EP1695044A2

EP1695044A2 - Filling level measurement device and filling level measurement and monitoring method

Info

Publication number: EP1695044A2
Application number: EP04804821A
Authority: EP
Inventors: Holger Steltner; Reinhard Schaefer; Dietmar Spanke; Edgar Schmitt
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2003-12-19
Filing date: 2004-12-14
Publication date: 2006-08-30
Also published as: WO2005062000A2; DE10360711A1; US20080302439A1; US7826309B2; WO2005062000A3

Abstract

The invention relates to a method for measuring the filling level (7) of a filling material (1) in a container (3) and for monitoring at least one predefined filling level (L min, L max) with the aid of a filling level measurement device (5), and a corresponding filling level measurement device (5). According to the invention, the monitoring corresponds to high security standards, wherein transmission signals are emitted in the direction of the filling material (1) in each measuring cycle and the echo signals (E) thereof are received, the echo signals (E) are used to determine the filling level (7) in a first evaluation method and it is possible to determine whether the filling level exceeds or falls below the predefined filling levels (Lmin, Lmax ) using the echo signals (E) in a second evaluation method which is independent from the first evaluation method.

Description

Level measuring device and method for level measurement and monitoring

The invention relates to a working according to the transit time principle Füllslandsmeßgerät and a method for measuring a level of a filling material in a container and for monitoring at least one fixed predetermined level with the level measuring device. In level measurement according to the transit time principle, transmission signals, eg microwave or ultrasonic signals, are periodically transmitted to the surface of a medium by means of a transmitting and receiving element and their echo signals reflected on the surface are received again after a distance-dependent transit time. A echo function representing the echo amplitudes as a function of the transit time is formed. Each value of this echo function corresponds to the amplitude of an echo reflected at a certain distance from the transmitting and receiving element. From the echo function, a useful echo is determined, which probably corresponds to the reflection of a transmission signal at the product surface. As a rule, it is assumed that the useful echo has a greater amplitude than the other echoes. From the transit time of the useful echo, the distance between the product surface and the transmitting and receiving element, and thus the filling level, results directly at a known propagation speed of the transmission signals. To determine the filling level, it is possible to use all known methods which make it possible to measure relatively short distances, for example distances of less than 100 meters, by means of reflected transmission signals. One known method is the Frequency Modulation Continuous Wave Radar (FMCW) method implemented in conjunction with microwave level gauges. The FMCW method continuously transmits a microwave signal that is periodically frequency modulated, for example, a sawtooth function. The frequency of the received echo signal therefore has a frequency difference with respect to the instantaneous frequency which the transmission signal has at the time of reception, which depends on the propagation time of the echo signal. The frequency difference between the transmitted signal and the received signal, which can be obtained by mixing both signals and evaluating the Fourier spectrum of the mixed signal, thus corresponds to the distance of the reflecting surface from the antenna. Further, the amplitudes of the spectral lines of the Fourier transform correspond obtained frequency spectrum the echo amplitudes. This Fourier spectrum therefore represents the echo function in this case.

Another known method is the pulse transit time method which is used both in microwaves and in ultrasonic level measuring devices. The pulse transit time method periodically sends short transmission signals, so-called transmission pulses, which are reflected by the product surface and whose echo signals are received again after a distance-dependent transit time. The received Signalatnplitude as a function of time represents the echo function. Each value of this echo function corresponds to the amplitude of a reflected at a certain distance from the transmitting and receiving element echo.

In the level measurement technique, a considerable effort is often used in order to operate under difficult measuring conditions, e.g. with built-in jammers in the container, sporadically in the signal path protruding stirrers or poor signal qualities to be able to perform reliable measurements.

For this very complex signal recording, signal conditioning and / or signal evaluation methods are sometimes used.

In a variety of applications, in addition to level measurement, it is necessary to monitor overshoot or undershoot of one or more fixed levels. Such a fixed predetermined level, for example, a level limit, which may not be exceeded in order to avoid overfilling of the container. Another example is a Füllslandsuntergrenze, which must not be fallen below, e.g. to prevent dry running of pumps.

