WO1999014561A1

WO1999014561A1 - Method and device for measuring flow characteristics and other process parameters

Info

Publication number: WO1999014561A1
Application number: PCT/DE1998/002740
Authority: WO
Inventors: Margit Barth; Frank Obergriesser; Frank Schmidt; Jörg Rupp; Jürgen STECK
Original assignee: Fraunhofer Ges Forschung; Margit Barth; Frank Obergriesser; Frank Schmidt; Rupp Joerg; Steck Juergen
Priority date: 1997-09-15
Filing date: 1998-09-14
Publication date: 1999-03-25
Also published as: DE19740549A1; DE19740549C2

Abstract

The invention pertains to a method, a number of applications thereof and a device for measuring the flow characteristics of a fluid. The suggested system enables measurement of flow characteristics in open channels, in partially filled pipes, in pressure pipes, on the bodies around which the fluid circulates or during mixing, separation, reaction or decantation processes. Other process parameters can be determined as well. The ultrasound system used according to the invention for the aforementioned applications takes advantage of the inhomogeneities of the fluid. It enables non interfering and locally-triggered flow rate measurement as well as real-time flow profile measurement in non homogeneous fluids. The locally triggered flow rate measurement rests upon the tracking method. The signals recorded in a sequence of pulse-echo cycles are examined as to their similarity. A special correlation algorithm permits the time-shift of compared signal sections and, consequently, the local rates of flow to be determined

Description

Method and device for measuring flow characteristics and other process parameters

The present invention relates to a method, various applications of the method and a device for measuring the flow characteristics of a medium and other process parameters.

A first application is in the field of flow measurement technology. The flow measurement of gases and liquids forms the essential basis for the process control as well as for the quantization and calculation of quantities in numerous industrial application areas. Measurements on multiphase flows and / or under unknown flow conditions prove to be particularly problematic. Some of the process parameters cannot be determined or can only be determined inaccurately with the conventional flowmeters.

For example, some known flowmeters deliver only the entire mass or flow rate when used in multi-phase flows. Volume flow, others only the throughput of one of the phases. Still others provide measurement results which depend in an insufficiently known manner on the flow of the different phases, so that measurement errors can occur as a result. In many applications, the simultaneous It is necessary to record the mass and volume flows of all phases. In addition, process parameters such as the fill level of partially filled pipes and open channels or the concentration and spatial distribution of the different phases in a medium are of interest. With the existing systems, these parameters are difficult to measure, inaccurate or not at all.

The accuracy of the flow measurement in many processes depends heavily on the current flow profile. In most applications, however, this flow profile is unknown. The area of application of many known flowmeters is therefore restricted to undisturbed axially symmetrical pipe flows. Corresponding systems fail with partially filled pipes, open channels and containers, which are characterized by a free liquid surface and a variable fill level. When the pipes are completely full, they set sufficiently long and straight inlet and outlet sections to form undisturbed areas

Flow profiles ahead. They can therefore only be used at very specific, defined points along the flow. The wrong choice of the measuring point or the failure to comply with the corresponding installation instructions for the device can therefore lead to major measuring errors.

In order to achieve a higher measuring accuracy or to achieve measurements independent of the flow profile, the flow characteristic itself must be recorded.

In the prior art, laser Doppler anemometers for the application mentioned are

Hot wire anemometer or dynamic pressure probes known. Although these permit a flow profile measurement, they require a very long measurement time, since the sensor must be repositioned for each individual measurement point. They are therefore for surveillance dynamic, non-periodic processes unsuitable. The use of laser Doppler anemometers also requires optical transparency of the media and the wall of the flow system. Hot wire anemometers and dynamic pressure probes are not without effects. They protrude into the flow and thus influence the measurand.

Furthermore, multi-gate Doppler systems based on ultrasound are known. These belong to the so-called pulse-echo systems, which enable a direct spatial assignment of received signals based on the respective signal delay. Here, for example, an ultrasonic sensor transmits short ultrasonic signals at continuous intervals T and is operated as a receiver after a certain time. The echoes of the spreaders (inhomogeneities) carried at different depths in the medium hit the sensor at different times. With the help of a time window, signal sections belonging to different depths can be recorded separately and with regard to their

Speed information can be evaluated. The spatial assignment is unambiguous if the signal transit time between the transducer and the maximum depth considered is smaller than the period T according to the following equation. C denotes the speed of sound of the medium.

