DE102012108462A1 - Method for laser-based determination of level of liquid filling material in container used in e.g. chemical industry, involves scanning reflected pulses received from surface of material, after emitting laser pulses toward material - Google Patents

Abstract

The laser pulses with defined transmission repetition frequency (fPulse) are emitted toward surface of filling material. The reflected laser pulses received from surface of filling material are scanned and the sample values are combined to form an echo curve. The actual signal characteristic of the reflected pulse is analyzed, based on echo curve. The actual signal waveform is compared with desired waveform. The echo curve determined measured value is used only to determine the level, if the actual and set signal waveforms match in a preset tolerance range. Independent claims are included for the following: (1) device for laser-based determination of level of filling material in container; and (2) system for laser-based determination of level of filling material in container.

Description

The invention relates to a method, a device and a system for the laser-based determination of the fill level of a product in a container according to a transit time method.

Nowadays known laser-based measuring instruments and methods for level measurement are poorly or not at all suitable for the measurement of water-based transparent liquids. The reason is that the laser radiation completely or partially penetrates the medium and generates a reflection on the bottom of the tank. Especially in stainless steel tanks, the direct reflection at the bottom of the tank is dominant compared to the scattered reflection (remission) on the surface of the medium and easily leads to faulty fill level readings.

In the most common cases, clear liquids are based on water and often contain no suspended particles or - for a sufficient remission on the liquid surface - too few suspended particles. In turbid media containing many suspended particles, a relatively strong absorption occurs, which also means that the proportion of laser radiation reflected at the surface is too small for reliable level determination.

Therefore, laser-based methods for level measurement of clear and strongly absorbing liquids rely on the direct reflection of the laser radiation on the liquid surface. The absorption of the laser radiation also depends strongly on the wavelength used, while the direct reflection is independent of the wavelength.

In principle, it should be noted that, depending on the angle of incidence and the optical media properties, a portion of the incident radiation is always refracted and reflected at a liquid surface.

Available laser-based level measurement systems operate on established or adaptive thresholds. In the simplest case, the transit time between the transmission and the reception of a laser pulse is measured, the point of reception being selected as the time at which the reception intensity exceeds a predetermined threshold. With the available systems, it is not possible to evaluate the quality of the received signals. Also, the known laser level measuring instruments are not optimized for the measurement of liquids and do not take into account in their signal evaluation the previously described properties of laser radiation reflection and emission from the media surface as well as transparent media from the container bottom or underlying layers. If a signal component of the media surface overlaps with a portion of the container bottom reflection, a mixed signal is produced which, in the case of a threshold-based measurement, can not be distinguished from a pure signal reflected on the media surface. Therefore, relatively large measurement errors can occur without the meter recognizing them as measurement errors.

The invention has for its object to provide a method, a device and a system for laser-based level measurement, which is also characterized in the field of level measurement for liquids by a high measurement accuracy.

The invention is achieved with respect to the method by the following features:
Laser pulses with a given pulse width are generated;
the laser pulses are emitted at a defined transmission repetition frequency in the direction of the surface of the medium;
the laser pulses are received after the reflection at the surface of the medium;
the reflected laser pulses are scanned;
the samples are assembled into an echo curve; the actual waveform or at least a defined actual signal characteristic of the reflected laser pulse is analyzed and / or determined on the basis of the echo curve;
the actual signal shape or the actual signal characteristic is compared with a predetermined desired signal form or a corresponding nominal signal characteristic;
Based on the echo curve (EK), the determined measured value is used only to determine the filling level if the actual signal shape and the nominal signal shape or the actual signal characteristic and the nominal signal characteristic coincide within a specified tolerance range.

Signal characteristic is understood to mean at least one signal property or one signal feature. The desired signal shape and the actual signal form are either compared directly with one another or they are analyzed for specific signal properties or signal characteristics, which provide information on the validity of the measurement signal on the basis of defined criteria.

