Trace Level Measurements with EPA Compliance 90 degree scattered light method The turbidity sensor of the FMTSC-10 (E) uses the 90 degree scattered light method, a global EPA standard. Built-in wiper cleaning system The built-in wiper cleaning system easily keeps the lenses clean. Sapphire glass optical windows The optical windows are made of hard-toscratch sapphire glass. This facilitates scrubbing of the window surface to keep the turbidity sensor clean. Compact design The compact design makes installation easy.