Absorption sensor for turbidity and suspended solids measurement in industrial wastewater and processes.

Situation analysis

Our offering:

  • Turbimax CUS51D: suspended solids and turbidity sensor mainly for waste water
  • Turbimax CUS52D: Hygienic turbidity sensor in drinking water
  • Missing: a turbidity sensor for industrial waste water and processes

Market opportunity:

  • The availability of a chemical robust turbidity sensor can lead to a huge MRO business
  • Challenges in these processes:
  • High temperatures
  • Low pH values
  • High chlorides

Requirement: Reliable measurements under these harsh environmental conditions

Endress+Hauser turbidity sensors in a nutshell

the turbidity sensor for wastewater.

the expert for potable water and low turbidities.

turbidity sensor mainly for F&B.

absorption sensor with hygienic design, usable for F&B.

CUS50D opens the door for new applications in chemistry, primaries & metals and for measuring turbidity in special media due to chemical resistant materials and the attenuation measuring principle according to ISO 7027.

Overall objective of the launch

  • Expand the Endress+Hauser turbidity portfolio for industrial waste water and processes
  • Gain market share in Chemical, Primaries & Metal and other industrial applications
  • Offer a 40 mm sensor design and Memosens for mechanical and electrical compatibility with existing products


  • Cover new applications:
  • For harsh chemical environmental conditions
  • For measuring turbidity and suspended solids in highly absorptive (dark) media
  • For applications with the need of turbidity measurement according to the turbidimetry principle in ISO 7027
  • For measuring absorbance

Turbimax sensor segmentation by measuring range

Measurement ranges:
CUS52D: 0,000 – 4000 FNU
CUS51D: 0 FNU – 300 g/l
CUS50D: 40 FAU – 60 g/l

Application examples

Industrial wastewater and utilities:

  • Measurement of the solids content in process and wastewater sludge
  • Flocculent dosing
  • Concentration measurement of milk products in the wastewater

Process media:

  • Concentration measurement
  • In the product, e.g. in titanium dioxide

Highly absorptive media:
• Concentration measurement in very dark media, e.g. activated carbon concentration in the fourth cleaning step of wastewater

Value proposition.

Turbimax CUS50D is a long lasting, robust, low maintenance absorption sensor for turbidity and suspended solids measurement. It provides stable and definite measured values in industrial wastewater, process water and utilities. Thanks to its measuring curve we can provide definite values from middle turbidity ranges up to high concentrations of suspended solids. In addition, due to the single point calibration we can reduce the maintenance effort drastically.
The sensor head consists completely of a dirt repellent Teflon derivative and enables CUS50D for measuring also in highly corrosive media.

Our promise with Turbimax CUS50D:

  • Reliable process control
  • Low maintenance efforts
  • Easy commissioning

Reliable process control.

  • Thanks to its absorption measuring principle CUS50D provides definite measured values which leads to a more reliable water treatment
  • Easy calibration and stable measured values even in highly absorptive media like eg. in the 4th cleaning step of WWTP
  • Memosens digital technology allows the failure-free transmission of measuring signals
  • High measuring accuracy and repeatability provides reliable process control

Low maintenance efforts

• Easily cleanable: dirt does hardly stick to the PCTFE sensor head and in addition the air cleaning removes
dirt traces immediately
• Long sensor life time: the epoxy-glue- free sensor with stands harsh environmental conditions such as highly corrosive or hot media (up to 85°C and pH=1) – no sensor failure due to leakage


Easy commissioning

  • Turbidity measurement: sensor comes pre-calibrated with Formazin – no calibration necessary
  • Automatic sludge model selects the optimal signal curve depending on the sludge type
  • Measurement of suspended solids: No need to perform a series of measurement or complicated calibration procedure. In most cases, a single-point calibration is sufficient.

Features – Advantages – Benefits: Low OpEx

Features – Advantages – Benefits: Easy handling

Which Turbimax sensor for which application? (1/2)

Which Turbimax sensor for which application? (2/2)

Field tests

Customer: Manufacturer of equipment for WWTP

  • The waste water fees that companies have to pay dependonthe organic load of the wastewater. In order to reduce these costs, flocculant is added to the wastewater to keep the COD on a low level.
  • Never the less flocculant is expensive->goal is to optimize flocculant dosage with CUS50D

Customer benefit with CUS50D:

  • No cleaning required->low maintenance effort
  • End-customers can save between € 30.000-€ 50.000 per year on flocculants
  • Measuring point with CUS50D is much cheaper than the one of its competitor

Titanium dioxide production

  • Turbidity measurement necessary to maximize out put of titanium dioxide
  • Competitor’s products failed because of glue that fixes the optical windows-> leakage
  • Turbidity up to 4000 FAU
  • Application with temperature up to 80° Cand pH= 1 (HCl)

