Gas Mass Flow Controller

Working Principle of Gas Mass Flow Controller

The gas mass flow controller adopts the principle of capillary heat transfer temperature difference calorimetry. Measure the mass flow of gas (no temperature and pressure compensation is required), and send the flow signal measured by the sensor heating bridge to the amplifier for amplification. The amplified flow detection voltage is compared with the set voltage. Then amplify the difference signal to control the regulating valve. Closed-loop control of the flow through the channel to make it equal to the set flow rate. The flow divider determines the flow rate of the main channel.

Use Sealing Materials and Corrosive Gases

The channel materials of this mass flow controller are: SUS 316L (00Cr17Ni14Mo2), SUS417J1 (00Cr30Mo2), fluoro rubber and other corrosion-resistant materials.

The user system is free of water vapor, low leakage, frequent cleaning, and proper use. It can be used to control general corrosive gases. When using highly corrosive gases and organic solvent gases. The sales staff should be informed when ordering.

When using special corrosive gases, all sealing materials must be adjusted accordingly. Commonly used sealing materials are: fluororubber, nitrile rubber, EPDM, perfluoroether, etc.

Gas flow coefficient conversion table

Conversion method for calibrating different gases

Mass flow controllers are usually calibrated with nitrogen (N₂) when leaving the factory. If other gases need to be calibrated, it needs to be specifically mentioned when ordering.

The flow reading displayed by the gas mass flow controller calibrated with nitrogen can be converted to the flow of the gas used by the conversion coefficient of the actual gas used. Multiplying it by the coefficient can get the actual flow of the measured gas under standard conditions.

Conversion formula:

Actual gas flow = gas display reading * actual inflow gas coefficient/calibration gas coefficient

For example, This gas mass flow controller is calibrated with nitrogen. Assuming that carbon dioxide is used, when carbon dioxide flows in, the flow feedback data is 75SCCM, then the actual flow of carbon dioxide is 55.5SCCM (75SCCM*0.740).

Mixed gas conversion formula:

Mixed gas conversion coefficient = 100/[(P1/first gas coefficient)+(P2/first gas coefficient)+(P3/first gas coefficient)]

Note:

P1=proportion of the first gas;

P2=proportion of the second gas;

P3=proportion of the second gas.

For example: The gas used is: 20% carbon dioxide + 80% helium, the total flow rate is 20SLM. The conversion coefficient of the mixed gas = 100/[(20/0.740)+(80/1.386)]=1.1799. The equivalent flow rate of nitrogen is: 20/1.1799=16.95SLM