DE102004051999A1 - Level measurement process based on runtime principle, e.g. used in food processing or chemical processing industry, involves using echo signals obtained from liquid filling container to determine level of liquid inside container - Google Patents

Abstract

Level measurement process involves measuring the level of the liquid (1) filling a container (3) based on runtime principle. A transmission signal (S) is sent to the liquid in the container. The echo signals (R) received from the liquid is then used to determine the level of liquid in the container. The amplitudes of the echo signals indicate the level of the liquid in the container.

Description

The The invention relates to a method for level measurement according to the transit time principle.

To Become the runtime principle level gauges used in a variety of industries, e.g. in the manufacturing industry, in chemistry or in the food industry.

at the level measurement transmit signals, e.g. short electromagnetic pulses, microwaves or sonic or ultrasonic waves sent to the surface of a medium and their on the surface reflected echo signals are received again after a distance-dependent transit time. It becomes one of the echo amplitudes as a function of the term representing Echo function formed. Each value of this echo function corresponds the amplitude of a reflected at a certain distance from the level gauge Echoes.

Based The echo function determines an echo, which is probably the Reflection of a transmission signal on the product surface corresponds. It will usually assumed that this echo, a larger amplitude has, as the other echoes. From the duration of this echo results at a fixed propagation speed the transmission signals directly the distance between the Füllgutoberfläche and the level gauge.

It become today mainly the following three types of run-time-based Level gauges used: A first type generates short electro-magnetic pulses in the area of a nanosecond running along a conductor in the direction of filling material guided become. Due to the product surface of the impedance jump reflected there, echo signals are propagated along the ladder back out of the container led out.

When Head can doing both a single and two or more parallel to each other arranged ladder extending from a point above the highest to be measured level down into the container extend into it.

One second type generates microwaves by means of an antenna in Direction of the product sent, reflected on the product surface and subsequently after a distance-dependent Runtime be received again.

One third type generates sound or ultrasonic waves in the direction of the contents sent, reflected on the product surface and then after a distance-dependent Runtime be received again.

For all level measuring instruments operating according to the transit time principle, the level measurement is carried out as follows:
Sending signals are sent in the direction of the contents, and their echo signals are received. Based on the echo signals, an echo function is derived which contains amplitudes of the echo signal as a function of their transit time. The echo of the echo function is determined, which originates from the reflection at the product surface and calculates the fill level on the basis of its transit time. It is assumed, for example, that the sought echo has the largest amplitude. Usually, the running time of the maximum of the selected echo is used for filling level calculation.

at depends on this known method the measurement accuracy crucially depends on how exactly the position of the maximum can be determined. However, there are measurement situations where the exact determination of the position of the maximum difficulties prepares.

One reason for this is, for example, a limited bandwidth of signal processing. For example, in order to evaluate signals with small amplitudes, a high gain of the incoming echo signals is made. If subsequently echoes are recorded with a comparatively very large amplitude, the signal processing reaches saturation and / or overload. Accordingly, portions of the very large amplitude echo signals are not sufficiently amplified. The resulting echo function then shows a flat profile instead of a localizable maximum. An example of this is in 1 shown. There, the amplitude A (t) of an echo is shown as a function of the transit time t. The solid line schematically shows the actual shape of the echo. The dashed line shows the associated echo, which is recorded if, for example, the gain is insufficient.

Likewise, problems occur when the echo originating from the filling level is superimposed by another echo, for example from internals in the container or at low levels from the container bottom. Although this superimposition is generally recognized as the echo to be used for level measurement, its maximum can be shifted from the maximum of the pure level echo. 2 shows an example of the amplitudes A (t) of two echoes E ₁ and E ₂ and their superposition as a function of the transit time t. Likewise, the transit times t ₁ , t _{2 of} the maxima M ₁ , M _{2 of} the two echoes E ₁ , E ₂ and the superposition are indicated. The transit time t _{N1 of} the maximum of the overlay coincides with none of the transit times t ₁ and t _{2 of} the maxima M ₁ , M _{2 of} the two echoes E ₁ , E ₂ . Similar conditions arise, if there is an additional layer on the medium. This occurs, for example, when there is foam on the product, or when, for example, an oil layer floats on the product.

As well can Cases occur in which e.g. a background signal or smaller interference signals too cause a deformation of the amplitude curve of the echo function.

The the latter problem is in the German patent application DE-A1 101 42 538. There is a method of measuring a filling level a filling material in a container with a fill-level measuring device operating according to the transit time principle, are sent in the transmission signals in the direction of the contents, and whose echo signals are received. In this method, the received echo signal sampled, digitized and with an already previously digitized stored received or transmitted signal or a provided synthetic signal. It is described to express the synthetic signal by suitable parameter-dependent model formulas the expected waveform of the echo signal as possible play well. The parameters are adjusted so that a Correlation coefficient of the correlation of the echo function and the synthetic function maximum or the sum of the Gaussian error squares the deviation of the two functions from each other is minimal. The for the level determination The runtime to be determined is then based on an envelope the optimized correlation function of the echo signal and the synthetic Signals determined. Although this method is suitable for avoidance errors caused by run-time-dependent shape changes the signals are generated. It can, however, by maximizing the correlation coefficient and the subsequent transit time determination the correlation function that form changes that are due to interference be simulated by the synthetic function and the measurement result distort.

It An object of the invention is a method for level measurement with a level measuring device operating according to the transit time principle, with the one higher Measuring accuracy can be achieved.

• – Sendesignale in Richtung des Füllgutes gesendet werden,
• – deren Echosignale empfangen werden,
• – anhand der Echosignale eine Echofunktion abgeleitet wird, die Amplituden des Echosignals in Abhängigkeit von deren Laufzeit enthält,
• – anhand der Echofunktion Echoeigenschaften eines Nutzechos abgeleitet werden,
• – anhand der Echoeigenschaften ein Hilfsecho erzeugt wird,
• – das Hilfsecho mit dem Nutzecho verglichen wird, und
• – anhand des Hilfsechos ein aktueller Füllstand bestimmt wird.

