Method for measuring the flow velocity of a medium

Abstract

Method for measuring the flow velocity of a medium in an open channel with a radar meter, wherein a primary emission direction of the radar meter forms with a direction of a surface of the medium a first angle from 20° to 80° and with a flow direction of the medium a second angle between 0° and 80°, comprising the following steps: Sending a transmission signal with a plurality of frequency ramps, Receiving a reception signal per frequency ramp of the transmission signal, Saving the reception signals, Performing a first spectral analysis of the reception signals, Performing a second spectral analysis of several receiving signals or output signals of the first spectral analysis, Determining a flow velocity based on the phase change yielded from the output signals of the second spectral analysis in at least one distance in the distance range.

Claims

1. A method for measuring the flow velocity of a medium in an open channel with a radar meter, wherein the radar meter is arranged and aligned in such a way that a primary emission direction of the radar meter forms with a direction of a surface normal of the medium a first angle between 20° and 80°, and with a flow direction of the medium a second angle between 0° and 80°, comprising the following steps: Sending a transmission signal with a plurality of frequency ramps, Receiving a reception signal per frequency ramp of the transmission signal, Saving the reception signals, Performing a first spectral analysis of the reception signals, Performing a second spectral analysis of several receiving signals or output signals of the first spectral analysis, Determining a flow velocity based on a phase change using the output signals of the second spectral analysis in at least one distance in a distance range, such distance range comprising a range from a minimum distance up to a maximum distance resulting on account of a distance of the surface of the medium from the radar meter in a main emission direction and the first angle and second angle, wherein the flow velocity is determined on account of an average phase change in the distance range, a level of the medium in the channel is determined, and the distance range is adjusted based on the determined level.

2. The method of claim 1, wherein the spectral analysis is a fast Fourier transformation.

3. The method of claim 1, wherein a transmission signal with at least 25 frequency ramps is transmitted.

4. The method of claim 1, wherein a transmission portal comprises a plurality of frequency ramps.

5. The method of claim 4, wherein the transmission signal contains 128, 256 or 512 frequency ramps.

6. The method of claim 1, wherein a frequency ramp has a duration between 1 μs and 1000 μs.

7. The method of claim 1, wherein a start frequency f1 and/or a slope and/or an increment of the frequency ramps varies.

8. The method of claim 1, wherein the first angle is determined by a position sensor.

9. The method of claim 1, wherein a transmission signal with at least 300 frequency ramps is transmitted.

10. The method of claim 1, wherein a frequency ramp has a duration of between 100 μs and 200 μs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a line drawing evidencing a simplified depiction of a radar meter for determining a flow velocity and a level of a medium in an open channel.

(2) FIG. 2a is a line drawing evidencing a simplified depiction of the second radar sensor from FIG. 1 when using a measurement method according to the prior art.

(3) FIG. 2b is a line drawing evidencing a FMCW modulated transmission signal.

(4) FIG. 3a is a line drawing evidencing a measurement curve, as it is obtained with the measurement method according to the prior art.

(5) FIG. 3b is a line drawing evidencing the measurement curve according to FIG. 3a for rain.

(6) FIG. 4 is a line drawing evidencing a simplified representation of the second radar sensor from FIG. 1 when using the measurement method according to the present application.

(7) FIG. 5 is a line drawing evidencing the transmission signal of a method for measuring the flow velocity according to the present application.

(8) FIG. 6a is a line drawing evidencing a measurement curve, as it is received with the measurement method according to the present application.

(9) FIG. 6b is a line drawing evidencing the measurement curve according to FIG. 5a for rain.

