Signal travel time flow meter

Abstract

A method for determining a flow speed of a liquid in a fluid conduit is provided. During a signal-generating phase, an impulse signal is applied to a first ultrasonic transducer. A response signal is then received at a second ultrasonic transducer. A measuring signal is later derived from the response signal, wherein the derivation comprises reversing a signal portion with respect to time. During a measurement phase, a liquid moves with respect to the fluid conduit. The measuring signal is then applied to one of the two transducers and a response signal of the measuring signal is measured at the other transducer. A flow speed is derived from the response signal of the measuring signal.

Claims

1. A method for determining a flow speed of a fluid in a fluid conduit with a travel time ultrasonic flow meter, the method comprising: applying an impulse signal to a first ultrasonic clamp-on transducer, the first ultrasonic clamp-on transducer being mounted to the fluid conduit at a first location, receiving a response signal of the impulse signal at a second ultrasonic clamp-on transducer, the second ultrasonic clamp-on transducer being located at the fluid conduit at a second location provided upstream or downstream of the first ultrasonic clamp-on transducer, the second location being offset along a longitudinal direction of the fluid conduit with respect to the first location, applying a pre-determined measuring signal to one of the first and the second ultrasonic clamp-on transducers, the measuring signal comprising a reversed signal portion with respect to time of a response signal of the impulse signal or of a signal derived therefrom, measuring a first response signal of the measuring signal at the other one of the first and the second ultrasonic clamp-on transducer, and deriving a flow speed of the fluid from the first response signal.

2. The method according to claim 1, comprising: repeating the steps of applying the measuring signal and measuring the response signal in the reverse direction to obtain a second response signal, deriving a flow speed of the fluid from the first response signal and the second response signal.

3. The method according to claim 1, wherein the signal portion that is used to derive the measuring signal comprises a first portion around a maximum amplitude of the response signal and a trailing signal portion, the trailing signal portion extending in time behind the arrival time of the maximum amplitude.

4. The method according to claim 1, comprising: repeating the steps of applying an impulse signal and receiving a corresponding response signal multiple times, thereby obtaining a plurality of response signals, deriving the measuring signal from an average of the received response signals.

5. The method according to claim 1, wherein the derivation of measuring signal comprises digitizing the response signal or a signal derived therefrom with respect to amplitude.

6. The method according to claim 5, comprising increasing the bit-resolution of the digitized signal for increasing an amplitude of a response signal to the measuring signal.

7. The method according to claim 5, comprising decreasing the bit-resolution of the digitized signal for increasing an amplitude of a response signal to the measuring signal.

8. The method according to claim 1, comprising processing of at least one of the response signals for determining a change in the wall thickness of the conduit or for determining material characteristics of the conduit walls by determining longitudinal and transversal sound wave characteristics.

9. A computer readable program code comprising computer readable instructions for executing the method according to claim 1.

10. A computer readable memory, the computer readable memory comprising the computer readable program code of claim 9.

11. An application specific electronic component, which is operable to execute the method according to claim 1.

12. A device for measuring a flow speed in a travel time ultrasonic flow meter, comprising: a first connector for a first ultrasonic clamp-on transducer, the first ultrasonic clamp-on transducer being located at a fluid conduit at a first location, a second connector for a second ultrasonic clamp-on transducer, the second ultrasonic clamp-on transducer being located at a fluid conduit at a second location provided upstream or downstream of the first ultrasonic clamp-on transducer, and the second location being offset along a longitudinal direction of the fluid conduit with respect to the first location, a transmitting unit, the transmitting unit being operative to send an impulse signal to the first connector, a receiving unit for receiving a response signal to the impulse signal from the second connector, an inverting unit for inverting the response signal or a portion thereof with respect to time to obtain an inverted signal, one or more processing unit for deriving a measuring signal from the inverted signal and storing the measuring signal, a measuring signal generator for generating a measuring signal from the stored measuring signal, the measuring signal generator being connectable to the first connector or to the second connector, wherein the transmitting unit is further operative to send the measuring signal to one of the first and the second connector, wherein the receiving unit is further operative to receive a response signal of the measuring signal from the other one of the first and the second connector, and wherein the one or more processing unit is further operative to derive a flow speed from the response signal of the measuring signal.

13. The device of claim 12, further comprising: a D/A converter, the D/A converter being connected to the first connector, an A/D converter, the A/D converter being connected to the second connector, a computer readable memory for storing the measuring signal.

14. The device according to claim 12, the device comprising: a direct digital signal synthesizer, the direct digital signal synthesizer comprising the ADC, a frequency control register, a reference oscillator, a numerically controlled oscillator and a reconstruction low pass filter, the ADC being connectable to the first and the second connector over the reconstruction low pass filter.

15. The device according to claim 12, the device comprising: a first ultrasonic transducer, the first ultrasonic transducer being connected to the first connector, a second ultrasonic transducer, the second ultrasonic transducer being connected to the second connector.

16. A method for determining a flow speed of a fluid in a fluid conduit with a travel time ultrasonic flow meter, the method comprising: applying an impulse signal to a first ultrasonic wet transducer, the first ultrasonic wet transducer being mounted to the fluid conduit at a first location, receiving a response signal of the impulse signal at a second ultrasonic wet transducer, the second ultrasonic wet transducer being located at the fluid conduit at a second location provided upstream or downstream of the first ultrasonic wet transducer, the second location being offset along a longitudinal direction of the fluid conduit with respect to the first location, applying a pre-determined measuring signal to one of the first and the second ultrasonic wet transducers, the measuring signal comprising a reversed signal portion with respect to time of a response signal of the impulse signal or of a signal derived therefrom and, measuring a first response signal of the measuring signal at the other one of the first and the second ultrasonic wet transducer, deriving a flow speed of the fluid from the first response signal.

17. A computer readable program code comprising computer readable instructions for executing the method according to claim 16.