The monitoring of predetermined levels of operational safety and is sometimes even required by law. Thus, e.g. The German Water Household Protection Act applies corresponding regulations.

[011] Due to the safety relevance of the monitoring of predetermined levels, it is imperative that the monitoring is consistently error-free. The monitoring must meet high safety standards. Preferably, the functioning of the monitoring can be checked in advance with respect to all possible measuring situations occurring during operation.

[012] In many applications, fill level limit switches are therefore used in addition to continuous level measuring devices which monitor the exceeding or falling below of the predetermined fill levels.

[013] Signal recording, signal processing and / or signal evaluation methods are Customary Füllslandsgrenzeschalter are usually much simpler compared to level measuring devices. Correspondingly, their error-free functioning can be tested more easily and, in relation to all measurement situations that possibly occur during operation, can be checked in advance.

However, it represents a significant cost, space and maintenance requirements to use these devices in addition to the level gauge.

[015] It is possible to monitor an overshoot or undershoot of the fixed fill levels by means of the fill level measured with the continuously operating fill level measuring device. However, since complex signal recording, signal processing and / or signal evaluation methods are generally used in the described conventional level gauges, it is often not possible to pre-test the limit level monitoring that can be carried out with respect to all possibly occurring measuring situations in order to detect possible erroneous measurements To exclude security.

[016] It is an object of the invention to allow level measurements and monitoring at least one fixed predetermined level with a working according to the transit time level measuring device, the monitoring meets high safety standards.

For this purpose, the invention consists in a method for measuring a filling level of a filling material in a container and for monitoring at least one predetermined level in a container with a working according to the running time principle level measuring device, in which

[018] - in each measuring cycle transmission signals in the direction of

[019] Sent filling goods and their echo signals received

[020]

[021] - Based on the echo signals in a first

[022] Evaluation method of the level is determined, and

[023] - Based on the echo signals in a second of the

[024] independent of the first evaluation method

[025] Evaluation method determines whether the level

[026] exceeds or falls below the predetermined fill levels.

The invention further relates to a method for measuring a filling level of a filling material in a container and for monitoring at least one predetermined level in a container with a level measuring device operating according to the transit time principle, in which [028] - in a Füllstandsmeßzyklus transmission signals in

[029] Sent direction of the contents and their

[030] echo signals are received,

[031] - based on the recorded in the Füllstandsmeßzyklus

[032] Echo signals in a first evaluation method of

[033] fill level is determined, and

[034] - in a Grenzstandsmeßzyklus send signals in

[035] Sent direction of the contents and their

[036] echo signals are received,

[037] - based on the recorded in Grenzstandsmeßzyklus

[038] Echo signals in a second of the

[039] independent of the first evaluation method

[040] Evaluation method determines whether the level

[041] exceeds or falls below the predetermined fill levels.

According to one embodiment of the above method, the level measuring device has a first signal processing branch, in which the echo signals are used, which are used to determine the filling level.

[043] According to a further embodiment, the level measuring device has a second signal processing branch, in which the echo signals are processed, which are used to determine the exceeding or falling below the fixed predetermined levels.

[044] According to a development of the above method, an echo function is derived from the echo signal to determine the overshooting or undershooting of the predetermined fill levels, which represents an amplitude of the echo signal as a function of a transit time. A measure of the area enclosed by the echo function in the region of a respective expected runtime for the given fill level is determined and it is determined that the fill level exceeds the respective predetermined fill level if the measure exceeds a predetermined reference dimension. It is also determined that the level falls below the respective predetermined level, if the measure falls below a predetermined reference level.

[045] According to a first embodiment, the measure corresponds to an integral over the echo function in the range of the respective transit time to be expected for the given fill level.

[046] According to another embodiment, the measure corresponds to an average, median or maximum of the amplitudes of the echo function in the region of the respective one for the predetermined level expected life.

