40 | Operation
Thermo Fisher Scientific CryoExtra CE8100 Series
Liquid Nitrogen Level
Calibration
This section describes the procedure to calibrate the LN
2
level. This procedure requires the cryogenic meter dip stick
supplied with each CryoExtra freezer. This calibration method
provides level measurements with a ± 0.5 inch (± 13 mm)
accuracy.
All new freezers equipped with controller have been calibrated
at the factory. The liquid level should only be calibrated if faulty
readings are suspected, the Controller itself has been
replaced, following a firmware update or as a part of a
preventative maintenance schedule.
Dip Stick Procedure
1. Open or remove the freezer lid to access the interior
storage space.
2. Hold the meter dip stick vertically with the 0.0 inch end
pointed down.
3. Lower the meter dip stick into the LN
2
at the bottom of
the freezer. Ensure the meter dip stick is vertical and
touching the bottom of the inner Dewar. Some LN
2
boiling will occur around the meter dip stick.
a. CryoExtra Freezers:
Insert meter dip stick into the rectangular channel on the
turn tray in order to access the liquid below the tray.
4. Leave the meter dip stick in the LN
2
for approximately
5 seconds.
5. Remove the meter dip stick from the liquid and
immediately wave it back and forth in the air. A distinct
frost line will begin to develop as moisture in the air
condenses on the meter dip stick predominately where it
was submerged.
6. Subtract 0.5 inches (13 mm) from the observed frost line
to account for the LN
2
boiling up around the meter dip
stick while it was submerged. This resultant level
measurement represents the actual liquid level inside the
freezer. Once you have obtained the measured level,
proceed to the liquid level calibration.
Figure 10. Meter dip stick showing example level
frost line. The resultant measured level
would be 5.5 inches after subtracting
0.5 inches from the frost line to account
for the LN
2
boiling.
Note:
LN
2
liquid at or above turn tray height will rise higher in
the dip stick channel.
Level dip stick inserted to measure the physical liquid nitrogen
level.
Liquid Level Calibration
Note:
Liquid level calibration cannot be performed while the
Controller is filling. If Controller is filling, press “Stop Fill” and
perform the calibration. Allow freezer plumbing to thaw 10 to
15 minutes before calibrating.
Note:
Liquid level calibration is most accurate when
calibrated at 10.0 inches (254 mm). Calibration must be
performed above 3.0 inches (75 mm).
Note:
Security Level 3 or higher is required to calibrate the
liquid level.
CAUTION :
Always wear protective gloves and
face shield when handling LN
2
. Refer to the
section of this manual.
CAUTION :
Picture is for demonstration only (on
an empty tank), Please use protective gear while
working with liquid nitrogen. Please refer section
for Safety while working
with Liquid nitrogen.
