Products > Avocet Sludge Blanket Monitor

Avocet Sludge Blanket Monitor

The Avocet Sludge Blanket Monitor gives highly accurate measurements of sludge blanket composition by utilising extremely high frequency ultrasound sensors (1.1MHz) that can detect the lowest sludge density found in primary and secondary clarifiers.

The Ultrasonic Transducer is immersed just below the surface of the water and pointed directly at the bottom of the tank.   The Avocet Sludge Blanket Monitor uses time of flight echo processing and advanced algorithms to lock on the true sludge interface level and ignore the floating solid particles and troublesome rag layers. The unique algorithms have been designed to automatically filter all floating particles and electrical noise interference for unrivalled performance.

A simple 3-button keypad is used by the operator to input the tank depth. The Avocet automatically does the rest with its advanced echo processing and signal gain adjustment. The LCD screen displays the echo profile for visual confirmation of the sludge level relative to the tank bottom. A 4-20mA signal is provided proportional to the sludge level for SCADA input.

To overcome build-up of solids on the sensor an air purge facility removes debris and reduces the need for continual maintenance.

Alarm states can be programmed for sensor failure/scum detection and high level sedimentation. An optional data storage facility enables the operator to observe the sedimentation performance over any historical period.

The Avocet Sludge Blanket Monitor sets itself apart from other sludge blanket monitors by using extremely high ultrasonic frequencies of 1.1 MHz, and coupled with advanced signal processing, this allows the detection of very small particles even in hostile environments and secondary clarifiers.


Powerful Signal Processing

Defining sludge blanket interfaces is quite a complex task, especially as secondary algorithms and multiple interface layers can cause confusion. The Avocet utilises a range of powerful processing algorithms that the user can programme to generate the optimum sludge return signal.

To aid the user, the Avocet allows the user to view the raw return echoes from the clarifier so he/she can tailor the signal processing algorithms to maximise performance.

In secondary clarifiers sludge layers are often diffuse and difficult to detect. In such clarifiers the Avocet does the signal processing for you and it decides on what is the strongest sludge return echo by utilising extremely powerful mathematical techniques.


High Frequency Sensor


The ability of an ultrasonic sensor to detect the smallest particles is directly equal to the ultrasonic frequency. At 1.1MHz the Avocet has the highest frequency of any product in the market which enables it to detect the smallest particle size and particularly in secondary clarifier with opaque sludge layers, its performance is second to none.

Large Clear Display

The Avocet has a large 5” 240×128 graphics display, that in the run mode, shows and marks the sludge level interface on a vertical graph and shows the status of the instrument parameters.

SLudge Blanket Facia

Air Purge Cleaning


The Avocet uses air purge cleaning that is programmable and controlled via one of its four relays. Air purge is preferred to wiper cleaning which are prone to mechanical failure through wiper seizure and water ingress. Air purging is simple, effective and more reliable.

Detailed Specification

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Measuring Principle

Underwater ultrasonic sludge level measurement

Measuring Range

0.6-12 metres (2-39 ft)



+/- 0.03m



Response Rate

Fully adjustable

Echo Processing

Sophisticated algorhithms using 32 bit Digital Signal Processing

Power Supply

115/230 VAC

Outputs and Communications


1 4-20mA output, 750Ω


d4 SPDT programmable relays, 5A @ 230 VAC (2 user programmable, 1 purge control, 1 LOE)

Telemetry (optional)

Site specific, range up to 2 miles (3km)


Standard RS232, optional RS485


User Interface

3-button keypad with menu driven programming

Echo Profile

Graphical LCD display of raw echo profile

Programming Security

Password protected

Data Integrity

Non-volatile RAM


Temperature Range (electronics)

-20°C to +60°C (-4°F to +140°F)

Outdoor Rating

IP65, UL Approved Enclosure with UV Protected Clear Lid



280 x 219 x 156 mm (11.0 x 8.6 x 6.1 inch)

Cable Entry

8 Available for Wall Mount: 1xM12, 1xPG9, 5xM20 bottom row


2 Fixed Holes & 1 Hanging Hole, Optional DIN Rail Tabs

Enclosure Material

Polycarbonate, flmae resistant to UL94-5V


Approximately 1.4Kg (3 lbs)

Transducer Specifications

Standard Cable Length

20 metres (66 ft), optional custom lengths

Cable Specification

Shielded Coax Cable

Maximum Cable Run

50 metres (150 ft)

Temperature Range (Transducer)

-40°C to +95°C (-40°F to +200°F)


50mm diameter x 75mm length (2 x 3 inches)


1 inch NPT Male Thread


PVC Housing, IP68 Rating

Beam Angle & Frequency

6° total, 12. MHz


Hose Tail Air Pipe Connector for Air Purge

Cleaning Frequency

User-programmable, 1-720 minutes (12 hours)


Approximately 0.5 Kg (1 lbs)

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The Old Mill Wainstalls
Halifax, West Yorkshire
HX2 7TJ, United Kingdom.
tel: +44 (0)1422 363 462

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