Method of operating a magnetic inductive flowmeter

Abstract

The invention relates to a method for operating a magnetic-inductive flowmeter (1), wherein the magnetic-inductive flowmeter (1) comprises a measuring tube (2) for conducting a flowable medium, at least two measuring electrodes (3) for detecting a measuring voltage induced in the medium which is dependent on the flow rate, and a magnetic-field generating device (4) for generating a magnetic field which passes through the measuring tube (2), wherein the magnetic-field generating device (4) comprises a coil system with at least one coil (5), characterized in that a deviation σ of the reactance of the coil system from a desired value or a deviation σ of a variable dependent on the reactance of the coil system from a desired value is determined. The invention also relates to a magnetic-inductive flowmeter (1).

Description

Technical Field

[0001] The present invention relates to a method for operating a magnetic induction flowmeter and a magnetic induction flowmeter. Background Technology

[0002] Magnetic induction flow meters are used to determine the flow rate and volumetric flow rate of a medium flowing in a pipe. A magnetic induction flow meter has a magnetic system that generates a magnetic field perpendicular to the flow direction of the medium. A single coil is typically used for this purpose. To achieve a predominantly uniform magnetic field, pole pieces are additionally formed and attached such that the magnetic field lines penetrate the entire cross-section of the pipe, thus being substantially perpendicular to the transverse axis or parallel to the vertical axis of the measuring pipe. Measuring electrodes attached to the side surface of the measuring tube tap an electrical measuring voltage or potential difference perpendicular to the flow direction and perpendicular to the magnetic field applied, and are generated when the conductive medium flows in the flow direction when the magnetic field is applied. Because, according to Faraday's law of induction, the tapped measuring voltage depends on the velocity and flow rate of the flowing medium. Q V Or the flow rate u, and the volumetric flow rate with the aid of a known pipe cross-section. It can be determined based on the induced measured voltage U.

[0003] Magnetic induction flow meters are commonly used in fluid processes and automation engineering, with conductivity reaching or exceeding approximately 5 µS / cm. The corresponding flow meters are sold by the applicant in various embodiments for a wide range of applications—for example, under the name PROMAG. Summary of the Invention

[0004] The purpose of this invention is to provide a method for operating a magnetic induction flow meter, which allows for the separate determination of the influence of an external magnetic field on flow measurement from its thermal effects.

[0005] This objective is achieved by the method according to the invention and the magnetic induction flowmeter according to the invention.

[0006] A method for operating a magnetic induction flowmeter according to the present invention, wherein the magnetic induction flowmeter comprises:

[0007] - Measuring tube, which is used to guide the flowable medium;

[0008] - At least two measuring electrodes for detecting a flow rate-related measuring voltage induced in the medium; and

[0009] - A magnetic field generating device for generating a magnetic field that passes through the measuring tube.

[0010] The magnetic field generating device has a coil system with at least one coil.

[0011] Its features are,

[0012] Determine the deviation between the reactance of the coil system and the expected value. s Or it depends on the deviation of the reactance of the coil system from the expected value. s .

[0013] Reactance is a frequency-dependent variable that limits alternating current by establishing an alternating voltage and causing a temporary phase shift between voltage and current. Reactance is the imaginary part of the complex impedance in complex alternating current calculations. The real part of the impedance is called the active resistance. The magnitude of the impedance is called the apparent resistance.

[0014] External magnetic fields affect the coil system of a magnetic induction flowmeter and cause measurement errors in the defined flow measurement variable. According to the invention, to determine the effect of the external magnetic field, the deviation of the reactance of the coil or coil system from a predetermined rating is determined. Active resistors have a frequency range that is substantially insensitive to external magnetic fields. Within the same frequency range, even the smallest influence of an external magnetic field will cause a deviation of several percent in the reactance. Temperature-related measurements can show that thermal effects within the same frequency range essentially affect only the active resistor.

