Hanna Instruments HI 88703 - Manual (Page 6)

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For the ratio turbidimeter range, the microprocessor of the instrument calculates the NTU value, from
the signals that reaches the two detectors, by using an effective algorithm. This algorithm corrects
and compensates for interferences of color, making the
HI 88703 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 88703 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 10 “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 Comitee).
The
HI 88703 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.