In terms of architecture and power requirements, which statement best distinguishes Foundation Fieldbus from HART?

• A. Foundation Fieldbus uses analog signaling; HART is digital only.
• B. Fieldbus requires no network infrastructure; HART requires a fieldbus backbone.
• C. Foundation Fieldbus is a fully digital, multi-drop fieldbus with bus-powered devices; HART is a hybrid analog loop with a separate digital comm channel.
• D. Fieldbus uses separate power supply for each device; HART is bus-powered.

Answer: (C)

Foundation Fieldbus and HART differ in how they handle signaling architecture and power delivery. Foundation Fieldbus is a fully digital two‑wire bus that allows many devices to share a single backbone in a multi‑drop arrangement, and the devices derive their operating power from the bus itself (bus‑powered). This means the network carries both power and digital communications across the same two wires, with all devices operating as part of a single digital field network.

HART, on the other hand, keeps the traditional analog 4–20 mA loop for the primary process signal and adds a separate digital communication channel superimposed on that loop. It is a hybrid system rather than a true digital bus network, and the devices are not powered by a shared fieldbus backbone in the same way; power typically comes from the loop power supply or an external source, while the digital channel provides diagnostic and configuration data without changing the fundamental analog loop as the primary power path.

So the best distinction is that Foundation Fieldbus is a fully digital, multi‑drop, bus‑powered network, whereas HART is a hybrid analog loop with a separate digital communication channel.