T> tmax = 2 * smax / c (")

The speed distribution along the sound beam axis can thus be detected. Appropriate processes require a multi-phase flow, as is currently the case in process technology, for example in the case of contaminated media. In the pulse-doubling method, the speed information sought is determined from the frequency shifts caused by the scattering on the moving inhomogeneities. Multi-gate Doppler systems based on the pulse Doppler method allow spatially resolved speed measurements for determining the flow profile, but are limited with regard to the maximum detectable speed and also with regard to their maximum measuring rate. In addition, spatial and frequency resolution place conflicting demands on the bandwidth of pulse Doppler systems.

A further measuring method and a device for flow measurement on open wastewater channels are described in US-A-5311781. In this pulse-echo system, an ultrasound transducer emits ultrasound pulses at short intervals at an angle to the flow direction and detects the echo resulting from scattering of inhomogeneities in the flow. An evaluation unit identifies certain inhomogeneities within the respective time window on the basis of their characteristic echo signal. In the subsequent pulse-echo cycles, this characteristic echo signal is then searched for in the time window and the flow velocity is determined from its displacement.

A second application relates to the measurement of the flow characteristics in open waters, for example in the offshore area or in the area of marine biology.

A third application concerns the area of industrial process technology, but in a completely different problem area.

In process technology, mixing, separating, Reaction and settling processes, which can take place in open and closed tanks, often have to accept long process times because real-time monitoring of crucial parameters is not possible or only to a limited extent.

To improve the process control, a system is required that records the concentration of the inhomogeneities (e.g. the different phases in a mixing process), the spatial distribution or stratification of the inhomogeneities and the degree of homogenization in real time. In addition, it is desirable to record the flow characteristics in order to optimize the process itself and, in the case of real-time measurements, the process control. The measurement of the flow profile is so far

Knowledge of the applicant is not used to monitor and manage the corresponding processes.

As already explained above, laser Doppler anemometers, hot wire anemometers or dynamic pressure probes in principle allow the measurement of

Flow distributions, however, require a very long measuring time and are therefore only suitable for monitoring dynamic processes to a limited extent. The use of laser Doppler anemometers requires optically transparent media and walls.

Multi-gate Doppler systems allow spatially resolved speed measurements, but they have the disadvantages mentioned above with regard to the maximum detectable speed and also with regard to their maximum measuring rate. Essential process parameters such as level, concentration and distribution of inhomogeneities and the degree of homogenization are not recorded with such systems.

A fourth application relates to the development and construction of flow-around bodies. Flow measurements are essential for the construction of flow-around bodies such as ship hulls, propellers, drilling platforms or buoys. When flowing around the body, gas enters the medium. Also arise

Cavitation bubbles. As these gas bubbles contribute to corrosion and reduce efficiency, knowledge of their distribution, concentration and speed is of great interest. For flow measurement are on this

So far only laser Doppler anemometers have been used. However, the long measuring times with laser Doppler anemometers are disadvantageous for monitoring the dynamic processes occurring here. Another disadvantage is that the optics or the upstream glass wall becomes soiled relatively quickly, especially when measuring in liquids.

The present invention is therefore based on the object of specifying a device and a method which enable the precise and reliable measurement of the flow profile of a medium in mixing, separating, reaction and settling processes in open and closed containers. The present invention is also based on the object of specifying a device and a method which enable the precise and reliable measurement of the flow profile of a medium on bodies which have flow around it. The present invention is based on the third object of specifying a device and a method which enable the precise and reliable measurement of the flow profile of a medium in open channels, partially filled pipes and pressure lines. The present invention is based on the fourth object of specifying an apparatus and a method which enable the exact and reliable measurement of the flow profile of a medium in open water.

The device according to the above tasks should also be inexpensive to implement and the measurement should be easy to carry out. Furthermore, the same device should be suitable for determining further parameters of the medium.

