can be performed on this.

5. The method according to claim 3

characterized,

that foaming and / or other inhomogeneities in the measuring medium are determined in this way.

6. A method of operating a magnetic flowmeter in which electrodes are distributed over the measuring tube circumference, via which a flow rate is determined by means of a magnetic field,

characterized,

signals are fed and measured into the distributed electrodes and impedances and / or voltages are measured via the permutation of respective pairs of electrodes, and

in that three electrodes are used, such that an upper top electrode is provided, the remaining two electrodes being distributed symmetrically in this respect downwards to the left and right of the top electrode, such that the top electrode is switched by one of the switching

Standard measuring electrodes can be used.

7. A method of operating a magnetic flow meter in which electrodes are distributed over the measuring tube circumference, by means of which a flow rate is determined by means of a magnetic field,

characterized,

In the distributed electrodes signals are fed and measured and measured by the permutation of respective electrode pairs impedances and / or voltages and that the injected signal a Low frequency signal is, in the range of less than 100 Hz.

8. A method of operating a magnetic flow meter in which electrodes are distributed over the circumference of the measuring tube, via which a flow rate is determined by means of a magnetic field,

characterized,

In the distributed electrodes signals are fed and measured and measured by the permutation of respective electrode pairs impedances and / or voltages and that at least two times

(Redundant) measuring arrangement in the flow direction arranged one behind the other and operated so that can be concluded by a correlation of the measuring signals in the two arrangements on an additional flow variable.

9. A method of operating a magnetic flowmeter in which electrodes are distributed over the measuring tube circumference, by means of which a flow rate is determined by means of a magnetic field,

characterized,

in the distributed electrodes signals are fed and measured and measured by the permutation of respective electrode pairs impedances and / or voltages and that a number of at least 4 electrodes are arranged distributed on the circumference of the measuring tube so that they lie on the edge line of a cross-sectional area, which is orthogonal to the flow direction, and that at least one further arrangement of at least four electrodes is provided, which are arranged on a second, to the first cross-sectional area in the flow direction shifted cross-sectional area, and that can be measured within a measuring tube at two offset locations.

10. A method of operating a magnetic flow meter in which electrodes are distributed over the circumference of the measuring tube, by means of which a flow rate is determined by means of a magnetic field.

characterized,

In the distributed electrodes signals are fed and measured and the permutation of respective pairs of electrodes impedance and / or Voltages are measured and that a multiplexing unit is provided for the electrode drive, so that a simplification of the cabling and / or intrinsic safety is achieved.

11. A method of operating a magnetic flowmeter in which electrodes are distributed over the measuring tube circumference, by means of which a flow rate is determined by means of a magnetic field,

characterized,

In the distributed electrodes signals are fed and measured and the permutation of respective pairs of electrodes impedance and / or voltages are measured and that additional measurements or parameters are determined by a plurality of measurements over time, in particular the mounting position, the calibration of the electrode position and the magnetic field distribution.

12. A method of operating a magnetic flowmeter in which electrodes are distributed over the measuring tube circumference, via which a flow rate is determined by means of a magnetic field,

characterized,

In the distributed electrodes signals are fed and measured and measured by the permutation of respective pairs of electrodes impedance and / or voltages and that by combining a

Fill height determination with an impedance measurement, a conductivity measurement of the medium at partial filling takes place.

13. A method of operating a magnetic flowmeter in which electrodes are distributed over the measuring tube circumference, via which a flow rate is determined by means of a magnetic field,

characterized,

In the distributed electrode signals are fed and measured and measured by the permutation of respective pairs of electrodes impedance and / or voltages and that by combining the

Impedance values with the voltage values between the electrodes by the magnetic field and the flow of the medium, an improved determination of the flow profile is carried out and this particular for a detection and Correction of flow inhomogeneities can be used.

14. Method for operating a magnetic flow meter, in which electrodes are distributed over the measuring tube circumference, by means of which a flow rate is determined by means of a magnetic field,

characterized,

that more than one evaluation unit is used, which perform measurements independently or synchronized and thereby a redundancy of the measurement is achieved.

15. The method according to any one of the preceding claims,

characterized,

that a multiplicity of data are stored in an adaptive data field, whereby specific patterns for filling height determination, for

Foaming in the flowing medium, for sedimentation and for conductive deposits on the inner surface of the measuring tube are created, and from patterns of values on fill levels and / or foaming in the medium and / or sedimentation and / or conductive deposits on the inner surface of the measuring tube is closed.