Flow control system with build-down system flow monitoring

A method for controlling a flow rate by using a flow control system, the method comprising:

• providing the flow control system comprising:
• an upstream side valve that opens/closes distribution of a gas from a gas supply source having a desired gas supply pressure;
• a pressure type flow control device connected to a downstream side of the upstream side valve and including a control valve, an orifice or a critical nozzle, a pressure sensor P1, and a flow rate arithmetic and control unit;
• a build-down capacity being an internal volume of a passage connecting an outlet side of the upstream side valve and an inlet side of the pressure type flow control device;
• a temperature detection sensor arranged to detect a temperature of a gas distributed inside the build-down capacity;
• and
• a pressure sensor P arranged to detect the pressure of the gas distributed inside the build-down capacity;
• opening the upstream side valve to set a gas pressure inside the build-down capacity to a set upper limit pressure value or more and then closing the upstream side valve to drop the gas pressure from the set upper limit pressure value to a set lower limit pressure value;
• computing a monitoring flow rate Q by the following equation:
• Q
• =
• 1000
• 760
• ×
• 60
• ×
• 273
• (
• 273
• +
• T
• )
• ×
• V
• ×
• Δ
• 
• 
• P
• Δ
• 
• 
• t
• wherein T is a gas temperature (° C.), V is a volume of the build-down capacity (l), ΔP is a pressure drop range (the set upper limit pressure value−the set lower limit pressure value) (Torr), and Δt is a pressure drop time (sec) required for dropping of the gas pressure inside the build-down capacity from the set upper limit pressure value to the set lower limit pressure value;
• and
• monitoring a controlled flow rate of the flow rate arithmetic and control unit of the pressure type flow control device based on the computed monitoring flow rate Q.