4. Residual atmosphere measurement

4.1 General

You ask a chemist-analyst: what's in this product? The answer is: what are you looking for? The chemist can't guess which of the millions of chemical species you're looking for. That's why expertise in gaseous atmospheres requires a special approach. These are difficult measurements, as they result from a balance between the molecules in the gas phase and the molecules absorbed on the walls. The slightest energy input on the surface will return new molecules to the gas phase, which will then re-adsorb elsewhere. The measuring instrument also creates a certain amount of disturbance in the medium (degassing caused by the filament).

So, what resources does the vacuum expert have at his disposal? Given the specific nature of vacuum, i.e. very low molecular...