Suspended Solids Monitor Inline Tip

SoliSense® Inline Tip

Whatever level of suspended solids or turbidity monitoring you want to measure, the SoliSense® is the solution. A sophisticated sensor that ranges from 10 NTU to 2% solids (in waste water, up to 50% in other solids), this turbidimeter suspended solids monitor is the solution, and is unique in its ability to measure from low NTU to percent solids in one sensor. Suitable for potable water monitoring, mixed liquor suspended solids monitoring, return activated sludge, centrate monitoring, filtrate monitoring, sludge, and many more applications where a traditional turbidimeter or suspended solids analyzer would be used.

With the SoliSense® range of Suspended Solids/Turbidity analyzers you get a world’s first sensor. The first sensor to successfully incorporate four measuring technologies. For multiple measuring ranges the one sensor can monitor Turbidity and Suspended Solids from 10 NTU to 2% solids in one sensor.

The SoliSense® Turbidity Meter Suspended Solids Analyzer instrument uses two light emitters and four detectors arranged around a circular aperture. This eliminates interference from extraneous light sources and compensates for detector soiling and the aging of the optical modules. The arrangement of this 8 beam technology allows measurement of the light transmitted, scattered or reflected by a medium. This allows for the most precise measurement of turbidity or suspended solids in a liquid from 10 NTU up to 2% solids!

The SoliSense® suspended solids meter is suitable for dip monitoring, in line monitoring and flow through monitoring.

Suspended Solids Monitor Dip Tip

SoliSense® Dip Tip

  • Auto-clean optical sensor
  • Stable and reliable – excellent process control
  • Suitable for all potable, waste and process waters
  • Up to 6 months between maintenance
  • Up to 3 months between calibration
  • From 10 NTU to 2% Solids

The SoliSense® suspended solids sensors are available with different controllers giving you the same great performance with different communication, display, and control options. With the SoliSense® range of suspended solids meters, you get everything that you need – and nothing that you don’t, without sacrificing the quality of measurement.

Suspended Solids Monitor Lab Installation

SoliSense® installed in Pi’s test lab

  • Inlet monitoring (turbidity 10-4,000 NTU)
  • Effluent monitoring (suspended solids 5-1,000 mg/l)
  • Distribution monitoring (turbidity 10-100 NTU)
  • Hydrant monitoring (turbidity 10-20,000 mg/l)
  • Fire hydrant monitoring (turbidity 10-20,000 mg/l)

Traditional monitoring applications where the SoliSense® is particularly suited:

  • RAS (Return Activated Sludge)
  • MLSS (Mixed Liquor Suspended Solids)
  • WAS (Waste Activated Sludge)
  • Thickened sludge
  • Centrate
  • Filtrate
  • Effluent
  • Inlet
  • Filter
Each probe is equipped with 2 light sources and 3 detectors. Each light source uses long-life emitters (at least 20,000 operating hours), and these are turned off when not required to conserve energy and extend the life.

By using multiple light emitters and detectors in a single probe it is possible to:

  • Measure solids from 10 NTU to 2% solids
  • Monitor and compensate for fouling of the optics
  • Monitor and compensate for aging of the optics
  • Measure the side scattering of light (ISO7027 requires a 90° side scatter measurement). (NTU)
  • Measure transmitted light (low % solids)
  • Measure the back scatter of light (higher % solids)

The electronics provide a fully scalable output allowing the SoliSense® to measure any part, or the whole of the scale. The sensor probe comes equipped with the capability of having a water jet regularly sweep over the optical lenses keeping them clean. If you have an application that ranges from low NTU all the way to %age solids then the SoliSense® is certainly the monitor for you! With only 3 or 4 calibration points you can accurately monitor your process all the way from low NTU to medium solids.

The probes are stainless steel and are built to work in the demanding environment of a WwTW. If you want to monitor solids at any point in your waste water treatment plant, this instrument has the self cleaning sensor and accessories to do it, even if other instruments have failed.

Small water treatment plants, secondary disinfection plants etc. tend to suffer from similar problems wherever they are in the world. The first is lack of communications SCADA infrastructure. The cost of which to install can be prohibitive. The second is the lack of a central DCS control infrastructure, again the installation of which can be cost prohibitive. The third is the remote location. Often these water plants are in remote and difficult to access locations.

With these three issues facing many water engineers around the world, a low cost solution providing solutions to all three issues is available from Pi. A CRIUS® controller has the on board capacity to provide small scale SCADA, and full online PID control whilst the sensors (e.g. chlorine, pH, Turbidity etc.) are suitable for long term operation without operator intervention.

To demonstrate the remote access capability of the CRIUS® please click here.

To learn more about the control capability of the CRIUS® please click here.

To hear more about other customers using the CRIUS® multiparameter controllers in a similar way why not contact us?

