Patent ID: 7437944

Claim:
An apparatus for gas control, comprising: a first flow sensor having an inlet connected to a first gas line adapted for coupling a gas supply; a first control valve connected with an outlet of the first flow sensor; a first upstream pressure sensor connected to the first gas line; a second flow sensor having an inlet connected to a second gas line adapted for coupling a gas supply; a second control valve connected with an outlet of the second flow sensor; a second upstream pressure sensor connected to the second gas line; a controller configured to control the ratio of a gas flow from the first gas line and a gas flow from the second gas line, wherein the controller receives measurement signals from the first and second flow sensors and the first and second upstream pressure sensors, and sends control signals to the first and second control valves, and wherein measurements of the first flow sensor are compensated by measurements of the first upstream pressure sensor so that the measurements of the first flow sensor are pressure insensitive, and wherein measurements of the second flow sensor are compensated by measurements of the second upstream pressure sensor so that the measurements of the second flow sensor are pressure insensitive; and a third gas line having an inlet coupled to outlets of both the first control valve and the second control valve.