[0015] In one embodiment, this is achieved by means of a polynomial function, particularly based on deviation. s The corrected flow measurement value is determined by using the currently detected measurement voltage or a linear function of a variable that depends on the detected measurement voltage. Q V ,

[0016] The polynomial function may optionally have a correction factor. k .

[0017] The deviations of the flow measurement variable determined under external magnetic field interference from the reference measurement value without external interference, and the deviations of the reactance from the expected value. s Relevant. Able to base decisions on bias. s Correction was achieved using polynomial functions. Further investigation revealed that, based on the bias... s It is sufficient to use a linear function of the current measurement voltage detected at the measuring electrode or the flow measurement variable that depends on the detected measurement voltage, so that the interference effect on the flow measurement can be compensated.

[0018] However, there are also applications where only the bias is used. s Simply correcting for the currently detected measurement voltage or a variable dependent on it is insufficient. In these cases, the additional use of a correction factor can further reduce flow measurement errors. This correction has been found to be particularly advantageous for battery-powered magnetic induction flow meters, whose coil systems typically operate at lower current intensities than in electrically powered magnetic induction flow meters.

[0019] According to another embodiment, the following applies to the correction factor. k 0.75≤ k ≤1.25, especially 0.95≤ k ≤1.05, and preferably 0.995≤ k ≤1.005.

[0020] In one embodiment, an excitation signal is provided at the coil system.

[0021] The excitation signal includes: a pulse sequence of one frequency, at least two pulse sequences each having at least one frequency, and / or at least one sinusoidal signal.

[0022] The excitation signal is used to operate the coil system and to generate a magnetic field with a constant magnetic field strength over time that passes through the measuring tube. The excitation signal can be a time-varying coil current or a time-varying coil voltage applied in a controlled manner.

[0023] The pulse sequence is preferably applied to the coil system in two consecutive measurement phases. It goes without saying that the measurement phases of the separately applied pulse sequence do not need to follow each other directly, and the pulse sequence does not need to be synchronized with the switching of the magnetic field. More precisely, the pulse sequence can be applied synchronously and asynchronously by means of the tapping of the measuring electrodes and the induced measuring voltage. The pulse sequence is, for example, a square wave pulse sequence. However, other types of pulse sequences, such as sinusoidal pulses or pseudo-noise, can be used in conjunction with this invention.

[0024] In one embodiment, the measurement signal is determined at the coil system.

[0025] Among them, at least for monitoring frequency f Ü The variables dependent on the reactance of the coil system are determined by means of transformation, particularly integral transformation and / or Fourier analysis of the time portion of the excitation signal and the time portion of the measurement signal, or the time portion of the variables depending on the excitation signal and / or the measurement signal.

[0026] When the excitation signal is the coil voltage, the measurement signal corresponds to the coil current.

[0027] It is advantageous to determine the reactance to transform the time portions of the excitation signal and the measurement signal, or the time portions of variables depending on the excitation signal and / or the measurement signal, from the time domain to the frequency domain, so as to obtain the spectrum belonging to the measurement signal and / or the excitation signal, or the spectrum belonging to the variables depending on the excitation signal and / or the measurement signal. Furthermore, in order to determine the deviation... s This determines the change in reactance in the spectrum. In this case, the deviation... sThe determination can include reactance across the entire spectrum or only a selected frequency of reactance, hereinafter referred to as the monitoring frequency. f Ü .

[0028] To determine the spectrum of reactance, one can either first convert the excitation signal and the measurement signal into a spectrum and then determine the reactance based on the quotient of the two signals, or first form a time signal of reactance based on the excitation signal and the measurement signal and then convert that time signal into a spectrum.

[0029] Suitable transformation methods include integral transform and Fourier analysis, where Fourier analysis includes Fourier series methods, continuous Fourier transform, discrete Fourier transform, and Fourier transform for discrete-time signals.

