Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
  • G01F1/58—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by electromagnetic flowmeters
  • G01F1/60—Circuits therefor

Definitions

• the invention relates to a method for operating a process measuring device with which at least one physical measured variable, in particular a flow rate, a viscosity or the like, of a medium held in a process container or flowing in a process line is to be measured.
• the invention relates to a method for operating a magnetic-inductive flow meter, with which the volume flow of an electrically conductive and flowing liquid is to be measured.
• the process variables to be recorded in each case can be, for example, a volume flow, a mass flow, a density, a viscosity, a fill level or a limit level, a pressure or a temperature or the like, a liquid, powder, vapor or gaseous process Act medium that is carried or held in a corresponding process container, such as a pipeline or a tank.
• the process measuring device has a corresponding, mostly physical-electrical, measuring sensor, which is inserted into a wall of the container carrying the process medium or in the course of a process line leading the process medium and which is used to generate at least one, in particular electrical, measurement signal that represents the primary detected process variable as precisely as possible.
• the measuring sensor is also connected to a corresponding measuring device electronics, in particular also a further processing or evaluation of the at least one measuring signal. This usually has an operating circuit driving the measuring sensor and a measuring and evaluation circuit which further processes its measuring signals.
• Process measuring devices of the type described are usually also connected to one another and / or to corresponding process control computers via a data transmission system connected to the measuring device electronics, where they send the measured value signals e.g. Send via (4 mA to 20 mA) current loop and / or via digital data bus.
• the data transmission systems used here especially serial, fieldbus systems, e.g. PROFIBUS-PA, FOUNDATION FIELDBUS as well as the corresponding transmission protocols.
• the transmitted measured value signals can be further processed and e.g. visualized on monitors and / or in
• Control signals for process actuators e.g. Solenoid valves, electric motors etc., are converted.
• such process measuring devices further comprise an electronics housing which, e.g. in US-A 63 97 683 or the
• WO-A 00 36 379 proposed, arranged away from the process measuring device and can only be connected to it via a flexible line, or as also shown, for example, in EP-A 903 651 or EP-A 1 008 836, is arranged directly on the sensor or on a sensor housing which houses the sensor separately.
• the electronic housing as shown for example in EP-A 984248, US-A 45 94 584, US-A 47 16 770 or US-A 63 52 000, then often also serves to serve some mechanical components of the sensor to record, such as membrane, rod, sleeve or tube-shaped deformation or vibration bodies that deform operationally under mechanical influence, cf. also US-B 63 52 000 mentioned at the beginning.
• Flow meters with a magnetic-inductive flow sensor are often used to measure electrically conductive fluids.
• the volume flow of an electrically conductive liquid can be measured with magnetic-inductive flow meters and mapped into a corresponding measured value that flows in a pipeline; by definition, the volume of the liquid flowing through a pipe cross-section per unit of time is measured.
• Flow transducers of the type described usually each have a non-ferromagnetic measuring tube which is used in the pipeline in a liquid-tight manner, for example by means of flanges or screw connections.
• the part of the measuring tube that contacts the liquid is generally electrically non-conductive, so that a voltage is not short-circuited which, according to Faraday's law of induction, is caused by a magnetic field passing through the measuring tube Liquid is induced.
• Metal measuring tubes are therefore usually provided on the inside with an electrically non-conductive layer, for example made of hard rubber, polyfluoroethylene etc., and also generally non-ferromagnetic; in the case of measuring tubes made entirely of a plastic or a ceramic, in particular of aluminum oxide ceramic, the electrically non-conductive layer is not required.
• the magnetic field is generated by means of two coil arrangements, each of which, in the most common case, is arranged on the imaginary diameter of the measuring tube from the outside.
• Each coil arrangement usually consists of a coil without a core or a coil with a soft magnetic core. So that the magnetic field generated by the coils is as homogeneous as possible, in the most common and simplest case they are identical to one another and electrically connected in series in the same direction, so that the same excitation current can flow through them during operation. However, it has also already been described to have an exciting current flow through the coils alternately in the same or opposite directions, in order to be able to determine, for example, the viscosity of liquids and / or a degree of turbulence in the flow, cf. see also EP-A1 275 940, EP-A 770 855 or DE-A 4326 991.
• the above-mentioned excitation current is generated by a
• Operating electronics generated it is set to a constant current value of e.g. 85 mA regulated, and its current direction is periodically reversed.
