A new monitoring system has been developed for continuously measuring the concentration of total nonvolatile impurities in ultrapure water. The measuring method is based on the principle of determining the Residue After Evaporation (RAE) of atomized droplets, taking account of the particle deposition loss. The system consists of a water atomizing unit, a droplet evaporating and drying unit, an air diluter, a fine particle counter, etc. For the particle counter, a Condensation Nucleus Counter (CMC) is used; this counter is a mixing type, able to detect particles larger than 0.01 μm. It is verified from both the theoretical analysis and the experimental results that this monitor can rapidly detect very low impurity concentrations by counting the number concentration of aerosol particles.

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