[047] According to a further development of the method, an echo function is derived from the echo signal to determine whether the predetermined fill levels are exceeded or fallen short of, which represents an amplitude of the echo signal as a function of a transit time. A first measure is determined for the area enclosed under the echo function in the region of a respective expected running time for the given fill level. In the same way, a comparative measure for a predetermined reference range of the echo function is determined, and determined based on a comparison of the respective first measure with the comparative measure, whether the level exceeds the respective predetermined level or below.

[048] According to a development, based on results of the second evaluation method, a plausibility check of results of the first evaluation method is carried out.

[049] According to a development of the method, in which the level measuring device is a level measuring device operating with ultrasound, to determine whether one of the predetermined fill levels has exceeded or fallen short of, transmit signals having a fixed transmission frequency are transmitted.

Furthermore, the invention consists in a fill-level measuring device operating according to the transit time principle

[051] a transmitting and receiving element for transmitting

[052] transmit signals and receive them

[053] echo signals,

[054] - a first evaluation module, to execute a

[055] first evaluation method for determining the

[056] level, and

[057] - a second evaluation module, for executing a

[058] second evaluation method for detection

[059] an overrun or underrun of at least one fixed predetermined

[060] level.

According to one embodiment of the Füllstandsmeßgeräts this has a first signal processing branch, which is used for the preparation of echo signals, which are used to determine the level, and a second signal processing branch, which serves for the processing of echo signals, to determine the over- or Fall below the fixed predetermined levels are used. [062] The invention and further advantages will now be explained in more detail with reference to the figures of the drawing, in which three embodiments are shown; the same elements are provided in the figures with the same reference numerals.

FIG. 1 shows an arrangement for level measurement; FIG.

Fig. 2 shows a simplified representation of an echo function, as they are

[065] can be accommodated with the arrangement of FIG. 1;

Fig. 3 shows a construction of one with microwaves

[067] working level measuring device;

FIG. 4 shows a sequence of a measuring cycle with a measurement; FIG.

FIG. 5 shows a sequence of a measurement cycle with two measurements; FIG.

Fig. 6 shows a construction of one with microwaves

[071] working level measuring device with two separate

[072] signal conditioning branches; and

[073] Fig. 7 shows a structure of one with ultrasound

[074] working level measuring device;

[075] FIG. 1 shows an arrangement for level measurement and for monitoring an overshoot or undershoot of at least one predetermined fill level. It is a filled with a product 1 container 3 shown. On the container 3, a working according to the transit time level measuring device 5 is arranged. As a level measuring device 5 is suitable, for. a level measuring device operating with microwaves or a level measuring device working with ultrasound. The level measuring device 5 serves to measure a level 7 of the filling material 1 in the container and to monitor the exceeding or falling below at least one predetermined level.

[076] The level measuring device 5 has at least one transmitting and receiving element 11 for transmitting transmission signals S and for receiving echo signals E. In the illustrated embodiment, a working with microwaves level measuring device is shown, which has as a transmitting and Ernangangselement 11, a single antenna 11 which both transmits and receives. Alternatively, however, it is also possible to provide an antenna for transmission and at least one further antenna for reception. In an ultrasonic level gauge, as an emitting and receiving element, instead of the antenna, an ultrasonic sensor with an electromechanical transducer, e.g. a piezoelectric element.

[077] The transmission signals S are sent in the direction of the filling material 1 and reflected on a product surface. The reflected transmission signal forms the echo signal E.

[078] In the level measurement according to the transit time principle are in each measurement cycle Transmission signals S, eg short microwave or ultrasonic pulses, sent out in the direction of a filling 1. Their echo signals E are recorded and fed to a signal processor 13. 3 shows a simplified structure for a fill level measuring device 5 operating with microwaves. The signal processing 13 is connected to the transmitting and receiving element 11 and comprises a high-frequency module 14 and an analog module 16.

The high-frequency module 14 is constructed as follows, for example. It has a microwave generator that continuously generates microwaves with a gigahertz frequency. It is provided with a pulse repetition frequency oscillating generator which is connected to a control circuit. The control circuit starts the microwave generator 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 the voltage applied to the control circuit pulse repetition frequency. This is e.g. a few megahertz. The microwave generator is connected via a directional coupler or circulator with the transmitting and receiving element 11.