• – Die Anstiegsflanke und/oder die Rückflanke des reflektierten Laserpulses sind/ist in zumindest einem vorgegebenen Bereich des Laserpulses monoton steigend bzw. monoton fallend.
• – Die Signalform des reflektierten Laserpulses ist zu schmal oder zu breit. Erklärung: Die Ursache für einen schmalen reflektierten Laserpuls kann in einer fehlerhaften Abtastung liegen. Beispielsweise wird der reflektierte Laserpuls nicht vollständig abgetastet, der Laserpuls ist also zu schmal, weil er zu schnell weggespiegelt wird, d.h. die Zeitdauer zur Abtastung ist größer als die Zeit, während der der Reflex unverändert ist. Ein zu breiter reflektierter Laserpuls kann die Folge einer Übersteuerung der Elektronik sein, oder aber die Pulsform wird durch Störreflexionen verzerrt.
• – Der reflektierte Laserpuls weist deutliche Zacken auf, insbesondere lassen sich mehrere Maxima u. Minima in kurzer Folge in der Signalform ermitteln.
• – Der reflektierte Laserpuls klippt stark. Hervorgerufen wird das Klippen üblicherweise, wenn die Signaländerung so schnell ist, dass sie außerhalb der für den Empfänger tolerierbaren Signaldynamik liegt. In diesem Fall kann der Füllstandsmesswert nicht ausreichend bezüglich der Signaldynamik korrigiert werden. Je genauer die Messung sein soll, desto enger müssen z.B. die Grenzen für die erlaubte Signaldynamik ausgelegt werden. Üblicherweise geschieht dies auf Kosten der Messgeschwindigkeit, da der Anteil der nicht für die Messwertbestimmung geeigneten reflektierten Signale zunimmt.
• – Anstelle eines Signals bzw. Laserpulses treten mehrere schmale Signale auf.
• – Das reflektierte Signal weist schmale Höcker auf.
• – Aufgrund der überlagerten Signale ist keine reine Puls-Signalform erkennbar.
• – Störsignale bzw. Rauschen aufgrund von Nebel, Staub etc. überlagern sich dem reflektierten Laserpuls. Eine Trennung der Störanteile ist nicht möglich.

Examples for determining the characteristics of an evaluable or non-evaluable reflected laser pulse are not listed exhaustively below:

• The rising edge and / or the trailing edge of the reflected laser pulse are / is monotonically increasing or monotonically decreasing in at least one predetermined region of the laser pulse.
• - The waveform of the reflected laser pulse is too narrow or too wide. Explanation: The cause of a narrow reflected laser pulse may be a faulty scan. For example, the reflected laser pulse is not completely scanned, so the laser pulse is too narrow, because it is mirrored away too fast, ie the time to scan is greater than the time during which the reflex is unchanged. A too wide reflected laser pulse may be the result of overloading the electronics, or the pulse shape is distorted by spurious reflections.
• - The reflected laser pulse has significant spikes, in particular, several maxima u. Determine minima in a short sequence in the waveform.
• - The reflected laser pulse taps heavily. The clipping is usually caused when the signal change is so fast that it lies outside the tolerable signal dynamics for the receiver. In this case, the level measurement can not be sufficiently corrected for the signal dynamics. The more accurate the measurement should be, the closer the limits for the permitted signal dynamics must be designed. This usually takes place at the expense of the measuring speed, since the proportion of reflected signals not suitable for determining the measured value increases.
• - Instead of a signal or laser pulse occur on several narrow signals.
• - The reflected signal has narrow bumps.
• - Due to the superimposed signals no pure pulse waveform can be seen.
• - Noise or noise due to fog, dust, etc. are superimposed on the reflected laser pulse. A separation of the interference components is not possible.

In general, the stricter the criteria for the validity of reflected laser pulses, i. The tighter the tolerance bands are, the more reliable the determination of the level will be. However, the high measuring accuracy usually comes at the expense of the measuring speed. Therefore, the tolerance bands are preferably matched to the particular application. If, with the same filling material, the change in the filling level or the surface condition is relatively slow, it is possible to measure with a high measuring accuracy. If the change in the fill level or the surface finish occurs quickly, it makes sense to accept a reduction in the measurement accuracy. Furthermore, the width of the tolerance bands can be dependent on the properties of the particular liquid product whose level is to be determined.

The waveform of a reflected laser pulse is determined via a scan. The scanning of the reflected laser pulse can be done in real time - a sampling technique that requires a high quality and expensive sampling circuit. Alternatively, a scanning method is used, as used for example in microwave-based Pulsradargeräten, which are sold and sold by the applicant under the name Micorpilot M, Micropilot S and Levelflex. Here, one sample is sampled per reflected laser pulse, wherein successive samples are each shifted by a defined distance from the respective preceding sample. As soon as the laser pulse has been completely scanned in this way, the signal shape of the reflected microwave pulse can be reconstructed on the basis of the sampled values, and the fill level in the container can be determined on the basis of the echo curve.

According to a preferred embodiment of the method according to the invention, the laser pulses of a given fundamental frequency reflected at the surface of the medium are scanned at a slightly different sampling frequency in such a way that several sampled values are recorded per laser pulse and respectively stored as a subchoice curve. The stored subecho curves are assembled after a measurement cycle to form a total technology curve. Based on the total technology curve, the actual signal shape of the laser pulse reflected on the surface of the medium is determined and / or analyzed and compared with the predetermined desired signal shape. This process is detailed in the non-prepublished German patent application DE 10 2012 106 149.1 , registered on 09.07.2012. The corresponding content of DE 10 2012 106 149.1 is to be added to the disclosure of the present application.

According to an advantageous embodiment of the method according to the invention, it is provided that the measured values which are not used to determine the fill level are qualified as invalid. Based on the number of measured values that are qualified as invalid, a statement regarding the quality of the level measurement is then made. The more measured values are qualified as invalid - the smaller the tolerance bands are - the greater the accuracy of the laser-based level measurement.

