D U N I W A Y S T O C K R O O M C O R P .
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J. Zero
Default Value: 0.0 (internal value)
This allows the user to adjust the zero for each CDG. Before making this adjustment, the CDG
should be connected to a vacuum system at a pressure lower than 0.01% of the full scale for the
CDG. This adjustment may also be used to set the display to a specific value if you know the pres-
sure through other means. For example, if the CDG to be adjusted is attached to a system that has
another CDG which has been independently calibrated, the CDG may be made to read the same
as the calibrated gauge.
The
ZERO
function may be adjusted only when the CDG pressure is at 10% of full scale or lower.
NOTE: INITIAL ZERO
When using installing a CDG for the first time, it is good practice to reset
the 908A internal settings. This will prevent errors in set up, e.g. if the CDG
has not had its internal zero properly adjusted. To reset the 908A, see
Reset
of Stored Values
, just below. To adjust the zero, the vacuum system to
which the CDG is connected should be at a pressure lower than 0.001 times
the full scale range of the CDG. For example for a 10 Torr CDG, the system
should be at a pressure lower than 0.01 torr, or 10
-2
torr.
Adjust the zero adjustment on the CDG (usually a trimpot) until the 908A display shows a value
close to zero. After this initial adjustment, the display may be conveniently be set to zero using
front panel controls on the Model 908A.
NOTE: HEATED CDGs
When using heated or temperature-controlled CDGs, you should wait for an
hour or two before making any adjustments to the 908A or the CDG. This
will allow the CDG to come to its regulated temperature. When you are con-
fident the CDG is at a stable temperature, adjust the zero adjustment on the
CDG until the 908A display shows a value close to zero.
K. Reset of Stored (Default) Values
This allows you to recover the factory (default) settings for all stored values and resets the
SET
POINTS
to off. For a system that is far out of calibration, the factory settings provide a good start-
ing point for re-calibrating or adjusting the gauge controller. To recover the factory settings, un-
plug the 908A from its power source. Press and hold
RAISE
and
LOWER
buttons at the same time;
while holding the
RAISE
and
LOWER
buttons depressed, plug the power cord in. You will hear a
few short ‘chirps’ from the loudspeaker confirming the factory settings have been entered. The
digital display will show
RST
to confirm the reset has been entered.
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