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 magnetic-inductive flowmeter with a measuring tube, which is traversed by a medium substantially in the direction of the measuring tube axis, with a magnet arrangement which generates a measuring tube penetrating and extending substantially perpendicular to the measuring tube axis, alternating magnetic field with two measuring electrodes arranged essentially on a connecting line, wherein the connecting line is oriented substantially perpendicular to the measuring tube axis and to the magnetic field, and with a control / evaluation unit which determines the volume or mass flow of the medium on the basis of the measuring voltage tapped off at the measuring electrodes determined by the measuring tube.
• Magnetic-inductive flowmeters exploit the principle of electrodynamic induction for the volumetric flow measurement: vertically to a magnetic field moving charge carriers of the medium induce in equally substantially perpendicular to the flow direction of the medium arranged measuring electrodes a voltage. This measuring voltage induced in the measuring electrodes is proportional to the mean flow velocity of the medium over the cross section of the measuring tube; it is therefore proportional to the volume flow. In the case of a known density of the medium, it is also possible to make a statement about the mass flow of the medium flowing through the measuring tube.
• the measuring electrodes are usually galvanically or capacitively coupled to the medium.
• the invention has for its object to improve a magnetic-inductive flowmeter to the effect that it provides information regarding a defect of the meter or individual components of the meter.
• the object is achieved in that the control / evaluation unit determines the current settling time until a stable measuring state of the measuring device is reached, that the control / evaluation unit reaches the actual settling time with a desired setpoint time for the measuring device until it is reached the stable measurement state compares and that the control / evaluation generates an error message when the actual settling time is greater than the predetermined target settling time.
• Under settling time is In this case, it is understood that it takes the time it takes for the magnetic-inductive flowmeter to reach a stable operating state after commissioning.
• the measuring device achieves this stable operating state via an iterative approximation process during which the control variable / control variables for, for example, the optimum sensor-specific switching of the magnetic field are / are determined. Corresponding approximation processes have already become known from the prior art and will be explained in more detail below. If the usual, predetermined settling time of the flowmeter is exceeded at a later time, this is an indication that there is a defect in the flowmeter.
• control / evaluation unit generates the error message when the deviation between the current actual settling time and the setpoint settling time until reaching a stable measuring state of the measuring device is outside a predetermined tolerance value.
• the control / evaluation unit generates the error message that the mechanical stability of the magnet arrangement is disturbed due to an actual settling time exceeding the predetermined target settling time until a stable measuring state of the measuring device is reached .
• an extended settling time is an indication that e.g. the attachment of the pole pieces of Magnetanordung is no longer given.
• the vibrations caused by the mechanical instability when switching the magnetic field substantially lengthen the settling time of the coil current. According to the invention, therefore, a mechanically unstable magnet system is reliably detected by monitoring the settling time.
• the target settling time is the time it takes for the measuring device to have determined an optimum value for at least one control variable.
• the control variable is a sensor-specific variable, in particular the magnetic field strength or the coil current flowing through a coil arrangement of the magnet arrangement after switching the magnetic field.
• the sensor-specific variable or the control variable preferably via an iterative approximation process, wherein the approximation process starts with a predetermined starting value of the sensor-specific variable or the control variable.
• the sensor-specific variable or the control variable, which the control / evaluation unit determines iteratively is the minimum period of time it takes to reach that through the coil arrangement flowing current has a substantially constant current end value has reached.
• the switching of the magnetic field is controlled by the current flowing through the coils of the magnet assembly coil current.
• the current profile in the coil arrangement corresponds to the course of the magnetic field. Due to eddy currents, which occur during the switching of the magnetic field in the pole shoes and cores of the coil assembly, deviations from the ideal case occur in reality.
• the coil current measured outside the coil arrangement therefore corresponds to the sum of the current flowing in the coil and the current generated by the eddy currents. If the current measured outside the coil arrangement is used as the controlled variable, then the current is not constant but the magnetic field is constant. This applies as long as the eddy currents have not decayed.
