Physical Principles of Electron Microscopy: An Introduction to TEM ...

The Transmission Electron Microscope 91
These different pumps must work together in the correct sequence. If the
TEM column has been at atmospheric pressure (perhaps for maintenance),
most of the air is removed by a rotary pump, which can then function as a
backing pump for the DP, TMP, or IP. The pumping sequence is controlled
by opening and closing vacuum valves in response to the local pressure,
monitored by vacuum gauges located in different parts of the system. In a
modern TEM, the vacuum system is automated and under electronic control;
in fact, its circuit board can be the most complicated in the entire electronics
of the microscope.
G
viewing
chamber
RP
gun
Figure 3-18. Simplified diagram of the vacuum system of a typical TEM. Vacuum valves are
indicated by � and vacuum gauges by G. Sometimes a turbomolecular pump is used in place
of the diffusion pump, resulting in a cleaner “oil-free” vacuum system.
DP
G
G
IP
G