What Is A Turbidity Sensor?


Share This Post

Turbidity sensors are a piece of equipment used to measure the cloudiness or haziness and the concentration of total dissolved/suspended solids of a solution. 

A turbidity sensor is an analytical sensor that measures turbidity. They are highly useful and effective instruments to identify the clarity and particle content in a solution, like water. Turbidity sensors are used to reduce waste, improve yields, and analyze water quality in a wide range of industries. 

How Do Turbidity Sensors Work?

Turbidity sensors measure the amount of light that is scattered by suspended solids in a liquid, such as water. When the concentration of total suspended solids (TSS) and total dissolved solids (TDS) in a liquid increase, the turbidity also increases. 

Turbidity sensors are used to measure the cloudiness or haziness (turbidity) of a liquid, usually to determine water quality

For samples with high amounts of TSS and TDS, the difference in the light intensity from the transmission beam is measured to obtain the turbidity result, while light scattering is more suitable for samples with low amounts of TSS and TDS. Since turbidity sensors use light to detect a solution’s turbidity level, it is important to reduce the amount of external light when using the sensor.

Turbidity sensors must comply with the Environmental Protection Agency (EPA): 180.1, therefore, a tungsten type meter or ISO specified design turbidity meter is used. 

Turbidity Units

When measuring turbidity, most often, you will see the units NTU or JTU.

  • NTU = Nephelometric Turbidity Units 
  • JTU = Jackson Turbidity Units

However, you may also come across alternative turbidity units, such as:

  • FNU = Formazin Nephelometric Units
  • FTU = Formazin Turbidity Units
  • FAU = Formazin Attenuation Units (common when using colorimeters or spectrophotometers)

As the optical design of the light, aperture, and photodetector differ between turbidity instruments, samples must be calibrated with an NTU standard or other turbidity standard

How To Use A Turbidity Sensor?

Most modern turbidity sensors work the same; a sample is collected and added into a vial. 

The vial is then placed in the instrument where a fixed light beam passes through the sample to measure how much light is transmitted, and how much light is scattered via photodetectors, which are usually set at 90° to the sample. 

Selecting A Turbidity Sensor

The type of turbidity sensor you select depends on the application it is being used for. However, for quantitative turbidity measurements, all turbidity probes require calibration, following the regulation by ISO 7027:1999, which has now been revised to ISO 7027-2:2019

There are three main types of turbidity sensors available:

  • Nephelometric turbidity sensors
  • Absorption turbidity sensors
  • Total solid/suspended solid turbidity sensors

Nephelometric Turbidity Sensors

Nephelometric turbidity sensors detect how light energy scatters through a liquid. The sensor uses a light detector (positioned at a 90° angle), and an LED lamp. 

Once the lamp is switched on, the beam shines directly into the sample, where the light scatters when it hits a particle in a defined area. When the light scatters inside the sample, reflection occurs. It is the reflection in the sample that a nephelometric turbidity sensor measures by converting the received light intensity into an electrical signal. 

The greater the reflection intensity, the greater the turbidity of the sample, and vice versa. The result is shown on the turbidity sensor’s electronic display in the desired unit. 

Nephelometric sensors are used to measure drinking water or other types of water with low turbidity according to ISO 2027/ EN 27027

Absorption Turbidity Sensors

Absorption turbidity sensors measure how many particles absorb light (light absorbance) in a solution. Similar to nephelometric sensors, they also contain a light detector and an LED lamp, however, the light detector and lamp are placed directly opposite. 

The particles in the solution attenuate the emitted light, which is then converted into an electric signal by the detector, and then into a final turbidity reading. 

Advanced absorption turbidity sensors are equipped with a second lamp detector arrangement, which allows for more reliable turbidity measurements. The second light detector can correct light intensity variations, color changes, and reduces lens fouling. 

Absorption turbidity sensors are used for water that experiences regular fluctuations in turbidity.

Total Solid/Suspended Solid Turbidity Sensors

Total solid/suspended solid turbidity sensors use a backscattered light, containing two light detectors and an LED lamp positioned at 90° and 135° angles. 

The turbidity of the solution and the amount of TSS present are calculated when the detectors receive the amount of scattered light, which is then displayed by the transmitter in the desired unit (usually g/L or %TS).

Any solid particles in the solution will cause the incident light emitted by the LED lamp to effectively scatter. 

Total solid/suspended solid turbidity sensors are used for measuring water with high turbidity.

Benefits Of A Turbidity Sensor

There are many benefits to using a turbidity sensor:

  • There are so many different turbidity sensors available to accommodate your needs. 
  • They are highly accurate. 
  • They are easy to use. 
  • They can be used in a wide variety of environments, for example, they can be fed down a pipe, or they can be handheld, immersing the probe into a sample. 
  • You can obtain turbidity measurements in different metrics (NTU, FTU, etc.)

Limitations Of A Turbidity Sensor

Turbidity sensors are great, however, they do not come without some limitations. 

  • As samples are usually sent to the lab for testing, the transportation process can alter the results due to TDS and TSS aggregating, allowing algae and bacteria to grow in the sample. 
  • They must be constantly maintained.
  • They require calibration. 
  • Turbidity sensors can be expensive.
  • They require a power supply, which is why older methods like a Secchi disc are also used to measure water clarity. 

Turbidity Sensor Applications

Applications that use turbidity sensors include:

  • Water quality testing 
  • Groundwater testing 
  • Water and wastewater treatments
  • Effluent and industrial control systems
  • Leak detection of filters and gaskets 
  • Food and beverage industry (for example, yeast harvesting and phase separation in cream and milk industries)


Turbidity sensors are useful pieces of equipment to measure the cloudiness or haziness of a sample. They are often used to measure water quality in different aquatic environments. 

A turbidity sensor consists of a fixed light beam that passes through a sample to measure how much light is transmitted, and how much light is scattered via photodetectors.

Now you have a better understanding of what a turbidity sensor is, all that is left is to identify which turbidity sensor will best suit your needs. 

If you have any questions regarding turbidity/water quality or the water testing kits we have to offer, please feel free to reach out to our world-class team at Atlas Scientific, we are always happy to help!

Subscribe To Our Newsletter

Get product updates and learn from the best!

More To Explore


How To Reduce BOD In Wastewater

There are many easy ways to reduce biochemical oxygen demand (BOD) in wastewater. These include reducing total suspended solids (TSS) via physical filtration and chemical processes. Another method is aeration in activated sludge treatment facilities, which reduces BOD by supporting beneficial bacteria. Maintaining optimal temperatures is also essential in reducing BOD in wastewater. Alternative methods


What Causes High BOD In Wastewater?

The cause of high biochemical oxygen demand (BOD) in wastewater comes from excessive organic matter in the water. The source of the organic matter typically comes from human and animal waste like sewage and industrial processes. Other causes of high BOD include agricultural runoff, untreated wastewater, and food processing industries. In addition to organic matter,

Want to learn more about our products?

Scroll to Top

To track your order please enter your Order ID in the box below and press the "Track" button. This was given to you on your receipt and in the confirmation email you should have received.