FR2607922A1 - Method and device for measuring flow rates - Google Patents

Abstract

According to the invention, a piezoelectric measuring sensor 1 receives, by solid conduction in a steel component having the form of a seal 34, the acoustic waves generated by the interaction between the flow 31 whose flow rate is to be measured, and a lug 32 formed on this component inside this flow. A reference sensor 11 makes it possible to disregard the background noise existing in the same frequency range. The invention applies in particular to the monitoring of auxiliary systems in nuclear power stations.

Description

Method and device for flow measurement
The present invention relates to the measurement of the flow rate of a fluid, in particular of a liquid which flows in a pipe. It finds particular application in nuclear power plants.

 According to a first known method for such a measurement, a diaphragm limiting the cross-section of the fluid and creating a pressure drop is placed in the fluid flow, and the difference in pressures on either side of this diaphragm is measured.

 This first known method has in particular the following drawbacks - I1 requires the installation of special flanges pierced with orifices on either side of the diaphragm to transmit the upstream and downstream pressures to a sensor which is external to the piping and which measures the difference of these pressures.

- And there is a risk of fluid leaking out of the piping by breaking the connection between these orifices and this sensor. As a result, there may be dispersion of the fluid at points distant from this piping. Such a risk is particularly troublesome in the case where the piping is part of an auxiliary circuit of a nuclear reactor.

 According to a second family of known methods, absolute speeds of propagation of acoustic waves in the fluid are measured, for example according to the direction of the flow and according to the opposite direction, the difference of these two speeds giving the speed of the flow. .

 Generally in such methods, the measurement waves, that is to say those used for measurement, are generated by transmitters from an electrical signal, and the measurement parameters, c> is ie those whose measurement gives the desired flow, are propagation velocities of these waves.

 Such methods are for example described in patent documents FR-A-2 467 392 (PANAMETRICS) - FR-A-2 551 204 (FAES) and US-A 2 826 912 (KRITZ). They have the drawback of requiring electronic time measurement circuits which are relatively complex and which exhibit particularly poor reliability in the presence of ionizing radiation. Such radiation is encountered in nuclear power plants and can damage semiconductor components.

The object of the present invention is in particular to allow a simple and precise measurement of a flow of fluid, in particular of liquid, using
a device whose manufacture and installation are inexpensive and whose reliability is good and relatively little compromised by the presence of ionizing radiation in the vicinity of the piping transporting the fluid.

 It relates to a method and a device for measuring the flow rate of a flowing fluid in a piping of known section.

 The method according to the invention comprises, like those of the second family of known methods indicated above, an operation of forming acoustic measurement waves interacting with this flow so that at least one parameter of these waves constitutes a representative measurement parameter of the speed of this flow, - and an operation of measuring this parameter to know this speed and therefore the flow rate of said fluid.

 Compared to this family of known methods, the method according to the present invention is characterized in that said measurement wave formation operation is carried out by placing a fixed flow-disrupting element in said piping, this disturbing element having the form of an irregularity in relief and / or recess on a generally regular internal surface of this piping, so that said measurement waves are generated by the interaction between this disturbing element and said flow, - said measurement parameter being a amplitude and / or frequency parameter of these waves.

 Using the attached schematic figures, a more specific description will be given below, by way of non-limiting example, of how the present invention can be implemented. When the same element is represented in several figures, it is designated therein by the same reference sign. It should be understood that the elements indicated may be replaced by other elements ensuring the same technical functions.

 Figure 1 shows a sectional view of a pipe carrying a device according to the invention, the sensors and electronic circuits being represented symbolically.

 FIG. 2 represents a block diagram of the circuits of this device.

 In the context of this description, we will first of all indicate specially various additional characteristics of the method and of the device given by way of example. This is because these characteristics appear to be advantageous in a more general manner, that is to say for the implementation of the present invention in many cases of application.

 These generally advantageous characteristics of the method are as follows: said measurement parameter is an amplitude in at least one predetermined measurement frequency domain.

- The amplitude of the acoustic waves in said measurement frequency range is measured not only (in 2 and 6) on a measurement sensor (1) which strongly receives the measurement waves and which provides a first measurement amplitude, but also (in 14 and 16) on a reference sensor (11) which receives these measurement waves more weakly and which provides a reference amplitude, and this reference amplitude is subtracted (in 19) from this first measurement amplitude to obtain a second measurement amplitude independent of the acoustic waves which propagate in said pipework in the range of measurement frequencies and which are generated at a distance from said flow-disturbing element (32).

