IEEE Instrumentation & Measurement - September 2023 - 33

of absorption and scattering between the light source and the
sand particles, to establish their relationship and to realize
the measurement of different sand content. The optical measurement
method can achieve the sand content measurement
of 0.1-30 kg/m³, meets the needs of river channel measurement,
and can be achieved with smaller equipment which
is easy for field testers to carry. At the same time, combined
with the current common wireless technology, an optical
method can achieve real-time online measurement of sand
content, which meets the needs of this study.
This paper proposes to use an optical measurement method
to measure the sand content of river channels, selecting a suitable
spectral band and light intensity reception method to
study the complex change relationship between the received
light intensity and sand content and realize the accurate measurement
of sand content. A suitable wireless measurement
method is selected to realize real-time online measurement
of sand content, and the development of online sand content
measurement equipment is completed. Sand samples
of different sites and different concentrations were selected
for testing to verify the accuracy and stability of the developed
equipment in terms of relative error and uncertainty of
measurement.
Sediment
Content Online
Measurement
Equipment
Measurement
Principle
Optical measurement depends
on the interaction
between light and the sand
sample in the water, and
the measurement of sand
content is achieved by the
transmission or scattering
of light as the light
source passes through the
water stream holding the
sand. Therefore, a suitable
measurement method
and emitting light source
are required to achieve a
wide range and high accuracy
of sand content
measurement.
There are two main types
of measurements based on
optical sand content: transmitted
light measurements
and scattered light measurements.
Transmitted light
measurements are mainly
based on Lambert Beer's
September 2023
Light source
law of light absorption [7] and are shown schematically in Fig.
1. The principle is defined as:
Is Ie= ∗
− ∗∗
KT L
(1)
where: T is the turbidity of the turbidity solution to be measured;
K is the turbidity proportionality constant; I0 is the
incident light intensity of the emitting light source; and Is is
the intensity of transmitted light corresponding to turbidity
T. The transmitted light intensity decays exponentially with
the increase in turbidity of the turbid solution. The higher the
turbidity of the water, the higher the sand content, so the linearity
of the transmitted light measurement of the sand content is
poor. In addition, during the measurement process, a large part
of the emitted light source is transmitted, so that small changes
in the sand content cause very weak changes in the transmitted
light intensity, which requires a high degree of sensitivity of the
photodetector. Moreover, the transmittance method of measurement
requires the emitting and receiving light sources to be kept
horizontal, thus resulting in a large overall structure of the developed
equipment, which is not conducive to field portability.
Scattered light measurements are mainly based on Rayleigh's
scattering law and Mie's scattering law [8], schematically
Incident light
Transmitted light
River channel to be tested
Photodetector
Fig. 1. Schematic diagram of scattered light.
Photodetector
Backscattered light
θ > 90°
Incident light
Transmitted light
Light source
Fig. 2. Schematic diagram of backscattered light.
IEEE Instrumentation & Measurement Magazine
33
River channel to be tested
IEEE Instrumentation & Measurement - September 2023

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