The task is with the device and the

Method according to the features of claims 1 to 4 and 25 solved. Advantageous embodiments of the method and the device are the subject of the dependent claims.

The ultrasound system used according to the invention for the above applications uses inhomogeneities in fluids. It allows non-intrusive, spatially resolved speed measurements and flow profile measurements (or flow profile reconstructions) in inhomogeneous fluids in real time.

The spatially resolved speed measurement is based on the tracking process. Signals recorded in successive pulse-echo cycles are examined for their similarity. A special correlation algorithm determines the temporal shift of compared signal sections and from them the local flow velocities. A single ultrasonic transducer is sufficient to measure the flow profile along the axis of the sound beam. This reduces costs and simplifies the measurement. However, several converters can also be used. The measurement of a two-dimensional

Speed distribution requires two or more Converter. Finally, three-dimensional measurements are possible with three or more ultrasonic transducers.

The system enables flow rate-independent measurement of the flow in open channels, partially filled pipes and pressure lines. Compared to other systems, the restrictive installation conditions no longer apply. The measuring accuracy is increased. At the same time, process parameters such as the degree of turbulence, the fill level, the temperature, the concentration of the inhomogeneities and the spatial distribution or stratification of the inhomogeneities can be recorded in real time.

The tracking process determines the speed of the inhomogeneities. If there is slippage, i.e. If the speed of the inhomogeneities does not match that of the carrier medium, then a combination of the tracking method with a method that is independent of the inhomogeneities (e.g. the known one) can be used

Transit time difference method) the mass flows of the carrier medium and the inhomogeneities are recorded separately. As a result, the flow of the different phases in a multi-phase flow can be detected.

The spatial distribution and concentration of the inhomogeneities is recorded by means of ultrasonic damping measurements in various local windows. Attenuation measurements at one or more frequencies provide information about the proportion of absorption and scattering in the overall attenuation.

In addition, sound velocity measurements can be used to determine the concentration. Process monitoring and process control can be improved with the system. The areas of application here are, for example, the chemical industry, the food industry, the paper industry, conveyor technology, the wastewater sector and the monitoring of pipelines or cooling circuits.

With the ultrasound system used, process parameters such as the temperature, the

Level, the concentration of inhomogeneities, the spatial distribution or stratification of the inhomogeneities and the degree of homogenization can be recorded in real time.

In this application, too, the spatial distribution and concentration of the inhomogeneities can be detected by means of ultrasonic damping measurements in different local windows. Attenuation measurements at one or more frequencies provide information about the share of absorption and scatter in the total attenuation. In addition, sound velocity measurements can be used to determine the concentration. The degree of turbulence can be beyond the standard deviation of the

Speed measurement can be calculated. The evaluation of the signals scattered on inhomogeneities enables monitoring of the degree of homogenization or. Separation.

The degree of homogenization can be derived from the temporal change in the amplitudes, the temporal change in the speed of sound or a pattern recognition of the scattered ultrasound signals. If, for example, the second phase goes into solution in the first, it takes place when the phase is complete Homogenization no longer takes place, ie the amplitudes approach the zero point with increasing homogenization. The reverse case of a separation process provides an increase in the amplitudes over time. In the case of mixtures that do not go into solution, the degree of homogenization can be inferred from the evaluation of the signal pattern. In both cases, the speed of sound will also change with the degree of homogenization. The necessary information can advantageously be obtained from the echo signal data acquired for the flow profile measurement, so that the simultaneous detection of the degree of homogenization or separation is made possible without additional devices.

The system thus enables the monitoring and assessment of mixing, separation, reaction and settling processes in open and closed tanks, reaction and mixing vessels. It provides the parameters necessary to manage the corresponding processes and makes a significant contribution to reducing process times. Areas of application include, for example, the chemical industry, the food industry, the paper industry, the pharmaceutical industry, the wastewater sector or process engineering.

The system is also suitable for flow analysis on flow-around bodies such as Ship hulls, propellers, inflow bodies, drilling platforms or buoys. The concentration, spatial distribution and dynamics of inhomogeneities such as Air bubbles can be captured in real time.

