HART (Highway Addressable Remote Transducer) The very known 4-20 mA signal is a tried, tested and widely used standard for transmitting sensor data to the Control system. However only limited amount of information is sent by a 4-20 mA signal. HART (Highway Addressable Remote Transducer) protocol enhances these operations by transmitting digital data along with the 4-20 ma signal – without disturbing the signal. HART also permits two-way communications. It also has a digital modes that allows instrument to be connected to a single cable, cutting installation costs drastically. HART makes use of the Bell 202 frequency shift keying (FSK) standard to superimpose low-level digital signals on the 4-20 mA circuit enabling more information than just the process variable to communicate between transmitters and receivers. HART and The Conventional Process Loop HART is best understood by looking at how it evolved from a conventional process loop. Figure is a simplified diagram of the...