Abstract:
This work is concerned with the development of an instrument
capable of measuring simultaneously both the size and concentration
. of suspended fine sands in the presence of silt. A review of the
literature of the measurement of suspended solids showed that the most
promising approach to develop such an instrument would use ultrasonic
methods.
A theoretical study of the scattering of ultrasound for suspensions
is presented and this shows that an appropriate choice of frequency and
scattering geometry will give reduced sensitivity to silt size particles
whilst yielding information on the size and concentration of the
suspended particles. Laboratory experiments were conducted using a
vertical sedimentation test facility and single angle scattering from
suspensions of sand and glass balls. The experiments showed that the
theory is adequately modelled in practice.
A laboratory model of a field instrument, employing analogue
and digital signal processing, was then constructed and tests were
performed on a range of suspended sediments with different mean size,
The ratio of ultrasound scattered through 10° and 170° was found to be
concentration independent, being a function of size only. The ultrasound
scattered through 10°. suitably processed, was a measure of concentration.
A measure of agreement between theoretical predictions and
experimental results was obtained and design recommendations for the
manufacture of a field instrument are given.