• the reversal of the current direction is achieved in that the coils are located in a so-called T circuit or a so-called H circuit; for current regulation and reversal of direction cf. US-A 44 10 926 or US-A 6031 740.
• the induced voltage mentioned arises between at least two galvanic measuring electrodes, that is to say wetted by the liquid, or between at least two capacitive measuring electrodes, that is, for example, arranged within the tube wall of the measuring tube, each of the electrodes tapping a potential for itself.
• the measuring electrodes are diametrically opposed to one another arranged opposite one another so that their common diameter is perpendicular to the direction of the magnetic field and thus perpendicular to the diameter on which the coil arrangements lie.
• the induced voltage is amplified and processed by means of an evaluation circuit to form a measurement signal that is registered, displayed or in turn processed.
• Corresponding measuring electronics are also known to the person skilled in the art, for example from EP-A 814 324, EP-A 521 169 or WO-A 01/90702.
• the absolute value of the potential at the respective electrode is irrelevant for the measurement of the volume flow, but only on the condition that, on the one hand, the potentials are in the modulation range of a differential amplifier following the measuring electrodes, i.e. So that this amplifier must not be overdriven by the potentials, and that on the other hand the frequency of potential changes differs significantly from the frequency of the current direction reversal mentioned.
• the potential at each electrode is not only dependent on the magnetic field due to the Faraday law - this depends on the geometrical / spatial dimensions of the measuring tube and the properties of the liquid - but also on the Faraday law and as a purely desired use -Measurement signal, as already discussed in EP-A 12 73 892 or also in EP-A 1 273 891, has interference potentials of different origins superimposed, which in turn can make a considerable contribution to the deterioration of the measurement result.
• a first type of interference potential comes from inductive and / or capacitive interference, which emanate from the coil arrangements and their feed lines and change the electrical charge of the capacitor that exists at the interface between the electrode and the liquid. Because of asymmetries in the specific structure of the flow sensor, especially as regards the wiring to the coil arrangements and the measuring electrodes As a result, the interference potential of one electrode generally deviates from the interference potential of the other electrode.
• a second type of interference potential originates from particles of a foreign substance or from air bubbles which are carried along by the liquid and which, when they strike an electrode, cause sudden changes in their potential.
• the decay time of these changes depends on the type of liquid and is usually longer than the rise time of the changes.
• This - second - effect also leads to a disturbed useful measurement signal.
• the error caused by this also depends on the potential of the electrode.
• the second effect is added to the first effect, so that the individual specimens of the flow sensor show very different behavior, which is of course extremely undesirable.
• a third type of interference potential is caused by deposits on the measuring electrodes, which are deposited there by the liquid.
• the formation of the deposits depends very much on the speed of the liquid.
• the differences in the behavior of the individual specimens of the flow transducers can be increased even further by the formation of deposits.
• EP-A 1 273 892 proposes a method for operating a magnetic induction flow sensor, whereby the occurrence of the mentioned interference potentials, of whatever type, is thereby prevented or at least their effect is significantly reduced by using at least one of the two measuring electrodes by means of the evaluation and operating circuit generated voltage pulses are applied at least temporarily.
• the application of this method can primarily with single-phase or also with well-mixed multi-phase liquids to a considerable improvement in the measuring accuracy of magnetic-inductive
• a disadvantage of the above-described measuring method or corresponding flow sensor is that, for example, in the case of multi-phase liquids with a pronounced separation of the individual liquid phases or in mushy-viscous liquids with a rather stochastic, previously practically no longer sensible and therefore hardly calibratable distribution any foreign matter particles or gas bubbles that have been carried along are to be expected. To a corresponding extent, interference potentials of the second type can no longer be removed from the measuring electrodes to a sufficiently safe degree.
• the invention consists in a method for operating a process measuring device, in particular a magnetic-inductive flow meter, with a measuring tube which is inserted into the course of a line through which a medium, particularly a fluid, flows, which method comprises the following steps comprising:
• the invention consists in a magnetic-inductive flow meter for a fluid flowing in a line, which comprises: a measuring tube that can be inserted into the line for guiding the fluid,
• At least two measuring electrodes for tapping potentials which are induced in the fluid flowing through the measuring tube and permeated by the magnetic field, - Means at least temporarily connected to the measuring electrodes for generating at least one measuring signal derived from the tapped potentials and
• the evaluation and operating circuit detects an anomaly in the measurement signal based on the first data set, which is caused by at least one of the measuring electrodes applied interference, - extracts the detected anomaly from the stored first data set and generates a second data set free of the detected anomaly, and - by means of the second data record freed from the anomaly, generates at least one measured value which represents a physical quantity of the flowing fluid.