18. A computer readable memory, the computer readable memory comprising the computer readable program code of claim 17.

19. An application specific electronic component, which is operable to execute the method according to claim 16.

20. A device for measuring a flow speed in a travel time ultrasonic flow meter, comprising a first connector for a first ultrasonic wet transducer, the first ultrasonic wet transducer being located at a fluid conduit at a first location, a second connector for a second ultrasonic wet transducer, the second ultrasonic wet transducer being located at the fluid conduit at a second location provided upstream or downstream of the first ultrasonic wet transducer, and the second location being offset along a longitudinal direction of the fluid conduit with respect to the first location, a transmitting unit for sending an impulse signal to the first connector, a receiving unit for receiving a response signal to the impulse signal from the second connector, an inverting unit for inverting the response signal or a portion thereof with respect to time to obtain an inverted signal, one or more processing unit for deriving a measuring signal from the inverted signal and storing the measuring signal, a measuring signal generator for generating a measuring signal from the stored measuring signal, the measuring signal generator being connectable to the first connector or to the second connector, wherein the transmitting unit is further operative to send the measuring signal to one of the first and the second connector, wherein the receiving unit is further operative to receive the measuring signal from the other one of the first and the second connector, and wherein the one or more processing unit is further operative to derive a flow speed from the response signal of the measuring signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject matter of the present specification is now explained in further detail with respect to the following Figures, wherein:

(2) FIG. 1 shows a first flow meter arrangement with two piezoelectric elements.

(3) FIG. 2 shows the flow meter arrangement of FIG. 1 with one direct signal.

(4) FIG. 3 shows the flow meter arrangement of FIG. 2 in the viewing direction A-A.

(5) FIG. 4 shows a second flow meter arrangement with four piezoelectric elements and four direct signals.

(6) FIG. 5 shows the flow meter arrangement of FIG. 4 in the viewing direction B-B.

(7) FIG. 6 shows a schematic diagram of a test signal.

(8) FIG. 7 shows a schematic diagram of a test signal response.

(9) FIG. 8 shows a schematic diagram of an inverted signal.

(10) FIG. 9 shows a schematic diagram of a response from the inverted signal.

(11) FIG. 10 shows a first inverted signal in high resolution.

(12) FIG. 11 shows a response of the inverted signal of FIG. 10.

(13) FIG. 12 shows a further inverted signal in high resolution.

(14) FIG. 13 shows a response of the inverted signal of FIG. 12.

(15) FIG. 14 shows a further inverted signal in high resolution.

(16) FIG. 15 shows a response of the inverted signal of FIG. 14.

(17) FIG. 16 shows a further inverted signal in high resolution.

(18) FIG. 17 shows a response of the inverted signal of FIG. 16.

(19) FIG. 18 shows a further inverted signal in high resolution.

(20) FIG. 19 shows a response of the inverted signal of FIG. 18.

(21) FIG. 20 shows a further inverted signal in high resolution.

(22) FIG. 21 shows a response of the inverted signal of FIG. 20.

(23) FIG. 22 shows a further inverted signal in high resolution.

(24) FIG. 23 shows a response of the inverted signal of FIG. 22.

(25) FIG. 24 shows a further inverted signal in high resolution.

(26) FIG. 25 shows a response of the inverted signal of FIG. 24.

(27) FIG. 26 shows a further inverted signal in high resolution.

(28) FIG. 27 shows a response of the inverted signal of FIG. 26.

(29) FIG. 28 shows a further inverted signal in 12-bit resolution.

(30) FIG. 29 shows a response of the signal of FIG. 28.

(31) FIG. 30 shows a further inverted signal in 3-bit resolution.

(32) FIG. 31 shows a response of the signal of FIG. 30.

(33) FIG. 32 shows a further inverted signal in 2-bit resolution.

(34) FIG. 33 shows a response of the signal of FIG. 32.

(35) FIG. 34 shows a further inverted signal in 1-bit resolution.

(36) FIG. 35 shows a response of the signal of FIG. 34.

(37) FIG. 36 shows a short impulse at a piezoelectric element of the flow meter of FIG. 1.

(38) FIG. 37 shows a signal of a piezoelectric element of the flow meter of FIG. 1, which is derived from the inverted response of the signal of FIG. 36.

(39) FIG. 38 shows a response of the signal of FIG. 37.

(40) FIG. 39 shows an upstream and a downstream cross correlation function.

(41) FIG. 40 shows a sectional enlargement of FIG. 39.

(42) FIG. 41 shows a schematic diagram of a device for measuring a flow speed according to the present specification.

(43) FIG. 42 shows a schematic diagram of a direct digital synthesizer for use in the device of FIG. 41.

(44) FIG. 43 shows a first multi-transducer arrangement. and

(45) FIG. 44 shows a second multi-transducer arrangement.

(46) FIG. 45 shows a Z-configuration of clamp-on transducers.

(47) FIG. 46 shows a V-configuration of clamp-on transducers.

(48) FIG. 47 shows a W-configuration of clamp-on transducers.

(49) FIG. 48 shows a one-cycle sending signal.

(50) FIG. 49 shows a ten cycle sending signal.

(51) FIG. 50 shows a TRA sending signal.

(52) FIG. 51 shows a response signal to the one-cycle sending signal of FIG. 48.

(53) FIG. 52 shows a response signal to the ten cycle sending signal of FIG. 49.

(54) FIG. 53 shows a response signal to the TRA sending signal of FIG. 50.

(55) FIG. 54 shows a pressure curve of a TRA sending signal and a response signal to the TRA sending signal.

(56) FIG. 55 shows a pressure curve of a TRA sending signal and a response signal to the TRA sending signal.

(57) FIG. 56 shows an impulse signal that is used to generate the signal input of FIG. 55.

(58) FIG. 57 shows a first response signal indicating channel properties.

(59) FIG. 58 shows a second response signal indicating channel properties.

(60) FIG. 59 shows a further response signal.

(61) FIG. 60 shows a further response signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(62) In the following description, details are provided to describe the embodiments of the present specification. It shall be apparent to one skilled in the art, however, that the embodiments may be practised without such details.

(63) FIG. 1 shows a first flow meter arrangement 10. In the flow meter arrangement, a first piezoelectric element 11 is placed at an outer wall of a pipe 12, which is also referred as a tube 12. A second piezoelectric element 13 is placed at an opposite side of the pipe 12 such that a direct line between the second piezoeloelectric element 11 and the downstream piezoelectric element 13 is oriented at an angle to the direction 14 of average flow, which is at the same time also the direction of the pipe's 12 symmetry axis. The angle is chosen to be approximately 45 degrees in the example of FIG. 1 but it may also be steeper, such as for example 60 degrees, or shallower, such as for example 30 degrees.

