DE102011089427B4 - Procedure for adjusting a level gauge - Google Patents

Abstract

Method for adjusting a fill level measuring device for measuring a fill level (L) of a filling (1) in a container (3) - which in a measuring operation by means of a transmitting and receiving device (5) sends electromagnetic signals (S) in the direction of the filling (1) transmits and receives its signal components (R1) reflected on a filling material surface (9) after a transit time (tL) dependent on the fill level (L), and based on this transit time (tL) the fill level (L) in the container (3) in relation to an in determined at a reference distance (H) from the transmitting and receiving device (5) in the container (3), in measuring arrangements in which- at least in the case of levels (L) lying within a level range, a signal component (R2) of the transmitted signals ( S) penetrates the filling material surface (9) and is received via a reflection on a reflector located at a reference distance (H) from the transmitting and receiving device (5) after a transit time (tB) dependent on a distance covered in the container (3), a total reflection amplitude (Atot(t)) as a function of the transit time (t) can be calculated or has been experimentally determined in advance, which is equal to an amplitude that would have a reflected signal component received in the container (3) after the transit time (t) if am total reflection would have taken place at the associated place of reflection, and- either one of the propagation speeds (v0, v1) of the signals above or below the surface (9) of the filling material or the reference distance (H) is a known variable, at which- if the filling level is within the filling level range (L) the propagation times (tL, tB) of a signal component (R1, R2) reflected on the filling material surface (9) and of a signal component (R1, R2) reflected on the reflector and an amplitude (AL) of the signal component (R1) reflected on the filling material surface (9) are measured, based on a physical dependency of a signal component (R1) reflected on the surface (9) of the filling material due to a ratio of the amplitude (AL) to the total reflection amplitude (Atot(tL)) during the transit time (tL) of the signal component (R1) reflected on the surface of the filling material (9). ) Given reflection coefficients (r) from a ratio of the roots of the dielectric constants (εL, εG) of the filling material (1) and a gas located above the filling material (1) a ratio (v1/v0) of the propagation velocities (v0, v1) above and is determined below the filling material surface (9), and- on the basis of the ratio (v1/v0) of the propagation velocities (v0, v1), the measured propagation times (tL, tB) and the known variable, an assignment is determined, the propagation times ( tL) of signal components (R1) reflected on the surface (9) of the filling material, which are related to the reference level (R) of filling levels (L).

Description

The invention relates to a method for adjusting a fill-level measuring device for measuring a fill level of a filling in a container, which in measuring operation sends electromagnetic signals in the direction of the filling by means of a transmitting and receiving device and receives their signal components reflected on a filling material surface after a running time dependent on the filling level, and on the basis of the transit times, the fill level in the container is determined in relation to a reference level located at a reference distance from the transmitting and receiving device.

Fill level measuring devices of this type, which work according to the transit time principle, are used in a wide range of industrial measurement technology for measuring the fill level of filling goods located in containers.

Filling level measuring devices that are commercially available today and that work according to the transit time principle with electromagnetic signals, especially with microwaves, are divided into two classes; a first class, in which transmission signals are freely radiated in the direction of the filling material by means of a transmission and reception device, and their signal components reflected back in the container in the direction of the transmission and reception device according to one of the in the container from the transmission and reception device to the respective reflector and distance covered are received again, and a second class, in which, by means of a transmitting and receiving device, transmission signals are guided into the container along a probe designed as a waveguide, and their signal components reflected back along the probe to the transmitting and receiving device according to one of received again depending on the transit time in the container from the transmitting and receiving device to the respective reflector and the distance covered.

Based on the transit time principle, fill level measuring devices usually derive an echo function from the received signal components reflected in the container, which reproduces the amplitudes of the received reflected signal components as a function of the transit time required for the path to the associated reflector and back.

On the basis of the echo functions, a maximum of the echo function, which is usually referred to as a filling level echo and which is associated with a reflection on the surface of the filling material, is determined. With a known propagation speed of the electromagnetic signals above the filling material, the distance between the filling material surface and the transmitting and receiving device of the filling level measuring device results from the propagation time of this filling level echo.

So that the fill level in the container can be determined using the transit times of the fill level echoes measured during measurement operation, an adjustment is required via which fill levels related to a reference height in the container can be assigned to the measured transit times of the fill level echoes.

In the case of level gauges of the first class, the reference height is usually given by the bottom of the tank. If the propagation speed of the signals above the filling material is known, the adjustment here requires an exact determination of the distance between the transmitting and receiving device and the container bottom so that the filling level can be output based on the measured transit time of the filling level echo in relation to the reference height.

This adjustment can be carried out by completely emptying the container once during the commissioning of the fill-level measuring device and measuring the reference distance between the transmitting and receiving device and the bottom of the container with the fill-level measuring device using the known propagation speed of the signals.

Alternatively, a filling level that is currently present during commissioning can be measured using an independent measuring method in relation to the reference level. At the same time, the distance between the surface of the filling material and the transmitting and receiving device at this filling level is measured with the filling level measuring device using the known propagation speed of the signals above the filling material. The distance of the transmitter and receiver device to the surface of the filling material measured by the level gauge and the level measured with the independent measuring method in relation to the reference height then results in the reference distance between the transmitter and receiver device and the container bottom required for the adjustment.

In the second class level gauges, the reference height is given by the position of the free end of the probe. If the propagation speed of the signals above the filling material is known, the adjustment here requires an exact determination of the distance between the transmitting and receiving device and the free end of the probe. This corresponds to the mechanical length of the probe. If the propagation speed of the signals above the medium is known, an adjustment is only necessary for the level measurement related to the end of the probe if the mechanical length, e.g. due to a probe shortening carried out on site, is not known or only imprecisely known.

Since the propagation speed of the signals below the surface of the filling material depends on the dielectric properties of the filling material and is therefore usually not readily known, it is usually necessary for this comparison to empty the container during commissioning of the level measuring device at least to such an extent that the entire probe is above the medium. In this state, the length of the probe can be measured with the fill-level measuring device based on the propagation time of signal components of the transmitted signal reflected at the free end of the probe and the known propagation speed of the signals above the filling material.

In addition, there are applications in which the mechanical length of the probe is known, but the propagation speed of the signals above the medium is not known or only known very imprecisely. This is the case, for example, when a probe of known length is subsequently coated or is used in an environment that changes the signal propagation along the probe, such as a stilling well. If the mechanical length of the probe is known, the adjustment can be made here by lowering the filling level below the free end of the probe, and using the known length of the probe and the propagation time of signal components reflected at the free end of the probe, the propagation speed of the signals above the filling material is determined.

