HART based 4-20mA Transmitter supports communication for transferring process variables from field transmitter to control room DCS/PLC Host via HART signals also in-additional to the standard 4-20mA signals.
Yes, in general we use 4-20mA signal for process variables to read data in the control room.
In addition to that, we can transfer process variables signal using HART signals also.
So in this case we can either use Normal Mode in HART Transmitter in which HOST (DCS/PLC) requests the required process variables and then Transmitters sends the data after receiving the request.
Now we can use Burst Mode also, in this case HOST (DCS/PLC) DO NOT SEND ANY Request to the transmitter, The Transmitter continuously sends the data to the HOST with predefined time intervals.