Sludge Blanket Measurement System
The Avocet monitors the sedimentation
and scum accumulation in remote settlement tanks and
clarifiers in water treatment works, waste water reclamation
works and factories with treatment plant.
The Avocet is particularly suited for identifying auto-desludging
and overspill alarm signals and for monitoring the general
biological health of thick sludge blankets.
Designed to operate in most if not all aspects of sludge
level monitoring the Avocet system comprises three components.
The outstation consists of an ultrasonic sensor and a
local instrumentation unit, which provides a histogram
display of the sedimentation layer.
The telemetry link enables the local data to be
transmitted to a base station up to 2km away.
The base station will centrally monitor and display the
information from multiple outstations via the telemetry link.
Principle of Operation
The Avocet uses ping-echo sonar to determine the distribution
of solids particles scattered throughout the settling
effluent and thereby determining the sludge interfaces. Scum
formation is detected by the damping effect this has on the
An ultrasonic sensor is immersed just below the surface of
the effluent point directly to the bottom of the tank. By
sending out a pulse of energy a backscatter effect occurs
throughout the body of the liquor and the sensor picks this
up. Computation of the speed of sound and the time return
echo shows the relative position of the particles in
suspension. This is then displayed in a histogram form on the
Typically the outstation is fixed
to the handrail of the scrapper gantry on the settlement tank.
The instrument panel displays the sediment relative density
through out the tank. During normal operation the signal
strength will vary due to many factors but one these will be
the build up of solids on the sensor. To overcome this an air
purge facility is installed and at a pre-determined interval
a blast of compressed air is forced across the sensor which
removes debris and reduces the need for continual maintenance.
The base station comprises of one control module, power
supply unit and will accept up to six control modules. These
modules facilitate replication of the measurement outstation
with a display showing the identical histogram. Each of these
modules has three built in relays for control, one relay for
sensor failure/scum detection, and analogue outputs for data
transmission. A data storage facility will enable the
operator to observe the sedimentation performance review over
the previous twenty four hours. An optional pc interface is
Depth 1.7 – 7.0 metres Resolution 0.03 m @ 5 metres Stability 0.1% /°C dead zone 0.8 metre Temperature range -20 to +60°C
for the internal temperature of the outstation
Base Station IP64
Power 110 VAC, 240 VAC Outputs 4 x single pole
change over contacts; 4 –20 mA; 0 – 5 V
Radio Telemetry Site specific ranges
up to 2km can be specified dependent of topography.
All brackets and
sensor mounting requirements have been designed to be clamped
onto the handrails or similar structure on the scrapper. The
compressor for the air purge is installed in the same support
structure and forms an integral part of the measuring
Pulsonic Technologies Ltd.
Campus House, 10 Hey Street, Bradford,
West Yorkshire, BD7 1DQ, UK
Tel : 01274 741681 Fax : 01274 722842
© Copyright May 1996. All rights reserved Pulsonic
Technologies Ltd have a policy of continued product
improvement and consequently we reserve the right to alter
specifications and prices without prior notice. © Copyright
notice since May 1996