11 Checking, Adjusting and Calibrating the Instrument
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11.2.2
Performing Density Checks
With density checks, carried out in regular intervals, you can ensure a high and
stable accuracy of your density and concentration measurements.
During a density check, you fill a medium of known density (air, water or any
customer-specific standard liquid) into the measuring cell and compare the
measured density with the reference value.
The M series DMA performs the water checks and air checks automatically at the
measuring temperature of the method that is currently active. Also the
predetermination/equilibrium type of measurement is used according to the
selected method. The density of water and air at the measuring temperature is
calculated and the actually measured density is compared with the calculated
value. With water checks and custom checks, this calculated value is calculated
for the set temperature. With air checks, the calculated value is calculated for the
set temperature and the measured air pressure.
Custom checks have to be defined for a certain method and are always performed
at the temperature of the selected method with the corresponding
predetermination/equilibrium type of measurement.
Air checks and water checks are available for any method.
When to do water checks and custom checks
Use the water check and custom check to verify that the instrument is measuring
with satisfactory accuracy. We recommend performing a water check or custom
check every day before starting the measurements. Perform additional water
checks or custom checks on demand depending on your judgment, e.g. when you
get unexpected results.
When to do air checks
Use the air check to evaluate the efficiency of your cleaning and drying procedure.
We recommend performing an air check every day after the measurements have
been finished and the measuring cell was cleaned and dried.
Perform additional air checks on demand depending on your judgment, e.g. after
the measurement of critical samples that might stick to the measuring cell (e.g.
samples containing adhesives, sticky particles, proteins).
To perform a density check
1. Tap <Menu> and select
"Checks/Adjustments > Checks"
to open the
checks list.
2. Highlight a list item and tap <Start>.
3. Follow the instructions on the screen.