This is achieved by the invention by a method for measuring a filling level of a filling material in a container with a filling level measuring device operating according to the transit time principle, in which

• - transmission signals are sent in the direction of the contents,
• - whose echo signals are received,
• An echo function is derived on the basis of the echo signals, which contains amplitudes of the echo signal as a function of their transit time,
• Echo properties of a useful echo are derived on the basis of the echo function,
• An auxiliary echo is generated on the basis of the echo properties,
• - the auxiliary echo is compared with the useful echo, and
• - Based on the auxiliary echo a current level is determined.

According to one Further development of the method is the auxiliary echo to the useful echo customized.

According to one Further development, the auxiliary echo is a phase and amplitude-accurate overlay of two or more parts echoes. The auxiliary echo becomes with the useful echo compared. The current level is determined by the part echo that is a reflection assigned to the product surface becomes.

According to one Design becomes a measure of a deviation between the auxiliary echo and the wanted echo, and the deviation minimized by adjusting the auxiliary echo.

According to one Continuing a Hilfsechosignal is generated and this goes through at least a part of a signal processing that the echo signals for generating go through the echo function.

According to one First embodiment, the level gauge comprises at least one in the container protruding conductor and the transmission signals are short electromagnetic Pulses directed along the conductor to the product surface and back.

According to one second embodiment, the level gauge at least a sonic or ultrasonic transducer, and the transmit and receive signals are sound or ultrasonic signals.

According to one third embodiment, the level gauge is a with Microwave operating level gauge, the one Antenna for transmitting transmission signals and for receiving their echo signals having.

According to one Development of the first, second or third embodiment has the auxiliary echo one described by a mathematical function Amplitude curve whose shape adapted to sections of the echo is.

The Invention and further advantages will now be described with reference to the figures of Drawing in which five embodiments are shown, closer explains; the same elements are denoted by the same reference numerals in the figures Mistake.

1 shows an amplitude of an overdriven echo as a function of time compared to the actual amplitude of the echo;

2 shows an amplitude curve of an echo, which is due to a superposition of two individual echoes;

3 shows a level measuring device with a level gauge, which leads in operation short electromagnetic pulses along a conductor into a container into it;

4 shows a typical course of an echo function of the level gauge of 3 ;

5 shows the measuring arrangement of 3 with two additional circuits for generating component echo signals;

6 shows a level measuring arrangement with a microwave level gauge;

7 shows an amplitude of an intermediate frequency signal of the level measuring arrangement of 6 as a function of time;

8th shows the measuring arrangement of 6 with two additional circuits for generating component echo signals; and

9 shows a level measuring device with a working with sonic or ultrasonic level gauge.

In 3 a first embodiment of a level measuring device is shown with a running on the transit time principle level gauge. The level gauge is used to measure a level of a product 1 in a container 3 ,

The level gauge includes meter electronics housed in an in 1 not shown housing is arranged and with a conductor 5 connected to the container 3 protrudes into it. It is a coupling connected to the housing 7 provided, as in 1 is shown only schematically, in an opening of the container 3 is mounted.

The leader 5 is for example a mechanically rigid rod or a mechanically rigid wire. Equally, however, a tensioned rope can be used, one end of the housing or the coupling 7 and the other end to a bottom of the container 3 is attached. Instead of attaching the other end to the container bottom, a weight may also be attached to the other end, through which the cable is tensioned.

According to the method of the invention, transmission signals S in the direction of the filling material are produced during operation 1 Posted. For this purpose, the meter electronics has an electronic circuit 9 which generates electromagnetic signals S during operation. These signals S are via the coupling 7 from the circuit 9 on the ladder 5 transferred and along the conductor 5 in the container 3 led into it.

The signals S are reflected on the product surface and their echo signal R is transmitted through the conductor 7 from the container 3 led out.

The echo signal R is a receiving and evaluating circuit 11 fed, which receives this, and determines the level.

The propagation speed of the transmit and receive signals S, R and the distances between the electronic circuit 9 and the container bottom and between the receiving and evaluating circuit 11 and the bottom of the container are either known anyway or can be obtained by simple reference measurements. With the aid of the echo signal R, these data can be used to determine the height of the filling material above the container bottom and thus the filling level.

In the illustrated embodiment, the transmission signals S are short electromagnetic pulses. The electronic circuit 9 has a transmit clock 13 and a transmit pulse generator 15 on. A send clock of the transmit clock 13 is the transmit pulse generator 15 fed. Preferably, a transmit pulse generator 15 used, which generates electromagnetic signals that have the form of low-energy high-frequency short pulses. Such transmit pulse generators as well as electronic circuits usable in conjunction therewith and receiving and evaluating circuits are described, for example, in US Pat. No. 5,345,471 and US Pat. No. 5,361,070. They are pulses with a peak line of less than 1 μW and an effective power 1 nW or less with frequencies of 100 MHz and more can be generated. The transmission rate is for example a few MHz.

The transmission signals S are a directional coupler 17 and from there via the coupling 7 the leader 5 fed. Along the ladder 5 reflected Signals form the echo signal R, via the conductor 5 , the coupling 7 , the directional coupler 17 and a directional coupler 17 downstream high pass 19 the reception and evaluation circuit 11 is supplied.

Based on the echo signals R, an echo function is derived, which reproduces the amplitudes of the echo signal R as a function of their transit time. This includes the reception and evaluation circuit 11 a time delay 21 , at whose input the transmission clock of the transmission clock generator 13 is present The time delay 21 generates a sampling clock which corresponds to the transmission clock delayed by a variable delay time. The variable delay time is provided, for example, by means of a sawtooth generator. The sampling clock is a sampling pulse generator 22 supplied, which generates in response to the sampling clock sampling pulses and a first input of a sample and hold circuit 23 supplies. Sample and transmit pulse generator 22 . 15 are preferably identical, so that the electromagnetic signals generated by them differ only by the variable delay time.

The echo signals R are above the directional coupler 17 and the high pass 19 at a second input of the sample and hold circuit 23 at.

