Methods for measuring fluid velocity

Abstract

A method for measuring fluid velocity and an ultrasonic fluid meter suitable for implementing the method. The method comprises the following steps: measuring the travel time taken by a measuring ultrasonic signal to travel a path of defined length, the measuring ultrasonic signal being generated by a transducer subjected to an excitation electrical signal (16). The excitation electrical signal (16) comprises a first signal portion (17) followed by a second signal portion (18). The first signal portion is a periodic signal having a pattern (19) and a decreasing amplitude. The second signal portion is a periodic signal having the same pattern (21) and a constant amplitude.

Description

[0001] The present invention relates to the field of methods of measuring the velocity of a fluid. Background Art

[0002] In order to measure the flow velocity of a fluid flowing in a pipe, an ultrasonic flow meter generally uses a device that measures the velocity of the fluid by transmitting and receiving ultrasonic measurement signals.

[0003] The measuring device comprises a conduit connected to a pipe in which a fluid flows. To measure the fluid velocity, an ultrasonic measuring signal is emitted into the conduit to travel along a path of a defined length, the travel time taken by the ultrasonic measuring signal to travel along the path of the defined length from upstream to downstream and from downstream to upstream is measured, and also the fluid velocity is estimated based in particular on the difference between the defined length and the travel time.

[0004] This type of measuring device 1 (sometimes referred to as a classic pipe device) is used in Figure 1 The measuring device 1 comprises a first transducer 2a, a second transducer 2b, and a measuring module 3 connected to the first transducer 2a and the second transducer 2b.

[0005] The first transducer 2a and the second transducer 2b are paired in terms of frequency and emission level. As an example, the first transducer 2a and the second transducer 2b are piezoelectric transducers.

[0006] Therefore, the path of defined length is a straight path of length L between the first transducer 2a and the second transducer 2b.

[0007] The measuring module 3 generates an electrical excitation signal 4 which is applied as input to the first sensor 2a.

[0008] On the basis of the electrical excitation signal 4, the first transducer 2a transmits an ultrasonic measurement signal 5. The second transducer 2b receives a received ultrasonic measurement signal 6 resulting from the ultrasonic measurement signal 5 propagating in the fluid.

[0009] The measurement module 3 measures the travel time taken by the ultrasonic measurement signal 5 to travel from upstream to downstream along a path of defined length.

[0010] In practice, the measurement module 3 measures the global transmission time T from the first transducer 2a to the second transducer 2b AB .

[0011] The global transmission time T AB So that:

[0012] T AB =TA A +ToF AB +TR B ,in:

[0013] ·TA A is the on-time of the first transducer 2a;

[0014] ToF AB corresponds to the flight time taken by the ultrasound measurement signal 5 to travel along a path of defined length between the first transducer 2a and the second transducer 2b; and

[0015] TR B is the reception time of the second transducer 2b.

[0016] Likewise, the second transducer 2b transmits an ultrasonic measurement signal which is received by the first transducer 2a.

[0017] The global transmission time T BA So that:

[0018] T BA =TA B +ToF BA +TR A ,in:

[0019] ·TA B is the on-time of the second transducer 2b;

[0020] ToF BA corresponds to the flight time taken by the ultrasound measurement signal 5 to travel along a path of defined length between the second transducer 2b and the first transducer 2a; and

[0021] ·TR A is the reception time of the first transducer 2a.

[0022] Assumptions:

[0023] TA A =TA B TR A =TR B ,but:

[0024] ΔT=t ba -t ab =ToF BA -ToF AB =DToF

[0025] where dtoF is the differential time of flight.

[0026] However, DToF and the mean velocity of the fluid The measurement module 3 then uses the following formula to calculate the mean velocity of the fluid:

[0027] Where C is the speed of ultrasound in the fluid. For example, the speed of ultrasound in water is approximately equal to 1500 meters per second (m / s), and it depends on the temperature of the water.

[0028] The measurement module 3 then uses the signed mean velocity The flow rate of a fluid flowing in a pipe is derived from.

