WO2019121101A1

WO2019121101A1 - Method for detecting defects in the signal line between a measuring electrode and a measuring and/or evaluation unit of a magneto-inductive flowmeter

Info

Publication number: WO2019121101A1
Application number: PCT/EP2018/084163
Authority: WO
Inventors: Markus RÜFENACHT; Andre Spahlinger; Mihai Vitanescu
Original assignee: Endress+Hauser Flowtec Ag
Priority date: 2017-12-20
Filing date: 2018-12-10
Publication date: 2019-06-27
Also published as: DE102017130720A1

Abstract

The invention relates to a method for detecting a defect in a signal line (4) of a first measuring electrode (E1 or E2) of a magneto-inductive flowmeter (1) and in a measuring and/or evaluation unit (7) of the magneto-inductive flowmeter (1), wherein the magneto-inductive flowmeter (1) at least the measuring and/or evaluation unit (7) and a measuring tube (2) having at least two measuring electrodes (E1, E2) comprising the first measuring electrode (E1 or E2) of a third electrode (EPD), which is defined as the EPD electrode, for detecting the filling level of the measuring tube (2), and a grounding electrode (GND), wherein the method for detecting defects has the following steps: a) providing an excitation voltage signal on the EPD electrode (EPD); b) tapping off a first measured signal with reference to ground on the first measuring electrode ( E1); c) tapping off a second measured signal with reference to ground on the second measuring electrode (E2); and d) comparing the two measured signals to detect the defect in the signal line (4), and a magnetoinductive flowmeter.

Description

Method for defect detection of the signal line between a measuring electrode and a measuring and / or evaluation unit of a magnetic inductive flowmeter

The present invention relates to a method for defect detection of

Signal line between a measuring electrode and a measuring and / or

Evaluation unit of a magnetic-inductive flowmeter and a magnetic-inductive flowmeter.

From the prior art, a number of impedance measurement methods and their evaluation in the field of magnetic-inductive flow measurement are known. Relevant in this context are u.a. EP 2 245 430 A2 and DE 10 2006 033 112 A1. Usually, the impedance measurements are used to determine the level or, if necessary, to perform a coating or corrosion detection of the measuring electrodes.

However, in the life cycle of a magnetic-inductive flowmeter in process measurement technology, it can happen that individual sensor components fail. While reviewing features and monitoring capabilities for

Magnetic systems or for the connection between magnet system and

Transmitters are already known, a defect monitoring of the signal line between individual electrodes, in particular the measuring electrodes, and the

Transmitter on a defect has so far been carried out only very limited.

In this context, however, GB 2 333 161. This document describes a cable break detection based on a capacitive measurement. In this case, a signal is generated by a power generator, which is characterized by a voltage ramp.

Furthermore, the generic WO 2016/102 193 A1 is known. In the practical implementation of this variant was excited with an AC voltage but the excitation is carried out on all electrodes, which is known to the measuring electrodes E1 and E1 and the flow measurement signal is tapped. However, this tap is disturbed because the measuring electrodes themselves carry a DC voltage which is not zero.

The present invention therefore sets in the task of a defect of

Signal line between a measuring electrode and a measuring and / or

Detecting evaluation unit in a magnetic-inductive measuring device, wherein However, this recognition or monitoring program disturbs the flow measurement to a lesser extent than has previously been the case.

The present invention solves this problem by providing a

Method with the features of claim 1 and by a magnetic-inductive flowmeter with the features of claim 10.

The present invention differentiates between defect detection and mis-measurement. While a faulty measurement only outputs a faulty measured value, the defect detection is concerned with the fact that individual electrodes of the measuring device due to a cable break, a dissolved contact or due to corrosion no electrical connection to the measuring and / or

Have evaluation of the meter.

An inventive method is used to detect a defect of a

Signal line between a first measuring electrode of a magnetic-inductive flowmeter and a measuring and / or evaluation unit of the magnetic-inductive flowmeter. In this respect, the method is a monitoring method which is continuous or temporal

Interruptions can be performed. In the latter case, the method can be carried out intermittently with a method for determining the filling state.

A filling state in the context of the present invention is preferably state such as "fully filled" and "partially filled or empty". An exact level indication of the measuring tube of a magnetic-inductive flowmeter is not necessarily in the context of the present invention for the determination of a

Filling state but it is only about the information whether the tube is filled to a measuring period fully.

The magneto-inductive flowmeter has, in a manner known per se, at least the aforementioned measuring and / or evaluation unit and a measuring tube.

The measuring tube is provided with at least two measuring electrodes, wherein the

the aforementioned measuring electrode is one of these two measuring electrodes. The

Measuring electrodes are used to tap a measuring voltage to determine the

Flow. They are typically, but not necessarily, diametrically opposed to the measuring tube.