[080] Echo signals E received by the transmitting and receiving element 11 are fed via the directional coupler or circulator to the receiving and evaluating circuit, amplified and fed to a first input of a mixer. The pulse frequency oscillating generator is connected to a second microwave generator via a time delay stage and a second control circuit operating identically to the first control circuit. The second microwave generator is constructed identically to the first microwave generator. The control circuit causes the second microwave generator with the pulse repetition frequency recurrently generates microwave pulses. These are applied to a second input of the mixer. The time delay stage delays the incoming signals by a variable delay time, eg, increasing according to a sawing function of finite width. In the mixer, therefore, a microwave signal delayed by a level-dependent transit time is superimposed on a substantially identical-shaped microwave signal delayed by a variable delay time. The signal available at the output of the mixer 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 of the frequencies contains the essential given by the difference of the frequencies applied to the inputs. The low-frequency component is filtered out by means of a low-pass filter and supplied to the analog module 16. There, the incoming signal is recorded, for example by means of a Ablast- and holding circuit and the respective signal amplitude A recorded along with the associated delay time t as an echo function.

[081] The echo signals E processed in the signal processing 13 are supplied to an evaluation unit 17. The actual evaluation is preferably carried out in digital form. For this purpose, the processed echo signals are fed to an analog-to-digital converter 18 whose output signal is present at an input of the evaluation unit 17.

By means of the evaluation unit 17, the filling level is determined on the basis of the echo signals E in a first evaluation method. For this purpose, the evaluation unit 17 has a digital unit 19, e.g. a microcontroller or a digital signal processor, and a first memory 21 associated therewith. The first evaluation process is carried out by applying evaluation programs stored on the digital unit 19 in the first memory 21 to the processed echo signals E.

[083] _' Usually, an echo function A (t) is derived from the received echo signals E which contains amplitudes A of the echo signal E as a function of their transit time t.

FIG. 2 shows a greatly simplified example of such an echo function for the arrangement of FIG. 1. The echo function has two pronounced maxima. These maxima are echoes L and B, of which the echo L is due to a reflection on the product surface and the echo B is due to a reflection at a bottom 15 of the container 3. The echoes L and B occur after running times t, t, which correspond to a distance between the transmitting and receiving element 11 and the filling material surface or the bottom 15. [085] In the first evaluation method, the echo L originating from the reflection at the product surface is determined. For this purpose, a large number of sometimes very complex methods are already used in today's level gauges, which allow a precise analysis of the echo signals and detection of the echo L originating from the filling land. In this case, for example, signal filtering is carried out, multiple echoes attributable to repeated reflections in the container are masked out, echoes which are due to reflections on interferers built into the container. to be returned are hidden and much more. At the end of the first evaluation process is usually the detection of originating from the reflection on the product surface echoes L, from the running time t is the current level 7 L results. [086] According to the invention, the echo signals E are additionally subjected to a second evaluation method, which is independent of the first evaluation method, in which it is determined whether the filling level 7 exceeds or falls below at least one predetermined filling level. [087] Two predetermined fill levels L and L are shown by way of example in FIG. The height of the predetermined levels results from the application in which the level measuring device 5 is used. The upper predetermined level L is an upper one Limit value for the level 7. This should not be exceeded in the illustrated application, so that no filling material 1 can leak through an inspection opening 23 drawn at this height. The lower predetermined level L is a lower limit for the level 7. min This should not be exceeded in the illustrated application so that a built-in an outlet 25 of the container 3 pump 27 does not run dry. [089] For monitoring the predetermined filling levels L and L, the ejection unit 17 additionally comprises a second memory 22 assigned to the digital unit 19. The second evaluation method is carried out by evaluation programs stored in the second memory 22 on the digital unit 19 the echo signals E are applied. The level measurement and the monitoring of the predetermined fill levels L and L are carried out alternatively according to one of the process flows illustrated in FIGS. 4 and 5. [091] In the sequence shown in FIG. 4, a measurement is performed in each measurement cycle in which transmission signals S are sent in the direction of the contents 1 and their echo signals E are received and processed. The band of the echo signal E of each measuring cycle is determined by the first evaluation of the level 7, and with the second of the first evaluation independent method evaluation is determined whether the level 7 at least a predetermined level, here L min and L exceeds or falls below. ax