The calibration procedures mentioned above always require active participation by the user during commissioning and, under certain circumstances, an interruption to a process running in the tank. Emptying the container is always particularly complicated and therefore time-consuming and costly. However, an independent measurement of the fill level related to the reference height also represents an additional expenditure of time and money. In addition, the operator always needs to be involved in specifying the presence of the emptied container or the result of the independent measurement at the respective point in time for the fill level measuring device.

It is an object of the invention to specify a method for adjusting a filling level measuring device that works with electromagnetic signals according to the transit time principle, which method can be carried out automatically by the filling level measuring device.

• - das im Messbetrieb mittels einer Sende- und Empfangsvorrichtung elektromagnetische Sendesignale in Richtung des Füllguts sendet und deren an einer Füllgutoberfläche reflektierten Signalanteile nach einer vom Füllstand abhängigen Laufzeit empfängt, und
• - anhand dieser Laufzeit den Füllstand im Behälter bezogen auf eine in einem Referenzabstand von der Sende- und Empfangsvorrichtung befindliche Referenzhöhe im Behälter bestimmt,

in Messanordnungen, in denen

• - zumindest bei innerhalb eines Füllstandbereichs liegenden Füllständen ein Signalanteil der Sendesignale die Füllgutoberfläche durchdringt und über eine Reflektion an einem im Referenzabstand von der Sende- und Empfangsvorrichtung befindlichen Reflektor nach einer von einer im Behälter zurückgelegten Wegstrecke abhängigen Laufzeit empfangen wird,
• - eine Totalreflektionsamplitude als Funktion der Laufzeit berechenbar ist oder vorab experimentell bestimmt wurde, die gleich einer Amplitude ist, die ein nach der Laufzeit empfangener im Behälter reflektierter Signalanteil aufweisen würde, wenn am zugehörigen Reflektionsort eine Totalreflektion stattgefunden hätte, und
• - entweder eine der Ausbreitungsgeschwindigkeiten der Signale oberhalb oder unterhalb der Füllgutoberfläche oder der Referenzabstand eine bekannte Größe ist, bei dem
• - bei Vorliegen eines innerhalb des Füllstandsbereichs liegenden Füllstands die Laufzeiten eines an der Füllgutoberfläche und eines am Reflektor reflektierten Signalanteils und eine Amplitude des an der Füllgutoberfläche reflektierten Signalanteils gemessen werden,
• - anhand einer physikalischen Abhängigkeit eines durch ein Verhältnis der Amplitude des an der Füllgutoberfläche reflektierten Signalanteils zur Totalreflektionsamplitude bei der Laufzeit des an der Füllgutoberfläche reflektierten Signalanteils gegebenen Reflektionskoeffizienten von einem Verhältnis der Wurzeln der Dielektrizitätskonstanten des Füllguts und eines oberhalb des Füllguts befindlichen Gases ein Verhältnis der Ausbreitungsgeschwindigkeiten ober- und unterhalb der Füllgutoberfläche bestimmt wird, und
• - anhand des Verhältnisses der Ausbreitungsgeschwindigkeiten, den gemessenen Laufzeiten und der bekannten Größe eine Zuordnung bestimmt wird, die vom Füllstandsmessgerät gemessenen Laufzeiten von an der Füllgutoberfläche reflektierten Signalanteilen auf die Referenzhöhe bezogene Füllstände zuordnet.

For this purpose, the invention includes a method for adjusting a fill level measuring device for measuring a fill level of a filling material in a container,

• - which, in measuring operation, sends electromagnetic transmission signals in the direction of the filling material by means of a transmitting and receiving device and receives their signal components reflected on a filling material surface after a transit time that is dependent on the filling level, and
• - based on this running time, the fill level in the container is determined in relation to a reference height in the container located at a reference distance from the transmitting and receiving device,

in measurement arrangements in which

• - at least in the case of filling levels within a filling level range, a signal component of the transmission signals penetrates the surface of the filling material and is received via a reflection on a reflector located at a reference distance from the transmitting and receiving device after a transit time dependent on a distance covered in the container,
• - a total reflection amplitude can be calculated as a function of the propagation time or has been experimentally determined beforehand, which is equal to an amplitude that a signal component reflected in the container received after the propagation time would have if total reflection had taken place at the associated reflection location, and
• - Either one of the propagation velocities of the signals above or below the filling material surface or the reference distance is a known variable at which
• - if the filling level is within the filling level range, the propagation times of a signal portion reflected on the filling material surface and of a signal portion reflected on the reflector and an amplitude of the signal portion reflected on the filling material surface are measured,
• - based on a physical dependency of a reflection coefficient given by a ratio of the amplitude of the signal portion reflected on the surface of the filling material to the total reflection amplitude during the transit time of the signal portion reflected on the surface of the filling material, from a ratio of the roots of the dielectric constants of the filling material and a gas located above the filling material, a ratio of the propagation velocities is determined above and below the filling material surface, and
• - Based on the ratio of the propagation velocities, the measured running times and the known size, an assignment is determined which assigns the measured running times of the filling level measuring device of signal components reflected on the filling material surface to filling levels related to the reference height.

• - das Abgleichverfahren bei Vorliegen eines beliebigen Füllstands im Behälter begonnen wird,
• - während des Abgleichs ein Prozess in dem Behälter abläuft, durch den sich der Füllstand in Abhängigkeit vom Prozess verändert,
• - das Füllstandsmessgerät während des Abgleichs solange Sendesignale in den Behälter sendet und anhand der empfangenen im Behälter reflektierten Signalanteile Echofunktionen ableitet, die die Amplituden der empfangenen Signalanteile als Funktion von deren für die im Behälter zurückgelegte Wegstrecke benötigte Laufzeit wiedergeben, bis in einer der Echofunktionen ein auf eine Reflektion an der Füllgutoberfläche zurückzuführendes Maximum und ein auf eine Reflektion am Reflektor zurückzuführendes Maximum auftritt.

