STUDY AND IMPROVEMENT OF TURBIDITY SENSOR

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STUDY AND IMPROVEMENT OF TURBIDITY SENSOR

Luis Gabasa, Javier Cornago

May 29, 2006

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A survey of existing turbidity sensors has been made, whereby attention is given to the accuracy. Data have been collected for 18 devices. ISI 31 + 223 has been chosen as the most accurate device. It works taking a nephelometric measurement. A new design has been developed using the Rayleigh’s and Mie’s scattering theories. Three intensity measurements are taken by three beam detectors allowing a measurement of the Mie’s and Rayleigh’s scatters, this means a new working principle in the turbidity sensor market.

1 Justification

All natural waters contain a variety of contaminants arising from ero- sion, leaching and weathering processes. To these natural contaminations is added contaminations from domestic and industrial wastewa- ters which are disposed of in various ways, e.g. into the sea, onto land, into underground strata or, most commonly, into surface waters.

Any body of water is capable of assimilating a certain amount of pollution without serious effects because of the dilution and self- purification capacity of water. If additional pollution occurs the na- ture of the receiving water will be altered and its suitability for various uses may be impaired. Thus an understanding of the effects of pollution and of the control measures which are available is of considerable importance to the efficient management of water resources.

Due to possible water pollution, it is necessary to detect water pollution and if need be control the water quality. In the industrial environment, this necessity becomes compulsory, especially in sanitary and nutritional industry because of health reasons.

The controls in these kinds of enterprises have to be very strict, therefore is necessary to arrange devices which have high accuracy.

In our particular case, we measure the turbidity of the water by means of a sensor. This sensor should have high accuracy to detect if the water is between the limits of the allowed range.

The aim of this project is to design a sensor with suitable accuracy for these kinds of applications.

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2 Introduction

2.1 Turbidity

The term turbid is applied to water containing suspended matter that interferes with the passage of light through the water or in which visual depth is restricted.

Turbidity is an aggregate property of the solution, water in most cases. Turbidity is not specific to the types of particles in the water. They could be suspended or colloidal matter and they can be inorganic, organic or biological. At high concentrations turbidity is perceived as cloudiness or haze or an absence of clarity in the water.

The scattering of light results in a change in the direction of the light passing through the liquid. This is most often caused when the light strikes particles in solution and is scattered backward, sideways and forward. If the turbidity is low much of the light will continue in the original direction. Light scattered by the particles allows particles to be detected in solution, just as sunlight passing through a window is scattered by dust particles in the air, allowing them to be seen.

In the past 10 years, turbidity has become more than just a measure of water clarity. Because of the emergence of pathogen such as Cryptosporidium and Giardia, turbidity now holds the key to assuring proper water filtration. In 1998, the EPA (Environmental Protection Agency) published the IESWTR (Interim Enhanced Surface Water Treatment Rule) mandating turbidities in combines filter effluent to read at or below 0.3 NTU (defined in the next section). By doing so, the EPA hoped to achieve a 99% removal of Cryptosporidium.

Presently there is consideration to lower this to 0.1 NTU. The trend has been to check the calibration of on-line turbidementer with hand- held units.

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2.2 Standard unit of turbidity

Because of the wide variety of material that cause turbidity in natural waters, it has been necessary to use an arbitrary standard. By the law ISO 7027 we know that:

The turbidity associated with the concentration of 1mg of SiO₂ per litre is equivalent with the unit of turbidity, and the silica used had to meet certain specifications as to particle size and weight.

Standard suspension of pure silica are not now used for measuring turbidity. They were used originally to calibrate the Jackson candle turbidimeter, the former standard instrument for turbidity measurement. This was rather crude instrument in which the turbidity of a suspension was measured by the depth of suspension through which the outline of a flame forma a standard candle just disappeared. The Jackson candle turbidimeter was removed as a standard procedure from the 17th edition of ”Standard Methods” [1] as it has generally been replaced in practice by more reliable, sensitive, and easier to use instruments that depend upon the principle of nephelometry. Also, silica as standard reference material has been replaced by standardized preparations of formazin polymer. The formazin suspensions were first calibrated against the Jackson candle turbidimeter, and thus there is some relationship between turbidity measurements by the Jackson candle turbidimeter and nephelometry. However, the Jackson candle turbidimeter measures the interference to light passage in a straight line while nephelometry measures the scattering of light from particles. Because of the basic difference in the phenomena measured, results from the two different procedures on different suspensions can vary widely. In order to avoid any confusion this may cause, turbidity measurements by the standard nephelometry procedure are now reported in NTU.

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2.3 Measurements of turbidity

Turbidity is measured by detecting and quantifying the scattering of light in water (solution), which can be measured in many ways, using visual methods and instrumental methods. Visual methods are more suitable for samples with high turbidity. Instrumental methods can be used on samples with both high and low levels of turbidity.

Two visual methods are the Secchi Disk method [2] and the Jackson Candle method. The Secchi Disk method is often used in natural waters. A black and white Secchi Disk is lowered into the water until it can no longer be seen. It is then raised until it can be seen again.

The average of these two distances is known as the ”Secchi Depth”.

The Jackson Candle method uses a long glass tube over a standard candle. Water is added or removed from the tube until the candle flame becomes indistinct. The depth of the water measured with a calibrated scale is reported as Jackson Turbidity Units (JTU). The lowest turbidity that can be determined with these methods is about 25 NTU.