[092] In the process shown in FIG. 5, two measurements are performed in parallel. In each case in a Füllstandsmeßzyklus send signals S are sent in the direction of the contents 1 and receive their echo signals E and edited. On the basis of recorded in Füllstandsmeßzyklus echo signals E is determined by the first evaluation of the level 7. In parallel, Grenzstandsmeßzyklen be performed in which transmission signals S sent in the direction of the contents 1 and their echo signals E are received. Based on the recorded in Grenzstandsmeßzyklus echo signals E is determined in the second independent of the first evaluation process evaluation, whether the level of 7 at least a predetermined level, here L and L min, exceeds or falls below. Max

[094] The evaluation of the measurements according to the first and the second evaluation method is carried out separately. For this purpose, a first evaluation module 23, for carrying out the first evaluation method for determining the filling level 7, and a second evaluation module 25, for carrying out the second evaluation method for determining the exceeding or falling below the fixed predetermined levels, here L and L, min max provided. In the exemplary embodiment illustrated in FIG. 3, the first evaluation module 23 comprises the digital unit 19 and the first memory 21 associated therewith.

The second evaluation module 25 comprises the digital unit 19 and a second memory 22 assigned to it. The second evaluation method is carried out by applying evaluation programs stored on the digital unit 19 in the second memory 22 to the echo signals.

[096] The first and second evaluation methods are completely independent of each other and can be tested and tested separately from each other before commissioning. The second evaluation procedure is described in more detail later in the text. It is very simple in comparison to the first evaluation procedure and can therefore be checked much more thoroughly in advance. This also simplifies the whole development process with specification, analysis, design, implementation and testing. This allows the guarantee of a high degree of measuring reliability for the limit level monitoring.

[097] The signal processing 13 preferably has a first and a second signal processing branch 29, 31. The first signal processing branch 29 serves to process the echo signals E, which are used to determine the filling level 7. In the exemplary embodiment illustrated in FIG. 3, this comprises the high-frequency module 14 and the analog module 16.

The second signal processing branch 31 is used to process the echo signals E, which are used to determine the overshoot or undershoot of the fixed predetermined levels L and L. In the embodiment shown in Fig. 3 The second signal processing branch 31 comprises the high-frequency module 14 and an additional analog module 33. The analog module 33 is preferably constructed very simply. For example, it may be a rectifier that rectifies the incoming signals. The output signals of the additional analog module 33 are applied to the analog-to-digital converter 18 and are supplied from there in digital form to the digital unit 19. The splitting of the signal processing 13 into a first and a second signal processing branch 29, 31 offers the advantage that the two signal processing branches 29, 31 can be tested separately. The second signal processing branch 31 is simpler in comparison with the first one. Accordingly, its reliable operation can be more easily and completely tested out with regard to all possibly occurring measurement situations. This offers the advantage that for the second signal processing branch 31 using monitoring of the predetermined levels, here L and L, by eαtsprechende tests a higher min mυt level of security can be guaranteed andsmessung for Fülls.

FIG. 6 shows a further exemplary embodiment for the construction of a fill level measuring device 5 operating with microwaves. Due to the great agreement with the exemplary embodiment illustrated in FIG. 3, only the existing differences are explained in more detail here.

[101] The exemplary embodiment illustrated in FIG. 6 has two signal processing branches 29 and 35 which are completely separate. The first signal processing branch 29 is identical to the first signal processing branch 29 shown in FIG. 3. The second signal processing branch 35 has an additional high-frequency module 37 which is connected to the transmitting xmd receiving module 11 parallel to the high-frequency module 14. Furthermore, the second signal processing branch 35 comprises the analogue module 33, which is connected to the additional high-frequency module 37.