In operation, short transmission signals S are preferably generated periodically with the transmission clock frequency and the reflected echo signals R of the sample and hold circuit 23 fed. There, a sampling pulse is superimposed on each echo signal R and a resulting total signal is recorded by means of a downstream amplifier 24 amplified, by means of one in series with the amplifier 24 arranged analog-to-digital converter 25 digitized and a microprocessor 26 supplied as a sample.

The total signal is a measure of the match of echo signal R and sample pulse. The echo signals R arrive periodically, and successive sampling pulses differ from one another by the time delay running according to a sawtooth function. Assuming that successive echo signals R do not differ significantly, the sample and hold circuit provides 23 a stroboscopic recording of the echo signals R. This requirement is typically always met, since the level in the period between two transmission signals S practically does not change.

The microprocessor 26 is over a first line 27 with the transmission clock generator 13 and over a second line 28 with the sampling clock generator 21 connected. During operation, the microprocessor starts 26 regular measuring cycles. During a measuring cycle, the transmission signals S are generated periodically as described above and the echo signals R are sampled. A measurement cycle ends when all the time delays provided in accordance with the sawtooth function have been completed. The individual samples are each recorded in conjunction with the associated instantaneous delay. This gives the echo function.

4 shows an example of such an echo function. The echo function has two pronounced echoes E ₃ and E ₄ . Each echo E ₃ , E ₄ has a pronounced maximum M ₃ and M ₄ . The first echo E ₃ is due to reflections in the region of the coupling 7 conditionally, where inevitably impedance jumps occur. The second echo E ₄ is due to a reflection on the product surface.

The accuracy with which the fill level can be determined depends essentially on how exactly the position of the maximum M ₄ can be determined.

According to the invention, a useful echo is first determined on the basis of the echo function. The useful echo is that echo E which is at least partly due to a reflection on the product surface. It is possible that the wanted echo is not the pure sought-after level echo, but this level echo staccato, which are due to other reflections, or other interference signals, such as noise, are superimposed. To determine the useful echo a variety of different methods are used in the industry today. For example, the useful echo can be determined in such a way that the echo, in this case E ₄ , having the largest amplitude is selected as the useful echo. In the determination, this remains due to reflections in the region of the coupling 7 conditional first echoes E ₃ unconsidered.

Subsequently, according to the invention, at least one echo property of the useful echo is derived. Echo properties are significant physical quantities of the useful echo, such as the transit time t _{M of} the maximum of the useful echo, the associated amplitude A _M and the width b _{M of} the useful echo. Likewise, individual values of the amplitude of the echo function as a function of the associated propagation time can be derived as echo properties. The echo properties can be derived, for example, by simple algorithms based on the echo function. The determination of the echo properties is preferably carried out directly in the microprocessor 26 ,

Based These echo properties generate an auxiliary echo.

In the simplest case, it is sufficient to set up the echo function of the auxiliary echo by simulation calculations. It is exploited that echoes un optimal conditions, ie without the influence of disturbances, which in 4 have shown prominent shape. The transit time t _{M of} the maximum corresponds to the level, the amplitude A _{M of} the maximum and the width b _{M of} the echo depend directly on the transit time t _{M of} the maximum. These dependencies can be determined beforehand, preferably ex works, in reference measurements.

In This simplest case is based on the echo properties of the useful echo the auxiliary echo, or its echo function, determined by on the basis the previously determined dependencies Simulation calculations performed become.

The Auxiliary echo is compared with the useful echo. Preferably, the Auxiliary echo here on the basis of the determined echo properties adapted to the true echo, the greatest possible match between useful echo and auxiliary echo is achieved. In this case, preferably a measure of a deviation between the auxiliary echo and the wanted echo, and minimizes. As a measure of the deviation known methods, e.g. a minimization of the distance squares, which are applied to the echo functions of payload and auxiliary echo can. The minimization of the deviation may e.g. be done by that add correction values to one or more echo properties and the auxiliary echo based on the corrected echo properties is determined. It can Criteria for the reliability of the individual echo properties. Leave these e.g. based on the previously described dependencies of the echo properties set up among themselves. Likewise or additionally, a weighting the echo properties take place.

At the At the end of this adjustment process, an auxiliary echo is available a best possible reproduction based on the echo properties representing the useful echo. In contrast to the useful echo, this is Auxiliary echo, however, free of overlays of interfering signals and / or background signals.

Subsequently, the filling level is determined on the basis of the auxiliary echo obtained by the comparison. This happens, for example, in the same way as in conventional level measurements, in which the level is determined directly on the basis of the useful echo. For example, the level can be calculated based on the running time t _{M of} the maximum of the auxiliary echo. Since the auxiliary echo is free from disturbance variables and / or background signals, this significantly improves the accuracy of the fill level measurement.

alternative to the described simplest case, in which the auxiliary echo through Simulation calculations is determined, the auxiliary echo can also circuitry be generated.

In the in 3 illustrated embodiment is to generate the auxiliary echo an additional circuit 29 intended. The circuit 29 includes one to the microprocessor 26 connected clock 30 and a pulse generator 31 that with the clock from the clock 30 predetermined frequency pulses generated. clock 30 and pulse generator 31 are preferably identical to the corresponding components of the electronic circuit 9 built up. The generated pulses are successively a time delay stage 32 with adjustable delay time τ, a signal expansion device 33 with adjustable time expansion factor ε and an attenuator 34 supplied with adjustable damping δ. The setting of the delay time τ, the time expansion factor ε and the attenuation δ takes place via the microprocessor 26 ,

At the output of the additional circuit 29 the auxiliary echo is available in the form of an auxiliary echo signal. This is recorded in the same way as the echo signal R and an echo function of the auxiliary echo is determined.

This is the clock 30 to the time delay 21 connected and the auxiliary echo signal is an input of the sample and hold circuit 23 fed. Again, the time delay generates 21 a sample clock which is the clock generator delayed by a variable delay time 30 equivalent. The variable delay time is provided, for example, by means of a sawtooth generator. The sampling clock is the sampling pulse generator 22 supplied, which generates in response to the sampling clock sampling pulses and the first input of the sample and hold circuit 23 supplies. Sample and pulse generator 22 . 31 are preferably identical, so that the electromagnetic signals generated by them differ only by the variable delay time.

