IKA C 7000 Grundausstattung Set 2 - Manual (Page 41)

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Calibration must be carried out under conditions similar to those that will be used for
subsequent tests. If combustion tests are to be carried out with absorption liquid
(e.g. distilled water or a solution) in the decomposition vessel, then calibration
should be carried out with the same quantity of the same substance.
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• At a starting temperature of 25 °C, the C 7000 calorimeter has a maximum tem-
perature increase of 25 K. For accurate results, a combustion test should yield a
temperature increase of approximately 20 Kelvin. If you do not use benzoic acid
for calibration, the quantity of material should be adjusted to meet this condition.
• For calibration, use benzoic acid (accessory C 723) compressed to a pellet.
Weigh out approximately 1 g, this corresponds to a temperature increase of
ca. 20 K.
• Calorific-value determinations must yield approximately the same temperature
increase as calibration. The optimum sample quantity must be found by making
several tests if necessary.
• The pre-test time should be at least 120 seconds.
• When calibrating to DIN, the C value is specified as the average of at least 5
calibration tests. Individual results should only be used in calculating the aver-
age if the difference between the highest and lowest values (scatter) is not more
than 0.4% of the average.
If the scatter is greater, then the result which is farthest from the average is dis-
carded first. A sixth calibration test must now be carried out. The result of this
determination must not deviate by more than 0.2% from the average of the four
valid results. For further details, please see the relevant standard.
• In the calorimeter, the C value from the last calibration of a decomposition ves-
sel is stored in memory. If several calibration tests are used to determine the
C value (e.g. when calibrating to DIN), the calculated average C value for this
decomposition vessel must be entered manually before carrying out a calorific
value determination.
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Because a calorimeter can operate in a wide range of ambient temperatures, the
C value of a system must be seen as WHPSHUDWXUH GHSHQGHQW . This fact must be
taken into account both during calibration and during normal testing. The calibration
values printed out use 25 °C as reference temperature. This applies also to manu-
ally entered C values. When carrying out combustion tests, the C value must be
corrected to the current ambient temperature (temperature of the metal casing at the
start of combustion). This also explains why the C value printed after a test does not
agree with the value entered manually by the user.
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