turbidimeters

Turbidimeters are analytical instruments used to measure turbidity, the cloudiness or haziness of a liquid caused by suspended particles. Turbidity is commonly quantified in nephelometric turbidity units (NTU) or Formazin nephelometric units (FNU), with Formazin standards providing traceable references. Most turbidimeters operate on nephelometry: a controlled light source irradiates a sample in a cuvette or flow cell, and light scattered by particles at a defined angle is detected by a photodetector, typically at about 90 degrees to the incident beam. The measurement is influenced by particle size, concentration, color, and temperature; many instruments include automatic temperature compensation and optical path length correction. ISO 7027 and related standards describe the nephelometric approach for turbidity measurement.

Common light sources include green LEDs around 550 nm to minimize interference from sample color; some models use tungsten or infrared sources for specific applications. Calibration is performed with standard Formazin suspensions, and results are expressed in NTU or FNU with traceability to Formazin standards. Some instruments also report in other units to align with regional guidelines.

There are benchtop, portable, and inline (continuous process) turbidity meters. Benchtop and portable units are suitable for field sampling and spot checks, while inline meters monitor process streams in real time. Typical measurement ranges span from near zero to several hundred NTU, with higher-end models capable of higher readouts through optimized optics and dynamic range.

Applications include drinking-water quality and disinfection control, wastewater and environmental monitoring, food and beverage processing, pharmaceutical manufacturing, and various industrial processes. Limitations include interference from colored substances, high turbidity causing multiple scattering, air bubbles, and cuvette contamination; proper calibration, cleaning, and adherence to standards are essential for reliable results.