Maintenance By The User; Function Checks Of Cooling Capacity - Knauer K-7400 Benutzerhandbuch

Maintenance by the User

Maintenance by the User

Function Checks of Cooling Capacity

Fig. 22
The cooling capacity can be checked by measuring the temperature in
the cooling cavity (-13 to -16°C during cooling down and ~ 20°C in stand-
by position).
To perform this test, the instrument must be calibrated. Connect the
measuring head cable and place it on top of the instrument (Fig. 5). Press
Start/Stop to start the measurement and wait 5 minutes to get the error
message <MEASUREMENT TIMEOUT>. After this press quickly twice
the  key to read out the cooler value on cool menu (Fig. 8.2).
The value must be in the range of -13 to -16°C. If the value is not
reached, please check that the cooling limit is set to -16°C (Fig. 8.5). If
you use for this test a different cooling limit than -16°C you get different
results. Retry the test and press quickly twice the  key after 5 minutes
without displaying the error message. If you change the cooling limit, you
must perform a new calibration after this test.
Additionally a calibrated reference thermometer can be used for
measuring the temperature in the cooling block of the osmometer. Please
verify, that the reference thermometer has contact to the cooling unit and
displays quickly temperature changes. Fill the copper cooling cavity close
to the top with pure water and install the thermometer. Perform the test
as described above and observe the reference thermometer. After the
test, it is necessary to dry completely the copper cooling room with a
tissue.
The cooling capacity is usually sufficient for a sample volume of 0.15 ml if
the freezing turbulence in the solution is initialized by a start of the
vibrator within 150 seconds.
If the temperature of -13°C cannot be obtained, the Osmometer K-7400
must be returned for repair.
The thermistor should always be placed in the sample centre 0.5 to 1 mm
above the bottom of the measurement vial.
Be sure not to bend the vibration wire.
Fill 150 µl of a sample or calibration solution into the measurement vial.
Carefully insert the measuring vial all the way into the adapter. The
thermistor should now be approximately 0.5 to 1 mm above the bottom of
the measurement vessel.
Thermistor Adjustment
0.5 – 1 mm
25