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IP258
6
The relationship between attenuation and suspended solids is
shown graphically in Figure 2. Calibration of the unit involves
adjustment of the zero point, by setting up the sensors in
clean liquid (supernatant), and then setting the slope of the
straight line graph, either according to past data or from site
samples.
In the memory of the MSM400 there is information on various
slurry types, to enable simple initial set-up. More accurate
adjustment can then be made once site samples have been
taken.
Zero Ref
Attenuation
(dB)
S
l
o
p
e
% Solids
Figure 2 : Ultrasonic Attenuation versus
Suspended solids
SLURRY CHARACTERISTICS
The relationship between the measurement of ultrasonic attenuation and the percentage solids of a particular slurry
type is dependent on the density of the slurry particles and their average size distribution. This is known from
experience for most slurry types, and is expressed as a number, which is the ultrasonic attenuation in deciBels (dB),
per mm gap between sensor faces, per one percent suspended solids.
Calibration:
The Mobrey experience with using ultrasonics for suspended solids monitoring has been developed over 25 years.
Calibration systems for the MSM400 use this experience, allowing the plant operator to choose whether to set up the
unit based on Mobrey site and slurry experience, or whether to take site samples to fine tune that data to suit the
specific site conditions. The MSM400 is versatile enough to allow simple or complex calibrations.