In addition, it is proposed that the number of valid measured values used for level measurement is set in relation to the number of measured values qualified as invalid, and that a warning message is generated if the number of measured values qualified as invalid exceeds a specified or specifiable maximum limit.

An advantageous embodiment of the method according to the invention stimulates the echo curve or to analyze several successive echo curves with regard to temporary and / or permanent sources of interference in the container. The temporary sources of interference are, for example, a signal distortion caused by fluctuating reflection properties of the surface. In particular, these changes in reflection properties can be so fast that they can not be recorded correctly.

The solution according to the invention is therefore not only about sources of interference, such as fittings in the container. In the case of the optical reflection based ToF (time of flight) method, the signal evaluation relies on a typical signal shape to avoid possible correction calculations due to e.g. the signal dynamics or the temperature to perform. In particular, due to fluctuations in the reflectivity of liquids, even when the level remains constant, unusable signals or signals often result, which lead to incorrect measurement results after application of the correction algorithms. These must also be eliminated.

It is considered to be particularly advantageous if the number of measured values qualified as invalid is reduced by emitting the laser pulses directed into the container. Direction means in this context that the laser pulses impinge on the surface of the medium, in particular of the liquid product at an angle below which the signal component reflected by the surface of the product is maximal.

Furthermore, in order to increase the number of valid signals, the signal divergence of the laser beam is e.g. to substantially greater than 10-20 mrad, e.g. 70mrad increase or expand. This increases the probability that the laser pulses reflected from the surface will arrive in the receiver. It is also possible to adapt the signal divergence of the laser beam to the respective conditions.

The task is solved with respect to the laser-based level gauge by the following features:
a signal generating unit that generates laser pulses of a predetermined pulse width;
a transmitting unit which emits the laser pulses at a defined transmission repetition frequency in the direction of the surface of the medium; a receiving unit which receives the laser pulses after reflection at the surface of the contents;
a sampling circuit that samples the reflected laser pulses at a sampling frequency;
a control / evaluation unit which is designed such that it uses the echo curve to determine and analyze the actual signal shape or at least one actual signal characteristic of the reflected laser pulse, the actual signal shape or the actual signal characteristic with a predetermined desired signal shape or one corresponding nominal signal characteristic compares, and which uses a determined based on the echo curve measurement for determining the level, when the actual waveform and the desired waveform or the actual signal characteristic and the corresponding target signal characteristic in a predetermined tolerance range match.

The transmitting unit is preferably a pulse laser diode, a laser driver circuit and an optical lens for focusing the laser radiation. The receiving unit preferably consists of a photodiode and an optical converging lens for focusing the laser radiation reflected from the surface of the medium onto the photodiode. The photodiode may be an avalanche photodiode and a transimpedance amplifier.

An advantageous embodiment of the device according to the invention suggests that the sampling circuit is an analog / digital converter and the evaluation unit is a microprocessor.

According to the invention, a laser-based level measuring device for liquids, in particular, is realized according to the transit time principle, which is able to record the signal form of a reflected laser pulse and to subject it to a plausibility check. The measuring device is e.g. able to distinguish pure surface reflections from mixed signals from surface and tank floor reflections as well as signal forms in which both pure surfaces and pure tank bottom reflections occur. Signal forms based on mixed reflections are qualified as invalid. They are not included in the measurement.

According to the invention, the recorded "envelope" or the echo curve is analyzed for its signal shape by means of intelligent digital signal processing. Reflected laser pulses of different origin can in principle be distinguished from one another.

Furthermore, it is proposed that the scanning circuit scans the laser pulses reflected at the surface of the medium at a sampling frequency slightly different from the fundamental frequency in such a way that several sampled values are recorded per laser pulse and stored in each case as subchoice curve, and
wherein the control / evaluation unit, the Subechokurven composed after a measurement cycle to a total technology curve and based on the total technology curve determines the actual waveform of the laser pulse reflected at the surface of the medium and analyzed. Of course, as previously mentioned, it is also possible to perform the sampling in an alternative manner: for example, via a real-time sampling or sampling, as already known from microwave level gauges. The advantages and disadvantages of these solutions with respect to the favored solution are in the DE 10 2012 106 149.1 described in detail.

In addition, in connection with the level measuring device according to the invention, it is proposed that the control / evaluation unit be designed to invalidate measured values which are not used to determine the filling level, and to make a statement on the basis of the number of measured values qualified as invalid Generated with regard to the quality of the level determination.

An advantageous embodiment of the filling level measuring device according to the invention provides that the control / evaluation unit is configured such that it sets the number of measured values used for level measurement in relation to the number of measured values qualified as invalid and generates a warning message if the number of times is invalid qualified measured values exceeds a specified or specifiable upper limit.

