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how to defeat contamination
Prevent it!
- use gloves, change them frequently
- clean anything going inside the vacuum chamber
- opening the chamber? pump nitrogen into it first, keep the nitrogen flowing while the chamber is open - prevents water from getting in.
nitrogen gas has no water vaporhumidity, unlike air.
- use gloves, change them frequently
- clean anything going inside the vacuum chamber
- worried about dust? don't let it get in your chamber!
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For detailed discussion on leaks, how to find them, and what to do about them see the Leak Checking pages
How much is too much? Time to talk numbers
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We use numbers and units in discussing vacuum systems. The way we use And the way vacuum uses some units can be very counterintuitive (*cough* log scale). This section breaks down the ideas behind the way we talk numbers around vacuum.
Units Used with Pressure
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-Different, but in both cases the difference is 4 orders of magnitude (4 zeros). look at the difference between exponents: 7 - 3 = 4, tiny or huge, doesn't matter.
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In linear counting the numbers increase one at a time. It's what we're used to. tit's how we normally count: 1, 2, 3, 4, 5, etc...
In logarithmic (i.e.: log) counting the numbers increase by bigger amounts each time. Log counting is strange, counterintuitive and, unfortunately, useful.
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Ultra-High Vacuum (UHV) is an official term for really really fancy vacuum of a certain (extremely low) range of pressures. And it's the type of vacuum we care about the most.
For molecules in UHV the mean free path is at least 200 miles. Any molecule in UHV is going to see the chamber walls thousands of times before it will see another molecule.
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For more details on Vacuum System parts and how they actually work, see the confluence pages on vacuum components
External resources
approachable, practical information on vacuum