Technical sciences /6. Electrical engineering and radioelectronics

Kharisova Z.I.

Ufa State Aviation Technical University

Perspective directions of liquid disperse systems concentration measuring

Liquid disperse systems are represented by a liquid formation of two or more phases which are substantially immiscible and which do not chemically react with each other, wherein it is assumed that the first substance (dispersed phase) is finely distributed into the second (dispersion medium).

Determination of particles concentration in liquid disperse systems is usually done by photometric methods. The turbidity is a measured optical parameter, which characterizes the medium ability to scatter light emission of suspended particles in different directions [1].

Information of suspended solids concentration (turbidity) is often important in many of technological control problems, for example, in determining the quality of drinking water in centralized water supply, reverse water quality control in the oil industry, the analysis of various processes in the food, pharmaceutical, aerospace, biological and medical industries.

Instruments for concentration (turbidity) measuring are based on one of photometric analysis methods [2]. As a rule, the turbidity is determined by nephelometric or turbidimetric method using appropriate measuring means, which may be constructed like turbidimeter (light detector is located on the radiation axis and receives the attenuated radiation passing) or a nephelometer (receiver located at an angle to the radiation axis and receives the scattered radiation) [3].

Since turbidimeters method sensitivity worse that nephelometers, this method of measuring concentrations of disperse phase is ineffective. Due to its sensitivity, accuracy and applicability in a wide range of particle size and concentration, turbidimeters are recognized like standard methods so it is considered a main instruments for determining the turbidity.

By type of interaction with the investigated environment sensors contact and contactless nephelometers are distinguished. The most widespread group of contactless nephelometers - devices that don't have direct contact windows emitters and photodetectors investigated liquid medium. Contactless nephelometer are compared with contact advantage that they are not influenced by parasitic deposits on the windows and photodetectors emitters and therefore can operate at much longer industrial facilities unattended.

On the registration corner of scattered radiation are distinguished classic nephelometers performing measurements of the intensity of the scattered light at an angle of 90˚; backscatter nephelometers for measure the intensity of radiation reflected from suspended particles at an angle to 180˚; forward scattering and multi-angle nephelometes for measuring intensity of the scattered light at an angle of 12˚ to 360˚ and up (Figure 1).

Nephelometers types depending on the angle of scattered radiation detection

Classic nephelometers

Back scattering nephelometers

Forward scattering nephelometers

Multiangle nephelometers

Figure 1. Classification of nephelometers depending on the angle of the scattered radiation detection

There are many varieties of nephelometers for different applications. The most particularly important nephelometric devices and systems of small scattering angles - FS-analyzers (Forward Scattering analyzers). FS-analyzers allows to evaluate the distribution of particle sizes, which depends on the diffraction pattern at low scattering angles. Many of turbidimeters are equipped with devices to change the angle between the axes of the emitter and receiver, as well as the working portion of the spectrum. It provides information not only on the concentration of suspended particles, but also on their size and shape [4]. There are several types of performance photodetectors in nephelometric measurement systems: a single fixed, movable single, multiple and distributed matrix (Figure 2).

One of the drawbacks of modern turbidimeters and nephelometers is using a single photodetector (photodiode). Such a sensor detects the light level of its surface and the slightest contamination on the window sensor will inevitably affect its output signal, which is an integral function of the surface area of the entire light box. Furthermore, deposits on the surface of the window do not appear uniformly on their area, but are formed as separate spots that extend over time, progressively reducing the signal of the photodetector. As a result, the reading will be heavily distorted. In developing nephelometric systems is the most profitable multiple distributed and matrix (implemented using video facilities) performance of photodetectors.

Construction of the photodetectors in the nephelometer

Fixed unit

Movable unit

Multiple distributed

Matrix

Figure 2. Construction of the photodetectors in the nephelometer

In most applications of environmental and industrial monitoring fluids often necessary to monitor the concentration of dispersed phase in a wide range of turbidity (0.1.. 5000 NTU [5]). Implementation of flow measurement is complicated by the factor to deposits on the optical elements. Therefore useful for in-line measurements are nephelometric contactless measurement methods [6]. However, these methods can compete based on matrix of photodetectors which are not non-contact, but have a redundancy of information and may include means for neutralizing the effect algorithmic result stains sediment.

References

1. Fetisov V.S. Photometric measurements of the liquid dispersions. - Ufa: USATU, 2005. – 233p. (In russian).

2. Karpishchenko A.I. Medical laboratory technology. SPb .: Intermedika, 1998. - 608 p. (In russian).

3. Measurements in industry: A Guide, volume 3. The methods of measurement and equipment: / Ed. Warder P. - 2nd ed., Rev. and add. - M .: Metallurgy, 1990. - P. 106-107 (In russian).

4. Kazovsky L.G. Particle analysis using forward scattering data. // Applied Optics. - 1984. - V.23 (3). - P.448-454 (In russian).

5. Fetisov V.S., Kharisova Z.I., Intelligent liquid analyzer for measurements of turbidity and suspended particles concentration // Ecological systems and devices - 2014 - №5. - P.3-9 (In russian).

6. Dmitriev O.A., Kharisova Z.I., Flow control water quality by ink jet nephelometers // Actual Problems of Science and Technology - 2012 - №2 . – P.72-75 (In russian).