FR2777354A1 - Turbidity probe for checking effluent discharges - Google Patents

Abstract

The interface (19,20) between the optical emitter (121) and sensors (122) of a turbidity probe (1) is kept clean by ultrasonic waves at a frequency of 20-50 kHz which cause micro-cavities at the sensor surface which implode and clean the surface between measurements. An Independent claim is included for a turbidity meter using the above process. Infrared light at a wavelength of 700-1200 nm is emitted and deflected light is captured by a sensor (9). The two optical pieces used are positioned at 30 deg to the surface. The probe is sealed and can be immersed totally in the liquid being tested.

Description

l 2777354 Method and device for optical measurement of the transparency of a

  The present invention relates to a method and device for

  optical measurement of the transparency of a liquid.

  The technical sector of the invention is the field of research or analysis of materials, in particular for liquids, by optical means. The main application of the invention is to be able to determine the turbidity of water, essentially to control its quality, by detecting in particular suspended or emulsion materials, such as hydrocarbons, which would be mixed therewith; the determination of this turbidity is described in the European and French standard NF, EN 2707 of 1994, which fully reproduces the ISO 7027 standard of 1990 and to which the person skilled in the art can refer for better

  possible understanding of the present invention.

  It is recalled in particular that in liquids, the turbidity results from the presence of undissolved materials which are finely dispersed: it can be determined by measuring the attenuation of the luminous flux during its passage through the liquid, or by measuring the intensity of the scattered light; light scattering is indeed a property of liquids which can be used to measure this turbidity; the European standard referenced above describes four optical methods for determining the turbidity of water to obtain field information on surface water, drinking water and waste water. As turbidity is a global parameter for determining the level of pollution or efficiency of an industrial process, the present invention can have many uses such as: - monitoring of discharges at the outlet of treatment plants, loaded waste water, - control of the purification process or industrial process, - quality of the water in the settling basins, river waters and lakes, - detection of anomaly of operation on filters, industrial separators,

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  - control of industrial effluents, such as in particular petroleum, control of deballasting of oil tankers,

  - control of discharges into sea of bilge water from ships.

  Numerous devices have thus been developed to allow the measurement of turbidity in an aqueous medium and more recently, to meet the above standard; some of these devices have been the subject of patent applications, such as application EP 596231 published on May 11, 1994, or international application WO 9800701 published on January 8, 1998, which describes the combination of a nephelometer and a turbidimeter; remember that nephelometry is the measure of

  concentration of an emulsion according to its transparency.

  If these optical measuring devices are entirely satisfactory with regard to taking the measurement of the optical intensity of a given light after having crossed a determined distance in the liquid to be controlled, the actual measurement is often altered by the fact that dirt such as hydrocarbons can be deposited on the surface of optical interfaces immersed in the liquid; these allowing on the one hand the emission of light in this liquid, and on the other hand the reception of this one to make the measurement of it: to date, the processes and devices based on the principle of wiper

  are insufficient and require diligent maintenance.

  The problem is therefore to be able to guarantee a cleanliness of said optical interface surfaces before each measurement so that they are reliable and without mechanical device requiring a

heavy maintenance.

  One solution to the problem posed is a method for optical measurement of the transparency of a liquid from a turbidity analyzer, comprising at least one light emitter passing through an optical part, such as a bar, an optical fiber or the like. , interfacing with the liquid thus illuminated, and at least one measurement cell receiving, through a second optical interface piece, part of said light having traveled a given distance in said liquid. According to the invention:

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  - In the vicinity of the optical / liquid interfaces, transmitters and receivers of said optical parts in contact with said liquid, ultrasonic waves are generated; - This creates gaseous micro-cavities in the liquid and pickles and cleans said interface surfaces when these microcavities implode - we stop the emission of said ultrasonic waves and we then note

  the measurement of the light received by the cell.

  In a preferred embodiment, the device according to the invention comprises a probe submersible in the liquid, and the sealed housing of which comprises at least the light emitter, the measurement target, their associated optical interface parts and the generator ultrasound whose flag integrates the two said optical parts which have

  thus a common emission surface with the latter.

  The result is new methods and devices for measuring the transparency of a liquid responding to the problem posed and making it possible in particular to measure the turbidity of said liquid with all the reliability desired. In fact, unlike current turbidimeters, the device according to the invention allows, in particular for in situ measurements, good measurement qualities, whatever the degree of soiling of the liquid analyzed: in fact, the ultrasound emitted prevents on the one hand, any development of microorganisms and on the other hand, the deposition of any

  dirt on the optical interfaces.

  In addition, the micro-cavitation caused by ultrasonic waves makes it possible to homogenize the liquid medium by emulsifying it when it is in particular confined in a measurement cell: this phenomenon makes it possible to make reliable and simplify detection such as hydrocarbons residual in oil discharges; because otherwise they amalgamate in certain parts of the liquid, which can distort the measurement since if this amalgam passes through the optical beam, the measurement taken will give a measurement much higher than the average turbidity of the medium, and conversely, if this amalgam is out of the beam, the measurement will be much too weak and therefore, in all cases, not representative

  the average turbidity of the liquid.