A further development of the invention includes a method in which

• - the calibration procedure is started when there is any filling level in the tank,
• - a process is taking place in the container during the calibration, which causes the fill level to change depending on the process,
• - the level measuring device sends transmission signals into the container during the adjustment and, based on the received signal components reflected in the container, derives echo functions which reflect the amplitudes of the received signal components as a function of their travel time required for the distance covered in the container, until one of the echo functions shows an on a maximum that can be attributed to a reflection on the filling material surface and a maximum that can be attributed to a reflection on the reflector occurs.

• - sind die Sendesignale frei abgestrahlte Mikrowellensignale, insb. Mikrowellenpulse oder frequenz-modulierte Signale, und
• - der Referenzabstand ist ein Abstand zwischen der Sende- und Empfangsvorrichtung und einem Behälterboden des Behälters.

According to a first embodiment of the invention

• - Are the transmission signals freely radiated microwave signals, esp. Microwave pulses or frequency-modulated signals, and
• - The reference distance is a distance between the transmitting and receiving device and a container bottom of the container.

• - weist das Füllstandsmessgerät eine an die Sende- und Empfangsvorrichtung angeschlossene in den Behälter hinein ragende Sonde auf, die die Sendesignale in den Behälter hinein und deren im Behälter entlang der Sonde reflektierten Signalanteile zur Sende- und Empfangsvorrichtung zurück führt, und
• - der Referenzabstand ist gleich einer mechanischen Sondenlänge der Sonde.

According to a second embodiment of the invention

• - The filling level measuring device has a probe connected to the transmitting and receiving device and protruding into the container, which returns the transmitted signals into the container and their signal components reflected in the container along the probe to the transmitting and receiving device, and
• - the reference distance is equal to a mechanical probe length of the probe.

• - ist die Ausbreitungsgeschwindigkeit der Signale oberhalb der Füllgutoberfläche bekannt,
• - wird anhand der Ausbreitungsgeschwindigkeit der Signale oberhalb der Füllgutoberfläche, des Verhältnisses der Ausbreitungsgeschwindigkeiten, und den gemessenen Laufzeiten des an der Füllgutoberfläche reflektierten Signalanteils und des am Reflektor reflektierten Signalanteils der Referenzabstand bestimmt, und
• - erfolgt die Zuordnung, indem vom Füllstandsmessgerät gemessenen Laufzeiten von an der Füllgutoberfläche reflektierten Signalanteilen über die Ausbreitungsgeschwindigkeit oberhalb des Füllguts ein Abstand zwischen der Sende- und Empfangsvorrichtung und der Füllgutoberfläche zugeordnet wird, und diesem ein auf die Referenzhöhe bezogener Füllstand zugeordnet wird, der einer Differenz zwischen dem Referenzabstand und dem Abstand zwischen der Sende- und Empfangsvorrichtung und der Füllgutoberfläche entspricht.

According to a first variant of the invention

• - the propagation speed of the signals above the product surface is known,
• - the reference distance is determined on the basis of the propagation speed of the signals above the filling material surface, the ratio of the propagation speeds, and the measured propagation times of the signal component reflected on the filling material surface and the signal component reflected on the reflector, and
• - the assignment is made by assigning a distance between the transmitting and receiving device and the filling material surface to the propagation speed above the filling material, measured by the filling level measuring device, of signal components reflected on the surface of the filling material, and assigning a filling level related to the reference height that corresponds to a difference between the reference distance and the distance between the transmitting and receiving device and the filling material surface.

• - ist die Ausbreitungsgeschwindigkeit der Signale unterhalb der Füllgutoberfläche bekannt,
• - wird anhand der Ausbreitungsgeschwindigkeit der Signale unterhalb der Füllgutoberfläche und des Verhältnisses der Ausbreitungsgeschwindigkeiten die Ausbreitungsgeschwindigkeit der Signale oberhalb des Füllguts bestimmt,
• - wird anhand der Ausbreitungsgeschwindigkeit der Signale unterhalb der Füllgutoberfläche, des Verhältnisses der Ausbreitungsgeschwindigkeiten, und den gemessenen Laufzeiten des an der Füllgutoberfläche reflektierten Signalanteils und des am Reflektor reflektierten Signalanteils der Referenzabstand bestimmt, und
• - erfolgt die Zuordnung, indem vom Füllstandsmessgerät gemessenen Laufzeiten von an der Füllgutoberfläche reflektierten Signalanteilen über die Ausbreitungsgeschwindigkeit oberhalb des Füllguts ein Abstand zwischen der Sende- und Empfangsvorrichtung und der Füllgutoberfläche zugeordnet wird, und diesem ein auf die Referenzhöhe bezogener Füllstand zugeordnet wird, der einer Differenz zwischen dem Referenzabstand und dem Abstand zwischen der Sende- und Empfangsvorrichtung und der Füllgutoberfläche entspricht.

According to a second variant of the invention

• - the propagation speed of the signals below the product surface is known,
• - the propagation speed of the signals above the filling is determined on the basis of the propagation speed of the signals below the filling material surface and the ratio of the propagation speeds,
• - the reference distance is determined on the basis of the propagation speed of the signals below the surface of the filling material, the ratio of the propagation speeds, and the measured propagation times of the signal portion reflected on the filling material surface and the signal portion reflected on the reflector, and
• - the assignment is made by assigning a distance between the transmitting and receiving device and the filling material surface to the propagation speed above the filling material, measured by the filling level measuring device, of signal components reflected on the surface of the filling material, and assigning a filling level related to the reference height that corresponds to a difference between the reference distance and the distance between the transmitting and receiving device and the filling material surface.

• - ist der Referenzabstand bekannt,
• - wird anhand des Referenzabstands, des Verhältnisses der Ausbreitungsgeschwindigkeiten, und den gemessenen Laufzeiten des an der Füllgutoberfläche reflektierten Signalanteils und des am Reflektor reflektierten Signalanteils die oberhalb des Füllguts auftretende Ausbreitungsgeschwindigkeit bestimmt, und
• - erfolgt die Zuordnung, indem vom Füllstandsmessgerät gemessenen Laufzeiten von an der Füllgutoberfläche reflektierten Signalanteilen über die Ausbreitungsgeschwindigkeit oberhalb des Füllguts ein Abstand zwischen der Sende- und Empfangsvorrichtung und der Füllgutoberfläche zugeordnet wird, und diesem ein auf die Referenzhöhe bezogener Füllstand zugeordnet wird, der einer Differenz zwischen dem Referenzabstand und dem Abstand zwischen der Sende- und Empfangsvorrichtung und der Füllgutoberfläche entspricht.

