Eppendorf R Series 48R CO2 Incubator - Manual (Page 62)

62
CO48R-0050 Š Galaxy R Series 48 R Personal Size CO
2
Incubator User’s Guide
8.7.4 Important Notes for O
2
Levels >80%
If you are running the incubator with a dry chamber and no CO
2
, the
recommended maximum O2 level is 95%. In addition, open samples inside the
chamber can cause RH to increase, and the O2 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 wapor 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).
8.7.5 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 rearming 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