HF scientific Micro1000 Laboratory Turbidimeter - 0-10,000 NTU - Manual (Page 11)

Rev. 3.2 5
4. Routine Operation
4.1. Measurement Principle & Methodology
This instrument is designed to measure the turbidity of a sample in nephelometric turbidity units
(NTU). In addition, the instrument is capable of measuring in several other standardized scales:
Applicable Instrument (s)
Scale Definition
White Light Infrared
Ratio - NTU Turbidity measured via a combination of
transmitted and 90° scattered light using
the 90° scattered light as the primary
detector signal. This is used to eliminate
effects of colored samples. Yes Yes
FNU Formazin Nephelometric Units (1 FNU =
1 NTU) No Yes
FAU Formazin Attenuation Units (turbidity
measured via transmitted light according
to ISO 7027 and DIN 27027) No Yes
EBC Turbidity scale of the European Brewery
Commission Yes Yes
Nephelos A turbidity scale used in microbiological
research to report progress of bacterial
growth (e.g. immunological assays). 6.7
Nephelos = 1 NTU. Nephelo is the Greek
word for cloud. Yes No
The system measures these scales using five (5) separate detectors. Two detectors are located 90°
from the path of the light (nephelometric detectors) to ensure measurement redundancy and to
minimize variations in cuvettes. One detector is a reference detector that monitors the light output
by the light source (both white light and infrared). The reference detector is used to generate a more
accurate measure of turbidity should there be any fluctuation in lamp intensity (via voltage spikes or
lamp ageing). Finally, two detectors are used to measure transmission of light for the extended
turbidity range, for ratio measurement, and for determination of FAU’s (see below for definition).
In the course of normal operation, the embedded software measures the intensity of light at each
detector. During this operation, several advanced fuzzy logic techniques are used to determine if air
bubbles or large particles are passing through the path of light at the detector. If an anomaly is
detected, the algorithm identifies it and repeats the measurement prior to reporting the turbidity
levels. By monitoring all detectors, the instrument is able to perform system self-diagnostics; it is
able to ensure that all data collected from the detectors is consistent. Then, the calculations for
turbidity are made according to the methods described in the specifications section of the instrument
(section 1).