Detailed Syllabus

V-202 Vacuum System Gas Analysis

This tutorial is intended for those who wish to understand how to analyze the performance of a vacuum system. Basic vacuum gauges that measure pressure in the low vacuum and in the high vacuum region will be described. Residual gas analyzers provide a useful method of analyzing the performance of a system and how various components are operating by looking at the partial pressures of individual gases. The class concludes with a discussion of leak detection: when it should be attempted and how to detect leaks with a pressure gauge, an RGA, and a mass spectrometer leak detector.

Gas laws

• Gas flow
• Vacuum gauges
• Residual gas analyzers
• Leak detection

Attendees in this tutorial receive the text, A User’s Guide to Vacuum Technology, 3rd edition, John O’Hanlon (John Wiley & Sons, 2003).

Gas Laws

The important laws that describe the behavior of gas in a vacuum system are described in this module. These laws and concepts explain how vacuum systems behave.

• The laws of Boyle, Charles and Dalton describe the relationship between pressure, volume and temperature.
• The Ideal Gas Law simplifies these laws in one relationship.
• The average velocity of a gas and the mean free path between gas collisions are two most important ideas that help define how gas behaves in real situations.
• Review questions and summary of answers

Gas Flow

How gas flows in pipes and through chambers is most important. It is the basis of how pumps and pipe sizes are chosen. This module describes the important flow regions and how they apply to a vacuum system.

• Viscous, intermediate, and rarefied gas states
• Turbulent flow
• Choked turbulent flow
• Molecular flow
• Describing molecular flow with transmission probability
• Calculating the transmission probability of a pipe or component.
• Why traps collect condensable vapors but not non-condensable gases
• Review questions and summary of answers

Vacuum Gauges

Although there are dozens of pressure measuring techniques, this module is limited to describing only the most common commercial gauges used today.

• Thermocouple gauge
• Pirani gauge
• Capacitance manometer
• Direct versus indirect pressure measurement
• Bayard-Alpert ionization gauge
• Pressure measurement errors
• Review questions and summary of answers

Residual Gas Analyzers

A residual gas analyzer—often called a mass spectrometer—is an instrument that can measure a signal proportional to the quantity of individual gas and vapor components. This module is limited to describing the analyzer—the equipment—used to separate and identify individual components in a vacuum atmosphere

• Ionization stage
• Magnetic sector mass sorting stage
• Radio frequency mass sorting stage
• Detection stages
• Examining a typical analysis pattern
• Sampling a system background gas
• Sampling a gas in a sputtering system by means of a pressure reduction stage
• Review questions and summary of answers

Residual Gas Analysis

The analysis of the measured analysis pattern is often not so complex as first thought. In this module we break the observed spectrum into many small parts and examine each separately. Then, we put these together and learn characteristic shapes of spectra for typical situations such as a clean vacuum system, a leaky vacuum system, an oil-contaminated system, synthetic fluids, greases, O-rings, a gas line leak, a water line leak, and so on.

• Gas dissociation
• Gas isotopes
• Multiply ionized gases
• Typical spectra of clean and leaky systems
• Spectra from mineral oils, silicone and other synthetic pump fluids
• Spectra from elastomer gaskets
• Spectra from cleaning fluids
• Why residual gas analyzers cannot measure partial gas pressures very accurately.
• Review questions and summary of answers

Leak Detection

Detecting leaks is a most important application that uses pressure gauges or residual gas analyzers. This module describes when and how to check for leaks in components and systems. It also provides many nuts-and-bolts tricks to leak check difficult locations and components

• How gas flows through leaks
• When to leak detect and when not to leak detect
• Using pressure gauges to detect leaks
• Using sound and hearing to detect leaks
• Using a helium mass spectrometer to detect leaks
• Using a residual gas analyzer to detect leaks
• Where to connect a leak detector: sensitivity versus response time
• Practical hints for detecting leaks
• Review questions and summary of answers