When generating the auxiliary echo, short pulses are periodically generated at the clock frequency and the auxiliary echo signals derived therefrom of the sample and hold circuit 23 fed. There, a sampling pulse is superimposed on each auxiliary echo signal and a resulting total signal is recorded by means of the amplifier 24 amplified, by means of the analog-to-digital converter 25 digitized and a microprocessor 26 supplied as a sample.

The total signal is a measure of the coincidence of the auxiliary echo signal and the sampling pulse. The auxiliary echo signals arrive periodically and successive sampling pulses differ from one another by the time delay running according to a sawtooth function. The sampling and hold circuit 23 provides a stroboscopic recording of the auxiliary echo signal.

The microprocessor 26 is via a third line 35 with the clock generator 30 and over the second line 28 with the sampling clock generator 21 connected.

During operation, the microprocessor starts 26 regular measuring cycles. Following each or on selected measurement cycles, the echo function of the echo signal R determines the useful echo and at least one echo property of the echo is determined. Subsequently, the auxiliary echo signal is generated based on the echo properties, recorded and derived its echo function.

Of the further sequence corresponds to that of the previously described embodiment, in which the auxiliary echo was determined purely by calculation. It will be that Auxiliary echo compared to the useful echo and based on the auxiliary echo the current level certainly.

The auxiliary echo signal passes through a part of the signal processing, namely the sample and hold circuit 23 to the microprocessor 26 that the echo signals R make to produce their echo function. Signal processing, whether hardware or software, always has a slight impact on the shape of the echoes it processes. Since the auxiliary echo signal experiences the same shape changes as the received echo signal R, these shape changes are automatically taken into account and do not lead to deviations between the signals to be compared in the subsequent comparison. This applies to both hardware and software components of signal processing.

With The method described can be very accurate level measurements perform, there the level determined by the optimally adjusted auxiliary echo. Uncertainties, the e.g. by background noise and smaller superimposed on the echo signal R. noise arise are avoided by the method according to the invention.

However, the method can not only be used with small disturbances, but can also be used when the useful echo not only by reflection on the medium 1 The resulting echo, but this is superimposed on another pronounced echo. This case can occur, for example, if an interferer, eg an agitator or container installations, is located in the vicinity of the product surface.

Preferably will in these cases an auxiliary echo is used, which is a phase and amplitude accurate overlay of two parts echoes is. This auxiliary echo is compared with the useful echo and Based on the comparison, the level is certainly. In the process, that of the two part echoes is evaluated, assigned to the reflection on the product surface becomes.

First of all to determine if a useful echo is a superposition of two or more echoes is, or is it a single echo, the smaller one Interferences superimposed are.

there can e.g. the previously described measure of the deviation between the Auxiliary echo and the useful echo are used. If e.g. the measure also after completed adjustment of the auxiliary echo still exceeds a predetermined threshold, So it can be assumed that the useful echo by a only a single echo containing auxiliary echo is not sufficiently accurate can be given again. Accordingly, in this case, a Auxiliary echo used, which is a phase and amplitude-accurate overlay of two or more parts echoes.

2 shows an example of a typical course of the echo function of the useful echo, as it occurs when the useful echo denoted here by E _N is a superposition of two echoes E ₁ , E ₂ . The useful echo E _N is a superimposition of the echo E ₁ attributable to the reflection on the product surface and of another echo E ₂ .

The echo function differs significantly from the in 4 echo function shown, wherein the useful echo E ₄ goes back only to the reflection from the product surface. The useful echo has here not only a pronounced maximum, but two closely adjacent maxima M _N1 , M _N2 .

Due to the superposition, the absolute maximum M _N1 has an amplitude that is greater than the corresponding amplitudes of the maxima of the individual echoes E ₁ , E ₂ . These differences represent criteria by which it is possible to determine if a useful echo is a simple echo, superimposed on minor perturbations, or if the useful echo is a superposition of two or more individual echoes. The criteria can be checked by appropriate algorithms using the echo function of the useful echo.

Corresponding the result of this review will be an auxiliary echo is used, which is a phase and amplitude accurate overlay of two or more parts echoes.

The measure of the deviation between the first determined only containing an echo Auxiliary echoes, as well as the above criteria represent two different process steps, which can be applied either alternatively or side by side.

At the At the end of these process steps, the level is as described above determined on the basis of an auxiliary echo containing only one echo, if In this way, the useful echo can be reproduced sufficiently accurately. If this is not the case, the echo function is determined by the echo properties of the useful echo generates an auxiliary echo, which has a phase and amplitude-faithful overlay of two or more parts echoes.

In most cases enough it to generate an auxiliary echo that is an overlay of two part echoes is.

This auxiliary echo is created on the basis of the echo properties of the echo function of the useful echo. As echo properties, the transit times t _N1 , t _N2 and the amplitudes A _N1 , A _{N2 of} the first and second maximum M _N1 , M _{N2 of} the useful echo, and the width b _{N of} the useful echo are preferably determined. On the basis of these echo properties, parameters of the two part echoes are derived. These are eg transit time t ₁ , t ₂ and amplitude A ₁ , A _{2 of} the maxima M ₁ , M _{2 of} the two part echoes E ₁ , E ₂ . In this case, the amplitude A ₁ , A ₂ can be estimated or calculated, or derived, for example, based on the transit time t ₁ , t ₂ . In addition, an estimated value for the width b ₁ , b _{2 of} each part echo E ₁ , E ₂ can be determined on the basis of the echo properties. However, the width b ₁ , b ₂ can also be derived from run time t ₁ , t ₂ and amplitude A ₁ , A _{2 of} the maximum M ₁ , M _{2 of} the respective part echo based on the knowledge of the distinctive echo shape to be expected for a single echo. In the level measurement principle described here, in which short electromagnetic pulses are guided along a conductor, the echo form of a single echo can be described very well, for example, by a simple mathematical function, eg a Gaussian curve.

On the basis of these characteristics, the two parts echoes E ₁ , E _{2 are} generated. This can be done by simulation calculations as described above.