[0029] Purpose of the Invention

[0030] An object of the present invention is to improve flow rate measurements made by ultrasonic flow meters and to reduce the amount of power consumed to make such measurements. Summary of the invention

[0031] To achieve this object, a method for measuring the velocity of a fluid is provided, the method comprising the step of measuring the travel time taken by an ultrasonic measurement signal to travel along a path of defined length, the ultrasonic measurement signal being generated by a transducer subjected to an electrical excitation signal. According to the invention, the electrical excitation signal comprises a first signal portion followed by a second signal portion, the first signal portion being a periodic signal presenting a pattern with a decreasing maximum amplitude, while the second signal portion is a periodic signal having the same pattern with a constant maximum amplitude.

[0032] By means of the above-mentioned electrical excitation signal, the ultrasound measurement signal as received after travelling along this path exhibits almost the same lobes.

[0033] The fact of having almost identical lobes facilitates velocity measurements and improves the accuracy of those velocity measurements (and therefore the accuracy of flow velocity measurements). Furthermore, this makes it possible to use the initial lobe of the received ultrasonic measurement signal for travel time measurements, making it possible to reduce the amount of power consumed for velocity measurements.

[0034] There is also provided an ultrasonic fluid meter comprising a first transducer, a second transducer and a measurement module connected to the first transducer and the second transducer, the ultrasonic fluid meter being arranged to perform the measurement method as described above.

[0035] There is also provided a computer program comprising instructions for enabling a microcontroller of an ultrasonic fluid meter to perform a measurement method as described above.

[0036] A storage device is also provided, the storage device comprising instructions for enabling a microcontroller of an ultrasonic fluid meter to execute the measurement method as described above.

[0037] Other characteristics and advantages of the invention will become apparent on reading the following description of a particular, non-limiting embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] With reference to the accompanying drawings, in which:

[0040] · Figure 1 A prior art ultrasonic fluid meter is shown;

[0041] · Figure 2 An ultrasonic fluid meter for performing the measuring method of the present invention is shown;

[0042] · Figure 3 shows received ultrasonic measurement signals and electrical excitation signals used in performing the measurement method of the present invention; and

[0043] · Figure 4 Received ultrasound measurement signals and electrical excitation signals used when performing a prior art measurement method are shown. DETAILED DESCRIPTION

[0044] Reference Figure 2 In this example, the method for measuring fluid velocity of the present invention is performed in an ultrasonic water meter.

[0045] The ultrasonic water meter 10 comprises both a conduit through which the flow of water is delivered by a distribution network to an installation and a water velocity measurement device 11 .

[0046] As indicated by arrows F, water flows in the conduit from upstream to downstream, however, it can also flow from downstream to upstream.

[0047] The measuring device 11 includes a first transducer 12a, a second transducer 12b, and a measuring module 13 connected to the first transducer 12a and the second transducer 12b.

[0048] The first transducer 12a and the second transducer 12b are a pair. In this example, the first transducer 12a and the second transducer 12b are piezoelectric transducers.

[0049] The measurement module 13 comprises a processor component adapted to execute program instructions for performing the measurement method of the invention. Specifically, the processor component is a microcontroller, but it may be some other component, such as a processor, or a Field Programmable Gate Array (FPGA).

[0050] The measuring module 13 controls the first transducer 12a and the second transducer 12b.

[0051] Each of the first transducer 12 a and the second transducer 12 b successively performs the function of a transmitter of the ultrasonic measurement signal 14 and the function of a receiver of the received ultrasonic measurement signal 15 .

[0052] The measuring module 13 generates an electrical excitation signal 16 and transmits the electrical excitation signal 16 to the transmitter.

[0053] The transmitter converts each electrical excitation signal 16 into an ultrasonic measurement signal 14. The measurement module 13 acquires the received ultrasonic measurement signal 15 received by the receiver.

[0054] The transmitter transmits the ultrasonic measurement signal 14 at a transmission frequency fus. The frequency fus conventionally lies in the range 600 kilohertz (kHz) to 4 megahertz (MHz), and in this example it is equal to 1 MHz.

[0055] Thus, the ultrasonic measurement signal 14 travels from upstream to downstream and from downstream to upstream along a path between the first transducer 12a and the second transducer 12b of defined length L. In this example, the path of defined length is a straight path between the first transducer 12a and the second transducer 12b.

[0056] exist Figure 2 , the first transducer 12a is shown as performing the function of a transmitter, while the second transducer 12b is shown as performing the function of a receiver. Thus, an electrical excitation signal 16 is applied as input to the first transducer 12a in order to transmit an ultrasonic measurement signal 14. Thus, the ultrasonic measurement signal 14 follows a path of defined length from upstream to downstream. The ultrasonic measurement signal 14 is transmitted by the transmitter at a level NE. The received ultrasonic measurement signal 15 is received by the receiver at a level NR lower than the level NE.