There are two common methods for instruments to measure turbidity. Instruments can measure the attenuation of a light beam passing through a sample and they measure the scattered light from a light beam passing through a sample. In the attenuation method, the intensity of a light beam passing through a turbidity sample is compared with the intensity passing through a turbidity-free sample at 180^◦ from the light source. This method is good for highly turbid samples. The most common instrument for measuring scattering light in water samples is a nephelometer. A nephelometer measures light scattered usually at 90^◦ to the light beam. Light scattered at others angles may also be measured, but the 90^◦ angle defines a nephelometric measurement.

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3 Review of available turbidity sen- sors in the market

The aim of this project is to find a new turbidity sensor working principle to improve the accuracy of the devices available in the current different companies in the market.

The turbidity sensor market has been studied, through eighteen devices which belong to thirteen companies. Lamotte, Global Water, Hanna Instruments, Horiba, Wedgewood Analytical, ISI, ATI, En- dress + Hausser, Kobold, Usfilter, Hach Hydrolab, YSI, Technes and Tintometer.

In the following data chart have been compiled the accuracy and turbidity range of each eighteen devices doing easy to realize about values existing.

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Company Model Accuracy Range

LAMOTTE 2020 e/i ±2 below 100NTU and

±3 above 100 NTU

0/2000 NTU

GLOBAL WATER WQ710+

WQ770

±5 0/50 NTU

0/1000 NTU

HANNA INSTRU-

MENTS

C102 or C114 ±5 0/50 NTU

HANNA INSTRU-

MENTS

C124 ±3 below 40NTU and

±5 above 40 NTU

0/40 NTU

10/1000 NTU

HORIBA U-20 XD ±5 800 NTU

WEDGEWOOD AN- ALYTICAL

670 + TF10 ±1 20 NTU

WEDGEWOOD AN- ALYTICAL

870-872 ±2 1000 NTU

ISI 31 + 223 ±1 1000 NTU

ATI A15/76 ±5 in 40/400 scale and

±10 in 400/4000 scale

4/400 4/4000 NTU

ATI C10/77 laser

particle counter

±5 0/1000 NTU

ENDRESS +

HAUSSER

Liquisys M CUM 223/253

±2 0/1000 NTU

KOBOLD LAT-N1 ±1 0/20/40/200/

400/1000 NTU

USFILTER TMS 561 ±2 below 40NTU and

±5 above 40 NTU

0/100/1000 NTU

HACH HYDROLAB MS5-DS5-

DS5X

±5 0/3000 NTU

YSI 600 OMS- 6136 ±5 0/1000 NTU

TECMES TS 289 ±3 0/100/250/500/

1000/2000 NTU TINTOMETER Turbidirect ±2 below 500NTU and

±3 above 500 NTU

0/1100 NTU

TINTOMETER DRT 15-CE ±1 below 10NTU,

±2 from 0 NTU to 100NTU and ±5 above 100 NTU

0/10/100/1000 NTU

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4 Results

From the study we have taken the following conclusions:

The usual accuracy in the turbidity sensors available in the market is around 3%. This accuracy depends of the turbidity range being higher when the turbidity range decrease. Taking care this data, four devices have been chosen to continue the study. Kobold LAT-N1, Wedgewood Analytical 670+TF10, Tintometer DRT 15-CE and ISI 31+223. The data sheets of these turbidity sensors are available in the appendix 1. All these devices are highly accurate, arranging 1%

of accuray.

The Kobold LAT-N1 is a special device to measure turbidity in pipes. It is not able to measure turbidity in a sample.

The Wedgewood Analytical 670+TF10 sensor has a low turbidity range 20 NTU. This range is not enough in many applications.

By the same way Tintometer DRT 15-CE just arrange accuracy of 1% measuring turbidity below of 10 NTU and in a higher range, its accuracy decrease.

The final choice has been, the ISI 31+223, which has 1% accuracy in a big range 1000 NTU.

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5 Properties of the ISI 31 + 223

The ISI 31 + 223 turbidity measuring instrument is a nephelometer.

A nephelometer is an instrument for measuring concentration of suspended particulates in a liquid or gas colloid. It does so by employing a light beam (source beam) and a light detector set to one side, 90^◦ of the source beam. The particle density is then a function of the light reflected into the detector from the particles. How much light reflects for a given density of particules is dependent upon properties of the particles such as their shape, color, and reflectivity. Therefore, establishing a working correlation between turbidity and suspended solids (a more useful, but typically more difficult quantification of particulates) must be established independently for each situation. A more popular term for this instrument in water quality testing is a turbidimeter.

Figure 1: Working principle of the ISI 31 + 223. Nephelometric measure.

To improve this device, it is necessary to know the physical laws which are acting in a nephelometer. The nephelometer is an optical device, the different optical laws acting in the light scattering will be studied. Moreover, the relations between these laws and the particles suspended in a liquid should be found. After this study of the optical laws, a device with better accuracy will be able to be designed.

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6 Scattering theory

The turbidity sensor working method are based in the scattering theories which give scattered light intensity in relation with other param- eters like the wavelength, angle between the scattered light and the emitted light, distance, . . .

We use two scattering theories (Rayleigh’s and Mie’s) which are explained in the following lines.

6.1 Rayleigh’s scattering theory

Is the scattering of light by particles much smaller than the wavelength of the light λ. It occurs when light travels in transparent solids, liquids and gases.

