What is a passive output device?

• A. A device that supplies its own power to drive the loop current.
• B. A device that converts digital to analog signals.
• C. A device that requires an external power supply to drive current through the loop.
• D. A device that only measures loop current.

Answer: (C)

A passive output device is one that does not generate its own power for the loop. It relies on an external power supply to drive current through the loop, effectively using that outside power to produce its output signal while acting as a load in the circuit. This means it cannot source energy itself; it only modulates or uses the current that’s supplied from an external source. So describing it as requiring an external power supply to drive current through the loop captures the idea that the device is powered externally and does not generate the loop current on its own. In contrast, a device that supplies its own power is active, a digital-to-analog converter is about signal processing, and a device that only measures loop current is a sensor rather than an output device.