Flow control system with build-down system flow monitoring

Abstract

To provide a flow control system with build-down system flow monitoring that realizes flow monitoring close to real-time monitoring by combining build-down system flow rate measurement with the upstream side of the flow control system without using a thermal type flow sensor by effectively utilizing high pressure fluctuation resistance characteristics of the flow control system, and can be significantly downsized and reduced in cost.

1 - 18 . (canceled) 
     
     
         19 . 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 P 1 , 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. 
       
     
     
         20 . The method for controlling a flow rate according to  claim 19 , wherein the monitoring flow rate Q is computed at least once per second and the controlled flow rate is monitored successively. 
     
     
         21 . The method for controlling a flow rate according to  claim 19 , further comprising opening the upstream valve once the gas pressure reaches the set lower limit pressure value. 
     
     
         22 . The method for controlling a flow rate according to  claim 19 , wherein a bar piece is inserted to the inside of a gas flow passage between the upstream side valve and the pressure type flow control device so that a passage sectional area of the gas flow passage is changed to adjust the build-down capacity and linearize the gas pressure drop characteristic. 
     
     
         23 . The method for controlling a flow rate according to  claim 19 , wherein a chamber with an appropriate internal capacity is interposed in the gas passage between the outlet side of the upstream side valve and the pressure type flow control device, and by changing the internal volume of the chamber, the volume of the build-down capacity is adjusted. 
     
     
         24 . The method for controlling a flow rate according to  claim 19 , wherein the gas pressure drops to the set lower limit pressure value after a predetermined time of t seconds after setting the gas pressure to the set upper limit pressure value by opening the upstream side valve. 
     
     
         25 . The method for controlling a flow rate according to  claim 24 , wherein the build-down capacity is set to 1.0 to 20 cc, the set upper limit pressure value is set to 400 to 200 kPa abs, the set lower limit pressure value is set to 350 kPa abs to 150 kPa abs, and the predetermined time t is set to be within 1 second. 
     
     
         26 . The method for controlling a flow rate according to  claim 24 , wherein the build-down capacity is set to 1.78 cc, the set upper limit pressure value is set to 370 kPa abs, the set lower limit pressure value is set to 350 kPa abs, the pressure drop range ΔP is set to 20 kPa abs, and the predetermined time t is set to be within 1 second. 
     
     
         27 . The method for controlling a flow rate according to  claim 19 , wherein the upstream side valve is a fluid pressure-operated solenoid direct-mounting type motor-operated valve or solenoid direct-operated type motor-operated valve, and a recovery time of the gas pressure from the set lower limit pressure value to the set upper limit pressure value by opening of the upstream side valve is set to be shorter than the pressure drop time Δt. 
     
     
         28 . The method for controlling a flow rate according to  claim 19 , wherein the flow rate arithmetic and control unit and a build-down monitoring flow rate arithmetic and control unit for computing the monitoring flow rate Q are integrally formed.