The intensity of the light of wavelenght λ scattered in any direction making an angle θ with the incident light I₀, is directly proportional to (1+cos²θ) and inversely proportional to λ⁴. The latter point is noteworthy in that it shows how much greater the scattering of the short wavelengt is. The intensity of light scattered I_measured formula is given by:

I_measured= I₀8π⁴N α²

λ⁴R² (1 + cos²θ) (1) I0 is the intensity light beam emitted by the lamp source

I_measured is the intensity light scattered

α is the polarizability¹ (e.g. water polarizability value is 1.47A³) N is the number of scatters (equivalent to concentration of particles) λ is the wavelength of the light beam

θ is the scattering angle

R is the distance between where the light is emitted to where the light is measured

1Polarizability is the relative tendency of the electron cloud of an atom to be distorbed from each normal shape by the pressence of a nearby ion or dipole. The electronic polarizability α is defined as the ratio of the induced dipole moment P of an atom to the electric field E that produces this dipole moment (P=αE). Polarizability has the SI units of Cm²V⁻¹ but is more often expressed as polarizability volume with units of cm³ or in angstrom cubed A³= 10⁻²⁴cm³

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6.2 Mie’s scattering theory

Mie’s scattering occurs when the particles are the same size or slightly larger than the wavelength of radiation in contact with them. Gustave Mie first obtained a solution for the scattering of plane waves from a sphere when the spheres diameter is slightly larger than the wavelength of light. The Mie Theory provides exact solutions of scattered intensity from spherical particles to a given angle.

The Mie calculation output provides the scattering cross section², C_sca. Often this parameter is divided by the geometric cross-sectional area, in which r is the particle radius, to give a dimensionless scattering efficiency parameter, Q_sca.

Q_sca= C_sca

πr² (2)

In pigment applications, the formulation properties and costs depend on particle volume rather than cross-sectional area.

Therefore , a more meaningful efficiency parameter is the Scat- tering Coefficient Per Micron, SCPM, defined as the scattering cross section divided by particle volume.

SP CM =Csca 4πr³ 3

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2The scattering cross section is defined by the probability to observe a scattered particle in a given quantum state per solid angle unit, such as within a given cone of observation, if the target is irradiated by a flux of one particle per surface unit

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Since the intensity of scattered light varies with the scattering angle, the asymmetry parameter must be considered [3] to give the Scattering Coefficient S, which dimenssions are [mm⁻¹]. It is the pre- ferred parameter for correlations with experimental data for systems in which multiple scattering is predominant. The relationship is:

S = 3

4(1 − cos θ)SP CM (4)

where the asymmetry parameter, cosθ , is the average cosine of the scattering angle. Therefore, the intensity of light scattered Imeasured

formula will be:

I_measured= I₀− I₀S = I₀(1 −3

4(1 − cos θ)C_sca

4πr³ 3

) (5)

To measure the turbidity, we need the relation between the intensity of light scattered Imeasured and the number of scatters N , which is equivalent to the number of particles. This relation is given through the Beer’s law [4] described by:

T_c = e^−µ^t^d (6)

where d³is the pathlength, µ_t is the total attenuation coefficient and Tc4 is the collimated transmission.

3The optical pathlength (OPL) is the product of the geometric length of the path light follows through the system, and the index of refraction of the medium through which it propagates

4The collimated transmission is the light that has not interacted with the sample through absorption or scattering.

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Since the sample has little absorption, the total attenuation is dominated by scattering.

µ_t≈ µ_s = C_scaN_v (7)

where µs is the scattering attenuation coefficient and Nv is the number of scatters per volume. Therefore:

Tc= e^−C^sca^N^v^d (8)

Now we have the relation between the scattering cross section and the number of scatters per volume given by the formula:

Csca= − ln T_c

Nvd (9)

To obtain the relation between the scattering cross section and the scatter numbers, we multiply the number of scatters per volume N_v by the liquid sample volume V , so:

Csca= − ln T_c

N d V (10)

Therefore, the formula which gives the intensity of light scattered I_measured respect of the number of scatters N is:

I_measured= I0(1 − 3

4(1 − cos θ)

− ln Tc

N d V

4πr³ 3

) (11)

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6.2.1 How to calculate the collimated transmission To obtain the value of the collimated transmission we can use two different methods. The first one consists in the use of the IAD program in which are introduced some values expressed in a chart and then the collimated transmission value is given by the program. The second one is an experimental method, explained in the next figure:

Figure 2: Design to measure the colllimated transmission

The beam from the laser passed through a pinhole aperture and through a pathlength cuvette. The total distance from the sample cuvette to the detector should be sufficiently long to ensure that only collimated light is measured. The unscattered portion of the beam is directed to a photodetector which is shielded from the scattered light by enclosing it in a black container. Measurements are first taken with a water-filled cuvette to account for losses due to the cuvette walls.

The collimated transmission T c is computed from:

Tc= PH2O

Ps

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where P_H₂_Oand P_sare the detected powers of the blank and sample cuvettes, respectively

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6.3 Differences between the Rayleigh’s and Mie’s scattering theories

Rayleigh scattering refers to the scattering of energy by objects smaller than the wavelength of radiation. This is done mainly by atmospheric gases. Because the scattering agents are so small there is a scattering bias toward shorter wavelengths.

Mie scattering primarily involves suspended particles which are much larger than gases. These particulate scatter energy in a forward manner resulting in grey skies when large amounts of particulate are present.

Moreover, the way of scatter is different. In the Rayleigh’s scatter, back, side and forward scatter are practically the same. However, in the Mie’s scatter, forward scatter predominate.

