A turbidity sensor quantifies the clarity of a liquid, most commonly water. It measures the cloudiness or haziness caused by tiny suspended particles. By providing a quantifiable value for this optical property, the sensor continuously monitors water quality in various natural and engineered systems. The measurements assess the concentration of solid matter suspended within a fluid.
Understanding Turbidity
Turbidity is an optical characteristic of a fluid that causes light to be scattered and absorbed rather than transmitted straight through the sample. It is not a direct measure of the weight or volume of suspended solids, but an indicator of the water’s lack of transparency. Higher concentrations of suspended matter result in a greater degree of light scattering and a higher turbidity reading.
The physical sources of turbidity are diverse, including inorganic matter like silt and fine clay particles eroded from soil and riverbeds. Organic contributions include decaying plant material, algae, phytoplankton, and various microorganisms.
Human activities, such as construction runoff, agricultural practices, and wastewater discharge, frequently introduce these suspended particles into water bodies. Measuring turbidity helps assess the impact of both natural processes and human influence on water quality.
How the Sensor Measures Light Scatter
The primary mechanism used by most high-accuracy turbidity sensors is called nephelometry, which measures the intensity of scattered light. This method involves a fixed light source, often an LED emitting infrared or white light, and a photodetector. The light beam is directed through the water sample.
When the incident light beam strikes a suspended particle, the light is deflected in various directions. Nephelometric sensors place the detector at a 90-degree angle relative to the path of the original light beam to capture the scattered light.
The intensity of the light registered by the 90-degree detector is directly proportional to the number and size of the particles present. This perpendicular measurement minimizes interference from the sample’s color and provides accurate readings, especially for fluids with low turbidity levels like finished drinking water.
Practical Applications and Measurement Units
Turbidity sensors are employed across numerous fields for quality control and regulatory compliance.
In environmental monitoring, they track river and lake health, assessing the impact of storms, erosion, and sediment transport. Industrial applications include monitoring filtration efficiency in manufacturing, such as ensuring the clarity of beverages or controlling boiler water quality.
A primary application is in public water treatment, where continuous monitoring is required. High turbidity in drinking water is a concern because suspended particles can shield pathogenic microorganisms, such as bacteria and viruses, from chemical disinfectants like chlorine. This shielding reduces the efficacy of the disinfection process, posing a health risk.
The measurements are standardized using specific units: Nephelometric Turbidity Units (NTU) and Formazin Nephelometric Units (FNU). NTU is typically used in the United States and Canada, aligning with EPA standards (Method 180.1), which often specify a white light source. FNU is associated with the international standard (ISO 7027), which dictates the use of an infrared light source to minimize color interference. Both units use the 90-degree light scatter principle and a standardized polymer suspension called formazin for calibration.