FUNCTIONAL OVERVIEW The Fluke 51 and 52 K/J Thermometers take nonlinear voltages from thermocouples and convert the voltages to meaningful temperature readings. These thermometers are actually microvoltmeters with additional features to compensate forthe reference junction and non-linearities of thermocouples. The heart of these instruments 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 I, thermocouple 2, and the signal that represents the temperature of the reference junctions. To measure the three signals, the a/d converter is connected to each of these signals one at a time. A microcomputer (U2) coordinates the switching and a/d activity performed by U1. U2 also interprets the numbers sent by the a/d converter, including reference junction compensation, linearization, and degrees Celsius and Fahrenheit conversion. U2 also monitors the instrument control buttons and drives the liquid crystal display (LCD)