Customer benefit with CUS50D:

  • Competitor’s turbidity sensors failed every 3 months because of environmental conditions -> cost saving just for new sensors of
    about € 10.000,– per year + commissioning
  • Increased uptime and therefore higher product output ->Major savings but details undisclosed

Wastewater from titanium dioxide production

Application: control of titanium dioxide concentration in the wastewater (0-2 gr/L TiO2 )
Purpose of the measurement: at value >1,0 gr/L , the wastewater cannot be discharged to the river Sensor CUS50D installed in CYA251 assembly incl. aeroclean


Customer benefit with CUS50D: Comply to discharge regulations

Optimization of gas washer with solids measurement

Customer: Fertilizer producer

Application: Measurement of suspended solids in gas washer Range: 0 – 80 gr/L
Temperature: 40-65 °C
Special: 20-50 gr/L dissolved Chlorides, therefore plastic version is required

During production, gasses (such as NH3) and fertilizer dust appears. This dust is filtered with dust filters + cyclones. After drying, this dust (and the gasses) come in the gas washer

At high solids concentrations, the pipes and spray heads will clog. This is also an indication that there is a problem in the fertilizer granulation process.

Customer benefit: CUS50D is able to detect clogging and enables the customer to control its process better -> higher uptime

Open-pit mine.

Customer: nickel mine
Application: measurement of concentration in the nickel thickening process

  • CUS50D installed in the effluent of the thickener
  • Temperature > than 55°C
  • One application in Finland are running successfully
  • Air cleaning needed

Measurement of activated carbon concentration in 4th cleaning step.

Customer: Wastewater treatment plant
Application: Measurement of activated carbon in the 4th cleaning step
Measuring range: a few 100 mg/l to a few g/l

Customer benefit with CUS50D:

  • Highly absorptive media measured with attenuation principle -> single point calibration sufficient
  • Easy commissioning


What makes Turbimax CUS50D so special?

Attenuation measurement principle

  • Definite turbidity values with defined 0|0 value for all models
  • Single point calibration possible for a turbidity range from 40 – 20.000 FAU
  • Better measurement in dark, highly absorptive media

Chemically resistant material

  • Sensor head made completely of Teflon derivative PCTFE
  • Glass- and epoxy-free
  • Plastic sensor housing available
  • Chemically resistant material and wide temperature range up to 85°C enable turbidity measurements even in dark, hot and highly corrosive media

CUS50D – the measuring principle

  • In many media there is a mixture of several effects, mainly:
    • Reflection: whole energy of light is changed in its direction (“mirrored”). In liquid media in reality a minor effect.
    • Turbidity: scattering of light at suspend solids particles. Scattering is also sometimes called “diffuse reflection” (e.g. titanium dioxide is a highly scattering media)
    • Absorption: energy of light is taken (“absorbed”) by atoms or molecules (e.g. activated coal, dark sludge)
      -> In general, the phrase “absorption” is used for all kinds of light attenuation through a media
      -> CUS50D is the absorption sensor for turbidity and suspended solids measurements

Physics behind absorption.

  • Energy of emitted light is absorbed by atoms or molecules
  • Out of the reduction of light intensity a concentration of the absorbing atoms or molecule can be calculated
  • Absorbance is the measuring of the absorption of a media

Absorption Measurement and Law of Lambert-Beer.

Absorption and Law of Lambert-Beer.

Effects of the absorption principle.

  • The signal curve of CUS50D delivers unique measuring values: every turbidity or concentration value is related to one signal height
  • Derived from the law of Lambert Beer absorbance is proportional to the concentration or turbidity and absorbance starts at 0|0 -> single point calibration is possible
  • CUS50D’s best sensor performance and therefore measuring range just starts from the middle turbidity range
  • Thanks to the two measuring channels with optical path lengths of 10 mm and 5 mm the measuring range is extended from 0 to 5 AU or from 0 to 10 OD

CUS50D – Signal behavior compared to CUS51D and CUS52D.

The automatic range functionality selects autonomously the correct signals of each measuring channel to provide
the best measuring signals -> The automatic range is especially for users who measure suspended solids or absorption over a wide measuring range and are not able to stay with one optical pathlength

Note: a single point calibration is always recommended!

Automatic sludge model – working principle

Benefit: the automatic sludge model automatically selects the right measuring values -> no need to create a calibration curve.

