Systems and methods for measuring entrained vapor

A system for supplying precursor gas to a substrate processing chamber, comprising:

• a first mass flow controller including an inlet to receive a carrier gas and an outlet;
• an ampoule configured to supply a precursor gas;
• a momentum-based flow restriction member including an inlet and an outlet;
• a valve system, in fluid communication with the first mass flow controller and the ampoule, configured to supply the precursor gas and the carrier gas to the momentum-based flow restriction member;
• a pressure sensing system configured to sense an inlet pressure at the inlet of the momentum-based flow restriction member and an outlet pressure at the outlet of the momentum-based flow restriction member;
• and
• a controller configured to determine a flow rate of the precursor gas at the outlet of the momentum-based flow restriction member based on a difference between the inlet pressure and the outlet pressure.