(10) FIG. 7 is a flow chart evidencing the sequence of the method for measuring flow velocity according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(11) The invention is a method for measuring the flow velocity of a medium in an open channel using a radar meter, wherein the radar meter is arranged and aligned such that a main direction of emission of the radar meter forms with a direction of a surface normal of the medium a first angle from 20° to 80°, preferably from 30° to 60°, and with a flow direction of the medium a second angle from 0° to 80°, preferably from 0° to 60°, comprising the following steps: Emitting a transmission as a plurality of frequency ramps, Receiving a reception signal per frequency ramp of the transmission, Saving the reception signals, Performing a first spectral analysis of the reception signals, Performing a second spectral analysis of several output signals of the first spectral analysis in at least one specified distance from the radar meter, Determining a flow rate based on the phase change using the output signals of the second spectral analysis.

(12) For each measurement, the transmission signal has a plurality of frequency ramps. For such frequency ramps, which are also referred to as chirps, the transmission signal runs at a ramp duration from a few microseconds to a few hundred microseconds, for example, 100 μs or 200 μs, at a frequency range of some GHz, e.g. 5H GHz or 10 GHz, preferably at a frequency range between 75 GHz and 85 GHz. The frequency ramps can be continuously cycled through, so that a continuous change in the frequency or in a fine hatching may occur, e.g. in 5 Hz steps, comprising discrete frequency values within the frequency range.

(13) Receiving signals are received and, for example, stored in an intermediate memory, whereby one receiving signal is obtained per frequency ramp.

(14) The receiving signals are transferred with a first spectral analysis from the time range to the frequency range, whereby a frequency shift of the receiving signal relative to the transmission signal is proportional to a distance of the reflection to the transmitter, i.e., the fill gauge, so that in general reflections and their distance from the fill gauge, in the present case therefore e.g., the distance of the surface of the medium in the channel from the fill gauge can be determined from the signal obtained. With consideration of the first angle and the second angle, here generally a level of the medium in the channel can also be determined.

(15) Through the second spectral analysis, which is carried out at least at the location, i.e. the frequency of reflection via the output signals of the first spectral analysis, a dependent phase of the signal is determined based on the speed of the reflection, i.e. a speed indicating a velocity of motion at the point where the medium moves causing the reflection. From the change in the phase over the individual reception signals, a speed distribution can be determined at the location of the reflection and thus in the area of the surface of the medium flowing in the channel.

(16) For this purpose, the second spectral analysis can be limited to a distance in which the surface of the medium lies in the channel, i.e. only signal components are used for determining the flow velocity which actually represent a speed of the medium.

(17) The first angle α is measured in the present application in a lateral view, perpendicular to the plane defined by the surface normal and the second main direction of emission, the second angle in a plan view from the top, i.e. with a view towards the surface normal.

(18) It is noted at this point that the first and second spectral analysis can also be carried out in reverse order.

(19) In order to make the measurement independent of any individual, locally elevated measured values, the flow rate can be determined based on an average phase change in a distance range. For this, the second spectral analysis is evaluated in the entire distance range, which means an average phase change and correspondingly an average speed can be determined in the distance range.

(20) At this point, it is noted that the distance range is dependent on the diagonal irradiation of the measurement signals relative to the surface of the medium, i.e. the first and second angle. In determining the flow rate, therefore, the first angle and additionally the second angle, which describes the alignment of the radar meter relative to the flow direction, must be taken into consideration. The distance range, i.e., a range with intervals from a minimum distance up to a maximum distance, will show an elliptic shape on a planar surface in the main direction of radiation with a conical emission characteristic. If the surface of the medium is not in the channel, then this form is adapted accordingly.

(21) The determination of the flow rate can occur, for example, at a distance or distance range specified in the main emission direction from the radar meter, in which the surface of the medium is expected. However, if the determination of the flow rate is to be done with a higher accuracy or if a fluctuating level is to be expected, then first a level measurement may occur for determining the distance or distance range in which the surface of the medium is given, thus the distance in which the flow rate is to be determined. The distance or distance range can then be adjusted based on the level measurement.