  • The automatic sludge model uses the different signal behavior of the two measuring channels (5mm and 10 mm) in sludge
  • With each measuring channel you get independent information about the sludge
  • The ratio between the two measuring channels depends on the suspended solids concentration and the sludge type
  • With the use of both measuring channels and the correlation of the two measuring channels to different sludge types you can determine the sludge concentration

Measurement categories

Turbimax CUD50D is able to measure various measurement categories that can be selected in the Liquiline transmitter:

• CUS50D works according to the light attenuation principle (ISO 7027)
• Formazin is the measuring parameter for turbidity measurement (FAU)
• The sensor is pre-calibrated with Formazin and works directly without calibration
• For Formazin measurements 10 mm optical pathlength is fixed

• Absorption measurement with the use of a factory-calibrated curve created in a solution that absorbs at the wavelength of 860 nm
• Choice of 5 mm, 10 mm optical pathlength and automatic range possible

Measurement categories

Suspended Solids
• Kaolin: suspended solids measurement with the use of a kaolin calibration curve. Choice of 5 mm, 10 mm optical pathlength and automatic range possible
• Sludge: suspended solids measurement with the use of a sludge calibration curve. Choice of 5 mm, 10 mm optical pathlength and automatic range possible
• Auto sludge: suspended solids measurement with the use of the measuring signals of the 5 mm and the 10 mm measuring channels and a 2D curved surface created out of a set of calibration curves in different sludges

Product Loss
• Absorption measurement with the possibility of using the measuring unit “%”. 100% product loss = 5 AU (can be adjusted by customer)
• Choice of 5 mm and 10 mm optical pathlength possible

Turbimax CUS50D – technical overview

Mechanical characteristics:
• 40 mm Sensor
• Immersion sensor with thread G1, NPT3/4
• Clamp 2” variant available
-> Compatible with all relevant assemblies

Connection to Liquiline:
• With fixed cable with crimp sleeves or M12 plug and individual cable lengths
-> electrical connection according to customers’ wishes possible
• Works with Liquiline CM44 from software version 1.06.06-0021 or higher

• Sensor head made from dirt repellent PCTFE
• Choice of shaft material between stainless steel or PPS GF40
-> Epoxy-free sensor head and chemical robust sensor body out of plastics for harsh environments
• Sensor with two measuring channels at two different optical pathlengths (5 mm and 10 mm)

At suspended solids measuring ranges can vary strongly on the measured media

Measurement categories

• Absorption: 0,5% of upper range value (corresponds +/- 50 mOD )
• Formazin: 10% of measuring value or 10FAU (the greater value applies in each case)
• Kaolin: 5% of upper range value ; for sensors which are calibrated on the measuring range
• Sludge/auto sludge: 10% of measuring value or 5% of upperrange value (the greater value applies in each case); for sensors which are calibrated on the measuring range
• The in accuracy encompasses all inaccuracies of the measuring chain (sensor and transmitter). However, it does not include the inaccuracy of the reference material used for calibration.

Repeatability, drift, LOD.

• Absorption: 0,001 OD or 0,2% of measuring value wert (the greater value applies in each case)
• Formazin: 10 FAU at 800 FAU
• Formazin: Drift 0,04% per day (at 2000 FAU)
• Absorption: Drift 0,015% per day (at 5 OD)
Limit of Detection:
• Absorption: 0,004 OD at 0,5 OD
• Formazin: 10 FAU

Air cleaning tool

Compressed air cleaning for CUS50D
• Connection: 6mm
• Pressure: 1.5 to 2 bar (22 to 30 psi)
• Materials: POM, PE, PA 6.6 30% glass fiber
• Order No.: 71395617

Compressor for air cleaning unit
• For compressed air cleaning
• 230 V AC order no. 71072583
• 115 V AC order no. 71194623

Calibration tool

• CUS50D kit, solid state reference
• Calibration tool for CUS50D turbidity sensor
• Easy and reliable inspection of CUS50D turbidity sensors.
• Order No.: 71400898

Process connections

CUS50D can be connected to following assemblies:

Accessories and process connections for harsh environments

• CTSP-UA4FP1 (modification position 30: 71407261) Flow cell PVDF version, Flange DN50
• CTSP-UA4FP1 (modification position 30: 71407533) Flow cell PVDF like above, with cleaning option

Accessories and process connections for harsh environments

• CTSP-UA4FP1 (modification position 30: 71407261) Flow cell PVDF version, Flange DN50
• CTSP-UA4FP1 (modification position 30: 71407533) Flow cell PVDF like above, with cleaning option

Accessories and process connections for harsh environments

  • CTSP-UR1CR1 (modification position 30: 71408856).
    Compressed air cleaning out of PTFE/PEEK and Teflon coated fixing screw


  • CTSP-UA2WP1 (modification position 30: 71406978).
    A833 Retractable assembly out of PVDF, Flange DN50

System overview