There is a growing need for real-time characterization of droplet size distribution (DSD) for the continuously produced emulsions. In this study, we developed an at-line DSD characterization method using a turbidity-based soft sensor and demonstrated its application for continuously generated oil in water emulsions using a vortex-based hydrodynamic cavitation device. The concept of using an off-line turbidity meter and an ANN-based soft sensor for estimating DSD was recently demonstrated in our previous study. In this study, we further developed this concept for real-time characterization of DSD using an inexpensive, at-line turbidity meter providing an output in terms of voltage. Combined with the previously developed ANN-based soft sensor, the at-line voltage measurements were shown to be useful for the estimation of DSD and characteristic diameters. The emulsions of rapeseed oil (RO) in water with oil volume fractions of 0.15, 0.30, and 0.45 were produced in a continuous mode. Vortex-based cavitation device was used in a loop configuration with a key operating parameter being the ratio of the circulating flow rate through the loop (