IMPROVED PRESSURE-TYPE FLOW RATE CONTROL APPARATUS

摘要

Provided is an improved pressure-type flow rate control apparatus that can control The flow rate of a fluid with great precision using an empirical formula. The empiric al formula can provide values that closely fit with the actual flow rates of a compressible fluid under non-critical conditions. The improved pressure-type flow rate control apparatus can control the flow rate of fluid passing through an orifice 4 to a target flow rate with accuracy and at a hi gh speed. The empirical formula for the compressible fluid under non-critical conditions (sub-sonic) is expressed as Qc = KP2m(P1 - P2)n and the flow rate of fluid passing through orifice 4 is calculated by: Qc - KP2m(P1 - P2)n (K is a proportional constant; and m and n are constants) so that the flow rate of fluid passing through the orifice 4 can be controll ed to the target flow rate with high precision at a high speed. Also provided is an improved pressure-type flow rate control apparatus in which a pressure ratio P2/P1 = r, obtained from an upstream pressure P1 and a downstream pressure P2 is constantly compared with a critical value rc, and under critical conditions (r .ltoreq. r c), the flow rate is calculated by Qc = KP1. Under non-critical conditions (r = r c), the flow rate is calculated by Qc = KP2m(P1 - P2)n, so thatthe glow rate is controlled to the target flow rate with accuracy at a high spee d depending upon the conditions of fluid.