An instrumentation system using combined sensing strategies for on-line mass flow rate measurement and particle sizing

On-line, 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 based 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, whilst the volumetric concentration of particles is obtained from a digital imaging sensor. The imaging sensor also provides particle size distribution data. Results obtained from a pneumatic conveyor system are presented which 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.