Patent ID: 7463991

Claim:
A flow verifier for verifying measurement of a flow rate of a fluid by a device, the flow verifier comprising: a vessel configured to receive a flow of the fluid from the device; an outlet valve configured to regulate flow of the fluid out of an outlet of the vessel; a pressure sensor configured to measure pressure of the fluid within the vessel; a temperature sensor configured to measure temperature of the fluid within the vessel; a flow restrictor located along a flow path of the fluid from the device to the vessel, the flow restrictor adjacent to and upstream of the vessel; and a controller configured to control the outlet valve, the controller further configured to verify the measurement of the flow rate of the fluid by the device, by measuring a rate of rise in the pressure of the fluid within the vessel during the time period after the closing of the outlet valve, and using the measured rate of rise to calculate the flow rate of the fluid from the device; wherein the flow restrictor is configured to restrict the flow of the fluid along the flow path so as to induce a shock in the flow path, and is further configured to sustain the shock during a time period sufficient to render the flow rate verification substantially insensitive to an element upstream of the flow restrictor; wherein the time period is given by: t =( V/A t )[(γ+1)/ c ]−( P i /P STP )( VT STP /QT ) where t is the time period; V is the volume of the vessel; c is speed of sound just upstream of a shock front of the shock; A t is a cross sectional area of the flow restrictor; γ is a ratio of specific heats of the gas; P i is an initial pressure within the vessel in the beginning of the time period; P STP is standard pressure; T STP is standard temperature; Q is a volumetric flow rate of the fluid into the vessel; and T is temperature of the fluid within the vessel.