DE102008022370A1 - Method for determining reference values for measured values of a capacitance to be measured with a capacitive measuring device - Google Patents

Abstract

It is a method for determining reference values (R) for measured values of a probe (3) which is inserted horizontally into a container (1) which can be filled with at least one filling material (A, B) during measurement operation, serving as an electrode ( 5) which, together with the container (1) serving as the counterelectrode (13), forms a capacitor whose capacitance is to be measured during measurement operation by the measuring device (3), the capacitance to be measured which the capacitive measuring device (3) has when the container is empty (1) or in the case of a probe (5) completely covered with a single filling material (A, B), in which an approximation of a field line (F) of an electric field is established in the free space between the probe (5) and the counterelectrode (13) would form due to a voltage applied between probe (5) and counterelectrode (13), the probe (5) i is determined, for each segment (Sx) an average field line length (LFx), have the field lines (Fx) of the electric field originating from this segment (Sx) and the contribution of this segment (Sx) to the reference value (R) is determined approximately on the assumption that the respective segment (Sx) together with an area (Wx) the counterelectrode (13), to which the field lines (Fx) emanating from this segment (Sx), form a cylindrical capacitor whose inner electrode is defined by the segment (Sx) and its outer surface (Sx).

Description

The The invention relates to a method for determining reference values for measured values one with a capacitive measuring device with a horizontal in one with at least one medium refillable container built-in probe to be measured Capacitance of a probe serving as an electrode and the counter electrode serving as a container formed Capacitor.

capacitive Measuring instruments are used in level measurement technology used in a variety of industrial applications. you will be esp. for level measurement, for level monitoring and used for interface measurement. In level measurement is taken with the meter a in the container from the contents Level or a degree of filling determined. at The limit level monitoring is an over- or Below a predetermined level in the container monitored. Interface measurements are used when in the container two different products to each other. The border between the two contents becomes referred to as a release layer. Separating layers occur, for example in the petrochemical, where they z. By water and hydrocarbons, z. As oil, are formed. Another example is the Food industry, where separating layers, for example, in Form grease separators. Interface measurements make a special form the level measurement, and serve to the location of the separation layer in the container and / or the filling heights or the amount of the two products in the container determine.

usual Way, capacitive gauges have a rod-shaped Probe in the measuring mode in one with at least one medium refillable container is introduced. The probe serves as an electrode, which together with the container forms a capacitor. This forms the usual way grounded wall of the tank the counter electrode. The on this condenser has one of the current filling state container dependent capacity, by means of a suitably designed capacitance measuring circuit of the measuring device is detected.

usual The way the probe is used for level and interface measurement inserted vertically into the container. At the limit level measurement is regularly a horizontal in the Container inserted probe used for this purpose in the container at the height of the predetermined to be monitored Level is arranged.

The Applicant offers for these different measuring tasks a variety of different capacitive measuring devices at. The individual meter variants differ esp. by the best possible to the respective application adapted probe. For example, probes are more different Length available. In addition, a Isolation can be provided, which surrounds the probe. Also, the probe can from an inactive probe section and an adjoining one consist of serving as an electrode active probe section. The inactive Probe section denotes a fully shielded not acting as an electrode portion of the probe, the more common Way arranged in the field of container introduction is. Among other things, it serves to short circuits between the container wall surrounding this area and prevent.

If a capacitive measuring device for a specific measuring task is usually reviewed today by professionals, if necessary, an optimally tailored to this measurement task Select meter from the range that then can be obtained from the manufacturer. It will be through the Measuring task given boundary conditions, such. B. type and shape of the container, the desired installation of the Probe and the properties of the product or of the contents, considered. A key criterion in the review, whether the specified measuring task of a capacitive measuring device can be executed is to estimate whether a change caused by the measurand the measured capacity with the meter the measuring range is sufficiently large to a sufficiently accurate To ensure measurement of the measured variable. This estimate is usually based on two reference values for the expected capacity measurements in measuring mode performed. The first reference value is when the container is empty expected reading, and the second reference value at maximum Filling or when completely with the contents covered probe expected reading.

The reference values for capacitive measuring instruments with probes inserted vertically into the container can generally be determined or approximated by calculation instructions, as explained, for example, in the 1990 issue of: 'Level Measurement in Theory and Practice' by Wim vd Kamp. However, these calculation rules are generally not applicable to capacitive gauges with probes installed horizontally in the vessel. In practice, the reference values for capacitive measuring instruments with horizontally integrated probes are based on empirical knowledge that must be considered high safety margins or by reference measurements on site.

If a suitable capacitive measuring device could be found, the measuring device is installed at the measuring location and put into operation taken. During commissioning, an adjustment of the measuring device performed. The two reference values are measured determined by the capacity when empty container and at maximum filling of the container or with completely covered with the product probe be measured with the capacitive measuring device.

at the capacitive level monitoring is based on this two reference values a limit for the measured Capacity determines from which the meter is exceeding to indicate the predetermined level. This limit is stored, for example, as a switching point in the device.

Either checking if a given measurement task reliably executable with a capacitive measuring device is, the selection of an optimally designed for the measurement task capacitive measuring device from the large number of available on the market Meter variants, as well as the subsequent in the frame commissioning required adjustment of the corresponding meter require the determination of the reference values by correspondingly well trained staff. It can be the adjustment of the meter locally lead to change production processes or even have to be interrupted for a short time corresponding fill levels for obtaining the reference values to approach.

In The measurement and control technology are becoming increasingly computer-aided Systems already used today for a variety of measurement tasks are capable of a variety of different Measuring devices to select those meter types and to suggest that suitable for a given measurement task are. Also, there are some cases where such systems for a selected meter type from the available variety of variants of this type of meter select and propose that for the special application is optimally suited. Can do that be connected to electronic ordering and delivery, the the user an automatic order for his Application optimally suitable variant of the appropriate measuring device type allow.

Examples of this are in the DE 101 04 165 A1 , of the DE 10 2006 060441.5 and the DE 10 2006 060919.0 described.

In Connection with capacitive measuring devices is the use However, such systems only limited possible because already when checking whether a given measurement task be carried out by a capacitive measuring device can, detailed knowledge of the above Reference values are required to be able to judge whether by the measurand over the measuring range caused capacitance change enough is to get the measurand with sufficient accuracy to be able to determine.

For capacitive gauges with vertically installed probes is it already possible today the expected reference values to estimate mathematically as described above. Examples These are in the 1990 issue of: Füllstandsmesstechnik in theory and practice of Wim v. d. Kamp explained.

For horizontally installed probes, on the other hand, there are only or experience, usually only by professionals on the Area can be used meaningfully, and an experimental On-site reconciliation usually can not replace.

It It is an object of the invention to provide a method with which Reference values for measured values one with a capacitive Measuring instrument with a horizontally in a container built-in probe to be measured capacity can.

