Kurt J. Lesker 979 Series, Operation And Maintenance Manual

Page: 35 / 54

Series 979 ATV Transducer 35
Degassing the Sensor
Sensitivity of the Hot Cathode sensor may drift if the sensor elements
become contaminated with system process gasses. This becomes more of a
problem the lower the pressure being measured (i.e., (
≤
10
-8
Torr). To rid the
sensor elements of the excess system process gasses, periodically degas
the sensor. How frequently to run degas varies for each system installation.
The Hot Cathode uses Electron Bombardment (EB) degas to remove
adsorbed gas from the sensor. Pressure can still be measured during degas,
but due to the gas rapidly coming off the sensor elements, sensor pressure
may be significantly higher than system pressure.
Degas is only activated if the indicated pressure is below 1x10
-5
Torr.
Set points are active during degas.
When degas is turned on, it is likely that the sensor pressure will increase to
values exceeding 1x10
-4
Torr. When the indicated pressure exceeds 1x10
-4
Torr, degas turns off. Degas automatically turns on again when the indicated
pressure drops back below 1x10
-4
Torr (patent pending).
The temperature inside the Hot Cathode increases during degas; for electronic
component life, keep degas time as short as possible. Degas operation
automatically terminates after 30 minutes. When the sensor’s indicated
pressure has dropped back near pre-degas values, there is not much benefit
to further degas operation; therefore, degas should be terminated.
Do not operate in degas mode more than 30 minutes every 4
hours.