How do you interpret HART data when the loop is being used by a programmable logic controller (PLC) with analog input?

How do you interpret HART data when the loop is being used by a programmable logic controller (PLC) with analog input?

• A. The HART digital data is read by a HART communicator or gateway; the PLC reads the analog current and optionally uses a HART gateway to fetch digital data
• B. HART data is ignored
• C. The PLC reads digital data directly
• D. The loop cannot be used with PLCs

Answer: (A)

HART overlays digital data on top of the 4-20 mA loop, so the analog input in the PLC reads the actual process signal (the current), while the digital information about the device (status, diagnostics, configuration, etc.) is accessed through a HART interface. A HART communicator or gateway decodes that digital data and presents it to the PLC, either directly through a HART-enabled card or via a gateway that exposes the digital data to the PLC as registers or I/O. If the PLC has built-in HART support, it can read digital data directly, but the essential idea remains: the PLC uses the loop current for the analog measurement, and digital HART data is retrieved via a dedicated HART interface rather than through the analog input alone.

HART overlays digital data on top of the 4-20 mA loop, so the analog input in the PLC reads the actual process signal (the current), while the digital information about the device (status, diagnostics, configuration, etc.) is accessed through a HART interface. A HART communicator or gateway decodes that digital data and presents it to the PLC, either directly through a HART-enabled card or via a gateway that exposes the digital data to the PLC as registers or I/O. If the PLC has built-in HART support, it can read digital data directly, but the essential idea remains: the PLC uses the loop current for the analog measurement, and digital HART data is retrieved via a dedicated HART interface rather than through the analog input alone.