The OPSA-150 is a organic pollutant monitor that uses HORIBA's proprietary Rotary Cell Length Modulation, a measuring technique incorporating 25 years of expertise. The unit can be used as an organic pollutant monitor at drainage systems for determining compliance with COD monitoring regulations, for monitoring quality of water measuring levels of organic matter at water supply intakes, and as an organic monitor on process lines (phenol meter). This sensor can makes full use of Rotary Cell Length Modulation with Zero drift correction is perfomed in every cycle of measurement. This correction can eliminate the effect of any interference on cells. Also, cell length modulation provides readings from multiple measurements, making available results from various cell lengths. This allows the single device to make measurements on a large range of concentrations from as low as 0 to 0.1 Abs, up to 0 to 5.0 Abs.