How does a turbidity sensor work?
The most widely used turbidity sensor operates on the backscatter principle. The sensor emits an infrared light beam into the medium. Solid particles, fat droplets or other particles in the liquid reflect part of that light back to the receiver. The more particles present, the stronger the backscatter signal. A microprocessor processes the signal and produces an output of 4…20 mA that directly corresponds to the level of turbidity.
This measuring principle is particularly suitable for media with high turbidity and for situations where rapid phase transitions need to be detected. The sensor is installed directly in the process pipe and requires no bypasses or external measuring cells.
For lower turbidity levels — such as in drinking water or industrial process water — the transmission principle is sometimes used, measuring the loss of light intensity through the medium. For more information on complementary process instrumentation, see our level meters.
Which types of turbidity sensors are available?
The choice between a backscatter or transmission sensor depends on the medium and the required measuring range. The table below helps with selection:
| Characteristic |
Backscatter sensor |
Transmission sensor |
| Turbidity range |
+ High (turbid media) |
- Low (clear media) |
| Suitable for food industry |
+ Yes, EHEDG versions available |
- Limited |
| Installation |
+ Direct in-line installation |
- Often measuring cell or bypass |
| Response speed at phase transition |
+ Very fast |
- Slower |
| Suitable for drinking water |
- Less accurate at low NTU |
+ Yes |
| Calibration |
Product-specific (e.g. milk, whey) |
Standard NTU calibration |
Choose a backscatter sensor when working with turbid or fatty media where rapid phase transitions need to be detected. Choose a transmission sensor when accurate measurement at low turbidity levels — such as in drinking water or reverse osmosis — is required.
Typical applications for a turbidity sensor
Turbidity sensors are widely used in processes where the composition of a liquid must be monitored continuously. Common applications include:
- Phase separation in the dairy industry – detection of the milk/cream/whey transition based on fat content
- Milk fat quality control – continuous monitoring of fat content for skimmed, semi-skimmed and whole milk
- CIP monitoring – tracking contamination levels in rinse water to control cleaning cycles
- Filter breakthrough detection – monitoring the filtrate to immediately signal filter failure
- Beer yeast and fruit juice – detection of yeast during harvesting or monitoring juice clarity
- Drinking water production – measurement of surface water, source water and desalination installations
- Industrial wastewater – monitoring water quality in recycling and cooling tower applications
In all these applications, a turbidity sensor provides a continuous signal that allows you to detect process changes immediately — without sampling or laboratory analysis.
How to select a turbidity sensor: key parameters
Medium and particle type
Are you working with fat droplets (milk, cream), solid particles (yeast, sludge) or fine suspended matter? Backscatter sensors are suitable for all three, but calibration differs per medium.
Temperature and CIP compatibility
Process temperatures up to 100°C are standard for most industrial sensors. For CIP and SIP cleaning processes, you need a sensor that can withstand temperatures up to 141°C for short periods. Check for EHEDG certification if hygienic design is required.
Process connection and pipe diameter
Backscatter sensors are mounted directly in the process pipe. The minimum pipe diameter varies per sensor — verify that the connection is compatible with your installation (e.g. VARIVENT, DIN 11851 or Tri-Clamp).
Calibration and measuring range
Calibration is tailored to the medium being measured. For dairy applications, standard data points are available for water, skimmed milk, semi-skimmed and whole milk. The signal for the highest fat content is standardised at 20 mA. For water treatment applications, NTU calibration in accordance with international standards applies.
Output signal
Standard output is an analogue 4…20 mA signal (3-wire) combined with one switching output. Some transmitters also offer a digital interface or Modbus communication. See also our pressure sensors and flow meters if you want to combine multiple process parameters in a single measurement setup.
Turbidity sensors from Hengesbach and Georg Fischer
Ebora supplies turbidity sensors from two manufacturers, each with their own field of application.
Hengesbach Turbimess NEO
The Turbimess NEO from Hengesbach is an optical backscatter sensor for direct installation in process pipelines. The sensor is EHEDG-certified and suitable for hygienic processes in the food industry. It provides phase separation for fat content differences greater than 40%, is CIP and SIP compatible up to 141°C, and delivers an analogue 4…20 mA signal combined with one switching output. Minimum pipe diameter is DN40 with VARIVENT connection type N.
Georg Fischer type 4170
The GF turbidity sensor type 4170 from Georg Fischer is designed for water treatment applications where accuracy and long service life are the priority. The sensor is suitable for drinking water, source water, seawater/desalination, reverse osmosis and industrial wastewater. It is combined with the GF transmitter type 8640, supplied with a 7-point calibration and meets international standards and regulations for water installations.
Not sure which sensor best suits your application? Contact Ebora — we will consult with the manufacturer to determine which version is most suitable for your medium, temperature and process connection.
Frequently asked questions
What is the difference between NTU and FTU in turbidity measurement?
NTU (Nephelometric Turbidity Unit) and FTU (Formazin Turbidity Unit) are both units for turbidity and are numerically equivalent in practice. NTU is primarily used in water treatment in accordance with ISO 7027, while FTU is more common in European standards. For sensor selection and calibration, the distinction makes no difference in most cases — the measuring principle and calibration points are what matter.
Is a turbidity sensor suitable for CIP cleaning?
This depends on the version. Sensors such as the Hengesbach Turbimess NEO are specifically designed for CIP and SIP processes and can withstand temperatures up to 141°C for short periods. Always check whether the sensor is EHEDG-certified and whether the process connection is hygienically designed. A backscatter sensor installed in the pipeline can also be used during CIP to monitor the contamination level of the rinse water.
How often does a turbidity sensor need to be calibrated?
The calibration interval depends on the medium and process conditions. In highly variable or aggressive processes, more frequent calibration is required. For dairy applications with fixed calibration points, periodic verification against a reference standard is common practice. Ebora can advise on the appropriate calibration strategy for your specific application.
