Thermocouple temperature transmitters convert the small millivolt (mV) output of a thermocouple to a current signal (typically 4-20mA DC) that is immune to noise and voltage drops over long distances.
Thermocouple Temperature Transmitter
They are used with thermocouple temperature probes, bimetallic devices that are suitable for various temperature sensing applications.
Isolated thermocouple temperature transmitters eliminate ground loop problems by isolating the transmitter input from the transmitter output.
Output options include analog current, analog voltage, or relay/switch output.
Source: Prisma instruments