Patent ID: 6125869
Filing Date: 2000-10-03
Classification: F16K,Y10T

Abstract:
A self-diagnosis method for a mass flow controller comprising a control valve for controlling a pressure or for controlling a flow rate, a first shut off valve for performing opening/closing operation on an inflow side of said control valve, a fixed throttle disposed on an outflow side of said control valve for establishing an output pressure on an outflow side of said control valve, a pressure sensor for detecting a pressure on an inflow side of said fixed throttle, and a second shut off valve for performing opening/closing operation on an outflow side of said fixed throttle, where said control valve, said first shut off valve, said fixed throttle, and said second shut off valve are provided in a pipework for supplying a process gas from a process gas supply source to a process equipment,said self-diagnosis method comprising the steps ofusing said second shut off valve to close said outflow side of said fixed throttle in a state in which said control valve has a previously determined opening degree;using said first shut off valve to open said inflow side of said control valve so that a previously determined process gas having a predetermined pressure is charged via said first shut off valve into a pipework ranging from said first shut off valve to said second shut off valve;using said first shut off valve to close said inflow side of said control valve for a gas-charging period which ranges from a point of time at which said first shut off valve is opened to a point of time at which said first shut off valve is closed, said gas-charging period being about five times as much as a charge time constant of said pipework ranging from said first shut off valve to said second shut off valve;using said second shut off valve to open said outflow side of said fixed throttle so that said process gas charged in said pipework is allowed to cause outflow; andperforming diagnosis for said mass flow controller on the basis of a period of time required to lower a detection pressure detected by said pressure sensor to a previously determined detection pressure as a result of said outflow.