In addition, the laser-based level measuring device can be extended by means of the alignment device according to the invention mentioned below to a particularly advantageous system for determining the filling level of a filling material in a container according to a transit time method. The alignment device is designed so that it allows an alignment of the level gauge in an optimal for each application measurement position. In this optimum measuring position, the level gauge is aligned so that the emitted laser pulses impinge at an angle on the surface of the medium, below which the determined quality of the filling level determination is maximum. This is usually the case when the signal component reflected on the surface of the medium is at least approximately maximum.

It is also considered to be particularly advantageous if a sight glass, which is substantially transparent to the laser pulses, is provided, which is coupled to the fill level gauge via an adjusting mechanism, wherein the fill level gauge and the sight glass are arranged outside the container, so that the transmitted and reflected laser pulses pass the sight glass on its way.

Furthermore, we proposed in connection with the system according to the invention that the sight glass and the level gauge or the sight glass with the coupled level gauge in a wall of the container, preferably in the region of the lid, is positioned. This solution is particularly advantageous when the level gauge is used in chemical or pharmaceutical manufacturing processes, since the meter is separated from the actual process by the sight glass. It is further provided that a pivot mechanism is provided between the sight glass and the level gauge, which is designed so that the level gauge is folded away from the sight glass and that when folded back into the measuring position, the previously set measuring position is reached again. Here, the sight glass can also be used for the inspection of the container interior by the operator.

In addition, it is proposed that to avoid or minimize windshield reflections the blocking distance of the level gauge is chosen so that it lies inside the container and therefore behind the sight glass.

An advantageous development of the system according to the invention provides that the laser level gauge is associated with a display unit on which the quality of the level determination is displayed, which is achieved in the respective alignment position. In particular, on the display unit during the alignment process, the alignment position which has produced the best measurement result is graphically displayed. In order to lock the level gauge in the optimal alignment position or measuring position, a corresponding fixing device is provided.

The invention will be explained in more detail with reference to the following figures. It shows:

1 FIG. 2 is a block diagram of a preferred electronics system that generates and emits laser pulses and determines the waveform of the reflected laser pulses through a scanning method.

2a -C: a representation of mixed signals arising from surface and container floor reflections,

3a -P: representations of signal types evaluated as valid and invalid,

4 FIG. 2: a perspective view of a first embodiment of the system according to the invention with an alignment device, FIG.

• a) außerhalb des Messbetriebs
• b) im Messbetrieb

5 : An alternative embodiment of the system according to the invention (sight glass light) for level measurement in the position:

• a) outside the measuring operation
• b) in measuring mode

6a FIG. 2 shows a plan view of a first embodiment of a display unit for finding the optimum measuring position, FIG.

6b : A plan view of a second embodiment of a display unit for finding the optimum measuring position and

7 : A representation of the beam path of laser pulses taking into account the optimum blocking distance.

1 shows a block diagram of a preferred electronics, which generates and emits laser pulses and determines the waveform of the reflected laser pulses via a scanning process. The scanning method shown is preferably used in conjunction with the method according to the invention and the level measuring device according to the invention.

The signal generation unit 1 generates signals with a fundamental frequency f. These signals with the fundamental frequency f become the pulse shaper 6 and the microprocessor 5 fed. The pulse shaper 6 generates from the signals laser pulses with a predetermined pulse width Tp or a predetermined transmission repetition frequency f _pulses . Preferably, the predetermined pulse width Tp of the laser pulses is between 1ns and 10ns. The measurement accuracy achieved here allows level measurement on moving surfaces in liquid products.

The laser pulses are from the transmitting unit 2 towards the surface of the 3 also not shown separately presented contents. At the same time the microprocessor receives 5 a start signal, for the start of the measurement.

The laser pulses reflected at the surface of the medium or at the bottom of the container become in the receiving unit at a time dependent on the distance and therefore on the filling level of the product 3 receive. The received laser pulses become the sampling circuit 4 , here an AD converter, fed. The scanning of the laser pulses is carried out at a sampling frequency f _S , which differs slightly from the fundamental frequency f. The sampling frequency is from the signal generation unit 7 , eg an oscillator. The difference frequency f _diff between the sampling frequency f _S and the fundamental frequency f is regulated to a constant value. Number examples are in the DE 10 2012 106 149.1 called. A measuring cycle is performed by the microprocessor 5 after a floating of the difference frequency f _diff completed, so if the difference frequency f _diff has passed through a period T and the fundamental frequency f and the sampling frequency f _{S are} back in phase.

Depending on the desired resolution or measurement accuracy, a plurality of subchannel curves SEKx are recorded, the sample values of the individual subchoice curves SEKx being shifted relative to one another by a defined time interval Δt due to the fundamental frequency f, the sampling frequency f _S , the difference frequency f _diff and the divider factor TF , Preferably, the divider factor TF 1/2 ⁿ , with n = 1, 2, 3, ... This is an optimal utilization of the memory, the microprocessor 5 is assigned, ensured. In addition, the evaluation is simplified. Further details of the method used in connection with the present invention can be found in the previously cited DE 10 2012 106 149.1 which is to be added to the disclosure content of the present solution.

