Discovery DSC™ Getting Started Guide
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This simple relationship, however, does not take into account extraneous heat flow within the sensor. The
TA Instruments DSC is specifically designed to account for those latter heat flows.
The cell sensor consists of a constantan transducer with separate chromel disk welded to the surface under
the sample platform. Chromel wires are welded to the Chromel disks to generate the delta-T signal. A third
thermocouple measures the temperature at the base and one of those wires with the sample platform wire
generates the delta-T zero signal. The T4 equation below shows the thermal network model which repre-
sents this cell arrangement, and the resultant heat flow expression that describes this cell arrangement (des-
ignated the T
0
[Tzero
®
] cell):
The first term in this expression is the equivalent of the conventional single-term DSC heat flow expres-
sion. The second and third terms account for differences between the sample and reference sensor resis-
tances and capacitances respectively. These terms have their largest impact during regions of the thermal
curve where the heat capacity of the sample is the predominant contributor to heat flow. The fourth term
accounts for the difference in heating rate between the sample and reference. This term has its largest
impact during enthalpic events (e.g., melting). This equation can be further adapted to account for pan heat
flow effects T4P.
The DSC can deliver any of three separate heat flow signals, including:
•
The conventional (single-term) heat flow (commonly designated as “T1 heat flow”).
•
The expanded four-term heat flow (designated as “T4 heat flow”), which accounts for the cell
resistances and capacitances and the heating rate difference between the sample and reference.
•
A third heat flow (designated as “T4P heat flow”), which also accounts for pan effects.