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  In addition, the installation conditions are fairly simple and adaptable to many sites, either by simple immersion of a probe in the liquid, or by the insertion of optical and ultrasonic interfaces in the wall of a pipe or in a mini emulsion tank, etc ... We could cite other advantages of the present invention but those mentioned above already show enough to prove the

novelty and interest.

  The description and the figures below represent an example of

  embodiment of the invention but have no limiting character. Other embodiments are possible within the scope and scope of this invention, in particular: - by changing the arrangement of the constituent elements of the submersible probe as shown, - by arranging the elements necessary for the following method: invention, not in a probe, but behind a wall of a container or a shell or a pipe, etc ..., - by using the device or the method for transparency measurements which are not only those of turbidity, - by measuring not the light scattered by an incident beam, but the light directly emitted by it after it has crossed a given distance in the liquid, thus after diffusion and partial absorption in it this, and then arranging the cell

  receiver and its optical interface part in front of the transmitter beam.

  Figure 1 is an overview of a following device

  the invention, comprising a probe submersible in a tank.

  Figure 2 is a simplified and enlarged sectional view of the probe

  submersible shown in Figure 1.

  The device for optical measurement of the transparency of a liquid 2 according to the invention comprises a turbidity analyzer of known type, comprising at least one light emitter 7 passing through an optical piece 121 of interface with the liquid 2 thus lit, and at least one measurement cell 9 receiving, through a second optical interface piece 122, part of said light 10 having traveled a distance

given in said liquid 2.

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  According to the invention, at least one ultrasonic generator 15 whose horn 13 is disposed near at least one optical interface part 12 defined above, emits ultrasonic waves 211 sweeping at least the surface of the interface 19, 20 of this part, in contact with said liquid 2, and propagating in said liquid 2, in the vicinity of this surface 19, 20 and in all directions around it, covering

at least said surfaces 19, 20.

  Preferably, the optical interface part (s) 121, 122 is, or are integral and even integrated in the pavilion 13, as shown in the attached figures, and the emitting surface 19 and / or the receiving surface 20 is, or are located in the plane of that 21 of said pavilion 13. In the case where it is desired to measure the light scattered 8 laterally by the light cone 62 emitted by the emitter 7 in the liquid medium 2, said optical parts 121 and 122 are arranged at a given angle ca with their emission 19 and reception 20 surfaces in the same plane: the angle ax is determined such that the optical part 122 of the interface of the measurement cell 9 is captured, the light 8 diffused at least 90 from that 62 emitted in the liquid 2 through the optical interface part 121. Preferably, said optical parts 12 are arranged at an angle cc, such that the light beams 61 and 10 which pass through them, make an angle of at least 30, or in fact preferably 30, or 180, in the liquid 2 in taking into account the indices and the refraction coefficients between the material of said optical parts and the

liquid 2.

  The beam of emitting light 61 is preferably infrared light at a wavelength between 700 and 1200 nanometers, such as for example of the order of 850 nanometers, but could also be ultraviolet light of length d wave between 150 and 400 nanometers, or even visible with a wavelength between 400 and 700 nanometers, said beam 61 being concentrated towards said optical part 121 by a lens 111 collimating the light emitted by the emitter 7. Similarly , the light beam 10 captured through the optical interface piece 122 passes through a lens 112 of

  convergence to focus it on the measuring cell 9.

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  The ultrasonic generator 15 comprises in a known manner, in addition to the horn 13 for transmitting the ultrasonic waves 211, which can be made of titanium to be as light as possible, a rear counterweight

  14, preferably brass to be heavy, and piezo- ceramics

  electrics 16 supplied, by contact with the electrodes, with high voltage current 17, generating vibrations at the desired frequency to the assembly of the generator 15: the latter is fixed, on the one hand by a prestressing screw holding the assembly secured and, on the other hand by any suspension device, such as elastic studs isolating it from the other elements constituting the device, such as in particular, the sealed housing 11 of the probe 1 submersible in the liquid 2 and shown on the

  attached figures as an example of embodiment.

  Said box It in fact comprises at least the light emitter 61, the measurement cell 9, their optical interface parts 12 and the ultrasound generator 15: said probe 1 is connected to any connecting cable 3 to a box control 4 located on the surface, above the tank 22 for example, measurement; said housing 11 also comprises at least one housing 18 providing the electrical interface between said connecting cable 3 and the three basic elements making up said probe, and which are the light emitter 7, the measurement cell 9 and the generator d ultrasound 15 integrating the two optical interface parts associated with

  the light emitter and the measuring cell.