The 2a -C show different forms of mixed signals due to surface reflections and tank bottom reflections that typically occur with transparent or at least partially transparent liquids. In particular, based on the 2a C illustrates the problem underlying the invention. Whether a tank bottom reflex mixes with a surface reflex ultimately depends on two factors, the height of the fill level and the width of a laser pulse.

2a shows the case that the surface reflection (left) can be clearly distinguished from the tank bottom reflex (right). Usually, the signal of the container bottom reflection is still significantly attenuated with respect to the signal of the surface reflection. In the case shown, a reliable measured value can be calculated on the basis of the signal shape.

In 2 B the case is shown that the level is not sufficiently high and the distance between the signal reflected at the surface and at the bottom of the container becomes so small that the two signals mix to form a mixed signal. Due to the signal shape, the mixing is clearly recognizable in this case. Therefore, the total signal can be declared invalid. Eventually, such mixed signals can also be declared valid, and indeed whenever the signal reflected at the surface can be reconstructed from the mixed signal.

In 2c the case is shown that the level is even lower. Here it is no longer recognizable with simple methods that the signal is a mixed signal. As a consequence, a faulty measured value would be determined. However, if the principally very sharp and narrow signal profile of a surface reflection in the respective application is known through a teach-in process, the mixed signal can be recognized as valid or invalid by comparing actual and desired signal properties or actual and desired signal form become. The closer the tolerance ranges are in the actual-target comparison, the more numerous will be the number of measured values that are rejected as invalid. The consequence of a higher measuring accuracy is a lower measuring rate with which the measured values are made available per unit of time. If lower requirements are placed on the measuring accuracy, the measuring rate is higher.

Typical pulse widths of lasers are, for example, in the range of 3-5 ns and thus have a spatial extent between 0.9 m and 1.5 m. Thus, at low levels or small containers, statistically frequent signal mixing is very likely. A measurement that is unable to detect invalid mixed signals does not provide sufficient measurement accuracy in level measurement.

In the 3a - 3p are valid waveforms ( 3a - 3e ) and invalid - and thus unsuitable for the determination of measured values - waveforms ( 3a - 3p ) graphically.

3a shows a valid waveform that has been taken in the linear area of the receiving unit.

3b shows a slightly weak, deformed but still validated signal.

3c shows a valid waveform that has been recorded in the overdriven area of the receiving unit.

3d shows a strongly attenuated waveform that is barely valid.

3e shows a deformed waveform, which is still valid, because here the average signal range and the rising edge of the signal can be evaluated.

3f shows an invalid waveform consisting of split signals caused by spurious reflections.

The 3g - 3y show four invalid waveforms characterized by non-monotonically rising edges. The pips appearing in the signal are indicative of false samples caused by signal reflections that are too fast for sampling.

The 3k and 3l show invalid waveforms with many fragments.

In the 3m shown waveform is invalid because the signal does not reach a required minimum strength.

The 3n - 3p show invalid waveforms, which have due to very fast perturbations peaks.

As already stated, the angle of incidence of the laser pulses or of the laser radiation and the wavelength of the laser pulses or of the laser radiation have a decisive influence on whether or not a container bottom reflection arises. Therefore, in the context of a laser-based level measuring device, it is very important to emit the laser radiation at an optimum angle of incidence in the direction of the medium. In 4 is a perspective view of an alignment device 8th represented, as it can be used by way of example in connection with the level measuring device according to the invention.

Laser-based methods and devices for level measurement of clear and strongly absorbing liquids rely on the direct reflection of the laser radiation at the liquid surface. It should be noted that the absorption in the liquid is dependent on the wavelength of the laser radiation, while the direct reflection on the surface of the liquid is not affected by the wavelength of the laser radiation.

Depending on the angle of incidence and the optical media properties, a portion of the incident radiation is always refracted and reflected at a liquid surface. In order for the proportion of the radiation reflected back from the surface of the liquid to reach a maximum value, it is important to direct the laser radiation to the surface at the ideal angle of incidence, usually perpendicularly. Even with larger measurement distances even small changes in angle of the incident laser radiation cause a significant radiation loss.

In addition, when using common wavelengths of the laser radiation, there is the problem that the laser radiation penetrates the more or less transparent liquid and undergoes a reflection at the container bottom. This leads to the already described mixing of the container floor or wall reflex with the surface reflection.

Known level gauges, their arrangements or process connections and container geometries often do not allow a desired precise alignment of the incident radiation. In radar instruments, it is known to align the measuring radiation via an adjustable flange. Corresponding flange arrangements do not meet always the required hygiene guidelines and therefore can not be used without restriction. Due to the already mentioned high sensitivity of the laser-based level measurement systems, it is not possible for a service technician or customer without additional aids to ensure a precise alignment of the laser beam manually.