Furthermore, the exemplary embodiment illustrated in FIG. 6 has two completely separate evaluation modules 23 and 41. The first evaluation module 23 corresponds to that shown in FIG. The second evaluation module 41 has an additional digital unit 43, which is connected via an analog-to-digital converter 39 to the analog module 33. The additional digital unit 43 is associated with the second memory 22.

FIG. 7 shows an exemplary embodiment of an inventive ultrasonic level measuring device 5.

It has, as transmitting and receiving element 11 an ele tromechanical transducer on, which is arranged in a cup-shaped housing, which is closed by a bottom. The electromechanical transducer is, for example, a piezoelectric element. However, other types of electromechanical transducers can be used. The housing consists for example of a plastic, eg polypropylene. The electromechanical transducer serves to transmit and receive ultrasound through the ground.

[105] At the heart of the level gauge 5 is a digital unit 45, e.g. a digital signal processor. For example, a transmit signal generator 47 periodically generates short ultrascronic wave pulses that are supplied to a transmit amplifier 49. The amplified analog output signals are supplied to the transmitting and receiving element 11 and sent from this as a transmission signal S in the container 3 in the direction of the filling material 1. Echo signals E of the transmission signals S are received by means of the transmission and reception element 11 and fed to a reception amplifier 51. Its output signals are supplied to an analog signal processor 52, which has, for example, as shown in Fig. 7, a band-pass filter, a rectifier and a logarithm. The output signals of the analog signal processing branch 52 are fed to an analog-to-digital converter 53, which is again connected to the digital unit 45.

In analogy with the previously described Ausführangsbeispiel with a working with microwaves level measuring device according to the invention the fill level 7 is also determined based on the echo signals E in a first evaluation, and determined in a second of the first evaluation independent evaluation method, if the level 7 at least one predetermined level, here L and L min over or under. Here are the explained with reference to Figures 4 and 5 max procedures available to choose from.

[107] Analogous to the Ausführangsbeispiel shown in Fig. 3, the level measuring device 5 shown in Fig. 7, a first evaluation module 55, for carrying out a first evaluation method for determining the level 1, and

[108] a second evaluation module 57, for carrying out a second evaluation method for determining the exceeding or falling below the fixed predetermined levels, here L and L, on. The first evaluation module 55 includes the digital unit 45 and min max one of these associated first memory 59th The first evaluation process is carried out by applying evaluation programs stored on the digital unit 45 in the first memory 59 to the echo signals E. [109] The second evaluation module 57 comprises the digital unit 45 and one of these ordered second memory 61. The second evaluation process is carried out by applying on the digital unit 45 in the second memory 61 stored evaluation programs on the echo signals E. When working with ultrasound level measuring devices, which operate on the transit time principle, an optimum transmission frequency is preferably determined for level measurement, which have the transmission signals S for level measurement. This optimum transmission frequency depends on a resonance frequency of the electromechanical transducer and depends on the temperature. By using this optimum transmission frequency, an improvement of the signal quality is achieved and thus improves the accuracy of the level measurement. Determination and adjustment of this transmission frequency, however, contain sources of error that are undesirable in the monitoring of the predetermined levels L and L and are usually not outweighed by the min max benefits of improved signal quality for the level monitoring. In the case of fill level measuring devices 5 operating with ultrasound, transmission signals S are therefore preferably transmitted with a fixed transmission frequency in order to determine whether one of the predetermined fill levels L and L exceeds or exceeds min. This provides a higher degree of safety for point level monitoring.

Of course, the invention is not limited to the level measuring devices ¹ described. It can also be used on the run time principle working Füllslandsmeßgeräte. For example, level measuring devices are also suitable in which transmission signals, eg short electromagnetic pulses, are guided along a probe, eg a metallic cable or rod, into the container in the direction of the filling material and reflected on the filling material. Here, too, echo signals of the transmission signals are recorded, the amplitudes of which are determined as a function of their transit time and the level determined therefrom. This form of level measurement is known as time domain reflectometry.

[112] All level measuring devices operating according to the transit time principle have in common that an echo function can be derived based on the echo signals E, which represents an amplitude of the echo signal E as a function of a transit time. Such an echo function is shown in greatly simplified form in FIG.

