Gas delivery method and system including a flow ratio controller using antisymmetric optimal control

A system for dividing a single mass flow into two or more secondary flows comprising:

• (A) an inlet adapted to receive the single mass flow;
• (B) at least two secondary flow lines connected to the inlet and connected to carry corresponding ones of the secondary flows, each flow line including:
• (1) a flow meter connected to measure flow through the corresponding flow line and providing a signal representative of the measured flow through that flow line;
• (2) a valve connected to control flow through the corresponding flow line based upon a control signal;
• (C) a controller connected to the flow meters and the valves for controlling the ratio of the secondary flows at a preselected value;
• wherein the controller is configured so that at least one of the valves is kept at the optimal valve current which provides a maximum allowable valve conductance position at any one moment of operation, while the other valve is actively controlled to maintain the preselected value of the flow ratio, and further including a SISO controller connected so as to generate a first control signal as a function of the difference between the ratio as preselected and the ratio as measured, and a pair of linear saturators, one for each of the secondary flow lines, configured so as to provide valve control signals in response to the to the first control signal so as to control each of the valves.

A system for dividing a single mass flow into two or more secondary flows comprising:

• (A) an inlet adapted to receive the single mass flow;
• (B) at least two secondary flow lines connected to the inlet and connected to carry corresponding ones of the secondary flows, each flow line including:
• (1) a flow meter connected to measure flow through the corresponding flow line and providing a signal representative of the measured flow through that flow line;
• (2) a valve connected to control flow through the corresponding flow line based upon a control signal;
• (C) a controller coupled to the flow meters and the valves for controlling the ratio of the secondary flows so as to maintain the ratio at a preselected set point;
• and
• further including a SISO controller connected so as to generate a first control signal as a function of the difference between the ratio as preselected and the ratio as measured, and a pair of linear saturators, one for each of the secondary flow lines, configured so as to provide valve control signals in response to the to the first control signal so as to control each of the valves.

A gas delivery system comprises a flow ratio controller including:

• a pair of secondary flow lines;
• a pair of valves configured to respectively control the flow through secondary flow lines in response to control command signals, and
• a flow controller configured to control the flow through each of valves in accordance with a preselected flow ratio, the controller including a feedback loop, a single output SISO controller and a pair of linear saturators, one for use with each of the valves, the SISO controller having an output;
• wherein the control command signals for the valves are a function of output of the SISO controller and respective ones of the linear saturators, and the two valve control commands are virtually antisymmetric to the maximum allowable valve conductance position of the valves.