Endress+Hauser Turbimax CUS51D - Function and System Design

Turbimax CUS51D
2 Endress+Hauser
Function and system design
Measuring principle For turbidity measurement a light beam is sent through the medium and is diverted from its original direction
by optically denser particles, e.g. solid matter particles. This process is also called scattering.
The impinging light will be scattered in different angles. Two angles are of interest in this matter:
• The scattered light in the 90° direction is less influenced by the size of the particles.
• The scattered light in the 135° direction gives enough information also at a high number of particles.
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Principle operating mode of the turbidity sensor
1 Light source
2 135° light receiver
3 90° light receiver
If only a small number of particles is in the medium, most of the light will be scattered to the 90° channel and
less light will be scattered to the 135° channel. When the number of particles increases the relationship will
change (more light scattered to the 135° channel, less light scattered to the 90°channel).
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Signal distribution depending on the number of particles
Ir Relative intensity
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Deflection of the light
1
2
3
4
Light source
Light beam
particle
Scattered light
1
2
3
4
4
4
90°
135°
1
2
3
1
Ir
FNU
90°
135°