Sample is introduced to the center of an inclined turbidimeter body. Water rises to the top of the body and overflows a weir into a drain ring, forming an optically flat surface. The light source and photocell do not contact with the sample, and there is no sample cell to maintain. A light beam is focused on the liquid surface at an acute angle.
Light striking the surface is refracted down the inclined body.
A photocell, placed at 90 to the incident light path, is positioned above the sample surface. Light which strikes particles within the illuminated area scatters and is detected by the photocell. Light not scattered continues down the turbidimeter body and is absorbed. Light reflected from the surface is negligible and is absorbed by the enclosure without reaching the detector. Absorbing reflected light and excess refracted light provides negligible stray light in all applications of the instrument.