(64) A piezoelectric element, such as the piezoelectric elements 11, 13 of FIG. 1 may in general be operated as an acoustic transmitter and as an acoustic sensor. An acoustic transmitter and an acoustic sensor may be provided by the same piezoelectric element or by different regions of the same piezoelectric element. In this case, a piezoelectric element or transducer is also referred to as piezoelectric transmitter when it is operated as transmitter or sound source and it is also referred to as acoustic sensor or receiver when it is operated as acoustic sensor.

(65) When a flow direction is as shown in FIG. 1, the first piezoelectric element 11 is also referred to as upstream piezoelectric element and the second piezoelectric element 13 is also referred to as downstream piezoelectric element. A flow meter according to the present specification works for both directions of flow in essentially the same way and the flow direction of FIG. 1 is only provided by way of example.

(66) FIG. 1 shows a flow of electric signals of FIG. 1 for a configuration in which the upstream piezoelectric element 11 is operated as a piezoelectric transducer and the downstream piezoelectric element 13 is operated as an acoustic sensor. For the purpose of clarity, the application works upstream and downstream, i.e. the position of the piezoelectric elements can be interchanged.

(67) A first computation unit 15 is connected to the upstream piezoelectric element 11 and a second computation unit 16 is connected to the downstream piezoelectric element 13. The first computation unit 15 comprises a first digital signal processor, a first digital analog converter (DAC) and a first analog digital converter (ADC). Likewise, the second computation unit 16 comprises a second digital signal processor, a second digital analog converter (DAC) and a second analog digital converter (ADC). The first computation unit 15 is connected to the second computation unit 16.

(68) The arrangement with two computation units 15, 16 shown in FIG. 1 is only provided by way of example. Other embodiments may have different numbers and arrangements of computation units. For example, there may be only one central computation unit or there may be two AD/DC converters and one central computation unit, or there may be two small-scale computation units at the transducers and one larger central computation unit.

(69) A computation unit or computation units can be provided by microcontrollers or application specific integrated circuits (ASICs), ACIDs or field programmable gate arrays (FPGAs), for example. Specifically, the synthesis of an electrical signal from a stored digital signal may be provided by a direct digital synthesizer (DDS), which comprises a digital to analog converter (DA, DAC).

(70) A method for generating a measuring signal according to the present specification comprises the following steps.

(71) A pre-determined digital test signal is generated by synthesizing an acoustic signal with the digital signal processor of the first computation unit 15. The digital test signal is sent from the first computation unit 15 to the piezoelectric transducer 11 along signal path 17. The piezoelectric transducer 11 generates a corresponding ultrasound test signal. Units 15 and 16 can also be provided in one single unit.

(72) The test signal is provided as a short pulse, for example by a single 1 MHz oscillation or by 10 such oscillations. In particular, the test signal may be provided by a small number of oscillations with constant amplitude, thereby approximating a rectangular signal. The oscillation or the oscillations may have a sinusoidal shape, a triangular shape, a rectangular shape or also other shapes.

(73) The ultrasound test signal travels through the liquid in the pipe 12 to the piezoelectric sensor 13. In FIG. 1, a direct signal path of the ultrasound signal is indicated by an arrow 18. Likewise, a direct signal path of the ultrasound signal in the reverse direction is indicated by an arrow 19. A response signal is picked up by the piezoelectric sensor 13, sent to the second computation unit 16 along signal path 20, and digitized by the second computation unit 16.

(74) In a further step, a digital measuring signal is derived from the digitized response signal. The derivation of the measurement a reversal of the digitized response signal with respect to time. According to further embodiments, the derivation comprises further steps such as a conversion to a reduced resolution in the amplitude range, a bandwidth filtering of the signal to remove noise, such as low frequency noise and high frequency noise. In particular, the step of bandwidth filtering may be executed before the step of reversing the signal with respect to time.

(75) The signal reversal may be carried out in various ways, for example by reading out a memory area in reverse direction or by reversing the sign of sinus components in a Fourier representation.

(76) In one embodiment, a suitable portion of the digitized response signal is selected that contains the response from the direct signal. The portion of the response signal is then turned around, or inverted, with respect to time. In other words, signal portions of the response signal that are received later are sent out earlier in the inverted measuring signal. If a signal is represented by a time ordered sequence of amplitude samples, by way of example, the abovementioned signal inversion amounts to inverting or reversing the order of the amplitude samples.

(77) The resulting signal, in which the direction, or the sign, of time has been inverted, is also referred to as an inverted signal. The expression inverted in this context refers to an inversion with respect to the direction of time, and not to an inversion with respect to a value, such as the amplitude value.

(78) FIGS. 10 to 19 show, by way of example digital signals according to the present specification.

(79) In a flow meter according to one embodiment of the present specification, the same measuring signal is used for both directions 18, 19, the downstream and the upstream direction, providing a simple and efficient arrangement. According to other embodiments, different measuring signals are used for both directions. In particular, the measuring signal may be applied to the original receiver of the test signal. Such arrangements may provide benefits for asymmetric conditions and pipe shapes.

(80) A method of measuring a flow speed of a liquid through a pipe, which uses the abovementioned inverted signal as a measuring signal, comprises the following steps.

(81) The abovementioned measuring signal is sent from the first computation unit 15 to the piezoelectric transducer 11 along signal path 17. The piezoelectric transducer 11 generates a corresponding ultrasound measuring signal. Examples for such a measuring signal are provided in FIGS. 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 37 and 38.

(82) The ultrasound measuring signal travels through the liquid in the pipe 12 to the piezoelectric sensor 13. A response signal is picked up by the piezoelectric sensor 13, sent to the second computation unit 16 along signal path 20, and digitized by the second computation unit 16.

(83) The second computation unit 16 sends the digitized response signal to the first computation unit 15. The first computation unit 15 determines a time of flight of the received signal, for example by using one of the methods described further below.

