4. Stir/Freeze Test
This menu item enables visually and aurally checking the stir and freeze
vibration amplitudes. Please refer to the “Stir/Freeze Amplitude
Adjustment” section shown later on in this chapter for instructions.
5. Probe Bin Test
This test is used to determine the resistance and bin number of the sam-
ple probe at a specific temperature (-0.093°C). It is essentially the same
as any other sample test except that the sample probe resistance and cor-
rect bin number are determined and displayed, in place of the sample
freezing point.
On entry, the probe bin test will display “[Start] Ready?”.
At “[Start] Ready?”, pipette or measure a sample of probe bin-setting
fluid into a clean sample tube, place the tube in the freezing chamber
and press the START key. The 4250 will run a special freezing-point
test to determine the sample probe resistance and bin number.
NOTE In emergency, H
2
O may be used in place of probe bin-setting
fluid for this test. The bin number thus determined will be
acceptable for bin setting though the probe resistance displayed
will be that at the freezing point of the H
2
O sample used and
will be different from that at a freezing point of -0.093°C.
The display will flash “Cooling Sample” (as in a normal test) until the
sample probe resistance reaches 4990 ohms. Then the test proceeds nor-
mally except that the display is in ohms rather than mOsm. At the end
of each test, the final display will be the test result in ohms and the sam-
ple probe bin number (e.g., “12345.67 Ohms Bin 10”).
A test in progress can be stopped by pressing the STOP key. Another
test may be run by replacing the sample and pressing START again. At
a specific freezing point, each probe has a unique resistance which
should vary very little from test to test. Therefore, the results of this test
may be used as a troubleshooting aid, in conjunction with the sample-
probe checks described in section “Sample Probe Checks and
Advanced
®
Cryoscope Model 4250 User’s Guide
52
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