Application Footnotes; Gas Correction - Varian sentorr Instruction Manual

Troubleshooting
Figure 4-1. Power Entry Module
4-4

APPLICATION FOOTNOTES

Gas Correction

The gas correction factor tables are reproduced for the convenience of the user and do not imply that
use with other gases will be safe with filament gauge controllers.
The senTorr gauge controller is normally calibrated to read pressure in nitrogen. To automatically con-
vert readings of the senTorr to a different gas speciesd, enter the relative gas correction constant
through the front panel key functions.
By entering the gas correction constant, the gauge will divide the result by the gas correction constant and
display the correct adjusted value. However, a proper understanding for the transformation is required. The
correction for the different gas species is purely mathematical. The sensitivity of the tube is affected by dif-
ferent gases, which, in turn, are responsible for the tube outpute being manipulated by the pressure equa-
tion. There will be some loss in resolution of the instrument when gas correction factors are used. The loss
in resolution will become more apparent as the correction factors approach 0.5 from either direction.
When the correction constants are 0.1 or 10, the tube output is 1/10 or 10 times normal. This will
cause the instrument to lose the high vacuum decade, respectively.
Programming Gas Correction
Enter the Program mode by pressing the "Option select" key. The first available parameter, beginning
from the top of the column and depending on the senTorr model and options installed, will flash in the
appropriate gauge display. Repeated "Option Select" key presses will advance through the parameters,
returning the unit to the Run mode after the last key press.
4-2