In the installed position preferably at the highest point and preferably offset by 90 ° relative to the measuring electrodes on the inner circumference of the measuring tube is a third electrode arranged. This third electrode is defined in the context of the present invention as the EPD electrode. It serves to recognize the

Filling state of the measuring tube. EPD electrodes are themselves also u.a. from patent applications of the Applicant known.

Furthermore, according to the invention, a grounding electrode, also called a ground electrode, is provided on the measuring tube. Through the ground electrode is a

Measured value determination against grounding or ground possible. Typically, but not necessarily in the context of the present invention, the grounding electrode is arranged in the installed position in the lower region of the measuring tube.

The defect detection method according to the invention has the following steps: a Provision of an excitation voltage signal at the EPD electrode

The excitation signal, unlike in GB 2 333 161 A1, is not an excitation current signal generating a voltage ramp, but an excitation voltage signal. This excitation voltage signal is

preferably a square-wave voltage signal, which is preferably generated by a voltage source. The specification of the rectangular signal is carried out by a micro-controller of the measuring and / or evaluation. The voltage source generates a square wave signal with a fixed voltage value. The excitation voltage signal is passed through the medium in the measuring tube. b tapping a first measurement signal to ground at the first measuring electrode;

At the first measuring electrode, a tapping of a first measuring signal generated from the excitation voltage signal against ground or ground at the first measuring electrode takes place. The measurement between the ground electrode and the EPD electrode can be used as a reference to the measurement at the two

Measuring electrodes are used. c picking up a second measuring signal against ground at the second measuring electrode;

Analogously and in particular also simultaneously, a second measuring signal can be tapped off at the second measuring electrode. d Comparison of the two measuring signals to detect the defect of the signal line Finally, by comparing the two measurement signals, for example by quotient or difference formation and comparison with a desired value, a defect in the signal line, eg a cable break or cable break, can be detected.

Further advantageous embodiments of the invention are the subject of

Dependent claims.

The rectangular voltage signal preferably has a constant amplitude or a constant voltage value. The square-wave signal can therefore have a first voltage value, e.g. Zero and a second voltage value e.g. 250 mV, wherein the second voltage value is to be understood as the aforementioned constant voltage value.

The excitation voltage signal at the EPD electrode is preferably designed as an AC signal. While a DC signal causes disturbances in the flow measurement, these disturbances do not occur in the AC operation of the measurement or only to a very limited extent.

In step d), a comparison value can be determined from the two measurement signals, which is compared with a setpoint value, and if the setpoint is overshot or undershot, a cable break or a defect of the signal line is displayed.

In addition, a defect of the ground electrode can be detected, provided that both the first and the second measurement signal and a third measurement signal whose tap against ground at the EPD electrode, a second set value, e.g. exceed a high voltage of 1 volt. Unlike the signal for comparing a defect of the signal line of the measuring electrodes, which is done by comparing the measurement of the two measuring electrodes, a defect of the signal line of the

Ground electrode against an absolute value, so the setpoint detected.

The magneto-inductive flowmeter can advantageously have a bandpass filter for signal conversion of the rectangular signal into a DC signal having corresponding amplitudes, which is arranged between the measuring electrode (s) and the measuring and / or evaluation unit.

The magneto-inductive flowmeter can also have a bandpass filter, preferably the aforementioned bandpass filter, which is arranged between the EPD electrode and the measuring and / or evaluation unit. On corresponding voltage divider for the conduction of the excitation signal and the measurement signal can also be provided.

A magnetic-inductive flowmeter according to the invention comprises a measuring tube with at least two measuring electrodes, a third electrode for detecting the filling state of the measuring tube and with a grounding electrode, wherein the magnetic-inductive flowmeter at least one measuring and / or

Evaluation unit comprises, which is designed for carrying out the aforementioned method according to the invention.

A magnetic-inductive flowmeter according to the invention can advantageously have a first operating mode in which the aforementioned method is carried out and a second operating mode in which the degree of filling by the EPD electrode is determined.

It is possible to change between the two operating modes, for example at periodic intervals, which is determined by the measuring and / or evaluation unit.

The invention will be explained in more detail with reference to the accompanying figures by means of an embodiment. Show it:

Fig. 1 is a schematic circuit diagram with impedances between individual electrodes;

Fig. 2 is a schematic circuit diagram relating to the circuit diagram for operating the empty tube detection electrode;

The measuring principle of a magnetic-inductive flowmeter is

basically known. According to Faraday's law of induction, a voltage is induced in a conductor moving in a magnetic field. With the magnetic-inductive measuring principle, the flowing medium corresponds to the moving conductor.

A generic magnetic-inductive flowmeter is shown in WO 2016/102193 A1, to which reference is made in full with regard to the structure s of a magneto-inductive flowmeter.

