Patent ID: 6631334
Filing Date: 2003-10-07
Classification: G05D

Abstract:
A mass flow controller for controlling the flow rate of a vapor from a source, the mass flow controller comprising:A) a flow path for connection to the source of vapor; B) a flow restrictor dividing the flow path into an upstream reservoir and a downstream reservoir; C) an upstream pressure measurement device connected to the upstream reservoir; D) a flow valve connected to the flow path before the upstream reservoir; E) a control device programmed to, i) receive and store a desired flow rate from a user input device, ii) receive an indication of upstream pressure from the upstream pressure measurement device, iii) receive an indication of downstream pressure from a remote downstream pressure measurement device connected to the downstream reservoir, iv) determine an actual mass flow rate of vapor through the flow path in accordance with a linear function of the upstream pressure when the upstream pressure is at least equal to about twice the downstream pressure, v) determine the actual mass flow rate of the vapor through the flow path in accordance with a nonlinear function of the upstream pressure and the downstream pressure when the upstream pressure is less than about twice the downstream pressure, vi) instruct the flow valve to increase flow if the actual flow rate is less than the desired flow rate, and vii) instruct the flow valve to decrease flow if the actual flow rate is greater than the desired flow rate.