• the second data set also includes digital measurement data originally contained in the first data set.
• the step of detecting the anomaly comprises the step of determining a first time value based on the first data record, which time value is one Represents the time of onset of an interference voltage corresponding to the interference potential.
• the step of determining the first time value comprises the steps of comparing the digital data of the first data record with a predeterminable first threshold value and generating a first comparison value which signals that the first threshold value has been exceeded.
• the step of detecting the anomaly comprises the step of determining a second time value on the basis of the first data record, which time value represents a point in time of the disappearance of the interference voltage.
• the step of determining the second time value comprises the steps of comparing the digital data of the first data record with a predeterminable second threshold value and generating a second comparison value which signals that the second threshold value has been fallen below.
• the step of detecting the anomaly comprises the step of determining an amplitude value on the basis of the first data record, which amplitude value represents an amplitude of the measurement signal within the predefinable time interval, in particular the largest amount.
• the step of detecting the anomaly comprises the step of determining a third time value on the basis of the first data record, which time value represents a time of occurrence of the amplitude of the measurement signal within the predefinable time interval, in particular the largest amount.
• the step of detecting the anomaly comprises the step of forming a time difference between the first and the second time value for determining a fourth time value representing the duration of the occurrence of the interference voltage.
• the step of detecting the anomaly comprises the step of comparing the amplitude value with a predefinable, in particular variable third threshold value and generating a third comparison value which signals that the third threshold value has been exceeded.
• the step of generating the interference-free second data record comprises the step of determining an average value for the voltage induced in the flowing fluid using the measurement signal, in particular already digitized.
• the step of generating the interference-free second data set comprises the step of determining an average value for the voltage induced in the flowing fluid using digital data of the first data set.
• the step of generating the interference-free second data record comprises the step of determining an average value for the voltage induced in the flowing fluid using digital data with a time value that is less than the first time value.
• the step of generating the suppressed second comprises
• the step of generating the suppressed second data record comprises the step of generating an artificial third data record of digital data approximating the temporal course of the interference voltage, using at least part of the data from the data group representing the anomaly.
• the step of generating the artificial third data record comprises the step of determining at least one compensation function for at least some of the digital data from the data group representing the anomaly.
• the step of generating the artificial third data record comprises the step of generating digital data using data values from the data group representing the anomaly and using the determined compensation function.
• the step of generating the faulty second data record comprises the step of forming a difference between one of the data values from the data group representing the anomaly and one of the data values from the artificial third data record, the two each being Form the difference used data values have mutually corresponding, in particular the same, time values.
• the step of generating the at least one comprises Compensation function the step of determining at least one coefficient, in particular a time constant, for the compensation function using data values from the data group representing the anomaly.
• the step of generating the at least one compensation function comprises the step of determining a coefficient, in particular a time constant, for the compensation function using the mean value currently determined for the voltage induced in the flowing fluid.
• the step of determining the coefficient for the compensation function comprises the steps of forming a first difference between a first data value from the data group representing the anomaly and the mean value currently determined for the voltage induced in the flowing fluid, Forming a second difference between a second data value from the data group representing the anomaly and the mean value currently determined for the voltage induced in the flowing fluid and forming a quotient of the first and the second difference.
• the step of determining the coefficient for the compensation function comprises the steps of generating a digital coefficient sequence of provisional coefficients for the compensation function and digital, in particular recursive, filtering of the coefficient sequence.
• the step of generating the third data record comprises the step of determining at least one second compensation function for at least a second part of the digital data from the data group representing the anomaly.
• the exciter arrangement used comprises a coil arrangement for generating a magnetic field, in particular also penetrating the medium carried in the measuring tube.
• the sensor arrangement used comprises measuring electrodes arranged on the measuring tube and the method comprises the following further steps:
• a basic idea of the invention is to detect the highly variable interference potentials in the at least one measurement signal on the basis of anomalies corresponding to the interference potentials, in particular directly and in the time range or rather in the scanning range, which in at least one are provided by the sensor arrangement of the flow sensor
• Measurement signal or occur in digitally stored data records derived from the measurement signal.