Here, too, the spatial distribution and concentration of the inhomogeneities are recorded by means of ultrasonic damping measurements in different local windows. Attenuation measurements at one or more frequencies provide information about the proportion of absorption and scattering in the overall attenuation.

In addition, sound velocity measurements can be used to determine the concentration of the gas bubbles.

Areas of application include flow analysis on flow-around bodies such as Ships in flow channels or shipbuilding into consideration.

In this application, the multi-gate Doppler system described above can be used as an alternative to the tracking method for spatially resolved speed measurement.

In the following, the tracking process will first be discussed in more detail. The tracking method detects the change in position of spreaders (inhomogeneities) during a predetermined time T. If the position of an individual scatterer within the sound beam is tracked, its speed can be determined from the distance Δs covered during a time T. The ultrasound beam and the speed vector enclose the measuring angle α as shown in FIG. 1.

An ultrasound pulse sent at time tO hits the spreader in position 1 and is reflected. The transducer receives the echo at time t = t0 + tl. Another pulse sent at time tO + T hits the same spreader at location 2. Its echo reaches the transducer at time t = t0 + T + t2. The transit time of the pulse reflected in position 2 is thus greater than that of the return from position 1 by Δt = t2-tl. At a constant speed of sound c, pulse 2 covers a longer path than pulse 1 by c * Δt = 2 * Δsa Spreader therefore has the distance T during the time

Δsa = c • Δt / 2 (2)

moved in the direction of the sound field axis. The axial velocity component va (for va cosα «c) is calculated from this

va = c • Δt / 2 • T, (3)

the overall speed too

v = (c • Δt) / (2 • T • cosα). (4)

The runtime difference sought can be determined by correlating the two received signals el (t) and e2 (t), the reference point of which is the associated transmission time. The correlation function of the echoes is defined by

R (τ) = Jel (t) • e2 (t + τ) dt. (5)

The shift τmax in the maximum of the cross correlation (KKF) corresponds to the one sought

Transit time difference Δt. The equation (4) gives the axial speed of the spreader under consideration.

In the real case, all the scatterers in the sound beam contribute to echo signals. In order to determine the displacement of the signal section belonging to a certain measurement volume and thus the axial speed component of a corresponding scattering volume, time windows (gates) are taken from the echo signals (FIG. 2). From their start in time tg and the length τp of the transmitted ultrasound signal results in the depth sa in which the local window begins

sa = c • (tg-τp) / 2. (6)

The axial extent, that is, the length 1 of the examined volume range, is calculated according to equation (7) from the length τg of the time window and the length τp of the transmitted ultrasound pulse. The spatial resolution of the speed detection is therefore a function of the gate length and the system bandwidth.

l = c • (τg-τp) / 2 (7)

The depth and length of the local window as well as the "width" and shape of the sound beam define the measurement volume, the so-called "Sample Volume" (SV). The echoes of all the spreaders located in the SV interfere with a reception signal that is characteristic of the present configuration. If there is a change in position between two measurements, part of the scattering volume, which in the first echo represents the SV, leaves the area under consideration (FIG. 2). Only the signal portion of the volume remaining in the measuring window, the s. G. Remaining volume allows speed detection.

A key parameter in this context is the pulse repetition frequency PRF = 1 / T (measuring rate). At a given speed, it must be chosen to be sufficiently large that a sufficiently large scattering volume remains in the SV in order to ensure similar signal sections in successive echoes.

In the simplest case, the shift Δt is estimated by locating the maximum of the time-limited KKF. The height of the correlation maximum increases increasing displacement and increasing turbulence, in practice the echoes are digitized with a sampling rate fa (= l / Ta). N signal points represent the scatter pattern in the SV. The maximum of the discrete correlation

returns the runtime shift as a number of n discrete points. The axial

Velocity component is calculated according to equation (3):

va = n PRF / 2 • fa. (9)

The temporal resolution is ± Ta / 2. Interpolation algorithms allow an increase in the resolution or a decrease in errors caused by time discretization in the detection of the delay shift.

The normalized correlation function

with values between -1 and 1 provides a measure of the correspondence of compared signal sections.

