The OFS-2000 has a range of 0-40m/sec and is the only flow sensor that gives a true non-contracting cross-stack flow measurement of the process. OSi's patented Optical Flow Sensor (OFS) makes drift-free measurements across the entire stack, duct or pipe diameter and calculates an accurate average  flow reading. It is the only flow sensor that gives a true non-contacting cross-stack flow measurement of the process. The OFS uses our EPA Method 14 approved optical scintillation technology. The optical scintillation technique relies on advanced Digital Signal Processing (DSP) electronics to "see" and measure the movement of turbulence found in a gaseous flow stream to provide highly accurate.