Appendix A Gas Correction Factor Table - Varian sentorr Instruction Manual

Appendix A
GAS CORRECTION FACTOR TABLE
Gas correction factor tables are only reproduced for the convenience of the user and do not imply that
use with other gases will be safe with hot filament gauge controllers.
The following table lists relative gauge gas correction factors for various gases. The values are derived
by empirical methods substantiated by measurements reported in literature. This table has been com-
piled and published by Robert L. Summers of Lewis Research Center, NASA Technical Note TND-
5285, National Aeronautics and Space Administration, Washington, DC, June 1969.
To automatically convert readings of the senTorr Controller (normally calibrated for nitrogen), enter the
relative gas correction constant through the front panel key function GAS CORR. By entering the gas
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 of the result is required. The
correction for 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 output being manipulated by the pressure
equation. There will be some loss in resolution of the instrument when gas correction constants are
used. The loss in resolution will become more apparent as the correction constants 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 or the near atmosphere decade, respectively.
Note: The default for Gas Correction is 1.
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