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Sample Bin Setting Advanced
™
Osmometer 3250/Cryoscope 4250 Service Manual
The following situations indicate a problem with either the probes or the cooling assembly:
• The resistance reading is replaced by the number 0. Scrolling from right to left indicates
an open circuit.
• The target temperature cannot be reached, but probe readings that vary around ambient
indicate a cooling system problem.
To determine if a faulty probe is causing the problem:
1. Disconnect the probe from the main board.
2. Place a 6 Kohm fixed resistor across pins 1 and 2.
3. If the resistance display changes to approximately 6,000 ohms, replace the probe.
If the resistance does not change, replace the main control board or application board.
If the resistance on both channels does not increase, or if the temperature reads
approximately ambient while a target temperature is set, the situation indicates a problem
with either the cooling assembly or application board.
To determine which component is faulty:
1. Remove the empty tube from the freezing chamber.
2. Set the target temperature to -8 °C.
3. Raise the head manually and place a thermometer inside of the freezing chamber.
4. If the temperature inside the freezing chamber drops to approximately -8 °C, the cooling
assembly is working, and the application board needs to be replaced.
If the temperature remains at room temperature, replace the cooling assembly.
Note When the A/D channel is open, there is a thirty-second delay in response to any
resistance change.
CAUTION: If the A/D test sample freezes, allow it to thaw before attempting to remove
the sample probe.
Sample Bin Setting
If you do not know the sample bin number, or if you want to verify the sample bin number:
1. Turn on the instrument. If there is a Supervisor/Operator keyswitch, turn it to the
Supervisor position (if required).
2. Press TEST.
3. Press < or > to select Probe Bin Test, and then press START.
4. Place a sample of Probe Bin-Setting Fluid into the freezing chamber.
5. At [START] Ready?, press START.
6. At the end of the test, record the sample probe resistance and the bin number, and then
press STOP. The display will change to Probe Bin Test.
To set the correct sample bin number, follow steps 7-9.
7. If the current sample bin number matches the number just recorded, press STOP twice to
exit the menu.
8. Press SETUP. The Supervisor/Operator keyswitch must be in the Supervisor position.
9. At Select Setup Item, press < or > to select Select Sample Bin #, and then press START.
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