• – das eine im Messbetrieb horizontal in einen mit mindestens einem Füllgut befüllbaren Behälter eingeführte als Elektrode dienende Sonde aufweist, die zusammen dem als Gegenelektrode dienenden Behälter einen Kondensator bildet, dessen Kapazität im Messbetrieb von dem Messgerät zu messen ist,
• – die das kapazitive Messgerät bei leerem Behälter oder bei vollständig mit einem einzigen Füllgut bedeckter Sonde messen würde, bei dem
• – näherungsweise ein Verlauf von Feldlinien eines elektrischen Feldes ermittelt wird, das sich im freien Raum zwischen der Sonde und der Gegenelektrode aufgrund einer zwischen Sonde und Gegenelektrode anliegenden Spannung ausbilden würde,
• – die Sonde in zylindrische Segmente unterteilt wird,
• – für jedes Segment eine mittlere Feldlinienlänge bestimmt wird, die von diesem Segment ausgehenden Feldlinien des elektrischen Feldes aufweisen, und
• – der Beitrag dieses Segments zum Referenzwert näherungsweise unter der Annahme bestimmt wird, dass das jeweilige Segment zusammen mit einem Bereich der Gegenelektrode zu dem die von diesem Segment ausgehenden Feldlinien führen einen Zylinderkondensator bildet,
• – dessen innere Elektrode durch das Segment und dessen äußere Elektrode durch eine die innere Elektrode konzentrisch in einem der mittleren Feldlinienlänge entsprechenden Abstand umgebende hohlzylindrische Elektrode gebildet ist,
• – der bei leerem Behälter leer ist bzw. der bei vollständig mit dem Füllgut bedeckter Sonde vollständig mit dem Füllgut gefüllt ist, und
• – der Referenzwert anhand einer Mediumskapazität bestimmt wird, die der Kapazität einer Parallelschaltung dieser Zylinderkondensatoren entspricht.

For this purpose, the invention consists in a method for determining reference values for measured values of a capacitive measuring device,

• - Has a horizontally inserted in measuring operation in a filled with at least one medium container serving as an electrode probe which together forms the counter electrode serving as a capacitor whose capacitance is to be measured in the measuring operation of the meter,
• - which would measure the capacitive measuring instrument when the container is empty or when the probe is completely covered with a single product
• Approximately a course of field lines of an electric field is determined, which would form in free space between the probe and the counterelectrode due to a voltage applied between probe and counterelectrode,
• The probe is divided into cylindrical segments,
• For each segment, an average field line length is determined which has field lines of the electric field originating from this segment, and
• The contribution of this segment to the reference value is determined approximately on the assumption that the respective segment forms a cylindrical capacitor together with a region of the counterelectrode leading to the field lines emanating from this segment,
• The inner electrode of which is formed by the segment and the outer electrode thereof by a hollow cylindrical electrode surrounding the inner electrode concentrically in a distance corresponding to the average field line length,
• - Is empty with empty container or is completely filled with completely filled with the filling material probe with the contents, and
• - The reference value is determined based on a medium capacity, which corresponds to the capacity of a parallel connection of these cylinder capacitors.

According to one Further development of the method, the probe has a in the container protrude into inactive probe section, and the inactive Probe section is used to determine the course of the field lines considered as part of the counter electrode.

• – die Sonde von einer Isolation umgeben ist,
• – eine Isolationskapazität bestimmt wird, und
• – der Referenzwert anhand der Kapazität einer Serienschaltung bestimmt wird, in der die Isolationskapazität in Serie zu der Mediumskapazität geschaltet ist, wobei
• – die Beiträge der von der Isolation umgebenen Segmente der Sonde zur Isolationskapazität anhand von Zylinderkondensatoren bestimmt werden, deren innere Elektrode einen Außendurchmesser aufweist, der gleich dem Außendurchmesser des Segments ohne Isolation ist, deren äußere hohlzylindrische äußere Elektrode die innere Elektrode konzentrisch in einem Abstand umgibt, der gleich der Dicke der Isolation ist, und deren Innenraum vollständig mit dem Material der Isolation gefüllt ist, und
• – die Isolationskapazität gleich der Kapazität einer Parallelschaltung dieser Zylinderkondensatoren ist.

According to a further development, the invention comprises a method in which

• - the probe is surrounded by insulation,
• - an insulation capacity is determined, and
• - The reference value is determined by the capacity of a series circuit in which the isolation capacity is connected in series with the medium capacity, wherein
• The contributions of insulation isolation segments of the probe to insulation capacitance are determined by cylindrical capacitors whose inner electrode has an outer diameter equal to the outer diameter of the segment without insulation whose outer hollow cylindrical outer electrode concentrically surrounds the inner electrode at a distance, which is equal to the thickness of the insulation, and whose interior is completely filled with the material of the insulation, and
• - The isolation capacity is equal to the capacity of a parallel connection of these cylinder capacitors.

• – anhand der Leitfähigkeit des Füllguts für jedes Segment ein ohmscher Widerstand bestimmt wird, der gleich dem Widerstand ist, den eine den dem jeweiligen Segment zugeordneten Zylinderkondensator vollständig ausfüllende aus dem Füllgut bestehende Füllung zwischen der inneren und der hohlzylindrischen äußeren Elektrode des jeweiligen Zylinderkondensators ausbildet,
• – ein Mediumswiderstand bestimmt wird, der gleich dem Widerstand einer Parallelschaltung aller dieser ohmschen Widerstände ist,
• – und der Referenzwert anhand der Kapazität einer Hilfsschaltung bestimmt wird, in der die Isolationskapazität in Serie zu einer Parallelschaltung aus Mediumswiderstand und Mediumskapazität geschaltet ist.

Furthermore, the invention comprises a development of the method for determining the reference value for the measured value of the capacitance to be measured, which would measure the measuring device with completely covered with a conductive filling material probe with insulation, in which

• - Based on the conductivity of the medium for each segment, an ohmic resistance is determined, which is equal to the resistance, the one of the respective segment associated cylinder capacitor completely filling consisting of the filling material between the inner and the hollow cylindrical outer electrode of the respective cylindrical capacitor,
• A medium resistance is determined, which is equal to the resistance of a parallel connection of all these ohmic resistors,
• - And the reference value is determined based on the capacity of an auxiliary circuit in which the insulation capacity is connected in series with a parallel circuit of medium resistance and medium capacity.

• – wird das Messgerät im Messbetrieb bei einer Messfrequenz betrieben,
• – anhand der Messfrequenz ein Blindwiderstand der Hilfsschaltung bestimmt, und der Referenzwert wird anhand der Messfrequenz und des Blindwiderstandes bestimmt.

According to a development of the latter method

• - the measuring device is operated at a measuring frequency during measuring operation,
• - Determines a reactance of the auxiliary circuit based on the measurement frequency, and the reference value is determined based on the measurement frequency and the reactance.

• – wird ein Wirkwiderstand der Hilfsschaltung bestimmt,
• – es wird anhand des Blindwiderstandes und des Wirkwiderstandes eine durch die Hilfsschaltung bei der Messfrequenz bewirkte Phasenverschiebung bestimmt, und
• – der Referenzwert wird anhand der Messfrequenz, des Blindwiderstands und der Phasenverschiebung bestimmt.

According to another embodiment

• A resistance of the auxiliary circuit is determined,
• - It is determined based on the reactance and reactance caused by the auxiliary circuit at the measurement frequency phase shift, and
• - the reference value is determined on the basis of the measuring frequency, the reactance and the phase shift.

• – eine Messaufgabe vorgegeben wird,
• – für die Messaufgabe relevante Referenzwerte bestimmt werden, und
• – anhand der Referenzwerte überprüft wird, ob die Messaufgabe von dem kapazitiven Messgerät ausgeführt werden kann, indem anhand der Referenzwerte abgeschätzt wird, ob eine durch die Messgröße verursachte Änderung der zu messenden Kapazität über den Messbereich hinweg einen vorgegebenen Mindestwert überschreitet.

Furthermore, the invention comprises a verification method in which

• - a measurement task is specified,
• - reference values relevant to the measurement task are determined, and
• It is checked by means of the reference values whether the measuring task can be performed by the capacitive measuring device by estimating from the reference values whether a change of the capacitance to be measured caused by the measurand exceeds a predetermined min exceeds the minimum value.

