Why do online turbidimeters read lower than the 2100Q?
2100Q results are higher than online turbidimeters
Process (online) turbidimeters will nearly always read lower than a portable or benchtop unit. The reason behind this is that most process turbidimeters do not contain sample cells. Sample cells can change how the light scatters (especially if they are dirty or scratched), raising the readings. Also there is more possibility for user error on a portable instrument (i.e. obtaining a representative sample).