Closed loop powder flow regulator

In a powder feeding system including in combination an enclosed hopper for a powder, a feed gas conduit adapted to discharge a feed gas under constant pressure into the hopper, a carrier conduit for a carrier gas stream, and intake orifice means for entraining powder at a flow rate from the hopper into the carrier conduit in the presence of the feed gas pressure, the carrier conduit being connected to a carrier gas supply and extending to a point of powder carrier gas utilization, a closed loop regulator of powder flow rate comprising:

• a first control loop having a first time constant in response to a change in powder flow rate, comprising set point means for generating a set point signal representing a selected powder flow rate, flow measuring means for producing a flow rate signal corresponding to the powder flow rate, first controller means for producing a reference signal representative of the difference between the set point signal and the flow rate signal, and pressure means disposed in the carrier conduit between the intake orifice means and the point of utilization for varying carrier gas pressure, the pressure means being responsive of the reference signal to correspondingly vary the carrier gas pressure such as to regulate the powder flow rate;
• and
• a second control loop having a second time constant in response to a change in powder flow rate, comprising pressure measuring means for measuring carrier conduit pressure between the intake orifice means and the pressure means and for producing a pressure signal corresponding to the carrier conduit pressure, second controller means for producing a control signal responsive of the pressure signal, and the pressure means, the pressure means being responsive of the pressure signal to correspondingly vary the carrier gas pressure such as to correspondingly regulate the powder flow rate, and the first time constant being longer than the second time constant.

In a powder feeding system including in combination an enclosed hopper for a powder, a feed gas conduit adapted to discharge a feed gas under constant pressure into the hopper, a carrier conduit for a carrier gas stream, and intake orifice means for entraining powder at a flow rate from the hopper into the carrier conduit in the presence of the feed gas pressure, the carrier conduit being connected to a carrier gas supply and extending to a point of powder carrier gas utilization, a closed loop regulator of powder flow rate comprising:

• set point means for generating a set point signal representing a selected powder flow rate, flow measuring means for producing a flow rate signal corresponding to the powder flow rate, first controller means for producing a reference signal representative of the difference between the set point signal and the flow rate signal, pressure means disposed in the carrier conduit between the intake orifice means and the point of utilization for varying carrier gas pressure, pressure measuring means for measuring carrier conduit pressure between the intake orifice and the pressure means and for producing a pressure signal corresponding to the carrier conduit pressure, and second controller means for producing a control signal representative of a combination of the pressure signal and the reference signal, the pressure means being responsive of the control signal to correspondingly vary the carrier gas pressure such as to regulate the powder flow rate.

In a powder feeding system including in combination an enclosed hopper for a powder, a feed gas conduit adapted to discharge a feed gas under constant pressure into the hopper, a carrier conduit for a carrier gas stream, and intake orifice means for entraining powder at a flow rate from the hopper into the carrier conduit in the presence of the feed gas pressure, the carrier conduit being connected to a carrier gas supply and extending to a point of powder carrier gas utilization, a closed loop regulator of powder flow rate comprising:

• set point means for generating a set point signal representing a selected powder flow rate, flow measuring means for producing a flow rate signal corresponding to the powder flow rate, first controller means for producing a reference signal representative of the difference between the set point signal and the flow rate signal, valve means disposed in the carrier conduit between the intake orifice means and the point of utilization for constricting the carrier gas stream by an adjustable amount, pressure measuring means for measuring pressure difference between the gas feed pressure in the hopper and a carrier conduit pressure taken between the intake orifice and the valve means, the pressure measuring means producing a differential signal corresponding to the pressure difference, and second controller means for producing a control signal representative of the difference between the differential signal and the reference signal, the valve means being responsive of the control signal to correspondingly constrict the carrier gas stream such as to regulate the powder flow rate.