Subsequently, a phase and amplitude accurate superposition of the two part echoes is made. This can also be done by appropriate calculations in the microprocessor 26 respectively.

The thus obtained auxiliary echoes is compared with the useful echo. Preferably the auxiliary echo is based on the determined echo properties adapted to the true echo, the greatest possible match between useful echo and auxiliary echoes is achieved. In this case, preferably a measure of a deviation between the auxiliary echo and the wanted echo, and minimizes. As a measure of the deviation known methods, e.g. a minimization of the distance squares, which are applied to the echo functions of payload and auxiliary echo can. The minimization of the deviation takes place by an adaptation of the Part echoes. In doing so, e.g. one or more characteristics of Part returns added correction values. The part-echoes will be on the basis of the corrected parameters and determined to a corrected Auxiliary echo phase and superimposed on amplitude. It can Criteria for the reliability the individual parameters with be included. These can be e.g. based on the previously described dependencies the echo properties among themselves, of course, for the characteristics of the Parts echoes apply, set up. Likewise or additionally, a weighting the parameters take place.

At the At the end of this adjustment process, an auxiliary echo is available a best possible reproduction based on the echo properties representing the useful echo. The auxiliary echo consists of two parts echoes, unlike the two echoes that make up the useful echo composed, free of overlays of interfering signals and / or background signals. The parameters of the part returns are available level determination to disposal. It can now be determined that part of the echo, the reflection is due to the product surface. You can do this Again, all known methods are used. In general it is assume that the part-echo whose maximum is the larger amplitude has the sought part echo. In addition, however, also data from previous Measurements are used, from which e.g. a temporal evolution the level can be derived. Based on this data, a forecast can be created will be used to select the partial echo you are looking for can.

An auxiliary echo consisting of two parts echoes can not only be determined by simulation calculations, it can also be generated by circuitry. This is in 5 shown. Since that in 5 illustrated embodiment largely identical to the in 3 illustrated embodiment, only the existing differences will be explained in more detail below.

In the in 3 illustrated embodiment is to generate the auxiliary echo an additional circuit 29 intended. At the in 5 illustrated embodiment are two additional circuits 29a . 29b whose structure and mode of operation are identical to those of 3 shown additional circuit 29 are. Every additional circuit 29a . 29b generates a partial echo signal in each case. The delay times τ1, τ2, the time expansion factors ε1, ε2 and the attenuations δ1, δ2 for the individual component echo signals are independent of each other by the microprocessor 26 adjustable. At the output of each additional circuit 29a . 29b the corresponding part echo signal is applied. The component echo signals are an adder 36 supplied to the output of the auxiliary echo signal is present as a phase and amplitude true superposition of the two part echoes. The auxiliary echo signal is the sample and hold circuit 23 fed. The further signal processing takes place exactly as in the 3 illustrated embodiment.

In a completely analogous way, the method can also be used in conjunction with microwave level measuring devices. This is below based on the in 6 illustrated embodiment illustrated. The level gauge includes an antenna 37 , By means of periodically short transmission signals S in the direction of the medium 1 sent and their echo signals R are received again. In the pulse radar method described here as an example, the transmission signals S are short microwave packets.

In the in 6 illustrated embodiment, the transmission signals S by means of a microwave generator 38 generated. It is a generator oscillating at a pulse repetition frequency fs 39 provided with a control circuit 40 connected is. The control circuit 40 starts the microwave generator 38 for a very short time interval, which corresponds to the desired pulse duration of the microwave pulses to be transmitted, and then stops it again. This process is repeated with that at the control circuit 40 applied pulse repetition frequency f _S. This is eg a few megahertz. The microwave generator 38 is via a directional coupler 41 or one in 6 not shown circulator with the antenna 37 connected.

About the antenna 37 Sending transmitted signals S are reflected at the Füllgutoberfläche and their echo signals R after a level-dependent run time again from the antenna 37 receive. The received echo signals R are transmitted via the directional coupler 41 an amplifier 42 whose output is connected to a first input of a mixer 43 connected is.

The oscillating with the pulse repetition frequency f _S generator 39 is over a time delay stage 44 and a second identical to the first control circuit 40 working control circuit 45 with a second microwave generator 46 connected. The second microwave generator 46 is identical to the first microwave generator 38 built up. The second control circuit 45 causes the second microwave generator 46 with the pulse repetition frequency recurrently generates microwave pulses. These are located at a second input of the mixer 43 at. The time delay level 44 Delays the incoming signals by a variable, eg according to a sawtooth function of finite width increasing delay time. In the mixer 43 Thus, a microwave signal delayed by a level-dependent propagation time is superimposed with a substantially form-equal microwave signal delayed by a variable delay time. That at the outlet of the mixer 43 The available signal corresponds to the correlation of the incoming microwave signals at its two inputs. It contains a high-frequency component which contains frequencies which are essentially given by the sum of the frequencies applied to the inputs and a low-frequency component which contains frequencies which are essentially given by the difference of the frequencies present at the inputs. It is done by means of a low pass 47 the low-frequency component filtered out and another amplifier 48 fed to a further processing and / or evaluation. The low-frequency component is usually referred to as an intermediate frequency signal and is a low-frequency image of the echo signal R.

The amplified intermediate frequency signal is detected by a sample and hold circuit 49 recorded and then in an analog-to-digital converter 50 digitized. In addition, optionally, between the sample and hold circuit 49 and the analog-to-digital converter 50 a rectifier and a logarithmic be provided. The two optional components are in 6 together with O. Instead of corresponding components, the functions of the components can also be simulated software-technically. An output of the analog-to-digital converter 50 is with a microprocessor 51 connected, which records the respective signal amplitudes together with the associated delay time. The delay time corresponds to the transit time of the corresponding segment of the echo signal R. In the microprocessor 51 There is thus an echo function that reproduces the amplitudes of the echo signal as a function of their transit time. Preferably, the immediate recording of the actual intermediate frequency signal is not used as echo function, but their envelope.