The invention has for its object to provide a system for laser-based level measurement, which ensures a non-contact, non-intrusive level measurement on transparent liquids. Preferably, the main components of the system should be outside the container 9 be arranged so that any hygiene requirements can be met easily. In particular, the measurement is preferably carried out from the outside through a sight glass 10 , The precise alignment of the laser radiation via an adjustable mechanical support of the level gauge and is by an optical and / or acoustic display unit 11 , on which the quality of the received signal is readable, supported.

Examples of the display or user guidance of a vertical alignment of the laser level gauge are in the 6a and 6b shown. Here, the alignment is not based on the signal quality.

• – Eine Ausrichtvorrichtung 8, die in der optimalen Position fixiert werden kann, sobald das Gerät justiert ist. Eine nachträgliche Dejustage wird dadurch vermieden.
• – Einen Schwenkmechanismus 13, der ein Wegklappen des Füllstandsmessgeräts 12 ermöglicht, wodurch das Sichtfeld des Schauglases 10 wie gewöhnlich zur visuellen Inspektion des Behälterinnenraums freigegeben wird. Bei anschließendem Zurückschwenken, rastet das Füllstandsmessgerät 12 wieder in der ursprünglich eingestellten bzw. justierten optimalen Position ein.
• – Die Blockdistanz der Optik des Füllstandsmessgeräts 12 wird so ausgelegt, dass die Laserpulse bzw. die Laserstrahlung erst innerhalb des Behälters 9 direkt auf die Empfangseinheit 2 abgebildet werden. Dargestellt ist dieser bevorzugt verwendete Fall in 7. Durch diese Auslegung der Optik wird das Auftreten von Reflexionen an der Frontscheibe des Schauglases 10 minimiert.

In the 5a and 5b an alternative embodiment of the system according to the invention for level measurement is described. The level gauge 12 is by means of an adjustable bracket 13 , similar to a hinged sight glass, over a sight glass 10 attached and consists of the following components:

• - An alignment device 8th , which can be fixed in the optimum position as soon as the device is adjusted. Subsequent misalignment is thereby avoided.
• - A swivel mechanism 13 , the folding away of the level gauge 12 allowing the field of view of the sight glass 10 as is usually released for visual inspection of the container interior. When subsequently swinging back, the level gauge locks 12 again in the originally set or adjusted optimal position.
• - The blocking distance of the optics of the level gauge 12 is designed so that the laser pulses or the laser radiation only within the container 9 directly to the receiving unit 2 be imaged. This preferred case is shown in FIG 7 , Due to this design of the optics, the occurrence of reflections on the windscreen of the sight glass 10 minimized.

Preferably, the level gauge has 12 via a special commissioning mode, the correct orientation of the level gauge 12 in relation to that in the container 9 supported filling material is supported. While this commissioning mode is active, the level gauge leads 12 For example, in a comparison with the normal measurement operation increased refresh rate by a level measurement. The received signals are evaluated for their quality. The quality is in this case a measure of the level of evaluability of a signal and indicates whether the signal is suitable with respect to a required measurement accuracy for the level measurement or not.

In the assessment of the quality of the fill level measurement signals, not only the received signal intensity is decisive according to the invention; Rather, there is a qualitative analysis of the received signals with regard to their signal shape and / or with regard to at least one predetermined signal characteristic. Invalid signals are sent by the level gauge 12 detected due to the waveform or at least one defined signal characteristic and counted accordingly and / or discarded.

On the other hand, as already described above, known laser level measuring devices can not differentiate between valid and invalid signals, since their signal intensities often do not differ at all.

• – Die Beurteilung erfolgt auf der Basis der empfangenen Signalintensität: Je höher die empfangene Signalintensität ist, desto höher ist die Güte der Füllstandsmessung. Der Nachteil bei dieser Art der Auswertung ist darin zu sehen, dass durchaus auch ungültige Signale, z.B. Mischsignale von Behälterboden- und Oberflächenreflexen akzeptiert werden, was zur Ausgabe von fehlerhaften Messwerten führt.
• – Die Bewertung erfolgt auf der Grundlage der Signalform des Laserpulses: Die höchste Güte hat ein Signal, das weitgehend dem Idealbild einer Direktreflexion ohne Mischeffekte durch Behälterboden- oder Wandeffekte entspricht. Sind zwei Signale bezüglich der Signalform gleichwertig, so hat das Signal mit der höheren Intensität auch die höhere Güte.
• – Die Beurteilung erfolgt auf der Basis der Anzahl gültiger und ungültiger Signale: In einer bevorzugten Ausführung werden hierbei pro Messgeräteposition mehrere Signale aufgenommen und auf Ihre Gültigkeit hin überprüft. Je höher der Anteil der gültigen Signale während eines definierten Zeitraums an der Gesamtzahl der Signale ist, desto höher ist die Signalgüte und desto günstiger ist die gewählte Ausrichtung des Füllstandsmessgeräts 12 für die Messung. Erfolgt die Bewertung auf der Basis der Signalintensität, so muss ein als gültig bewertetes Signal einen festgelegten Schwellwert überschreiten.
• – Die Beurteilung erfolgt auf der Basis statistischer Werte, wie z.B. komplexe Histogrammanalysen oder Beurteilung der Varianzen und Mittelwerte von Bewertungskriterien.

