FR3036191B1 - METHOD FOR DETECTING FLUIDS MEASURING THE ULTRASONIC WAVE REFLECTED ON AN OUTER SURFACE OF THE HOUSING - Google Patents

Abstract

A method of detecting fluids by ultrasound, using cells (10) emitting and receiving ultrasonic waves through a front face (8) having an outer surface (12) in contact with the fluid to be detected in the external medium (44) ), this method emits ultrasonic waves (40), and then measures the amplitude (A) of the received waves (42) coming from the reflection on the outer surface of the front face (12), and compares it with that of the emitted waves.

Description

The present invention relates to a method for detecting the presence of fluids by ultrasound, and a device implementing such a method.

Many applications require detections or measurements of the presence of fluids, which can be liquid or gaseous, possibly with the presence of several mixed or laminated fluids. In particular, the presence or the level of liquids, or the proportions of several types of liquids can be detected in a mixture which is homogeneous or laminated.

However in some applications the fluid can be loaded with solid waste which disturb the operation of the detection devices.

In particular, water treatment in urban areas includes a sewage system that recovers sewage from homes and sends them to a treatment plant, which also receives rainwater in some cases.

In the case of thunderstorms resulting in a large water flow, a clogging of the sewerage network and an overload of the treatment plant which can damage it, it is generally used in water drainage pipes. spillway rain including a passageway at a defined level, allowing above this level to directly discharge water into the natural environment.

In this way, the flow of water directed to the treatment plant is automatically limited.

The regulation imposes a monitoring of the quantities of water discharged into the nature in the event of overflow, in particular the number of overflows and their durations, with penalties that can be attached to them. It is therefore necessary a reliable measuring means to perform this detection of water discharge.

One type of known detection means, presented in particular by the documents FR-A1-2949571 and FR-A1-2982362, uses a sensor with a technology of the capacitive type, which measures the variation of the permittivity of the medium with which it is in contact. forming the dielectric. Indeed the permittivity of the water being very different from that of the air, one can easily detect the presence of the liquid.

Low-cost, low-power detection means are provided which can make it energy-independent for measurement and data transmission with a built-in battery or battery.

However, experience in the field shows that this technology poses problems in the event of clogging of the sensor, in particular for rainwater that may contain waste, especially sludge or dead leaves.

It is noted with a lack of water overflow, a waste impregnated with water remaining stuck on the sensor, such as a sheet of paper or vegetable waste, causes the detection of presence of water. It is then possible to obtain a detection of the presence of continuous water between two thunderstorms, which distorts the quantity of overflows measured, as well as the duration of these overflows. The results can then be strongly modified.

Another type of known detection means uses mechanical sensors, including in particular a float rising on the surface of the liquid with a measurement of the height of this float, or a closed tube containing a water column whose underside is immersed in the liquid, with a measure of the pressure in this tube.

This type of sensor is economical and has low energy consumption, however it is also sensitive to the presence of waste that easily disrupt its operation. In addition hydraulic problems can arise. For example, in the case of a liquid level close to the detection threshold of the float, slight variations in the surface caused by eddies or waves can lead to multiple detections.

Another type of known detection means uses resistive sensors comprising two spaced-apart conductive electrodes arranged in the volume receiving the overflow water. Since the water has a much lower resistivity than air, the measurement of the current flowing between the electrodes indicates the presence of the liquid.

However, these sensors also have a reduced cost and low energy consumption, are highly susceptible to fouling by the deposition of waste, which retain moisture maintain a higher conductivity in the absence of overflow water.

Another type of known detection means uses ultrasonic sensors which measure the travel time, also called flight time, set by an ultrasonic wave emitted by this sensor to reach the surface of the liquid and return to it. By sending series of short ultrasonic pulses that propagate at the speed of sound in the air, we obtain the distance traveled which is proportional to the measured flight time.

These sensors remaining outside the liquid are insensitive to fouling by waste. By cons not immersed, they have installation constraints that make it difficult to use in a number of books. In addition they consume a lot of energy, which also imposes monitoring constraints and replacement of the means of supply.

In addition, the measurement of the liquid level is disturbed by the presence of foam or eddy on the surface. The sanitation networks often have a surface scum, this scum has the effect of absorbing the signal emitted by the sensor, preventing detection of the level. In general, the various failures caused by the fouling of the sensors have a direct consequence on the respect of the legislation, as well as on the dimensioning and the cost of the installations of water treatment.