7 shows a typical course of such an echo function, as occurs under ideal conditions, when the transmission signal S is reflected exclusively on the product surface. The envelope of the intermediate frequency signal is in 7 shown as a solid line. This echo function has two pronounced maxima M ₅ , M ₆ . A form of the associated echoes E ₅ , E ₆ becomes very good described by a Gaussian function. If the echo signal R is rectified and logarithmized, the shape of these echoes is very well described by a parabola. The first echo E ₅ , corresponds to the short microwave pulse of the transmission signal S, via the directional coupler 41 is recorded immediately. The second echo E ₆ is due to a reflection of the transmission signal S at the product surface.

In conventional methods for level measurement, the second echo E ₆ is usually identified as the useful echo at this point, and the fill level is determined on the basis of the difference between the transit times t ₅ and t _{6 of} the maxima M ₅ , M _{6 of} the two echoes E ₅ , E ₆ .

The measurement accuracy of this conventional method depends very much on how exactly the position of the maxima M ₅ , M ₆ can be determined. In this case, the inaccuracies described in the introduction can occur.

According to the invention, therefore, the useful echo is determined in a conventional manner. Subsequently, at least one echo property of the wanted echo is derived. Echo properties are, just as in the embodiments described above, significant physical quantities of the wanted echo, such as the time of the maximum of the wanted echo, the associated amplitude and the width of the useful echo, and the slope of the echo function in the region of the maximum and in the region of its two lateral edges , The echo properties can be derived, for example, by simple algorithms based on the echo function. The determination of the echo properties, for example, directly in the microprocessor 51 be made.

Based These echo properties generate an auxiliary echo.

In the simplest case, it is sufficient to set up the echo function of the auxiliary echo, or its envelope, by simulation calculations. It is exploited that echoes under optimal conditions, ie without the influence of disturbances in 7 have shown prominent shape. Preferably, this form can be described by a simple mathematical function, here a Gaussian curve or a parabola. The duration of the maximum corresponds to the level. The amplitude of the maximum and the width of the echo depend directly on the duration of the maximum. These dependencies can be determined beforehand, preferably ex works, in reference measurements.

In This simplest case is based on the echo properties of the useful echo the auxiliary echo, or its echo function, determined by on the basis the previously determined dependencies Simulation calculations performed become.

The Auxiliary echo is compared with the wanted echo and the useful echo the current level certainly.

there become three cases distinguished. In the first case, it is assumed that the useful echo contains only an echo, the smaller interference signals or background signals superimposed are.

Based the echo properties, an auxiliary echo is generated by a a mathematical function, here preferably a Gaussian function or having a parabola, amplitude characteristic described. In the simplest Case is enough it here, by appropriate simulations the echo function of the auxiliary echo. Based on the knowledge of under optimal Conditions to be expected form of echo and echo characteristics of the Echo function of the useful echo becomes the echo function of the auxiliary echo derived. This has the form of a Gaussian curve or a parabola here. The characteristics of the Gaussian curve or the parabola, e.g. Width, height and slope in the area the edges and the maximum are derived from the echo properties.

The Auxiliary echo is compared with the useful echo. Preferably, the Auxiliary echo here on the basis of the determined echo properties adapted to the true echo, the greatest possible match between useful echo and auxiliary echo is achieved. In this case, preferably a measure of a deviation between the auxiliary echo and the wanted echo, and minimizes. For this purpose, known methods, such as e.g. a minimization of the distance squares, which are applied to the echo functions of payload and auxiliary echo can. The minimization of the deviation may e.g. be done by that add correction values to one or more echo properties and the auxiliary echo based on the corrected echo properties is determined. It can Criteria for the reliability of the individual echo properties. Leave these e.g. based on the previously described dependencies of the echo properties set up among themselves. Likewise or additionally, a weighting the echo properties take place.

At the At the end of this adjustment process, an auxiliary echo is available based on the echo properties, determined best possible reproduction representing the useful echo. In contrast to the useful echo, this is Auxiliary echo, however, free of overlays of interfering signals and / or background signals.

Subsequently, will Based on the auxiliary echo obtained by the comparison of the level certainly. This happens e.g. in the same way as with conventional ones Level measurement, where the level determined by the useful echo. For example, the level determined directly from the duration of the maximum of the auxiliary echo become. Since the auxiliary echo is free from disturbing variables and / or background signals is, thereby the accuracy of the level measurement is significantly improved.

In the second case, it is assumed that the useful echo contains only an echo, and at least parts of the wanted echo have amplitudes at which overdrive or saturation occurs in the signal processing. In addition, the useful echo may contain minor spurious signals or background signals. This case can be identified, for example, by the slope of the envelope of the useful echo in the region of the maximum. The useful echo has in this case in the range of the maximum in 1 shown flat course.

This Case can occur with all three types of level gauges mentioned and is here representative of all three types explained. For the other two types, the following procedure is analogous apply.

Also in this second case, the auxiliary echo is determined by the echo properties of the useful echo. Preferably, only the Width of the useful echo and its slope in the region of the flanks used.

As also in the first case, the auxiliary echo is compared with the useful echo and adapted to this. This can also be done here by appropriate simulation calculations happen. In this case, the comparison and the adaptation is preferred on cuts the amplitude curve of the useful echo and the auxiliary echo limited. The sections are selected based on the echo properties of the useful echo. there those areas of the useful echo are selected as sections, in which the override and / or saturation does not come to fruition. These can be e.g. based on the slope of the envelope determine the useful echo.

alternative to the described case where the auxiliary echo is simulated is determined, the auxiliary echo can also be generated by circuitry become.

It could be analogous to the basis of the 3 and 5 be described embodiments described. In this case, microwave signals would be generated by appropriate control circuits and microwave generators periodically, the mixer 43 are fed and recorded in the same way as the echo signals. However, this circuitry is very complex and expensive.

In 6 Therefore, another variant of the circuit generation of the auxiliary echo signal is shown. This is done by an additional circuit 52 generates an intermediate frequency signal of the auxiliary echo. The additional circuit 52 includes a control circuit 53 , an oscillator 54 and an adjustable amplifier 55 , The control circuit 53 starts the oscillator 54 for an adjustable time interval and then stops it again. The time interval and the gain are controlled by the microprocessor 51 depending on the echo properties. The intermediate frequency signal of the auxiliary echo thus generated becomes the amplifier 48 fed and subjected from there to the same signal processing which also passes through the echo signal.

