What is HART protocol and its typical use in instrument loops?

What is HART protocol and its typical use in instrument loops?

• A. HART is a digital replacement for 4-20 mA in all cases.
• B. HART is used for transmitting only alarm signals digitally.
• C. HART is a wireless protocol for field devices independent of analog signals.
• D. HART is a digital communication protocol superimposed on a 4-20 mA current loop, enabling device configuration, diagnostics, and data retrieval without affecting the analog signal.

Answer: (D)

HART is a digital communication method that rides on the same two wires as the 4-20 mA analog current loop. It powers the transmitter from the loop and superimposes a digital signal using frequency shift keying, so the analog current still represents the process variable while digital data is exchanged simultaneously. This lets you configure devices, run diagnostics, and retrieve data (such as device ID, status, calibration info) without altering the analog signal or rewiring the loop. It’s designed to be backward compatible with legacy 4-20 mA systems and is typically accessed with a handheld or control system that supports HART. It is not a wireless protocol, and it does not replace the 4-20 mA signal in all cases; the digital communication is simply an additional channel on top of the analog loop.

HART is a digital communication method that rides on the same two wires as the 4-20 mA analog current loop. It powers the transmitter from the loop and superimposes a digital signal using frequency shift keying, so the analog current still represents the process variable while digital data is exchanged simultaneously. This lets you configure devices, run diagnostics, and retrieve data (such as device ID, status, calibration info) without altering the analog signal or rewiring the loop. It’s designed to be backward compatible with legacy 4-20 mA systems and is typically accessed with a handheld or control system that supports HART. It is not a wireless protocol, and it does not replace the 4-20 mA signal in all cases; the digital communication is simply an additional channel on top of the analog loop.