• – durch die Messaufgabe vorgegebene anwendungs-spezifische Randbedingungen, insb. die Dielektrizitätskonstante und die Leitfähigkeit des oder der Füllgüter, die Behälterform sowie die Einbauhöhe, vorgegeben werden,
• – messgerät-spezifische Parameter, insb. die Länge der Sonde, die Länge des inaktiven Sondenabschnitt, die Länge des aktiven Sondenabschnitts und/oder das Material und die Dicke der Isolation, als Variablen betrachtet werden, die in einer mit den anwendungspezifischen Randbedingungen verträglichen Weise zur Findung eines für die Messaufgabe optimal geeigneten Variante des Messgeräts variiert werden,
• – für jede Variante jeweils die für die Messaufgabe relevanten Referenzwerte bestimmt werden, und
• – anhand der Referenzwerte diejenige Variante als optimal geeignet ausgewählt wird, bei der eine durch die Messgröße verursachte Änderung der zu messenden Kapazität über den Messbereich hinweg maximal ist.

The invention further comprises a selection method for selecting a variant of the capacitive measuring device which is optimally adapted to a given measuring task using reference values determined according to the invention, in which

• - Specified application-specific boundary conditions, in particular the dielectric constant and the conductivity of the material (s), the container shape and the installation height, specified by the measuring task,
• - Instrument-specific parameters, in particular the length of the probe, the length of the inactive probe segment, the length of the active probe segment and / or the material and the thickness of the insulation, are considered to be variables compatible with the application-specific constraints Finding a suitable variant of the measuring device for the measuring task can be varied,
• - for each variant, the relevant reference values for the measurement task are determined, and
• On the basis of the reference values, that variant is selected as being optimally suitable in which a change in the capacitance to be measured caused by the measured variable is maximal over the measuring range.

• – ein Referenzwert für den bei leerem Behälter zu erwartenden Messwert der gemessenen Kapazität und ein Referenzwert für den bei vollständig mit dem Füllgut bedeckter Sonde zu erwartenden Messwert ermittelt wird,
• – anhand der ermittelten Referenzwerte ein Grenzwert für die zu messende Kapazität ermittelt wird, ab dem das Messgerät ein Überschreiten des vorgegebenen Füllstandes anzeigen soll,
• – der Grenzwert im Messgerät abgespeichert wird, und
• – das Messgerät im Messbetrieb ein Über- oder Unterschreiten des vorgegebenen Füllstands durch einen Vergleich der gemessenen Kapazität mit dem Grenzwert bestimmt.

An embodiment of the method according to the invention comprises a method for determining reference values for measured values of a capacitive measuring device with probe horizontally installed in the container, which serves to monitor an exceeding or falling below of a predetermined filling level of a single filling material in the container, in which

• A reference value is determined for the measured value of the measured capacitance to be expected when the container is empty, and a reference value for the measured value to be expected when the probe is completely covered with the product,
• - Based on the determined reference values, a limit value for the capacitance to be measured is determined, from which the measuring device is to indicate that the predetermined fill level has been exceeded,
• - the limit is stored in the meter, and
• - The meter determines in measuring operation over or under the predetermined level by comparing the measured capacity with the limit.

• – ein Referenzwert für den bei vollständig mit dem ersten Füllgut bedeckter Sonde zu erwartenden Messwert ermittelt wird,
• – ein Referenzwert für den bei vollständig mit dem zweiten Füllgut bedeckter Sonde zu erwartenden Messwert ermittelt wird,
• – anhand der ermittelten Referenzwerte ein Grenzwert für die zu messende Kapazität ermittelt wird, ab dem das Messgerät anzeigen soll, dass sich die Trennschicht Über- bzw. unterhalb der durch die Einbauhöhe der Sonde vorgegebenen Lage befindet,
• – der Grenzwert im Messgerät abgespeichert wird, und
• – das Messgerät im Messbetrieb ein Über- oder Unterschreiten der zu überwachenden Lage der Trennschicht durch einen Vergleich der gemessenen Kapazität mit dem Grenzwert bestimmt.

A further refinement of the method according to the invention comprises a method for determining reference values for measured values of a capacitive measuring device with a probe horizontally mounted in the container, which serves to monitor a position of a separating layer formed between two filling products in the container, in which

• A reference value is determined for the reading to be expected when the probe is completely covered by the first filling material,
• A reference value is determined for the measured value to be expected when the probe is completely covered with the second filling material,
• - Based on the determined reference values, a limit value for the capacitance to be measured is determined, from which the measuring device is to indicate that the separating layer is above or below the position determined by the installation height of the probe,
• - the limit is stored in the meter, and
• - The meter determines in measuring operation overrun or falls below the monitored position of the separation layer by comparing the measured capacitance with the limit.

According to one Continuing the procedure will be used in determining the reference values factory-known measuring device-specific and / or production-related Dimensions and / or physical properties of individual components of the meter.

• – ein Anwender eine Messaufgabe vorgibt, und
• – anhand von für diese Messaufgabe relevanten Referenzwerten überprüft wird, ob die Messaufgabe von dem kapazitiven Messgerät ausführbar ist.

The invention further comprises a method for using the above-mentioned verification method in a computer-aided selection, design and / or ordering method for measuring instruments for industrial installations, in which

• - a user specifies a measuring task, and
• - It is checked on the basis of relevant for this measurement task reference values, whether the measurement task of the capacitive measuring device is executable.

• – ein Anwender eine Messaufgabe vorgibt, und
• – anhand von durch die Messaufgabe vorgegebenen Randbedingungen eine für diese Messaufgabe optimal geeignete Variante des kapazitives Messgerät ausgewählt, und dem Anwender angeboten wird.

The invention further comprises a method for using the above-mentioned selection method in a computer-aided selection, design and / or ordering method for measuring instruments for industrial installations, in which

• - a user specifies a measuring task, and
• - Is selected on the basis of specified by the measurement task boundary conditions for this measurement task optimally suitable variant of the capacitive measuring device, and offered to the user.

• – bestellt der Anwender das angebotene Messgerät, und
• – die für die Messaufgabe für die bestellte Variante abgeleiteten Referenzwerte und/oder daraus abgeleitete Grenzwerte werden werkseitig vor der Auslieferung des Messgeräts in dem Messgerät abgespeichert.

According to a development of the latter method

• - the user orders the meter offered, and
• - the reference values derived for the measurement task for the ordered variant and / or the limits derived therefrom are factory-stored in the meter prior to delivery of the meter.

The Invention and its advantages will now be described with reference to the figures of the drawing, in which two embodiments are shown, closer explains; the same elements are the same in the figures Provided with reference numerals.

1 shows a capacitive measuring device with a horizontally inserted into a container filled with a single filling container probe, as it is used for level monitoring;

2 shows a capacitive measuring device with a horizontally inserted into a container filled with two filling container probe, as it is used to monitor the position of the separation layer;

3 to 7 show a schematic overview of all possible cases of configurations of electric field lines of an applied between the probe and the counter electrode electric field for a probe without inactive probe section;

8th to 18 show a schematic overview of all possible cases of formations of electric field lines of an applied between the probe and the counter electrode electric field for a probe with inactive probe section;

19 shows an equivalent circuit diagram for a capacitive measuring device, in which an insulation capacitance formed by an insulation of the probe is arranged in series with a medium capacity; and

20 shows an equivalent circuit diagram for a capacitive measuring device, in which the insulation capacity is arranged in series with a parallel circuit of medium capacity and medium resistance.

1 shows a filled with a product A container 1 on the a capacitive measuring device 3 is mounted. The capacitive measuring device 3 points horizontally into a container 1 introduced rod-shaped probe 5 on, by means of a fastening device 7 on the container 1 is mounted. Outside the container 1 is one with the probe 5 connected measuring device housing 9 provided in which a meter electronics 11 located. The probe 5 serves as an electrode, which together with one through the wall of the container 1 formed counter electrode 13 forms a capacitor. The meter electronics 11 serves, in measuring mode, one of a current filling state of the container 1 dependent capacitance C to measure this capacitor, and based on the measured capacitance derive and display or output a measurement signal that reflects the desired measurement.

