6875D Freezer/Mill
1300-87052-1A, REV 1
SPEX SamplePrep LLC
Page 21 of 36
6.1 Standard Auto Fill
(Cont’d)
During a long run, if the lower LN sensor detects a low liquid nitrogen level, the LN valve will
only open during a re-cooling period. Note, the valve may open and close several times while
the tub is filling however the timer will continue to countdown for the cooling period while the
tub is filling. At the end of a run the liquid nitrogen level in the tub may seem low, but this is
only because the lower LN sensor has not triggered the Auto Fill System to fill the tub with
liquid nitrogen. The 6875D Freezer/Mill Auto Fill System has been designed to work with typical
grinding programs that involve a precooling period and repeated short grinding and re-cooling
periods.
If you want to use the Freezer/Mill in a different way
–
for example, by having a single long
period of continuous grinding
–
please call us first to make sure your plans and the Freezer/Mill
are compatible. The lower LN sensor may not trigger the Auto Fill System to add liquid
nitrogen during a single long period of continuous grinding.
6.2 Manually Adding Liquid Nitrogen
CAUTION: When working with liquid nitrogen directly or indirectly, cryogenic gloves must be
worn to protect hands. Safety goggles should be worn at all times to protect eyes
from accidental splashes or liquid nitrogen vapor.
Liquid nitrogen (LN) should only be added to 6875D Freezer/Mill with the lid open. To open the
lid, hold the lid down with one hand, and with the other hand pull the upper end of the latch
toward you. Then pull the lower end of the latch to detach it from the cabinet. Release the lid
and it will raise up by the gas spring arms. The gas spring arms will keep the lid in the upright
position.
The Freezer/Mill tub should be filled
until the unit sounds with a series “Beeps” indicating the
proper liquid nitrogen level has been reached (approximately 2 inches (5.1 cm) below the rim of
the tub). If the liquid nitrogen is above this level when the lid is closed, LN can splash outside
the tub and drain excess LN out the vent in the rear of the Freezer/Mill.
Always close the lid
slowly to avoid splashing
.
Liquid nitrogen is generally available either in a large tank with a flexible steel hose, or in a
smaller Dewar. The 6875D Freezer/Mill typically consumes 15-19 liters of LN during initial cool-
down, and another 4-6 liters per hour, depending on use.
Insert loaded sample vials in the chambers and lower the lid to chill unit. Initially, liquid
nitrogen will boil off vigorously, but as the tub cools the boiling will subside. Gradually add
more liquid nitrogen until the
unit “Beeps” indicating the proper operating level has been
reached. When boiling has subsided, slowly lower the lid and secure the latch. Allow unit to
remain closed for 1 to 2 minutes, then open the lid
. If the unit “
Beeps
”
then the liquid nitrogen
is at the proper oper
ating level. If unit does not sound a series of “B
eep
s”
when lid is opened
then add more liquid nitrogen.
