Determining a level and flow speed of a medium

Abstract

A measurement device is provided for determining a distance of the measurement device from a medium and a flow speed of a medium by evaluating a transmission signal emitted by the fill level measurement device and reflected by the medium. The measurement device includes an antenna arrangement for emitting the transmission signal in two different directions. The flow speed of the medium can be determined using the Doppler shift of the transmission signal.

Claims

1. A fill level measurement device, comprising: a signal generator module generating a first transmission signal; an antenna arrangement including a first antenna and a second antenna, the antenna arrangement emitting the first transmission signal in a first direction perpendicular to a flow direction of a medium and a second direction, the second direction being different from the first direction; and a processor unit configured to determine a distance from the medium by evaluating a second transmission signal, the second transmission signal being generated when the first transmission signal is reflected by the medium and received by the antenna arrangement, and a non-transitory computer-readable medium on which a program element is stored which, when executed by the processor unit, causes the fill level measurement device to: determine whether the distance to the medium has changed by more than a predetermined threshold value over a predetermined period of time; and determine the flow speed of the medium when the distance to the medium has changed by more than the predetermined threshold value over the predetermined period of time.

2. The fill level measurement device according to claim 1, wherein the first antenna is configured to emit the first transmission signal in the first direction and the second antenna is configured to emit the first transmission signal in the second direction.

3. The fill level measurement device according to claim 2, wherein the first and second antennas are connected to the signal generator module via a directional coupler, a switch or a power splitter.

4. The fill level measurement device according to claim 1, wherein the signal generator module is a frequency-modulated continuous wave (FMCW) module and at least a first part of the first transmission signal is an FMCW signal.

5. The fill level measurement device according to claim 4, wherein the first transmission signal has a second part which is a continuous wave (CW) signal and wherein the fill level measurement device is configured to emit the first part of the first transmission signal only in the first direction and the second part of the first transmission signal only in the second direction.

6. The fill level measurement device according to claim 4, wherein the FMCW module is configured to generate a frequency-modulated transmission signal, which has a rising and a falling frequency ramp.

7. The fill level measurement device according to claim 1, wherein the processor unit is configured to determine the distance from the medium and the flow speed of the medium within a single measurement cycle.

8. The fill level measurement device according to claim 1, wherein the fill level measurement device is a fill level radar.

9. The fill level measurement device according to claim 1, wherein the fill level measurement device is a 2-wire line sensor.

10. The fill level measurement device according to claim 1, wherein the processor is configured to determine the flow direction of the medium.

11. The fill level measurement device according to claim 1, wherein the antenna arrangement includes a planar antenna array.

12. A non-transitory computer-readable medium on which a program element is stored which, when executed on a processor unit of a fill level measurement device, causes the fill level measurement device to carry out the steps of: generating a transmission signal; emitting the transmission signal in a first direction perpendicular to the flow direction of the medium and in a second direction different from the first direction; determining whether the distance to the medium has changed by more than a predetermined threshold value over a predetermined period of time; and when the distance to the medium has changed by more than the predetermined threshold value over the predetermined period of time, determining the flow speed of the medium, wherein the distance from the medium and the flow speed of the medium are determined by evaluating the transmission signal reflected by the medium and received by an antenna arrangement of the fill level measurement device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a measurement device in accordance with an embodiment of the invention.

(2) FIG. 2 shows a measurement device in accordance with a further embodiment of the invention.

(3) FIG. 3 shows a measurement signal and a received signal in accordance with an embodiment of the invention.

(4) FIG. 4 shows FFT-transformed signals at the receiver output of ramp 1 and ramp 2.

(5) FIG. 5 shows a measurement device in accordance with an embodiment of the invention.

(6) FIG. 6 shows a further FFT-transformed signal at the receiver output of the measurement device.

(7) FIG. 7 shows a further FFT-transformed signal at the receiver output of a measurement device.

(8) FIG. 8 is a flow chart of a method in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) The drawings are schematic and not to scale.

(10) FIG. 1 shows a measurement device 100 in accordance with an embodiment of the invention. The measurement device is a distance measurement device, for example in the form of a fill level radar.

(11) The measurement of the flow speed of the medium, which is a fluid, and of the distance from the sensor 100 are combined in a single measurement system, for example an FMCW radar system. The measurement device comprises either two antennas (cf. FIG. 2) or a single antenna, the radiation characteristic of which is adapted in such a way that a first part of the transmission signal (in other words one beam of the transmission signal) can be used for distance measurement and a second part (second beam of the transmission signal) can be used for flow speed measurement (cf. FIG. 1).

(12) If two antennas are used, the distance or the flow speed of the medium can be measured alternately by means of a switch.

(13) If the two antennas are connected to the transmission signal generator module (for example an HF module) together via a directional coupler or a power splitter, the two measurements can be taken simultaneously, since the transmission signal is actually emitted in both directions simultaneously.