(84) A similar process is carried out for a signal travelling in the reverse direction 19, namely the abovementioned measuring signal is applied to the downstream piezoelectric element 13 and a response signal is measured by the upstream piezoelectric element 11 to obtain an upstream time of flight TOF_up in the reverse direction 19. The first computation unit 15 determines a velocity of flow, for example according to the formula

(85) $v=\frac{c^2}{2.Math.L.Math.\cos }.Math.\left({\mathrm{TOF}}_{\mathrm{up}}-{\mathrm{TOF}}_{\mathrm{down}}\right),$

(86) wherein L is the length of the direct path between the piezoelectric elements 11, 13, is the angle of inclination of the direct path between the piezoelectric elements 11, 13 and the direction of the average flow, and c is the velocity of sound in the liquid under the given pressure and temperature conditions.

(87) The squared velocity of sound c{circumflex over ()}2 can be approximated to second order by the expression

(88) $c^2\frac{L^2}{{\mathrm{TOF}}_{\mathrm{up}}*{\mathrm{TOF}}_{\mathrm{down}}}$
which leads to the formula

(89) $v=\frac{L}{2*\cos }.Math.\frac{{\mathrm{TOF}}_{\mathrm{up}}-{\mathrm{TOF}}_{\mathrm{down}}}{{\mathrm{TOF}}_{\mathrm{up}}*{\mathrm{TOF}}_{\mathrm{down}}}$

(90) Thereby, it is not necessary to determine temperature or pressure, which in turn determine the fluid density and the sound velocity, or to measure the sound velocity or the fluid density directly. By contrast, the first order of the error does not cancel out for only one measurement direction.

(91) Instead of using a factor 2.Math.L.Math.cos , a proportionality constant can be derived from a calibration measurement with a known flow speed. The proportionality constant of the calibration takes into account further effects such as flow profiles and contributions from sound waves that were scattered and did not travel along a straight line.

(92) According to a further embodiment, the process of generating an impulse signal, recording a response signal and deriving an inverted measuring signal from the response signal is simulated in a computer. Relevant parameters, such as the pipe diameter of the pipe 12 and the sensor placements are provided as input parameters to the simulation.

(93) According to yet another embodiment, the measuring signal, which is to be supplied to a transmitting piezoelectric element, is synthesized using a shape of a typical response signal to an impulse signal, such as the signal shapes shown in FIGS. 37 and 38. For example, the measuring signal may be provided by a 1 MHz sinusoidal oscillation, which is amplitude modulated with an envelope according to a Gaussian probability function having a half width of 10 microseconds. The half-width may be chosen as an input parameter, which depends on the actual arrangement, such as the pipe diameter and the sensor placement.

(94) A flow meter according to the present specification may also be provided as a pre-defined flow meter in which the measuring signal is generated during a test run at a factory site, in particular when the flow meter is supplied together with a pipe section.

(95) According to a simple embodiment of the present specification, a time of flight in upstream and in downstream direction is determined by evaluating a time of a peak amplitude of a received signal with respect to a sending time of the measuring signal. To achieve a higher precision, the maximum may be determined using an envelope of the received signal. According to a further embodiment, the measurement is repeated multiple times and an average time of flight is used.

(96) According to a further embodiment of the present specification, the time of flight of a signal is evaluated using a cross-correlation technique. In particular, the respective time shifts can be evaluated by cross-correlating the received downstream or upstream signal with the received signal at zero flow speed according to the formula:

(97) $\mathrm{CCorr}\left(\right)=\underset{t=-}{\overset{}{.Math.}}{\mathrm{Sjg}}_{\mathrm{Flow}}\left(t\right).Math.{\mathrm{Sig}}_{\mathrm{NoFlow}}\left(t+\right),$

(98) wherein Sig_Flow represents an upstream or downstream signal under measurement conditions, when there is a fluid flow through the pipe, and wherein Sig_NoFlow represents a signal under calibration conditions at zero flow. The infinite sum limits represent a sufficiently large time window [T1, +T2]. In more general words, T1 and +T2 do not need to be same and for practical reasons this can be advantageous for the flow meter.

(99) The time shift TOF_up-TOF_down is then obtained by comparing the time of the maximum of the upstream correlation function with the time of the maximum of the downstream correlation function. The envelope of the correlation function may be used to determine the location of the maximum more accurately.

(100) In a further embodiment, a separate evaluation unit is provided between the first computation unit 15 and the second computation unit 16, which performs the calculation of the signal arrival times and the flow speed.

(101) In general, the measured signal of the acoustic sensor results from a superposition of scattered signals and a direct signal. The scattered signals are scattered from the walls of the pipe once or multiple times. This is shown, by way of example, in FIGS. 2 and 3.

(102) The transducer configuration of FIG. 1 is a direct-line or Z configuration. Other arrangements, which make use of reflections on an opposite side of the pipe, are possible as well, such as the V and the W configuration. V and W configuration work based on reflections on the pipe wall which induce more scatterings than the Z configuration. The subject matter of the application will benefit from these configurations as long as the paths are understood properly.

(103) In a V-configuration, the two transducers are mounted on the same side of the pipe. For recording a 45 degree reflection they are placed about a pipe diameter apart in the direction of the flow. The W-configuration makes use of three reflections. Similar to the V-configuration, the two transducers are mounted on the same side of the pipe. For recording a signal after two 45 degree reflections they are placed two pipe diameters apart in the direction of the flow.

(104) FIG. 2 shows, by way of example a first acoustic signal which travels directly from the piezoelectric element 11 to the piezoelectric element 13,

(105) For simplicity, the scattering events are shown as reflections in FIGS. 2 to 5 but the actual scattering process can be more complicated. In particular, the most relevant scattering occurs typically on the pipe wall or at material that is mounted in front of the piezoelectric transducers. The received scattering also depends on the sensor arrangement. By way of example, FIGS. 45, 46, and 47 show Z, V, and W sensor arrangements. FIG. 3 shows a view of FIG. 2 in flow direction in the viewing direction A-A.

(106) FIGS. 4 and 5 show a second sensor arrangement in which a further piezoelectric element 22 is positioned at a 45 degree angle to the piezoelectric element 11 and a further piezoelectric element 23 is positioned at a 45 degree angle to the piezoelectric element 13.

