turbidimeter

A turbidity meter, or turbidimeter, is an instrument used to measure the turbidity of a liquid, which is the cloudiness caused by suspended particles. Turbidity is a key indicator of water quality and process efficiency in many industries, including drinking water, wastewater treatment, and manufacturing.

Principle and operation: Most modern turbidity meters are nephelometers. They illuminate a sample with light, typically in the near-infrared range (around 860 nm), and detect light scattered by suspended particles at approximately a 90-degree angle to the incident beam. The amount of scattered light correlates with particle concentration and size, and the result is reported as turbidity in nephelometric turbidity units (NTU). Some instruments report Formazin Nephelometric Units (FNU), which are related to NTU when calibrated with Formazin standards.

Types and calibration: Turbidity meters come in portable handheld, benchtop, and inline process configurations. They are calibrated with Formazin-based standards and used across a wide measurement range, depending on the model and application. In some contexts, dilution is used to bring highly turbid samples within the instrument’s accurate range.

Applications: Common uses include monitoring drinking water and treated wastewater, supervising industrial processes, environmental monitoring, and quality control in food, beverage, and pharmaceutical production.

Standards and interpretation: Standards such as ISO 7027 define nephelometric turbidity measurement principles, while EPA methods (e.g., 180.x) specify turbidity procedures for drinking water. Turbidity is a surrogate for particulate contamination and does not directly measure microbial content.

Measurement considerations: Sample color and colorants can affect results; nephelometric measurements are designed to reduce color interference but may still be biased by high coloration. Factors such as stray light, cuvette cleanliness, temperature, and optical path length should be controlled.