How To Start Hot Cathode Low Power Degassing
Chapter Four: Operation in Normal Mode
122
How To Start Hot Cathode Low Power Degassing
During a low power degas, the filament inside the hot cathode stays on, and valid pressure
readings continue to be obtained. During low power degas (I
2
R resistance heating), all the power
remaining (after powering the filament) is delivered to the grid inside the tube. The front panel
display for the degassing hot cathode continuously toggles between a pressure reading and dG
(the degas code).
Note
1. The 146 unit can only perform the degassing procedure on one hot
cathode gauge at a time. All other channels will continue to function
during the degassing procedure.
2. A hot cathode must be on (channel on) in order to degas it.
1. Repeatedly press the [
DISPLAY MODE
] key until the 146 unit is in Normal Mode.
The system responds by scrolling through modes.
2. Press the [
DEGAS
/
SET POINT
] key, then the [
ON
/
LEAD
] key, followed by [1], [2], [3], or
[4].
The system responds by turning on the low power degas of the hot cathode on the
selected channel, and causing that channel’s display to toggle between a pressure reading
and dG .
Caution
Damage to a hot cathode gauge can occur if pressure is allowed to get
too high. Monitor the pressure, and control it within the
specifications stated for the hot cathode gauge.
Degas is only effective if the pressure remains less than 1 x 10
-5
Torr.
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