Patent ID: 8459290

Claim:
A material gas concentration control system that is used for a material evaporation system comprising a tank to accommodate a material, an inlet line to input a carrier gas for evaporating the accommodated material into the tank and an outlet line to output a mixed gas consisting of a material gas formed by the evaporated material and the carrier gas from the tank, and characterized by comprising: a first valve arranged in the outlet line, a concentration measuring part that measures a concentration of the material gas in the mixed gas, and a concentration control part that controls an open degree of the first valve so as to make the measured concentration of the material gas measured by the concentration measuring part become a previously determined set concentration, wherein the concentration measuring part comprises a pressure measuring part that measures a pressure in the tank, and wherein the concentration control part comprises: a set pressure setting part that changes the set pressure so as to reduce a deviation between the measured concentration and the set concentration, and a first valve control part that controls an open degree of the first valve so as to make a measured pressure measured by the pressure measuring part become the set pressure, and controls the measured concentration of the measured material gas so as to be the previously determined set concentration.