Document Type Size
SoliSense Brochure 546kB
CRONOS® Brochure 560kB
CRIUS® Brochure 573kB
CRIUS® Remote Communications Brochure 596kB
CRONOS® and CRIUS® Control Options Technical Note 534kB
Remote Access GPRS Technical Note 501kB

Suspended solids are particles suspended in water. They occur naturally and can be seen for example in rivers after a rainfall event when the river appears ‘muddy’.
Water treatment is largely about; removing particles and organics, and then disinfecting water. Being able to measure suspended solids can help in determining the best treatment for example by measuring the suspended solids in the raw water coming in to a plant.

Typically suspended solids in waste water treatment has specific names such as MLSS (Mixed Liquor Suspended Solids) or RAS (Return Activated Sludge) etc.

Typically suspended solids are measured in mass per volume units such as mg/l or mgl-1.
Suspended solids is a ‘unit per volume measurement’ e.g. 1 mg of suspended solids in 1 litre of water. Turbidity is a measurement of ‘ cloudiness’. Although each suspended material will have a different relationship (which will change over the range) a useful ‘rule of thumb’ is that 1 mg/l = 2 NTU.
This depends entirely on how ‘optically clean’ the medium is. So for example if we are measuring sand (silica) in a clean water suspension we can measure up to 50%. If, however, we are measuring black sludge in a waste water plant it may be as low as 2%. Typically in most waste water works it is 3%.
This can happen, for example with a water treatment plant inlet where for much of the time the raw water is in the range 0-20 mg/l but when it rains it can go to 0-700 mg/l. The SoliSense® allows several outputs for the same sensor. This means for example you might have 2 output ranges; one scaled 0-20 mg/l and one scaled 0-750 mg/l. Up to four outputs are possible.
Each SoliSense® has temperature compensation built in so the effect of temperature is negligible. It should be noted though that the SoliSense® is a large mass that can take time to reach thermal equilibrium so any process where the temperature is changing rapidly >2°C per 10 min is probably not an ideal application.

Focus Ons are a series of short articles distributed by email providing technical information regarding instrumentation, process measurement in potable, waste, process and pool waters. If you would like to join the mailing list, please contact us.

Many different sites ranging across the whole water industry have a daily struggle to keep instrumentation functioning correctly due to fouling. However did you know that…

… self cleaning and self flushing systems are now available from Process Instruments for most types of sensors?
… these fouling removal systems can extend the life of sensors and drastically reduce maintenance regimes?
… Pi’s self cleaning/flushing systems are affordable, simple and trouble free by design?

What is the problem?

Sensor Fouling

Sensor FoulingWhatever the process being monitored is, there is often something in the sample water capable of fouling a sensor, and therefore causing erroneous results. The obvious solution to this problem is to clean the sensor, but how regular should inspection and cleaning programs be for each piece of instrumentation? Too regular and the inspection and cleaning regime is time consuming and unnecessarily costly. Not often enough and the instrumentation will give false results and probably fail prematurely.

What is the solution?

Process Instruments’ Autoclean and Autoflush Systems

Simple, reliable and easy to maintain, Process Instruments’ Autoclean/Autoflush systems are an alternative to mechanical cleaning mechanisms which can clog and break. By regularly spraying the sensor/probe with clean water or air, the sensor remains clean and free from fouling for extended periods of time. The sensor cleaning cycle is activated by Pi’s controller for a user selectable length of time and frequency so that no matter how dirty the application, the probe remains clean. With no moving parts in the sensor body or in the cleaning attachment there is nothing to replace or check other than a simple valve positioned in an easy to reach location.

Pi’s Autoclean and Autoflush systems can give trouble free and fouling free functioning of sensors for weeks, if not months, at a time.

A solution for each application

Autoclean Cap


This option can be added to our pH, ORP, Turbidity, Suspended Solids and Dissolved Oxygen (DO) sensors. Consisting of an end cap to direct the flow of clean water (or air for a DO sensor) across the face of the sensor blasting any dirt away. The cleaning is controlled by a single valve positioned in an easily accessible location.


If using air to clean a DO sensor the system can also automatically verify that the sensor is still responding correctly, removing any need to remove the sensor from the sample for months at a time.
Autoflush System


For sensors that require flow cell mounting like Chlorine, Ozone and Chlorine Dioxide, an Autoflush system has inbuilt valves which automatically start/stop the sample flow and control the flow of clean water past the probe. The user can set the flushing interval and duration to keep the flow cell and sensor clear from fouling. For particularly dirty or stubborn contaminants, warm water can be used as the flush water to aid cleaning.

With the above options, whatever the application or parameter being measured, Process Instruments will be able to provide a monitoring system that will not only be accurate, precise and long lasting but that will also remain free from fouling and save the operator both time and money.

Contact us on...

Tel: 6459 0785

Email: [email protected]

"Give me a ring, I'd love
to hear from you."

Aden Chiu Kay Yew

Singapore Team Leader

Tel: +44 (0)7854 133327

Email: [email protected]

"Get in touch, I'd be
happy to help."

Rob Paramore

Head Office Contact