DEVICE FOR MEASURING A FLOW PARAMETER OF A FLUID

Abstract

A device for measuring at least one flow parameter of a fluid through a duct, in particular the flow rate thereof, including a portion forming an obstacle, intended to be brought into contact with the flow, the shape of which being chosen so as to generate turbulence in the flow; a vibration sensor sensitive to vibrations caused on the portion forming an obstacle by the turbulence; a processing unit configured to calculate the flow parameter of the fluid based on at least one vibration signal delivered by the vibration sensor.

Claims

1. A device for measuring at least one flow parameter of a fluid in a duct, comprising: an obstacle-forming part, configured to be placed in contact with the flow, having a form chosen so as to generate turbulences in the flow, a vibration sensor sensitive to the vibrations induced on the obstacle-forming part by the turbulences, a processing unit configured to calculate the flow parameter of the fluid from at least a vibratory signal delivered by the vibration sensor, by performing a frequency analysis of this vibratory signal.

2. The device as claimed in claim 1, wherein the processing unit is configured to calculate, in the frequency analysis, a frequency spectrum over a frequency range at least 500 Hz wide.

3. The device as claimed in claim 1, wherein the processing unit is configured to calculate a quantity representative of the flow rate of the fluid, by integration over a range of frequencies of a quantity representative of the amplitude of the vibrations, this integration being performed preferably over a frequency range ranging from a frequency F_min lying between 50 and 150 Hz.

4. The device as claimed in claim 1, further comprising a support coupled at one of its ends to the obstacle-forming part, and a fixing element making it possible to fix the support to the duct, comprising an element ensuring a vibration-damping function.

5. The device as claimed in claim 1, wherein the vibration sensor is arranged inside the obstacle-forming part.

6. The device as claimed in claim 4, wherein the support has a tubular form.

7. The device as claimed in claim 5, wherein the interior of the support is connected with the internal housing of the obstacle-forming part.

8. The device as claimed in claim 4, wherein the interior of the support receives at least one cable linked to the vibration sensor, the cable making it possible to electrically power the vibration sensor and/or transmit the vibratory signal delivered by the vibration sensor to the processing unit.

9. The device as claimed in claim 4, wherein the fixing element is a cable gland that makes it possible to fix the support to the duct.

10. The device as claimed in claim 4, wherein the fixing element comprises an antivibratory baseplate.

11. The device as claimed in claim 1, further comprising at least one external vibration sensor sensitive to the vibrations of the duct, the processing unit configured to calculate the flow parameter of the fluid from at least the vibratory signal delivered by the vibration sensor and from an external vibratory signal delivered by the external vibration sensor.

12. The device as claimed in claim 1, wherein the flow parameter of the fluid is its speed or its flow rate.

13. The device as claimed in claim 1, wherein the vibration sensor is an accelerometer.

14. The device as claimed in claim 1, wherein the obstacle-forming part has a general form of a sphere, a half-sphere, a disk, a cylinder, a half-cylinder or a beam.

15. The device as claimed in claim 1, wherein the obstacle-forming part has a surface in contact with the flow whose area lies between 1 and 500 cm.sup.2, better between 1 and 250 cm.sup.2, even better between 1 and 100 cm.sup.2.

16. The device as claimed in claim 1, wherein the obstacle-forming part is produced in a metallic material.

17. An installation for measuring at least one flow parameter of a fluid, comprising: a fluid flow duct, at least one measurement device as claimed in claim 1, for measuring the flow parameter of the fluid in the duct.

18. The installation as claimed in claim 17, further comprising a plurality of measurement devices in a restricted portion of the duct or distributed along the duct.

19. The installation as claimed in claim 18, wherein the plurality of measurement devices share a single processing unit.

20. The installation as claimed in claim 17, wherein the duct is a ventilation duct.

21. The installation as claimed in claim 17, wherein the length of the obstacle-forming part is less than or equal to half the internal diameter of the duct.

22. A method for measuring at least one flow parameter of a fluid in a duct, using a measurement device as defined in claim 1, comprising the steps of: a) detecting, using the vibration sensor, the vibrations induced on the obstacle-forming part by the turbulences, b) calculating, using the processing unit, the flow parameter of the fluid from at least the vibratory signal delivered by the vibration sensor.

23. The measurement method as claimed in claim 22, wherein the fluid is a liquid or a gas.

24. The measurement method as claimed in claim 22, wherein the duct is a ventilation duct.

25. The measurement method as claimed in claim 22, further comprising a step consisting in detecting the vibrations induced on the fluid flow duct using at least one external vibration sensor sensitive to the vibrations of the duct, and in calculating, using the processing unit, the flow parameter of the fluid from at least the vibratory signal delivered by the vibration sensor and from an external vibratory signal delivered by the external vibration sensor.