(107) Furthermore, FIGS. 4 and 5 show direct, or straight line, acoustic signal paths for a situation in which the piezoelectric elements 11, 22 are operated as piezo transducers and the piezoelectric elements 13, 23 are operated as acoustic sensors. Piezoelectric element 23, which is on the back of the pipe 12 in the view of FIG. 4 is shown by a dashed line in FIG. 4.

(108) FIGS. 6 to 9 show, in a simplified way, a method of generating a measuring signal from a response of a test signal. In FIGS. 6 to 9, losses due to scattering are indicated by hatched portions of a signal and by arrows.

(109) For the considerations of FIGS. 6 to 9 it is assumed that the acoustic signal only propagates along a straight line path, along a first scattering channel with a time delay of t, and along a second scattering channel with a time delay of 2t. Signal attenuation along the paths is not considered.

(110) A test signal in the form of a rectangular spike is applied to the piezoelectric element 11. Due to scattering, a first portion of the signal amplitude is lost due to the first scattering path and appears after a time t, and a second portion of the signal amplitude is lost due to the second scattering path and appears after a time 2t. This yields a signal according to the white columns in FIG. 7, which is recorded at the piezoelectric element 13.

(111) A signal processor inverts this recorded signal with respect to time and it applies the inverted signal to the piezoelectric element 11. The same scattering process as explained before now applies to all three signal components. As a result, a signal according to FIG. 9 is recorded at the piezoelectric element 13, which is approximately symmetric.

(112) In reality, the received signals will be distributed over time and there often is a surface wave which has travelled through material of the pipe and arrives before the direct signal. This surface wave is discarded by choosing a suitable time window for generating the inverted measuring signal. Likewise, signals that stem from multiple reflections and arrive late can be discarded by limiting the time window and/or by choosing specific parts of the signal.

(113) The following table shows measured time delays for a direct alignment, or, in other words, for a straight line connection between clamped-on piezoelectric elements on a DN 250 pipe in a plane perpendicular to the longitudinal extension of the DN 250 pipe. The flow rate refers to a flow of water through the DN 250 pipe.

(114) Herein TOF 1 cycle refers to an impulse such as the one shown in FIG. 36, that is generated by a piezoelectric element, which is excited by an electric signal with 1 oscillation having a 1 s period. TOF 10 cycle refers to a signal that is generated by a piezoelectric element, which is excited by an electric signal with 10 sinusoidal oscillations of constant amplitude having a 1 s period.

(115) TABLE-US-00001 Flowrate/Method 21 m.sup.3/h 44 m.sup.3/h 61 m.sup.3/h TOF 1 cycle 7 ns 18 ns 27 ns TOF 10 cycle 9 ns 19 ns 26 ns Time reversal 8 ns 18 ns 27 ns

(116) FIGS. 10-27 show high resolution inverted signals and their respective response signals. The voltage is plotted in arbitrary units over the time in microseconds.

(117) The time axes in the upper Figures show a transmitting time of the inverted signal. The transmitting time is limited to the time window that is used to record the inverted signal. In the example of FIGS. 10-27 the time window starts shortly before the onset of the maximum, which comes from the direct signal and ends 100 microseconds thereafter.

(118) The time axes in the lower Figures are centered around the maximum of the response signals and extend 100 microseconds, which is the size of the time window for the inverted signal, before and after the maximum of the response signals.

(119) FIGS. 28-35 show digitized inverted signals in a high resolution and in 12, 3, 2 and 1 bit resolution in the amplitude range and their respective response signals. The voltage is plotted in Volt over the time in microseconds. The signals of FIG. 28-35 were obtained for a water filled DN 250 pipe.

(120) The length of the time window for the inverted signal is 450 microseconds. Hence, the time window of FIGS. 28-35 is more than four times larger than in the preceding FIGS. 9-27.

(121) In FIGS. 28-35 it can be seen that even a digitization with 1 bit resolution produces a sharp spike. It can be seen that the spike becomes even more pronounced for the lower resolutions. A possible explanation for this effect is that in the example of FIGS. 28-35 the total energy of the input signal is increased by using a coarser digitization in the amplitude range while the response signal remains concentrated in time.

(122) FIG. 36 shows a signal that is generated by a piezoelectric element after receiving an electric pulse that lasts for about 0.56 microseconds, which is equivalent to a frequency of 3.57 MHz. Due to the inertia of the piezoelectric element, the maximum amplitude for the negative voltage is smaller than for the positive voltage and there are multiple reverberations before the piezoelectric element comes to rest.

(123) FIG. 37 shows an electric signal that is applied to a piezoelectric element, such as the upstream piezoelectric element 11 of FIG. 1. The signal of FIG. 37 is derived by forming an average of ten digitized response signals to a signal of the type shown in FIG. 36 and time reversing the signal, wherein the response signals are received by a piezoelectric element such as the downstream piezoelectric element 13 of FIG. 1.

(124) In the example of FIG. 37, the digitized signals are obtained by cutting out a signal portion from the response signal that begins approximately 10 microseconds before the onset of envelope of the response signal and that ends approximately 55 microseconds behind the envelope of the response signal. The envelope shape of the response signal of FIG. 37 is similar to the shape of a Gaussian probability distribution, or, in other words, to a suitable shifted and scaled version of exp(x{circumflex over ()}2).

(125) FIG. 38 shows a portion of a response signal to the signal shown in FIG. 37, wherein the signal of FIG. 37 is applied to a first piezoelectric element, such as the upstream piezoelectric element 11, and received at a second piezoelectric element, such as the downstream piezoelectric element 13 of FIG. 1.

(126) FIG. 39 shows a an upstream cross correlation function and a downstream cross correlation function, which are obtained by cross correlating the upstream signal and the downstream signal of the arrangement of FIG. 1 with a signal obtained at zero flow, respectively.

(127) FIG. 40 shows a sectional enlargement of FIG. 39. Two position markers indicate the positions of the respective maxima of the upstream and downstream cross correlation function. The time difference between the maxima is a measure for the time difference between the upstream and the downstream signal.

