Thermocouples are very interesting, indeed. The basics are that there are two wires made of dissimilar materials which are precisely welded together at one end. When this junction of wire is exposed to a temperature it creates a very small voltage. How small? Through the range of a normal roast (about 50F to about 400F), a K-Thermocouple produces from 0.001 to about 0.008 volts DC. As the temperature changes, the voltage changes.
This voltage produced can be measured by a special circuit and that data can be then used to do things like display a temperature (a digital thermometer), or control a circuit. They react quickly and are accurate repeatable. K-thermocouples (the type used in the Hottop coffee roasters) can easily measure temperatures well over 1000F. Degrees! They also last a long time if handled carefully.
The one caveat is that many thermocouples use solid conductor wires (not stranded wire). A common household electrical cord is quite flexible and that is because each of the two or three wires (three for grounded plugs) are made up of a bundle of small gauge wires. Thermocouples have just one wire for each conductor. Because of that they tend to be stiffer and more prone to breaking. That is particularly true at the end which plugs into the control panel.
So when working on your roaster, and particularly when removing the control panel, use care when manipulating the wires and when connecting and disconnecting the thermocouple (or in the case of the KN-8828B-2K+, thermocouples). Never pull on the wire to disconnect the thermocouple from the control panel. Small needle-nose pliers are recommended.