There are various possibilities for calculating the correlation function of the signal sections with a shift k bei O limited to N measured values. The data fields can be supplemented by N zeros in each case, or the summation in equation (8) takes place in Dependence on the shift over Nk summands. In both cases, the number of products that contribute to the functional value of the KKF decreases linearly with the shift. The amplitude of the KKF is not only dependent on the agreement of the signals for the respective shift, but also on the shift itself. The same applies to the standardized

Correlation function when normalized to the total energy of the signal sections. Since only the number of summands not equal to zero, but not the respective sum decreases linearly with the shift, this effect cannot be compensated for by a weight function. However, the effect does not apply when using block matching algorithms. Signal sections of different lengths are compared here, i.e. a shorter section is searched for in a longer section acquired later.

While the calculation of discrete values of the KKF or short sections of the correlation function can advantageously be carried out in the time domain, a Fourier transformation of the signals supplemented by N "zeros" is recommended for calculating the entire KKF, especially in the case of long windows. Multiplying the spectra and transforming it back into the time domain gives the KKF we are looking for.

Since the tracking process is based on the detection of changes in transit time, speed and location resolution make no contradictory demands on it

System. A simultaneous optimization of both sizes is possible without additional technical effort. The frequency-dependent damping alters successive echoes equally, so that the change in transit time calculated by means of cross correlation remains unaffected by the damping. The decisive advantage of the tracking process lies in the fact that higher speeds can be measured at greater depths than is possible with conventional pulse Doppler systems.

In principle, in the present method, two pulse-echo cycles (one measuring cycle) are sufficient for the

Determine speed in a location window. This enables higher measuring rates than with pulse Doppler systems.

The method only requires a one-element converter to record the flow profile along a line, and is therefore inexpensive to implement. The spatial assignment of the measuring depths results directly from the corresponding signal transit time.

The invention is explained in more detail below with reference to the drawings, in which

1 shows the principle of the tracking method using the example of a single spreader,

2 shows the principle of the tracking method for spatially resolved speed measurement,

3 shows the schematic representation of a measurement path of an embodiment, and

4 show the result of a flow profile measurement in a cylindrical stirred tank.

As an example of a universal system for use in the above applications, an implementation of the functions to be carried out in a DSP (digital signal processor) is proposed below. The implemented software allows the system parameters to be freely specified within wide limits. These include the center frequency of the ultrasonic wave, the PRF, the number, depth and length of the measurement window, the sampling frequency, the level of the transmission amplitudes and

Reception amplification factors (for the different local windows). In this example, the (digitized) window length is set to 512 points. The software also offers a number of options with regard to data acquisition and signal processing. For example, the number of echoes to be recorded in a measurement cycle can be selected. Search area limitation or limitation of the measuring range to a measuring interval and nonlinear filtering (e.g. median filtering) can be activated or deactivated. The position and length of the measuring interval as well as the dimension of the filter are adjustable parameters. By restricting the measurement interval, the processing time can be shortened and the probability of an incorrect maximum being detected (measurement error) can be reduced. If false maxima are nevertheless detected, their influence on the measurement result is suppressed by the non-linear filtering.

Before starting the measurement, the parameters are entered. After the user has confirmed the values, the hardware is initialized and the measurement is started. The set number of echoes is acquired and the KKF of successive signals is calculated, for example by conjugated complex multiplication in the frequency domain.

Additional fixed target suppression is possible. This can be done, for example, by subtracting successive echo signals and correlating the respective difference values. When the measuring range limitation is activated, the search for the maximum of the KKF occurs in the specified one O ω t to HH in o in o in o in

ω w t to H H in o in o in o in

m

30

>

00

30 mΩ m ro

Capture depths in parallel. In this example, the number of pulse-echo cycles that are used to determine a speed value per gate is 28, and the pulse repetition frequency is 800 kHz. The search range for the correlation maxima was limited to 0-30 points. The median filtering rank was set to 2, which means the filter length is 5.

FIG. 4 shows the flow profiles determined at different speeds of the stirrer. Discontinuities in the profiles are due to the additional motion components mentioned and the associated strong turbulence.