[0030] In one embodiment, regarding the monitoring frequency f Ü To determine the change in reactance or variable that depends on the reactance of the coil system.

[0031] In one embodiment, the following applies to monitoring frequencies. f Ü : 0.1 Hz ≤ f Ü ≤10 kHz Especially 1≤ f Ü ≤1,000 Hz And preferably f Ü ≤250 Hz .

[0032] Surprisingly, low-frequency values ​​have been found ( f Ü ≤10 kHz Especially ≤1 kHz And preferably ≤250 Hz ) monitoring frequency f Ü The spectral lines contain enough power to determine the deviation caused by the external magnetic field. s .

[0033] In one embodiment, the expected value of the reactance, or the expected value of a variable of the reactance depending on the coil system, describes the reactance in the adjusted state or the adjusted variable of the reactance depending on the coil system.

[0034] The required reactance value is determined during the adjustment process of the magnetic induction flowmeter. This takes place in a controlled and known environment. Alternatively, the desired value can also be determined via simulation methods.

[0035] The required reactance value is stored in the evaluation circuit of the magnetic induction flowmeter. The deviation in the currently determined reactance... s The evaluation circuit compares the result with the expected value.

[0036] In one embodiment, the variable that depends on the reactance of the coil system includes the apparent resistance of the coil system.

[0037] In one embodiment, the excitation signal corresponds to the coil exciter signal.

[0038] The coil exciter signal has at least one measurement phase, wherein the coil current is substantially constant and the induced measurement voltage is measured.

[0039] The coil exciter signal has a transient phase between two particularly continuous measurement phases, during which the coil current and / or the direction of the coil current in the coil system changes.

[0040] The coil exciter signal corresponds to the signal applied to the coil system in a conventional magnetic induction flowmeter to generate a constant magnetic field during the measurement phase. During the measurement phase, the measurement voltage induced in the medium is determined at the measuring electrodes. The function of the coil exciter signal is to generate a time-constant magnetic field during the measurement phase.

[0041] Coil exciter signals typically consist of essentially pulsed coil voltages or pulsed coil currents with a clock sign. There is always a range where the coil current and / or coil voltage is constant. Some embodiments also include coil exciter signals comprising two or more pulsed coil voltages, one of which is used to reduce the decay duration of the coil current and thus accelerate the generation of a time-constant magnetic field.

[0042] In one embodiment, the excitation signal corresponds to the coil exciter signal and an additional external diagnostic signal.

[0043] The coil exciter signal has at least one measurement phase, wherein the coil current is substantially constant and the induced measurement voltage is measured.

[0044] The coil exciter signal and the diagnostic signal each include: a pulse sequence of one frequency, at least two pulse sequences each having at least one frequency, and / or at least one sinusoidal signal.

[0045] Wherein, at least one frequency of the diagnostic signal is different from at least one frequency of the diagnostic signal, and / or the amplitude of the diagnostic signal is different from the amplitude of the coil exciter signal.

[0046] Furthermore, it is advantageous that the excitation signal consists not only of the coil exciter signal but also includes diagnostic signals. These diagnostic signals include: a pulse sequence at one frequency, at least two pulse sequences each having at least one frequency, and / or at least one sinusoidal signal. This also includes so-called pseudo-noise at multiple frequencies, i.e., the spectrum.

[0047] The excitation signal can have a phase between the coil exciter signals, in which a diagnostic signal is applied to the coil system. This can be achieved by increasing the time interval between pulsed coil voltages, or by temporarily interrupting the coil exciter signal.

[0048] According to an alternative embodiment, diagnostic signals can also be applied to coil exciter signals, but preferably away from the measurement stage.

[0049] The frequency and / or amplitude of the diagnostic signals are preferably different. This allows for the determination of deviations. s The sensitivity is set independently of the coil exciter signal during this period.