[0057] The measurement module 13 generates a travel time measurement representing the time taken by the ultrasonic measurement signal 14 to travel from upstream to downstream along a path of defined length L, and then generates a travel time measurement representing the time taken by the ultrasonic measurement signal 14 to travel from downstream to upstream along a path of defined length L, and ultimately estimates the water speed as a function of these travel time measurements.

[0058] Reference Figure 3 , the following is a description of the electrical excitation signal 16.

[0059] The electrical excitation signal 16 comprises a first signal portion 17 followed by a second signal portion 18 .

[0060] The first signal portion 17 is a periodic signal presenting a pattern 19 which is periodically repeated with a first period T1 and has a decreasing maximum amplitude. The first signal portion 17 is a rectangular signal. Therefore, the pattern 19 of the first signal portion 17 is rectangular. The pattern 19 may also be referred to as a "square wave" signal.

[0061] In this example, the first signal portion 17 has four patterns 19 : a first pattern 19_1 , a second pattern 19_2 , a third pattern 19_3 , and a fourth pattern 19_4 .

[0062] The first signal portion 17 has a first duration D1 which is therefore equal to 4 times the first period T1.

[0063] In this example, because each pattern 19 is rectangular, the maximum amplitude of the pattern 19 is the amplitude of the high state of the pattern 19 .

[0064] The maximum amplitude of the pattern 19 of the first signal portion 17 decreases according to a linear function.

[0065] The term "function" is used here to mean a relationship that relates a pattern to the maximum amplitude of the pattern for a given arrival instant or a given arrival order in the pattern.

[0066] In this example, the maximum amplitude of the first pattern 19_1 is equal to 3 volts (V). The maximum amplitude of the second pattern 19_2 is equal to 2.75 V. The maximum amplitude of the third pattern 19_3 is equal to 2.5 V. The maximum amplitude of the fourth pattern 19_4 is equal to 2.25 V. The maximum amplitude of the pattern 20 that follows the fourth pattern 19_4 and is the first pattern of the second signal portion 18 is equal to 2 V.

[0067] The second signal portion 18 is a periodic signal presenting a pattern 21 which is periodically repeated with a second period T2 and has a constant maximum amplitude. Naturally, the term "constant maximum amplitude" is used to cover a maximum amplitude which may vary, but only with a small amplitude (e.g. in the range of 1% to 5% of the mean maximum amplitude of the pattern 21).

[0068] The second period T2 is equal to the first period T1. The second signal portion 18 is a rectangular signal. Therefore, the pattern 21 of the second signal portion 18 is a rectangle.

[0069] The second signal portion 18 has a greater number of patterns 21 , so that the second duration D2 of the second signal portion 18 is longer than the first duration D1 of the first signal portion 17 .

[0070] In this example, the first signal portion 17 constitutes the starting portion of the electrical excitation signal 16, and the second signal portion 18 extends from the end of the starting portion to the end of the electrical excitation signal 16, and the electrical excitation signal 16 is used to obtain a time representative of the time taken by the ultrasonic measurement signal 14 to travel from upstream to downstream along a path of a defined length L.

[0071] Receiver (i.e. Figure 2 The second transducer 12b) in the embodiment activates the reception of the ultrasonic measurement signal 15 at a time T0 synchronized with the transmission of the ultrasonic measurement signal 14. This synchronization is made possible by pairing the transmitter and the receiver.

[0072] It should be observed that the received ultrasonic measurement signal 15 presents an almost completely sinusoidal ultrasonic waveform. In particular, it should be observed that the first four lobes 24 of the received ultrasonic measurement signal 15 corresponding to the pattern 19 of the first signal portion 17 of the electrical excitation signal 16 present an amplitude that is almost equal to the amplitude of the other lobes of the received ultrasonic measurement signal 15.

[0073] The upstream to downstream travel time is measured based on determining the arrival time T1 of a predetermined lobe of the ultrasonic measurement signal 15 .

[0074] In this example, the arrival time T1 is the time at which the rising edge of the predetermined lobe arrives. The arrival time T1 is measured by the zero-crossing type method.

