Galvanic Applied Sciences USA, Inc.
101 Billerica Ave, Bldg. 5, Suite 104.
North Billerica, MA. 01862
Tel: 978-848-2701
Fax: 978-848-2713
Email: [email protected]
8
Measurement methods
The typical scattered light turbidity measurement methods are:
•
Side scattering (90°) The detector is positioned in a right angle (90°) to the light beam.
•
Forward
scattering
(12°) The position of the detector is 12° shifted to the axis of the light.
beam
As shown in the figure above, an intense collimated beam of light is projected through a sample contained
within the sensor. The intensity of this light beam is measured by the direct beam detector, which is
positioned opposite the light source.
A scatter light detector measures the light scattered by the particles in the sample.
Depending on sensor specification, this detector can be located 12° or 90°, displaced from the direct light
axis.
The signals caused by scattered and direct light will be amplified, divided and then processed by the electronics. The result
displayed
is the turbidity value.
Turbidity
signal
light
Direct
signal
light
Scatterd
=
The particles inside the flowing liquid decrease the intensity of direct light beam while increasing the intensity of the scattered
light (i.e. the turbidity rises).
Color decreases the intensity of direct and scattered light in the same ratio, therefore the turbidity value is
constant.
Lamp ageing and window coatings are compensated as well by this ratio.
Comparing the different measurement methods
The two different measurement methods (12° forward scattering / 90° side scattering) are not comparable.
Even when you use the same calibration standard to calibrate the systems, different samples will have
different measurement results.
The deviations of the results are caused by the different particle size distributions within different
samples. The measurement methods will respond differently, depending on the current particle
distribution of the actual sample.
Important note:
When comparing measurement results. The same methods must be compared to one another.
For example, 90 vs. 90, 12 vs. 12. Never 90 vs. 12.