(22) The level measurement can generally take place with the same radar meter, with which the flow rate is also determined. Due to the diagonal alignment of this radar meter relative to the surface of the medium, a level measurement error can become quite major, particularly in case of unfavorable measurement conditions, which can be caused by environmental influences, such that a level measurement with an independent measurement, in particular a second radar sensor, is to be preferred perpendicular to the surface of the medium. The level measurement value can then be used for determining the distance or distance range.

(23) The term level measurement, in the present application, is understood both as a determination of the distance of the measuring instrument from the surface of the medium and a measurement of the distance of the surface of the medium from the base of the channel. In the present measuring arrangement, these values can each be converted to each other, so that the level can be determined from the level of the distance of the measuring device from the surface of the medium, and from the distance of the measuring device from the surface of the medium.

(24) In this way, the distance range can be adjusted based on the determined level.

(25) As a method for the first and/or second spectral analysis, a fast Fourier transformation (FFT) can be used for example. The fast Fourier transformation is a widely used and effective method in signal processing for transmitting signals between the time and frequency range.

(26) The emitted signal preferably comprises at least 25, further preferably at least 50, and ideally a few hundred frequency ramps which are transmitted.

(27) The number of frequency ramps, which are included in a transmission signal, specifies the number of possible receiving signals. This number determines a maximum possible temporal resolution for the emitted signal of the second spectral analysis, so that the number of signal points is also associated with the determination of the phase change and thus the flow rate.

(28) In the practical implementation of the method, the transmission signal shows a number of 2.sup.nd frequency ramps, wherein the transmission signal typically contains 128, 256 or 512 frequency ramps. A corresponding number of frequency ramps offers a sufficiently fine resolution for applications to measure a flow rate of media in channels, so that all relevant speeds can be recorded.

(29) A frequency ramp can have a duration between 1 μs and 1,000 μs. Typically, the duration of the frequency ramps ranges from 50 μs to 300 μs and, in particular, amounts to 100 μs or 200 μs.

(30) The steeper the frequency ramps, i.e., the shorter the duration of the frequency ramp relative to a frequency stroke, i.e. the distance of a lower limit frequency is to an upper limit frequency of the frequency ramp, the greater the frequency shift of the receiving signal relative to the transmission signal. Consequently, steeper frequency ramps are preferred, since commercially available evaluation circuits which show increasingly smaller geometric dimensions are designed rather for the processing of high frequencies.

(31) To exclude measurement errors, a start frequency and/or a slope and/or an increment and/or an end frequency of the frequency ramps can be varied.

(32) Through a variation of the parameters of the method, e.g., the number of frequency ramps, the start frequency, the target frequency, the sweep period, or the break time between the frequency ramps in a transmission signal, here disturbances, e.g., by other transmitters, can be minimized and an analysis can be dynamically altered and optimized. For example, corresponding changes can be made depending on the speeds of the reflections observed so far, so that, for example, with regard to the speed analysis the resolution can be increased or decreased by adjusting the number of frequency ramps.

(33) For example, the first angle can be determined using a position sensor.

DETAILED DESCRIPTION OF THE FIGURES

(34) In the following figures, unless stipulated otherwise, identical reference characters mark identical components with the same function.

(35) FIG. 4 shows the illustration of the radar meter 100 from FIG. 2, wherein the measurement method is used according to the present application. In principle, radar meter 100 is constructed as described in connection with the prior art and FIGS. 1 and 2.

(36) Through the present method, a visual area B of the radar meter 100 can be divided into a first area I, which is not considered for a measurement, and a second area II which is used for determining a flow velocity v of a medium 101.

(37) Through the limitation of the range relevant for the measurement of the flow velocity v to the second area II, a significantly improved measurement result can also be achieved in the case of a variety of disturbances.

(38) The procedure of the present application comprises the following steps: Sending a transmission signal 105 with a plurality of frequency ramps, Receiving a reception signal per frequency ramp of the transmission signal 105, Saving the reception signals, Performing a first spectral analysis of the reception signals, Performing a second spectral analysis of several output signals of the first spectral analysis in a specified distance range from the radar meter 100, Determining at least one phase change between the receiving signals in at least one distance d2 in the distance range, Determining a flow velocity v based on the phase change.

