The Fluke 52 K/J Thermometer takes nonlinear voltages from thermocouples and converts the voltages to meaningful temperature readings. The thermomether is actually a microvoltmeter with additional features to compensate for the reference junction and non-linearites of thermocouples.
The heart of the instrument is an analog-to-digital converter (a/d converter) that develops a numerical representation of an analog voltage. The a/d converter (UI) works in the range of -10 mV to +55 mV. For the Fluke 52, three signals must be measured: Thermocouple 1, thermocouple 2, and the signal that represents the temperature of the reference junctions.