App Note: Pressure and Flow Control for Gas Analysis
Some Analytical Processes Are Best Standardized At A Fixed Gauge Pressure.
An Alicat PC-30PSIG Pressure Controller is used to set the pressure in the analytical device.
The outflow from the device is controlled by an Alicat MC-200SCCM-D Mass Flow Controller.
Other Analytical Processes Are Best Standardized At A Fixed Absolute Pressure.
In the illustration below, an Alicat MC-200SCCM-D Mass Flow Meter is used to control the flow into the process. An Alicat PC-30PSIA-D Pressure Controller (with a downstream valve) is used to maintain the analysis chamber at a fixed absolute pressure. Typically, the back pressure controller is set to 14.70 PSIA, to standardize the process to sea-level standard conditions.