According to a third variant of the invention

• - is the reference distance known,
• - the propagation speed occurring above the filling material is determined on the basis of the reference distance, the ratio of the propagation velocities, and the measured propagation times of the signal portion reflected on the filling material surface and the signal portion reflected on the reflector, and
• - the assignment is made by assigning a distance between the transmitting and receiving device and the filling material surface to the propagation speed above the filling material, measured by the filling level measuring device, of signal components reflected on the surface of the filling material, and assigning a filling level related to the reference height that corresponds to a difference between the reference distance and the distance between the transmitting and receiving device and the filling material surface.

The adjustment method according to the invention has the advantage that a relationship between the measured propagation time of signal components reflected on the surface of the filling material and the filling level related to the reference height can be determined, which is required for determining the filling level in relation to the reference height, without any intervention in one at the place of use of the level gauge running process is required. In particular, neither an independent measurement nor the setting of a specific fill level in the container is required.

A further advantage is that the method can be carried out automatically by the level gauge. No action or participation by the user is required.

• 1 zeigt: eine Füllstandsmessanordnung mit einem Füllstandsmessgerät, das elektromagnetische Sendesignale mittels einer Sende- und Empfangsvorrichtung frei in einen Behälter abstrahlt;
• 2 zeigt: eine mit dem Füllstandsmessgerät von 1 aufgezeichnete Echofunktion;
• 3 zeigt: eine Füllstandsmessanordnung mit einem Füllstandsmessgerät, das elektromagnetische Sendesignale mittels einer Sende- und Empfangsvorrichtung entlang einer Sonde in einen Behälter führt; und
• 4 zeigt: eine mit dem Füllstandsmessgerät von 3 aufgezeichnete Echofunktion.

The invention and its advantages will now be explained in more detail with reference to the figures of the drawing, in which two exemplary embodiments are illustrated; the same parts are provided with the same reference symbols in the figures.

• 1 shows: a filling level measuring arrangement with a filling level measuring device which emits electromagnetic transmission signals freely into a container by means of a transmitting and receiving device;
• 2 shows: one with the level gauge from 1 recorded echo function;
• 3 shows: a filling level measuring arrangement with a filling level measuring device, which guides electromagnetic transmission signals by means of a transmitting and receiving device along a probe into a container; and
• 4 shows: one with the level gauge from 3 recorded echo function.

The subject matter of the invention is a method for adjusting a fill-level measuring device for measuring a fill level of a product in a container, which the fill-level measuring device can carry out automatically. It can be used in conjunction with level gauges which, during measurement operation, send electromagnetic signals in the direction of the filling material by means of a transmitting and receiving device and receive the signal components reflected on a filling material surface after a transit time that is dependent on the fill level, and based on the transit times determined by the fill level gauge, the fill level in the container based on a reference height located at a reference distance from the transmitting and receiving device.

The method according to the invention can only be used in measuring arrangements in which, at least when there is a filling level within a filling level range, a signal component of the signals transmitted by the filling level measuring device penetrates the surface of the filling material and is transmitted again via a reflection on a reflector located at a reference distance from the transmitting and receiving device - And receiving device is received.

In addition, in order to carry out the method according to the invention, it is necessary for either one of the two propagation speeds of the electromagnetic signals above or below the filling material surface or for the reference height to have a known value.

The invention is first described below using the example of a filling level measuring device that works with electromagnetic signals, especially with microwave signals, according to the transit time principle and that emits the electromagnetic signals freely into a container.

1 shows a measuring arrangement for this purpose, in which a corresponding filling level measuring device is arranged above a container 3 partially filled with a filling material 1 . It comprises a transmitting and receiving device 5, such as an antenna, with which it transmits electromagnetic transmission signals S into the container 3 in the direction of the filling material 1 and their signal components R1, R2 reflected back in the container 3 in the direction of the transmitting and receiving device 5 receives again after a running time t that is dependent on the distance covered in the container 3 and is to be determined by the fill level measuring device.

All known methods that make it possible to measure relatively short distances by means of reflected electromagnetic signals can be used to determine the propagation times t. The best known examples are pulse radar and frequency modulation continuous wave (FMCW) radar.

In the case of pulse radar, short microwave transmission pulses are periodically transmitted, which are reflected in the container 3 and are received again after a transit time t which is dependent on the distance covered by them.

With FMCW radar, a microwave signal is transmitted continuously, which is periodically linearly frequency-modulated, for example according to a sawtooth function. The frequency of the received signal therefore has a frequency difference from the instantaneous frequency that the transmitted signal has at the time of reception, which frequency difference depends on the propagation time t of the associated microwave signal. The frequency difference between the transmitted signal and the received signal, which is caused by mixing the two Signals and evaluation of the Fourier spectrum of the mixed signal can be obtained, thus corresponds to the transit time t. Furthermore, the amplitudes of the spectral lines of the frequency spectrum obtained by Fourier transformation correspond to the amplitudes A(t) of the signal components received after the propagation time t.

The fill-level measuring device comprises measuring electronics 7, which, on the basis of the received reflected signal components R1, R2, derives a function usually referred to as the echo function A(t), which defines an amplitude A of the received signal components as a function of their for the path from the transmitting and receiving device 5 to the reflection point in the container 3 and back, the required runtime t is reproduced. Corresponding methods for deriving echo functions are used as standard in today's pulse and FMCW radar fill level measuring devices and are therefore not explained in detail here.

In the echo functions A(t), reflections from reflectors in the container 1 cause local maxima, hereinafter referred to as echoes E, at the transit times t required for the route from the transmitting and receiving unit 5 to the respective reflector and back. 2 shows an example of one of the level gauge in the measurement arrangement of FIG 1 recorded echo function A(t).

In order to be able to measure the filling level L in the container, a filling level echo E _L is determined on the basis of the echo function A(t), which echo can be traced back to a reflection of the electromagnetic transmission signal S on the filling material surface 9 . For this purpose, for example, the first echo occurring in the echo function A(t) is recognized as the filling level echo E _L . Other methods and algorithms are known from the prior art. With a known propagation speed v ₀ of the signals above the filling material 1, a distance D between the transmitting and receiving device 5 of the filling level measuring device and the filling material surface 9 results directly from the associated transit time t _L at which the level echo E _L occurs.

