Look inside
a sensor.

Imagine Priya installing a connected temperature logger on a greenhouse hot water pipe. Her thermocouple produces a tiny voltage, but she also needs the temperature where its wires meet the instrument. The probe has two wires made from different metals, joined at the measuring end. A temperature change along a metal wire generates a voltage along it: the Seebeck effect. The metals respond differently to the same temperature gradient, so the instrument measures the difference between their voltages at the free ends. Interpreting that signal requires the temperature at those reference connections, often called the cold junction. Using the course's linear approximation, a type K sensitivity of forty one microvolts per degree Celsius turns four point one zero millivolts into a temperature difference of one hundred degrees Celsius. The cold junction is at twenty two degrees Celsius. Adding that gives a pipe junction temperature of one hundred twenty two degrees Celsius. Priya had assumed voltage alone gave the pipe temperature. In this example, leaving out cold junction compensation would underread by twenty two degrees. She includes the reference temperature before accepting the reading. The takeaway: a thermocouple needs both its voltage and its reference connection temperature to report the measuring junction's temperature.