The absorbance A is a constant characteristic of the material in suspension and depends on its refractive index. It is proportional to the concentration, C of the dissolved or suspended materials.
The phenomenon of light scattering by particles in a suspension is best explained by theories of Mie and Rayleigh Greswell et al. Indeed, the beam of light passing through a fluid containing particles is scattered in various directions by the solid particles present in suspension; scattering effect is similar to that of the emission lobes of an antenna.
As in the case of absorption, the diffusion coefficient is a constant characteristic of the material in suspension and depends on the wavelength of the light. The SFH emits an infrared beam of a narrow spectral density centered on nm. It consumes very little electrical power and provides a very high intensity light output. The infrared sensor used in the design and implementation of the conditioner of the transmitted and scattered signals is a Silicon Pin photodiode: the Siemens BPW34F.
It is shaped as a parallelepiped, with a receiving face is of 20 mm2 of which 7mm2 for the sensor surface. The BPW34F is highly appreciated for its spectral sensitivity which is selective to the IR band from to nm , centered on nm. It is of very high photo sensitivity and generates a current of 0. Its dark current is very low about 2 nA when powered at 10V, which is particularly interesting for minimizing of the shift from zero in the output of the instrumentation system.
The photo-current generated by the BPW34F increases linearly with lighting. Natural surface water generally has a characteristic colour which depends on the nature of the colloidal particles dissolved or suspended. In order to simulate natural water, two different types of synthetic aqueous suspensions wee used, each containing a material of a different refractive index, namely, titanium dioxide and aluminum oxide.
Thus the problem associated with systems of multiple type particles as in natural water was avoided.
The TiO2 was an Anatase powder consisting of fine particles of uniform size about nm and refractive index 2. The used is also a product of Riedel -de Haen, Germany. The Al2O3 was also of. Preparation of synthetic suspensions was conducted in order to provide stable suspensions. The preparation of a synthetic suspension of titanium dioxide was done by gradually adding mg of TiO2 in ml of distilled water under magnetic stirring. The mixture was then kept under stirring while gradually adding a further ml of distilled water to raise the volume to ml.
The mixture obtained ml was stirred for 3 minutes and total the volume raised to 1L with distilled water. The entire suspension was sonicated for 1 minute with ultrasound in order to homogenize it.
Finally, suspension pH was adjusted to 10 to improve the stability of the suspension. The resulting dispersion was allowed to stand for at least six hours to allow coarse particles to settle out, and the supernatant was collected to serve as stock suspension. The stock suspension was stored in a glass bottle tightly closed, to facilitate stirring before taking samples. The preparation of Al2O3 suspension was made by pouring instead 3. Figure 1 schematically shows the optical bench mounted for our experimental setup.
It consists of an IR generator, a stilling well, a signal conditioner, multimeters and a central data logger. The entrance to each floor is interfaced by a photodiode BPW 34F that will convert directly the luminous flux received into electric current of the order of micro Ampere. The current thus generated is converted into voltage and amplified by devices based on operational amplifiers of high input impedance.
The amplification gain of the scattered signal conditioner is calculated to be The output signal conditioner has a very high signal to noise ratio, a stability and a minimum threshold measurement very apt to interface with a datalogger, a microcontroller for data processing or digital multimeters. The stilling well is a dark and opaque chamber, shaped as a parallelepiped 51x51mm x 10cm.
It is made of polystyrene plates, and then covered with black tape. It is constructed so that its internal dimensions best match the dimensions of the measurement cell of the standard turbidimeter HACH Ratio XR, ie, be 27 x 27mm x 9.
The IR emitting diode, and the two sensors are each placed in one of the three holes, and connected by very thin cables to their electronic circuits. No collimating device is inserted between the transmitter and the IR sensors. The optical path is 3. The turbid water was simulated by synthetic suspensions prepared according to the protocol presented in Section 3. The reference for zero turbidity is distilled water. The conditioner of the turbidity signal that was designed and constructed is an electronic circuit comprised of two.