The present invention is intended to avoid these disadvantages of the prior art.

To this end, it proposes a method for detecting fluids by ultrasound, using cells emitting and receiving ultrasonic waves through a front face having an external surface in contact with the fluid to be detected in the external medium, remarkable in that it emits ultrasonic waves, then measures the amplitude of the waves received in return from the reflection on the external surface of the front face, and compares it to that of the waves emitted.

An advantage of this method of detecting the presence of fluids is that the ultrasonic wave is transmitted with different amplitudes with respect to its emission, in the front face of the housing and in the materials of the external environment of this front face, because of the different acoustic impedances of these materials, by measuring the amplitude of the received waves reflected on the external surface of the front face which constitutes a controlled and stable wall in time forming a reference, it can be deduced by taking the ratio of the amplitude received on that emitted, the part of the wave which has been transmitted in the external environment and thus the nature of the materials of this medium.

We can then know the presence of different materials, for example the presence of water, or a wet fouling layer on the housing, or the stack of several fluids. In particular, the method provides reliable information on the presence of water, regardless of the fouling of the detection box.

The method for detecting the presence of fluids according to the invention may further comprise one or more of the following characteristics, which may be combined with one another.

The detection method may advantageously automatically adjust the measurement of the amplitude of the waves received in return as a function of the temperature measured at the front face. This thus makes it possible to compensate for the variation of this amplitude due to the modification of the acoustic impedance of the constituent material of the front face as a function of the temperature. This results in a constant quality detection over a wide temperature range.

The detection method may advantageously measure the time taken for the return on the reflected wave cells in the external medium, to deduce distances of different surfaces separating fluids from this medium. This gives the same system additional indications on fluid levels.

Advantageously, the method calculates the thickness of a fouling layer deposited on the front face, by measuring the time taken for the return on the reflected wave cells on the surface of this layer. It is easy to remotely monitor the clogging of the device to provide maintenance.

In addition, the method can measure the amplitude of the waves received in return from the reflection on surfaces of the external medium, and compare it to that of the waves emitted.

According to one embodiment, the method measures the number or duration of water flows in a spillway of a stormwater flow conduit. A reliable measure is obtained over time to follow the evolution of spills in relation to the requirements of the regulations. The invention also relates to a device for detecting the presence of fluids in an external medium, comprising means implementing a detection method comprising any one of the preceding characteristics.

Advantageously, the device comprises a sealed housing containing the cells. The device can then be disposed without damage at a submergible location.

Advantageously, the cells are applied to the inner surface of the front face transmitting the ultrasonic waves.

In particular the device may comprise two independent cells performing one emission and the other receiving ultrasonic waves.

Advantageously, the front face is formed in a plastic material of the "PVC" polyvinyl chloride type. This economical material, which can be molded easily, has an acoustic impedance very different from the air which facilitates the measurement of the amplitude of the wave reflected on the outer surface of the front face.

Advantageously, the device comprises, in a same housing containing the cells, means for measuring the amplitude of the reflected waves, and means for transmitting the results of the measurement to the outside. This provides a compact and economical package, containing in an integrated manner the various functions that can ensure its autonomous operation.

Advantageously, the device comprises measurement and adjustment means for adjusting the amplitude of the waves received in return as a function of the temperature measured at the front face. This makes it possible to compensate the variation of the amplitude resulting from the modification of the acoustic impedance of the constituent material of the front face as a function of the temperature. The invention furthermore relates to a stormwater spillway receiving overflow water from a rainwater flow conduit, having a surge water detection device comprising any of the above features. The invention will be better understood and other features and advantages will emerge more clearly on reading the following description given by way of example, with reference to the appended drawings in which: FIGS. 1 and 2 are respectively views front and section along the sectional plane ll-ll, a housing of a detection device according to the invention comprising a single cell carrying out the emission and reception of ultrasonic waves; - Figure 3 is a cross-sectional view of a spillway of a rainwater network, having a detection device according to the invention; FIG. 4 is a diagram of a detection device according to the invention, comprising two cells carrying out one transmission and the other receiving ultrasound waves; - Figures 5 and 6 are diagrams for a case without fouling, the amplitude of the waves emitted and received respectively in the air and in the liquid; and FIGS. 7 and 8 are diagrams showing, for a box with fouling, the amplitude of the waves emitted and received respectively in the air and in the liquid.

