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4. Turbidity Measurement Principles
The measured Turbidity of determined sample, is the reading referred by light
dispersed and absorption that goes thru the sample.
Turbidity does not mean suspended solids measurement, but a effect determination
of light refracted through solids.
Turbidity measurements are used to evaluate the quantity of water sample. To
understand turbidity it is helpful to think about the characteristics of mixtures.
A mixture is defined as Homogenous or Monophasic, when the components of
the mixture are uniformly dispersed, or dissolved, throughout the mixture, Salt water
is an example of a homogenous mixture or Solution. Heterogenous or Polyphasic
mixtures are those whose components are not well distributed throughout the
mixture. The components may simple be floating in the mixture, given enough time
these components will settle out. This type of mixture is also called Suspension.
The clarity of a water sample is directly related to the amount of material suspended in
the water. Turbidity measurements are a way to measure the amount of material
suspended in a water sample. They are commonly used to monitor the effectiveness of
filtration processes.
The OMEGA Turbidity meter uses the principle of Nephelometry. As light of a known
intensity is passed through a sample some of the light will be scattered by particles in the
sample. A detector is placed at 90° to the sample to collect the scattered light. The
intensity of the scattered light is compared to that of the source. This value is reported as
a Nephelometric Turbidity Unit, or NTU. The meter is calibrated with Formazine
standards of a known NTU.
Water can sometimes have color of its own (from humic sources, for example). This
color may interfere with the light source, absorbing some of the light, and reducing the
amount of light reaching the detector. This can cause the measurement to be skewed.
The OMEGA Turbidity Meter LED light source emits at a range close to infrared. In this
range absorption is minimized, and turbidity measurements are more accurate.
TURBIDITY MEASUREMENT
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