- The amplitude of the acoustic waves is measured on each of the two so-called measurement sensors (1) and of reference (11) not only in said range of measurement frequencies to obtain said amplitudes of measurement (in 2 and 6) and of reference (in 14 and 16) but also in at least one control frequency domain essentially external both to this measurement domain and to the frequency domain of the waves generated by said interaction between the disturbing element and the flow, in order to obtain measurement sensor control amplitudes (in 3 and 5) and reference sensor control amplitudes (in 13 and 15), respectively, so that the possible appearance of a significant difference between these last two amplitudes indicates a difference of the operation of one of these sensors with respect to the other, this difference possibly being in particular a defect in a sensor which should be repaired.

- A difference signal between the two said control amplitudes is established (in 7) and a correction is made (in 10) whose importance increases with this signal and which affects said second measurement amplitude to obtain a third measurement amplitude independent of any moderate differences in sensitivity between said measurement and reference sensors.

- Said ranges of measurement and control frequencies are situated between 0.2 and 2 MHz and between 20 and 200 kHz, respectively, approximately, when said fluid is a liquid, in particular when this liquid is water. In this case, in fact, the waves whose frequencies are between 20 KHz and 200 KHz appear essentially due to the background noise of the installation of which the piping is a part (mechanical, friction, shocks) and to the background noise of the hydraulic, which makes it possible to compare the performance of the two sensors by comparing two signals which should follow analogous variations. On the contrary, the waves of frequencies between 200 KHz and 2 MHz appear essentially due to local anomalies created by said disturbing element 34 in the flow.

 Said generally advantageous characteristics of the device are as follows: - Said disturbing element (32) is formed on an internal surface (36) of a rigid wave exit piece (34) passing through said piping (30), this surface being internal to this piping, this part further having at least one lateral surface (38) through which it is in contact with this piping so as to maintain the sealing thereof, this part finally having a surface (40) external to this piping, said measurement sensor (1) being fixed to this external surface (40) so as to receive said measurement waves with little loss by solid conduction in the volume of this output piece from said disturbing element (32).

 - Said wave outlet part has the form of a wave outlet seal (34) which goes around said pipe (30) and interposed between two consecutive sections (42, 44) thereof, so to allow a simple realization of the device.

- Said wave outlet joint (34) is clamped between two flanges (46, 48) connecting the two said consecutive sections (42, 44) of the piping (30), so as to allow a simple installation of the device .

- Said wave outlet seal (34) is separated from each of the two said flanges (46, 48) by a seal (50, 52) made of a relatively soft material so as to both ensure the sealing of said piping (30) and limiting the transmission of acoustic waves from these flanges to this wave outlet joint at least in a range of measurement frequencies.

- In addition to said measurement sensor (1), which provides a first measurement amplitude in a range of measurement frequencies, the device includes a reference sensor (11) disposed on said piping (30) at a distance upstream from said disturbing element ( 32) for measuring a reference amplitude which is the local amplitude of the acoustic waves in the same range of measurement frequencies, and means (19) for subtracting this reference amplitude from this first measurement amplitude to obtain a second amplitude from independent measurement of the acoustic waves which propagate in said piping in the range of measurement frequencies and which are generated at a distance from said flow disturbing element (32).

- Each of the two so-called measurement (1) and reference (11) sensors is a piezoelectric chip provided with a mechanical damper and an electronic amplifier (2, 12) supplying two filters, a filter (4, 14) selecting the acoustic waves in said measurement frequency domain, the other filter (3, 13) selecting the acoustic waves in a control frequency domain external to the frequency domain of the acoustic waves generated by the interaction between the flow and said disturbing element, so that the possible appearance of a difference between the amplitudes measured by these two sensors in the control frequency range indicates a malfunction of one of the sensors and / or a correction to be made (in 10 ) at said second measurement amplitude.

 These generally advantageous characteristics having been indicated, a description will now be given more particularly of the elements represented.

 In FIG. 1 we see a pipe 30 which is for example part of an auxiliary circuit of a nuclear power station and in which water flows according to an arrow 31.

 The flow speed is close to one meter per second but could take significantly higher values without detracting from the effectiveness of the present invention.

 This piping is made of steel. Its section is circular. It has a number of valves, taps, elbows and flanges.

 According to the figure, an upstream section 42 and a downstream section 44 of this piping are connected by two flanges of the usual type 46 and 48 attached by welding and tightened by bolts 49. Between the two flanges, instead of a simple joint d The seal is interposed with a special hard steel seal 34 produced by machining and itself disposed between two seals made of softer material 50 and 52 in contact with its two lateral surfaces such as 38.

 This special seal constitutes the previously mentioned wave exit seal. The seals 50 and 52 isolate it to a certain extent from the waves which propagate in the wall of the pipe 30.

 The internal surface 36 of this seal is in continuity with that of the piping 30 except that it has a lug 32 which projects radially in the flow. The shape and the cross section of this lug are chosen so as to create disturbances within the flow, this lug constituting the flow-disturbing element previously mentioned.