Figures 1 and 2 show an ultrasonic sensor 2 comprising a sealed housing comprising the front side indicated by the arrow "AV", a front face 8 transmitting ultrasonic waves, having an outer surface 12 intended to come into contact with a fluid. The rear face of the housing 2 has two lateral lugs 4 each having a bore 6, allowing it to be fastened flat on a support.

The housing comprises inside a piezoelectric cell 10 bonded to the inner surface of the front face 8, which emits ultrasonic waves 14 through this front face to the fluid, and which receives the waves reflected back. In particular one can use for the cell 10 a quartz, a synthetic ceramic "PZT", or a synthetic polymer such as polyvinylidine difluoride "PVDF".

An electronic card 16 connected to the piezoelectric cell 10, generates the electrical activation signal of this cell which emits the ultrasonic wave, and receives back the electric signal produced by this cell with the return of the reflections of this wave. The electronic card 16 also comprises means for processing the signal received to perform a processing, and means of communication to the outside which can use a connecting cable 18, or means without physical connection such as radiofrequency waves. In addition, a temperature sensor 17 is connected to the electronic card 16 to measure the temperature of the material of the front face 8, said electronic card 16 comprising adjustment means for adjusting the amplitude (A) of the reflected waves depending on the temperature measured at the front panel 8.

The housing has inside a temperature sensor 20 connected to the electronic card 16, which measures the ambient temperature.

The housing is made of a solid material resistant to external elements, sealing. The front face of the housing 8 is made of a material transmitting ultrasonic waves, such as a plastic material, a complex polymer material or a metallic material. Preferably, for the front face 8, a material having a thickness which may be of the order of a few millimeters is used, having an acoustic impedance close to that of the liquid to be measured in the case of a liquid detection, and remote from that air or gas present, to facilitate the detection of this liquid.

The housing can be made in particular by molding a plastic material such as a "PVC" polyvinyl chloride, a silicone, an acrylonitrile butadiene styrene "ABS" or a polyetheretherketone "PEEK", which allows in a single molding to achieve economically the different forms of this case.

The principle used by the ultrasonic sensor 2 comprises the emission of an ultrasonic wave 40 by the cell 10, which is partly transmitted externally to the medium containing the fluids, and partly reflected 42 on the outer surface of the housing 12.

If the acoustic impedance of the external medium is high, in particular in the presence of air, the amplitude of the wave 14 transmitted in this medium is very small, and the amplitude of the reflected wave 42 is then close to that On the other hand, if the acoustic impedance of the acoustic medium is low, in particular in the presence of water, then the amplitude of the transmitted wave 14 is large, and the amplitude of the reflected wave 42 is then very small compared to the transmitted wave 40.

It is also possible to detect the presence of a variety of fluids, comprising different liquids or gases, from measurements giving an indication of the acoustic impedance of the different materials encountered.

Note that the outer surface of the housing 12 is a reference surface that does not change over time, regardless of the fluids on the outside, and the fouling deposited on this surface.

In particular, it is possible to produce the front face 8 made of PVC which has the advantage of giving a ratio of the acoustic impedances of the water with respect to this material which is 2.1, whereas the ratio of the air with respect to this material is 7600. The great difference between these ratios makes it possible to obtain amplitudes of reflected waves very far apart.

Figure 3 shows a storm weir on a rainwater flow conduit 22 receiving water upstream 24 to discharge downstream 26 to a purification plant. As long as the flow of water is not too great, with normal rainfall, the flow conduit 22 is sufficient to evacuate this flow with a level not reaching the top of a partition wall 28.

When the flow of water becomes important, in the event of a pronounced storm, the level reaches the top of the partition wall 28, the surplus water flowing into a parallel channel 30 which discharges it into the nature.

An ultrasonic overflow sensor 2 is fixed in the parallel channel 30 on the partition wall 28, a little below the top of this partition, so as to face the opposite wall of this channel. In the event of a sufficiently strong thunderstorm, the overflow of water outside the flow duct 22 filling the parallel channel 30 is detected by the overflow sensor 2.

FIG. 4 shows, as a variant, a sensor comprising a front face 8 having the outer surface 12 facing the external medium 44, which in this example comprises a gas, and an inner surface formed by two inclined facets arranged symmetrically with respect to a perpendicular to this surface. external.