Capacitive measuring instruments 3 measure the level-dependent capacity in the rule by an electrical drive signal in the form of an alternating electrical voltage with a predetermined frequency f is applied to the capacitor and an associated capacitance-dependent response signal, usually a current signal, the z. B. is converted via a resistor into a voltage signal, recorded and evaluated. For this purpose, as a rule, a calculation algorithm is used which evaluates the admittance of the response signal, its magnitude and the phase between the drive signal and the response signal, and determines the capacitance C therefrom. Corresponding capacity measuring methods are for example in the DE 10 2004 047 413 A1 or the DE 101 61 069 A1 described.

Depending on the design and application, the probe 5 in the area of the introduction of the probe 5 in the container 1 , as in 1 shown, an inactive probe section 15 have the length LI. In this inactive section 15 is the probe 5 completely shielded to the outside, so that only an adjoining active probe section 17 the length LA as the electrode for the probe 5 and the container 1 formed capacitor acts. As a result, z. B. ensures that the meter is insensitive to contamination or deposits, located in the usually narrow insertion range of the probe 5 in the container 1 can deposit.

Furthermore, the probe 5 depending on the application and design of an insulation 19 vice be ben. In the in 1 The embodiment shown is the entire active probe section 17 completely from the isolation 19 surround. Fully isolated probes 5 are used in particular for measurements in conductive and / or polluting media in order to avoid a capacitive short circuit.

In the 1 illustrated measuring arrangement with the capacitive measuring device 3 with horizontally mounted probe 5 is used, for example, to monitor a predetermined level. For this purpose, the probe 5 at a height H in the container 1 introduced, which corresponds to the predetermined level to be monitored. In measuring mode, the capacity of the probe through the 5 and the counter electrode 13 serving containers 1 measured capacitor formed and determined by comparing the measured capacitance with a limit to be determined in advance, whether the level is above or below the predetermined level.

Capacitive measuring instruments with horizontally installed probes 5 However, not only to limit level monitoring but also to monitor the location of one between two in the container 1 located fillers A, B trained separating layer T can be used. In that case the probe becomes 5 introduced at a height H, which corresponds to the position of the separating layer T to be monitored. An embodiment of this is in 2 shown. Again, in the measuring mode, the capacity of the probe 5 and the counter electrode 13 serving containers 1 measured and determined by comparing the measured capacitance with a threshold to be determined in advance, whether the separation layer T is above or below the position to be monitored.

For the reasons already mentioned in the introduction to the description, it is necessary to determine reference values R for the measured values of the capacitance C to be expected during measurement operation. At the in 1 shown monitoring a predetermined level, these are a reference value RE, the empty container 1 represents the expected measured value of the measured capacitance C, and a reference value RF representing the probe completely covered by the medium A 5 expected value of the measured capacitance C reproduces.

When monitoring the position of the separating layer T, a reference value RFa for the probe completely covered by the first filling material A is produced by the method according to the invention 5 expected measured value of the measured capacitance C and a reference value RFb for the probe completely covered with the second filling material B. 5 expected value of the capacitance C determined. Preferably, in addition, a reference value RE for the empty container 1 expected measured value of the measured capacitance C determines.

To determine the reference values R, the procedure according to the invention is such that approximately a course of field lines F of an electric field is determined, which is in free space between the probe 5 and the counter electrode 13 due to a between probe 5 and the counter electrode 13 would form adjacent voltage. The physical fact is used that the field lines F along the probe 5 each along the shortest connecting line between the probe 5 and counter electrode 13 run and perpendicular to the probe 5 and the counter electrode 13 incident. The field lines F are preferably approximated by straight lines and circle segments, in particular by semicircles and quarter circles.

The course and the length of the field lines F is determined by the geometry of the container 1 , the length LI of the optionally provided inactive probe section 15 the probe 5 , the length LA of the active probe section 17 the probe 5 , the length L of the probe 5 in total, and the installation height H of the probe 5 certainly.

For a in a cylindrical container 1 horizontally installed probe with the radius RB 5 without inactive probe section 15 can depend on the length L of the probe 5 , the installation height H of the probe 5 , and the container radius RB along the probe 5 form three different field line types.

The first type of field line is formed by field lines Fi, which are quarter-circle shaped from the probe 5 to the container wall 21 run into which the probe 5 is introduced. The length LFi of these field lines Fi corresponds to the length of a quarter circle with a radius r, which is equal to the distance r between the container wall 21 and the area of the probe 5 from which the field line Fi originates, ie LFi = π / 2 r.

The second type of field line is formed by field lines Fj, which are straight from the probe 5 to the tank bottom 23 run. The length LFj of these field lines Fj corresponds to the installation height H of the probe 5 ie LFj = H.

The third type of field line is formed by field lines Fk, which are quarter-circle shaped from the probe 5 to the container wall opposite the probe insertion 25 run. The length LFk of these field lines Fk corresponds to the length of a quarter circle with a radius rk equal to the distance between the container wall 25 and the area of the probe 5 from which the field line Fk originates, ie LFi = π / 2 rk. For this radius rk: rk: = 2 RB - r where RB is the radius of the vessel 1 and r is the distance between the vessel wall containing the probe inlet 21 and the area of the probe 5 is, from which the field line Fk emanates

The course of the field lines F is now necessarily given by the fact that along the probe 5 in each area of the probe 5 each forms that field line type having the smallest length LFi, LFj, LFk.

This results in dependence on the length L of the probe 5 , the installation height H of the probe 5 , and the container radius RB in the 3 to 7 schematically illustrated cases.

In the in 3 In the case illustrated, only field lines Fi of the first field line type are formed, which are quarter-circle-shaped from the probe 5 to the region Wi of the container wall associated with the quarter-circle-shaped field line course 21 through which the probe 5 introduced, run away.

In the in 4 In the case illustrated, both field lines Fi of the first field line type and field lines Fk of the third field line type are formed.

In the in the 5 and 6 As shown, both field lines Fi of the first field line type and the field lines Fj of the second field line type are formed. The two cases differ only in that the probe 5 in the 6 case beyond the container center protrudes. However, it is not long enough in both cases, as that also field lines to the container wall opposite the probe insertion 25 form. This case is in 7 shown. There, all three field line types occur.

In the in the 3 to 7 Illustrated embodiments of a probe 5 without inactive probe section 15 went out. In many applications, however, makes sense in the field of introduction of the probe 5 in the container 1 an inactive probe section 15 of length LI.

In this inactive section 15 is the probe 5 completely shielded, leaving the inactive section 15 not part of the probe 5 formed capacitor. In that case, only that goes to the inactive probe section 15 subsequent active probe section 17 the probe 5 Field lines F off. When determining the field line history, the inactive probe section becomes 15 as part of the counter electrode 13 considered.

In this case, depending on the length LI of the inactive probe section 15 , the length LA of the active probe section 17 , the length L of the probe, the installation height H of the probe 5 and the container radius RB forming the four field line types described below.

The first type of field line includes field lines F1 derived from the active probe section 17 to that as part of the counter electrode 13 acting inactive probe section 15 run. These field lines F1 are approximated by a semicircle. The length LF1 of these field lines F1 corresponds to the length of a semicircle with a radius r 'equal to the distance of the region of the active probe section 17 from which the field line Fl goes out to the inactive probe element 15 is, ie LFl = π r '.

The second type of field line includes field lines Fm from the active probe portion 17 to the vessel wall containing the probe inlet 21 run. These field lines Fm are approximated by a quarter circle and an adjoining straight line. The radius r 'of the quadrant corresponds to the distance of the region of the active probe section 17 from which the field line Fm goes out to the inactive probe element 15 , The length of the straight line is equal to the length LI of the inactive probe element 17 , The length LFl of these field lines Fl is: FLI = π / 2 r '+ LI.