Figure 3: Light scattered in the Mie’s and Rayleigh’s theories

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6.4 Light behavior with Rayleigh and Mie scat- tering

The Rayleigh’s equation is given by the expression:

Imeasured= I0

8π⁴N α²

λ⁴R² (1 + cos²θ) (13)

Figure 4: Light scattered in the Rayleigh’s theory with ^N_λ^R4R^α²²= 0.001283

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The Mie’s equation is given by the expression:

Imeasured= I0(1 − 3

4(1 − cos θ)

− ln Tc

N d V

4πr³ 3

) (14)

Figure 5: Light scattered in the Mie’s theory with SPCM = 0.43mm⁻¹

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If we join the two expressions to calculate the final scatter formula of the two scattering theories we obtain:

I_measured= I₀[8π⁴N_Rα²

λ⁴R² (1 + cos²θ)

| {z }

Rayleigh

+ 1 −3

4(1 − cos θ)

− ln Tc

NMd V

4πr³ 3

| {z }

M ie

] (15)

Figure 6: Light scattered in the Mie’s and Rayleigh’s theories with SPCM = 0.43mm⁻¹ and ^N_λ4^RR^α²²= 0.001283

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6.5 Final calculation of the scatter number

From the final scatter equation we can find the number of scatters.

I_measured= I₀[8π⁴N_Rα²

λ⁴R² (1 + cos²θ)

| {z }

Rayleigh

+ 1 −3

4(1 − cos θ)

− ln Tc

NMd V

4πr³ 3

| {z }

M ie

] (16)

To obtain the number of scatter which belong from the Rayleigh’s and Mie’s scattering theories are taken two measurements with different scattering angles θ obtaining two equations:

I_m1= I₀[8π⁴N_Rα²

λ⁴R² (1 + cos²θ₁) + 1 −3

4(1 − cos θ₁)

− ln Tc

NMd V

4πr³ 3

] (17)

Im2= I0[8π⁴NRα²

λ⁴R² (1 + cos²θ2) + 1 −3

4(1 − cos θ2)

− ln Tc

NMd V

4πr³ 3

] (18)

Changing the scattering angle, the number of scatters remain constants but the light intensity measured change. Thereby, we arrange a system, which could be solved, of two equations with two variables NR and NM.

Due to α, R, λ, T_c, d, V , r,θ₁ and θ₂ are constants we reduce the equations using the following constants(K₁ and K₂ in the first equation and K₁⁰ and K₂⁰ in the second equation):

K1 = 8π⁴α²

λ⁴R² (1 + cos²θ1) (19)

K₂ = 3

4(1 − cos θ₁)

− ln Tc

d V

4πr³ 3

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K₁⁰ = 8π⁴α²

λ⁴R² (1 + cos²θ₂) (21)

K₂⁰ = 3

4(1 − cos θ2)

− ln Tc

d V

4πr³ 3

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We obtain the following reduced equations:

I_m1= I₀(N_RK₁+ 1 − K₂ NM

) (23)

Im2= I0(NRK₁⁰ + 1 − K₂⁰

N_M) (24)

Solving the system we obtain the value of the scatter number of each theorie (Rayleigh’s and Mie’s):

N_M = I0(K₁⁰K2+ K1K₂⁰)

K₁⁰(I_m1− I₀) + K₁(I₀− I_m2) (25)

N_R= (Im1− I₀)(2K₁⁰K2+ K1K₂⁰) + K1K2(I0− I_m2)

(K₁⁰K₂+ K₁K₂⁰)I₀K₁ (26) Using this values we obtain the turbidity of the sample.

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7 Improvements of the ISI 31 + 223

After making a study of the ISI 31 + 223, we are going to explain possible different options to improve the accuracy of the measuring instrument.

In all of the following design, the emitter device is the same. The emitter is composed of a lamp which, using filters and lenses, project a parallel beam of light through the liquid. This beam is called the direct beam.

Figure 7: The emitter device is the same for all the possible options

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7.1 Forward and side scatter optical design

The diagram below illustrates the basic principles of the forward and side scatter optical design. Ahead of the beam detectors is an anti- reflection coated ban neutral density filter. This filter attenuates the beam an more importantly attenuates any reflect light from the detector window (reflected light from the beam detector windows can be further reflected from the flow cell windows and cause an optical error)

If the fluid in the sample cell is free of particles, all light projected from the lamp is not seen by the beam detectors. If particles are present in the fluid, the light is scattered in all directions, most of the scattering taking place in a forward direction. The optical system was designed to measure scattered light centered close to 0^◦ in the forward direction. This viewing angle of the scatter beam detector assures that most of the available scatter signal is detected. Further, this low view angle assures that the pathlenghts for the direct and scattered beam are, for practical purposes, equal resulting in excellent colour compensation. The side beam scatter is detected by a nephelometric measure; this means that a scatter beam detector is placed at 90^◦ of the parallel light beam. Using this design are taken two measurements, therefore with the equations of the section 5.5, we calculate the scatter number from each theory (Mie and Rayleigh) and by means of this we obtain the turbidity of the sample.

Figure 8: Forward and side scattering desing with an angle close to 0^◦

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7.2 Forward, side and back optical scatter de- sign

The diagram below illustrates the basic principles of the forward, side and back scatter optical design. In this design are taken three measurements by means of three beam detectors (side, back and forward).

The forward and side beam scatter detection is made in the same way than in the forward and side scatter optical design.

To measure the back scatter exist a special lens. This lens is like if it does not exist when the light beam is emitted from the lamp and it works like a mirror (reflecting the light beam towards the back detector) when the scattered light beam returns.

