Method and apparatus for mass flow control

A mass flow controller comprising:

• a chamber configured to receive a fluid;
• an upstream valve disposed upstream of the chamber;
• a downstream control valve disposed downstream of the chamber;
• a pressure drop element disposed downstream of the downstream control valve;
• a first pressure sensor that detects fluid pressure in the chamber;
• a second pressure sensor that detects fluid pressure downstream of the downstream control valve and upstream of the pressure drop element;
• and
• a controller configured to control actuation of the downstream control valve, the controller maintaining controlled flow based on a pressure as detected by at least one of the first pressure sensor and the second pressure sensor and recalibrating pressure-based flow control based on pressure detected by the second pressure sensor with rate of decay of pressure detected by the first pressure sensor during controlled flow.

A mass flow controller comprising:

• a chamber configured to receive a fluid;
• an upstream valve disposed upstream of the chamber;
• a downstream control valve disposed downstream of the chamber;
• a pressure drop element disposed downstream of the downstream control valve;
• a first pressure sensor that detects fluid pressure in the chamber;
• a second pressure sensor that detects fluid pressure downstream of the downstream control valve and upstream of the pressure drop element;
• and
• a controller configured to control actuation of the downstream control valve, the controller configured to:
• provide pressure-based flow control based on monitoring of a pressure upstream of the pressure drop element as detected by the second pressure sensor,
• determine a verification flow rate based on a rate of decay of pressure in the chamber as detected by the first pressure sensor upon closure of the upstream control valve while maintaining the pressure-based flow control or flow control based on the rate of decay pressure in the chamber, and
• recalibrate the pressure-based flow control based on the verification flow rate.

A method of controlling a flow rate comprising:

• providing pressure-based flow control of actuation of a downstream control valve of a mass flow controller;
• determining a verification flow rate based on a rate of decay of pressure in a chamber of the mass flow controller while maintaining the pressure-based flow control or flow control based on the rate of decay pressure in the chamber;
• and
• recalibrating the pressure-based flow control based on the verification flow rate, the rate of decay of pressure based on a pressure as detected by a first pressure sensor upon closure of an upstream control valve, the first pressure sensor detecting fluid pressure in the chamber, the pressure-based flow control based on monitoring of a pressure upstream of a pressure drop element as detected by a second pressure sensor, the pressure drop element disposed downstream of the downstream control valve, the second pressure sensor detecting fluid pressure downstream of the downstream control valve and upstream of the pressure drop element.