Claims

claims

1. Method for measuring the flow characteristics of a medium in mixing, separating, reaction and

Settling processes in open and closed containers with the following process steps:

Providing at least one ultrasonic transducer on or in an open or closed container in which mixing, separating, reaction and settling processes take place;

Emitting a first short ultrasound signal in a direction which has a directional component in the flow direction;

Receiving first echo signals from portions of the first short ultrasonic signal scattered due to inhomogeneities in the flow in a predetermined time window that corresponds to a first location window in the flow;

Digitizing the first echo waveform; - storing the digitized first echo waveform;

Emitting a second short ultrasound signal at a predetermined small time interval for emitting the first short ultrasound signal in the same direction;

Receiving second echo signals from portions of the second short ultrasound signal scattered due to inhomogeneities in the flow in a predetermined time window which corresponds to the first location window in the flow;

Digitizing the second echo waveform; Forming the cross correlation between one or more areas of the first echo waveform and one or more areas of the second echo waveform;

Determination of the flow velocity (s) in the first local window in the flow from the position of a local maximum of the cross-correlation or of local maxima of the cross-correlations;

Repeating the measuring cycle in accordance with the preceding method steps with shifted time windows which correspond to other local windows in the flow, if the acquisition of the complete flow characteristics in the desired area has not yet been completed.

2. Method for measuring the flow characteristics of a medium on bodies with flow around it with the following method steps:

Providing at least one ultrasound transducer in the area of the flow around the body; Emitting a first short ultrasound signal in a direction which has a directional component in the flow direction on the body being flowed around;

Receiving first echo signals from portions of the first short ultrasonic signal scattered due to inhomogeneities in the flow in a predetermined one

Time window that corresponds to a first location window in the current;

Digitizing the first echo waveform; Storing the digitized first echo waveform;

Emitting a second short ultrasound signal at a predetermined small time interval for emitting the first short ultrasound signal in the same direction; - Receiving second echo signals from on

Inhomogeneities of the second short ultrasonic signal scattered in the flow in a predetermined time window which corresponds to the first local window in the flow; - Digitize the second echo waveform; Form the cross-correlation between one or multiple areas of the first echo waveform and one or more areas of the second echo waveform;

Determining the flow velocity (s) in the first local window in the flow from the position of a local maximum of the cross correlation or of local maxima of the cross correlations;

3. Method for measuring the flow characteristics of a medium in open channels, partially filled pipes and pressure lines with the following method steps:

Providing at least one ultrasonic transducer on or in an open channel, partially filled pipe or a pressure line;

Receiving second echo signals from on Inhomogeneities of the second short ultrasonic signal scattered in the flow in a predetermined time window which corresponds to the first local window in the flow; - Digitize the second echo waveform; Forming the cross correlation between one or more areas of the first echo waveform and one or more areas of the second echo waveform; - Determination of the flow velocity (s) in the first local window in the flow from the position of a local maximum of the cross correlation or of local maxima of the cross correlations;

4. Method for measuring the flow characteristics in open waters with the following method steps:

Providing at least one ultrasonic transducer in an open body of water; Emitting a first short ultrasonic signal in a direction which has a directional component in the flow direction;

Time window that corresponds to a first location window in the current;

Digitizing the first echo waveform; Storing the digitized first echo waveform;

Send a second short ultrasound signal at a predetermined small time interval for the transmission of the first short ultrasound signal in the same direction;

Digitizing the second echo waveform; Forming the cross-correlation between one or more areas of the first echo waveform and one or more areas of the second echo waveform;

5. The method according to claim 3, characterized in that the flow of the medium in the open channel, partially filled pipe or the pressure line is calculated via the level and the determined flow profile.

6. The method according to claim 3, characterized in that when slip occurs between the

Inhomogeneities and the medium, an additional flow measurement, for example using the transit time difference method, is carried out in order to detect the speed of the medium.

7. The method according to claim 1, characterized in that the degree of homogenization or separation is determined on the basis of the change in the amplitudes of the scattered ultrasound signals or on the basis of the change in the speed of sound in the medium or on the basis of a pattern recognition.

8. The method according to any one of claims 1, 3 to 7, characterized in that the fill level or the level of the medium is determined by means of a transit time measurement by means of ultrasound by reflection on the surface of the flowing medium.

