page 36 Preparing a measurement
!
At temperatures higher than 70°C the space above the surface gets hot. To avoid
overheating of the balance system, the doors of the measurement chamber should
be kept open and only be closed when a measurement is running.
*
The (optional) gas space thermostatting system TJ20 can help avoiding
temperature changes even when the measurement chamber is open.
6.2 Setting up and filling the sample vessel
The K11 is supplied with the SV20 sample vessel with a diameter of 70mm.
!
Vessels with a diameter of less than 50 mm should not be used because boundary
effects at the glass walls could affect the results.
• The sample vessel should be positioned on the stage as centrally as possible for
the measurement. Thus, interference from the walls of the vessel is avoided.
• If a large enough volume of the sample liquid is available the sample vessel should
be filled to about 5-10mm below its upper rim. A larger volume is more easily able
to compensate any interference. If you have to use your sample liquid sparingly the
filling level must be at least double the given immersion depth (see chapter 10.2.1).
If a magnetic stirrer bar is used then its height must also be taken into account.
!
Please ensure that the required measuring temperature is reached. If you do not
use a thermostat jacket you must nevertheless take care that the temperature does
not alter after the sample vessel has been filled.
Interfacial tension
In this case the sample vessel should also be filled as full as possible (up to 5-10mm
below the vessel rim) in order to compensate for any interference.
Measuring the interfacial tension takes place in two stages (except in the option
Ring
method
–
Push
):
• The probe is first tared in the light phase. The filling level of the light phase for the
ring method
should also be at least twice the immersion depth. However, in the
plate method
the plate must be completely immersed in the light phase in order to
tare it, so that at least 13mm (=height of the plate + 3mm play) is required.
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