Using this design are taken three measurements, therefore with the equations of the section 5.5, we calculate three values of the scatter numbers, so the turbidity of the sample is obtained with more accuracy.

Figure 9: Back, side and forward scattering design

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8 Conclusions and recomendations

Finally, to improve the accuracy of the nephelometric turbidimeter design, the direct, side and back optical scatter design is used because with this design it is possible to obtain three values of the scatter numbers, so the accuracy is better than in the ISI 31 + 223 where is only taken the nephelometric measurement (90^◦ scatter).

In the following lines is explained how can this values of the scatter numbers be obtained.

With the direct, side and back optical scatter design are measured three light intensities from each beam detector (I_mf, I_ms and I_mb):

I_mx = I₀[8π⁴N_Rα²

λ⁴R² (1 + cos²θ_x) + 1 − 3

4(1 − cos θ_x)

− ln T_c NMd V

4πr³ 3

] (27)

By means of the section 5.5 are calculated the scatter numbers due to Mies and Rayleighs theories using two intensity measurements. In this design three intensity measurements are taken thus, three equation systems are arranged. Solving these systems, three scatter numbers from each theory are found. After that, the average is calculated obtaining a more accurate turbidity value.

Figure 10: Back, side and forward scattering design

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From the back and side beam detector are obtained N_msband N_rsb; from the back and forward beam detector are obtained Nmbf and Nrbf

and from the forward and side beam detector are obtained N_{mf s} and N_{rf s}.

Thus, the final scatter numbers is the average of the three measurements:

N_{mief inal} = N_msb+ N_mbf+ N_{mf s}

3 (28)

Nrayleighf inal = N_rsb+ N_rbf+ N_{rf s}

3 (29)

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9 References

1. Whipple, G.C & D.D.Jackson 1900. A comparative study of the methods used for the measurment of turbidity of water. Kass.

Inst. Technol. Quart. 13:274

2. Berman. T.P.D. Walline, A. Schneller, J.Rotherberg and D.W.

towsend 1985: Secchi disk depth record a claim for the eastern Mediterranean Limnol. Oceanorg 30:447-448

3. Ross, W.D., J.Paint technology 43(563):51

4. Ricci, Robert W., Mauri A. Ditzler, and Lisa P. Nestor. ”Discov- ering the Beer-Lambert Law.” Journal of Chemical Education 71 (November 1994):983-985.

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10 Appendix 1

.

28 Features

• Factory Calibrated Plug and Play Operation

• No Formazine Required for Start-Up

• Measurement Principal to DIN / ISO Standards

• Sapphire Measuring Window

• Optional Cleaning Wiper Blade

• Compact Design

• Enclosure Rating IP67 (NEMA 6) Waterproof

• Distance Between Sensor and Transmitter Up To 200 meters (656 /ft.)

Applications

• Potable Water

• Filter Efficiency and Backwash

• Surface Water Monitoring of Lakes, Rivers and Streams

• Water Recycle and Discharge

• Plant Effluent

• Phase Separation

Description

The Model 31 Turbidity Sensor employs the Nephelometric 90^o scattered light method with a measuring frequency in the near-infrared light range of 880 nm according to ISO 7027 / EN 27027. This guarantees a measurement of the turbidity value under standardized,

comparable conditions. Digital filter functions including interference signal suppression and sensor self-monitoring increase measurement reliability. Every sensor in the FNU field of application is carefully factory calibrated using standard procedures. Other customer and substance specific calibration data can be stored.

Specifications

Measuring Ranges 0.000 to 9999 FNU

0.0 to 3000 ppm 0.0 to 3.0 g/l 0.0 to 200%

Wavelength 880 nm

Optical Reference Photodiodes

Factory Calibration Formazine Standard and SiO²

Temperature Sensor NTC

Temperature Rating -5 to 50^oC (23 to 122^oF)

Pressure Rating 6 bar @ 25^oC (87 psi @ 77^oF)

1 bar @ 50^oC (14.5 psi @ 122^oF)

Process Connection 1” Sensor, ¾” FNPT Flow Cell

Enclosure Rating (Waterproof) IP68

Maximum Cable Length 200 meters (656 ft.)

Model 31 Turbidity Sensor

Toll Free: (800) 835-5474 ISI

Telephone: (714) 779-8781 4745 East Bryson Street

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Model 223 Turbidity & Suspended Solids Trasmitter

Toll Free: (800) 835-5474 ISI

Features

• Measures Turbidity and Suspended Solids in FNU, ppm, g/l, % or %SS

• 96 X 96 mm Panel Mount Enclosure Takes Up Less Panel Space

• Sensors are Factory Calibrated with Formazine Standard and Silicon Dioxide (SiO2)

• “Live Check” Continuously Monitors Sensor Performance

• Up To Four Alarm Contacts Including Temperature

• Dedicated Fault Alarm

• NAMUR Fault Current Alarm

• PID Controller

• 2^nd Current Output for Temperature

Applications

• Wastewater & Sewage Treatment Plants

• Surface Water in Ponds, Lakes and Rivers

• Drinking Water

• Effluent Monitoring & Water Recycle

• Filter Breakthrough Monitoring

Description

The Model 223 Turbidity and Suspended Solids Transmitter employs the nephelometric 90^o scattered light method with a measuring frequency in the near-infrared light range of 880 nm according to ISO 7027 / EN 27027. The basic transmitter is available with either a 115 VAC or 24 Volt AC/DC power supply, linear isolated current output and one alarm. Features include the addition of a second output for temperature and up to four alarms which may be configured for on-off control functions, alarm limits, timer for cleaning or PID control functions. The TS version adds the diagnostic function Live Check as well as a non-linear programmable current output. Live Check signals an alarm when the sensor signal does not change over a defined period.