On a first facet there is a transmitting cell 10a sending the transmitted wave 40 on the outer surface 12, and on the second facet a receiving cell 10b receiving the reflected wave 42 on this outer surface. The two transmitting cells 10a and 10b of reception are connected to the electronic card 16. The operating principle of this sensor comprising two separate cells remains the same.

FIGS. 5 to 8 show on the horizontal axis the displacement D of the ultrasonic wave coming from the cell 10, which first passes through the front face of the casing 8 forming a solid, then leaves this casing towards the outside medium 44 perpendicular to the outer surface 12. The amplitude of the waves is indicated by the height of the drawn wave reported on the vertical axis A.

The method of detecting the presence of fluids is as follows. The cell 10 emits a wave 40 having an amplitude of 100%.

In FIG. 5 the external medium 44 is composed of the ambient air having a very strong acoustic impedance, the amplitude of the wave transmitted in this medium 14 is very small. On the other hand, the amplitude of the reflected wave 42 returning to the cell 10 is important.

The method then performs a measurement of the ratio of the amplitude of the reflected wave 42 to that of the transmitted wave 40, to obtain the percentage represented by this reflected wave. It can be deduced for a very high percentage that the external medium 44 is the ambient air. This percentage is then automatically adapted by the adjustment means of the electronic card 16 as a function of the temperature measured by the sensor 17.

In Figure 6 the outer medium 44 is composed of water coming directly into contact with the outer surface 12 which is clean. The amplitude of the wave transmitted in the water 14 is strong, equal to about two-thirds of that of the transmitted wave 40. The amplitude of the reflected wave 42 is then equal to substantially one-third of that of the emitted wave 40.

The method then performing the measurement of the ratio of the reflected wave 42 on the transmitted wave 40, obtains a ratio of about 33%. It is deduced that the external medium 44 is water.

Note that the transmitted wave 14 in the external medium 44 can then be reflected on a surface opposite to the outer surface 12, being at a variable distance, especially in the case of the parallel channel 30, and return to the cell 10.

However, the method knowing the thickness of the front face of the housing 8 and the speed of propagation of the wave in this front face, takes into account only the reflected wave 42 on the outer surface 12 which returns to the cell 10 with a predetermined time that does not change. It does not take into account a possible reflection on a surface of the external environment 44 returning later.

The outer surface 12 constitutes a reference forming for the transmitted wave 40 an invariable geometry, independent of the external environment that can be composite comprising several liquids or gases, and have adjustable shapes with for example a variable water level.

It is also possible from the device for detecting the presence of fluids to carry out additional calculations of distance of surfaces in the external medium 44, in particular calculations of a water level, by using the known technology for measuring the time of the fluid. Feedback response of the signal reflecting on these surfaces.

For this we record the return of the signals reflected on these surfaces, coming after the reflected wave 42 on the outer surface 12 which is the closest, and the distances are calculated knowing the speed of propagation of the wave in the materials crossed. .

The temperature probe 20 disposed in the housing makes it possible to correct the speed of propagation of the wave in the materials as a function of their temperature, in order to improve the accuracy of the distance measurements.

In Figure 7 the outer surface 12 first receives a fouling layer 52 having a surface 50 which is in contact with the external medium 44 consisting of air.

The fouling layer 52 may in particular comprise dead leaves or vegetable waste carried by the rainwater, being deposited progressively on the outer surface of the housing 12, which can maintain an internal humidity a certain time after stopping the water. flow of water into the external environment 44.

An amplitude of the wave 54 transmitted in the fouling layer 52 is obtained, which is strong because of the low acoustic impedance of the moisture impregnating this medium, then an amplitude of the wave 14 transmitted in the middle air. outside 44 which is very weak.

We then return to the cell 10 a first reflected wave 42 on the outer surface of the housing 12 which has a relatively small amplitude, substantially equal to one third of the transmitted wave 40, with a slight attenuation compared to the same device without fouling .

A second wave is then reflected on the surface of the fouling layer 50, which has a strong amplitude because of the small amplitude of the wave 14 transmitted in the air of the external medium 44. It is deduced from FIG. measuring these amplitudes with respect to that of the emitted wave 40, the presence of a wet fouling layer 52, then the absence of water in the external medium 44.

Moreover by measuring the additional time set for the return of the second ultrasonic wave reflected on the surface of the fouling layer 50, with respect to the first wave 42, and knowing the speed of propagation of the wave in this layer of fouling 52, it is possible to determine the thickness of this layer which gives interesting indications for facilitating the maintenance of the equipment.