The third type of field line includes field lines Fn from the active probe section 17 to the tank bottom 23 run. These field lines Fn are approximated by straight lines whose length LFn is equal to the installation height H. The length LFn of these field lines Fn is thus equal to the installation height H: LFn = H.

RB

der Radius des Behälters,

LI

die Länge des inaktiven Sondenabschnitts und

r'

der Abstand des Bereichs des aktiven Sondenabschnitts 17 von dem die Feldlinie Fo ausgeht zu dem inaktiven Sondenelement 15 ist.

The fourth field line type includes field lines Fo from the active probe section 17 to the container wall opposite the probe insertion 25 run. These field lines Fo are approximated by a quadrant whose radius r "equals the mean distance of the region of the active probe section 17 from which the field line Fo emanates from the container wall opposite the insertion 25 is. For this radius r '': r '' = 2RB - (LI + r ') in which

RB

the radius of the container,

LI

the length of the inactive probe section and

r '

the distance of the area of the active probe section 17 from which the field line Fo emanates to the inactive probe element 15 is.

Corresponding results for the field lines Fo of the fourth field line type a field line length LFo of LFo = π / 2 r '', or LFO = π / 2 (2RB - (LI + r ')).

The course of the field lines F results inevitably here in that along the probe 5 in each area of the probe 5 each of those field line type forms, which has the smallest length LFl, LFm, LFn, LFo.

This results in dependence on the length LI of the inactive probe section 15 , the length LA of the active probe section 17 , the length L of the probe 5 , the installation height H of the probe 5 and the container radius RB in the 8th to 18 schematically illustrated cases.

In the in 8th illustrated case form along the entire active probe section 17 excluding field lines F1 from the first field line type.

In the in 9 illustrated case arise two areas. A first to the inactive probe section 15 adjacent region of the active probe section 17 in which field lines Fl of the first field line type form and a second area adjoining the first area in which field lines Fm of the second field line type are formed.

In the in 10 illustrated case form along the entire active probe section 17 excluding field lines F1 from the first field line type.

In the in 11 illustrated case, two areas form. A first to the inactive probe section 15 adjacent region of the active probe section 17 in which field lines Fl of the first field line type form and a second area adjoining the first area in which field lines Fo of the fourth field line type are formed.

In the in 12 illustrated case, three adjoining areas form. In the first immediately adjacent to the inactive probe section 15 adjacent field form field lines Fl of the first field line type, in the middle region form field lines Fm of the second field line type and in the third of the inactive probe section 15 In the opposite region, field lines Fo form from the fourth field line type.

In the in the 13 to 18 As shown, the installation height H is so low that even between the active probe section 17 and the container bottom 23 Running field lines Fn of the third field line type occur.

In the in 13 and 14 In each case, three areas are formed. In the first immediately adjacent to the inactive probe section 15 In the adjacent area, field lines F1 of the first field line type are formed, in the middle area field lines Fm of the second field line type are formed and in the third of the inactive probe section 15 Facing away from the field field Fn form of the third field line type. The two cases differ only in that the probe 5 by in 14 case protrudes beyond the container center.

In the in 15 area shown form four areas. In the first directly to the in active probe section 15 In the adjacent area, field lines F1 of the first field line type are formed, in the subsequent second area field lines Fm of the second field line type are formed, in the third area field lines Fn of the third field line type form, and in the fourth of the inactive probe section 15 In the opposite region, field lines Fo form from the fourth field line type.

In the in 16 and 17 In each case, two areas are formed. In the first immediately adjacent to the inactive probe section 15 adjacent field form field lines Fl of the first field line type and in the second of the inactive probe section 15 Facing away from the field field Fn form of the third field line type. The two cases differ only in that probe 5 by in 17 case protrudes beyond the container center.

In the in 18 illustrated case, three areas are formed. In the first immediately adjacent to the inactive probe section 15 In the adjacent area, field lines F1 of the first field line type are formed, in the subsequent second area field lines Fn of the third field line type are formed, and in the third of the inactive probe section 15 In the opposite region, field lines Fo form from the fourth field line type.

In a next step, the probe becomes 5 is divided into N cylindrical segments Sx with x = 1, ..., N of length Lsx. For probes 5 containing an inactive probe section 15 have, it is sufficient, the active probe section 17 into segments S1, S2, ... SN because the inactive probe section 15 not used as an electrode. For probes 5 without inactive probe section 15 becomes the entire probe 5 divided into segments S1, S2, ..., SN. The division is preferably made on the basis of the areas resulting from the different forming field line types. Based on the previously determined course of the field lines F, each segment Sx of the probe 5 an area Wx of the counter electrode 13 to which the field lines Fx originating from the segment Sx lead.

In a next step, an average field line length LFx is determined, that of the respective segment Sx outgoing between the respective segment Sx and this by the field line course associated region Wx of the counter electrode 13 extending field lines Fx have. For determining the average field line length LFx, the above-mentioned calculation rules are used for the field line length of the individual field line types, with the first and third field line types for probes 5 without inactive probe section 15 for the radius r, the mean distance of the segment Sx from the vessel wall containing the probe inlet 21 and at the first, second and fourth field line types for probes 5 with inactive probe section 15 for the radius r ', the mean distance of the segment Sx from the inactive probe section 15 is used.

After the associated mean field line length LFx has been determined for each segment Sx, for each segment Sx the contribution of this segment Sx to the respective searched reference value R is approximately determined on the assumption that the respective segment Sx together with the region Wx of the counterelectrode associated therewith 13 forms a cylindrical capacitor whose inner electrode is formed by the segment Sx and whose outer electrode is formed by a wood cylindrical electrode surrounding the inner electrode concentrically in a distance corresponding to the average field line length LFx. It is assumed that the cylinder capacitors are each completely filled with a medium. When determining the reference value RE for the empty container 1 the expected measured value of the measured capacitance C is the medium air. When determining the reference value RF or RFa for the probe completely covered with the product A 5 expected measurement value of the measured capacitance C, the medium is the corresponding contents A. In the determination of the reference value RFb for the fully covered with the medium B probe 5 Expected measured value of the measured capacitance C, the medium is the corresponding contents B.

wobei:

ε₀

die elektrische Feldkonstante,

ε_r

die Dielektrizitätskonstante des im Zylinderkondensator befindlichen Mediums (hier Luft, das Füllgut A oder das Füllgut B),

Lsx

die Länge des Segments Sx,

LFx

die mittlere Feldlinienlänge im Segment Sx, und

d

der Durchmesser des Sondensegments Sx

bedeuten.The capacities Cx of these cylinder capacitors were determined according to:

in which:

ε ₀

the electric field constant,

ε _r

the dielectric constant of the medium contained in the cylinder capacitor (here air, the product A or the product B),

Lsx

the length of the segment Sx,

LFx

the mean field line length in segment Sx, and

d

the diameter of the probe segment Sx

mean.

Based This single capacity Cx will be referred to below as one Medium capacity CM denotes designated capacity, which is equal to the capacity of a circuit through formed a parallel connection of the individual cylinder capacitors is.

Thus applies to the medium capacity: CM = Σ N x = 1 cx

Subsequently the respective searched reference value R is calculated on the basis of this medium capacity CM determines.

For probes 5 that of an isolation 19 surrounded, the isolation works 19 such as an additional capacity hereinafter referred to as insulation capacity Ci, which is connected in series to the medium capacity CM. This is in the in 19 shown equivalent circuit diagram. In this case, the isolation provides 19 a contribution to the capacitance C measured by the capacitive measuring device. Therefore, in determining the reference values R, this additional insulation capacitance Ci is preferably taken into account by determining the reference value R on the basis of the capacitance CMi of a circuit in which the insulation capacitance Ci is connected in series with the circuit Medium capacity CM is connected.

