METHOD FOR DEFECT DETECTION FOR THE SIGNAL LINE BETWEEN AN ELECTRODE AND A MEASURING- AND/OR EVALUATION UNIT OF A MAGNETO- INDUCTIVE FLOW MEASURING DEVICE

Abstract

A method for defect detection for a signal line between an electrode and a measuring- and/or evaluation unit of a magneto-inductive flow measuring device having at least one measuring- and/or evaluation unit, as well as a measuring tube with at least two measuring electrodes and a third electrode, comprising steps as follows: A) ascertaining a ratio of at least two measured electrical impedances between the measuring electrodes and/or between at least one of the two measuring electrodes and the third electrode; B) comparing the impedance ratio with a desired value range and C) outputting a defect report, when the impedance ratio exceeds or subceeds the desired value range, and a magneto-inductive flow measuring device.

Claims

1. Method for defect detection for a signal line (4) between an electrode (E1, E2, EPD, GND) and a measuring-and/or evaluation unit (7) of a magneto-inductive flow measuring device (1) having at least one measuring-and/or evaluation unit (7), as well as a measuring tube (2) with at least two measuring electrodes (E1, E2) and a third electrode (GND, EPD), comprising steps as follows: A) ascertaining a ratio of at least two measured electrical impedances (R.sub.E1, R.sub.E2, R.sub.EPD) between the measuring electrodes (E1, E2) and/or between at least one of the two measuring electrodes (El or E2) and the third electrode (EPD or GND); B) comparing a ratio (R.sub.x/R.sub.y) of the electrical impedances (R.sub.E1, R.sub.E2, R.sub.EPD) measured in step A with a desired value range, and C) outputting a defect report, when the impedance ratio exceeds or subceeds the desired value range.

2. Method for defect detection as claimed in claim 1, characterized in that the desired value range lies between 0.2 and 5.0.

3. Method for defect detection as claimed in claim 1, characterized in that the defect report indicates a signal line break, when the highest one of the impedances (R.sub.E1, R.sub.E2, R.sub.EPD) trends approximately toward infinity.

4. Method as claimed in claim 1, characterized in that the measuring of the impedances (R.sub.E1, R.sub.E2, R.sub.EPD) according to step A occurs by applying a voltage with at least one frequency, especially a number of frequencies, to a preresistor (R.sub.pre) on a measuring path composed of two of the aforementioned electrodes (E1, E2, EPD, GND) .

5. Method as claimed in claim 1, characterized in that the third electrode is a ground electrode (GND), by means of which a potential equilibration of the measured medium guided in the measuring tube (2) with the environment is effected.

6. Method as claimed in claim 1, characterized in that the third electrode is an EPD electrode (EPD), by means of which complete filling of the measuring tube (2) with measured medium is monitored during the measuring.

7. Method as claimed in claim 1, characterized in that impedance ratios of at least three measured impedances (R.sub.E1, R.sub.E2, EPD and GND) between each of the measuring electrodes (E1, E2) and the third electrode (GND or EPD), as well as, in given cases, additional electrodes, are ascertained and compared with the desired value range.

8. Method as claimed in claim 1, characterized in that the magneto-inductive flow measuring device (1) has a fourth electrode, especially an EPD electrode or a ground electrode.

9. Method as claimed in claim 1, characterized in that the magneto-inductive flow measuring device (1) has at least two measuring electrodes (E1, E2), an EPD electrode (EPD) and a ground electrode (GND) and at least three impedances between, in each case, one of three of the aforementioned electrodes (E1, E2 or EPD) and the fourth (GND) of the aforementioned electrodes are measured and evaluated by ratio formation and reconciliation with the desired value range.

10. Magneto-inductive flow measuring device, characterized in that the magneto-inductive flow measuring device (1) includes an operating mode, which works according to a method as claimed in claim 1.

Description

[0023] The invention will now be explained in greater detail based on the appended drawing illustrating examples of embodiments. The figures of the drawing show as follows:

[0024] FIG. 1 a schematic representation of a magneto-inductive flow measuring device;

[0025] FIG. 2 a schematic circuit diagram showing impedances between individual electrodes;

[0026] FIG. 3 a first schematic circuit diagram showing circuitry for ascertaining impedance between two electrodes;

[0027] FIG. 4 a second schematic circuit diagram showing circuitry for ascertaining impedance between two electrodes; and

[0028] FIG. 5 a simplified schematic circuit diagram showing circuitry options for ascertaining impedance between any electrode and a ground electrode.

[0029] The measuring principle of a magneto-inductive flow measuring device is basically known. In Faraday's law of induction, a voltage is induced in a conductor, which moves in a magnetic field. In the case of the magneto-inductive measuring principle, flowing measured medium corresponds to the moved conductor.