They represent nephelometric and turbidimetric measurements of turbidity respectively. Their correlations with mathematical regression are 0. On the areas of the linear concentration, the correspondence concentration — signal is larger 2. This operating form of device is said to be direct since it directly expresses the concentration of suspended particles in terms of measurable electric magnitudes. Rs C. Dust Prot. Yoc Heating Block. For 8 X Cuvettes Diameter 13x46 Mm. Digital Ph-meter Provides Three Operator Selectable.
Copyright www. We stock and service Hach equipment, replacement parts and related systems - both current and discontinued products. Hach Hq40d Ph Meter. HQd HQ30d. Hach Carle Model Valve Oven. Hach Model: a Turbidmeter, Model: a, It consumes very little electrical power and provides a very high intensity light output. The infrared sensor used in the design and implementation of the conditioner of the transmitted and scattered signals is a Silicon Pin photodiode: the Siemens BPW34F.
It is shaped as a parallelepiped, with a receiving face is of 20 mm2 of which 7mm2 for the sensor surface. The BPW34F is highly appreciated for its spectral sensitivity which is selective to the IR band from to nm , centered on nm. It is of very high photo sensitivity and generates a current of 0. Its dark current is very low about 2 nA when powered at 10V, which is particularly interesting for minimizing of the shift from zero in the output of the instrumentation system.
The photo-current generated by the BPW34F increases linearly with lighting. The turbidimeters can be used in static mode, or online to determine in real time the optimum clarification point Huang et al. Marketed turbidimeters are relatively expensive and do not always take account of the requirements of the field and the work environment of the users, especially as regards South countries. They can perform only a single type of measurement either nephelometry or turbidimetry or ratio on the working sample whereas it remains true that the result of measurement of turbidity depends on the measurement technique used disposition of sensors and transmitters , the type of light source, particle size, concentration and colour of suspended particulate matter Lawler, Altogether these factors raise, on one hand, the need to reduce errors likely to occur in the measurement and on the other hand, the curiosity to explore and appreciate simultaneously the contributions of each of the measurement techniques and types of light source in the turbidity measurements.
The second option is that which best fits our research approach. Many investigators have developed appropriate systems, usually based on simple electronic sensors and light sources Bedidi et al. USA but they are all limited to a single type of measurement technique and do not allow comparison between them. This work presents the design and implementation of a prototype simple Infrared turbidimeter to use in industrial and laboratory applications. The device allows one to explore, evaluate and compare in a single test and simultaneously the three basic optical techniques applied in turbidity measurements.
Direct and indirect assessment of the experimental device was made using synthetic aqueous suspensions. The intensity of the transmitted beam at after the sample is traversed is related to the incident beam intensity by the Beer Lambert law:.
I0 the intensity of the incident light of wavelength, I the intensity of the light exiting from the cell, is a constant called the absorption coefficient m2mol-1 or m3mol-1cm-1 L the optical path length cm or m traversed, C the concentration of the absorbing species in the medium molm In the case of synthetic suspensions or solutions of chemical compounds, the Beer-Lambert law involves concentrations in a linear form as follows.
Reagents and synthetic materials Natural surface water generally has a characteristic colour which depends on the nature of the colloidal particles dissolved or suspended. In order to simulate natural water, two different types of synthetic aqueous suspensions wee used, each containing a material of a different refractive index, namely, titanium dioxide and aluminum oxide. Thus the problem associated with systems of multiple type particles as in natural water was avoided.
The TiO2 was an Anatase powder consisting of fine particles of uniform size about nm and refractive index 2. The used is also a product of Riedel -de Haen, Germany. The Al2O3 was also of. The entrance to each floor is interfaced by a photodiode BPW 34F that will convert directly the luminous flux received into electric current of the order of micro Ampere.