On the basis of this echo function, it is determined according to the invention in the second evaluation method whether at least one pre-set fill level, L min irax or below. In the second evaluation method, it is preferable for this to be a measure of the echo function in the region I, II of a given fill level L , L expected term t, t trapped area determined. Alternatively, max min max, of course, a measure of a reciprocal of the enclosed area can be determined. [115] The expected life t is determined from a distance of the predetermined fill level L, L to be transmitted by the user premix, from the transmit and receive minima 11 and the propagation speed of the transmit and receive signals S, E in the container 3. In FIG Running times t, t min max, the assigned to the predetermined maximum level L area I and the maximum predetermined minimum filling land L associated area JJ for the set in Fig. 1 darmin arrangement marked. According to the invention, it is found in the second evaluation method that the fill level 7 exceeds the respective predetermined fill level L, L when the max min level exceeds a predetermined reference level, or it is determined that the fill level 7 the respective predetermined level L falls below, if the imx min measure falls below a predetermined reference level. If a measure is used which depends on the reciprocal of the enclosed area, it is of course analogous that it is determined that the filling level 7 exceeds the respective predetermined filling level L, L over-max min if the measure falls below a predetermined reference value or if it is detected in that the fill level 7 falls below the respective predetermined fill level L, L max min when the measure exceeds a predetermined reference dimension. [117] A suitable measure is, for example, an integral over the echo function in the region I, II of the respective transit time t, t expected for the given fill level L, L. max min min max

[118] Equally, an average, median or maximum of the amplitudes of the echo function A (t) in the range of the respective transit time t, t to be expected for the given fill level L, L max can be determined as a measure. min max

[119] As a measure but also any strictly monotonous function such. Integral, mean, median or maximum are used.

[120] The current measure can be evaluated individually as described above by comparing it with a given reference measure.

Alternatively, however, to determine whether the predetermined fill levels L, L are above or below the echo function A (t), a first measure of the min max under the echo function A (t) in the region I, II of a respective one for the predetermined fill level L, L expected life t, t enclosed area determines min max min max and in the same way a comparative measure for a given reference range R of the echofuntion A (t) can be determined. By comparing the respective first measure with the comparative measure is then determined whether the level 7 exceeds the respective predetermined level L, L or below. min max

[122] The reference region R is shown in FIG. It is preferably chosen so that it lies outside of all areas in which pronounced maxima of the echo function A (t) are to be expected. These are, for example, areas in which transit times of echoes attributable to reflections on the filling material 1, on the bottom 15 or even on interference built into the container 1 are to be expected. These ranges can be determined on the basis of the distances of ground and Störem to the transmitting and receiving element 11 and the level measurement.

[123] Of course, it is sufficient to monitor an overshoot of the upper level limits and an undershooting of the lower level limits. If an upper level limit is exceeded or falls below a lower level, so preferably an alarm is triggered and / or issued an error message.

[124] Preferably, a plausibility check of the Meßergebenisse achieved with the level measuring device is made.

[125] Based on the results of the second evaluation procedure, a plausibility check of the results of the first evaluation procedure is carried out. From the second evaluation method it is known whether the current fill level exceeds or falls below the predetermined fill levels L, L. It follows that deϊ min max determined by the first evaluation current level 7 must be above each predetermined level L, L, which is exceeded according to the result of the first min max evaluation. Conversely, the current fill level 7 determined using the first evaluation method must be below any given fill level L, L which has fallen short of min according to the result of the first evaluation method. If this is not the case, the result of the first evaluation procedure is incorrect and should be discarded or at least checked. [126] Of course, a reverse plausibility check is also possible, in which the results of the second evaluation procedure are checked on the basis of the results of the first evaluation procedure. However, this form is to be assigned a low priority, since the safety and reliability of the results obtained with the second evaluation method is higher than that of the results obtained with the first evaluation method.