• the invention is based on the surprising finding that interference potentials of the type described can be distributed in a highly stochastic manner, but the anomalies to be detected mostly have a typical course or a typical form, the detection of which both identifies such interference potentials in the digitally stored data records derived from the measurement signal and also a Clean them up by manipulation, in particular a non-linear digital filtering, which enables digital data affected by the interference potentials, the actual information contained in the measurement signal originally about the physical quantity to be measured being largely retained on the one hand and also for determining the measurement value on the other hand is made available very quickly.
• FIG. 1a, b show schematically and partly in the form of a block diagram a process measuring device which is suitable for the execution of the method of the invention, here a magnetic-inductive flow meter,
• FIGS. 1a, 1b schematically shows a time diagram of an excitation current flowing during operation of the process measuring device according to FIGS. 1a, 1b,
• FIGS. 3a, b schematically show time diagrams of potentials measurable during operation of FIGS. 3a, b process measuring device according to FIGS. 1a, 1b and FIGS. 4a, b, 5a, b
• FIGS. 1a, 1b schematically show digitally stored curves of measured potentials during operation of the process measuring device according to FIGS. 1a, 1b.
• FIG. 1 schematically and partly in the form of a block diagram shows a process measuring device which is suitable for the execution of the method of the invention - here designed as a magnetic-inductive flow meter - by means of which measured values for at least one physical quantity of a - Not shown here - pipeline flowing medium, in particular a fluid, can be generated.
• the flow meter can be used to measure a volume flow and / or a flow rate of an electrically conductive liquid.
• the flow meter shown here comprises a flow sensor 1 for generating measurement potentials corresponding to the physical quantity to be measured, an operating circuit 2 for detecting the measurement potentials and for generating at least one measurement signal corresponding to the physical quantity, as well as an evaluation circuit 3 which serves the operating circuit 2 and thus also to control the flow sensor 1 and to generate measured values representing the physical quantity using the at least one measurement signal.
• the operating circuit 2, and possibly also some components of the flow sensor 1, can be accommodated in an electronics housing 10 of the flow meter, for example, as indicated schematically in FIG. 1a.
• the flow sensor 1 includes a measuring tube 11 which can be inserted in the course of the above-mentioned pipeline and which has a tube wall and through which the fluid to be measured flows in operation in the direction of a measuring axis.
• an inner part of the measuring tube 11 that contacts the fluid is designed to be electrically non-conductive.
• Metal measuring tubes are usually provided with an electrically non-conductive layer, e.g. made of hard rubber, polyfluoroethylene etc., and also i.a. non-ferromagnetic; in the case of measuring tubes consisting entirely of a plastic or a ceramic, in particular of aluminum oxide ceramic, the electrically non-conductive layer is not required.
• FIG Embodiment An excitation arrangement of the flow meter controlled by driver electronics 21 provided in the operating circuit 2 has been shown in FIG Embodiment a first field coil 12 arranged on the measuring tube 11 and a second field coil 13 arranged on the measuring tube 11.
• the field coils 12, 13 lie on a first diameter of the measuring tube 11.
• the exciter arrangement is used in operation to generate a magnetic field H passing through the tube wall and the fluid flowing through it. This occurs when one of the field coils 12, 13 connected here in series the driver electronics 21 driven excitation current I is allowed to flow.
• the excitation current I in particular bipolar, can be rectangular, triangular or sinusoidal, for example.
• the field coils 12, 13 do not contain a core, that is to say they are so-called air coils.
• the field coils 12, 13 can, however, as is customary in the case of such coil arrangements, be wound around a core which in general. is soft magnetic, whereby the cores can interact with pole pieces, cf. e.g. US-A 55 40 103.
• the exciter arrangement which in the exemplary embodiment shown acts as an electromagnetic coil acting on the medium, is designed here, in particular the two field coils 12, 13 are shaped and dimensioned such that the magnetic field H thus generated within the measuring tube 11 at least with respect to a second one perpendicular to the first diameter Diameter is symmetrical, especially rotationally symmetrical.
• the driver electronics 21 generate a direct current, in particular regulated to a constant amplitude, which is then periodically switched by means of a corresponding switching mechanism configured, for example, in an H or T circuit, and thus to an alternating current with regulated Amplitude is modulated.
