This paper describes several types of sensor use in measuring mass flow rate of solids
flowing in pneumatic conveyors. Each sensor will applied different principle but most of them are
able to achieve 10% homogeneity error. These sensor techniques include capacitance sensor,
electrostatic sensor, microwave sensor, radiological sensor, combination of electrostatic and digital
imaging sensor and others. The sensing filed designs need to be uniform, thus particles exist within
the sensing field will contribute equally to the flow signal.