Thermopile, Mettler

Figure 6.5. Five thermocouple thermopiles used in the Mettler TA 3000 DSC system.

For the Mettler Toledo thermopiles, the thermocouples form a star-shaped symmetric pattern around a measuring point. Because of the symmetric arrangement of the thermocouples, the thermopiles will cause imbalances to cancel that would otherwise result in distortions in heat flow. Each thermocouple in a thermopile forms a junction under the pan and away from the pan so that each has an associated AT signal at both measuring points. Each thermopile signal is the summation of the AT signals from each thermocouple junction. A final AT signal is obtained from the difference between the sample and reference thermopiles. The heat flow rate (Q) can now be expressed as... 

Figure 2.3. Schematic of a thermopile used in a Mettler Toledo DSC (courtesy of Mettler Toledo).

Mettler Toledo (Mettler) now markets the DSC 1 unit, but at the time that this instrumental brief was written, marketed only the DSC823 (its design is further discussed in Section 2.3, The Basics of Differential Scanning Calorimetry). For both units, Mettler now offers a two-sensor option based on a thermopile construction embedded in a chemically inert and corrosion resistant ceramic material. The sensors differ structurally in their design, although the primary difference is the number of thermocouples incorporated into each thermopile. The performance specifications are given in Table 2.8. 

The next diagram, on the left, displays a top view of the heat leak disk of the Mettler DSC 20 and 25 thermal analysis systems. The disk is made out of quartz with a vapor-deposited 10-junction thermopile. The reference and sample crucibles each sit on one of the two circularly arranged spots with five or more sensors. The two central terminals bring the temperature difference signal to the measuring module. Absolute temperature information and... 

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