HART (Highway Addressable Remote Transducer) Protocol is a widely used communication protocol in the field of industrial process measurement and control. It was developed as a way to superimpose digital communication on top of the traditional analog 4-20 mA current loop used in instrumentation.
HART Protocol allows for bidirectional communication between field devices, such as sensors and actuators, and control systems. It achieves this by using a frequency shift keying (FSK) technique to modulate digital information on the analog current loop. This means that the analog 4-20 mA signal is used for transmitting the primary process variable, while digital information is simultaneously transmitted without interrupting the analog signal.
The digital information carried by the HART Protocol includes additional data, such as device status, diagnostics, configuration parameters, and calibration values. This enables enhanced functionality, remote configuration, and advanced diagnostic capabilities for field devices.
One of the significant advantages of HART Protocol is its backward compatibility with existing 4-20 mA analog systems. HART-enabled devices can be connected to the same loop as traditional analog devices, allowing for seamless integration and coexistence. Analog devices can continue to operate normally, while HART devices can provide additional digital information when required.
HART devices typically use a master-slave architecture, where a master device, such as a DCS or PLC, communicates with one or more slave devices in a point-to-point manner. The master initiates communication and sends commands or requests to the slaves, which respond with the requested data or perform the required action.
HART Protocol supports various communication speeds, with the most common being 1,200 and 9,600 bits per second (bps). The slower speed is typically used for configuration and maintenance purposes, while the higher speed allows for real-time monitoring and control.
HART Protocol has widespread adoption in industries such as oil and gas, chemical, pharmaceutical, and power generation. Its ability to provide digital communication and advanced diagnostics over existing analog infrastructure makes it a cost-effective and practical choice for integrating digital intelligence into process control systems.