• EP 0 969 268 A1 proposes not to use the current directly for tracking the voltage across the coil arrangement.
• an overvoltage is applied to the coil assembly upon switching the magnetic field for a rise time.
• the duration of the over-voltage is successively adjusted so that the current maximum is reached with the end of the rise time, so that no further increase of the coil current occurs.
• the coil current asymptotically approaches the final current value.
• the magnetic field has a constant maximum magnetic field value corresponding to the constant current end value when the current maximum is reached.
• the duration of the switching phase is given by the characteristic of the coil current. Since the stability of the measuring signal u.a.
• the measured values determined during a switching phase are used to optimize the period of time sh ⁇ il for the subsequent switching phase.
• the procedure is as follows:
• the control / evaluation unit sets during a first switching operation for a predetermined period of time
• control / evaluation unit detects a plurality of current measured values within the predetermined period of time
• control / evaluation unit checks the actual settling time in predetermined periodic or aperiodic intervals.
• control / evaluation unit triggers the determination or the verification of the actual settling time by means of a command.
• FIG. 1 a schematic representation of the flowmeter according to the invention
• FIG. 2 shows a flow chart for controlling the control / evaluation unit.
• Fig. 1 shows a schematic representation of an embodiment of the flowmeter according to the invention 1.
• the measuring tube 2 is flowed through by the medium 11 in the direction of the measuring tube axis 3.
• the medium 11 is at least to a small extent electrically conductive.
• the measuring tube 2 itself is made of a non-conductive material, or it is lined at least on its inner surface with a non-conductive material.
• the magnetic field B oriented substantially perpendicular to the flow direction of the medium 11 is generated via the diametrically arranged coil arrangement 6, 7 or via two electromagnets. Under the influence of the magnetic field B, charge carriers located in the medium 11 migrate, depending on the polarity, to one of the two oppositely poled measuring electrodes 4, 5.
• the voltage which builds up on the measuring electrodes 4, 5 is proportional to the flow velocity of the medium 11, averaged over the cross section of the measuring tube 2. H. it is a measure of the volume flow of the medium 11 in the measuring tube 2.
• the measuring tube 2 is incidentally via connecting elements, for. As flanges, which are not shown separately in the drawing, connected to a pipe system through which the measuring medium 11 flows.
• the measuring electrodes 4, 5 are in direct contact with the measuring medium 11;
• the coupling can also be capacitive, as already mentioned above.
• the connection between the coil arrangements 6, 7 and the control / evaluation unit 8 takes place via the connection lines 14, 15.
• the control / evaluation unit 8 is connected via the connection line 16 to an input / output unit 9.
• the evaluation / control unit is assigned to the memory unit 10.
• a flowchart for controlling the control / evaluation unit 8 is shown.
• the starting values for the individual control variables are each provided as a function of the iterative approximation process used. If, for example, the iterative approximation process proposed in EP 0 969 268 A1 is used, start values for the rise time during which an overvoltage is applied to the coil arrangement and the overvoltage itself must be specified.
• the desired settling time is determined via the selected iterative approximation process; under program item 21, the determined target settling time is stored.
• the measuring device 1 is determined at a later time - for example, after a re-commissioning of the flowmeter 1 - the actual control time until reaching a stable operating state and compared with the stored target delay time. If the actual control time exceeds the predetermined setpoint control time by a period ⁇ , this check is made under program point 23, this is an indication of a mechanical defect on the measuring device which has effects on the correct switching of the magnetic field , In this case, an error message is output at program point 24.
• the defect is, for example, a loosening of the magnet assembly due to a loose attachment. Due to the mechanical instability of the magnet arrangement and the vibrations excited subsequently when the magnetic field is switched on, the regulation of the coil current and consequently the desired settling time are prolonged.
• the actual settling time is again determined at a suitable later point in time and compared with the predetermined target settling time.

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

Applications Claiming Priority (2)

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• 2005
  • 2005-10-20 DE DE102005050655A patent/DE102005050655A1/de not_active Withdrawn
• 2006
  • 2006-09-22 WO PCT/EP2006/066638 patent/WO2007045540A1/de active Application Filing
  • 2006-09-22 RU RU2008119820/28A patent/RU2396522C2/ru not_active IP Right Cessation
  • 2006-09-22 EP EP06806799A patent/EP1941242A1/de not_active Ceased
  • 2006-09-22 US US12/083,693 patent/US8220342B2/en active Active
  • 2006-09-22 CN CN2006800391314A patent/CN101310166B/zh not_active Expired - Fee Related

Non-Patent Citations (1)

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