(39) FIG. 5 shows the transmission signal 105 of a method for fill level measurement according to the present application.

(40) The transmission signal 105 is divided in this exemplary embodiment during a measurement cycle T in a period between t=0 and t=T into several frequency ramps 501, 502, 503, 504, within which a frequency f of the radiated radar signal is respectively modulated linearly from a start frequency f1 towards a target frequency f2. These individual frequency ramps are also called chirps. In contrast to the previously used modulation forms from the prior art, a pre-defined number of individual frequency ramps 501-504 with defined time behavior and defined frequency behavior in the direction of medium 101 is radiated and received again during a measurement cycle T between t=0 and t=T.

(41) Defined time behavior is here understood as a pre-known and precisely implemented timing of start and stop times for each frequency ramp 501-504 and the breaks between frequency ramps 501-504. A defined frequency behavior refers to the exact compliance with start frequency f1 and stop frequency f2 and the slope of the respective frequency ramp.

(42) In FIG. 5, only four frequency ramps 501-504 are shown for better clarity. In an actual implementation of the present method, at least several dozen, preferably several hundred such frequency ramps 501-504 are emitted. The number of frequency ramps 501-504 is often a dual potency, in particular 128, 256, 512 or 1024. Higher or lower potencies can also be used depending on the respective application.

(43) FIGS. 6a and 6b show measurement curves, as they are received with the measuring method according to the present application, with good measurement conditions (FIG. 6a) and in rain (FIG. 6b). The amplitude A is shown in decibels of the received signals over the flow velocity v in meters per second.

(44) From a comparison of FIGS. 6a and 6b it is discernible that the measurement result is significantly less distorted by the disturbances, so that the determination of the flow velocity v is significantly more reliable.

(45) FIG. 7 shows a sequence of the method of the present application in a flow chart.

(46) In a first step, a transmission signal 105 is emitted with a plurality of frequency ramps 501-504. The transmission signal 105 is reflected on the surface of the medium 101 in the open channel 104 and, one receiving signal per frequency ramp 501-504 in the transmission signal 105 is reflected to the radar meter 100.

(47) The receiving signals are received and stored by the radar meter 100.

(48) The receiving signals are then subjected to a first spectral analysis, in the present case subjected to a fast Fourier transformation. From the signals obtained from this, a distance of a reflector on which the transmission signal was reflected to the radar meter 100 can be determined. This distance is the second distance d2 in the present application. From the second distance d2, in knowledge of the alignment of the radar meter to the surface of the medium, a vertical distance of the radar meter to the surface of the medium can be determined, i.e. the first distance d1. The first distance d1 can be converted into a level of medium 101 in the channel 104.

(49) Then a second spectral analysis of several output signals of the first spectral analysis is carried out in a specified distance range to the radar measuring device. The distance range can be specified or determined by a level measurement. Ideally, the distance range is selected in such a way that only one area of the surface is captured.

(50) From the results of the second spectral analysis, a change in the phase between the receiving signals is determined in at least one distance in the distance range. This change in the phase is proportional to a speed of the reflectors in the distance, so that the flow velocity v can be determined based on the change in the phase.

(51) Finally, the flow velocity v is displayed and/or processed further.

LIST OF REFERENCE NUMERALS

(52) 100 Radar meter 101 Medium 102 First transmission signal 103 Second transmission signal 104 Channel 105 Transmission signal 201 First radar sensor 202 Second radar sensor 501-504 Frequency ramp α First angle β Second angle I First area II Second area, distance range A Amplitude B Visual area d1 First distance d2 Second distance F Flow direction f Frequency f1 Start frequency f2 Stop frequency H1 First main emission direction H2 Second main emission direction t Time T Measurement period, period duration