Why aren’t thermocouples used for all of temperature measurement jobs? Because designing a good thermocouple interface is not easy. There are two main reasons. The first reason is that the output voltage is very small, on the order of tens of microvolts per degree C. Secondly, the designer will need to measure the temperature at the cold junction. Thermocouples measure relative, not absolute temperature. Absolute temperature is calculated by adding the absolute temperature at the cold junction to that of the thermocouple. Therefore, a temperature sensor is required at the cold junction. At a minimum, the discrete solution requires a high-resolution ADC with input multiplexer, precision resistors, an accurate voltage reference, and a temperature sensor to digitize a thermocouple output with discrete components.