Thermo Fisher Scientific TN100 Turbidimeter - Manual (Page 25)

Instruction Manual TN-100/ T-100
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Figure 14 shows the waterproof TN-100/ T-100 turbidimeter basic optical system. It
includes a light source and a detector to monitor the light scattered at 90° with respect
to the incident beam.
Figure 14: Basic Nephelometric arrangement for turbidity measurement
8.4
Nephelometric Turbidity Units (NTU)
Nephelometric Turbidity Units (NTU): Unit of measure used when relating the light
scattered by a liquid media to the light scattered by a known concentration of a
standard solution. This unit of measure is recognized as a measure of the optical clarity
of an aqueous sample. NTU is the accepted unit of measurement for turbidity.
Another unit commonly used to measure turbidity is Formazin Turbidity Unit (FTU). The
two units of measure of turbidity are equivalent: 1 NTU = 1 FTU.
8.5 Indexing a Vial
The United States Environmental Protection Agency (US EPA) recommends that vials
used for turbidimeter calibration or sample measurement be indexed.
To index a sample vial, slowly rotate the vial throughout one complete revolution
(360°). While rotating the sample vial, observe the display and locate the position that
the vial is in which provides the lowest turbidity reading. This position is the indexed
position of the vial.
Mark this position on the vial (not on the cap) against the mark on the meter.
After indexing a vial, make sure the vial will always be placed inside the sample well in
the indexed position.
90°
Lens
Glass Sample Vial
Transmitted
Light
Scattered Light
Lamp