What does the HART protocol add to a standard 4-20 mA loop?

What does the HART protocol add to a standard 4-20 mA loop?

• A. Digital communication layered on the analog loop for device configuration, diagnostics, and extended data.
• B. It creates a redundant second current loop for fail-safe operation.
• C. It reduces the loop signal to a lower voltage for long cable runs.
• D. It converts digital data to a separate analog control signal.

Answer: (A)

HART adds digital communication by superimposing a digital signal on top of the existing 4-20 mA current loop. The analog current still carries the process variable, but a high-frequency digital signal travels alongside it, using the same two wires. This lets a handheld meter or control system configure devices, run diagnostics, and exchange extended data without disturbing the analog signal. It’s bidirectional, so you can both send commands and read responses while monitoring the process. The other ideas don’t fit because HART doesn’t create a second current loop, reduce voltage for long runs, or convert data into a separate analog signal. It simply uses the same loop to carry additional digital information alongside the standard analog output.

HART adds digital communication by superimposing a digital signal on top of the existing 4-20 mA current loop. The analog current still carries the process variable, but a high-frequency digital signal travels alongside it, using the same two wires. This lets a handheld meter or control system configure devices, run diagnostics, and exchange extended data without disturbing the analog signal. It’s bidirectional, so you can both send commands and read responses while monitoring the process.

The other ideas don’t fit because HART doesn’t create a second current loop, reduce voltage for long runs, or convert data into a separate analog signal. It simply uses the same loop to carry additional digital information alongside the standard analog output.