In terms of signal quality, several criteria can be used. By way of example, some are mentioned below:

• - The assessment is made on the basis of the received signal intensity: the higher the received signal intensity, the higher the quality of the level measurement. The disadvantage of this type of evaluation is the fact that even invalid signals, eg mixed signals from container bottom and surface reflections are accepted, which leads to the output of erroneous measured values.
• - The evaluation is based on the waveform of the laser pulse: The highest quality has a signal that largely corresponds to the ideal image of a direct reflection without mixing effects by container bottom or wall effects. If two signals are equivalent with respect to the signal shape, then the signal with the higher intensity also has the higher quality.
• - The assessment is based on the number of valid and invalid signals: In a preferred embodiment, several signals are recorded for each measuring device position and checked for their validity. The higher the proportion of valid signals over a defined period of time in the total number of signals, the higher the signal quality and the more favorable the selected orientation of the signal level Device 12 for the measurement. If the evaluation is based on the signal intensity, a validated signal must exceed a specified threshold.
• - The assessment is based on statistical values, such as complex histogram analysis or assessment of variances and mean values of evaluation criteria.

In conclusion, it should be noted that the signal shapes of the laser pulses can be used to distinguish valid from invalid level signals based on defined criteria.

Below some advantageous developments of the solution or alternative solutions are presented:
The level gauge 12 is equipped with a position sensor. This makes it possible on the one hand, the exact alignment of the level gauge 12 to recognize, and on the other hand, the vertical positioning of the level gauge 12 and thus to enable the laser beam through a corresponding software implementation with display unit. Corresponding apps are known in popular mobile phones. In general, it can be assumed that the best signal quality is achieved with vertical positioning. The disadvantages of this solution can be seen in the fact that a position sensor and a graphic display unit are required and, moreover, that a calibration of the laser optics on the position sensor must be carried out.

In some cases, it may happen that the vertical measurement position is not the optimal measurement position. In such cases, a combination of position detection by means of a position sensor and evaluation of the signal quality is proposed. A corresponding combination is also provided when calibration of the laser optics to the position sensor is undesirable.

For this purpose, the level gauge 12 initially moved into as many different positions as possible during commissioning or alignment. The signal quality per alignment position is automatically stored and displayed on the display unit. After completing this process, the optimal or ideal position of the level gauge can 12 graphically displayed and controlled accordingly. In this case, it is not necessary to calibrate the position sensor to the laser optics, since the absolute position on the display unit is irrelevant. This embodiment has the advantage that it is very cost-effective.

• – Das System ist zur nicht intrusiven Füllstandmessung geeignet;
• – Die Anordnung erlaubt die die optimale Ausrichtung eines Laserbasierten Füllstandmessgerätes 12 bei der Füllstandsmessung auf insbesondere transparenten Flüssigkeiten ohne diffus streuende Schwebeteilchen bzw. Partikel.
• – Das System ermöglicht den Einsatz der Laser-Füllstandmessung bei transparenten Flüssigkeiten, z.B. für Produktions- und Abfüllprozesse in der Pharma- und Lebensmittelindustrie.
• – Grundlegende Erhöhung der Messgenauigkeit von Laserbasierten Füllstandmessgeräten aufgrund der Ausfilterung ungültiger Signale und aufgrund der Auswertung der Signalgüte auf Basis der Signalform bzw. der daraus abgeleiteten Signalcharakterstik.

The advantages of the system according to the invention are summarized below:

• - The system is suitable for non-intrusive level measurement;
• - The arrangement allows the optimal alignment of a laser-based level gauge 12 in the level measurement on in particular transparent liquids without diffusely scattering suspended particles or particles.
• - The system enables the use of laser level measurement in transparent liquids, eg for production and filling processes in the pharmaceutical and food industry.
• - Fundamental increase in the measuring accuracy of laser-based level measuring instruments due to the filtering of invalid signals and due to the evaluation of the signal quality based on the signal shape or the signal characteristic derived therefrom.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102012106149 [0013, 0013, 0025, 0045, 0046]

Claims (15)

