DigiVac Bullseye Precision Gauge Pirani User Manual - page 17
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1 0 5 B C h u r c h S t , M a t a w a n , N J 0 7 7 4 7
7 3 2 - 7 6 5 - 0 9 0 0
s a l e s @ d i g i v a c . c o m
w w w . d i g i v a c . c o m
Copyright 2015, DigiVac, Inc., All rights reserved.
Press the UP and DOWN buttons appropriately to move the calibration number up and down so
the unit reads exactly 5 millitorr, or 5 0
Press the select button
until the 50mt variable is capitalized
Pump the vacuum system down to exactly 50 mT, and maintain that pressure
Press the UP and DOWN buttons appropriately to move the calibration number up and down so
the unit reads exactly “50 mT, or 500 0”
Press the select button
until the 30 Torr variable is capitalized
Then pressurize the vacuum system to exactly 30 Torr and maintain that pressure
Press the UP and DOWN buttons appropriately to move the calibration number up and down so
the unit reads exactly 30 Torr, or 30000 0
Press the select button
until the screen reads “Press up + down to Store”, then press up
and down button simultaneously. Screen will flash black and calibration offsets will be saved.
Note: If field calibration is required at a later date, calibration offsets should be deleted first. This
is done by pressing the arrow button and observing the ATM, MID and VAC will be capitalized
when selected. Press up and down buttons simultaneously to zero out the offsets.
Pump manifold down to 1 micron, and check unit reading at different points while slowly
decreasing pressure to ensure successful calibration.
At pressures above 50 Torr, the unit may display the text “Overrange”; this is typical as this is the
sensor's highest rated pressure range. For optimal accuracy, readings above 50 Torr, if displayed at all,
should not be used for precision readings.
This instrument, and many similar instruments use microns or “millitorr”, as the primary unit of
measurement. But what are microns, and how do we relate microns to other measures of pressure and
vacuum? Microns are not really a measure of vacuum at all, but rather of absolute pressure.
The pressure of the atmosphere on Earth is 14.696 or approximately 14.7 pounds per square inch at sea
level. This pressure is due to the weight of all of the air in the earth's atmosphere above any particular
square inch. This 14.696 PSI is equivalent to the pressure produced by a mercury column of
approximately 29.92 inches high or .76 meters (about ¾ of a yard) or 760 millimeters of mercury.
Atmospheric pressure varies greatly with altitude. It decreases approximately 1 inch of mercury per