[0075] Since the received ultrasonic measurement signal 15 presents an almost completely sinusoidal ultrasonic waveform, the first lobe 24_1 of the received ultrasonic measurement signal 15 may be selected as the predetermined lobe. Naturally, some other lobes may also be selected, such as the second lobe 24_2, the third lobe 24_3 or the fourth lobe 24_4.

[0076] An electrical excitation signal similar to electrical excitation signal 16 is then applied to the input of second transducer 12b by measurement module 13. A received ultrasonic measurement signal similar to received ultrasonic measurement signal 15 is then received by measurement module 13 after travelling along a path of defined length L from downstream to upstream.

[0077] The downstream to upstream travel time is measured based on determining the arrival time T1 of a predetermined lobe of the received ultrasonic measurement signal.

[0078] The water velocity is then estimated by the measurement module 13 as a function of the upstream to downstream travel time measurement and the downstream to upstream travel time measurement.

[0079] Water velocity is proportional to the difference between the downstream to upstream travel time measurement and the upstream to downstream travel time measurement.

[0080] It should be observed that, given that the velocity of the water mass is different from the center of the conduit to near the conduit wall, the measured water velocity is the average velocity of the water across the conduit diameter.

[0081] It should also be observed that since the speed of sound in water varies depending on the water temperature (this also applies to other fluids such as gas or oil), temperature compensation needs to be performed.

[0082] refer to Figure 4 , when the electrical excitation signal 27 is a simple rectangular signal (where the amplitude of the pattern 32 is constant), the following is observed. In this case, it can be seen that the first lobe 28 of the received ultrasonic measurement signal 29 exhibits a gradually increasing smaller amplitude.

[0083] The membrane of the piezoelectric transducer 12a or 12b used as a transmitter constitutes an oscillator excited by an electrical excitation signal.

[0084] The increased amplitude of the initial lobe 28 of the received ultrasonic measurement signal 29 is due to the transient condition in which the oscillator will be found when it begins to be excited by the electrical excitation signal 27. This transient condition precedes the steady state condition corresponding to the subsequent lobe of the received ultrasonic measurement signal 29.

[0085] Therefore, the initial lobe 28 exhibits a small and non-constant amplitude and is therefore difficult to use with the zero-crossing method.

[0086] The upstream to downstream travel time is measured based on the determination of the arrival instant T2 of a predetermined lobe of the ultrasonic measurement signal 29 which is received, which predetermined lobe is therefore not one of the initial lobes 28 .

[0087] In order to ensure satisfactory measurement, it is necessary to select as the predetermined lobe a lobe whose amplitude does not correspond to a transient condition, but to a stable sinusoidal condition. As an example, the selected lobe may be the fourth lobe of the received ultrasonic measurement signal 29, so that the received ultrasonic measurement signal exhibits an amplitude exceeding the predetermined amplitude threshold 30. In this example, it is the lobe 31, which is the sixth lobe of the received ultrasonic measurement signal 29. The upstream to downstream travel time is measured from the determination of the arrival time T2.

[0088] The initial lobe 28 is therefore not used.

[0089] By performing the measuring method of the invention, on the contrary, it is possible to use the first lobe 24_1 (or one of the first lobes) of the received ultrasound measurement signal 15 .

[0090] The fact of having almost identical lobes makes the measurement easier and therefore improves the measurement accuracy. Furthermore, since it is possible to use the first lobe 24_1 or one of the first lobes, the measurement can be made faster, making it possible to reduce the consumption of electricity associated with making the measurement.

[0091] It should be observed that when designing the measuring device 11 of the ultrasonic water meter 10 , the value of the maximum amplitude of the pattern 19 of the first signal portion 17 may be defined.

[0092] During the step of calibrating the measuring device 11, the value of the maximum amplitude of the pattern 19 of the first signal portion 17 may also be defined. The maximum amplitude value is then included in a table stored in the memory of the measuring device 11. As an example, the calibration step may be performed when the measuring device 11 is manufactured.

[0093] Naturally, the invention is not limited to the embodiments described but covers any variant coming within the ambit of the invention as defined by the claims.

[0094] According to some other functionality, it may naturally result in a reduction in the maximum amplitude of the pattern of the first signal portion.

