An Alicat Pressure Controller with an External Sensor is used to control the pressure of a vacuum coating process chamber by controlled introduction of argon gas.
The process pressure is measured by an Ion-Gauge, directly connected to the process chamber.
The measured pressure is sent via analog connection to the pressure controller. Additional reactive gases are introduced to the process chamber through Alicat Mass Flow Controllers with downstream valves.
The overall process pressure is set by the pressure controller. This determines the molecular mean free path in the chamber.
Advantages: Changes in the flow rate of the reactive gases would normally disturb the system pressure and hence the mean free path. The Alicat pressure controller quickly restores the chamber pressure to the desired level, while the reactive gases may be manipulated independently.
A common control interface is used for both pressure and flow.