(
Highway
Addressable
Remote
Transducer) A widely used wired sensor network protocol that dates back to the Bell 202 standard in the 1980s. An extension to the 4-20 mA analog signal, HART superimposes a 1,200 bps signal onto the line that provides bi-directional communications with instruments in the field. See
4-20 mA and
WirelessHART.