HART Protocol and 4–20 mA Loop Test 2026 – Complete Practice Exam

Four-wire transmitters are designed to offer flexible signal outputs because their separate power supply lets the transmitter generate different types of signals. The most common is the 4-20 mA current loop, which is highly robust over long cables and in noisy environments. But many transmitters can also provide voltage outputs, such as 1-5 V DC or even bipolar ±10 V, to match systems that expect voltage inputs or higher-impedance ADCs. Because these devices can be configured to drive either current or voltage signals, the broadest, most accurate statement about common outputs includes all three: 4-20 mA, 1-5 VDC, or ±10 V analog. The options that limit outputs to only current or only voltage miss the versatility these transmitters can offer.