(14) This results in a simple installation for measuring the distance from a surface of the medium and for simultaneously measuring the flow speed and optionally also the flow direction of the medium. The flow throughput can also be determined using a measurement device of this type if the geometry of the flow bed of the liquid is known.

(15) The measurement device 100 comprises a processor unit 105, which is connected to the HF module 101 (transmission signal generator unit). The HF module is connected to a planar antenna 102 via the signal line 110. The planar antenna 102 is located in a housing 111 and it may be provided that the antenna can be rotated counter to the HF module.

(16) The antenna 102 emits a transmission signal 112, 113, a relatively large portion of the transmission signal being directed in a direction 104 oblique to the flow speed 107 of the fluid 106. At least part of this obliquely emitted signal portion is reflected by the surface of the flowing fluid and returned to the antenna 102 in the direction 108. The antenna 102 subsequently receives this reflected signal portion of the transmission signal.

(17) It is advantageous for measuring the flow speed if the surface of the fluid 106 has a wave formation or rippling.

(18) At the same time, a second, for example smaller signal portion 113 is emitted perpendicular to the flow speed 107 of the fluid 106 in the direction 103, reflected on the surface of the fluid and radiated back to the antenna in the opposite direction 109. The antenna 102 subsequently receives this signal portion of the reflected transmission signal.

(19) Subsequently, from the received, reflected transmission signal portions, an echo curve is generated from which the distance d.sub.1, which is the shortest distance between the sensor 100 and the fluid 106, and the distance d.sub.2, which is the path length covered by the obliquely emitted transmission signal in the direction 104 before it is reflected on the fluid surface, are generated.

(20) The distance d.sub.1 is calculated by evaluating the signal portion of the transmission signal reflected perpendicular to the surface of the fluid, and the flow speed is determined by a Doppler evaluation of the signal portion emitted obliquely with respect to the flow direction 107.

(21) The primary radiation direction of the antenna can be used for measuring the flow speed, whilst the distance is detected using the secondary lobe.

(22) It may also be provided that the antenna comprises two foci for the radiation, in other words two primary radiation directions. This can be achieved for example using a patch array which radiates in two defined directions, as shown in FIG. 1. The directivity for the distance measurement may turn out smaller in this case, since better reflection properties are to be expected (as a result of the orientation of the radiation direction 103 perpendicular to the surface of the medium).

(23) The evaluation may take place in a measurement cycle. The first echo (which corresponds to the shortest distance between the sensor and the fluid surface) gives the distance; from the echo further away, the speed and the flow direction can be determined.

(24) FIG. 2 shows a measurement device in accordance with a further embodiment of the invention. By contrast with the embodiment of FIG. 1, two antennas 201, 202 are provided, and are each connected via their own signal line to a directional coupler, a power splitter or a switch 203 which connects the two antennas to the HF module 101.

(25) An FMCW module for both measurements (distance and flow speed) is thus provided, and is coupled to a respective antenna for the distance measurement and another antenna for the flow speed via a switch, a power splitter or a directional coupler. One of the two antennas in each case can be selected for measurement using the switch.

(26) In this way, alternating measurements of distance and flow speed are possible. Switching between the two measurement methods takes place on the HF signal path between the antennas and the HF module.

(27) The HF module may also, as described above, be connected to the two antennas via a directional coupler or power splitter 203, as is shown schematically in FIG. 2 in any case. In this case, an optimised antenna is used for each of the two measurements. The antenna 201 emits the transmission signal perpendicular to the flow direction 107, and this is represented by the transmission lobe 204. The second antenna 202, which is arranged obliquely with respect to the first antenna 201, emits the transmission signal in the oblique direction 104, and this is represented by the transmission lobe 205.

(28) By using two separate antennas, larger amplitudes of the two received signals can be achieved. The evaluation takes place as in the other embodiments.

(29) To determine the distance and the flow speed or flow direction, it may be provided that two frequency ramps are passed through in accordance with generally known FMCW radar methods. The horizontal axis 301 denotes the time t and the vertical axis 302 denotes the frequency f.

(30) The first ramp is for example increasing in frequency, starting at the frequency f1 and ending at the frequency 12. Subsequently, the falling second ramp starts at t2 and ends at the frequency f1 (cf. FIG. 3). The first ramp is denoted by reference numeral 303 and the second ramp by reference numeral 304.

(31) The curve 305, 306, which is displaced to the right, reproduces the received signal received by the antenna arrangement (transmission signal reflected by the filling material surface).

(32) The transmission signal reflected by the filling material surface is sampled using an analogue-digital converter and transformed into the frequency range in a microprocessor using a fast Fourier transform (FFT).

(33) This results in two spectra, which are shown in FIG. 4.

(34) In this context, the horizontal axis 401 denotes the distance d between the sensor and the corresponding reflector, and the vertical axis 402 denotes the amplitude of the received signal.