In order to be able to use the level gauge to measure a level L related to a reference height R in the container 3, an adjustment is required with which the transit times t _L determined by the level gauge during measurement operation of the level echoes E L determined using the received signal components R1 _are related to the reference height R Level L can be assigned.

In this type of measuring arrangement, the reference height R is typically given by the position of the container bottom 11 . The reference distance H thus corresponds to the installation height of the transmitting and receiving device 5 above the container bottom 11.

In most applications, the gas located above the filling material 1 in the container 3 is known. In the vast majority of applications, there is air above the filling material 1. Accordingly, the propagation speed v ₀ of the free electromagnetic signals above the filling material surface 9 is a known variable in most locations where the level gauges are used.

If the propagation speed v ₀ of the electromagnetic signals above the filling material 1 is known, the distance D between the transmitting and receiving device 5 and the filling material surface 9 can be measured with the filling level measuring device at any time using the propagation time t _L of the filling level echo E _L . In order to determine from this the fill level L related to the reference height R, the reference distance H of the reference height R from the transmitting and receiving device 5 must be determined in the adjustment process. The latter corresponds to the application-specific installation height of the transmitting and receiving device 5, which may depend on the conditions at the place of use. This is usually not known with sufficient accuracy and cannot be measured with sufficient accuracy in most applications or only with considerable effort. If the reference distance H has been determined by the level measuring device using the calibration procedure described below, the distance D results in measuring operation based on the transit time t _L of the level echo E _L , which is the level L := HD related to the reference height R as the difference between the reference distance H and the distance D to the filling material surface 9 is assigned.

For the adjustment method according to the invention, it is necessary that there is a reflector at the reference distance H from the transmitting and receiving device 5, and that the filling material 1—as stated above—is partially transparent to the electromagnetic signals used. In the embodiment shown, the container bottom 11 forms this reflector.

The adjustment takes place in that electromagnetic transmission signals S are sent into the container 3 and their signal components R1, R2 reflected back in the container 3 to the transmitting and receiving device 5 are received until the propagation times t _L , t _B of the signal components R1, R2 reflected on the filling material surface 9 and on the container bottom 11 and the amplitude A _L of the signal component R1 reflected on the filling material surface 9 can be determined.

For this purpose, echo functions A(t) are recorded until the filling level echo E _L and a reflector echo E _B that can be attributed to the reflection at the reflector can be identified in an echo function A(t). The reflector echo E _B is identified, for example, by checking whether the echo function A(t) has two pronounced echoes, in particular ones that exceed a predetermined minimum amplitude. As soon as this is the case, the echo with the longer transit time t is identified as the reflector echo E _B .

Whether these two echoes can be identified depends both on the current filling level L and on the reflectivity of the filling material 1 . As soon as a sufficiently low level L in the above-mentioned level range is reached in the container 3 due to the process taking place in the measuring arrangement, this is automatically recognized by the level measuring device, and it determines the transit time t _L and amplitude A _L of the level echo E _L as well as the transit time t _B of the reflector echo E _B .

The amplitude A _L of the level echo E _L depends on the amplitude A ₀ of the transmission signal S, the distance covered, the gas located above the filling material 1, properties specific to the measuring device, such as an antenna gain, and the reflectivity of the filling material 1. The latter is given by a reflection coefficient r, which corresponds to the amplitude ratio of incident to reflected amplitude.

The reflection coefficient r is accordingly also equal to a ratio of the amplitude A _L of the filling level echo E _L to an amplitude referred to below as the total reflection amplitude A _tot (t _L ), which the filling level echo E _L would have if a total reflection took place under otherwise identical conditions on the filling material surface would, in which the impinging signal would be completely reflected and no signal portion would penetrate into the filling material 1. $$\mathrm{right}=\frac{A_L}{A_{tOt}\left(t_L\right)}$$

In the 2 The total reflection amplitude A _tot (t) drawn as a dashed line can be approximated _as Function of the running time t can be calculated. The amplitude decrease of electromagnetic signals, which depends on the distance covered and the attenuation in air, is known in terms of a formula and can be converted directly into a runtime-dependent amplitude decrease via the known propagation speed v ₀ above the filling material 1, which is then usually at least approximately known by measuring devices. specific influences on the amplitude, such as an antenna gain, can be added.

However, the total reflection amplitude A _tot (t) as a function of the transit time t can also be determined experimentally by reference measurements and stored in the fill-level measuring device. In this case, amplitudes and propagation times of reflections of the transmission signals S on a mirror are recorded over a corresponding distance range between the transmitting and receiving device 5 and the mirror.

Since the free-field attenuation in most gases used above filling goods is at least approximately equal to the free-field attenuation in air, it is usually sufficient to determine the total reflection amplitude A _tot (t) for air. This can then be used in all applications in which another gas with a free-field damping comparable to the free-field damping in air is located above the filling material 1 .

Since the vast majority of filling goods have practically no magnetic components, a permeability µ _L of the filling goods of 1 is assumed below.

The amplitude ratio of the amplitude A _L of the level echo E _L to the total reflection amplitude A _tot (t _L ) at the transit time t _L of the level echo E _L can be calculated using Fresnel's formulas for perpendicular incidence as a function of the dielectric constant E _L of the filling material 1 and ε _G of the gas express as follows: $$\frac{A_L}{A_{tOt}\left(t_L\right)}=\frac{\sqrt{\frac{e_L}{e_G}}-1}{\sqrt{\frac{e_L}{e_G}}+1}$$

das nun anhand der Amplitude A_L des Füllstandsechos E_L, der Laufzeit t_L des Füllstandsechos E_L, und der bei der Laufzeit t_L des Füllstandsechos E_L auftretenden Totalreflektionsamplitude A_tot(t_L) berechnet werden kann.Equation (2) gives a ratio of the root of the dielectric constant E _L of the filling material 1 to the root of the dielectric constant ε _G of the gas located above the filling material 1 of: $$\sqrt{\frac{e_L}{e_G}}=\frac{A_{tOt}\left(t_L\right)+A_L}{A_{tOt}\left(t_L\right)-A_L}$$

which can now be calculated using the amplitude A _L of the filling level echo _{E L} , the transit time t _L of the filling level echo E _L , and the total reflection amplitude A _tot (t _L ) occurring during the transit time t _L of the filling level echo E L .