26. The method as claimed in claim 22, further comprising applying a measurement of the flow rate, comprising the following steps: a) calculation of a frequency spectrum of the vibratory signal delivered by the vibration sensor detecting the vibrations induced on the obstacle-forming part, b) calculation of a quantity (P*.sub.max) representative of the speed of the flow, called scalar indicator, by integration over a frequency spectrum from a low frequency F_min to a high frequency F_max of the amplitude of the vibratory signal or of a function X(f) representative thereof, c) determination of the flow rate or of the speed of flow with a transfer function giving, from the scalar indicator or from the image thereof by a function, the value of the flow rate or the speed of the flow, the parameter or parameters of this transfer function having been determined by prior calibration.

27. The method as claimed in claim 26, wherein the Reynolds number of the flow for which the flow rate is less than 4000.

28. A method for manufacturing a measurement device as claimed in claim 1, wherein the obstacle-forming part is manufactured by an additive manufacturing technique.

29. The manufacturing method as claimed in claim 28, further comprising a step of manufacturing the support by an additive manufacturing technique.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0113] FIG. 1 FIG. 1 is a schematic cross section of an example of a measurement device according to the invention in the transverse plane of a duct on which the device is mounted,

[0114] FIG. 2 is a view similar to FIG. 1 of a variant embodiment,

[0115] FIG. 3 FIG. 3 represents another example of a measurement device according to the invention,

[0116] FIG. 4 FIG. 4 represents another example of a measurement device according to the invention,

[0117] FIG. 5 FIG. 5 represents another example of a measurement device according to the invention,

[0118] FIG. 6 FIG. 6 represents another example of a measurement device according to the invention,

[0119] FIG. 7 FIG. 7 represents an example of a transfer function obtained after calibration, also called calibration curve, making it possible, with knowledge of a scalar indicator obtained by integration in a vibratory spectrum, to determine the speed of flow of the fluid,

[0120] FIG. 8 is a block diagram illustrating steps of an example of calculation of the flow rate.

DETAILED DESCRIPTION

[0121] FIG. 1 illustrates an example of a measurement device 1 according to the invention, mounted on a flow duct 11 of a fluid 12.

[0122] The device 1 comprises an obstacle-forming part 2, a vibration sensor 3, a support 7 and a processing unit 5.

[0123] The obstacle-forming part 2 is inserted into the fluid 12 flow duct 11. The obstacle-forming part 2 has a form chosen to generate turbulences in the flow, notably around the obstacle-forming part 2.

[0124] The obstacle-forming part 2 is arranged inside the duct 11. It can be positioned at the center of the duct 11, as illustrated in FIG. 1. As a variant, it can be positioned between the wall and the center of the duct 11.

[0125] The vibration sensor 3, preferably an accelerometer with one or three axes, is configured to detect the vibrations induced on the obstacle-forming part 2 by the turbulences and generate a corresponding vibratory signal 4. The vibration sensor 3 is arranged inside the obstacle-forming part 2, in an internal housing 6 defined by the body of the obstacle-forming part 2. Thus, the vibration sensor 3 is encapsulated in the obstacle-forming part 2, which makes it possible to tightly isolate it from the fluid 12 in flow. Within the internal housing 6, the vibration sensor 3 is fixed against a wall of the body of the obstacle-forming part 2.

[0126] The obstacle-forming part 2 is coupled at one of its ends to a tubular support 7, preferably made of a single piece. The interior of the support 7 is connected with the internal housing 6 of the obstacle-forming part 2.

[0127] The vibration sensor 3 is linked to a cable 4 which crosses the interior of the support 7. This cable 4 makes it possible to electrically power the vibration sensor 3 and/or transmit the vibratory signal 4 delivered by the vibration sensor 3 to the processing unit S.

[0128] The support 7 is fixed onto the duct 11 by means of a fixing element 8, notably a cable gland. The fixing element 8 can comprise an element ensuring a sealing and/or damping function, such as an antivibratory baseplate, for example.

[0129] The processing unit 5 receives the vibratory signal 4 delivered by the vibration sensor 3 and is configured to calculate a flow parameter of the fluid, notably the speed or flow rate thereof, from at least the vibratory signal 4 delivered by the vibration sensor 3.

[0130] The duct 11 can be a duct of a fluid installation, for example aeraulic, notably a suction duct, and the fluid 12 in flow in the duct 11 can be air, wet or not, for example filled with sawdust. The speed of flow of the fluid 12 within the duct 11 can be between 15 and 35 m/sec for example.

[0131] To calculate the value of the flow rate from the vibratory signal delivered by the sensor 3, the method can be as illustrated in FIG. 8.

