USEPA-COMPLIANT 2100N Laboratory Turbidimeter

Model 2100N 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. 

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. 

(U.S. Patent 4,198,161)