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9.4.3 CO
2
Injection Calibration
The CO
2
injection calibration can be performed separately from zero/span calibration to optimize the
gas injection time required to recover the CO
2
level to set point after a door opening. The recovery time
should be as minimal as possible with virtually no overshoot. Verify the CO
2
sensor calibration prior to
Performing an injection calibration. The injection calibration is not required after an “Open Door”
sensor calibration since it is performed automatically during the routine. The injection calibration
should be performed after a “Closed Door” sensor calibration when possible, if CO
2
supply pressure of
the incubator is changed, or if the CO
2
flow control valve is disturbed.
The following steps should be taken for the CO
2
injection calibration:
Press "SEL" to indicate LED next to CO
2
percent display.
Press and hold UP and DOWN keys simultaneously for three seconds. "CAL" and current
indicated CO
2
% will blink.
Open door for at least 1 minute to evacuate the CO
2
from the chamber. The value on the display
should be below 1% before closing the door to continue the routine
Press and hold UP and DOWN keys simultaneously again to start auto calibration procedure.
Observe display, which will indicate the following sequence:
a) dLY - Wait for door delay, prior inject delay, temp. in range.
b) INJ - Inject CO
2
for fixed time period according to the set point
c) dLY - Wait for post inject diffusion.
d) End - Done with Calibration
Press "SEL" to set current value and exit calibration.
If necessary, open glass door to vent excess gas.
9.4.4 CO
2
System Auto Zero Calibration Function
This Incubator is programmed to automatically check and adjust the zero calibration of the CO
2
sensor.
HEPA filtered room air is pumped through the sensor detector cell for 2 minutes. The CO
2
reading is
checked at this time. If it 0.5% or less different than the current zero the sensor will use the new value
as zero. When the value is greater than +
0.5%, the auto zero routine is aborted and an ACF alarm is
sounded. See Section 11.0 on Trouble Shooting for responses to this alarm.
The auto zero routine is scheduled to be initiated 12 hours after the Incubator is turned on and then
every 24 hours thereafter. This timing is structured to run the auto zero routine daily at a time that
would be considered "off hours". The timer for this routine can be reset at any time by simply turning
the Incubator off then back on. Power failures will reset the timer.
This routine is essentially transparent to the operation of the Incubator and the factory supplied options
like the chart recorder or the printer outputs while it is running. After the routine is done the CO
2
level
will be reduced by about 0.2% to 1.0% depending on the amount of air that has be injected to perform
the routine. The routine can run as long as 7 minutes because it will try to perform the zero function up
to 5 times before declaring an “ACF” alarm. If any calibrations are attempted during this routine "SLF"
shows in the display and the calibration is inhibited until the routine is complete. An independent
monitoring system will record a minor shift in CO
2
and temperature during the routine. This happens
because the air injected into the sensor, during the purge and while the sensor is performing the zero
function, is passed into the chamber.
This routine compensates for minor shifts in zero due to electronic drift. Regularly scheduled checks of
the calibration by an independent instrument must still be performed.
To abort the Auto Zero routine open the inner glass door and close it again.
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