G-1
Models 947, 948 and 960 Leak Detectors Operations and Service Manual
Appendix G. Leak Detection Theory
G.1 Leak Testing—Why is it Needed?
Even with today's complex technology it is, for all practical purposes, impossible to
manufacture a sealed enclosure or system that can be guaranteed leak proof without first
being tested.
Using the modern mass spectrometer leak testing techniques implemented by the Varian
Vacuum Technologies 947/948/960 Helium Leak Detectors, leak rates in the
10
−
10
atm cc/
sec range can be reliably detected. The discussion that follows is a summary of information
pertinent to the subject of leak detection.
G.2 Classes of Leak Detection
There are four general classes of leak detection:
Hermetic Enclosures
(or parts thereof)
These are tested to prevent entrance of contaminants or loss of fluid
that would affect performance of the enclosed unit. Examples
include: electronic devices, integrated circuits, sealed relays,
motors, ring pull tab can ends, and multi-pin feedthroughs.
Hermetic Systems
These are tested to prevent loss of fluid or gas within. Examples
include: hydraulic systems and refrigeration systems.
Evacuated Enclosures
(or parts thereof)
These are tested to prevent excessively rapid deterioration of a
vacuum over time. Examples include: TV picture tubes, bellows
sensing elements, and full-panel opening can ends.
Vacuum Systems
These are tested to minimize inleakage and allow attainment of
better vacuum or higher gas removal ability at any given vacuum
(absolute pressure).
Summary of Contents for 948
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