Advanced Instruments 4250, Руководство пользователя

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Reinstall the operating head cover. Do one last freeze test with the oper-
ating head cover reinstalled; the freeze pulse characteristics are slightly
different with it in place.
If the freeze vibration is still not enough, do not proceed further without
obtaining Hot-Line
®
service as recommended in Chapter 5, “ Obtaining
Service ” .
If you succeed in obtaining enough freeze vibration, the stir vibration
amplitude must be readjusted as follows:
1. Press the
SETUP soft key. If the Supervisor/operator keyswitch is in
the Supervisor position, the display will change to “ Select Setup
Item ” .
2. At “ Select Setup Item ” , press the START soft key. The display will
change to “ Setup Menu #: 0 ” .
3. At “ Setup Menu #: 0 ” , press the 4 soft key, then press ENTER .
The display will change to “ Set Stir Amplitude ” .
4. At “ Set Stir Amplitude ” , press the START soft key. The display
will change to “ Amplitude = xxx ” , with “ xxx ” being a value of
approximately 140.
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 2-mL to 2.5-mL
cryoscope operation, the stir vibration blur at the very tip of the stir/
freeze wire should be between 1/8 ” and 1/4 ” or 3 and 6 mm. A small
amount of stirring is necessary to minimize temperature gradients in
viscous samples but more than 1/4 ” or 6 mm can cause poor repeatabili-
ty 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 “ xxx ” value or press < to decrease the stir amplitude
and the “ xxx ” value. Continue to increase or decrease the “ xxx ” value as
necessary, until the stir vibration blur at the very tip of the stir/freeze
wire is between 1/8 ” and 1/4 ” or between 3 and 6 mm.
64
Advanced
®
Cryoscope Model 4250 User’s Guide