 Although the disturbing element here is a lug, it should be understood that it could possibly consist of a hollow or undulations machined on the internal surface of the seal 34 or of any other element such as restriction orifices.

 On the outer surface 40 of the seal 34 is welded a measurement sensor 1 consisting of a piezoelectric pad behind which is arranged a shock absorber, not shown. The latter is intended to authorize a response in a global frequency range extending from 20 KHz to 2 MHz. It consists of an adhesive paste having, after thermosetting, a characteristic Zo impedance for acoustic waves. The material chosen is inorganic and has good thermal and electrical conductivity. By way of example, the JMI-46-13 glass paste sold by MATTEHEYLEC is used.

 Thanks in particular to the choice of the resonant frequency of the sensor 1, for example 600 KHz, this sensor is sensitive to the acoustic energy released by shocks on contact with the lug 34. It is also sensitive to vortex phenomena and whirlpool dropout.

 On the outside surface of the upstream section 42 at a distance from the seal 34 close to ten times the inside diameter of this section is welded the reference sensor 11 previously mentioned. It has the same structure as the sensor 1. This distance is suitable because the upstream section 42 is straight, at least between the two sensors. Such rectilinearity is desirable in order to minimize the background noise of hydrodynamic origin in the vicinity of the sensor 1.

 The functions of the reference sensor 17 have been previously indicated.

 The two sensors 1 and 11 are each arranged in a waterproof case 60 and 62 which contains a differential amplifier, 2 and 12 respectively. They are connected to amplification and conditioning circuits for the acoustic signal, signal analysis and measurement correction, interfacing delivering a standard output signal at 4 and 20 mA, control for performing a verification at least periodically of the sensor and conditioning part, and, optionally, switching making it possible to use the same conditioning block, analysis and interfacing for various types of sensors.

 The two booters are connected to these circuits and to the control station of the nuclear power plant by a triaxial cable with high immunity to radiation. This cable ensures the electrical supply of the active elements and the passage of the high frequency signals supplied by the amplifiers 2 and 12.

 The signals supplied by each amplifier, 2 or 12, are applied to two passive filters, one, 4 or 14, selecting the measurement frequency domain, the other, 3 or 13, that of control. The output signals of these filters are rectified at full alternation by rectifiers 6 or 16 and 5 or 15, respectively. The output signals from rectifiers 15 and 16 pass through inverters 17 and 18. The signals thus obtained have continuous components and variations at frequencies up to approximately 1 kHz.

 An adder 19 receives on the one hand said first measurement amplitude supplied by the rectifier 6, on the other hand said reference amplitude supplied by the inverter 18 to perform the subtraction which provides said second measurement amplitude.

 An adder 7 receives on the one hand said measurement sensor control amplitude supplied by the rectifier 5, on the other hand said reference sensor control amplitude supplied by the inverter 17 to supply said difference signal which must always be as low as possible.

 The latter is applied by subtraction to an adder 10 to provide said third measurement amplitude.

 Weighting circuits 9 and 10 make it possible to correct slight differences in sensitivity of the sensors 1 and 77 or gains of the amplifiers 2 and 12, respectively.

 A control module 8 also receives said difference signal supplied by the adder 7, compares it to a predetermined threshold, and controls an alarm generator 23 in the event of being exceeded. It also controls, as shown in the weighting circuit 9.

 The alarm generator 23 can also be triggered by high and low discrimination circuits 21 and 22 which each receive the output signals from the amplifiers 2 and 12 and respond to the exceeding of predetermined high and low thresholds.

 The output signals from the adder 10 and the alarm generator 23 are supplied in the form of electrical voltages. An interfacing circuit 24 transforms them into standardized signals having the form of intensities of 4 or 20 mA.

Claims (14)