Method for the laser-based determination of the filling level of a filling material in a container according to a transit time method, wherein laser pulses having a predetermined pulse width (Tp) are generated, wherein the laser pulses are emitted at a defined transmission repetition frequency (f _pulses ) in the direction of the surface of the medium, the laser pulses are received after reflection on the surface of the medium, wherein the reflected laser pulses are sampled, wherein the samples are combined to form an echo curve, wherein the actual waveform or at least a defined actual signal characteristic of the reflected laser pulse is analyzed and / or determined based on the echo curve in which the actual signal shape or the actual signal characteristic is compared with a predetermined desired signal form or a corresponding nominal signal characteristic, and wherein the measured value determined on the basis of the echo curve (EK) is used only to determine the fill level if the IS T signal shape and the nominal signal or the actual signal characteristic and the nominal signal characteristic in a predetermined tolerance range match. A method according to claim 1, wherein the laser pulses of a predetermined fundamental frequency (f) reflected at the surface of the medium are scanned at a slightly different sampling frequency (f _S ) in such a way that several sampled values are recorded per laser pulse and respectively stored as subchoice curve (SEK) the stored subecho curves (SEK) are combined after a measuring cycle into a total technology curve (EK), and wherein the actual signal shape of the laser pulse reflected at the surface of the medium is determined and / or analyzed on the basis of the overall technology curve and compared with the predetermined desired signal shape. Method according to claim 1 or 2, whereby measured values which are not used to determine the filling level are qualified as invalid, and whereby, based on the number of measured values qualified as invalid, a statement is made regarding the quality of the fill level determination. Method according to claim 1, 2 or 3, wherein the number of measured values used for level measurement is set in relation to the number of measured values qualified as invalid, and wherein a warning message is generated if the number of measured values qualified as invalid exceeds a predetermined or specifiable maximum limit. Method according to one of the preceding claims, wherein the echo curve or a plurality of successive echo curves are analyzed with regard to temporary and / or permanent interference sources in the container. Method according to one of the preceding claims, wherein the number of measured values qualified as invalid is reduced in that the laser pulses are directed emitted into the container, so that they impinge on the surface of the medium at an angle below that of the surface of the medium reflected signal component is maximum. Laser-based level measuring device for determining the filling level of a filling material in a container according to a transit time method, comprising a signal generating unit which generates laser pulses of a predetermined pulse width (Tp), with a transmitting unit which transmits the laser pulses at a defined transmission repetition frequency (f _pulses ) in the direction of the surface of the medium With a receiving unit which receives the laser pulses after reflection at the surface of the medium, with a sampling circuit which scans the reflected laser pulses at a sampling frequency, with a control / evaluation unit which is designed so that it is based on the echo curve of the IST -Signalform or at least one actual signal characteristic of the reflected laser pulse is determined and analyzed, the actual waveform or the actual signal characteristic with a predetermined desired waveform or a corresponding desired signal characteristic compares, and the one based on the echo curve (EK) Me determined Use sswert for determining the level, if the actual waveform and the desired waveform or the actual signal characteristic and the corresponding nominal signal characteristic in a predetermined tolerance range match. Filling level measuring device according to claim 7, wherein the scanning circuit scans the laser pulses reflected at the surface of the medium at a sampling frequency (f _S ) which deviates slightly from the fundamental frequency (f) in such a way that several sampled values are recorded per laser pulse and stored in each case as subchoice curve (SEK). and wherein the control / evaluation unit, the subecho curves (SEK) after a measuring cycle to a total technology curve (EK) composed and using the total technology curve, the actual waveform of the laser pulse reflected at the surface of the medium and analyzed. Filling level measuring device according to claim 7 or 8, wherein the control / evaluation unit is designed so that they measured values that are not used to determine the level, qualified as invalid, and that they based on the number of qualified as invalid measurements a statement in terms of Generates the quality of the level determination. Filling level measuring device according to claim 7, 8 or 9, wherein the control / evaluation unit is configured so that it sets the number of measured values used for level measurement in relation to the number of measured as invalid qualified measurements and generates a warning if the number of invalid qualified measured values exceeds a specified or specifiable upper limit. A system for determining the level of a filling material in a container according to a transit time method with a laser-based level measuring device as described in at least one of claims 7-10, and an alignment device, wherein the alignment device is designed so that it aligns the level gauge in a for the respective application optimal measuring position allows, the level measuring device is aligned in the optimum measuring position so that the emitted laser pulses impinge at an angle to the surface of the medium, below which the signal component reflected at the surface of the medium is at least approximately maximum. The system of claim 11, wherein a sight glass substantially transparent to the laser pulses is provided coupled to the level gauge via an adjustment mechanism, the level gauge and the sight glass being located outside the container so that the transmitted and reflected laser pulses illuminate the sight glass Run way. The system of claim 12, wherein the sight glass and the level gauge or sight glass with the coupled level gauge is positioned in a container wall. The system of claim 9, wherein the laser level meter is associated with a display unit on which the quality of the level determination is displayed, which is achieved in the respective alignment position, wherein on the display unit preferably during the alignment process, the alignment position comes to the display, which is the best Display the measurement result graphically. System according to one or more of claims 9-14, wherein between the sight glass and the level gauge, a pivot mechanism is provided which is configured so that the level gauge is folded away from the sight glass and that when folded back the previously set measuring position is set again.

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