Mass flow verificaton based on rate of pressure decay

A method of verifying a mass flow controller, the method comprising:

• causing a gas to flow from a gas supply through a calibrated flow standard, a control volume, and a flow restrictor at a steady pressure measured in the control volume;
• terminating the gas flow from the gas supply;
• measuring a first rate of gas pressure decay in the control volume;
• replacing the calibrated flow standard with the mass flow controller;
• causing the gas to flow from the gas supply through the mass flow controller, the control volume, and the flow restrictor at a stable pressure measured in the control volume;
• terminating the gas flow from the gas supply;
• and
• measuring a second rate of gas pressure decay in the control volume for purposes of verifying the mass flow controller.

A system comprising:

• an inlet coupled to a mass flow controller, which is coupled to a gas supply;
• an outlet;
• a control volume serially coupled to the inlet to receive a gas flow;
• a flow restrictor serially coupled to the control volume and the outlet;
• and
• a controller adapted to allow the gas supply to flow gas through the control volume and the flow restrictor to achieve a stable pressure in the control volume, terminate the gas flow from the gas supply, and measure a rate of pressure decay in the control volume over time to verify the mass flow controller.