• the excitation current I is allowed to flow through the coil arrangement such that the coils 12, 13, as shown schematically in FIG. 2a, during a first switching phase PH 11 in each case in a first current direction and during a second switching phase PH12 following the first switching phase in one for flow through the opposite direction in the first current direction, cf. for current regulation and polarity reversal, for example, also US-A 44 10 926 or US-A 60 31 740.
• the second switching phase PH 12 is followed by a third switching phase PH21, during which the excitation current I flows again in the first current direction.
• the third switching phase is followed by a fourth switching phase PH22, during which the excitation current I flows again in the opposite direction.
• This is followed by a corresponding switching phase PH31 etc.
• two of the successive switching phases form a switching period P1, P2, P3, etc.
• the magnetic field H is also reversed, see FIG. Fig. 2a.
• a sensor arrangement arranged on the measuring tube or at least in the vicinity thereof is also provided in the measuring sensor.
• the sensor arrangement has electrodes practically directly attached to the measuring tube.
• the tube wall of the measuring tube 11 arranged first electrode 14 serves to tap a first potential e induced by the magnetic field H -
• a second electrode 15 arranged in the same way also serves to tap a second potential e ⁇ 5 induced by the magnetic field.
• the measuring electrodes 14, 15 lie on the second diameter of the measuring tube 11 perpendicular to the first diameter and to the longitudinal axis of the measuring tube, but they can, for example, also lie on a chord of the measuring tube 11 parallel to the second diameter, cf. see also US-A 56 46 353.
• the measuring electrodes 14, 15 are shown as galvanic measuring electrodes, that is to say as those which touch the fluid. However, two capacitive ones, that is to say for example arranged inside the tube wall of the measuring tube 11, Measuring electrodes are used. Each of the measuring electrodes 14, 15 taps an electrical potential eu, e- 15 which is induced in the fluid flowing through during operation due to Faraday's law.
• the measuring electrodes 14, 15 are at least temporarily connected to an inverting or non-inverting input of a differential amplifier 22 during operation.
• a potential difference of the two potentials e 1 , ice tapped by the measuring electrodes 14, 15 is thus formed, which corresponds to a voltage built up in the fluid flowing through and thus also to the physical quantity to be measured.
• the potentials e, ice applied to the measuring electrodes 14, 15 are usually approximately in the range from 10 mV to 100 mV.
• the measurement signal u present in the exemplary embodiment shown output of the differential amplifier 22 is, as shown schematically in FIGS. 1b, supplied to the evaluation circuit 3 provided in the flow meter.
• the evaluation circuit 3 serves, in particular, to digitize the supplied measurement signal u and to store sections of it in a first data record DS 1 , so that information about the temporal course of a section of the measurement signal u is available in digital form for determining the measured value XM ,
• the measurement signal u is fed to the evaluation circuit 3, as shown schematically in FIG. 1 a, in the exemplary embodiment shown via a low-pass filter 31 of a predefinable filter order, for example a passive or an active RC filter, and an adjustable cut-off frequency.
• the low-pass filter 31 serves to limit the measurement signal u in order to avoid aliasing errors and thus to preprocess it accordingly for digitization.
• the cut-off frequency is set to less than 0.5 times a sampling frequency with which the portion of the measurement signal u that is passed is sampled.
• the low-pass filter 31 can optionally also be dispensed with.
• the low-pass filter 31 is coupled to a signal input of an A / D converter (analog-to-digital converter) 32 of the evaluation circuit 3, which serves to convert the measurement signal u supplied via the low-pass filter 31 into a digital measurement signal UD representing it.
• the A / D converter 32 known to the person skilled in the art, e.g. serial or parallel converting, A / D converters can be used, which can be clocked with the sampling frequency mentioned above.
• a suitable A / D converter type is e.g. that of a delta-sigma A / D converter ADS 1252 from Texas Instruments Inc. with a resolution of 24 bits and a permissible sampling frequency of less than or equal to 40 kHz, wherein sampling frequencies of less than 10 kHz may be sufficient to implement the method according to the invention.
• a reference voltage of the A / D converter 32 is to be set accordingly so that an expected minimum signal value input of the converter is at least one bit, especially the highest significant bit (MSB). , of the measurement signal UD.