Base Transmitter (TU) Plus Package (TS)

Measurement, display and calibration of the process Live Check sensor signal monitoring and alarm.

variable (PV) and temperature.

Isolated current output (Code 0) Programmable non-linear current output.

Temperature output (Code 1) One alarm (Code 05)

• On – Off

Dedicated fault alarm (Standard) NAMUR fault current (Standard)

• 2.4 or 22.0 mA

Code 10 Additional Features

Two Alarm Contacts for PV and Temperature Concentration Measurement in Other Engineering Units

• On – Off

• Timer for cleaning Automatic Cleaning initiated by an internal alarm or limit

• P(ID) Controller violation

Code 16 Additional Features

Four Alarm Contacts for PV and Temperature

• On – Off Cleaning initiated externally or automatically by an internal

• Timer for cleaning alarm or limit violation

• P(ID) Controller

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30

Model 223 Turbidity & Suspended Solids Trasmitter

Toll Free: (800) 835-5474 ISI

Specifications

Turbidity Measurement with Sensor Model 31

Measuring Range 0.0 to 9999 FNU, 0.00 to 3000 ppm,

0.0 to 3.0 g/l, 0.0 to 200%

Resolution 0.001 FNU, 0.01 ppm, 0.1 g/l, 0.1%

Repeatability 1.0% of Measured Value (0.02 FNU min.)

Deviation, Output / Input 1.0% of Current Output Range (0.02 FNU min.)

Maximum Cable Length 200 meters

Sensor to Transmitter (656 feet)

Suspended Solids Measurement with Sensor Model 41

Measuring Range 0.0 to 9999 FNU, 0.00 to 9999 ppm,

0.0 to 300 g/l, 0.0 to 200.0%

Resolution 0.01 FNU, 0.01 ppm, 0.1 g/l, 0.1%

Repeatability 1.0% of Measured Value (0.01 FNU min.)

Deviation, Output / Input 1.0% of Current Output Range (0.02 FNU min.)

Maximum Cable Length 200 meters

Sensor to Transmitter (656 feet)

Temperature Measurement

Temperature Sensor NTC 30K @ 25^oC (77^oF)

Measuring Range -5 to 70^oC (23 to 158^oF)

Resolution 0.1^oC

Repeatability 1.0% of Measuring Range

Digital Inputs 1 and 2

Voltage 10 to 50 V

Power Consumption Maximum 10 mA

Current Output

Range Selectable 0 to 20 mA or 4 to 20 mA

NAMUR Fault Current 2.4 or 22.0 mA

Maximum Load 500 Ohms

Output Scale Expansion 10% to 100%

Output Isolation Max. 350Vrms / 500Vdc

Over Voltage Protection EN 61000-4-5:1995

Auxiliary Voltage Output

Output Voltage 15 V

Output Current Max. 30mA

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105

Technical data DRT 15-CE

Light source: bulb, white light Ranges

TE/F = NTU = FNU: 0-10, 0-100, 0-1000 Accuracy: 0-10: ± 1 %

0-100: ± 2 % 0-1000: ± 5 % Resolution: 0.01 NTU from 0 - 9.99

0.1 NTU from 10 - 99.9 1 NTU from 100 - 1000

Portable turbidity meter DRT 15-CE with white light source

The integral rechargeable battery allows use of the DRT 15-CE without mains supply for up to 20 hours. Results are displayed in the measuring ranges 0 - 10, 0 - 100 or 0 - 1000 NTU or TE/F units.

The unit uses round vials with a diameter of 28 mm. Operation is by means of a membrane key- pad and a switchover button.

The unit is supplied in a robust, impact-resistant plastic housing.

The total weight is only approx. 2.3 kg.

The housing also contains the sample holder and calibration solution together with the

battery charger as a ready-to-use unit.

The unit has been approved by the US environmental authorities for daily turbidity measurements as stipulated by the "Primary Drinking Water Regulations" of the "Safe Drinking Water Act". It also meets the requirements of the

"Standard Methods for the Examination of Water and Wastewater" (AWWA/APHA).

Portable turbidity meter MICRO IR

The portable waterproof turbidity meter MICRO IR with infrared light source (860 nm) is designed to measure turbidity over the range 0 to 1100 NTU with a detection limit of 0.01 NTU in accordance with ISO 7027 / DIN/EN 27 027.

The automatic 3-point calibration feature makes unit calibration easy. All the user has to do is press the CAL key and then measure the 3 turbidity standards.

The unit is supplied complete with the turbidity standards (0.02 / 10 / 100 and 1000 NTU) as well as 4 AAA alkaline manganese batteries and a 25 mm test vial.

Lovibond^® MICRO IR

Turbidity meter as described above, complete with turbidity standards 0.02, 100 and 1000 NTU, batteries and test vial, in carrying case, ready to use Order code: 19 38 00

Accessories

Secondary standards, set of 0.02, 10, 100, 1000 NTU Order code: 19 38 50

Set of 3 empty sample vials, 25 mm ø Order code: 19 38 60

Ambient 0-50 °C

temperature:

Sample volume: 16 ml

Output: analog, 0-1 mA

Full charge op. time: 20 hours Recharge time: 8 hours Power: 6 V, rechargeable Power supply: 220 V / 50 Hz

240 V / 60 Hz Dimensions: 280 x 180 x 130 mm (L x W x H)

Weight: 2.3 kg

EPA-approved: yes EG-conformity: CE

Lovibond^® DRT 15-CE

Turbidity meter white light, complete with turbidity standard 0.02 NTU, battery and test vial, in carrying case, ready to use.

