POWDER FEEDING SYSTEM WITH A CLOSED LOOP POWDER FLOW REGULATOR AND THE CORRESPONDING METHOD

摘要

A powder feeding system includes closed loop regulation of powder feed rate. A feed gas is discharged under constant pressure into an enclosed hopper (12). A valve (95) is disposed to constrict a carrier conduit (20) conveying powder in a carrier gas. A load cell measures the rate at which powder (14) is flowing from the hopper (12) through an intake orifice (22) into the carrier conduit (20), and a filtered flow rate signal is produced. A first controller (70) produces a reference signal representative of the difference between a set point signal and the flow rate signal. A differential signal is produced corresponding to the pressure difference between the hopper pressure and a carrier conduit pressure taken between the intake orifice (22) and the valve (88). A second controller (92) produces a control signal representative of the difference between the differential signal and the reference signal. The valve (88) is responsive to the control signal to proportionately constrict the carrier gas stream such as to regulate the powder flow rate. Preferably the time constant of the second controller (92) is faster than the time constant of the first controller.