Advanced Instruments 4250, User Manual

Page: 87 / 121

As this adjustment is completed, you may wish to hold a sample tube
containing a 2-mL sample of either an NaCl standard or H
2
O up in posi-
tion on the probe and stir/freeze wire to make sure that froth is not pro-
duced.
When the stir amplitude is correct, you may wish to record the stir-
amplitude “ xxx ” 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 soft key to exit the SETUP
program (or > or < to step to another SETUP item).
When STOP is pressed, the display will change to “ Cryoscope Ready ”
and the 4250 is ready for freezing point tests.
IMPORTANT After completing any probe and/or stir/freeze wire
adjustments, check the instrument calibration and re-
calibrate as necessary.
65
Troubleshooting & Service
The flange of the mandrel must
be flush with the head chassis.
The black bead in the probe tip must
be in the center of a 2-mL sample in
the sample tube, at equal distances
from all nearby surfaces. It must be
the same distance from the bottom of
the tube as it is from the side walls.
The stir/freeze wire should be
about the width of the
stir/freeze wire away from the
mandrel where it exits from
the mandrel.
The stir/freeze wire should be
about the width of the
stir/freeze wire away from the
tip of the probe. Bend the
wire if necessary. The tip of
the stir/freeze wire should be
even with the bottom of the
probe tip. Loosen the
stir/freeze wire setscrews to
enable vertical adjustment.
Figure 11: Mandrel Probe and Stir/Freeze Wire Adjustment