In a HART network, what does the current loop current represent?

• A. The process variable value encoded as current within the 4-20 mA range.
• B. The voltage level at the transmitter.
• C. A purely digital code separate from the analog signal.
• D. The power supply voltage only.

Answer: (A)

In a HART network, the loop current is the analog signal that represents the measured process variable. The transmitter modulates the current in the 4–20 mA range so that 4 mA corresponds to the minimum process value and 20 mA to the maximum, with the actual PV value mapped proportionally within that span. The digital data from HART is sent by superimposing high-frequency signals on top of this base current, but the fundamental meaning of the loop current remains the process variable. The current is not a voltage level, not a separate digital code, and not just the power supply voltage; it is the primary analog representation of the measurement, with digital communication riding alongside it.