IKA C 6000 isoperibol Package 2/12 - Manual (Page 26)

26
Calibration
To ensure precise, reproducible results of the mea-
surement, the calorimeter system is calibrated af-
ter it is initially placed in service, after service jobs,
after parts are replaced and at specifi c time inter-
vals. During calibration, the heat capacity of the
calorimeter system is redetermined.
Regular calibration is absolutely essential to
obtain accurate measurements!
For this purpose, a specifi c quantity of a reference
substance undergoes combustion in the IKA
®
C6000 global standards/isoperibol under the con-
ditions of the experiment. Since the gross calorifi c
value of the reference substance is known, it is
possible after combustion has occurred to calcula-
te the heat capacity based on the increase in tem-
perature of the calorimeter system.
The reference substance for calorimetry on an
international level is benzoic acid of the National
Bureau of Standards (NBS Standard Sample 39 J)
with a guaranteed gross calorifi c value.
The thermal capacity is derived from the formula
for the calorifi c value.
CV = (Ho * m + Qext) / DT
Depending on the standard used, determination
of the thermal capacity may require performance
of several measurements. Using various statistical
criteria the average value is calculated and is used
as the thermal capacity for subsequent determina-
tions of calorifi c values.
For more detailed information on calibration
please see the relevant standards. If the IKA
®
C 6000 global standards/isoperibol is operated
with several different decomposition vessels, you
will need to determine the heat capacity of the
system for each decomposition vessel. The parts
of each decomposition vessel must then not be
swapped with parts from other vessels.
In addition the thermal capacity depends to a
small extent on the measurement procedure used.
The thermal capacity determined for each measu-
rement procedure that is used.
Instructions on calibration
Ensure that calibration is carried out under the
same conditions as the subsequent tests.
If sub-
stances are used in the decomposition vessel in
combustion tests (e.g. distilled water or solutions),
you must use exactly the same amount of this
substance for calibration.
For determination of calorifi c values the increase
in temperature must be about as great as for the
calibration (e.g.: 2 tablets = approx. 1 g benzoic
acid =˜ 3 K). The optimum sample quantity must
de determined by several trials where necessary.
Working with the IKA ® C 6000 global standards/isoperibol calorimeter