What are "universal variables" in HART?

• A. Standard, vendor-agnostic data points such as PV, SV, device status, and other common diagnostics.
• B. Manufacturer-specific settings only accessible by the vendor.
• C. Only the current loop supply voltage and power status.
• D. User-defined calibration constants stored in the device.

Answer: (A)

Universal variables are the standard, vendor-agnostic data points that any HART device must expose. They provide a common set of readings and statuses that work across different manufacturers, making integration and monitoring straightforward. This includes the process variable (PV), the setpoint (SV), the device status, and other common diagnostic information. Because these values are defined by the HART specification and not tied to a specific vendor, a host can read them from any supported device without needing vendor-specific access.

Other descriptions describe data that isn’t guaranteed to be the same across devices or requires vendor-specific access, which is why they aren’t universal. For example, manufacturer-specific settings aren’t standardized and can vary, loop voltage/power status alone isn’t the complete, standard set, and user-defined calibration constants are device-specific rather than universally defined.