The current thus generated is converted into voltage and amplified by devices based on operational amplifiers of high input impedance. The amplification gain of the scattered signal conditioner is calculated to be The output signal conditioner has a very high signal to noise ratio, a stability and a minimum threshold measurement very apt to interface with a datalogger, a microcontroller for data processing or digital multimeters.
The stilling well is a dark and opaque chamber, shaped as a parallelepiped 51x51mm x 10cm. It is made of polystyrene plates, and then covered with black tape. It is constructed so that its internal dimensions best match the dimensions of the measurement cell of the standard turbidimeter HACH Ratio XR, ie, be 27 x 27mm x 9. Three small square holes of 1cm2 x 1cm depth are drilled therein on three sides of the stilling well : one to let in the incident light , the other at to allow the transmitted light through and the third at 90 to collect the scattered light.
The IR emitting diode, and the two sensors are each placed in one of the three holes, and connected by very thin cables to their electronic circuits. No collimating device is inserted between the transmitter and the IR sensors. The optical path is 3. Preparation of synthetic suspensions was conducted in order to provide stable suspensions.
The preparation of a synthetic suspension of titanium dioxide was done by gradually adding mg of TiO2 in ml of distilled water under magnetic stirring.
The mixture was then kept under stirring while gradually adding a further ml of distilled water to raise the volume to ml. The mixture obtained ml was stirred for 3 minutes and total the volume raised to 1L with distilled water. The entire suspension was sonicated for 1 minute with ultrasound in order to homogenize it.
Finally, suspension pH was adjusted to 10 to improve the stability of the suspension. The resulting dispersion was allowed to stand for at least six hours to allow coarse particles to settle out, and the supernatant was collected to serve as stock suspension.
The deposit was dried in an oven at C to evaluate the mass of settled powder. The stock suspension was stored in a glass bottle tightly closed, to facilitate stirring before taking samples. The preparation of Al2O3 suspension was made by pouring instead 3.
Turbidity measurement and Experimental setup Optical Bench Figure 1 schematically shows the optical bench mounted for our experimental setup.
It consists of an IR generator, a stilling well, a signal conditioner, multimeters and a central data logger. Scattered signal sensor. Turbidimetric and nephelometric measurements on water Figure 2 shows measurements of signals: scattered at 90 and transmitted at of turbid water samples. The turbid water was simulated by synthetic suspensions prepared according to the protocol presented in Section 3.
The reference for zero turbidity is distilled water. The conditioner of the turbidity signal that was designed and constructed is an electronic circuit comprised of two. Fig 3: Profile of the logarithm of the transmitted signal versus suspension concentration.
Each of the graphs shows that the scattered signal at 90 has a rising exponential profile while the transmitted signal at has a falling exponential profile. They represent nephelometric and turbidimetric measurements of turbidity respectively. Their correlations with mathematical regression are 0. On the areas of the linear concentration, the correspondence concentration - signal is larger 2. This operating form of device is said to be direct since it directly expresses the concentration of suspended particles in terms of measurable electric magnitudes.
Electrical output variables are stable and suggest that the device is easily exploitable and viable in the monitoring and static measurements of the concentration of suspended matter, mainly in laboratories, treatment and supply of drinking water plants, or in waste water management. An indirect calibration of our device in NTU units has been made in accordance with the common methodology developed by Lawer Figure 4 presents our scattered and transmitted signals in Nephelometric Turbidity Units.
Figure 3 shows that the application of the decimal logarithm on the signals transmitted at as provided by the Beer Lambert Law substantially extends the linear range of concentration of suspended particles. For each suspension, the linear part is substantially equal to that obtained by nephelometry. The linear correlations are obtained in the order of 0.
Moreover, this quadratic form can be strictly divided into two linear zones of measuring turbidity. Two reasons may explain the presence of these two zones of linearity: the phenomenon of multiple scattering at high concentrations of suspended particles beyond NTU , and the possible formation of aggregates between particles when the concentration becomes high.
For the specific case of titanium dioxide, the turbidity in NTU is very close to a linear function of the logarithm of the transmitted signal.
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