Of the further sequence corresponds to that of the embodiment described above, in which the auxiliary echo was determined purely by calculation. It will be that Auxiliary echo compared to the useful echo and based on the auxiliary echo the current level certainly.

There the auxiliary echo here experiences the same signal processing as However, the useful echo here is also in the presence of overdrive and / or saturation preferably the entire auxiliary echo compared with the useful echo. The above-described exclusion of individual sections is not mandatory.

In the third case, it is assumed that the useful echo is a superposition of two or more component echoes. Again, completely analogous to the basis of the 6 described embodiment proceeded.

It An auxiliary echo is used which provides a phase and amplitude-accurate superimposition of at least two parts echoes. This auxiliary echo is with the Useful echo compared and based on the comparison, the level is determined. In this case, that of the two parts echoes is evaluated, that of the reflection assigned to the product surface becomes.

First of all to determine if a useful echo is a superposition of two or more echoes is, or is it a single echo, the smaller one Interferences superimposed are.

In this case, for example, the previously described measure of the deviation between the auxiliary echo and the useful echo can be used. This comparison of auxiliary echo and true echo can be based both on the intermediate frequency signals as well the envelopes derived therefrom. If, for example, the measure even after the adaptation of the auxiliary echo still exceeds a predetermined limit, it can be assumed that the useful echo can not be given sufficiently accurately by a single echo containing auxiliary echo. Accordingly, an auxiliary echo is used in this case, which is a phase and amplitude-accurate superposition of two or more parts echoes.

2 shows an example of a typical course of the echo function of the useful echo, as occurs when the useful echo is a superposition of two echoes.

The echo function differs significantly from the in 1 illustrated echo function, in which the useful echo only goes back to the reflection on the product surface. The useful echo has here not only a pronounced maximum, but two closely adjacent maxima. This difference represents a criterion by means of which it is possible to determine whether a useful echo is a simple echo to which minor disturbances are superimposed, or whether the useful echo is a superimposition of two or more individual echoes. The criteria can be checked by appropriate algorithms using the echo function of the useful echoes.

Corresponding the result of this review will be Here, too, an auxiliary echo used, which is a phase and amplitude accurate overlay of two or more parts echoes.

The Measure of Deviation between the first certain echo-containing auxiliary echo and the above criterion represent two different process steps, either alternatively or side by side can be applied.

At the At the end of these process steps, the level is as described above determined by a single echo containing auxiliary echo, if so the useful echo can be reproduced sufficiently accurately. Is this not the case, is based on the echo properties of the echo function of the useful echo generates an auxiliary echo, which has a phase and amplitude-faithful overlay of two or more parts echoes.

In most of these cases enough it is to generate an auxiliary echo that a superposition of two parts echoes is.

This Auxiliary echo is determined by the echo properties of the echo function of the Useful echoes created. As echo properties are preferably the Running times and the amplitudes of the first and the second maximum of the useful echo, as well as the width of the useful echo. Based on these echo properties become characteristics of the derived from both parts echoes. These are preferably runtime and Amplitude of the maxima of the two parts echoes. In addition, an estimate of the width each part echo can be determined based on the echo properties. The However, width can also be determined by the duration and amplitude of the maximum of the respective parts echo due to the knowledge of the distinctive for a single echo expected echo form are derived.

Based on these parameters, the two part echoes are generated. This can be done by simulation calculations as described above. Unlike the one related to 6 described embodiment, it is not sufficient here to determine the echo function of the part echo. In addition to the amplitude as a function of the transit time, the associated phase of the component echo signal must also be determined. Preferably, this is also done here on the level of the intermediate frequency signal.

Subsequently, a phase and amplitude accurate superposition of the two part echoes is made. This can also be done by appropriate calculations in the microprocessor 51 respectively.

The thus obtained auxiliary echo is compared with the useful echo. Preferably In this case, the auxiliary echo is based on the determined echo properties adapted to the true echo, the greatest possible match between useful echo and auxiliary echo is achieved. In this case, preferably a measure of a deviation between the auxiliary echo and the wanted echo, and minimizes. As a measure of the deviation known methods, e.g. a minimization of the distance squares, which are applied to the echo functions of payload and auxiliary echo can. The minimization of the deviation takes place by an adaptation of the Part echoes. It can e.g. be done by one or more Parameters of the part returns Correction values are added, and the parts echoes on the base the corrected characteristics determined and superimposed on a corrected auxiliary echo in phase and amplitude become. It can Criteria for the reliability the individual parameters with be included. These can be e.g. based on the dependencies described above the echo properties among themselves, of course, for the characteristics of the Parts echoes apply, set up. Likewise or additionally, a weighting the parameters take place.

At the end of this adjustment process An auxiliary echo is available which represents a best possible reproduction of the wanted echo, which is determined on the basis of the echo properties. The auxiliary echo consists of two parts echoes, which, in contrast to the two echoes that make up the useful echo, are free of superimpositions of interference signals and / or background signals. The characteristics of the part returns are available for level determination. It is now possible to determine that part echo which is due to the reflection on the product surface. For this purpose, all known methods can be used again. As a rule, it can be assumed that the part-echo whose maximum has the greater amplitude is the partial echo sought. In addition, however, data from previous measurements can be used, from which, for example, a temporal evolution of the level can be derived. Based on this data, a forecast can be created, with which the sought part echo can be selected.

An auxiliary echo consisting of two parts echoes can not only be determined by simulation calculations, it can also be generated by circuitry. This is in 8th shown. Since that in 8th illustrated embodiment largely identical to the in 6 illustrated embodiment, only the existing differences will be explained in more detail below.