This will be the contributions of the isolation 19 surrounded segments Sx of the probe 5 for insulation capacity Ci determined by cylinder capacitors whose inner electrode has an outer diameter equal to the outer diameter of the segment Sx without insulation 19 is whose hollow cylindrical outer electrode concentrically surrounds the inner electrode at a distance equal to the thickness of the insulation 19 is, and whose interior is completely covered with the material of isolation 19 is filled.

wobei:

ε₀

die elektrische Feldkonstante,

ε_rl

die Dielektrizitätskonstante des im Zylinderkondensator befindlichen Isolationsmaterial,

Lsx

die Länge des Segments Sx,

D_I

der Durchmesser des Sondensegments Sx mit Isolation, und

d_s

der Durchmesser des Sondensegments Sx ohne Isolation 19 bedeuten.

The capacities Cix of these cylinder capacitors were determined according to:

in which:

ε ₀

the electric field constant,

ε _rl

the dielectric constant of the insulating material in the cylinder capacitor,

Lsx

the length of the segment Sx,

D _I

the diameter of the probe segment Sx with isolation, and

d _s

the diameter of the probe segment Sx without isolation 19 mean.

Based this single capacitance Cix becomes the isolation capacity Ci, which is equal to the capacity of a circuit, by a parallel connection of the individual cylinder capacitors is illustrated.

Thus, for the insulation capacity: Ci = Σ N x = 1 Cix

Now, the reference value RE for the empty container 1 expected value of the measured capacitance C determined.

This one is at probes 5 without isolation 19 set equal to the corresponding medium capacity CM. The following applies here: RE = CM

For probes 5 with isolation 19 it is set equal to the capacity of a series circuit of isolation capacity Ci and medium capacity CM. Here applies accordingly:

When determining the reference value RF for the probe completely covered with the product A 5 Expected measured value of the measured capacitance C are distinguished between conductive and non-conductive products A. Strictly speaking, all products A, which have a non-zero conductivity, are considered to be conductive. Alternatively, a threshold value for the conductivity can also be introduced to reduce the computational effort. In this case, only those contents A are classified as conductive contents A whose conductivity exceeds the threshold value. The threshold value is chosen such that the effect of the given by the conductivity ohmic connection between the probe 5 and counter electrode 13 to the measured capacitance C or the reference value RFa is negligible compared to the effect of the medium capacity CM on this size.

The reference value RF for non-conductive contents A is analogous to the reference value RE for the empty container 1 expected value of the capacitance C determined by the dielectric constant of the medium A is used in the determination of the medium capacity CM instead of the dielectric constant of air.

Accordingly applies here for probes 5 without isolation 19 : RF = CM and for probes 5 with isolation 19 applies:

For conductive fillers A, the probe forms 5 together with the counter electrode 13 no pure capacitor. Due to the conductivity σ of the filling material A, an ohmic connection between the probe additionally arises here 5 and the counter electrode 13 , which can be approximated by a medium resistance RM connected in parallel to the medium capacitance CM, as shown in FIG 20 shown equivalent circuit diagram is located. As in connection with conductive filling A regularly probes 5 with isolation 19 In addition, in the equivalent circuit diagram, the insulation capacitance Ci, which is arranged in series with the parallel connection of medium capacitance CM and medium resistance RM, is plotted.

In So this case provides both the isolation capacity Ci and the medium resistance RM contribute to that of the Capacitive meter measured capacitance C. The medium resistance RM and the insulation capacity Ci are therefore preferred in the determination of the reference value RF considered such that the reference value RF based on the Capacity CRMi is determined by a circuit in which the Insulation capacity Ci in series with a parallel circuit of medium capacity CM and medium resistance RM is.

For the determination of the medium resistance RM is again on the classification of the probe 5 into segments S1, S2,..., SN and the cylinder capacitors assigned to the respective segments Sx for determining the medium capacity CM. For determining the medium resistance RM, it is assumed that each of the cylinder capacitors is filled with the conductive filling material A.

wobei

σ

die Leitfähigkeit des Füllguts,

Lsx

die Länge des Segments Sx,

LFx

die mittlere Feldlinienlänge im Segment Sx, und

d

der Durchmesser des Sondensegments Sx bedeuten.

Based on the conductivity σ of the filling material A, an ohmic resistance Rx is determined for each segment Sx, which is equal to the resistance that forms a filling of the filling material A completely filling the associated cylinder capacitor between the inner and the hollow cylindrical outer electrode of the respective cylindrical capacitor. For this resistor Rx:

in which

σ

the conductivity of the product,

Lsx

the length of the segment Sx,

LFx

the mean field line length in segment Sx, and

d

mean the diameter of the probe segment Sx.

These individual resistors Rx are along the probe 5 arranged parallel to each other. Accordingly, the medium resistance RM is equal to the resistance which a parallel connection of all these resistors Rx has.

Accordingly:

Finally, the reference value RF is calculated using the capacity of the in 20 determined auxiliary circuit, in which the isolation capacitor Ci is connected in series with the parallel circuit of medium resistance RM and medium capacity CM.

For the determination of the reference value RF can be based on this Auxiliary circuit now both the reactance B of this auxiliary circuit, the effective resistance W of this auxiliary circuit, as well as through the auxiliary circuit caused phase shift φ be determined.

The following applies to the reactance:

und für die Phasenverschiebung φ gilt: φ = arctan (B/W).wobei ω das 2 π fache der Messfrequenz f ist, d. h. ω = 2 π fFor the effective resistance applies:

and for the phase shift φ: φ = arctan (B / W). where ω is 2 π times the measuring frequency f, ie ω = 2 π f

Without taking into account the phase shift φ, this results in a reference value RF for the probe completely covered by the product A 5 expected value of the capacity C of: RF = 1 ω B

Preferably, the phase shift φ is additionally taken into account in the form of a correction factor f (φ). RFkorr = RF f (φ)

The correction factor f (φ) is a function of the phase shift φ, and preferably depends on that in the measuring device 3 used capacity measurement method.

When determining the reference values relevant in connection with interface layer monitoring RE, RFa and RFb are carried out in a completely analogous manner, with the physical properties, in particular the conductivity σ _a or σ _b , of the respective contents A and B respectively being used in the determination of the reference values RFa and RFb.

The starting point for the use of the method according to the invention for determining the reference values RE and RF or RE, RFa and RFb is typically a predetermined measurement task. The measuring task can z. Example, to monitor the exceeding or falling below a predetermined level of a product A, or consist in determining whether the location of a between two contents A, B existing separation layer T exceeds or falls below a predetermined height. Due to the measuring task are boundary conditions, such. B. the shape of the container 1 , a predetermined by the container shape maximum allowable length L of the probe 5 , the installation height H of the probe 5 And the dielectric constant ε _r and the conductivity σ of the medium A and the filling substances A, B specified.

Preferably, it is determined in a first step on the basis of the inventive method described above, whether the predetermined measuring task can be performed by a capacitive measuring device. For this purpose, the reference values RE, RF or RE, RFa and RFb that are relevant for this measurement task are determined under the boundary conditions given by the measurement task, and the reference values RE, RF or RE, RFa and RFb are used to check whether the measurement task corresponds to a Boundary conditions formed capacitive measuring device 3 can be executed. For this purpose, the reference values RE, RF or RE, RFa and RFb are used to estimate whether a change in the capacitance to be measured caused by the measured variable exceeds a predetermined minimum value over the measuring range.