Claims

claims

For measuring a filling level (7) of a filling material (1) in a container (3) and for monitoring at least one predetermined filling level (L, L) with a level measuring device operating at maximum running time min max (5), in which each measuring cycle transmitting signals (S) in the direction of the filling material (1) and their echo signals (E) are received, based on the echo signals (E) in a first evaluation of the level (7) is determined, and based on the echo signals (E) in one second independent of the first evaluation process evaluation is determined whether the level exceeds the predetermined levels (L, L) or falls below. min max

2Nerfahren for measuring a level (7) of a filling material (1) in a container (3) and for monitoring at least one predetermined level (L, L) with a running on the transit time principle Füllstandsmeßgerät min max (5), in which a Füllstandsmeßzyklus send signals (S) in the direction of the contents (1) and their echo signals (E) are received, based on the recorded in Füllstandsmeßzyklus echo signals (E) in a first evaluation of the level (7) is determined, and in a Grenzstandsmeßzyklus send signals ( S) are sent in the direction of the filling material (1) and their echo signals (E) are received, based on the recorded in Grenzstandsmeßzyklus echo signals (E) is determined in a second independent of the first evaluation process evaluation, whether the level over the predetermined levels) or below.

3. The method of claim 1 or 2, wherein the level measuring device (5) has a first signal processing branch (27) in which the echo signals (E) are processed, which are used to determine the level (7).

4. The method according to claim 1 or 2, wherein the level measuring device (5) has a second signal processing branch (31, 35) in which the echo signals (E) are processed, which for determining the overshoot or undershoot the fixed predetermined Fill levels (L, L) are used. min max

5. The method of claim 1 or 2, wherein for determining the exceeding or falling below the predetermined levels (L, L) from the echo signal min mix (E) an echo function (A (t)) is derived, the one Represents amplitude of the echo signal (E) as a function of a transit time (t), a measure of the under the echo function (A (t)) in the range (I, II) of a respective one for the given Level (L) enclosed area is determined, it is determined that the level exceeds the respective predetermined level (L, L) when the measure exceeds a predetermined maximum refference mens measure, and it is determined that the level of the respective predetermined level (L ) falls below, if the measure falls below a preset reference measure irax. 6. The method of claim 5, wherein the measure an integral on the echo function ((t)) in the range (I, II) of the respective for the predetermined level (L, L) expected duration (t, t) equivalent. min max min max

[007] 7. Method according to claim 5, wherein the measure of an average, Mediän or maximum of the amplitudes of the echo function (A (t)) in the range (1, 11) of the respective for the given level (L, L) to be expected Running time (t min max, t) corresponds. min max

8. The method of claim 1 or 2, wherein for determining the exceeding or falling below the predetermined levels (L, L) from the echo signal min max (E) an echo function (A (t)) is derived, the one Represents the amplitude of the echo signal (E) as a function of a transit time (t), a first measure of the expected under the echo function (A (t)) in the range (I, JJ) of a given for the given ^• level (L, L) Running time (t, t) enclosed surface min max min max is determined in the same way a comparative measure for a predetermined reference range (R) of the echo function (A (t)) is determined, and determined by comparing the respective first measure with the reference measure If the level is the respective specified level (L ) falls below or below the minimum imx. 9. The method according to claim 1 or 2, wherein based on results of the second evaluation method, a plausibility check of results of the first evaluation is made. [010] 10. The method according to claim 1 or 2, wherein the level measuring device (5) is an ultrasonic level measuring device (5) working, which for determining whether one of the predetermined levels (L, L) is exceeded or fallen below senmin max designale (S) transmits with a fixed transmission frequency. [011] 11. Level measuring device (5) operating according to the transit time principle with a transmitting and receiving element (11) for transmitting transmission signals (S) and for receiving their echo signals (E), a first evaluation module (23) for executing a first Evaluation method for determining the filling land (7), and a second evaluation module (25, 41), for carrying out a second evaluation method for determining an overshoot or undershoot of at least one fixed predetermined fill level (L, L). min max 12. Working on the runtime principle FüTistandsmeßgerät (5) after addressing

11, with a first signal processing branch (27) for processing of echo signals (E), which are used to determine the level (7), and a second signal processing branch (31, 35) for processing of echo signals (E) for determining the Über - or falling below the fixed predetermined levels (L, L) are used. min max