System and method for determining a concentration of a constituent gas in a gas stream using pressure measurements

A mass flow control system comprising:

• a vaporizer disposed to receive a carrier gas and a source material to be vaporized, wherein the vaporizer is configured to vaporize the source material to provide a constituent vapor along with the carrier gas as a gas stream;
• means for obtaining a pressure of a chamber of the vaporizer;
• a mass flow meter coupled to the output of the vaporizer, wherein the mass flow meter is configured to provide a gas-stream-flow-rate signal indicative of a mass flow rate of the gas stream;
• a temperature sensor thermally coupled to the vaporizer, wherein the temperature sensor is configured to provide a vaporizer-temperature signal indicative of a temperature of the chamber of the vaporizer;
• a constituent vapor meter configured to provide a constituent-vapor-concentration signal using the pressure of the chamber of the vaporizer, the gas-stream-flow-rate signal, the vaporizer-temperature signal, and information about the carrier gas and the constituent vapor, wherein the constituent-vapor-concentration signal is indicative of a concentration of the constituent vapor in the gas stream;
• a constituent-vapor mass flow meter configured to provide a constituent-vapor-mass-flow-rate signal by multiplying the concentration of the constituent vapor in the gas stream by the mass flow rate of the gas stream, wherein the constituent-vapor-mass-flow-rate signal is indicative of a mass flow rate of the constituent vapor;
• and
• a mass flow control module configured to receive the constituent-vapor-mass-flow-rate signal and a single constituent-vapor-setpoint signal set by an operator of the mass flow control system that represents a constituent-vapor-setpoint, and the mass flow control module is configured to adjust a mass flow rate of the gas stream until the mass flow rate of the constituent vapor equals the constituent-vapor-setpoint and maintain the mass flow rate of the constituent vapor at the constituent-vapor-setpoint while enabling the mass flow rate of the gas stream, the temperature of the chamber and the pressure of the chamber to vary, wherein the constituent-vapor-setpoint is a desired mass flow rate of the constituent vapor.