Windowless cell for continuous sample flow in process turbidimeters.
Window contamination necessitates frequent servicing where the turbidity value is detected continuously. Water hardness and suspended substances build up on the windows under certain conditions and falsify the turbidity readings. Along with color compensation and the free-fall flow cell, the overflow cell is one of the means Sigrist employs to reduce the frequency of instrument servicing.
The flow cell consists of an overflow receptacle in which the water level remains constant. The measurement beam penetrates the surface into the body of water and is scattered by the turbidity matter present, as shown in the above Figure. The scatter angle used here is 135°. Unlike the free-fall flow cell, this arrangement requires only small flow rates and a minimal pressure drop. The latter point is very advantageous for the tapping of spring water, where the natural head is usually all that is available.