  The ultrasonic generator being suspended inside the housing 11 of the probe 1, is independent of the other electrical elements, since only the light beams 61 and 10 pass through its pavilion 13, and the housing 11 seals around its emitting surface 21 of ultrasound 211. In the case where the device according to the invention is not installed in a probe comprising a closed housing, the basic elements described above and making up the latter, can be simply installed in a housing or behind a wall integrated into that isolating the liquid to be checked, from the rest of an installation for example, such as for a ship's hull, a wall of piping or of a tank ... Preferably, for decrease the active surface which can trap the air from the micro cavitations created and which then implode, ensuring

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  cleaning of the surface 21 and therefore of that of the interface parts, the housing 11 of the probe has a convex conical part 5 surrounding the surface 21 of the horn 13 of ultrasound emission: said waves

  Ultrasonic are preferably of frequency from 20 to 50 kHz.

  Said control box 4 on the surface ensures, on the one hand, the control and the supply of the ultrasound generator 15 before any optical measurement, the supply of the light emitter 7, and the processing of the detected optical measurement by the receiver 9 having captured the light scattered laterally and / or emitted directly in the axis of the emitting beam, after transmission in the liquid 2, which signal from the sensor being preferably pre-amplified in the interface box 18 located in probe 1; the control unit 4 being supplied by any available current source 41 and comprising any device for displaying the result of the measurement 42; it is possible to process the measurements and the emission of ultrasound for two, four or six probes thanks to

  multi-channel devices by multi-plexing.

  The method and device for optical measurement of the transparency of a liquid according to the invention, in addition to its technical interest making it possible, for example in the context of a treatment plant, on the one hand, of upstream measurements where the water is very loaded and, on the other hand, downstream measures o

  the waters are lightly charged, offers a certain economic interest.

  The measurement ranges for the transparency of the turbidity of the liquid 2 can be adjusted as a function of the medium, either for example from 0 to 100 NTU or 0 to 5000 NTU for highly charged waters (NTU being the abbreviation for "Nephelometry Turbidimetry Unit "defined by

  standards in this area), or 0 to 20 grams per liter for sludge.

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Claims (10)

  1. Method for optical measurement of the transparency of a liquid (2) from a turbidity analyzer, comprising at least one light emitter (7) (61) passing through an optical part (121) interfacing with the liquid (2) thus illuminated, and at least one measuring cell (9) receiving, through a second optical interface part (122), part of said light (10) having traveled a given distance in said liquid (2) , characterized in that: - in the vicinity of the optical / emitting liquid (19) and receiving (20) interfaces, ultrasonic waves are generated; - This creates gaseous microcavities in the liquid (2) and pickles and cleans said interface surfaces (19, 20) when these microcavities implode i5 - we stop the emission of said ultrasonic waves (211), and we   notes the measurement of the light (10) received by the cell (9).   2. Method according to claim 1, characterized in that the light (8) scattered at least 30 of that (62) emitted is captured by the optical part (122) of interface of the measurement cell (9) in the liquid (2)   through the optical part (121) of the transmission interface.   3. Method according to any one of claims 1 or 2,   characterized in that ultrasonic waves are generated at frequencies of at 50 kHz.   4. Method according to any one of claims 1 to 3,   characterized in that infrared light (61) is emitted at a length   wave between 700 and 1200 nanometers.   5. Device for optical measurement of the transparency of a liquid (2) comprising a turbidity analyzer, comprising at least one light emitter (7) (61) passing through an optical part (121) interfacing with the liquid (2 ) thus lit, and at least one measuring cell (9) receiving, through a second optical interface piece (122), part of said light (10) having traveled a given distance in said liquid (2), characterized in that it comprises at least one ultrasonic generator (15) whose flag (13) is arranged near at least one optical interface part (12) and emits ultrasonic waves 9 2777354   scanning at least the surface (19, 20) of this interface which is in contact with said liquid (2).   6. Device according to claim 5, characterized in that the optical interface part (12) is integrated in the pavilion (13) and its emitting surface (19) is located in the plane of that (21) of said pavilion (13 ).   7. Device according to any one of claims 5 or   6, characterized in that it comprises a probe (1) submersible in the liquid (2), and whose sealed housing (1,) comprises at least the light emitter (61), the measurement cell (9) , their associated optical part (12)   interface and the ultrasonic generator (15).   8. Device according to any one of claims 5 to 7,   characterized in that the ultrasonic generator (15) is suspended inside a housing (11) which seals around the surface   transmitter (21) of the ultrasonic emission pavilion (13).   9. Device according to any one of claims 7 or   8, characterized in that said housing (11) comprises a conical portion (5) convex, surrounding the surface (21) of the horn (13) of ultrasonic emission.   10. Device according to any one of claims 5 to 9,   characterized in that the optical parts (12) are arranged so that the light beams passing through them make an angle of at least 30 in the liquid (2).