RU2471175C1 - Method of determining turbidity of medium - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method involves detecting radiation scattered by the analysed medium using a photodetector which is a photodetector matrix which enables to obtain an image of the scarred radiation. Contours of spots of parasitic deposits on the window are then selected on the image and their relative area is determined in order to determine the contamination level of the window. The brightness profile is determined from the middle horizontal line of the frame of the photomatrix. The brightness profile is corrected on sections distorted by deposit spots, and said profile is smoothed via a filtration procedure. Turbidity of the medium is then determined using an empirical formula.

EFFECT: image has higher noise-immunity and less dependence of the result on presence of parasitic deposits on the photodetector windows.

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Description

The invention relates to the field of measuring technology and can be used for flow control of water quality, environmental monitoring, measuring the concentration of emulsions and suspensions.

Turbidity is an optical quantity characterizing the ability of a medium to scatter light, which is measured in order to determine the concentration of suspended particles in a medium. Typically, turbidity of liquid or gaseous media is measured using turbidimetric or nephelometric methods.

A turbidimetric method for determining turbidity is such a method in which the emitter and radiation receiver are opposite each other, the photodetector detects radiation attenuated in the medium [Andreev B.C., Popechitelev EP Laboratory instruments for the study of liquid media. - L .: Mechanical engineering. - 1981. - S.99-101].

The nephelometric method for determining turbidity is characterized in that the radiation axis is located at a certain angle to the optical axis of the receiver, typically at an angle of 90 °, and the photodetector receives radiation scattered by the particles [Andreev B.C., Popechitelev EP Laboratory instruments for the study of liquid media. - L .: Mechanical engineering. - 1981. - S.99-101].

When measuring the turbidity of the medium in field (industrial) conditions, it is very important to ensure continuous continuous measurements without the participation of maintenance personnel. However, under conditions when parasitic deposits (sticky particles of oils, resins, clays, salt deposits, algae growths, etc.) are formed on the transparent windows of the photodetector, the transparency of the window gradually decreases, which leads to a significant error and loss of operability of the device.

To combat this drawback, various methods are used:

- periodically turned brushes [Model WW102: Window Wiper Controller and Actuator: Tech. Wedgewood Technology Company Information, http://www.wedgewoodtech.com];

- supply to the window of the photodetector jet of water, air [RF Patent for utility model No. 2370754, publ. 10/20/2009];

- periodic injection of solvents or detergents into the measuring chamber [Belyakov V.L. Automation of oil and water field preparation. - M .: Subsoil. - 1988. - P.133];

- exposure to windows with ultrasound [VisoTurb and ViSolid - new sensors for turbidity and solid matter measurement: Tech. Company Information WTW. http://www.wtw.com/media/US_O_05_TSS_028_033.pdf];

- heating the glass of the window of the photodetector [Belyakov V.L. Automation of oil and water field preparation. - M .: Subsoil. - 1988. - P.133].

However, all of these methods are not always cost effective and reliable. So, the cleaning device works irrationally (too often), and the presence of mechanical moving parts is often generally unacceptable according to technical conditions.

One of the common approaches to solving such problems in technology is to use hardware and information redundancy, due to which it is possible to organize an analysis of the incoming measurement information and the rejection of samples distorted by noise. The relative number of distorted readings is a measure of assessing the degree of susceptibility of measurements to interference, and can serve as a criterion for deciding whether to turn on one or another means of combating interference.

In this particular area, a possible solution to the problem lies in the use of multisensor systems. Such multisensor systems are photodetector arrays - devices containing a large number of photodetector elements - pixels (in contrast to discrete photodetectors with one sensitive element). Typically, a photomatrix is a specialized integrated circuit consisting of photosensitive elements and an electronic circuit for pre-processing and digitizing signals. Photomatrixes can be performed using CCD technology [Baker V.D., Barb D.F., Burke H.K. Charge coupled devices: Per. from English / Ed. D.F.Barba. - M .: Mir, 1982] or according to CMOS technology [Zimmermann H.K. Integrated Silicon Optoelectronics. - Springer, 2nd ed. Edition, 2009. - 388 p.].

Processing images obtained on a photomatrix can be performed using universal software products, such as LabView. It is convenient to analyze the information about the brightness distribution on the pixels of the matrix using a procedure that allows you to get the so-called brightness profile - the intensity curve of the image pixels along a given line, for example, a horizontal frame line [Yu.V. Visilter, S.Yu. Zheltov. etc. Processing and analysis of digital images with examples on LabView IMAQ Vision. - M.: DMK Press, 2007. - 464 p. - P.155].