Order code: 19 33 70

Accessories

Secondary standards, set of 0.02, 10, 100, 1000 NTU Order code: 19 34 00

Secondary standards, 0.02 NTU Order code: 19 22 40

Set of 3 spare sample vials, 28 mm ø Order code: 19 22 20

Technical data

Principle: nephelometric (90° scattered light) Light source: IR-LED (860 nm) Range: 0-1100 NTU, Auto Range Resolution: 0.01 NTU from 0 - 9.99 0.1 NTU from 10 - 99.9 1 NTU from 100 - 1100 Accuracy: ± 2 % of result

or ± 0.01 Reproducibility: < ± 1 % of result

or ± 0.01 NTU Calibration: automatic 3-point-

calibration Response time: 6 - 16 seconds Protection: IP67

Oper. temperature: 0 - 50 °C

Power supply: 4 alkaline-manganese- batteries (AAA) with expected life of over 1000 tests Weight: 0.325 kg with batteries

1.25 kg in case Dimensions: Unit: 165 x 70 x 35 (L x W x H mm) Case: 225 x 310 x 80 Approval: CE / TÜV/GS

Turbidity Meters

MICRO IR DRT 15-CE

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Model 670

Turbidity Monitor

The Model 670 turbidity monitor is used with a Model TF10 fl ow through sensor to measure low levels of non-dissolved solids, emulsions, or immiscible fl uids in process liquids

• Measures and displays turbidity up to 200ppm or 200 FTU

• One 4-20mA and one 0-10Vdc analog output

• Volt free alarm output contact is suitable for direct connection to a PLC or inclusion in a control scheme

• Lamp fail indication and relay output

• Type 4 DIN plug in unit 3U x 14HP x 160mm deep (2.8”W x 5.1”H x 6.7”D) conserves space and simplifi es mounting

Model 670 Specifi cations

Signal inputs Low level current from Model TF10 forward scatter online turbidity sensor

Range 0.2, 2, 20, 200 FTU or PPM

Accuracy +/- 1% of measurement

range

Linearity +/- 1% of measurement

range

Signal outputs Lamp fail relay contact NO, 0.5A 230Vac resistive load Process alarm relay contact NO/NC, 0.5amp, 230Vac resistive load

4-20mA tracking to range selected, 600 ohm load 0-10Vdc tracking maximum range, 10k ohm load

Power 115, 230Vac, 50-60Hz,

15VA

Operating environment Temperature 0-55°C;

relative humidity 0-90%

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Model TF10 Low Turbidity Sensor

Flow through scattered light sensor used with a Model 670 Analyzer for measuring low levels of non-dissolved solids, emulsions and immiscible fluids in process liquids

• Accurately measures low level particulates up to the equivalent of 200ppm SiO

₂

using scattered light detection at 11

^o

from excitation beam

• Pyrex optics deliver accurate and reproducible performance under harsh industrial conditions.

Quartz and Sapphire optional

• Low voltage incandescent lamp provides long dependable life

• Can be fitted with visible light blocking filters to minimise color related measurement errors

• Wide variety of process connections and line sizes available

• Ultra-hygienic, CIP and SIP resilient flow cell design available with material finish of 16μinch (0.4μm) R

a

• Air purge ports available for preventing condensate buildup on optical windows

• Patented window wiping system option eliminates process buildup on optical windows

• Air purge ports available for preventing condensate buildup on optical windows

• FM and ATEX approved explosion proof lamps for hazardous area applications

• All sensors are pre-tested at the factory and can be supplied with full certification package

Pathlength 40 mm

Wavelength Broadband VIS/NIR or NIR only

Signal output Low level current from high stability silicon photodetectors Process connections Tri-Clamp, ANSI flange, FNPT, DIN flange, dairy fittings.

Others available - contact factory Sensor housing

material 316L, Kynar^®, AL6XN^®, Hastelloy^®, Teflon^®, CPVC, PEEK, Nickel, Monel^®, Inconel^®, Tantalum, Titanium. Others available Sensor housing finish Sanitary 316L sensors - electropolished sensor interior

16μinch (0.4 μmeter) Ra or better. Standard sensors to fine machine finish

O-ring materials EPDM, Viton^®, Silicone, Teflon^® coated Viton^®, Buna, Kalrez^®, Specifications

Sensor with optional wiper installed

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Medidor de Turbiedad · Técnica de luz pulsante de 4 haces · Modelo LAT-N1

Descripción:

El Medidor de Turbiedad LAT-N1 de KOBOLD detecta valores medios muy débiles de turbiedad según el estándar Formazin (FTU); EBC también puede ser utilizado. El dispositivo funciona según DIN 38404 / ISO 7027 con la técnica de luz pulsante de 4 haces, por lo que la suciedad de los dispositivos ópticos así como los efectos de la luz de fuentes externas y de la deriva en los componentes electrónicos se compensan confiablemente. La electrónica de evaluación y la adecuación apropiada se combinan para hacer un instrumento robusto y compacto que puede ser instalado fácilmente. La conexión de proceso se ha diseñado según el estándar higiénico para atornillamientos de tubería (DIN 11864). Así los requisitos más rigurosos de higiene son satisfechos. Las entrerroscas hexágonales soldadas y conexiones sanitarias según DIN 11851 están también disponibles.

