A mass flow controller (MFC) is a device used to measure and control the flow of fluids and gases.   A mass flow controller is designed and calibrated to control a specific type of fluid or gas at a particular range of flow rates.   The MFC can be given a setpoint from 0 to 100% of its full scale range but is typically operated in the 10 to 90% of full scale where the best accuracy is achieved.

All mass flow controllers have an inlet port, an outlet port, a mass flow sensor and a proportional control valve.   The MFC is fitted with a closed loop control system which is given an input signal by the operator (or an external circuit/computer) that it compares to the value from the mass flow sensor and adjusts the proportional valve accordingly to achieve the required flow.