What is the Working Principle of a Mass Flow Controller?

A mass flow controller is an automated device that controls the rate of flow of a gas or fluid as per the set values of flow rate. It operates through an electric signal and remains unaffected by the change in the air pressure or other factors. Flow rates can be divided into two categories:

  • volumetric flow, and
  • mass flow.

The disadvantage of volumetric flow measurement is that it may get affected by surrounding conditions like temperature and pressure. However, mass flow measurement is much more reliable. The mass flow controllers can be used in a wide range of industrial equipments and appliances. It serves the best of its purpose where there is a need for accurate flow measurement and handling.

Working Principle

A mass flow controller includes a flow measurement section that further includes a

  • sensors
  • bypass valve
  • flow rate control valve
  • computer circuits

The gas enters the controller from an Inlet point. It gets divided into two parts such that one part flows through the flow rate sensor and the other one through the bypass valve. The sensor serves the purpose of measuring the mass flow rate of the gas. The purpose of the flow rate control valve is to adjust the flow rate of the gas such that it is neither less than or nor more than the desired flow rate.

The CPU is the integral part of the circuit, which makes the mass flow controller functional. It also contains a loop circuit. In case there is a change in pressure change or temperature that can affect the flow rate of the gas, it will be automatically corrected by the system to maintain an accurate flow rate.

Operating Principle

  1. First, the gas enters the inlet and goes through the sensor and the bypass.
  2. When gas passes through the sensor, it converts the flow rate into an electric signal.
  3. This signal is sent through the amplification and comparison control circuits.
  4. The comparison control circuit decodes the predefined flow rate signal and the real flow rate generated by the sensor and sends a difference signal to the circuit of the valve.
  5. The circuit of the valve makes the valve move according to the received difference signal and hence, adjust the flow accordingly.


A mass flow controller is an excellent device when it comes to measuring the mass flow of a gas. It has many applications in the industrial sector. It becomes easier to choose the best flow meter for your need if you know the operating and working principle behind the mass flow controller.flow controller


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