| 摘要 |
Disclosed is a method and apparatus for measuring and controlling volumetric flow rate of gases, and especially for delivering gases at a selected and measured volumetric flow rate. The apparatus includes a measurement chamber (14) of fixed volume in a flow line (11), a controllable inlet valve (15) upstream from the chamber, and flow regulator means (12, 13) for establishing constant flow output downstream from the chamber. Also provided are measuring and control equipment including a pressure sensor (16) in the chamber, means (17) for controlling operation of the inlet valve, timing means, and means for calculating volumetric flow rate. The method involves closing the inlet valve at a chosen time for a selected interval, to interrupt flow into the measurement chamber, while maintaining constancy of flow out of the chamber. During at least part of the interval in which the inlet valve is closed, the pressure decrease is measured, and the rate of pressure decrease is calculated by dividing the measured pressure drop by the time measured by the timing means. The thus calculated rate of fall of pressure is directly related to the volumetric flow rate, which is thus determined. If the nature of the gas and the flow conditions are such that the supercompressibility of the gas should be taken into account, rate of pressure fall is determined at two time intervals. If the two rates are the same, no correction is needed. If they differ, a supercompressibility correction factor is applied to the calculation of rate of pressure fall. |
