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Online concurrent measurement of mass flow rate and size distribution of particles in a pneumatic suspension is desirable in many industries. This paper presents the basic principle of and initial results from a novel instrumentation system that uses a combination of electrostatic and digital imaging sensors in order to achieve these goals. An inferential approach is adopted for the mass flow measurement of particles where velocity and volumetric concentration of particles are measured independently. The velocity of particles is determined by cross-correlating two signals derived from a pair of electrostatic sensors, while the volumetric concentration of particles is obtained using a novel digital imaging sensor, which also provides particle size distribution data. The basic principles and limits of operation of the imaging sensor are discussed and explained. Results obtained from a pneumatic conveyor system are presented that show good performance of the system for both mass flow metering (accurate to about ±4%) and particle sizing (reliable to around ±0.5%). A particle size distribution result is also included, and the insensitivity of particle sizing to changes in velocity and concentration is assessed. In general, the results obtained are encouraging, and the system shows great promise.