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Designed to be suitable for all waste water applications, including influent, effluent, sludge and silicates

Suspended Solids

Key features

  • Autoclean optical sensor meaning minimal operator intervention
  • Stable and reliable
  • Suitable for all potable, waste and process waters
  • Up to 12 months between calibration and maintenance
  • From 2 NTU (1mg/l) o 8%* solids
  • Up to 10 Bar


A single sensor with a large dynamic range which utilises measurement technology that eliminates the need for a “zero” and also eliminates the effect of background light. For multiple measuring ranges, the suspended solids sensor can monitor turbidity and suspended solids from 2 NTU (1mg/l) to 8%* solids.

The sensor uses lifetime optical technology to provide a stable, reliable low-maintenance sensor with no moving parts and no consumables.

How it works

The sensor determines the suspended solids concentration or the turbidity in the water using a measurement of the backscattered light.

Each sensor is fitted with an  infra-red LED emitter light source and two matched photodiodes detectors for making the measurements. Having two detectors, positioned at different distances from the light source, allows the sensor to be used over a wide range of suspended solids concentrations.

The detectors are positioned to detect backscattered light (light that is scattered by <90°). By measuring back scattered light, the sensor can be used to detect low and high concentrations of solids. The ORAKEL takes readings at four different light levels and uses the gradient between the readings to produce the sensor output, allowing for more accurate measurements of suspended solids and turbidity.


The sensor can be mounted on the end of a pole for dip mounting in the channel or tank, or inserted into a pipe via a valve which allows for retraction and removal of the sensor without shutting down the process.


The sensor is fitted with a cleaning nozzle to keep it clean. This can be used to clean the optical windows with a jet of water. The procedure can be programmed to be automated at predefined intervals.


Calibration for turbidity measurements or measurements of samples  with low concentrations of solids is very easy only requiring a single calibration sample. This sample can either be a reading from another method or a suitable standard.

The ORAKEL control unit calibrates the sensor by reducing the light output through four stages, taking measurements at each. This process provides an accurate and reliable zero and span without the requirement to use a ‘0’ NTU/solids sample.

Calibration of the sensor for measurement of samples with high concentration of solids uses a multipoint procedure. Up to 5 calibration points can be used to give accurate performance across a wide range of sample concentrations.


Up to 500g/l, 4000 NTU (depending on the optical properties of the sample)

Selectable g/l, mg/l, ppm, ppt or % (suspended solids) NTU or FNU (turbidity)


<2% of measured value or 0.01g/l or 0.8 NTU (whichever is greater)


<1% of measured value or 0.001g/l or 0.8 NTU (whichever is greater)

Limit of detection:

0.001g/l or 2.4 NTU


Up to 0.0001g/l or NTU

Response time:

T90 ≥ 10sec (adjustable based on averaging)

Drift (electronic):



Configurable (10sec-10min)

Lamp Source:

IR LED (860nm)


Approximately 1kg (35oz)

process Temperature:

0-50°C (32-122°F)

Operating Pressure:

10 bar (145psi) [maximum]

IP Rating:


Mounting thread (for dip installation):

1″ BSP

Max. power consumption:

70mA at 12 VDC

Cable length:

6m (20ft) as standard. (Talk to us if you need a longer length)

Wetted parts:

316 Stainless steel, sapphire


38mm (1.49in)


230mm (9.06in)


*8% in typical municipal waste water slurries. This value will vary depending on the optical properties of the sample.

Watch our Predictive Data Monitoring Video here

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Regent Street,
Whitewalls Industrial Estate,
Colne, Lancashire,