What does the HART protocol enable on a 4-20 mA loop?

What does the HART protocol enable on a 4-20 mA loop?

• A. Digital configuration only on the loop.
• B. Analog current without digital data.
• C. Digital configuration and diagnostics superimposed on the analog current.
• D. Wireless telemetry independent of current.

Answer: (C)

The main idea here is that the HART protocol lets digital information ride on top of the standard 4-20 mA loop. The transmitter still sends the process variable as the analog current (4-20 mA), but a high-frequency digital signal is superimposed on the same two wires to carry configuration commands, diagnostics, and other device data. This means you can configure the device, check status, and read diagnostics remotely without breaking or replacing the loop wiring. So, this isn’t just digital configuration, and it isn’t just the analog current with no digital data, and it isn’t wireless. It’s both the analog signal and digital data on the same loop, enabling both traditional measurement and rich device communication on one pair of wires.

The main idea here is that the HART protocol lets digital information ride on top of the standard 4-20 mA loop. The transmitter still sends the process variable as the analog current (4-20 mA), but a high-frequency digital signal is superimposed on the same two wires to carry configuration commands, diagnostics, and other device data. This means you can configure the device, check status, and read diagnostics remotely without breaking or replacing the loop wiring.

So, this isn’t just digital configuration, and it isn’t just the analog current with no digital data, and it isn’t wireless. It’s both the analog signal and digital data on the same loop, enabling both traditional measurement and rich device communication on one pair of wires.