(128) FIGS. 48, 49 and 50 show three different sending signals: FIG. 48 shows a conventional pulse (1 cycle) and FIG. 48 shows a 10 cycles pulse compared to the measuring signal generated by as described above, such as the signal of FIG. 50. The transducers have been clamped onto a DN250 pipe.

(129) FIGS. 51, 52 and 53 show the corresponding received signals after sending the signals of illustrated in the respective FIGS. 48, 59 and 50. By comparison it can be easily seen that measuring signal focus the energy and generates a more than two times larger amplitude of the receiving signal compared to the receiving signals in response to the conventional pulses (e.g. 1 or 10 cycles) of FIGS. 48 and 49.

(130) FIG. 41 shows, by way of example, a flow measurement device 60 for measuring a flow in the arrangement in FIG. 1 or other arrangements according to the specification. In the arrangement of FIG. 1, the flow measurement device 60 is provided by the first and second computation units 15, 16.

(131) The flow measurement device 60 comprises a first connector 61 for connecting a first piezoelectric transducer and a second connector 62 for connecting a second piezoelectric transducer. The first connector 61 is connected to a digital to analog converter (DAC) 64 over a multiplexer 63. The second connector 62 is connected to an analog to digital converter 65 over a demultiplexer 66.

(132) The ADC 65 is connected to a signal selection unit 67, which is connected to a signal inversion unit 68, which is connected to a band pass filter 69, which is connected to a computer readable memory 70. Furthermore, the ADC 65 is connected to a velocity computation unit 71.

(133) The DAC 64 is connected to an impulse signal generator 72 and a measuring signal generator 73. The measuring signal generator is connected to the impulse generator 72 over a command line 74. The velocity computation unit 71 is connected to the measuring signal generator 73 via a second command line 75.

(134) In general, the impulse signal generator 72 and the measuring signal generator comprise hardware elements, such as an oscillator, and software elements, such as an impulse generator module and a measuring signal generator module. In this case, the command lines 74, 75 may be provided by software interfaces between respective modules.

(135) During a signal generating phase, the impulse signal generator sends a signal to the DAC 64, the selection unit 67 receives a corresponding incoming signal over the ADC 65 and selects a portion of an incoming signal. The inversion unit 68 inverts the selected signal portion with respect to time, the optional bandpass filter 69 filters out lower and upper frequencies and the resulting measuring signal is stored in the computer memory 70. When the word signal is used with reference to a signal manipulation step, it may in particular refer to a representation of a signal in a computer memory.

(136) In particular, a signal representation can be defined by value pairs of digitized amplitudes and associated discrete times. Other representations comprise, among others, Fourier coefficients, wavelet coefficients and an envelope for amplitude modulating a signal.

(137) FIG. 42 shows a second embodiment of a flow measurement device 60 for measuring a flow in the arrangement in FIG. 1 or other arrangements according to the specification. The flow measurement device 60 comprises a direct digital synthesizer (DDS) 76. For simplicity, only the components of the DDS 76 are shown. The DDS 76 is also referred to as an arbitrary waveform generator (AWG).

(138) The DDS 76 comprises a reference oscillator 77, which is connected to a frequency controller register 78, a numerically controlled oscillator (NCO) 79 and to the DAC 64. An input of the NCO 79 for N channels is connected to an output of the frequency control register 78. An input of the DAC 64 for M channels is connected to the NCO 79 and an input of a reconstruction low pass filter is connected to the DAC 64. By way of example, a direct numerically controlled oscillator 79 with a clock frequency of 100 MHz may be used to generate an amplitude modulated 1 MHz signal.

(139) An output of the reconstruction low pass filter 80 is connected to the piezoelectric transducers 11, 13 of FIG. 1.

(140) Due to the inertia of an oscillator crystal, it is often advantageous to use an oscillator with a higher frequency than that of a carrier wave in order to obtain a predetermined amplitude modulated signal, for example by using a direct digital synthesizer.

(141) FIGS. 45, 47 and 48 illustrate the abovementioned Z, V and W flow measurement configurations. In the examples of FIGS. 45, 47, 48 clamp-on transducers are attached to a conduit via respective coupling pieces.

(142) FIGS. 54 and 55 show a comparison of respective receiving or response signals to respective sending signals that were generated without using a time reversal procedure and with the use of a time reversal procedure.

(143) In the example of FIG. 54, a modulated sine wave with a Gaussian shaped envelope is used as a sending signal. The signal energy of the sending signal is proportional to 1.310.sup.7 (Pa/m).sup.2 s and the signal amplitude is 0.1 Pa. The value is obtained by integrating the squared pressure per unit length over time. The response signal has a peak-to-peak amplitude of the receiving signal of about 0.09 Pa.

(144) In the example of FIG. 55, a time reversed signal, which is derived from the response signal to the impulse signal of FIG. 56, is used as a sending signal. The sending signal is adjusted to have the same signal energy of 1.310.sup.7 (Pa/m).sup.2 s as the sending signal of FIG. 54. This yields a peak-to-peak amplitude of the receiving signal which is about 0.375 Pa.

(145) The receiving amplitude of FIG. 55 is more than four times higher than the amplitude of the receiving signal of FIG. 54. The increased amplitude on the receiving side can provide easier and more stable signal recognition. Among others, the increase in amplitude can be adjusted by adjusting the bit resolution of the amplitude of the time reversed signal, in particular by increasing or decreasing the bit-resolution in order to obtain a larger amplitude.

(146) FIGS. 56 and 57 illustrate how the receiving signals can be used to derive information about the transmission channel and in particular about the wall thickness of the conduit, deposits on the wall. According to the present specification, a response to the measuring signal, which is the time reversed response signal, can be analysed to allow a determination of property changes of the pipe material, like cracks, crustification, etc. In a flow measurement according to one embodiment of the present specification, these property changes are determined by analysing the same receiving signal that is used for the time of flight measurement.

(147) FIG. 57 shows a first response signal, which contains information about a first transmission channel.