The ratio of the roots of the dielectric constants ε _L , ε _G is in turn inversely proportional to the ratio of the propagation velocities v ₀ , v ₁ in gas and filling material 1; ie the following applies: $$\frac{v_1}{{\mathrm{<figure-callout\; id="0"\; label="v"\; filenames="DE102011089427B4\_0008.png,DE102011089427B4\_0010.png"\; state="\{\{state\}\}">v</figure-callout>}}_0}=\frac{\sqrt{e_G}}{\sqrt{e_L}}.$$

From this, the searched reference distance H is determined on the basis of the propagation times t _L and t _B of the filling level echo E _L and the reflector echo E _B and the propagation speed v ₀ above the filling material 1, which is assumed to be known. For this purpose, the reference distance H is expressed as the sum of the measured distance D and the fill level L, and both summands are expressed as follows as a function of the previously known and determined quantities and: $$\begin{array}{c}\text{H}=\text{D}+\text{L}\\ ={\text{½v}}_0{\text{t}}_{\text{L}}+{\text{½v}}_1\left({\text{t}}_{\text{B}}-{\text{t}}_{\text{L}}\right)\\ ={\text{½v}}_0{\text{t}}_{\text{L}}+{\text{½v}}_0\left({\text{<figure-callout id="1" label="v" filenames="DE102011089427B4\_0008.png" state="{{state}}">v</figure-callout>}}_1/{\text{v}}_0\right)\left({\text{t}}_{\text{B}}-{\text{t}}_{\text{L}}\right)\end{array}$$

This is preferably done using an algorithm implemented in the fill level measuring device, which is started automatically by the fill level measuring device.

ermittelt, anzeigt, und/oder einer weiteren Verwendung zugänglich macht.This completes _the calibration process and the level gauge can automatically switch to measuring mode by then using _the known propagation speed v ₀ of the signals above the filling material 1 and the reference distance H den to the reference height R related level L according to $$\text{L}=\text{H}-\text{D}=\text{H}-{\text{½v}}_0{\text{t}}_{\text{L}}$$

determined, displayed and/or made accessible for further use.

The method described above, in which the propagation speed v ₀ above the filling material 1 is known, represents the main area of application of the method according to the invention. Here, by storing the total reflection amplitude A _tot (t) in Air, a very wide range of gases can be covered with a free-field attenuation comparable to the free-field attenuation in air in combination with any filling material 1.

• - nur die Ausbreitungsgeschwindigkeit v₁ im Füllgut 1 bekannt, die Ausbreitungsgeschwindigkeit v₀ oberhalb des Füllguts 1 und der Referenzabstand H dagegen jedoch unbekannt sind, oder
• - nur der Referenzabstand H bekannt ist, die beiden Ausbreitungsgeschwindigkeiten v₀, v₁ jedoch unbekannt sind.

In principle, however, the method can also be used in applications in which

• - Only the propagation speed v ₁ in the filling material 1 is known, but the propagation speed v ₀ above the filling material 1 and the reference distance H are unknown, or
• - only the reference distance H is known, but the two propagation velocities v ₀ , v ₁ are unknown.

The prerequisite for this, however, is that the total reflection amplitude A _tot (t) as a function of the transit time t for the gas located above the filling material 1 can be derived analytically or numerically at least approximately in advance or has been determined experimentally. In the above-mentioned cases of gases with a free-field attenuation comparable to the free-field attenuation in air, the total reflection amplitude A _tot (t) determined in air as a function of the transit time t can be used.

In all other cases, either additional information about the gas must be available that enables the calculation of the total reflection amplitude A _tot (t) in the respective gas, or the total reflection amplitude A _tot (t) must be determined experimentally in the respective gas. This inevitably means that the gas must be known in advance. In practice, this involves a not inconsiderable amount of effort, which is generally only worthwhile if the gas is used above the filling material 1 in a sufficiently large number of locations for these measuring devices.

In the first case, equations (3) and (4) result in the ratio v ₁ /v ₀ of the propagation speeds v ₁ , v ₀ , from which the propagation speed v ₀ in the gas is determined using the known propagation speed v ₁ in the filling material 1 . In addition, the required reference distance H is determined by appropriately rewriting the distance D and the fill level L in equation (5) in the now known quantities t _L , t _B , v ₁ , v ₁ /v ₀ .

In the second case, too, the ratio v ₁ /v ₀ of the propagation velocities v ₁ , v ₀ results from equations (3) and (4). The propagation speed v ₀ required here above the filling material 1 is obtained by expressing the distance D and the filling level L in Equation (5) by the now known variables H, t _L , t _B , v ₁ /v ₀ and Equation (5 ) according to the propagation velocity v ₀ above the filling material 1.

gegeben.Based on the propagation speed v ₀ above the filling material 1 and the reference distance H, the assignment of the transit times t _L of the filling level echoes E L measured with the filling level measuring device to be determined by the comparison to the associated filling levels _L related to the reference height R can be determined by the relationship in both cases : $$\begin{array}{c}\text{L}=\text{H}-\text{D}\\ =\text{H}-{\text{½v}}_0{\text{t}}_{\text{L}}.\end{array}$$

given.

The adjustment method according to the invention can also be used in an analogous manner in connection with fill level measuring devices which conduct electromagnetic transmission signals S into the container by means of a probe protruding into the container.

3 shows a measuring arrangement with such a fill level measuring device. Here, too, the fill level measuring device comprises a transmitting and receiving unit 5, which emits the transmission signals S to be routed into the container 3 and receives the signal components R1, R2 reflected back in the container 3 to the transmitting and receiving unit 5, and corresponding measurement electronics 7 for further processing supplies.

Here, a probe 13, which protrudes into the container 3 during operation, is connected to the transmitting and receiving device 5, along which the transmitted signals S are fed back into the container 3 and their signal components R1, R2 reflected along the probe 7 to the transmitting and receiving device 5 . Here, too, the reflected signal components R1, R2 are received by the transmitting and receiving device 5 after a transit time t dependent on the distance covered along the probe 13. The electromagnetic transmission signals S are periodically transmitted high-frequency pulses. The probe 13 is a waveguide such as a Sommerfeld waveguide, a Goubauch waveguide or a coaxial waveguide. Either a single conductor or two or more conductors arranged parallel to one another can be used as waveguides, which extend downwards into the container 3 from a point above the highest filling level to be measured.