[0050] The magnetic induction flowmeter according to the present invention comprises:

[0051] - Measuring tube, which is used to guide the flowable medium;

[0052] - At least two measuring electrodes, said at least two measuring electrodes for detecting a flow rate-related measuring voltage induced in the medium; and

[0053] - Includes a magnetic field generating device for generating a magnetic field that passes through the measuring tube.

[0054] The magnetic field generating device has a coil system with at least one coil.

[0055] And it is characterized by,

[0056] The operation, measurement, and / or evaluation circuitry is configured to perform the method according to the invention. Attached Figure Description

[0057] The invention will be explained in more detail with reference to the following figures. They are shown below:

[0058] Figure 1 A perspective view of the magnetic induction flowmeter according to the present invention;

[0059] Figure 2 Examples of excitation signal B and measurement signal A in the time domain and related frequency domain;

[0060] Figure 3 Two other embodiments of excitation signal B and measurement signal A in the time domain. Detailed Implementation

[0061] The structure and measurement principle of the magnetic induction flowmeter 1 are known in principle (see...). Figure 1 A conductive medium is conducted through the measuring tube 2. The measuring tube 2 typically comprises a metal tube, plastic, or ceramic tube with an electrically insulating lining. A magnetic field generating device 4 is installed such that the magnetic field lines are oriented substantially perpendicular to the longitudinal direction defined by the axis of the measuring tube. A saddle coil or a pole shoe with a coil 5 mounted thereon is preferably suitable as the magnetic field generating device 4. When a magnetic field is applied, a potential distribution is generated in the flowing medium of the measuring tube 2, which is branched by two measuring electrodes 3 mounted opposite each other on the inner wall of the measuring tube 2. Typically, two measuring electrodes 3 are used, which are arranged radially and form an electrode axis that extends perpendicular to the axis of symmetry of the magnetic field lines and the axis of symmetry of the longitudinal axis of the measuring tube 2. Based on the measured voltage and considering the magnetic flux density, the flow rate of the medium can be determined, and considering the cross-sectional area of ​​the tube, the volumetric flow rate can be determined. If the density of the medium is known, the mass flow rate can be determined.

[0062] The magnetic field established by means of the coil and pole shoe arrangement is generated by a clockwise DC current flowing in an alternating direction. The operating circuit 6 is connected to the two coils 5 and is configured to apply an excitation voltage with a characteristic curve to the coil system. The operating circuit 6 is used to adjust the coil current or coil voltage.

[0063] Advantageous implementation of the characteristic curve of excitation signal B, for example Figure 1 and Figure 2 As shown. The polarity reversal of the coil voltage ensures a stable zero point and makes the measurement insensitive to the effects of multiphase substances, inhomogeneities in liquids, or low conductivity. The measurement and / or evaluation circuit 7 reads the voltage applied to the measuring electrode 3 and outputs the flow rate of the medium and / or the calculated volumetric flow rate and / or mass flow rate. In the magnetic induction flowmeter 1... Figure 1 In the cross-section shown, the measuring electrode 3 is in direct contact with the dielectric. However, coupling can also occur capacitively. According to the invention, the measuring and / or evaluating circuit 7 is also configured to determine a measuring signal A at the coil system. The measuring signal A includes the coil voltage actually present at the coil system and / or the coil current passing through the coil system.

[0064] According to the present invention, the measurement and / or evaluation circuit is further configured to convert the excitation signal B and the measurement signal A, or variables depending on the excitation signal B and the measurement signal A, into a spectrum, and determine the deviation of the reactance from the desired value based on the spectrum. s And based on the determined deviation s To calibrate the determined flow measurement value.

[0065] The display unit (not shown) outputs the determined deviation. s Or it depends on the determined deviation. sThe variables. Alternatively, if these deviations deviate from the stored setpoint values ​​or setpoint intervals, a message or warning can be output. The setpoint values ​​are determined using mathematical models, calibration methods, and / or simulation programs. However, this is insufficient, especially in applications related to drinking water. Therefore, the measurement and / or evaluation circuit 7 is configured to measure and / or evaluate the determined deviations. s To correct the measured voltage or the flow measurement variable that depends on the measured voltage. Deviation s It is not necessary to determine it across the entire spectrum or all individual frequencies, but rather for selected monitoring frequencies. f Ü To determine.

