Discovery DSC™ Getting Started Guide
Page 53
Enthalpy (Cell) Constant Calibration
This calibration is based on a run in which a reference material (e.g., indium) is heated through its melting
transition. The measured heat of fusion is compared to the theoretical value. The cell constant is the ratio
between these two values. The onset slope, or thermal resistance, is a measure of the suppression of tem-
perature rise that occurs in a melting sample in relation to the thermocouple. Theoretically, a standard sam-
ple should melt at a constant temperature. As it melts and draws more heat, a temperature difference
develops between the sample and the sample thermocouple. The thermal resistance between these two
points is calculated as the onset slope of the heat flow versus temperature curve on the front of the melting
peak. The onset value is used for kinetic and purity calculations to correct for this thermal resistance.
Temperature Calibration
Temperature calibration is based on an experiment in which a reference material (e.g., indium) is heated
through its melting transition. The extrapolated onset of the recorded melting point of this reference mate-
rial is compared to the known melting point, and the difference is recorded for temperature calibration. The
same file used for the cell constant calibration can be used for this calibration.
In addition, you can use up to four other standards to calibrate temperature. If you use three or more
standards, the temperature correction is modelled by a cubic spline fit. The multiple-point temperature cal-
ibration is more accurate than the one-point calibration if absolute temperature measurements are required
over a broad (>300°C) temperature range.
If multipoint temperature calibration is used, it is recommended that you choose standards that will bracket
the desired measurement temperature range. This will ensure optimal calibration and performance.
Heat Capacity Calibration (Discovery DSC2500 only)
Heat capacity can be obtained in a single experiment with the Discovery DSC™. Heat capacity calibration
is required to optimize the accuracy of the sample’s heat capacity. The calibration uses a sapphire standard
material with a known heat capacity at a specific temperature of interest. Calibration is typically done at a
heating or cooling rate of 10 to 20°C/min.
The heat capacity calibration curve is calculated by dividing the theoretical value of heat capacity by the
measured value at a specific temperature. The resultant calibration data curve, as a function of temperature,
is sent to the instrument and applied to subsequent measurements.
Heat Capacity (MDSC
®
) Calibration
MDSC heat capacity calibration is only required to optimize the accuracy of the sample’s heat capacity or
when using periods less than or equal to 40 seconds. The calibration uses a sapphire standard material with
a known heat capacity at a specific temperature of interest. Except for heating rate, the calibration experi-
ment should be run under similar conditions (pan type, modulation amplitude, and period) to those that will
be used for subsequent samples. The heating rate can be set to a nominal value of 5°C/min or the calibra-
tion experiment can be performed isothermally if you are calibrating just the reversing heat capacity.
The Reversing Heat Capacity calibration curve is calculated by dividing the theoretical value of heat
capacity, as a function of temperature, by the measured value. The resultant calibration data, as a function
of temperature, is sent to the instrument over the entire temperature range of the calibration experiment.
See online help for more detailed information.