(148) FIG. 58 shows a second response signal, which contains information about a second transmission channel. The length of the horizontal arrow on the central main lobe extends between the left side lobe and the right side lobe, which are left and right to the main lobe, respectively. The length of the arrow represents the thickness of a pipe wall if the signal is generated according to the FIG. 46. The measured wall thickness is determined at the location where the wave is reflected at the lower part of the pipe in FIG. 46. If there is a deposit on the pipe wall, the measured wall thickness will increase.

(149) FIG. 59 shows a further response signal. The experimental setup for obtaining the signal of FIG. 59 comprises clamp-on, angle transducers, an acrylic transducer coupling head, a sound velocity of c=2370 m/s, a coupling angle of 40, a stainless steel wall, a transversal wave velocity of c=3230 m/s, 61.17, water as fluid, a sound velocity in the fluid of c=1480 m/s, a transversal wave angle axis of 23.67, and a flow angle of 66.33, extracted from FIG. 59

(150) FIG. 60 shows a further response signal. The experimental setup for obtaining the signal of FIG. 60 comprises an acrylic transducer coupling head, a sound velocity of c=2370 m/s, a coupling angle of 20, a stainless steel wall, longitudinal wave velocity of c=5790 m/s, 56.68, transversal wave c=3230 m/s, water as fluid, a sound velocity in the fluid of c=1480 m/s, a longitudinal wave angle axis=12.33, a transversal wave angle axis of 12.33, and a flow angle of 77.67, extracted from FIG. 60.

(151) The alternative set-up configurations for FIGS. 59 and 60 are shown in FIGS. 45, 46 and 47.

(152) According to one embodiment of the present specification the channel properties are deduced by analysing a receiving signal such as the signals of FIG. 57 to 60.

(153) The example of FIGS. 59 and 60 illustrates the differences in the receiving signals depending on the presence of longitudinal and transversal waves in the pipe material. The presence of these waves are typical for the selected material and the geometry and can be used for material analysis. Such material analysis based on ultrasonic test waves are used in the application field of Non-Destructive Testing (NDT). This present specification allows the simultaneous analysis of flow and e.g. piping material as the received signal contains the impulse response of the measurement system including the transmission channel and material environment.

(154) The analysis of the receiving signals can be carried out in various ways, such as comparing the receiving signal with a previously received impulse response or direct evaluation of an impulse response, for example for determining a wall thickness.

(155) Although the above description contains much specificity, these should not be construed as limiting the scope of the embodiments but merely providing illustration of the foreseeable embodiments. The method steps may be performed in different order than in the provided embodiments, and the subdivision of the measurement device into processing units and their respective interconnections may be different from the provided embodiments.

(156) In particular, the method steps of storing a digital representation of a signal and performing operations such as selection a signal portion, time reversing a signal and filtering a signal may be interchanged. For example, a signal may be stored in a time inverted form or it may be read out in reverse order to obtain a time inverted signal.

(157) While the present disclosure is explained with respect to a round DN 250 pipe, it can be readily applied to other pipe sizes or even to other pipe shapes. Although the embodiments are explained with respect to clamp-on transducers, wet transducers, which protrude into a pipe or installed in an open channel, may be used as well.

(158) Especially, the above stated advantages of the embodiments should not be construed as limiting the scope of the embodiments but merely to explain possible achievements if the described embodiments are put into practise. Thus, the scope of the embodiments should be determined by the claims and their equivalents, rather than by the examples given.

(159) The embodiments of the present specification can also be described with the following lists of elements being organized into embodiments. The respective combinations of features which are disclosed in the embodiment list are regarded as independent subject matter, respectively, that can also be combined with other features of the application.

Embodiment 1

(160) A method for determining a flow speed of a fluid in a fluid conduit comprising: providing the fluid conduit with a fluid that has a predetermined velocity with respect to the fluid conduit, applying an impulse signal to a first ultrasonic transducer, the first ultrasonic transducer being mounted to the fluid conduit at a first location, receiving a response signal of the impulse signal at a second ultrasonic transducer, the second ultrasonic transducer being located at the fluid conduit at a second location, deriving a measuring signal from the response signal, the derivation of the measuring signal comprising selecting a signal portion of the response signal or of a signal derived therefrom and reversing the signal portion with respect to time, storing the measuring signal for later use, providing the fluid conduit with the fluid, the fluid moving with respect to the fluid conduit, applying the measuring signal to one of the first and the second ultrasonic transducers, measuring a first response signal of the measuring signal at the other one of the first and the second ultrasonic transducer, deriving a flow speed of the fluid from the first response signal, wherein the following steps of applying an impulse signal to a first ultrasonic transducer, the first ultrasonic transducer being mounted to the fluid conduit at a first location, receiving a response signal of the impulse signal at a second ultrasonic transducer, the second ultrasonic transducer being located at the fluid conduit at a second location, deriving a measuring signal from the response signal, the derivation of the measuring signal comprising selecting a signal portion of the response signal or of a signal derived therefrom and reversing the signal portion with respect to time, storing the measuring signal for later use, are optional or can be left away if the measurement signal has been established earlier.

Embodiment 2

(161) The method according to embodiment 1, comprising repeating the steps of applying the measuring signal and measuring the response signal in the reverse direction to obtain a second response signal, deriving a flow speed of the fluid from the first response signal and the second response signal.

Embodiment 3

(162) The method according to embodiment 1 or embodiment 2, wherein the signal portion that is used to derive the measuring signal comprises a first portion around a maximum amplitude of the response signal and a trailing signal portion, the trailing signal portion extending in time behind the arrival time of the maximum amplitude.

Embodiment 4

(163) The method according to one of the preceding embodiments, comprising repeating the steps of applying an impulse signal and receiving a corresponding response signal multiple times, thereby obtaining a plurality of response signals, deriving the measuring signal from an average of the received response signals.

Embodiment 5

(164) The method according to one of the preceding embodiments, wherein the derivation of measuring signal comprises digitizing the response signal or a signal derived therefrom with respect to amplitude.

Embodiment 6

(165) The method according to embodiment 5, comprising increasing the bit-resolution of the digitized signal for increasing an amplitude of a response signal to the measuring signal.

Embodiment 7

(166) The method according to embodiment 5, comprising decreasing the bit-resolution of the digitized signal for increasing an amplitude of a response signal to the measuring signal.

