Automatic Sludge Blanket Level Detector

The Markland Advantage:

Optimize energy usage

  • Automate your desludge pumping. Rather than pumping at set times, pump when you need to, using this reliable sludge blanket level meter.

Optimize water removal to reduce costly additional processing (belt presses, digesters, centrifuges, etc.)

  • Maximize sludge blanket density automatically. Avoid pumping large volumes of thin sludge; avoid pulling a core hole and pumping water needlessly.

Maintain preferred sludge depth

  • Automate sludge blanket control  with this interface level analyzer. Avoid overflows and process problems.

Reduce wear and tear on pumps

  • Pump only when necessary.

Maximize operator’s time and energy

  • Installs quickly and easily – no need to calibrate. Simplify operation with a durable level measurement instrument.

Reduce the cost of inaccurate chemical dosing

  • Optimize flocculent precipitate (floc) process adjustment and coagulant dosage control.

Get answers when you have questions

  • Technical assistance is factory-direct from the designers and manufacturers of this sludge blanket level control equipment.

Used wherever solids are separated from liquids:

  • Municipal water and wastewater treatment plants
  • Primary and secondary clarifiers (gravity settlers)
  • Inclined plate clarifiers / separators (Lamellars ®)
  • Dissolved air flotation (DAF) tanks (floating bed)
  • Decanting tanks / Decanting control
  • Industrial process + Wastewater clarification
  • Sequential batch reactor (SBR)
  • Batch processes
  • Settlement tanks

Sludge Depth Monitor Applications

  • LED beam automatically adjusts its intensity to detect settled sludge blanket and supernatant interface levels in thick or thin sludges, or in light flocs
  • sludge level interface detection is not distorted by the curved walls of lamellar® tanks
  • advanced self-diagnostics
  • ultra high intensity infrared beams
  • automatic beam intensity control
  • 4 – 20 ma output linear with sludge interface level depth
  • high & low sludge blanket depth set-point relays

Sludge Blanket Level Detector Probe


A vertical Probe, submerged in the settlement tank, contains 64 infrared high intensity LEDs stacked vertically, which shine horizontally across a probe gap to 64 phototransistor detectors. This gap contains either liquid or sludge. The 64 pairs are sequentially scanned to locate the sludge bed. Beam power intensity is automatically adjusted to accommodate different sludge and overlying liquid concentrations. At its highest power level, the beam will shoot through your hand, you could count the bones, but there is not hazard since the beam is only on for a few microseconds. This high intensity beam easily penetrates fouling on the probe’s windows, and as long as the solids in the probe gap are high relative to the solids in the scum layers on the windows, the meter continues to read correctly. Eventually, the probe has to be removed and given a wipe with a soft cloth.

Sludge Blanket Level Control

Process Control
Automatic desludging yields thicker sludge than timers or manual methods, and reduces sludge disposal or processing cost. A desludge pump can be operated automatically from the Low Set-Point Relay along with a Pump Run Interval Timer, and the High Set-Point used as an alarm for excessive sludge depth. Alternatively, the desludge pump can be turned ON at the High Set-Point and OFF at the Low Set-Point, or the 4-20 ma output can be used for continuous variable speed drawoff. The 4-20 ma output can link the sludge blanket level meter to your computer for centralized process control.

Pause Switch Uses
An externally located switch, with a pair of Normally Open contacts, can be connected to act as a “Pause Switch”. When these contacts close, the Markland transmitter freezes its last reading, and the LCD displays “METER DISABLED HOLDING LAST READING”. This feature is used for a batch mix process to disable the meter during mixing. It is also used to lock out the meter, when the probe is tipped up by a traveling scraper. Both of these uses are illustrated in the accompanying diagrams. When the pause switch reopens its contacts, the sludge blanket level meter waits 30 seconds for the sludge to settle down before resuming normal operation.

