Thermocouples are industrial temperature sensors which involve a device that is compatible with thermocouples, a thermocouple thermometer, and two wires that join both devices. These wires, which are connected on one side, are not the same length, so they do not meet at the open end.
They can function as probes that have sheaths protecting the wires, surface probes that measure the exterior of solids, or beaded wire models that feature wires welded together. Different models offered by Watlow distributors such as Hi-Watt are appropriate based on the medium you are measuring and whether you want a surface or interior reading.