Embodiment 8

(167) The method according to one of the embodiments 5 to 7, wherein the bit resolution of the digitized signal with respect to the amplitude is a low bit resolution.

Embodiment 9

(168) The method according to one of the preceding embodiments, comprising processing of at least one of the response signals for determining a change in the wall thickness of the conduit or for determining material characteristics of the conduit walls by determining longitudinal and transversal sound wave characteristics.

Embodiment 10

(169) A device for measuring a flow speed in a travel time ultrasonic flow meter, comprising a first connector for a first ultrasonic element, a second connector for a second ultrasonic element, a transmitting unit for sending an impulse signal to the first connector, a receiving unit for receiving a response signal to the impulse signal from the second connector, an inverting unit for inverting the response signal with respect to time to obtain an inverted signal, a processing unit for deriving a measuring signal from the inverted signal and storing the measuring signal, wherein the following elements of a transmitting unit for sending an impulse signal to the first connector, a receiving unit for receiving a response signal to the impulse signal from the second connector, an inverting unit for inverting the response signal with respect to time to obtain an inverted signal, a processing unit for deriving a measuring signal from the inverted signal and storing the measuring signal, are optional or can be left away if the measurement signal has been established earlier so that it is readily available.

Embodiment 11

(170) The device of embodiment 10, further comprising: a D/A converter, the D/A converter being connected to the first connector, an A/D converter, the A/D converter being connected to the second connector, a computer readable memory for storing the measuring signal.

Embodiment 12

(171) The device of embodiment 10 or embodiment 11, further comprising a selection unit for selecting a portion of the received response signal or a signal derived therefrom, wherein the inverting unit is provided for inverting the selected portion of the response signal with respect to time to obtain the inverted signal.

Embodiment 13

(172) The device of one of embodiments 10 to 12, the device comprising a measuring signal generator, the measuring signal generator being connectable to the first connector or to the second connector, a transmitting means for sending the measuring signal to the first connector, a receiving unit for receiving a response signal of the measuring signal from the second connector, a second processing unit for deriving a flow speed from the received response signal.

Embodiment 14

(173) The device according to one of the embodiments 10 to 13, the device comprising: a direct digital signal synthesizer, the direct digital signal synthesizer comprising the ADC, a frequency control register, a reference oscillator, a numerically controlled oscillator and a reconstruction low pass filter, the ADC being connectable to the first and the second connector over the reconstruction low pass filter.

Embodiment 15

(174) The device according to one of the embodiments 10 to 14, the device comprising: a first ultrasonic transducer, the first ultrasonic transducer being connected to the first connector, a second ultrasonic transducer, the second ultrasonic transducer being connected to the second connector.

Embodiment 16

(175) The device according to one of the embodiments 10 to 15, comprising a portion of a pipe, the first ultrasonic transducer being mounted to the pipe portion at a first location, and the second ultrasonic transducer being mounted to the pipe portion at a second location.

Embodiment 17

(176) A computer readable program code comprising computer readable instructions for executing the method according to one the embodiments 1 to 9.

Embodiment 18

(177) A computer readable memory, the computer readable memory comprising the computer readable program code of embodiment 17.

Embodiment 19

(178) An application specific electronic component, which is operable to execute the method according to one of the embodiments 1 to 9.

Embodiment 20

(179) A method for determining whether a test device is measuring a flow speed of a fluid in a fluid conduit according to one of embodiments 1 to 5, comprising: providing the fluid conduit with a fluid that has a pre-determined velocity with respect to the fluid conduit, applying a test impulse signal to a first ultrasonic transducer of the test device, the first ultrasonic transducer being mounted to the fluid conduit at a first location, receiving a test response signal of the test impulse signal at a second ultrasonic transducer of the test device, the second ultrasonic transducer being mounted to the fluid conduit at a second location, deriving a test measuring signal from the response signal, the derivation of the test measuring signal comprising reversing the signal with respect to time, comparing the test measuring signal with a measuring signal that is emitted at the other one of the first and the second ultrasonic transducer, wherein the test device is using a method to determine a flow speed of a fluid in a fluid conduit according to one of embodiments 1 to 5, if the test measuring signal and the measuring signal are similar.

Embodiment 21

(180) A device for measuring a flow speed in a travel time ultrasonic flow meter, comprising a first connector for a first ultrasonic element, a second connector for a second ultrasonic element, a transmitting unit for sending an impulse signal to the first connector, a receiving unit for receiving a response signal to the impulse signal from the second connector, an inverting unit for inverting the selected portion of the response signal with respect to time to obtain an inverted signal, a processing unit for deriving a measuring signal from the inverted signal and storing the measuring signal in the computer readable memory, wherein using the device for determining a flow speed of a fluid in a fluid conduit by: providing the fluid conduit with a fluid that has a velocity with respect to the fluid conduit, applying a measuring signal to one of the first and the second ultrasonic elements, measuring a first response signal of the measuring signal at the other one of the first and the second ultrasonic elements, deriving a flow speed of the fluid from the first response signal, wherein when applying a test impulse signal to a first ultrasonic element of the test device, receiving a test response signal of the test impulse signal at a second ultrasonic element of the test device, the second ultrasonic element being mounted to the fluid conduit at a second location, deriving a test measuring signal from the response signal, the derivation of the test measuring signal comprising reversing the signal with respect to time, wherein the test measuring signal and a measuring signal that is emitted at the first or the second ultrasonic element are similar.

REFERENCE

(181) 10 flow meter arrangement 11 upstream piezoelectric element 12 pipe 13 downstream piezoelectric element 14 direction of average flow 15 first computation unit 16 second computation unit 17 signal path 20 signal path 22 piezoelectric element 23 piezoelectric element 31-52 piezoelectric elements 60, 60 flow measurement device 61 first connector 62 mulitplexer 63 multiplexer 64 DAC 65 ADC 66 demultiplexer 67 signal selection unit 68 signal inversion unit 69 bandpass filter 70 memory 71 velocity computation unit 72 impulse signal generator 73 measuring signal generator 74 command line 75 command line 76 DDS 77 reference oscillator 78 frequency controller register 79 numerically controlled oscillator 80 low pass filter