Different thermocouples are built for specific purposes and different ranges. The
secondary reference thermocouple thermometer is platinum verses platinum plus 10%
rhodium, with a range from 0,C, to 1,768,C.
b. The second type of secondary reference thermometer is, the mercury in glass. Mercury
is the best liquid because to its linear expansion and its low freezing point. The limits of a
mercury thermometer are -38,C to 360,C by the addition of inert gas (mercury freezes
at -38.87,C and boils 356.58,C.)
The secondary reference set is shown here as eight different thermometers. The smaller
set is a secondary reference set, but is being replaced by the (8) thermometer set.