[0030] FIG. 1 shows the schematic construction of a preferred embodiment of a magneto-inductive flow measuring device 1 of the invention. It includes a measuring tube 2 and two field coils 3, which are arranged diametrally relative to one another at or in the measuring tube 2 and produce a magnetic field. Also more than two magnetic field producing elements, e.g. four field coils, can be provided.

[0031] Additionally provided at the measuring tube 2 arranged diametrally relative to one another are two measuring electrodes E1, E2, which in the case of an arrangement of two field coils are preferably arranged on the measuring tube offset by 90° relative to the fields coils. The measuring electrodes E1, E2 sense the voltage produced by the measured substance, or measured medium, as it flows through the measuring tube. The induced voltage is proportional to the flow velocity and therewith also to the volume flow. The magnetic field coming from the field coils 3 is preferably produced by a clocked, direct current of changing polarity. This assures a stable zero-point and makes the measuring insensitive to influences of multiphase materials, inhomogeneities in the liquid or low conductivity.

[0032] In addition to the two measuring electrodes E1, E2, a magneto-inductive flow measuring device 1 can have a ground electrode GND and/or another electrode EPD, which is often called the MSM electrode (measured substance monitoring electrode), the fill level monitoring electrode or the EPD electrode (empty pipe detection electrode). Both of these extra electrodes are known from the state of the art. The EPD electrode monitors, in such case, whether the measuring tube is completely filled during the measuring. This occurs preferably by a measuring of conductivity.

[0033] The magneto-inductive flow measuring device 1 shown in FIG. 1 also includes at least one EPD electrode EPD for monitoring the fill state of the measuring tube 2 and at least one ground electrode GND.

[0034] Known are also design variants of a magneto-inductive flow measuring device, in which only an EPD electrode EPD or only a ground electrode GND is used. These are likewise included in the subject matter of the present invention.

[0035] The measured values and/or the states of the individual electrodes are evaluated and/or monitored by a measuring- and/or evaluation unit 7.

[0036] Arranged between the measuring- and/or evaluation unit 7 and the measuring electrodes E1, E2, the EPD electrode EPD and the ground electrode GND is, in each case, a conductive line 4, which transmits measurement signals to the measuring- and/or evaluation unit 7 or to a wireless transmitting unit, which transmits measurement signals to the measuring- and evaluation unit 7. In all cases, of concern is a signal line in the sense of the present invention, even when a part of this signal line occurs wirelessly.

[0037] FIG. 2 shows in simple manner the basic idea of the present invention. The evaluation can be done, in principle, with the two measuring electrodes and any third electrode. In the case of filled measuring tube, e.g. the impedances R.sub.E2, R.sub.E1 and R.sub.EPD can be measured on the measuring electrodes E1 and E2 and on the EPD electrode against the ground electrode GND. These impedances are, among other things, dependent on the measured medium, the electrode form, the electrode material and also on the measuring path between the respective electrodes. Particularly also the geometric arrangement of the electrodes is to be taken into consideration.

[0038] Shown in FIG. 1 are a number of measuring paths A, B, C and D between the measuring electrodes, EPD electrode and the ground electrode. An electrode arrangement is symmetric in the sense of the present invention, when the shortest distance B of an electrode to the next neighboring electrode is equal in magnitude to a distance C of this next neighboring electrode to an additional electrode.

[0039] Henceforth for simplification, only impedances will be discussed; it is recognized that the explanations could, however, be provided based on conductances. The ratio of R.sub.EPD to R.sub.E1, R.sub.E2 or R.sub.E1∥ R.sub.E2 is independent of the medium due to the geometric arrangement of the electrodes, thus the measuring electrodes E.sub.1, E.sub.2 and the EPD electrode to the ground electrode GND. As one can see in FIG. 1, the measuring paths B and C of the GND electrode to a respective measuring electrode E1 or E2 are clearly smaller than the separation A between the two measuring electrodes E1 and E2. The ratio of the impedances R.sub.E1 to R.sub.E2, thus the impedances via the measuring paths B and C, can be taken into consideration for detecting a break of the signal lines. Since the two measuring paths are equally large and the electrode types are likewise equally embodied, the ratio of the impedances R.sub.E1/R.sub.E2 is in the ideal case 1.0. Often, in the real case, however, deposits on the electrodes, flow disturbances and the like influence the ratio.

[0040] In the case of a malfunction, the impedance on the defective electrode can be very large or approximately infinitely large. Smaller impedance differences, which lie outside of the predefined reference value, can indicate a defect due to strong accretion or an asymmetric accretion on the electrodes.