Fig. 1 of the present application shows a much simplified representation of a magnetic-inductive flowmeter 1 with a measuring tube 2 and Magnetic field generating coils 3 and MS, which are operated via a measuring and / or evaluation unit.

At a measuring tube 2 of this magnetically inductive two diametrically

opposite measuring electrodes E1, E2 provided which at a

Arrangement of two field coils 3 are preferably arranged offset by 90 ° to the field coils 3 on the measuring tube 2. The measuring electrodes E1, E2 pick up the voltage generated during the flow of the medium or medium to be measured. The induced voltage is proportional to the flow velocity and thus to the volume flow. The magnetic field formed by the field coils 3 is preferably generated by a clocked DC alternating polarity. This ensures a stable zero point and makes the measurement insensitive to influences by multiphase substances, inhomogeneities in the liquid or low conductivity.

In addition to the two measuring electrodes E1, E2, the inventive magnetic-inductive flowmeter 1 in the illustrated

Embodiment variant, a ground electrode GND and a further electrode ERD, which often MSÜ electrode (medium pressure monitoring electrode),

Level monitoring electrode or EPD electrode (Empty Pipe Detection Electrode) is called.

Both electrodes are known in the art.

The EPD electrode monitors whether the measuring tube is completely filled during the measurement. This is preferably done by a conductivity measurement.

The measured values and / or the state of the individual electrodes are evaluated and / or monitored by a measuring and / or evaluation unit 7. Between the measuring and / or evaluation unit 7 and the measuring electrodes E1, E2, the EPD electrode EPD and the ground electrode GND, a cable line 4 is arranged, which transmits measuring signals to the measuring and / or evaluation unit 7. In FIG between the measuring electrodes E1 and E2 and the EPD electrode. In this case, the measuring path between the first measuring electrode E1 and the EPD electrode has a first impedance ZEPD.EI and the measuring path between the second measuring electrode E2 and the EPD electrode has a second impedance ZEPD, E2.

Further impedances are ZEI and ZE2 between the measuring electrodes E1 and E2 and the ground electrode GND and the impedance ZEPD between the EPD electrode EPD and the ground electrode GND.

In this case, the measuring path between the first measuring electrode E1 and the

Grounding electrode GND has a third impedance ZGND.EI and the measuring path between the second measuring electrode E2 and the grounding electrode GND has a fourth impedance ZGND, E2.

Furthermore, the measurement path between the ground electrode GND and the EPD electrode has a fifth impedance ZGND, EPD, and the measurement path between the second measurement electrodes E1 and E2 has a sixth impedance ZE1, E2.

According to the new method, AC square-wave voltages are applied to the EPD electrode in order to determine the impedances along the measuring path. The measurement and thus the tapping of the measurement signal takes place at the EPD electrode and at the measuring electrodes, preferably in series.

It is thus proceeded according to the following scheme

a) Excite at the EPD electrode and at the same time measure signal pickup at the EPD electrode

b) Measure at the EPD electrode at rain and at the measuring electrodes E1. c) excite at the EPD electrode and measure at the measuring electrode E2.

Some of the aforementioned measurement paths are the same size and the electrode types are likewise configured the same, therefore the ratio of the impedances ZEPD.EI and ZEPD, E2 ideally yields the value 1, 0. In many cases, however, deposits on the electrodes, flow disturbances and the like influence the ratio.

However, with a cable break, the impedance at the faulty electrode may be very large or approximately infinite in size. smaller

Impedance differences that are outside the predefined reference value may indicate errors due to heavy padding or asymmetric pad detection on the electrodes. Thus, with a cable break one of the

the aforementioned electrode, the impedance tends to infinity, even high limits for an impedance ratio are easily exceeded. If the

Impedances are therefore not in the sensor typical reference value range is a cable break before. The principle can also be used if distances B and C are not equal. As a cable break in the context of the invention, a cable break, for example, at the Lötstrecke to the corresponding electrode to understand.

In addition, a comparison of the impedances between the grounding and the EPD electrode with respect to the impedance of the measuring electrodes E1 and E2 can be made. In order to detect a cable break at this point by a comparison

Furthermore, analogously to WO 2016/102193 A1, a comparison of the measuring sections of the E1 with the grounding electrode and a comparison of the measuring section of the E2 with the

Grounding electrode done.

2 shows the structure of a circuit for operating the EPD electrode in the flowmeter 1 according to the invention. One recognizes a voltage source 10 and its impedance Z _que kke, an output signal U _excitation , the impedance of the

Medium Z _medium in the measuring tube 2 and a measuring signal U _measuring which is processed by a bandpass filter 1 1. Der _Medium wird dem Meßmedium U- _Mess .

