HART (Highway Addressable Remote Transducer) is a fieldbus and communication interface used in automation technology for connecting field devices and sensors to the control station. It is the analogcurrent loop interface that operates as a 4 mA to 20 mA interface and through which the measured values and control signals are transmitted bidirectionally to and from the field devices.
Up to 16 devices can be operated on the two- wire HART fieldbus. The data rate is very low and is two measured values per second. For the transmission of data, the two bit values "0" and "1" are modulated onto the measured value by means of frequency shift keying( FSK). With "0" the sampling frequency is 1.2 kHz, with "1" 2.2 kHz. This procedure allows further data to be transmitted without affecting the measured values. These data can be control signals, sensor information, process variables, status information or data for parameterization.
HART is a concept for sensor networks of the HART Communication Foundation( HCF). In addition to the wired HART fieldbus, there is also WirelessHART, which works wirelessly with radio links. The European Committee for Standardization( CEN) has adopted the Wireless-HART specification as European StandardEN 62591. Previously, the standard was already approved by the International Electrotechnical Commission( IEC).
In addition to the classic HART protocol, there is also HART- IP, which can be used as a backhaul protocol in process automation. This network protocol is intended to provide integration between devices at different levels, from the field device to the control station. Via this protocol, the data can be transmitted to the application layer on which the applications such as the SCADA protocol or Distributed Control System( DCS) reside.