It is also possible in the same way to determine a liquid level in the external medium 44 by measuring the return time of the wave reflected on the surface of this liquid.

In Figure 8 the outer surface 12 has a fouling layer 52 having a surface 50 in contact with the external medium 44 consisting of water.

We obtain an amplitude of the wave 54 transmitted in the fouling layer 52 which is strong, then an amplitude of the wave 14 transmitted in the external medium 44 which is also strong.

A first reflected wave 42 is then returned to the cell 10 on the outer surface of the housing 12 which has a relatively small amplitude, substantially equal to one third of the transmitted wave 40.

Then, a second wave reflected on the surface of the fouling layer 50, which has a small amplitude because of the high amplitude of the wave 14 transmitted in the water of the external medium 44, is then shortly thereafter. measurement of these amplitudes with respect to that of the emitted wave 40, the presence of a wet fouling layer 52, then water in the external medium 44. In general, a very high detection method is obtained. reliable, independent of sensor fouling which facilitates its implementation and maintenance, as well as the level of quality of the information given. In particular, it can be used for a rainwater weir, avoiding measurement errors and the costs they may incur.

It can also be used in many applications to detect the presence and thickness of various liquid or gaseous fluids, by detecting and measuring interfaces between these different fluids with different acoustic impedances.

Note that the housing which is advantageously sealed, has no fragile element in contact with the outside environment, nor any mechanical element in motion, which makes it a robust assembly. In particular, it is possible to produce a sealed housing that allows an approval for operation in an explosive atmosphere.

Claims (14)

1 - Method for detecting fluids by ultrasound, characterized in that it uses a sealed housing comprising a front face (8) having an outer surface (12) in contact with the fluid to be detected in the external medium (44), said sealed housing comprising cells (10, 10a, 10b) emitting and receiving ultrasonic waves through a front face (8), and emitting ultrasonic waves (40), and then measuring the amplitude (A ) waves received back (42) from the reflection on the outer surface of the front face (8), and compares it in percentage with that of the waves transmitted at a predetermined time. 2. Detection method according to claim 1, characterized in that it automatically adjusts the measurement of the amplitude (A) of the waves received back (42) as a function of the temperature measured at the front face (8) . 3. Detection method according to claim 1, characterized in that it measures the time taken for the return on the cells (10, 10b) of waves reflected in the external medium (44), to deduce distances of different reflecting surfaces of this medium (50). 4 - Detection method according to claim 3, characterized in that it calculates the thickness of a fouling layer (52) deposited on the front face (8), by measuring the time taken for the return on the cells (10, 10b) waves reflected on the surface of this layer (50). 5 - Detection method according to claim 3 or 4, characterized in that it measures the amplitude (A) of the waves received back from reflection on surfaces of the external medium (44), and compares with that of emitted waves. 6 - Detection method according to any one of the preceding claims, characterized in that it measures the number or duration of water flows in a spillway (30) of a rainwater flow pipe ( 22). 7 - Device for detecting the presence of fluids in an external medium (44), characterized in that it comprises means implementing a detection method according to any one of the preceding claims. 8 - Detection device according to claim 7, characterized in that it comprises a sealed housing containing the cells (10, 10a, 10b). 9 - Detection device according to claim 7 or 8, characterized in that the cells (10, 10a, 10b) are applied to the inner surface of the front face (8) transmitting the ultrasonic waves. 10 - Detection device according to any one of claims 7 to 9, characterized in that it comprises two independent cells carrying one emission (10a) and the other reception (10b) of ultrasonic waves. 11 - Detection device according to any one of claims 7 to 10, characterized in that the front face (8) is formed in a plastic material of the polyvinyl chloride type "PVC". 12 - Detection device according to any one of claims 7 to 11, characterized in that it comprises in a same housing containing the cells (10, 10a, 10b), means (16) for measuring the amplitude ( A) reflected waves (42), and means for transmitting the measurement results to the outside. 13 - Detection device according to any one of claims 7 to 11, characterized in that it comprises measuring and adjusting means for adjusting the amplitude (A) of the waves received in return (42) in function of the temperature measured at the front (8). 14 - Rainwater spillway (30) receiving the overflow water coming from a rainwater flow conduit (22), characterized in that it comprises a device for detecting the water of overflow according to one any of claims 7 to 13.