A mass flow controller automatically controls the flow rate of a gas according to a set flow rate sent as an electric signal, without being affected by use conditions or changes in gas pressure.  Flow rates can be roughly classified into two types: volumetric flow and mass flow.  A volumetric flow measurement is affected by ambient temperature and pressure.  To see the true flow, the pressure and temperature conditions need to be pressure conditions, therfore providing much more accurate and stable flow measurement and control.  Our mass flow controllers are used in a wide range of industrial fields as indispensable equipment when accurate control of flow rates is required or an automated production line is built.

Structure and operating principles

These mass flow controllers have a flow rate measurement section that includes a sensor, bypass, flow rate control valve, and special circuitry. A CPU is part of the circuitry, which makes it both multi-functional and highly efficient.
The gas is input from an Inlet joint, and is divided so that it flows over both the flow rate sensor and a bypass. The sensor measures the mass flow rate of the gas, and the flow rate control valve modifies the flow rate so that the difference between the measured flow rate and the flow rate received from the external flow rate setting signal is 0 (zero).
The units feature a loop circuit, so even if there is a secondary pressure change or ambient temperature change that could affect the supply pressure of the introduced gas, the flow rate is instantaneously corrected, which ensures stable flow rate control.

What is a Mass Flow Controller?

Operating Principle

  1. The gas, which enters from the inlet, first splits to flow past the sensor or through the bypass.
  2. At the sensor, the mass flow rate is detected as a proportional change in temperature and converted by the bridge circuits to an electrical signal.
  3. This signal passes through the amplification and correction circuits, and is output as a linear voltage between 0 to 5V.  At the same time, it is also sent to the comparison control circuits.
  4. The comparison control circuit compares the flow rate setting signal and the acutual flow setting signal from the sensor and sends a difference signal to the valve driving circuit.
  5. The flow rate control valve movers as appropriate to make the difference between the reguired flow set point and flow output signals approach zero.  In other words, the unit controls the flow so that it is always at the set flow rate.