A mass flow controller is a flow control device that measures mass flow and automatically controls it to a set flow rate. Fluids can be measured in two ways: mass flow (weight) and volume flow (volume). Mass flow controllers can accurately measure and control mass flow regardless of temperature and pressure variations. For this reason, mass flow controllers are widely used in semiconductor manufacturing processes, analytical equipment, and other situations where high repeatability and accuracy are required.

Mass flow is generally measured using thermal sensor. Thermal sensors measure mass flow based on the principle that temperature changes occur in response to fluid flow. The main components of a typical thermal mass flow controller are a flow sensor, control valve, and bypass.