• MSB highest significant bit
• a DC component must be added to the signal present at the output of the low-pass filter 31 in such a way that it acts on the A / D converter 32 practically as a DC signal of variable amplitude.
• the digital measurement signal u D present on the output side of the A / D converter 32 is loaded segment by segment, for example via an internal data bus, into a volatile data memory 33 of the evaluation circuit 3 and there as a finite scan sequence AF inform representing the measurement signal u of an ensemble of digitally stored measurement data , in particular for a digital flow computer 34 of the evaluation circuit 3.
• data memories 33 can serve, for example, static and / or dynamic read / write memories.
• a width for a current scanning window i.e. a time length of the section of the scanning sequence AF to be stored, which currently represents the measurement signal u, can be, for example, in the range of the entire duration of one of the switching periods P1, P2 with which the excitation current I is clocked or also in the range of Duration of one of the switching phases PH11, PH12, PH21, PH22, the clocking with which data is read into the data memory 33 being accordingly essentially in phase with the clocking of the excitation current.
• Typical cycle times are in conventional memorized using conventional memorized data to obtain a number of 100 to 1000 samples, so in 1000 the stored samples from the sampling sequence AF or the first record would result.
• the switching phases PH11, PH12, PH21, PH22, PH31 mentioned above are each illustrated in an associated first partial period T111, T121, T211, T221, T311 and the associated second partial period serving as a measuring phase T112, T122, T212, T222, T312 divided, see 2a, 2b and 2c.
• this is illustrated in an associated first partial period T111, T121, T211, T221, T311 and the associated second partial period serving as a measuring phase T112, T122, T212, T222, T312 divided, see 2a, 2b and 2c.
• Embodiment of the invention in each case only virtually in the course of the measurement signal u associated with the respectively current second of the partial period durations T112, T122, T212, T222 or T312 in the data memory 33, the evaluation of the measurement data and the generation of the measurement value then in each case during the next Magnetic field build-up phase T121, T211, T221, T311 can take place.
• the flow computer 34 has, at least temporarily, access to the data memory 33 and the data records stored therein, in particular via data bus, for example via an internal data bus.
• the flow computer 34 can, for example, as shown schematically in FIG. 1 a, be advantageously implemented by means of a microprocessor 30 and computer programs running in it.
• the evaluation circuit 3 further comprises a memory manager 35 designed as a separate subcircuit, which communicates with the microprocessor 30, for example via an internal data bus, to manage the data memory 33, in particular the sampling of the digital measurement signal u D and control the generation of the scan sequence AF, and thus relieve the microprocessor 30.
• the memory manager 35 is preferably implemented in a programmable functional memory, for example a PAL (programmable array logic) or an FPGA (field programmable gate array). If necessary, the memory manager 35 can also be implemented by means of the microprocessor 30 or another microprocessor (not shown here) and corresponding computer programs running therein. By means of the memory manager 35 it is also possible, for example, to implement a mean or median formation, customary for such flowmeters, over a plurality of scanning sequences.
• FIGS. 3a, 3b also show curves of the potentials e ⁇ 4 , e- ⁇ 5 recorded over approximately 10 seconds, which are temporarily superimposed by interference potentials, with a region of the recorded potential curves ⁇ 4 , ice which is disturbed in the manner described 4a, 4b are shown again in a different time scale; compared 5a, 5b, undisturbed areas of the potential curves e ⁇ , e ⁇ shown in FIGS. 3a and 3b are shown again.
• an anomaly in the temporal course of the measurement signal u which is at least partially caused by an interference potential, in particular pulse-shaped interference voltage, applied at least to one of the measurement electrodes 14, 15, is detected by the fact that, as shown schematically in FIG. a data group DSA is determined within the stored first data record DSi, which digitally represents the anomaly. Furthermore, the anomaly detected in this way is extracted from the stored first data record DSi in order to generate an interference-free second data record DS 2, the interference-suppressed data record DS 2 finally being used to determine the measured value XM representing the physical quantity of the flowing fluid to be measured.
• an interference potential in particular pulse-shaped interference voltage
• the method of the invention is vorg Eye, for generating the interference-free data set DS 2 an average value for the U in flowing fluid induced voltage using a range of the measurement signal u or the already digitized measurement signal UD ZU to determine and keep available in the data memory 33 for further calculations.