The method for determining turbidity closest to the proposed one is a method implemented in a nephelometer for measuring turbidity of water [US Patent No. 7,663,751 B1 IPC G01N 21/00, publ. 02.16.2010]. The method consists in the fact that probing radiation is passed through the analyzed medium and the radiation scattered by the photodetector is recorded, separated from the medium by a transparent window and located at an angle of 90 degrees relative to the optical axis of the emitter, then the sought value of the turbidity of the medium is calculated from the signals of the photodetector. The described method can have many options, differing from each other in various details, in particular, in the prototype use a special radiation wavelength equal to 525 nm, which provides increased sensitivity of the method.

Such a method, however, does not ensure measurement invariance with respect to the contamination of the photodetector window, which is used as a discrete device (for example, a photodiode), and in the case of depositing a sticky dispersed phase on the window, does not have any means of automatic protection from this factor, which necessitates the establishment of a short inter-regulatory period to maintain acceptable metrological reliability.

The problem solved by this invention is to increase the noise immunity of the method and to achieve independence of measurements of turbidity of the medium from the presence of spurious deposits on the windows of the photodetector with minimal use of the cleaning procedure.

The problem is solved due to the fact that in the method consisting in the fact that probing radiation is passed through the analyzed medium and the radiation scattered by the medium is detected by a photodetector, separated from the medium by a transparent window and located at an angle of 90 degrees relative to the optical axis of the emitter, then the sought-for signal is calculated the turbidity of the medium, according to the invention, the registration of scattered radiation is performed by a photodetector, which is a photodetector matrix, with which radiate a picture of the radiation scattered by the particles, then select the contours of stains of stray deposits on the window on the resulting image and calculate their relative area to determine the degree of contamination of the window, determine the brightness profile from the mid-horizontal line of the photomatrix frame, adjust the brightness profile in areas distorted by the spots of deposits, and it is smoothed out using the filtration procedure, then the turbidity of the medium is determined by the empirical formula:

where U1 is the output signal of the photodetector cell, measured at the center point of the frame,

U2 is the output signal of the photodetector cell, taken on the same line at the peripheral point of the frame, separated from the edge of the frame by a fixed small number of pixels.

The invention is illustrated by drawings.

Figure 1 presents a General diagram of a nephelometer that implements a method for determining turbidity.

On figa-2c shows a picture of the distribution of light on the photomatrix for different values of the turbidity of the medium.

Figure 2g shows a picture of the distribution of pixel brightness along the average horizontal line of the frame obtained from the photomatrix for different values of the turbidity of the medium.

On figa shows a picture of the distribution of light on a photomatrix, taking into account contamination of the window of the photodetector by parasitic deposits.

On figb shows a picture of the distribution of brightness of pixels along the average horizontal line of the frame obtained from the photomatrix, for the case when the picture is distorted by the presence of deposits.

Figure 3c shows a picture of the distribution of pixel brightness along the mid-horizontal line of the frame after applying a special procedure for “cutting out" distorted sections and replacing them with averaged values.

On figg shows a picture of the distribution of brightness of pixels obtained from the previous image by low-pass filtering.

Figure 4 shows a graph of the turbidity of the medium τ on the ratio R, calculated by the brightness of the pixels of the photomatrix.

The device (Fig. 1) contains a radiator 1, a window of a radiator 2, a lens 3, a window of a photodetector 4, a photomatrix 5, a cuvette 6. Position 7 denotes particles of a medium, 8 - a probe beam and 9 - scattered radiation. Photomatrix 5 is connected to the input of the measuring and computing device (IVU) 10 via the bus 11. The emitter 1 is powered from the corresponding control output of the IVU 10 through the bus 12.

The method is implemented as follows. At the beginning of the operation cycle, according to the signal of the IVU 10, the emitter 1 generates a probe beam 8, which passes through a transparent window 2 into the test medium 6. The scattered radiation 9, due to the presence of particles 7, enters the lens 3 located at an angle of 90 degrees relative to the optical axis of the emitter, through a transparent window 4. Using a photomatrix 5, a pattern of attenuated radiation is recorded, which may be distorted by contamination of the photodetector window. The signal from photomatrix 5 is fed to the IVU 10. The picture of the light distribution distorted by pollution obtained on the photomatrix (Fig. 3, a) is subjected to program processing, namely: the contours of stains of stray deposits on the window are distinguished in the image, relative to the total area occupied by particles pollution, to the entire image area determine the degree of contamination of the photodetector window k. If k exceeds a certain threshold value, for example, 20%, a decision is made to clean the window (the PMD gives a signal about the need to manually clean the device or enable automatic cleaning of the device). The brightness profile is also determined by the average horizontal line of the photomatrix frame (Fig. 3, b), the brightness profile is adjusted in the areas distorted by the spots of deposits (Fig. 3, c), and its smoothing is performed using the filtering procedure (Fig. 3, d) . Then calculate the ratio R:

The corresponding values of U ₁ and U ₂ on the brightness profile are shown in Fig. 3, g. Then, according to the empirical formula (1), the form of which is determined in advance during the calibration process, an example of which is shown in Fig. 4, the turbidity τ is determined.

An example of a specific implementation of the method

As a result of the action of the probe radiation 8 and its scattering by particles 7 on the photodetector matrix 5, the image shown in Fig. 3, a is obtained. It is distorted by stains of parasitic deposits. The width of the photomatrix frame is 800 pixels. After digitizing the pixel signals in the IVU 10 using the software procedure for spotting outlines, the boundaries of the spots are indicated and a separate image is obtained that contrasts strongly (stray spots are black, everything else is white), then the relative area of the spots on the frame is calculated, which determines the degree of window contamination photodetector. For example, for figure 3, and it is 2.2%. If necessary, this value is used to decide on the procedure for manual or automatic window cleaning. In addition, figure 3, and build the brightness profile along the mid-horizontal line of the frame. It will look, as shown in figure 3, b, the dark spots of the deposits will correspond to the dips on the curve. Further, the distorted sections of the profile curve are corrected using a procedure that replaces the brightness values of pixels corresponding to dark spots with average brightness values of pixels located before and after the spot. The result is a picture depicted in figure 3, c. The resulting image is subjected to low-pass filtering (smoothing), after which the profile curve acquires the correct bell-shaped shape shown in Fig. 3, d. Then, pixels with numbers 400 (mid-point of the profile) and 700 (peripheral point of the profile, 100 pixels apart from the edge) are then selected. ) and determine the values of their brightnesses, respectively, U1 and U2. Next, find the ratio by the formula (2). It does not depend on the instability of the brightness of the emitter. Then, using the calibration formula (1), the turbidity of the medium is determined. For example, for Fig. 3, R = 4, and in Fig. 4, τ = 2100 EMF (EMF is the turbidity unit of ISO Formazin 7027).

The proposed method for determining the turbidity of the medium can be implemented on the basis of various relatively inexpensive and affordable elements. As photomatrix 5 can be used one of the photomatrix manufactured by Micron.

The emitter 1 can be implemented on the basis of a red or infrared laser, or on the basis of an LED with a collecting lens.

IVU 10 can be implemented on the basis of a microcontroller or a single-board computer with a data collection prefix.

The development of software codes for image processing procedures, localization of sediment spots, extraction of a useful signal and calculation of turbidity, as well as determining the degree of contamination of the photodetector window is possible in the environment of the Lab View software package.

The proposed method for determining the turbidity of the medium compares favorably with the prototype with the possibility of continuous continuous turbidity measurements without the participation of maintenance personnel, which is achieved due to the redundancy of the information received from the photomatrix and the invariance of the measurements regarding contamination of the photodetector windows.

Claims (1)

The method for determining the turbidity of the medium, namely, that probing radiation is passed through the analyzed medium and the radiation scattered by the photodetector is recorded by a photodetector separated from the medium by a transparent window and located at an angle of 90 ° relative to the optical axis of the emitter, then the desired value of the turbidity of the medium, which differs, is calculated from the photodetector. the fact that the registration of scattered radiation is performed by means of a photodetector, which is a photodetector matrix, with which a picture is obtained deposited on the radiation particles, then the contour stains of stray deposits on the window are selected on the image and their relative area is calculated to determine the degree of contamination of the window, the brightness profile is determined from the mid-horizontal line of the photomatrix frame, the brightness profile is corrected in the areas distorted by the spots of the deposits, and produced smoothing using the filtering procedure, then the turbidity of the medium is determined by the empirical formula:
τ = f (R) = f (U ₁ / U ₂ ),
where U1 is the output signal of the photodetector cell, measured at the center point of the frame,
U2 is the output signal of the photodetector cell, taken on the same line at the peripheral point of the frame, separated from the edge of the frame by a fixed small number of pixels.

Images