Eppendorf Galaxy CO2 Sensor - Manual (Page 85)

Equipment options
Galaxy ® 170 R/170 S CO
2
Incubators
English (EN)
85
To disable oxygen control, follow the pattern used to enable it, but this time select USER, MANUAL
DISABLE, ENTER, OFF and then ENTER again.
12.6.4 Important notes for O
2
levels > 80 %
If you are running the incubator with a dry chamber and no CO
2
, the recommended maximum O
2
level is 95
%. In addition, open samples inside the chamber can cause RH to increase, and the O
2
sensor may require
recalibration to work properly in a completely dry atmosphere.
For a humidified chamber with no CO
2
, the recommended maximum O
2
level is 92 %, while for a
humidified chamber with 5 % CO
2
, we recommend no more than 87 % O
2
.
When the incubator is running at normal humidity level (i.e., 95 % RH), there is approximately 6 % (by
volume) water vapor present in the chamber. If 5 % CO
2
is also present, the maximum achievable level of
O
2
—without using excessive quantities of oxygen—is approximately 87 %. Oxygen direct from a cylinder
has a dewpoint temperature of < -45°C, corresponding to 0.06 % water vapor. As it enters the incubator,
therefore, its temperature is very low and even as it is warmed, its RH level is very low. Both of these factors
affect the performance of the O
2
detector. To minimize these effects, O
2
is fed continuously until it arrives
at 0.4 % below setpoint. To allow the detector signal to recover and the RH level to build, there is a
3-minute delay. If O
2
is still required, it is fed in for 10 seconds, with an additional 3-minute delay until
setpoint is achieved.
As the humidity level rises, the O
2
content in the chamber will diminish. The use of O
2
will rise considerably
as the setpoint approaches the sum contents of water vapor and CO
2
in the chamber. In the short term, it is
possible to achieve higher levels of O
2
, but as humidity rises and O
2
content is pushed down, there will be a
continuous demand for O
2
and RH will remain too low. At the same time, as O
2
is pumped in, the CO
2
level
will also diminish, causing the system to add CO
2
, which in turn causes the O
2
level to drop again.
If the O
2
setpoint is too high, the incubator can consume some 2,500 liters of O
2
per day—which does not
include the extra oxygen consumed each time the door is opened (about 500 liters).
12.6.5 Alarms
The alarm levels are set automatically to ± 0.5 % above and below the programmed value, but these points
can be altered in the
ALARM screen. In addition, the re-arming of the alarm can be delayed until the
Programmed Value is achieved by selecting the relevant option in the ALARM screen.
For example, it is possible at low oxygen levels that the CO
2
and O
2
levels might not fully recover within the
Alarm Limits after the 15-minute DELAY IN ARMING AFTER DOOR OPENING period has elapsed, so this
time period can be increased in the ALARM screen to suit individual circumstances.
12.6.6 Referencing to atmosphere
It is highly recommended to reference the sensor to atmospheric oxygen at least once per
month.