Glossary · HART
What is HART protocol?
A digital protocol carried on top of the 4-20 mA signal itself, allowing transmitter configuration, reading and diagnostics without interrupting the analogue measurement.
It uses FSK at 1200 and 2200 Hz superimposed on the current, so the average signal is unaffected. With it you re-range, read device status and calibrate transmitters from the control room or with a handheld.
Very common in refineries and oil facilities, and a core part of calibration and loop-check work.
Related terms
- 4-20 mA signal
- The most widely used analogue signal in industrial measurement: 4 mA is the bottom of the range and 20 mA the top, and current, unlike voltage, is not affected by cable length.
- Modbus protocol
- A simple, open industrial protocol dating from 1979: a client asks, servers answer from numbered registers. It runs over RS485 (RTU) or Ethernet (TCP).