In conjunction with the in 1 For this purpose, the difference between the two reference values RE and RF is determined for this purpose. This difference corresponds to the change in the capacitance to be measured over the measuring range caused by the measured variable. If the difference exceeds a specified minimum size, then the measuring task, here the limit level monitoring, can be carried out with a capacitive measuring device. From a purely metrological point of view, a difference of one pF suffices. A change in capacitance of one pF can be measured without further ado. However, in practice, for pure products in indoor constant temperature applications, a minimum difference of 4 to 10 pF is given as the minimum size to avoid too great a sensitivity of the measurement to condensation or light soiling. For applications outdoors and / or in connection with contaminants of the product causing the probe, a limit of 10 to 20 pF is specified.

For monitoring the location of a separation layer between two Fillings A, B will be the difference accordingly determined between the reference values RFa and RFb. So with the Measuring device can be reliably detected, whether the position of the separating layer predetermined by the installation height H. Height is above or below this difference greater than a predetermined minimum size be.

can the measuring task with a capacitive measuring device basically be executed, will be out of the variety of possible Meter variants that are among the by the default Measuring task given boundary conditions can be used, the one determined, which is best suited for this purpose. For this purpose is based on the reference values RE, RF or RE, RFa, RFb that variant selected as optimally suited, in which one by the Measured variable caused change in the measuring capacity across the measuring range is maximum.

In the example mentioned in FIG 1 The measurement task shown is that variant in which the two reference values RE and RF have the greatest difference. In monitoring the position of the separation layer T, this is the variant in which the difference between the reference values RFa and RFb is maximum.

For this purpose, the application-specific boundary conditions, esp. The dielectric constant ε _r and the conductivity σ of the or the contents A, B, the container shape and the installation height H, given, and the measuring device specific parameters, especially the length L of the probe 5 or the length of the inactive probe section 15 and the length LA of the active probe section 17 , the material and the thickness of the insulation 19 , are considered as variables which are varied in a manner compatible with the application-specific boundary conditions for finding a measuring device variant which is optimally suitable for the measuring task. The reference values RE and RF, or RE, RFa, RFb are respectively determined for each variant of the measuring device, and that variant selected to be optimally suitable in which the difference of the two reference values RE, RF is maximum or the difference between the reference values RFa and RFb is maximum is.

A variant of the measuring instrument that is optimally selected for the measuring task 3 can then be offered to the user and purchased from the manufacturer. If the user decides for the variant offered to him, the reference values RE and RF or RE, RFa, RFb relevant for the measuring task can be determined in advance in the manner according to the invention and already in the measuring device before commissioning, preferably at the factory 3 be stored. In this case, in the determination of the reference values RE and RF, or RE, RFa, RFb, preferably factory-known measuring device-specific and / or production-related dimensions and / or physical properties of individual components of the measuring device 3 considered.

In the limit level monitoring, the limit value for the measured value of the capacitance C to be measured, which is decisive for exceeding or falling short of the predetermined filling level, is preferably determined on the basis of the reference values RE and RF and stored in the measuring device. The limit value can be calculated, for example, from the reference value RE for the empty container 1 to be expected capacity measured value, in which this a small predetermined capacity change .DELTA.C, z. B. 2 pF, which is smaller than the difference between the two reference values RE and RF added.

In the interface layer monitoring, the limit value for the measured value of the capacitance C to be measured, which is decisive for the above or below the position of the separating layer T to be monitored, is preferably determined on the basis of the reference values RE, RFa, RFb and in the measuring device 3 stored. The limit value can be determined, for example, by the small amount of the two reference values RFa, RFb, a small predetermined capacity change .DELTA.C, z. B. 2 pF, is added, which is smaller than the difference between the two reference values RFa and RFb. Conversely, it can be determined by a small predetermined capacity change .DELTA.C, z. B. of the magnitude of the larger of the two reference values RFa, RFb. B. 2 pF, which is smaller than the difference between the two reference values RFa and RFb. In the container 1 floats the medium with the lower specific weight, here the product B, on the product with the larger specific weight, here the contents A. Has the lighter contents B a lower dielectric constant ε _r and thus a lower reference value RFb, as the heavier Filling A, so exceeding the limit value means that the separation layer T is above the predetermined by the installation height H location.

If the heavier filling material A has the lower dielectric constant ε _r and thus also the lower reference value RFa, exceeding the limit value means that the separating layer T is below the position predetermined by the installation height H.

The measuring device 3 is thus directly applicable. An adjustment of the device, in which the reference values must be laboriously determined suburb especially by reference measurements and the limit values must be derived is superfluous.

Especially Advantageously, the inventive method in computer-aided selection, design, and / or ordering procedures for measuring instruments for industrial plants, as already described in the introduction to the description are to be used. For this purpose, the individual process steps in Implemented software that is executed by a computer to the user via a menu driven user interface directly or via the Internet. Appropriate Systems on which these methods are executable are in the documents cited in the introduction to the description and therefore not described again in detail here.

Of the User gives the system its measuring task and the associated Boundary conditions via a correspondingly designed user interface in front. According to the invention Procedures are then, as described above, for the Measuring task relevant reference values R, z. B. RE and RF or RE, RFa and RFb, determined. The system checks against these reference values R according to the method described above, whether the measuring task can be carried out by a capacitive measuring device is. The result of this review will be the Informed users via the user interface.

If the measuring task can be performed by a capacitive measuring device, the user can continue by using the computer-aided selection, dimensioning and / or ordering method for measuring instruments for industrial installations, for the measuring task specified by him on the basis of the boundary conditions specified by the measuring task For this measuring task optimally designed capacitive measuring device can be selected and offered from the variety of available measuring device variants. This is done according to the method already described above. Again, the individual process steps are implemented in software and executed by the computer or the system to which the user via the menu-driven Benut surface directly or via the Internet.

The user then has the option of ordering the measuring device optimally designed for its application via the user interface. If the user orders, there is the possibility of factory pre-delivery of the meter 3 Based on the already existing reference values R an adjustment of the meter 3 in which the reference values R already determined for the measurement task for the ordered variant and, where appropriate, derived limit values in the measuring instrument 3 be stored. The limit values are, in particular, the limit values described above, in which the fill level or the position of the separating layer exceeds or falls below the predetermined height predetermined by the installation height H.

The The measuring device can then be used immediately after delivery. An on-site reconciliation is no longer required.

The entire process of checking whether a capacitive measuring device is suitable for the measuring task, the selection of the most suitable measuring device variant, as well as the determination of the reference values for the measuring device adjustment using the inventive method fully automatic and reliable, without the user via his already known him application must bring in additional expertise. 1 container 3 capacitive measuring device 5 probe 7 fastening device 9 meter case 11 meter electronics 13 counter electrode 15 inactive probe section 17 active probe section 19 isolation 21 Container wall into which the probe is inserted 23 container bottom 25 the container insertion opposite container wall

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 10104165 A1 [0012]
• - DE 102006060441 [0012]
• - DE 102006060919 [0012]
• DE 102004047413 A1 [0039]
• - DE 10161069 A1 [0039]

Claims (14)

