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The Vacuum Control Panel gives and overview of the vacuum status of the microscope and provides access to a few, often-used vacuum-control functions. A more detailed vacuum overview is also available.
Note 1: On systems equipped with the Turbo-Molecular Pump (TMP), to stop the TMP running (usually after inserting a specimen holder) either use the Turbo on button or simply open the Column Valves (if the Turbo Auto Off function on the Vacuum Cryo Control Panel is active).
Note on the Turbo-molecular pump (TMP) : When the TMP is switched off, it is forced to run down completely, otherwise there may be situations where it does not start up properly. The run-down of the TMP takes about 7 minutes. While it is running down it cannot be switched on.
Note 2: Vacuum terminology tends to be confusing. People talk about high or ultra-high vacuum when they mean very low pressures. Where it could be confusing, vacuum status will therefore be referred to as 'good' or 'poor'.
The status line of the Vacuum Control panel displays the status of the vacuum in words. Examples of status values are ready, off, stand-by, and start up. A green status display is used for ready, red status displays for not ready. In the example above, the display indicates that the Column Valves are closed.
The essential pressures of the microscope are read out, either by pressure gauges like Pirani's or Pennings or by converting the currents going through Ion Getter Pumps to pressures. The important pressures are listed in the Vacuum Control Panel. The pressure units are as set in the Vacuum Settings control panel (or defined by the supervisor for users). Possible units are Pascal, Torr and Log unit. For clarity Pascal and Torr units always go in steps of thousands for the exponent (10-3, 10-6, etc). Log units are defined in such a way that a realistic range of pressures (for that vacuum element) goes from 0 to 100. The advantage of the log units (which are similar to the units previously used on CM microscopes) is simplicity and high sensitivity for the good vacuum values (where it matters) and low sensitivity for poor vacuum values.
The Column Valves Closed button closes and opens the two valves in the column separating
the column from the projection chamber (V4) and the column from
the gun (V7). These two valves are always opened and closed
together. The high tension and filament can remain on when
opening and closing these valves. The functionality of the button
is chosen such that it highlights (yellow) when the column valves
are closed (as a warning that the beam will not be visible). The
same is indicated, when possible, by the status display.
It is good practice to keep these valves closed whenever
the microscope is not actively used, to keep the column vacuum at
its optimum condition and prevent air from entering the gun area
during specimen exchange.
In cases where the pre-pump airlock action is not necessary (all airlock actions without cryo holders), it may still be advantageous to switch the TMP on (or off). An example is the removal of the specimen holder in order to exchange the specimen. Since the TMP takes some time to reach Ready status, it can be switched on before removing the specimen holder, so it is ready immediately after the specimen has been exchanged. The switch on and off of the TMP can be done through the Turbo on button.
The Camera Air button starts the vacuum cycle that vents the camera chamber and, when the camera is vented, starts the cycle that pumps the camera chamber again. Camera Air must be confirmed. For this purpose, the button disappears and is replaced by two buttons, one with a 'V' sign for OK, the other with and 'X' sign for Cancel. The cursor is placed between the two buttons so that it is not possible to press one of them by accidentally pressing the Camera Air button twice. On some microscopes the Camera Air button may be absent. In that case the system Supervisor has chosen to remove the button (typically when no plate camera is used on the system so there is no reason for users to vent the camera).
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The Vacuum Control Panel with Log units displayed and the Camera Air button absent. |
Pressing the arrow button displays the flap-out containing the Vacuum Cryo control panel.
Page last modified on 11/26/01