El rango de medición del dispositivo se puede cambiar manualmente o con una señal digital. Así la exactitud de la medición a través del rango entero de turbiedad de 0,01 - 5 FTU a 0,01-1000 FTU es muy alta.

La señal de salida del 4 20 mA permite conectar diversos dispositivos de evaluación tales como indicadores digitales, reguladores del valor límite o un PLC.

Aplicaciones:

l Control de proceso l Secuencias de dosificación l Elaboración de la cerveza

l Separación de fase en medios levemente turbios l Agua y aguas servidas

Detalles Técnicos:

Método de medición: Luz pulsante de 4-haces según DIN 38404 (90 °C) Rangos de medida

(4-20 mA): 0,01 a 5/10 / 50 / 100 / 500/1000 TE/ F 0,01 a 5/10 / 50 / 100 /250 EBC Precisión de

medición: ± 1% del valor superior del rango Temperatura del

proceso: 0 a 80°C (corto-plazo 120°C) Temperatura

ambiente: 0 a 60°C

Temperatura de

almacenamiento: -20 a +80°C Máxima presión: 6 bar

Material del cuerpo: acero inoxidable 1.4404 (V4A, SS316L)

Material del bloque

óptico: PEEK con cuadros de cristal silica Conexiones del

proceso: DN 40, 50, 65, 80, 100

Conexión sanitaria según DIN 11851 tubo roscado (higiénico) según DIN 11864 mango de adaptación hexagonal (Conforme a EHEDG, 3-A) Longitud de onda: 875 nm

Entrada de control (rango de

sobre interrupcion): 3 x 24 VDC, BCD Salida analógica: 4- 20 mA,

Exceso de corriente limitante <22 mA

Carga: max. 500 Ω

Voltaje de

alimentación: 24 V_DC, aprox. 100 mA Indicador: LED 7- Segmentos,

4- posición (FTU o EBC) Altura de dígitos: 12,7 mm Tipo de protección: IP 67

Inmunidad al ruido: EN 50082-2 según IEC 801-4, Nivel de Interferencia 3 Emisión de

interferencia: EN 50082-2

Peso: aproximadamente. 3,8 kg

/Ko/10

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11 Appendix 2

Now are shown the dependence of the scattered light measured with respect to physical paramenters in Rayleighs expressions. The light beam intensity expressions which are measured by the detectors depend of the distance.

11.1 Nomenclature

I₀ is the intensity light beam emitted by the lamp source

I1 is the intensity light beam measured by the forward scatter detector I₂ is the intensity light beam measured by the side scatter detector I₃ is the intensity light beam measured by the back scatter detector I4 is the intensity light beam in the point 4

L₁ is the distance between the forward scatter detector and the lamp source

L2 is the distance between the side scatter detector and the direct light beam forming 90^◦

L₃ is the distance between the back scatter detector and the direct light beam forming 90^◦

L₄ is the distance between the side scatter detector and the lamp source

α is the polarizability α₁ is a material coefficient

N is the number of scatters (equivalent to concentration of particles) λ is the wavelength of the light beam

θ is the scattering angle

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Figure 11: Dependence of the scattering light with respect of the distance

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11.2 Forward scatter detector

First of all, we calculate the light beam forward intensity due to the L₁ losses:

I_{f orward} = Z L1

0

I₀e^−α¹^xdx = I₀ α1

(1 − e^−α¹^L¹) (30)

We find the losses due to the scatter by means of the Rayleigh’s law:

Iscatterf = I0

8π⁴N α²

λ⁴R² (1 + cos²θ) (31) In the forward scatter θ = 0^◦ therefore:

Iscatterf = I0

16π⁴N α²

λ⁴R² (32)

I_scatterf = I₀ Z L1

0

16π⁴N α²

λ⁴R² dR = I₀−16π⁴N α²

λ⁴L₁ (33) Finally, we calculate I₁ (intensity measured by the forward scattered detector):

I₁= I₀ α1

(1 − e^−α¹^L¹)−I₀16π⁴N α² λ⁴L1

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11.3 Back scatter detector

By means of the Rayleigh’s scattering law, we calculate the back scatter light intensity:

I_scatterb= I₀8π⁴N α²

λ⁴R² (1 + cos²θ) (35) In the back scatter θ = 180^◦ therefore:

I_scatterb= I0

16π⁴N α²

λ⁴R² (36)

I_scatterb= I₀ Z L1

0

16π⁴N α²

λ⁴R² dR = I₀−16π⁴N α² λ⁴L1

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Now we calculate the losses due to L₃, finding finally I₃:

I₃ = I_scatterb

α₁ (1 − e^−α¹^L³) = −I₀16π⁴N α² λ⁴L₁

1

α₁(1 − e^−α¹^L³) (38)

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11.4 Side scatter detector

First we calculate the losses due to L₄: I₄ = I₀

α₁(1 − e^−α¹^L⁴) (39) By means of the Rayleigh’s law we know the intensity of a side scatter:

I₂= I₄8π⁴N α²

λ⁴R² (1 + cos²θ) (40) In the side scatter θ = 90^◦ therefore:

I₂ = I₄8π⁴N α²

λ⁴R² (41)

Finally, we know the light beam intensity which is measured by the side detector:

I2= I4

Z L2

0

8π⁴N α²

λ⁴R² dR = −I4

8π⁴N α² λ⁴L2

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I₂ = −I₀8π⁴N α² λ⁴L₂

1

α₁(1 − e^−α¹^L⁴) (43)

STUDY AND IMPROVEMENT OF TURBIDITY SENSOR