#6750, FREEZER MILLS - Wolf Laboratories

7.3 Operation
6870 Freezer/Mill
When the 6870 Freezer/Mill is set up for the first run of the day, with a loaded vial in the coil,
make sure the LN valve on the supply tank or line is open. Go to the RUN screen and touch
RUN. The Auto-Fill valve will open and let LN into the Freezer/Mill tub. The valve may close
and open several times before the tub is full and PreCool timing starts, but this is normal. LN
boils and splashes as it enters the tub and this may temporarily “fool” the upper LN sensor.
However, the Auto-Fill System has a built-in pause for the LN to stabilize before measuring the
LN level again. Precool countdown will not begin until the tub is full of LN.
During a long run, if the lower LN sensor detects a low LN level, the LN valve will open during a
re-cooling period. Again, the valve may open and close several times while the tub is filling, but
during “Auto-Filling” the timer stops, and will not start again until the tub is full.
At the end of a run the LN 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 LN.
The 6820 Auto-Fill System has been designed to work with typical grinding programs that
involve a precooling period and repeated short grinding and recooling periods. If you want to
use the 6870 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 will not trigger the Auto-Fill System to add LN during a
grinding period, just during precooling before grinding, and during the re-cooling periods
between grinding periods.
Page 28 of 36 SPEX SamplePrep LLC March 2012