At the in 8th illustrated embodiment are two additional circuits 52a . 52b whose structure and mode of operation are identical to those of 6 shown additional circuit 52 are. Every additional circuit 52a . 52b generates in each case an intermediate frequency signal of the respective part echo. Here are the time intervals and the gains of the individual additional circuits 52a . 52b independently by the microprocessor 26 adjustable. At the output of each additional circuit 52a . 52b stands the associated intermediate frequency signal of the respective part echo. These are an adder 56 fed to the output of the intermediate frequency signal of the auxiliary echo is present as a phase and amplitude true superposition of the two part echoes. This is the amplifier 48 fed. The further signal processing and the determination of the level takes place exactly as in the 6 illustrated embodiment.

On completely analogous way the process of the invention for level measurement too in conjunction with sonic or ultrasonic level gauges.

9 shows an embodiment of this. Due to the great agreement, only the differences caused by the use of sound or ultrasound will be explained in more detail below. The level gauge includes a sonic or ultrasonic transducer 57 which serves to send signals S in the direction of the medium 1 in the container 3 to send and their echo signals R to receive. The transmission signals S are, for example, short wave packets which are transmitted periodically. The sonic or ultrasonic transducer 57 has an electro-mechanical transducer, eg a piezoelectric element. It is a control circuit 58 provided that periodically a transmitting oscillator 59 starts and after a transmission time corresponding time interval stops again. An output signal of the transmission oscillator 59 is by means of a transmission amplifier 60 amplified and the sound or ultrasonic transducer 57 fed. This sends a corresponding transmission signal S and receives its echo signal R. The received echo signal R is successively a receiving amplifier 61 , a bandpass filter 62 , a rectifier 63 a logarithm 64 and an analog-to-digital converter 65 fed. The echo signal R prepared in this way becomes a microcontroller in digital form 66 fed.

According to the method according to the invention, transmission signals S are also sent in the direction of the filling material 1 whose echo signals R are received, and derived from the echo signals R an echo function that contains the amplitudes of the echo signal R as a function of their transit time t. As an echo function is preferably an envelope of the microcontroller 66 used in digital form amplitude characteristic of the echo signal. The amplitude curve of the echo signal and its envelope are largely consistent with the corresponding in 7 shown functions of the intermediate frequency signal match.

Echo properties of at least one useful echo are derived on the basis of the echo function. This happens here as well as with the basis of the 6 and 8th illustrated embodiments. Based on the echo properties at least one auxiliary echo is generated, which is then compared with the useful echo. Then the current level is determined based on the auxiliary echo. Here, too, the same procedure as already described in the 6 and 8th illustrated embodiments has been explained.

Just as when using the method in conjunction with filling level measuring devices operating with microwaves, the auxiliary echo is either determined by calculation or by using an appropriate auxiliary echo signal when the method is used in conjunction with sonic or ultrasonic fill level measuring devices. Just as in the previous embodiments, this additional circuits 67a . 67b intended. The additional circuits 67a . 67b each comprise a control circuit 68 , an oscillator 69 and an adjustable amplifier 70 , The control circuits 58 start the oscillators 69 for an adjustable time interval and then stop again. The time interval and the gain are controlled by the microcontroller 66 depending on the echo properties.

If the auxiliary echo is a single echo, then it will be by means of one of the additional circuits shown 67a . 67b generated and the receiving amplifier 61 and the subsequent signal processing branch supplied. If the auxiliary echo is an amplitude and phase-true superimposition of two component echoes, then each additional circuit generates 67a . 67b each a partial echo signal and leads it to an adder 71 to whose output a phase and amplitude faithful superposition of the two parts echo signal is pending. For further processing of the auxiliary echo signal thus generated is the output of the adder with the receiving amplifier 61 and the subsequent signal processing branch connected.

With the described methods in which the auxiliary echo is a phase and amplitude-matched overlay of two parts echoes is not only pure level measurements, but also so-called interface measurements performed. Interface measurement be executed if on the contents an additional Layer, e.g. Foam or deposits of a lighter liquid, are located. A typical application is when, e.g. an oil layer on water or another liquid swims. The procedures are applied analogously and it Both part returns are analyzed for interface measurement. A partial echo comes from the reflection on the product surface, the other of the reflection on the surface the additional Layer. Accordingly results from the terms of the two Parts echoes both the level as well as the position of the surface the additional Layer. From the difference of level and surface the additional layer results in the thickness of the layer.

Claims (9)

Method for measuring a filling level of a filling material ( 1 ) in a container ( 3 ) with a level measuring device operating according to the transit time principle, in which - transmission signals (S) in the direction of the filling material ( 1 ), - whose echo signals (R) are received, - based on the echo signals (R) an echo function is derived, the amplitude (A) of the echo signal (R) as a function of their transit time (t), - based on the echo function echo properties a useful echo is generated on the basis of the echo properties, the auxiliary echo is compared with the useful echo, and a current fill level is determined on the basis of the auxiliary echo. The method of claim 1, wherein the auxiliary echo adapted to the wanted echo. The method of claim 1, wherein - the auxiliary echo a phase and amplitude accurate overlay of two or more Parts echo is, - the Auxiliary echo is compared with the useful echo, and - based that part echo of the auxiliary echo determines a current level is assigned to a reflection on the product surface. The method of claim 1, 2 or 3, wherein a Measure of a deviation between the auxiliary echo and the wanted echo, and the deviation is minimized by adjusting the auxiliary echo. Method according to claim 1 or 2, wherein an auxiliary echo signal is generated and this at least part of a signal processing goes through run through the echo signals for generating the echo function. The method of claim 1, wherein the level gauge at least one in the container ( 1 ) protruding ladder ( 5 ) and the transmission signals (S) are short electro-magnetic impulses traveling along the conductor ( 5 ) to the product surface and back. Method according to Claim 1, in which the filling level measuring device has at least one sound or ultrasound sensor ( 57 ), and the transmission signals (S) are sound or ultrasonic signals. The method of claim 1, wherein the level gauge is a microwave level gauge comprising an antenna ( 37 ) for transmitting transmission signals (S) and for receiving their echo signals (R). A method according to claim 6, 7 or 8, wherein the Auxiliary echo one described by a mathematical function Amplitude curve whose shape adapted to sections of the echo is.