[0041] Since, thus, in the case of a signal line break, the impedance R.sub.E1 or R.sub.E2 tends toward infinity, even high limit values e.g. of 0.2 or of 5.0 for an impedance ratio are easily exceeded.

[0042] When the impedances R.sub.E1 to R.sub.E2 are not located in the desired value range relative to one another typical for the sensor, a signal line break is present. The principle can also be applied, when the distances B and C are not equal.

[0043] The terminology, signal line break, means in the context of the invention also a signal line break e.g. at the solder location for the corresponding electrode.

[0044] Problematic in the case of a comparison of a ratio of only two impedances is that the two compared impedances are measured through measuring paths from two electrodes, in the concrete case the measuring electrodes E.sub.1 and E.sub.2, to a common electrode, in the concrete case the ground electrode GND. If there occurs, thus, a signal line break on the signal line of the GND electrode, then, since the two impedance values trend toward infinity, the ratio of the impedances is again approximately 1 and the measuring device thinks there is no reason to display a signal line break.

[0045] Therefore, in an especially preferred embodiment, a checking of the ratios of the impedances on the measuring paths A, B and C should be done. If one of the ratios of the impedances lies outside of the desired value range, then a signal line break is present.

[0046] It is problematic further, when a measuring tube is only partially filled. In this case, a signal line defect would also be displayed. Here, an EPD electrode is used, in order to display the degree of filling of the measuring tube.

[0047] Additionally, one or more impedances between the EPD electrode and the ground electrode GND or one or all of the measuring electrodes E1, E2 are measured and their ratios formed and reconciled with predefined desired value ranges. In this way, also a verification of a signal line break can occur using the EPD electrode.

[0048] The determining of the impedances is performed by a per se known circuit of the EPD electrode or the GND electrode, either of which is, in most cases, already present in the magneto inductive flow measuring device. In given cases, switches are required, in order that the impedances of the individual electrodes can be measured. Switch arrangements are shown in FIGS. 3 and 4. In such cases, it is assumed that the impedance is always determined against the ground, or earth, potential. This is, however, not absolutely required.

[0049] The invention relates to no particular measurement circuit, but, instead, to the evaluation of the, most often, already present measured values, i.e. the impedances.

[0050] The comparison of the individual impedances serves for detecting whether a malfunction of the measuring electrodes, EPD electrode and/or, in given cases, the ground electrode is present. Therewith, the device can automatically perform a self-test, whether damage to these components is present. This can be registered continuously with existing hardware. The measuring- and evaluation unit 7 compares, in such case, the ratio R.sub.EPD/(R.sub.E1∥ R.sub.E2) with a reference value. If a deviation occurs, this is displayed as a signal line break. Since this detection functions especially with filled measuring tube, such is preferably only performed when the EPD electrode is sensing a full measuring tube.

[0051] Since most magneto-inductive flow measuring devices already are provided with corresponding electrode arrangements and circuit arrangements, an existing device can be retrofitted also with the above-described functionality of an electrode self check by a corresponding software update.

[0052] FIG. 3 shows a possible circuit, in which impedances between all electrodes 11 of the magneto-inductive flow measuring device FIG. 1 and the ground electrode GND are being compared. For such purpose, a usual measurement circuit for determining impedances is used.

[0053] It is, however, also possible to ascertain and to compare any first impedance and any second impedance on measuring paths between E1, E2, EPD and/or

[0054] GND by means of the measurement circuit 8. This is shown in FIG. 4.

[0055] FIG. 5 shows a simplified circuit arrangement of a preferred embodiment. The circuit arrangement is supplied with a voltage. This can have one frequency, preferably, however, a number of frequencies, especially three frequencies.

[0056] The voltage is led via a preresistor R.sub.pre to one of the electrodes E1, E2, GND or EPD. The impedance is in the case FIG. 5 always ascertained relative to the ground electrode GND. The measuring path for ascertaining the impedance is thus the path between the ground electrode GND and one of the electrodes E1, E2 or EPD. Then, two of these impedances are converted into a ratio, which is compared with a reference value.

REFERENCE CHARACTERS

[0057] 1 magneto inductive flow measuring device [0058] 2 measuring tube [0059] 3 field coil [0060] 4 signal line, or conductive line [0061] 8 measurement circuit [0062] 11 electrodes [0063] E1 measuring electrode [0064] E2 measuring electrode [0065] GND ground electrode [0066] EPD fill level monitoring electrode [0067] R.sub.E1 impedance from E1 to GND [0068] R.sub.E2 impedance from E2 to GND [0069] R.sub.EPD impedance from EPD to GND [0070] R.sub.pre preresistor