1 / Method for measuring the flow rate of a flowing fluid in a piping (30) of known section, - this method comprising an operation of forming acoustic measurement waves interacting with this flow so that a parameter of at least these waves constitute a measurement parameter representative of the speed of this flow, - and an operation of measuring this parameter to know this speed and therefore the flow rate of said fluid, - this process being characterized by the fact that said operation of formation of measuring waves is carried out by placing a fixed flow-disrupting element (32) in said piping (30), this disrupting element having the shape of an irregularity in relief and / or in hollow on a generally regular internal surface of this piping , so that said measurement waves are generated by the interaction between this disturbing element and said flow, - said measurement parameter being an amplitude and / or frequency of these waves. 2 / A method according to claim 7, characterized in that said measurement parameter is an amplitude in at least one predetermined measurement frequency range. 3 / A method according to claim 2, characterized in that the amplitude of the acoustic waves in said measurement frequency range is not only measured (in 2 and 6) on a measurement sensor (1) which strongly receives said waves measurement and which provides a first measurement amplitude, but also (at 14 and 16) on a reference sensor (11) which receives these measurement waves more weakly and which provides a reference amplitude, and we subtract (at 19) this reference amplitude of this first measurement amplitude to obtain a second measurement amplitude independent of the acoustic waves which propagate in said pipework in the measurement frequency range and which are generated at a distance from said flow-disrupting element (32). 4 / A method according to claim 3, characterized in that the amplitude of the acoustic waves is measured on each of the two said measurement sensors (1) and of reference (11) not only in said range of measurement frequencies to obtain said amplitudes of measurement (in 2 and 6) and of reference (in 14 and 16), but also in at least one control frequency domain essentially external both to this measurement domain and to the frequency domain of the waves generated by said interaction between the disturbing element and the flow, to obtain amplitudes for measuring sensor control (in 3 and 5) and for reference sensor control (in 13 and 15), respectively, so that the appearance possible a significant difference between these last two amplitudes indicates a difference in the operation of one of these sensors compared to the other. 5 / A method according to claim 4, characterized in that it establishes (in 7) a difference signal between the two said control amplitudes of the measurement and reference sensor and a correction is made (in 10), the importance increases with this signal and which affects said second measurement amplitude to obtain a third measurement amplitude independent of any moderate differences in sensitivity between said measurement and reference sensors. 6 / A method according to claim 2, characterized in that said measurement frequency range is located between 0.2 and 2 MHz approximately when said fluid is a liquid. 7 / A method according to claim 4, characterized in that said ranges of measurement and control frequencies are located between 0.2 and 2 MHz and between 20 and 200 kHz respectively, approximately, when said fluid is a liquid. 8 / Device for measuring the flow rate of a flowing fluid in a piping of known section (30), - this device comprising means for forming acoustic measurement waves interacting with this flow so that a parameter of at least these waves constitute a measurement parameter representative of the speed of this flow, - and means for measuring this parameter to know this speed and therefore the flow rate of said fluid, - this device being characterized by the fact that said wave formation means essentially consist of a fixed flow-disturbing element (32) disposed in said piping (30) and having the shape of an irregularity in relief and / or recess on a generally regular internal surface of this piping, so that these waves are generated by the interaction between this disturbing element and said flow, - said measurement means comprising a measurement sensor (1) receiving these waves for ur measure an amplitude and / or frequency parameter, this parameter constituting said measurement parameter. 9 / Apparatus according to claim 8, characterized in that said disturbing element (32) is formed on an internal surface (36) of a rigid piece of wave outlet (34) passing through said piping (30), this surface being internal to this piping, this part further having at least one lateral surface (38) through which it is in contact with this piping so as to maintain the sealing thereof, this part finally having an external surface (40) to this piping, - said measurement sensor (1) being fixed to this external surface (40) so as to receive said measurement waves with little loss by solid conduction in the volume of this output piece from said disturbing element ( 32). 10 / Apparatus according to claim 9, characterized in that said wave outlet part has the form of a wave outlet seal (34) around said piping (30) and interposed between two consecutive sections (42, 44) thereof, so as to allow a simple embodiment of the device. 11 / Apparatus according to claim 10, characterized in that said wave outlet seal (34) is sandwiched between two flanges (46, 48) connecting the two said consecutive sections (42, 44) of the piping (30) , so as to allow a simple installation of the device. 12 / Apparatus according to claim 11, characterized in that said wave outlet seal (34) is separated from each of the two said flanges (46, 48) by a seal (50, 52) consisting of a relatively soft material so as to both seal said piping (30), and limit the transmission of acoustic waves from these flanges to this wave outlet joint at least in one area of measurement frequencies. 13 / Device according to claim 9, wherein said measurement sensor (1) provides a first measurement amplitude in a range of measurement frequencies, this device being characterized in that it further comprises a reference sensor (11 ) arranged on said piping (30) at a distance upstream from said disturbing element to measure a reference amplitude which is that of the acoustic waves in the same range of measurement frequencies, and means (19) for subtracting this reference amplitude from this first measurement amplitude to obtain a second measurement amplitude independent of the acoustic waves which propagate in said piping in the measurement frequency range and which are generated at a distance from said flow disturbing element (32). 14 / Apparatus according to claim 13, characterized in that each of the two said measurement sensors (1) and reference (11) is a piezoelectric pad provided with a mechanical damper and an electronic amplifier (2, 12) supplying two filters, a filter (4, 14) selecting the acoustic waves in said measurement frequency domain, the other filter (3, 13) selecting the acoustic waves in a control frequency domain external to the wave frequency domain acoustics generated by the interaction between the flow and said disturbing element (32), so that the possible appearance of a difference between the amplitudes measured by these two sensors in the control frequency range indicates a malfunction of one of the sensors and / or a correction to be made (at 10) to said second measurement amplitude.