[0066] Figure 2 An embodiment of the excitation signal B and measurement signal A in the time domain is shown, along with the resulting spectra E and F in the frequency domain. According to this embodiment, the excitation signal B comprises a coil voltage, and the measurement signal A comprises a coil current. The coil voltage comprises two clock pulses with different pulse amplitudes and pulse widths. This excitation signal B corresponds to a typical coil exciter signal D.

[0067] After transforming the time components of the measurement and excitation signals, a spectrum with discrete frequencies is obtained in each case. In cases deviating from the expected value, the influence of the external magnetic field can be inferred from the frequency-dependent reactance. The measurement and / or evaluation unit is configured for a set monitoring frequency. f Ü This is used to monitor changes in reactance. According to the illustrated embodiment, the monitoring frequency is approximately 100 Hz. Hz .

[0068] Figure 3 Two embodiments of excitation signal B and measurement signal A are shown. In both embodiments, excitation signal B includes coil voltage, and measurement signal A includes coil current. The two embodiments are related to... Figure 1 The difference between the two embodiments is that, in addition to the coil exciter signal D, a diagnostic signal C is applied to the coil system. The difference between the two embodiments shown lies in how the diagnostic signal C is related to the coil exciter signal D.

[0069] The first of the two embodiments illustrates a characteristic excitation signal B, in which a diagnostic signal C is applied in addition to the coil exciter signal D. Excitation signal B is a superposition of the coil exciter signal D and the diagnostic signal C. That is, the coil exciter signal D and the diagnostic signal C overlap. The measurement signal A depends on the excitation signal B, and therefore the coil system responds to the diagnostic signal C. The diagnostic signal C must be time-shifted from the coil exciter signal D so that it does not extend into the measurement phase. The response of the measurement signal A to the excitation signal B is sensitive to external magnetic fields. Therefore, the frequency and / or amplitude of the diagnostic signal C are defined independently of the coil exciter signal D, enabling the use of measurement and / or evaluation circuitry to address external influences.

[0070] The second of the two embodiments also illustrates a characteristic excitation signal B, in which a diagnostic signal C is applied in addition to the coil exciter signal D. However, the coil exciter signal D is interrupted during the period when the diagnostic signal C is applied. The diagnostic signal C and the coil excitation signal D thus alternate.

[0071] List of reference numerals

[0072] 1. Magnetic induction flow meter

[0073] 2 measuring tubes

[0074] 3 Measuring Electrodes

[0075] 4. Magnetic field generating device

[0076] 5 coils

[0077] 6. Operating Circuit

[0078] 7 Measurement and / or evaluation circuits

[0079] A measurement signal

[0080] B Excitation Signal

[0081] C Diagnostic Signals

[0082] D coil exciter signal

[0083] The spectrum of the E-measured signal

[0084] The spectrum of the excitation signal F

[0085] f Ü Monitoring frequency

Claims

1. A method for operating a magnetic induction flowmeter (1), wherein, The magnetic induction flowmeter (1) includes: - Measuring tube (2), the measuring tube (2) being used to guide a flowable medium; - At least two measuring electrodes (3) for detecting a flow-velocity-related measuring voltage induced in the medium; and - Magnetic field generating device (4), the magnetic field generating device (4) is used to generate a magnetic field passing through the measuring tube (2), The magnetic field generating device (4) has a coil system with at least one coil (5); Its features are, Determine the deviation between the reactance of the coil system and the expected value. σ Or it depends on the deviation of the reactance of the coil system from the expected value. σ , Specifically, a measurement signal (A) is determined at the coil system, an excitation signal (B) is provided at the coil system, and Among them, at least for monitoring frequency f Ü The variable of reactance depending on the coil system is determined by means of integral transform and / or Fourier analysis of the time portion of the excitation signal (B) and the time portion of the measurement signal (A), or by integral transform and / or Fourier analysis of the time portion of the variable depending on the excitation signal (B) and / or the measurement signal (A).

