A log-pressure versus time record from atmosphere to base. The rough section falls fast and steeply, then in high vacuum the curve flattens as outgassing takes over, and its shape tells an experienced eye what limits the system: a leak levels it off at a fixed pressure, while water gives a long, slowly falling tail. Saving a reference curve when the tool is new makes later trouble obvious by overlay.
Overlay the latest pump-down curve on the one from install, we're a decade high after thirty minutes.
Also heard as
- pumpdown curve
- P versus t
Related terms
Pump down
To evacuate a chamber from atmosphere to its working pressure, through roughing, crossover and high vacuum.
Base pressure
The lowest pressure a particular chamber reaches after pumping for a set time with no process gas flowing.
Wet
Said of a chamber whose walls still hold adsorbed water, so it pumps down slowly and stalls high.
Rate of rise
Test that isolates a pumped chamber and tracks how fast the pressure climbs, to estimate leaks and outgassing.
Outgassing
Slow release of gas from the surfaces and bulk of materials inside a vacuum system.