• the determination of the mean value U can be derived from the measurement signal u using the currently stored data record DSi and / or using an earlier point in time using a current switching phase, preferably the immediately preceding switching phase or the preceding switching phase and cached data set.
• preference is given to using data which do not belong to the data group DSA representing the anomaly and which can therefore be regarded as essentially free of interference.
• the suppressed second data record DS 2 is generated during operation by means of the evaluation circuit 3 on the basis of at least a portion of the data from the previously located Anomaly representing data group DSA is calculated and possibly also buffered again in data memory 33.
• the suppressed second data record DS 2 can now be generated in an advantageous manner by first selecting a data value x from the data group DSA representing the anomaly and from the third data record DSK, the two selected data values x corresponding to one another, in particular, have the same time values i, and that a difference between the two currently selected data values x is formed numerically. This is repeated until all data values x from the data group representing the anomaly DSA have been used.
• At least one compensation function for at least some of the digital data from the data group representing the anomaly, DSA is determined by means of the evaluation circuit 3 during operation, and the artificial data record DSK is determined using the compensation function.
• the compensating function in particular the coefficient Ti for the compensating function
• the coefficient Ti for the compensating function one can, for example, use the Gaussian principle of algorithm based on the smallest error squares are programmed into the evaluation circuit 3 and are used by means of the same to the data group DSA currently held in the data memory 33.
• Voltage pulses is very similar.
• the interference potentials usually have a relatively steep rising edge followed by an essentially exponentially falling edge.
• provisional coefficients in particular a sequence of provisional coefficients, are first generated for the compensation function, for example by repeatedly applying the aforementioned calculation rule sequentially to different data pairs from the data group DSA representing the anomaly.
• the provisional coefficients determined are digitally filtered, for example individually in each case immediately after their calculation or only after the calculation of the entire coefficient sequence. Investigations have shown that, in particular using a recursive digital filter on the coefficient sequence, even with a low filter order, good, in particular robust and also reproducible measurement results can be achieved even with a large spectrum in the resulting interference potentials.
• the sequence of the provisional coefficients can be determined in accordance with the following instruction:
• f n - a preliminary coefficient for the compensation function, f n _, calculated in the calculation step currently being carried out.
• T n an intermediate value previously determined for the current calculation step and ⁇ , (1- ⁇ ) - predetermined filter coefficients for the digital filter, with 0 ⁇ ⁇ 1.
• the calculation rule is now applied until a predetermined number, for example the amount of data in the data group DSA representing the anomaly, has been subjected to arithmetic loops and / or until a previously selected termination criterion, for example a sufficiently low change between the last calculated preliminary coefficients , are fulfilled.
• the last calculated coefficient then corresponds to the coefficient T- ⁇ searched for the compensation function.
• the calculation of the coefficient is carried out using a corresponding coefficient determined in an immediately preceding measuring phase, this older coefficient then, for example, as one current provisional coefficient f n . can serve.
• the coefficient or coefficients for the compensation function is calculated using the mean value U currently determined for the voltage induced in the flowing fluid.
• this can e.g. are already numerically implemented when determining the intermediate values for the provisional coefficients based on the following calculation rule:
• the natural logarithm is also determined numerically from a quotient determined from the first and the second difference, to which a previously formed difference between the time values or indicia h, i 2 of the currently used data values Xu, Xj 2 is then standardized.
• a first time value t s is determined on the basis of the first data set DSi, which represents a point in time at which the interference voltage is set.
• the digital data of the first data record DSi can be compared, for example, with a predeterminable first threshold value TH S , which can be changed during operation, and a corresponding first comparison value can be generated which signals that the first threshold value TH S has been exceeded.
• the digital data of the first data record DSi can be compared, for example, with a predefinable second threshold value TH e , which can be changed during operation, and a corresponding second comparison value can be generated, which signals that the second threshold value TH e is undershot.
• the aforementioned comparisons actually relate to the magnitude of the measurement signal u. In the event that these comparisons are also to be made taking into account the sign of the measurement signal u, the threshold values TH S , TH e for negative voltages are to be determined vice versa.
• the threshold values TH S , TH e is determined during operation and adapted to the fluid currently flowing in the measuring tube 11, in particular to a flow measurement value determined for an earlier switching phase.
• the threshold value TH S or TH e can advantageously be formed using an average value U of the measurement signal u determined in an earlier, especially an immediately preceding or a recent, undisturbed measurement phase. This can be implemented in a particularly simple manner, for example, by increasing the threshold value during operation by a value that corresponds to the maximum increase in the measured value to be expected within the time that has now passed, or by a corresponding percentage.