If the transmission signal S hits the filling material surface 9 in the container 3, then at least a signal component R1 of the transmission signal is reflected back due to the impedance jump existing at this media boundary. The transit time t of the received signal components R1, R2 is also generally determined with these level measuring devices by deriving an echo function A(t) from the received signal components R1, R2, which calculates the amplitudes A(t) of the received signals as a function of whose running time t represents.

In this variant, the reflector located at the reference distance H from the transmitting and receiving device 5 is provided by the probe end 15 facing away from the transmitting and receiving device 5 . The reference height R corresponds to the position of the probe end 15 in the container 3 and the reference distance H corresponds to the probe length. Signal portions R2 penetrating the filling material surface 9 are reflected here at the open end, as a result of which the sign of the signal amplitude is reversed. 4 shows an example of in the measurement arrangement of 3 derived echo function A(t). It has a filling level echo E _L that is due to the reflection of a signal portion R1 on the surface 9 of the filling material and a reflector echo E _B that is due to the reflection at the end of the probe 15 . The amplitude A _L of the level echo E _L has the same sign as the amplitude A ₀ of the transmitted signal S, while the amplitude A _B of the reflector echo E _B occurs with the opposite sign, since there is a physical reflection at the open end.

The same prerequisites mentioned above apply to the execution of the calibration according to the invention in connection with this type of filling level measuring device. This means that there must be a level range in which the level measuring device can identify both the level echo E _L and the reflector echo _EB , and either one of the propagation velocities v ₀ , v ₁ above or below the product surface 9 along the probe 13 or the reference distance H available as a previously known size.

Here, too, the propagation times t _L , t _B of the level echo E _L and the reflector echo E _B are measured, and an in 4 to calculate or to determine experimentally the total reflection amplitude A _tot (t _L ) drawn in dashed lines, which the filling level echo E _L would have if a total reflection were to take place on the filling material surface 9 under otherwise identical conditions. In contrast to the previous exemplary embodiment, however, instead of the free-field propagation of the signals, the line-bound propagation of the signals is to be taken as a basis here, which, however, is also known in terms of the formula for waveguides. It also applies here that the attenuation of the signals along the probe 13 in most gases is comparable to the corresponding attenuation in air, so that it is sufficient for most applications to calculate the total reflection amplitude A _tot (t _L ) as a function of the transit time t in air to calculate or to determine experimentally.

If the speed of propagation v ₀ of the electromagnetic signals S along the probe 13 above the filling material 1 and the length of the probe are known, no adjustment is required for a fill level measurement based on the reference height R.

However, with fill level measuring devices of this type, it is often provided that the probe length can be adapted to the needs of the respective application by subsequently shortening it becomes. In this case, the propagation speed v ₀ of the electromagnetic signals S along the probe 13 above the filling material 1 is generally known with an otherwise unchanged probe condition, but the reference distance H is no longer known or no longer with sufficient accuracy.

In this case, the adjustment described above for the case of a known propagation speed v ₀ above the filling material 1 with an unknown propagation speed v ₁ below the filling material 1 and an unknown reference distance H is also carried out in a completely analogous manner here by using equation (3) and ( 4) the ratio of the propagation velocities v ₁ /v ₀ and using equation (5) the reference distance H corresponding to the unknown probe length is determined, via which the searched assignment of the transit time t _L of the level echoes measured with the level measuring device to the reference height R related level L is given.

The same applies in the case of a known propagation speed v ₁ below the filling material 1 with an unknown propagation speed v ₀ above the filling material 1 and an unknown reference distance H.

A prerequisite for this, however, is that the total reflection amplitude A _tot (t) as a function of the transit time t for the gas located above the filling material 1 has previously been determined analytically, numerically or experimentally. In the above-mentioned cases of gases with an attenuation comparable to the attenuation in air, the total reflection amplitude A _tot (t) determined in air as a function of the transit time t can also be used here.

Also analogous to the corresponding exemplary embodiment described above, the adjustment method according to the invention can be used in connection with level measuring devices with guided electromagnetic signals in cases in which the probe length and thus the reference distance H is known, the propagation speed v ₀ of the guided signals above and below the However, filling material 1 is unknown.

The latter is the case, for example, when the probe 13 is subsequently provided with a coating that changes the signal propagation of the guided signals, or the probe 13 is placed in an environment that changes the signal propagation along the probe 13, such as a - in 3 dashed line indicated - surge pipe 17, is used.

The prerequisite for this is that the resulting propagation speed v ₀ above the filling material 1 is essentially constant over the entire length of the probe 13 . However, in applications in which this condition is not met, these level gauges cannot be used for level measurement anyway, regardless of the calibration method.

Here, too, the prerequisite is of course that the total reflection amplitude A _tot (t) as a function of the transit time t for the coated probe 13 or that inserted into the stilling well has been calculated in advance analytically or numerically or determined experimentally. Additional information about the surge pipe 17 or the coating is required for this in advance.

The adjustment method according to the invention offers the advantage that it can be carried out completely automatically by the respective filling level measuring device without a specific filling level L having to be set, specified or otherwise determined by the user. The adjustment method can thus be carried out at any time without the process running in the container 3 having to be interrupted or changed.

It can also be used when the attenuation of the signals in the filling material 1 is too high to clearly identify the reflector echo E _B when the container 1 is relatively full. In this case, the fill-level measuring device carries out the calibration process until the fill level L in the container 3 has dropped so far due to the process already taking place there that both required echoes E _B , E _L can be identified beyond doubt.

1

Füllgut

3

Behälter

5

Sende- und Empfangsvorrichtung

7

Messelektronik

9

Füllgutoberfläche

11

Behälterboden

13

Sonde

15

Sondenende

17

Schwallrohr

The same applies accordingly if the container 1 is empty at the beginning of the calibration, since the required amplitude A _L of the level echo E _L cannot be determined when the container 3 is empty. In addition, when the container 3 is empty, level measuring devices that emit their transmission signals S freely cannot distinguish whether the only identifiable echo originates from a level L or from the reflector. Here, too, the method is continued accordingly until a fill level L in the container 3 that is sufficiently high for the identification of the two required echoes E _L , E _B occurs.

