This dual beam turbidimeter can be made for under $1000. The light source is a 2 milliwatt helium neon laser. Use of a laser eliminates the need for collimating optics. The light detector is a photomultiplier tube, thus permitting the measurement of low particle concentrations. The reproducibility of the transmittance is 1%. The turbidity was measured for monodisperse and polydisperse particle suspensions in water. The results compared well with determinations of the turbidity made by use of an optical microscope and by use of a commercial particle analyzer, the Celloscope.

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