• the anomaly is further detected in that at least one amplitude value and an associated third time value are determined on the basis of the first data set DSi, the amplitude value representing an amplitude of the measurement signal within the predefinable time interval, in particular the largest amplitude , Furthermore, it is provided to compare several or all of the data of the first data set DSi or only the amplitude value with a predeterminable third threshold value TH a, which can be changed during operation, in order to detect the anomaly.
• This threshold value is chosen to be larger than the first threshold value TH S and represents a predetermined minimum amplitude for a voltage surge to be detected as an anomaly.
• a corresponding third comparison value is generated, the signal exceeding the threshold value TH a.
• the digital data of the first record DSi for detecting the anomaly to be compared with a predetermined third threshold value TH A and is generated in a corresponding manner, the third comparison value, which signals exceeding the threshold value TH a.
• a time difference t e - t s is also formed between the previously determined first time value t s representing the onset of the interference voltage and the second time value t e representing the disappearance of the interference voltage to detect the anomaly, which represents the duration of the occurrence of the interference voltage.
• this fourth time value can in turn be compared with a corresponding fourth threshold value, which represents a predefinable minimum duration for a voltage pulse to be regarded as an anomaly to be eliminated.
• the mean value U for the voltage induced in the flowing fluid can be calculated using digital measurement data from the data record DSi, to which a time value is assigned which is less than the previously determined first time value t s and / or of digital measurement data of the data set DSi with a time value that is greater than the second time value t e .
• a further compensation function for at least a second part of the digital data from the data group DSA ZU representing the anomaly, for example a simple rising straight line for the rising edge of the interference voltage pulse, and the data of the to generate artificial data set DSK using this second compensation function.
• the evaluation circuit 3 can now be used in the usual manner, for example in US Pat. No. 4,382,387, US Pat. No. 4,422,337 or US Pat. No. 4,7 04,908 Flow measured value described, the measured value representing the physical quantity to be measured are calculated accordingly. As already mentioned, the determination of the flow, for example, is based on the
• Flow index a degree of turbulence of the flow or the like can be used.
• a corresponding signal amplifier can of course also be provided separately for each of the measuring electrodes 14, 15. Accordingly, for example, the potential difference between the two potentials tapped by the measuring electrodes 14, 15 e- ⁇ 4 , e- ⁇ 5 can also be calculated numerically using two separately digitized measuring signals.
• Both the evaluation methods required to generate the interference-free data record DS 2 by means of the data record DSi and the evaluation methods required to determine the measured values X M based on the interference-free data record DS 2 can be implemented in the manner known to the person skilled in the art, for example as a computer program running in the microprocessor 30.
• the program codes required for this can also be easily implemented in an, in particular permanent, writable memory 36 of evaluation stage 3, for example an EPROM, a flash EEPROM or EEPROM, to which the microprocessor 30 reads data during operation.
• the microprocessor 30 is implemented by means of a digital signal processor, for example of the TMS 320 C 33 type from Texas Instruments, Inc. If necessary, an additional signal processor can also be provided in the control unit 3, for example in addition to the microprocessor 30.
• the flow meter can, for example, be connected to a fieldbus, not shown, and can thus be connected to a remote control room and to an external power supply that feeds the flow meter, set via an internal supply unit 4.
• the flow measuring device further comprises a communication unit 5 with corresponding data interfaces 51.
• the communication unit 5 can also, in particular for visualizing measuring device data and / or for setting the flow measuring device on site to enable having a corresponding display and control unit 52.
• An advantage of the invention can also be seen in the fact that the determination of the measured values using the current first data record DS- ⁇ , in particular when there is no comparatively sluggish higher-order digital filter for the scanning sequence AF or for the first data record and when there is also no complex spectral analysis of the scanning sequence AF or the first data set in the frequency domain, performed comparatively promptly, even if the data set used is completely or partially disturbed. This can even be achieved for disturbances in the measurement signal u which are present over two or more measurement phases.
• the method according to the invention has, in addition to a very short computing time compared to digital filters of correspondingly higher order, which are comparable in effect, a much higher selectivity with regard to interference of the type described.

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• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Measuring Volume Flow (AREA)

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• 2003
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