HART Protocol
A communication protocol that enables digital data transmission over traditional 4-20 mA analogue lines in industrial installations.
What is HART Protocol?
HART (Highway Addressable Remote Transducer) is a communication protocol used in industrial automation that allows simultaneous transmission of a 4-20 mA analogue signal and digital data over the same pair of wires. It was developed in the 1980s by Rosemount and remains one of the most widely deployed protocols for field devices.
The HART protocol operates in two modes. In hybrid mode, the digital signal is superimposed on the analogue signal using FSK (Frequency Shift Keying) modulation, enabling bidirectional communication without disrupting the control loop. In multidrop mode, up to 15 devices can share a single wire pair, though the analogue signal is not used in this configuration.
Modern HART installations encompass millions of field devices - temperature, pressure, level and flow sensors. The protocol enables remote device configuration, diagnostics and reading of additional process parameters without requiring additional cabling.
Why does it matter?
From a security perspective, the HART protocol was not designed with cyber-attack protection in mind. Communication is neither encrypted nor authenticated, meaning an attacker with physical access to the cabling can eavesdrop on data, modify device configurations or inject false readings. OT security audits should include HART devices in asset inventory and risk assessments.
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