6
TURBIDIMETER
Turbidity of 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 93414
instrument 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 93414
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
0
) and a
transmitted light detector (180
0
). For the colorimeter range the optical system is based on the
turbidimeter tungsten lamp and a separate detector with a narrow band interference filter @ 525
nm to guarantee both high performance and reliable results for colorimetric measurements.
For the turbidimeter range 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 93414
instrument 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 93414
instrument 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
page 14 “General Tips for an Accurate Measurement” for sample preparation and measuring techniques).
PRINCIPLE OF OPERATION
