Advanced Instruments 3250 - Page 82

82
Advanced
™
Osmometer Model 3250 User’s Guide
Looking from the side of the instrument, you should be able to see
a stir vibration blur at the tip of the stir/freeze wire. For 0.2mL to
0.25mL osmometer operation, the stir vibration blur at the very tip
of the stir/freeze wire should be between
3

32
" and ⅛" or 2 and 3 mm.
Stirring is necessary to minimize temperature gradients in viscous
samples but more than ⅛" or 3 mm can cause poor repeatability
or frothing which may make it impossible to reliably determine the
freezing point.
If the stir vibration amplitude is not correct, press > to increase the stir
amplitude and the xx value or press < to decrease the stir amplitude
and the xx value. Continue to increase or decrease the xx value as
necessary, until the stir vibration blur at the very tip of the stir/freeze
wire is between
1
/" and " or between 2 and 3 mm.
As this adjustment is completed, you may wish to hold a sample tube
containing a 0.2-mL sample of either an NaCl standard or HO up in
position on the probe and stir/freeze wire to make sure that froth is not
produced.
When the stir amplitude is correct, you may wish to record the stir-
amplitude xx value in the Service Log for reference. Press ENTER to
store the new setting. The display will change to Set Stir Amplitude.
At Set Stir Amplitude, press the STOP key to exit the SETUP program
(or > or < to step to another SETUP item).
When STOP is pressed, the display will change to Osmometer Ready
and the 3250 is ready for freezing point tests.
IMPORTANT After completing any probe and/or stir/freeze wire
adjustments, check the instrument calibration and
recalibrate as necessary.