9. The method according to any one of claims 1 to 7, characterized in that the temperature of the medium is determined by means of ultrasonic transit time measurement.

10. The method according to any one of claims 1 to 9, characterized in that the concentration and distribution of inhomogeneities in the medium via an ultrasonic attenuation measurement or

Sound velocity measurement is determined.

11. The method according to any one of claims 1 to 10, characterized in that the degree of turbulence is determined from the standard deviation of measured values of the flow rate.

12. The method according to any one of claims 1 to 11, characterized in that the correlated time windows have the same length.

13. The method according to any one of claims 1 to 11, characterized in that time windows of different lengths are correlated (block matching algorithm).

14. The method according to any one of claims 1 to 13, characterized in that in addition a fixed target suppression takes place, for example via a difference method.

15. The method according to any one of claims 1 to 14, characterized in that a measuring cycle comprises the transmission of further short ultrasonic signals in predetermined small time intervals for transmitting the preceding short ultrasonic signal in the same direction, the reception of the echo signals from inhomogeneities in the flow scattered portions of the further ultrasonic signals in predetermined time windows, which correspond to the same location window in the flow, digitizing the further echo signal profiles and forming the cross-correlation between the echo signal profiles of the ultrasound signals, so that several measured values of the flow velocity for a location window in the flow are obtained.

16. The method according to claim 15, characterized in that initially all echo waveforms are stored and are only correlated after the completion of a measurement cycle.

17. The method according to claim 15 or 16, characterized in that a plurality of measured values for the same local window are subjected to a non-linear filtering, for example a median filtering, with subsequent statistical evaluation (e.g. mean value, standard deviation).

18. The method according to any one of claims 1 to 17, characterized in that with large changes in position in relation to the window length of the inhomogeneities between the adjacent pulse-echo cycles, the cross-correlation by means of Fourier transformation and conjugate complex Multiplication in the frequency domain, and with small changes in position of the inhomogeneities between the neighboring pulse-echo cycles in relation to the window length, the cross-correlation takes place by means of complex conjugate multiplication in the time domain.

19. The method according to any one of claims 1 to 18, characterized in that the reliability of the measurement is assessed on the basis of a normalized cross-correlation coefficient.

20. The method according to any one of claims 1 to 19, characterized in that the determination of the maximum of the cross-correlation takes place only within a predeterminable measurement interval or a measurement interval determined by an algorithm within the time window.

21. The method according to any one of claims 1 to 20, characterized in that an interpolation is carried out in the determination of the maximum of the cross correlation in the maximum found.

22. The method according to any one of claims 1 to 21, characterized in that the transmission amplitudes, the reception gain, the pulse repetition frequency, the measurement interval and, if appropriate, the window size are adjusted when the local window changes.

23. The method according to any one of claims 1 to 22, characterized in that by providing further

Ultrasonic transducer and a multiplexer, a two- or three-dimensional detection of the flow characteristics takes place.

24. The method according to any one of claims 1 to 22, characterized in that by providing further Ultrasonic transducer and additional evaluation channels, a two- or three-dimensional detection of the flow characteristics takes place.

25. Device for carrying out the method according to one of claims 1 to 24, which consists of at least one ultrasound transducer with control and evaluation electronics, wherein an input option is provided for the input of parameters according to which the control unit controls the ultrasound transducer and the evaluation electronics Evaluates, the parameters include the time interval of the ultrasound signals, the length, position and number of time windows, the center frequency, the number of ultrasound signals to be transmitted per measuring point and the transmission amplitudes and reception amplifications for the different time windows.

26. The apparatus according to claim 25, characterized in that the parameters further include the shape and length of the ultrasonic signals and the sampling frequency.

27. The apparatus of claim 25 or 26, characterized in that the parameters continue to be the

Measuring interval and the filter order include.

28. Method for measuring the flow characteristics of a medium on bodies with flow around it using a pulse-echo method using ultrasound, in particular using the multi-gate Doppler system.

29. Method for measuring the flow characteristics of a medium in mixing, separating, reaction and settling processes in open and closed containers with a pulse-echo method using ultrasound, in particular with the multi-gate Doppler system.