Patent ID: 9557744
Date: 2017-01-31
CPC Classifications: G01F,G05D,Y10T

Claim:
1. A mass flow controller for controlling a flow of gas from a source to a target, the mass flow controller comprising: a first flow meter, wherein the first flow meter is a thermal mass flow meter constructed and arranged to measure the flow rate of the mass of a gas through the mass flow controller as a function of thermal sensing mass flow; a second flow meter including a pressure sensor and a structure defining a predefined volume for receiving gas flowing through the mass flow controller, the second flow meter being constructed and arranged to measure flow rate of the mass of the gas through the mass flow controller as a function of measured rate of decay of the pressure of the gas when allowed to flow from a predefined volume; an upstream control valve constructed and arranged to selectively control the rate of flow of gas into the mass flow controller; a downstream control valve constructed and arranged so as to control the flow rate of the mass of the gas from the mass flow controller in response to a control signal generated as a function of a set point and the flow rate as measured by one of the flow meters; and a system controller constructed and arranged to generate the control signal, and to provide an indication when a difference between the flow rate of mass of the gas as measured by the first flow meter and the flow rate of the mass of the gas as measured by the second flow meter exceeds a threshold; wherein the pressure sensor, upstream flow control valve and system controller are further constructed and arranged so as to form a closed-loop pressure controller configured to regulate the pressure inside the predefined volume.