Hanna Instruments HI 83414 User Manual

Page 7

For the ratio turbidimeter range, the microprocessor of the instrument calculates the NTU value, from
the signals that reach the two detectors, by using an effective algorithm. This algorithm corrects and
compensates for interferences of color, making the

HI 83414 instrument color-compensated. The

optical system and measuring technique compensate also for the lamp intensity fluctuations,
minimizing the need of frequent calibration.
For the non ratio turbidimeter range, the NTU value is calculated from the signal on the scattered
light detector (90°). The method offers a high linearity on the low range. The method is more
sensitive to the lamp intensity fluctuations.
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 83414 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 12 “General Tips for an Accurate Measurement” for sample preparation and
measuring techniques).

MEASUREMENT UNITS
The most used units for turbidity are NTU (Nephelometric Turbidity Units). In the beer industry a
common unit is EBC (European Brewery Convention).
The

HI 83414 turbidimeter reports the measurements in NTU, EBC or Nephelos. One NTU is

equal with 0.245 EBC or 6.7 Nephelos.
Calibration and measurements are done only in NTU and the results in other units are obtained
by multiplying with the respective factors.

COLORIMETER

Absorption of light is a typical phenomenon of interaction between electromagnetic radiation and
matter. When light beam crosses a substance, some of the radiation may be absorbed by atoms,
molecules or crystal lattices.
If pure absorption occurs, the fraction of absorbed light depends both on the optical path length
through the matter and on the physical-chemical characteristics of the substance, according to the
Lambert-Beer law:

–log

c d