In this case, the impedance measurement takes place at the EPD electrode by measuring the amplitude in the AC range. The circuit shown in Fig. 2 is fully AC operated. DC interference is thereby advantageously avoided. The impedances shown in Fig. 2 are also AC moderate to consider. It applies

Zmedium ^- Zquelle (1 UAnregung / ÖMess)

The application of a signal U _excitation as an excitation voltage signal in the form of a rectangular signal at the EPD electrode and a measurement of a

Voltage signal U _measurement taking into account the self - impedance of

Voltage source Zquelle-

The measurement of the voltage signal is a the measuring electrodes E1 and E2. This is unusual because the measurement signal is significantly lower than when tapped at the EPD electrode. However, a comparison of the impedances is still possible with intact signal lines. The influence of this measurement on the flow measurement is relatively low in this procedure.

The evaluation unit 7 comprises a micro-controller. The signal U _excitation is a square wave signal which is generated directly by the microcontroller by means of the voltage source shown in FIG. The voltage source is capacitively coupled to the microcontroller and has a constant impedance. The bandpass filter 11 then enables the generation of a sine signal from the square wave signal. The bandpass filter also makes it possible to dampen interference. These disorders can be due to various chemical or mechanical

Reactions to medium or tube appear.

The determination of a cable break and the monitoring of the measuring function of the EPD electrode can thus be achieved by direct measurement of the amplitude and / or the

Amplitude distribution of the square wave signal and by evaluation of this square wave signal.

The measurement is always carried out by excitation from the EPD electrode and by measuring the voltage at the measuring electrode EPD or E1 or E2, wherein the measuring signal is measured to ground. Therefore, the excitation signal is also transmitted to the ground electrode GND. A rapid increase of all three measurement signals, the two measuring electrodes E1 and E2 and the EPD electrode are tapped, indicates an interruption of the signal line 5 to the ground electrode.

reference numeral

1 magnetic inductive flowmeter

2 measuring tube

3 field coil

4 signal line or cable line

5 signal line

7 measuring and / or evaluation unit

11 bandpass filter

E1 measuring electrode

E2 measuring electrode

GND grounding electrode

EPD level monitoring electrode

Claims

claims

1. A method for detecting a defect of a signal line (4) a first measuring electrode (E1 or E2) of a magnetic-inductive flowmeter (1) and a measuring and / or evaluation unit (7) of the magnetic-inductive flowmeter (1), wherein the Magnetic-inductive flowmeter (1) at least the measuring and / or evaluation unit (7), and a measuring tube (2) with at least two measuring electrodes (E1, E2) comprising the first measuring electrode (E1 or E2) of a third electrode (EPD), which is defined as the EPD electrode, for detecting the filling state of the measuring tube (2), and a ground electrode (GND), wherein the method for defect detection comprises the following steps:

a Provision of an excitation voltage signal (U _excitation ) at the EPD electrode (EPD)

b tapping a first measurement signal against ground at the first measuring electrode (E1);

c picking up a second measuring signal against ground at the second measuring electrode (E2); and

d Comparison of the two measuring signals for detecting the defect of the signal line (4).

2. The method according to claim 1, characterized in that the

Excitation voltage signal (U _excitation ) is a square-wave voltage signal.

3. The method according to claim 1 or 2, characterized in that

the excitation voltage signal (UAnregung) by a

Voltage source (Z _qU eiie) is provided.

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

characterized in that the rectangular voltage signal has a constant amplitude.

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

characterized in that the excitation voltage signal (UAnregung) at the EPD electrode (EPD) is formed as an AC signal.

6. The method according to any one of the preceding claims, characterized characterized in that in step d) from the two measurement signals, a comparison value is determined, which is compared with a desired value, wherein in case of exceeding or falling below the desired value, a cable break is displayed.

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

characterized in that in addition a defect of the signal line (5) at the ground electrode (GND) is detected, provided that both the first and the second measurement signal and more preferably also a third measurement signal whose tap against ground at the EPD electrode, a second Exceed setpoint.

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

in that the magnetic-inductive flowmeter (1) has a bandpass filter (11) which is arranged between the measuring electrode (s) (E1, E2) and the measuring and / or evaluation unit (7).

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

in that the magnetic-inductive flowmeter (1) has a band-pass filter (11), which is arranged between the EPD electrode (EPD) and the measuring and / or evaluation unit (7).

10. Magnetic-inductive flowmeter (1) comprising a

Measuring tube (2) with at least two measuring electrodes (E1, E2), a third electrode (EPD), for detecting the filling state of the measuring tube (2) and with a ground electrode (GND), wherein the magnetic-inductive flowmeter (1) at least one measuring - And / or evaluation unit (7), which is designed for carrying out a method according to one of the preceding claims.