1

contents

3

container

5

Transmitting and receiving device

7

measuring electronics

9

product surface

11

container bottom

13

probe

15

probe end

17

stillpipe

Claims (7)

Method for adjusting a fill-level measuring device for measuring a fill level (L) of a filling (1) in a container (3), - which, in a measuring operation, transmits electromagnetic transmission signals (S) in the direction of the filling (1) by means of a transmitting and receiving device (5) transmits and receives its signal components (R1) reflected on a filling material surface (9) after a transit time (t L ) dependent on the fill level ( _L ), and - based on this transit time (t _L ), the fill level (L) in the container (3) in relation to a reference level (R) located at a reference distance (H) from the transmitting and receiving device (5) in the container (3) is determined, in measuring arrangements in which - at least in the case of levels (L) lying within a level range, a signal component (R2) of the Transmission signals (S) penetrate the filling material surface (9) and are received via a reflection on a reflector located at a reference distance (H) from the transmitting and receiving device (5) after a transit time (t _B ) dependent on a distance covered in the container (3). - a total reflection amplitude (A _tot (t)) can be calculated as a function of the transit time (t) or has been experimentally determined beforehand, which is equal to an amplitude which a signal component reflected in the container (3) received after the transit time (t) has would have occurred if total reflection had taken place at the associated reflection site, and - either one of the propagation speeds (v ₀ , v ₁ ) of the signals above or below the filling material surface (9) or the reference distance (H) is a known size, at which - if present a fill level (L) within the fill level range, the propagation times (t _L , t _B ) of a signal component (R1, R2) reflected on the fill material surface (9) and of a signal component (R1, R2) reflected on the reflector and an amplitude (A _L ) of the signal component on the fill material surface (9) reflected signal component (R1) can be measured, - based on a physical dependence of a signal component (R1) reflected on the filling material surface (9) by a ratio of the amplitude (A _L ) to the total reflection amplitude (A _tot (t _L )) at the transit time (t _L ) of the signal portion (R1) reflected on the surface (9) of the filling material given reflection coefficient (r) of a ratio of the roots of the dielectric constants (ε _L , ε _G ) of the filling material (1) and a gas located above the filling material (1) a ratio (v ₁ /v ₀ ) of the propagation velocities (v ₀ , v ₁ ) above and below the filling material surface (9) is determined, and - using the ratio (v ₁ /v ₀ ) of the propagation velocities (v ₀ , v ₁ ), an assignment is determined from the measured transit times (t _L , t _B ) and the known quantity, the transit times (t _L ) measured by the level gauge from signal components (R1) reflected on the product surface (9) related to the reference level (R) levels (L ) assigned. procedure after claim 1 , in which - the adjustment procedure is started when any fill level (L) is present in the container (3), - a process takes place in the tank (3) during the adjustment, as a result of which the fill level (L) changes as a function of the process, - the fill level measuring device sends transmission signals into the container (3) during the adjustment and derives echo functions (A(t)) from the received signal components (R1, R2) reflected in the container (3) which determine the amplitudes (A) of the received signal components ( R1, R2) as a function of the travel time (t) required for the distance covered in the container (3) until in one of the echo functions (A(t)) a maximum attributable to a reflection on the filling material surface (9) and a maximum maximum due to reflection at the reflector. procedure after claim 1 , in which - the transmission signals (S) are freely radiated microwave signals, especially microwave pulses or frequency-modulated signals, and - the reference distance (H) is a distance between the transmitting and receiving device (5) and a container bottom (11) of the container (3) is. procedure after claim 1 , in which - the fill level measuring device has a probe (13) which is connected to the transmitting and receiving device (5) and protrudes into the container (3) and which transmits the transmitted signals (S) into the container (3) and those in the container (3 ) signal components (R1, R2) reflected along the probe (13) to the transmitting and receiving device (5) and - the reference distance (H) is equal to a mechanical probe length of the probe (13). procedure after claim 1 , in which - the propagation speed (v ₀ ) of the signals above the filling material surface (9) is known, - based on the propagation speed (v ₀ ) of the signals above the filling material surface (9), the ratio (v ₁ /v ₀ ) of the propagation velocities ( v ₀ , v ₁ ) and the measured propagation times (t _L , t _B ) of the signal component (R1) reflected on the filling material surface (9) and of the signal component (R2) reflected on the reflector, the reference distance (H) is determined, and - the assignment takes _place by adding a distance (D) _between the transmitting and receiving device (5 ) and the Filling material surface (9) is assigned, and a filling level (L) related to the reference height (R) is assigned to this, which corresponds to a difference between the reference distance (H) and the distance (D) between the transmitting and receiving device (5) and the Filling material surface (9) corresponds. procedure after claim 1 , in which - the propagation speed (v ₁ ) of the signals below the filling material surface (9) is known, - based on the propagation speed (v ₁ ) of the signals below the filling material surface (9) and the ratio (v ₁ /v ₀ ) of the propagation velocities ( v ₀ , v ₁ ) the propagation speed (v ₀ ) of the signals above the filling material (1) is determined, - using the propagation speed (v ₁ ) of the signals below the filling material surface (9), the ratio (v ₁ / v ₀ ) of Propagation velocities (v ₀ , v ₁ ) and the measured propagation times (t _L , t _B ) of the signal component (R1) reflected on the filling material surface (9) and of the signal component (R2) reflected on the reflector, the reference distance (H) is determined, and - the assignment is made by assigning a distance (D) between the transmitting and receiving device to the propagation speed (v ₀ ) above the filling material (1) measured by the filling level measuring device (t _L ) of signal components (R1) reflected on the filling material surface (9). (5) and the surface (9) of the filling material, and a filling level (L) related to the reference height (R) is assigned to this, which is a difference between the reference distance (H) and the distance (D) between the transmitting and receiving device (5) and the filling material surface (9). procedure after claim 1 , where - the reference distance (H) is known, - based on the reference distance (H), the ratio (v ₁ /v ₀ ) of the propagation velocities (v ₀ , v ₁ ) and the measured propagation times (t _L , t _B ) of the The propagation velocity (v ₀ ) occurring above the filling material (1) is determined from the signal portion (R1) reflected on the surface (9) of the filling material and the signal portion (R2) reflected at the reflector, and - the assignment is made by the propagation times measured by the filling level measuring device (t _L ) a distance (D) between the transmitting and receiving device (5) and the surface (9) of the filling material is assigned to signal components (R) reflected on the filling material surface (9) via the propagation speed (v ₀ ) above the filling material (1), and this is assigned a level (L) related to the reference level (R), which corresponds to a difference between the reference distance (H) and the distance (D) between the transmitting and receiving device (5) and the surface (9) of the filling material.

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