Model 2100AN Laboratory Turbidimeters measure turbidity in either ratio or non-ratio mode. Light from a tungsten-filament lamp is focused and passed through the sample. The 90-degree scatter detector receives light scattered by particles. Transmitted and forward scatter detectors receive light that passes through the sample. A back scatter detector in the 2100AN Model (shown here) measures light scattered back toward the light source.
Ratio and no-ratio turbidity measurement modes are selected using the ratio key located on the instrument keyboard. With ratio toggled off, turbidity is measured using only the single 90-degree detector. Benefits of the ratio mode include long-term calibration stability, wide measurement range with excellent linearity, and the ability to measure turbidity in the presence of color.