4.1 Principles
The general principle of classical DTA is shown schematically in Fig. 4.1.
Thermocouples are used for temperature measurement. The five basic
components are outlined by the boxes. The programmer is designed to
smoothly increase or decrease the furnace temperature at a preset, linear rate.
The control thermocouple checks the furnace temperature against the
program temperature. Any difference is used to adjust the power to the
heater. Reference, Rfc, and sample, Spl, are placed symmetrically into the
furnace, so that for the same temperature difference with respect to the
furnace the heat flow should be the same.
The reference temperature for the thermocouples may be provided by an
ice bath. Today it is best to use an automatic cell with Peltier cooling (see
Fig. 5.5) that can establish the triple point of water with an accuracy of 0.05