Hanna-instruments HI 98703 User Manual download pdf (Page 6)

Turbidity of the water is an optical property that causes light to be scattered and absorbed, rather than

transmitted. The scattering of the light that passes through a liquid is primarily caused by the

suspended solids. The higher the turbidity, the greater the amount of scattered light. Because even

the molecules in a very pure fluid scatter light to a certain degree, no solution will have zero

turbidity.

The USEPA Method 180.1 specify the key parameters for the optical system to measure turbidity

for drinking, saline and surface water in a 0 to 40 NTU range, using the nephelometric method.

The HI 98703 Portable Turbidimeter is designed to meet or exceed the criteria specified by the

USEPA Method 180.1 and Standard Method 2130 B.

The light beam that passes through the sample is scattered in all directions. The intensity and pattern

of the scattered light is affected by many variables like wavelenght of the incident light, particle size,

shape, refractive index and color.

The Hanna’s HI 98703 is based on a state-of-the-art optical system that guarantee both high

performance and reliable results.

This optical system includes a tungsten filament lamp, a scattered light detector (90

) and a

transmitted light detector (180

). The microprocessor of the instrument calculates from the signals

that reaches the two detectors, the NTU value, using an effective algorithm. This algorithm corrects

and compensates for interferences of color, making the HI 98703 turbidimeter color-compensated.

The optical system and measuring technique alow the compensation of lamp intensity fluctuations,

minimizing the need of frequent calibration.

The lower detection limit of a turbidimeter is determined by the so called “stray light”. Stray light

is the light detected by the sensors, that is not caused by light scattering from suspended particles.

The optical system of HI 98703 turbidimeter is designed to have very low stray light, providing

accurate results for low turbidity samples. However, special care must be taken when measuring low

turbidities (see General Tips for an Accurate Measurement for sample preparation and measuring

techniques).

PRINCIPLE OF OPERATION

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Hanna-instruments HI 98703 User Manual Page 6