(35) The first echo 407 at the location d.sub.1 (shortest distance) specifies the distance d1 from the medium; from the echoes further away in the vicinity of the location 406, the speed of the medium and the flow direction thereof can be detected.

(36) The reflection from the distance measurement gives the same difference frequency between the transmitted and received signals for both ramps.

(37) The reflection from the obliquely incident signal, which was emitted in direction 104 (cf. FIGS. 1 and 2), is used to determine the flow speed and is shifted in frequency by f.sub.Doppler as a result of the Doppler effect. This results in different difference frequencies in the rising and falling ramps. These differ by 2f.sub.Doppler, as can be seen at the peaks 403, 404. One peak 403, which is shifted to the left with respect to the actual distance d.sub.2, results from the received signal of the rising frequency ramp 303 (cf. FIG. 3), and the peak signal 404 shifted to the right results from the received signal of the falling frequency ramp 306.

(38) The arrow 405 represents the frequency difference f between the two peaks, which is twice the Doppler shift.

(39) The rising and falling flanks of the triangular modulation have a different Doppler shift direction. Signal processing takes place for example only after a brief pause after the inflection points of the transmitted frequency modulation. This is what is known as triangular modulation. The use of a triangular modulation shape provides the possibility of detecting the Doppler frequency as a measure of a radial speed as an independent measurement value aside from the distance measurement. The receiving frequency increases during approach and thus decreases the value of the difference frequency during the rising frequency ramp. As a result of the superposition with the Doppler frequency, the frequency difference when measuring an approach in the rising flank of the triangular modulation is smaller. In the falling flank it is larger by the same amount than for a stationary reflector. If the gradient of the frequency change is equal in size in the rising and falling flanks of the triangular signal, the average of the difference frequencies from the two measurement periods is a measure of distance, independent of the speed. The sum of the difference frequencies is a measure of the half radial speed of the object. In general, there are high requirements on the linearity of the frequency change.

(40) The expected distance for detecting the speed may additionally be calculated from the known angle between the two antenna radiation directions 103, 104 and the distance from the medium. As a result, in the event of ambiguous echo relationships a measurement window 603 can be produced and a higher measurement reliability can thus be achieved (cf. FIGS. 5 and 6).

(41) In FIG. 6, as previously in FIG. 4, the distance d 601 is plotted against the amplitude 602 of the received signal (reflected transmission signal) after it has undergone a Fourier transform. In this case too, the main peak 604, which corresponds to the distance between the sensor and the medium surface, and the two peaks 605, 606, which originate from the obliquely emitted transmission signal, can be seen. These two peaks are inside the measurement window 603.

(42) However, the flow speed of the medium may also be determined in another way. In particular if only one antenna having a primary radiation direction is used, the flow speed can also be measured directly in the reflected signal. In this context, only the echo can be taken into account at the distance d from the surface of the medium.

(43) Since an antenna also always emits and receives portions outside the primary radiation direction, and the sensor thus also measures obliquely with respect to the surface of the medium, signals which are affected by the Doppler frequency due to the movement of the medium are also always present at a receiver of the FMCW radar module.

(44) As a result, the IF signal (intermediate-frequency signal) transformed by FFT has a widening dependent on the flow speed, as is indicated by the peaks 703 and 704 of FIG. 7. As in FIGS. 4 and 6, the horizontal axis 701 denotes the distance and the vertical axis 702 denotes the amplitude. The narrower peak 703 corresponds to a lower flow speed of the medium and the wider peak 704 corresponds to a higher flow speed of the medium.

(45) The flow speed can be determined from this widening. A small widening means a low speed and a large widening means a high speed.

(46) The measurement device may have a corresponding calibration, in such a way that the flow speed can be determined sufficiently precisely by measuring the widening.

(47) If two antennas are used, as is shown in FIG. 2, the flow speed and optionally also the flow direction can be determined using the antenna 204 by the aforementioned method. In a second measurement sequence, likewise using the FMCW method, the fill level can be determined using the antenna 203.

(48) The two values can subsequently be outputted or used to calculate the flow throughput.

(49) FIG. 8 is a flow chart of a method in accordance with an embodiment of the invention. In step 801, a transmission signal is generated by a signal generator module. In step 802, the generated transmission signal is emitted in a first direction, for example perpendicular to the flow direction of the medium, and in a second direction different from the first direction by an antenna arrangement. In step 803, the reflected transmission signal is received by the antenna arrangement, and in step 804, the distance from the medium and the flow speed of the medium are determined by evaluating the transmission signal reflected by the medium and received by the antenna arrangement.

(50) For the sake of completeness, it should be noted that comprising and having do not exclude the possibility of other elements or steps, and an or a does not exclude the possibility of a plurality. It should further be noted that features or steps which have been described with reference to one of the above embodiments may also be used in combination with other features or steps of other above-described embodiments. Reference numerals in the claims should not be treated as limiting.