[0095] As an example, the maximum amplitude of the pattern of the first signal portion may be reduced according to the following function:

[0096]

[0097] wherein y is the maximum amplitude of the patterns of the first signal portion, N is the number of said patterns starting from the first pattern of the first signal portion, and a, b and c are constants.

[0098] As an example, one might choose a=3, b=7 / 8, and c=1 / 8.

[0099] Then, the first pattern presents a maximum amplitude equal to 3 V. The second pattern presents a maximum amplitude equal to 2.67 V. The third pattern presents a maximum amplitude equal to 2.4 V. The fourth pattern presents a maximum amplitude equal to 2.18 V. The first pattern of the second signal portion presents a maximum amplitude equal to 2V.

[0100] It is also possible to define constant and arbitrary decreasing values ​​for the pattern 19. In this case, the maximum amplitude of the pattern of the first signal portion decreases by certain discrete values.

[0101] Naturally, the first signal portion may have a pattern number other than four.

[0102] As mentioned above, the first signal portion is followed by the second signal portion. The term "follows" does not necessarily mean "immediately follows": there may be a third signal portion between the first and second signal portions. Likewise, the first signal portion may be preceded by a fourth signal portion and the second signal portion may be followed by a fifth signal portion.

[0103] The pattern above is described as a rectangle, however the pattern could be different: triangle, sawtooth, sinusoidal, etc.

[0104] Naturally, the invention applies regardless of the position and configuration of the first and second transducers. The ultrasound measurement signal can be emitted in any angular direction relative to the longitudinal axis of the catheter. The ultrasound measurement signal can be reflected by a reflector, for example by a mirror oriented at 45°.

[0105] The invention can also be used to measure the velocity of certain other fluids, such as gas or oil.

Claims

1. A method for measuring fluid velocity, the method comprising the following steps: The travel time taken by an ultrasonic measurement signal (14) to travel along a path of defined length is measured, the ultrasonic measurement signal (14) being generated by a transducer (12a, 12b) subjected to an electrical excitation signal (16), the measurement method being characterized in that the electrical excitation signal (16) comprises a first signal portion (17) followed by a second signal portion (18), the first signal portion being a periodic signal exhibiting a pattern (19) with a decreasing maximum amplitude, and the second signal portion being a periodic signal having the same pattern (21) with a constant maximum amplitude.

2. The measuring method according to claim 1, characterized in that: The maximum amplitude of the pattern (19) of the first signal portion (17) decreases according to a linear function.

3. The measuring method according to claim 1, characterized in that: The maximum amplitude of the pattern of the first signal portion decreases according to a function of the type: wherein y is the maximum amplitude of the patterns of the first signal portion, N is the number of the patterns starting from the first pattern of the first signal portion, and a, b and c are constants.

4. The measuring method according to claim 3, characterized in that: a=3, b=7 / 8, and c=1 / 8.

5. The measuring method according to claim 1, characterized in that: The maximum amplitude of the pattern of the first signal portion decreases by certain discrete values.

6. The measuring method according to claim 1, characterized in that: The electrical excitation signal (16) is a rectangular signal.

7. The measuring method according to claim 1, characterized in that: The maximum amplitude of the pattern of the first signal portion (17) lies in the range of 3V to 2V, whereas the maximum amplitude of the pattern of the second signal portion (18) is equal to 2V.

8. The measuring method according to claim 1, characterized in that: The transducer is a piezoelectric transducer.

9. The measuring method according to any one of the preceding claims, characterized in that The measuring method is performed in a measuring device (11), the measuring method comprising a step of calibrating the measuring device, the calibration step comprising defining a maximum amplitude value of the pattern (19) of the first signal portion (17) and including the maximum amplitude value in a table stored in a memory of the measuring device (11).

10. The measuring method according to claim 9, characterized in that: The calibration step is carried out during the manufacture of the measuring device.

11. An ultrasonic fluid meter comprising a first transducer (12a), a second transducer (12b) and a measurement module (13) connected to the first transducer and the second transducer, the ultrasonic fluid meter being arranged to perform the measurement method according to any preceding claim.

12. A computer program comprising instructions for enabling a microcontroller of an ultrasonic fluid meter according to claim 11 to perform a measuring method according to any one of claims 1 to 10.

13. A storage device, characterized in that: It stores a computer program including instructions for enabling a microcontroller of an ultrasonic fluid meter according to claim 11 to execute a measuring method according to any one of claims 1 to 10.

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