Sludge Detector in SBR and Clarifier

Materials Probe: PVC
Mast: PVC Pipe
Clamp: Stainless Steel & Polypropylene
Cable: Vinyl Jacketed
Enclosure: Fiberglass Body & Clear Plastic Cover
Dimensions Probe: Overall Length: 1330 mm (52¼ in.)
Active Element: Length 1219 mm (48 in.)
Cross Section: 64 mm (2½ in.) x 38 mm (1½ in.)
Gap: 25 mm (1 in.)
Mast: 3.5 meters (12ft.), 1 in. Sch. 80, shipped in 3 pieces with fittings
Enclosure: Width 343 mm (13½ in.) · Height 229 mm (9 in.) · Depth 200 mm (7 7/8 in.)
Cable Length 15 meters (50 ft.) pigtail supplied (measured from top of Probe). Maximum cable length 150 meters (500 ft).
Order extra cable separately if pigtail length not sufficient
Element Spacing 64 pairs infrared LED/Phototransistor, spaced vertically on 19 mm (¾ in.) centers. Dual Model has 128 pairs
Accuracy ± 2cm (± 1 in.)
Bottom Offset Adjustable, 0-700 cm or in. (NOTE: For ‘-DAF’ & ‘-UD’ types this is Top Offset)
Depth Units Selectable, inches or centimeters
Temperature Maximum 50°C (120°F)
Power 110/220 VAC, 220/240 VAC, 50/60 Hz (advise with order). 10 watts
Outputs · Liquid Crystal display (LCD) 2×20 Digit Alphanumeric
· 4 – 20 ma output signal, linear with sludge interface level
· Two DPDT, 5 Amp, Relays, independently adjustable set-points
· RS – 232 Serial Port
· RS – 485 Serial Port (Optional)
Models 602 Reads sludge depth up from tank bottom
602 – UD Reads sludge blanket location down from liquid surface
602 – DAF Reads sludge/liquid interface in Dissolved Air Flotation thickeners
602 – LP Special model for Drinking Water Plant upflow clarifiers where overlying water is very clear & sludge is thin (consult factory for further details)
602 DUAL &
Uses 2 probes, one mounted 48 in. (122 cm) above the other to give 96 in. (244 cm) continous span
CSA Approved and CE Conformance

The graphics below demonstrate the Markland difference. With Markland’s Fixed Sludge Level Control Equipment, you only pump when necessary, resulting in no overflows, no unnecessary pumping and running the risk of pumping water with sludge.

Light Desludging

LIGHT sludge loading can allow a timer to pull a core hole and pump water out the bottom.  The Automatic Sludge Level Detector does not turn on the desludge pump until it is required, and the sludge level is maintained within the high and low set-points.

Timer Desludging

Timed Desludge Control in Light Loading Application


Blanket Level Desludging

Automatic Desludge Control in Light Loading Application

Heavy Desludging

HEAVY sludge loading can overwhelm a timer-controlled desludge pump, allowing sludge to slip over the top, while the Automatic Sludge Level Detector maintains the sludge level within the high and low set-points.

Timer Desludging

Timed Desludge Control in Heavy Loading Application


Blanket Level Desludging

Automatic Desludge Control in Heavy Loading Application

To receive a quote for a Markland Automatic Sludge Blanket Level Detector, complete the form below.

Contact Information

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Your Requirements

Gravity ClarifierCircularRectangularInclined Plate ThickenerDissolved Air Flotation (Sludge above, liquid below)Other - specify:

Does the separator have a traveling bottom scraper? YesNo
Does the separator have a traveling top skimmer? YesNo

Liquid infeed: mg/L Color:
Underflow Sludge: mg/L Color:
Overflow Liquid: mg/L Color:
Note: Describe colour, i.e. pale gingerale, dark brown, water clear, milk, etc.

pH: Temperature: °C°F
Sewage, PrimarySewage, Secondary
Industrial Sludge - List Major Components:
Liquid is water
Other - List major chemicals:

Total Depth (Liquid + Sludge): inchescm
Sludge depth from bottom of tank ranges from to inchescm

Bottom of tank up to sludge/liquid interfaceLiquid surface down to sludge/liquid interface
120/60220/50240/50Other Specify:
MetresFeet from Probe to Controller (50ft/15m is standard)

Provide cross-section elevation with dimensions from sludge surface to bottom of skimmers, and to bottom of sludge baffle and to tank bottom. Also supply sludge layer thickness desired, both maximum and minimum. We prefer dimensioned plan and cross section drawings via mail or fax. Please do not fax us miniatures. Fax full size segments and we will paste it back together here.

How many instruments are required?

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