2. The method according to claim 1, in, The corrected flow measurement value is determined by using a polynomial function. Q V , The polynomial function has a correction factor. k .

3. The method according to claim 2, in, By means of the deviation σ The corrected flow measurement value is determined by a linear function of the currently detected measurement voltage or a variable that depends on the detected measurement voltage. Q V .

4. The method according to any one of claims 1 to 3, in, The excitation signal (B) includes a pulse sequence of one frequency, at least two pulse sequences each having at least one frequency, and / or at least one sinusoidal signal.

5. The method according to any one of claims 1 to 3, in, Regarding monitoring frequency f Ü To determine the change in reactance or the change in the variable that depends on the reactance of the coil system.

6. The method according to claim 1, in, The following applies to the monitoring frequency. f Ü : 0.1 Hz ≤ f Ü ≤10 kHz 。 7. The method according to claim 6, in, The following applies to the monitoring frequency. f Ü : 1≤ f Ü ≤1,000 Hz 。 8. The method according to claim 6, in, The following applies to the monitoring frequency. f Ü : f Ü ≤250 Hz 。 9. The method according to claim 5, in, The following applies to the monitoring frequency. f Ü : 0.1 Hz ≤ f Ü ≤10 kHz 。 10. The method according to claim 9, in, The following applies to the monitoring frequency. f Ü : 1≤ f Ü ≤1,000 Hz 。 11. The method according to claim 9, in, The following applies to the monitoring frequency. f Ü : f Ü ≤250 Hz 。 12. The method according to any one of claims 1 to 3, in, The expected value of the reactance, or the expected value of the variable of the reactance depending on the coil system, describes the reactance or the variable of the reactance depending on the coil system in the adjusted state.

13. The method according to any one of claims 1 to 3, in, The variable that depends on the reactance of the coil system includes the apparent resistance of the coil system.

14. The method according to claim 4, in, The excitation signal (B) corresponds to the coil exciter signal (D). The coil exciter signal (D) has at least one measurement phase, wherein the coil current is substantially constant, and wherein a measurement of the induced voltage occurs. The coil exciter signal (D) has a transient phase between two measurement phases, during which the coil current and / or the direction of the coil current in the coil system changes.

15. The method according to claim 14, in, The coil exciter signal (D) has a transient phase between two consecutive measurement phases.

16. The method according to claim 4, in, The excitation signal (B) corresponds to the coil exciter signal (D) and the additional external diagnostic signal (C). The coil exciter signal (D) has at least one measurement phase, wherein the coil current is substantially constant, and wherein a measurement of the induced voltage occurs. Wherein, the coil exciter signal (D) and the diagnostic signal (C) each include: a pulse sequence of one frequency, at least two pulse sequences each having at least one frequency, and / or at least one sinusoidal signal. Wherein, at least one frequency of the diagnostic signal (C) is different from at least one frequency of the diagnostic signal (D), and / or the amplitude of the diagnostic signal (C) is different from the amplitude of the coil exciter signal (D).

17. A magnetic induction flowmeter (1), comprising: - Measuring tube (2), the measuring tube (2) being used to guide a flowable medium; - At least two measuring electrodes (3) for detecting a flow-velocity-related measuring voltage induced in the medium; and - Includes a magnetic field generating device (4) for generating a magnetic field that passes through the measuring tube (2). The magnetic field generating device (4) has a coil system with at least one coil (5); Its features are, The operation, measurement, and / or evaluation circuits (6, 7) are configured to perform the method according to any one of claims 1 to 16.

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