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 empirical 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 high speed. The empirical formula for the compressible fluid under non-critical conditions (sub-sonic) is expressed as Qc = KP2(P1 - P2) and the flow rate of fluid passing through orifice 4 is calculated by: Qc = KP2(P1 - P2) (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 controlled 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≤rc), the flow rate is calculated by : Qc = KP1. Under non-critical conditions (r > rc), the flow rate is calculated by Qc = KP2(P1 - P2), so that the flow rate is controlled to the target flow rate with accuracy at a high speed depending upon the conditions of fluid.