TABLE OF CONTENTS This chapter begins by looking at the measurement of total pressure in vacuum systems. The procedures and methods for pressure measurement throughout the vacuum range (1 bar to 10 -13 mbar) are introduced. Important characteristics (including sensitivities to various gases) of some vacuum gauges are discussed in detail and illustrated by relevant examples.
The identification and quantification (partial pressure measurement) of the gaseous components in vacuum systems is of increasing importance in vacuum technology. This is achieved by the widely applied method of residual gas analysis. The simple theory of this is stated and relevant examples illustrate the application.
Introductory comments on pressure were made in Section 2.1. Particularly important is the fact that the pressure of gas in a system is a convenient expression of the particle number density ( n) in that system (see Equation (1.5)).
There are two general procedures for pressure measurement: direct and indirect.
Direct methods are based on the fact that the force that constitutes pressure can physically shift a surface to which it is applied. Indirect methods monitor either the particle number density or a property of the gas that depends on n. Direct methods yield pressure information that is independent of the nature of the gas whilst pressures indicated by indirect methods are dependent on gas type. The need to have the two methods arises from the fact that, at low pressure, the forces involved are extremely low, and direct measurement...
