A method for gas leakage detection using plc

A gas detecting method using a PLC is provided to shorten a search time by allowing another sampling point to prepare a search for next sampling point while searching gas at one sampling point. A gas detecting method using a PLC includes the steps of: detecting the density of air by passing the air introduced from one of a plurality of suction openings(111), which is introduced by a drive force of a pump through a valve connected to the suction opening, a pipe(114), and a density detection sensor(130); cleaning the pipe and the density detection sensor through fresh air by driving the pump connected to the pipe capable of sucking the fresh air; examining the density of a test gas by moving the test gas to the density detection sensor; and repeating the density search of the air by passing the air introduced for the other suction opening by the drive force of the pump through the valve connected to the other suction opening, the pipe, and the density detection sensor.