[0132] The processing unit 5 is for example a microcontroller, the sensor 3 being linked to an input thereof, such that the microcontroller can sample the vibration amplitude as a function of time over a predefined time period, for example 1 s or more.

[0133] 3.NP temporally consecutive values, from the sensor 3, can thus be stored in step 110 in three tables NPi (i=1, 2 and 3) of the processing unit 5, previously initialized in step 100 (each table being also called storage space).

[0134] Next, the values successively loaded into the three tables can be shifted in time in step 120, so as to constitute sliding sampling time windows, the values stored in the table NP2 being stored in the table NP3 and replacing the oldest values contained therein, the values contained in the table NP1 being stored in the thus freed table NP2, and the newly sampled values, the most recent ones, being loaded in the table NP1.

[0135] In step 130, the frequency spectrum is calculated from the set of 3.NP values stored in the three tables NP1, NP2, NP3, which follow one another with a delay linked to the sampling frequency.

[0136] Next, in step 140, a scalar indicator P*.sub.max is calculated that is equal to the integration of the square of the amplitude of the vibratory signal in the frequency spectrum, between the frequencies 100 and 1000 Hz, for example.

[0137] This value P*.sub.max is representative of the speed of the flow, as illustrated in FIG. 7. The logarithm of it can be taken in step 150 (optional).

[0138] In FIG. 7, the frequency spectrum having led to one of the points of the calibration curve is represented.

[0139] To calibrate the device, flow rate measurements can be conducted with any type of flowmeter whose measurement accuracy is known, which makes it possible to define the parameters of the transfer function giving, from the calculation of P*.sub.max or the logarithm thereof, the value of the speed of the flow or of the volume flow rate, knowing the passage section.

[0140] It is thus possible to determine the bijective curve, notably the straight line (at least by segments) giving the speed of the flow from P*max or from the logarithm of P*max.

[0141] Once the calibration has been done, it is possible, upon each new calculation of P*max, to determine, by application of the transfer function, the speed of the flow in step 160, then the flow rate, if appropriate.

[0142] Such a method which involves only the signal delivered by the vibration sensor 3 gives a satisfactory accuracy for many applications, and offers the advantage of great simplicity of implementation, since the obstacle-forming part 2 is of reduced size and can be easily introduced into the duct, and there is no need to use a second sensor to improve the useful signal/noise ratio.

[0143] However, as illustrated in FIG. 2, the measurement device 1 can comprise an external vibration sensor 9, preferably an accelerometer with one or three axes, configured to detect the vibrations of the duct 11, notably induced by the flow of the fluid 12, and generate a corresponding external vibratory signal 10.

[0144] The external vibration sensor 9 is arranged on an outer surface of the duct 11. The sensor 9 is linked to a cable 10 making it possible to electrically power it and/or transmit the external vibratory signal 10 delivered by the external vibration sensor 9 to the processing unit 5. Thus, the processing unit 5 also receives the external vibratory signal 10 delivered by the external vibration sensor 9 and is configured to calculate the flow parameter of the fluid, notably the speed or flow rate thereof, from at least the vibratory signal 4 delivered by the vibration sensor 3 and from the external vibratory signal 10 delivered by the external vibration sensor 9.

[0145] FIGS. 3 to 6 schematically represent examples of measurement devices 1 according to the invention, mounted on the duct 11, observed on a transverse plane of the duct 11 (FIGS. 3a), 4a), 5a) and 6a)) and on a longitudinal plane of the duct 11 (FIGS. 3b), 4b), 5b) and 6b)). The examples of devices 1 represented in FIGS. 3 to 6 differ by the form of the obstacle-forming part 2.

[0146] The latter can have a beam form whose longitudinal axis is oriented at right angles to the direction of flow of the fluid 12 (FIG. 3), or a cylinder form, the bases of which are oriented at right angles to the direction of flow of the fluid (FIG. 4).

[0147] The obstacle-forming part 2 can also have a hemispherical form whose base is oriented parallel to the direction of flow of the fluid 12 (FIG. 5) or a spherical form (FIG. 6).

[0148] The dimensions A, B, C, D, E and F of FIGS. 3 to 6 lie for example between 1 and 30 cm.

[0149] The invention is not limited to the examples which have just been described.

[0150] For example, the measurement device is not limited to the determination of a flow parameter of a fluid in a duct such as the speed or flow rate thereof. Other parameters can be determined on the basis of the vibratory signal 4 delivered by the vibration sensor 3 and possibly on the basis of the external vibratory signal 10 delivered by the external vibration sensor 9. The processing unit 5 can thus make it possible to know in real time the state of operation of the fluid installation, and can notably make it possible to conduct a diagnosis, even conditional and/or predictive maintenance of the installation.