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Hydrovision SediScat ™ Pro Sediment Meter

Sediment measurements of rivers, reservoirs and wastewater play an important role in the management of water quality and industrial processes. Due to changing particle size distributions, reliable realtime measurements are challenging since conventionally water samples have to be taken for re-calibration of such instruments to ensure consistent conversion of measurement data to suspended sediment concentrations. Water monitoring techniques, which measure low and high suspended sediment concentrations are used to optimize and improve processes for various industrial applications like monitoring water quality near construction sites where any increase of suspended sediment in the water may be a hazard for nature, such as corals, fishes, or sea grass. In another application, water monitoring techniques are in place for realtime control of suspended sediments in the intake of hydropower plants to prevent damages of pumps and turbines. Sediment concentration data are also input parameter to control processes of sewage water for water treatment plants. Over or under estimating the amount of suspended sediment concentration result in non-optimal monitoring & management.

Measurement Concept

A new approach has been developed measuring the suspended sediment concentration of non-cohesive sediments. This method overcomes the need of taking sediment samples for calibration of the instrument due to changing particle size distributions.
 
A realtime model has been implemented which estimates the particle size distribution and suspended sediment concentration simultaneously using the backscatter signal strength of 4 ultrasonic frequencies ranging from 0.5 MHz to 4 MHz. SediScat TM Pro has been optimized to measure particle sizes ranging from 20 μm - 1000 μm and sediment concentrations from 0.0 g/l to 50 g/l.
 
This optimized selection of four ultrasonic frequencies, 0.5, 1, 2 and 4 MHz, listens to the water and collects via backscattering sufficient information to solve complex equations and determine particle sizes. The newly developed SediScat™ Pro instrument computes a realtime model including the sound propagation and the wellknown SONAR equation to estimate the suspended sediment concentration and particle size distribution. The measurements based on the multi-frequency backscatter responses can be conducted along different bins of the water column applying the new SediScat TM Pro model.
 

Profiling

The presence of micro bubbles is one of the biggest distur bance factors when applying acoustic backscattering technology. Air bubbles scatter the acoustic signal much stronger than sediment. Thus, even a small amount of air bubble concentration can cause a significant signal change and indicate an erroneous high sediment concentration. Acoustic backscattering has the general advantage of collecting data over a wider range of the water column, known as profiling. Compared to conventional point measurements, e.g. achieved by optical based methods. Depending on the strength of the transducers and the sediment concentration, profiling of the water column of several meters can be realized. The range will be sequenced into cells and the parameters are determined for each measurement cell.
 

Advantages

 

Measurement Quality

The presence of micro bubbles is one of the biggest disturbance factors when applying acoustic backscattering technology. Air bubbles scatter the acoustic signal much stronger than sediment. Thus, even a small amount of air bubble concentration can cause a significant signal change and indicate an erroneous high sediment concentration.
SediScat™ Pro is able to detect the presence of air bubbles and provides the user with a warning message in the case of too high concentrations of air bubbles. Background of this innovative feature is the usage of a  signature in the backscattered signal, which is generated due the different scattering processes on the surfaces of sediments and of air bubbles.
 

Technical Specifications

Methodology
Multi-frequency ultrasonic backscattering of non-cohesive suspended sediments in water
No conversion of measurement results or calibration using samples are required
Sensor
Frequencies: 0.5, 1.0, 2.0 & 4.0 MHz
Sensor Dimension
Transducer Head: 67 mm × 44 mm (Diameter x Depth)
Performance
Particle size, radius: typically 20 μm to 1000 μm
Suspended Sediment Concentration: 0.0 g/l to 50 g/l
Accuracy: <± 10 % of measured value
Profiling Range: 18 cells, typically up to 150 cm (depending on the sediment load)
Particle Size Distribution: 24 classes; > 38 μm & < 2000 μm
Configuration
Protection Category Transmitter
IP: IP67
NEMA: 4x
Protection Category Sensor
IP: IP68
NEMA: 6P
Temperature Range
Operating Sensor: 5°C to 50°C (41°F to 122 °F)
Operating Transmitter: -20°C to 70°C (-4°F to 158 °F)
Interfaces
Communication:
Ethernet 10 / 100 Mbps
WLAN
GSM/GPRS
RS485 and MODBUS
Power Supply
DC Input: 9-36 VDC, 10 Watt
AC Input: 85 to 260 VAC (48 to 60 Hz), 10 Watt
Electrical Inputs
Digital Inputs: 2, optical isolated
Analogue Inputs: up to 4 analogue inputs, 4-20 mA programmable as to function isolated from ground
Electrical Outputs
Pulse Output: 2 pulse output, open collector selectable pulse units, polarity selectable (Normally Open or Normally Closed)
Analogue Output: up to 4 analogue outputs, 4-20 mA, programmable as to function isolated from ground