Patent ID: 8019481

Claim:
A flow rate ratio control device comprising: a main channel into which fluid flows; a plurality of branch channels branching from an end part of the main channel; control valves respectively provided in the branch channels; flow rate meters adapted to directly or indirectly measure a flow rate through the main channel and flow rates through the respective branch channels; a pressure sensor adapted to measure a pressure on an upstream side of one of the control valves provided in one of the branch channels; a valve control section adapted to control one of the control valves provided in one of the branch channels so as to make a pressure on the upstream side of the control valve equal to a given target pressure, and upon the pressure exceeding a pressure lower than the target pressure by a predetermined value, start to control other of the control valves so as to make flow rate ratios of the respective branch channels equal to predetermined ratios; and a target pressure setting section adapted to set the target pressure lower as the flow rate through the main channel decreases, and output the target pressure to the valve control section.