Method for determining reference values (R) for measured values of a capacitive measuring device ( 3 ), The one horizontally in measuring operation into a container which can be filled with at least one filling material (A, B) ( 1 ) used as an electrode probe ( 5 ), which together as the counter electrode ( 13 ) serving containers ( 1 ) forms a capacitor whose capacity in measuring operation of the measuring device ( 3 ) - the capacitive measuring device ( 3 ) with empty container ( 1 ) or in the case of a probe completely covered by a single product (A, B) ( 5 ), in which - approximately a course of field lines (F) of an electric field is determined, which is in free space between the probe ( 5 ) and the counter electrode ( 13 ) due to a between probe ( 5 ) and counterelectrode ( 13 ) voltage would form, - the probe ( 5 ) is subdivided into cylindrical segments (S1, S2,... SN), - an average field line length (LFx) is determined for each segment (Sx), which have field lines (Fx) of the electric field originating from this segment (Sx), and - the contribution of this segment (Sx) to the reference value (R) is determined approximately on the assumption that the respective segment (Sx) together with a region (Wx) of the counterelectrode ( 13 ) to which the field lines (Fx) emanating from this segment (Sx) form a cylindrical capacitor, - its inner electrode through the segment (Sx) and its outer electrode by a distance corresponding to the inner electrode concentrically in an average field line length (LFx) surrounding hollow cylindrical electrode is formed, - in an empty container ( 1 ) is empty or at completely covered with the medium (A, B) probe ( 5 ) is completely filled with the contents (A, B), and - the reference value (R) is determined based on a medium capacity (CM), which corresponds to the capacity of a parallel connection of the individual cylinder capacitors. Method according to claim 1, in which - the probe ( 5 ) one into the container ( 1 ) protrude inactive probe section ( 15 ), and - the inactive probe section ( 15 ) for the determination of the course of the field lines (F) as part of the counterelectrode ( 13 ) is looked at. Method according to claim 1, in which - the probe ( 5 ) of isolation ( 19 ), - an insulation capacity (Ci) is determined, and - the reference value (R) is determined on the basis of the capacitance of a series circuit in which the isolation capacitance (Ci) is connected in series with the medium capacitance (CM), where - the contributions the of isolation ( 19 ) surrounding segments (Sx) of the probe ( 5 ) to the insulation capacity (Ci) are determined by means of cylindrical capacitors whose inner electrode has an outer diameter (d _s ) equal to the outer diameter of the segment (Sx) without insulation ( 19 ), whose outer hollow cylindrical outer electrode concentrically surrounds the inner electrode at a distance equal to the thickness of the insulation ( 19 ), and whose interior is completely filled with the material of insulation ( 19 ), and - the insulation capacity (Ci) is equal to the capacitance of a parallel connection of these cylinder capacitors. Method according to Claims 1 and 3, for determining the reference value (RF) for the measured value of the capacitance to be measured, which the measuring device uses when the probe is completely covered with a conductive filling material (A) ( 5 ) with isolation ( 19 ), in which - based on the conductivity (σ) of the medium (A) for each segment (Sx), an ohmic resistance (Rx) is determined, which is equal to the resistance, the one of the respective segment (Sx) associated with the cylindrical capacitor completely filling from the filling material (A) existing filling between the inner and the hollow cylindrical outer electrodes of the respective cylindrical capacitor is formed, and - a medium resistance (RM) is determined, which is equal to the resistance of a parallel connection of all these resistive resistors (Rx), - and the reference value (RF) is determined on the basis of the capacitance of an auxiliary circuit, in which the insulation capacity (Ci) is connected in series with a parallel circuit of medium resistance (RM) and medium capacity (CM). Method according to claim 4, in which - the measuring device ( 3 ) is operated in measurement mode at a measurement frequency (f), - Based on the measurement frequency (f) a reactance (B) of the auxiliary circuit is determined, and the reference value (RF) based on the measurement frequency (f) and the reactance (B) is determined. The method of claim 5, wherein - one Effective resistance (W) of the auxiliary circuit is determined - based the reactance (B) and the effective resistance (W) by a the auxiliary circuit at the measuring frequency (f) caused phase shift (φ) is determined, and - the reference value (RF) based on the measurement frequency (f), the reactance (B) and the Phase shift (φ) is determined. Method according to one of the preceding claims, in which - a measuring task is specified, - reference values relevant for the measuring task (RE, RF, or RE, RFa, RFb) are determined, and - based on the reference values (RE, RF, or RE , RFa, RFb) is checked, whether the measuring task is performed by the capacitive measuring device ( 3 ) can be performed by using the reference values (RE, RF, or RE, RFa, RFb) to estimate whether a change in the capacitance to be measured caused by the measured variable exceeds a predetermined minimum value over the measuring range. Method for selecting a variant of the capacitive measuring device optimally adapted to a given measuring task ( 3 ) on the basis of reference values (R) determined in accordance with claims 1 to 6, in which the application-specific boundary conditions specified by the measuring task, in particular the dielectric constant (ε _r ), the conductivity (σ) of the product (s) (A, B) , the container shape and the installation height (H), are specified, - measuring device-specific parameters, esp. the length (L) of the probe ( 5 ), the length (LI) of the inactive probe section (FIG. 15 ), the length (LA) of the active probe section (FIG. 17 ) and / or the material and the thickness of the insulation ( 19 ) are considered to be variables which, in a manner compatible with the application-specific boundary conditions, can be used to find a variant of the measuring device which is optimally suited for the measuring task ( 3 ), - the reference values (R) relevant for the measurement task are determined for each variant, and - using the reference values (R) that variant is selected as being optimally suitable, at which a change in the capacitance to be measured caused by the measured variable the measuring range is maximum. Method according to Claim 1, for determining reference values (RE, RF) for measured values of a capacitive measuring device ( 3 ) with horizontally in the container ( 1 ) built-in probe ( 5 ), which is used for monitoring an exceeding or falling below a predetermined level of a single filling material (A) in the container ( 1 ), in which - a reference value (RE) for the measured value of the measured capacitance to be expected when the container is empty and a reference value (RF) for the probe completely covered by the product (A) ( 5 ) the expected measured value is determined, - based on the determined reference values (RE, RF), a limit value for the capacitance to be measured is determined, from which the measuring device ( 3 ) should indicate an exceeding of the specified filling level, - the limit value in the measuring device ( 3 ), and - the measuring device ( 3 ) in the measuring operation, an exceeding or falling below the predetermined level determined by comparing the measured capacity with the limit. Method according to Claim 1, for determining reference values (RE, RFa, RFb) for measured values of a capacitive measuring device ( 3 ) with horizontally in the container ( 1 ) built-in probe ( 5 ) used to monitor a position of one between two in the container ( 1 ) located filling material (A, B) formed separating layer (T) is used, in which - a reference value (RFa) for the completely covered with the first medium (A) probe ( 5 ) the expected measured value is determined, - a reference value (RFb) for the probe completely covered with the second medium (B) ( 5 ) the expected measured value is determined, - based on the determined reference values (RFa, RFb), a limit value for the capacitance to be measured is determined, from which the measuring device ( 3 ) should indicate that the separating layer (T) above or below the by the installation height (H) of the probe ( 5 ) predetermined position, - the limit value in the measuring device ( 3 ), and - the measuring device ( 3 ) in the measuring operation, an overshoot or undershoot of the monitored layer of the separation layer (T) by comparing the measured capacitance with the limit determined. Method according to claim 1, wherein in the determination of the reference values (R) factory-known measuring device-specific and / or production-related dimensions and / or physical properties of individual components of the measuring device ( 3 ). Method for using a method according to claim 7 in a computer-aided selection, design and / or ordering method for measuring instruments for industrial installations, in which - a user specifies a measuring task, and - is checked on the basis of relevant reference values for this measuring task (R) whether the measuring task of the capacitive measuring device ( 3 ) is executable. A method of using a method according to claim 8, in a computer-aided selection, design and / or ordering method for measuring instruments for industrial installations, in which - a user specifies a measuring task, - on the basis of given by the measurement task boundary conditions optimally suitable for this measurement task Variant of the capacitive measuring device ( 3 ) is selected and offered to the user. Method according to claim 13, in which - the user offers the offered measuring device ( 3 ), and - factory pre-delivery of the measuring instrument, the reference values (R) derived for the measurement task for the variant ordered and / or limits derived therefrom in the meter ( 3 ) are stored.