Turbidity (ATU)

Turbidity is an indicator of the visual “haziness” of a sample stream and is defined as a measure of the amount of light scattered by particulate matter suspended in the sample.

Historically, turbidity is defined as a measure of attenuated or scattered light (e.g. EPA Method 180.1). It is determined in the visual or near-infrared spectrum and reported as either nephelometric turbidity units (NTU), Formazin turbidity units (FTU), Formazin nephelometric units (FNU), or simply turbidity units (TU). In practice, turbidity is quantified by relating it back to a known standard.

However, despite these common practices it remains difficult to relate turbidity measurements between instruments and from one sample stream to another. This is because the intensity of scattered light is dependent on particle size, density, refractive index, the true color of the sample stream, bubbles, sample cell variations, and optical fouling of the optical cell. All of which will impact different instruments in varying ways depending on the wavelength(s) of incident light used in the measurement.

LiquID’s advanced approach to Turbidity 
The LiquID station uses patented multi-spectral technology for monitoring turbidity which produces a more accurate quantification of sample stream clarity than possible with NTU-type devices. Three key features of the LiquID Station are responsible for this extraordinary accuracy:

  1. High Sensitivity
    LiquID uses a high-quality photon counter combined with telescoping algorithms to ensure high performance in low (< 1 ATU) and high (>100 ATU) turbidity environments.
  2. Multispectral Flexibility
    LiquID stations employ patented HMA logic (Hybrid Multi-spectral Analysis) developed specifically for this system. HMA logic makes use of both transmission and scattering techniques. This produces a more accurate view of the overall effect of different types of particles on the dispersion of light than possible with other devices that use one type of measurement.
  3. Multiple Wavelenths
    Most turbidity devices collect information at a single wavelength. LiquID, on the other hand, measures attenuation over a large part of the particle-size distribution from colloidal material to aggregates and presents this information as highly accurate Attenuation Units (ATU).
  • Parameter Detection Range/Sensitivity Accuracy
    Turbidity (ATU) 0.1 to 100 m-1 ±10%

  • To learn more about the optical approach used by the LiquID to measure Turbidity please read the How It Works – Turbidity located in the Library and Resources section of our website.
  • Please Contact Us if you have additional questions about measuring Turbidity or general inquires into the LiquID Station.