How They Work
A specific gas blend within a chamber must be produced by a procedure known as ideal gas mixing (or gas blending). In this example, synthetic air composition is maintained at a mix ratio of 78% N2, 21% O2 and 1% Ar. A miniature Human/Machine Interface (HMI) with LCD touch screen monitors and controls the system automatically. The HMI communicates to three SmartTrak 2 mass flow controllers (via their attached Compods) and a pressure transducer mounted inside the tank. Each MFC regulates the flow of one gas into the tank. The HMI maintains the exact proportion defined above by constantly comparing MFC data with the mix equations. When the pressure reaches the set point, the PLC commands the Compod to stop the mass flow controller.
Should the chamber pressure drop below the set point, the PLC sends a flow command to each controller to resume gas flow into the tank manifold for continued gas blending. The system is fully automatic. Each Compod includes a safety program that monitors the gas flow through its attached controller systems. Should the flow through a controller drop off when the setpoint from the HMI remains on, the Compod detects that the gas supply has been interrupted (such as when a bottle running out) and triggers an alarm that shuts down the gas blending systems. If the ratio of the gases in the synthetic air mixture need to be modified (for example, if you want to add hydrogen into the mix), simply change the synthetic air gas mixing recipe in the PLC and the system provides the new mixture, immediately and automatically.