The raw analog output from a thermocouple (TC) or resistance temperature detector (RTD) must be converted into a digital signal before the temperature can be interpreted. It can be sent in its raw form to a simple digital display, small temperature loop controller, transmitter or the temperature I/O card of a larger automation system.
The signal also may be converted and sent using a more robust communication protocol such as 4 to 20 mA, with Hart or some variant of fieldbus. Both can transmit data such as status and diagnostics in addition to temperature to automation systems. In any case, how the signal is handled once it comes out of the sensor itself can have a major influence on overall system accuracy and reliability.