What does it mean when a transmitter is 'loop-powered'?

What does it mean when a transmitter is 'loop-powered'?

• A. It derives power from the loop itself.
• B. It uses a separate power supply.
• C. It requires an external DC supply of 24 V.
• D. It uses AC power.

Answer: (A)

Loop-powered means the transmitter gets its operating power from the same two-wire current loop that carries the 4-20 mA signal. The device is placed in series with the loop and draws the current it needs from the loop supply, so the loop both powers the electronics and conveys the measurement as a controlled current. No separate power supply is required, and it does not rely on an external DC or AC source. This two-wire arrangement is typical for loop-powered (two-wire) transmitters, where power and signal share the same pair of conductors. The loop must provide enough voltage headroom to power the transmitter and any load in the loop, but the current through the loop remains the output signal.

Loop-powered means the transmitter gets its operating power from the same two-wire current loop that carries the 4-20 mA signal. The device is placed in series with the loop and draws the current it needs from the loop supply, so the loop both powers the electronics and conveys the measurement as a controlled current. No separate power supply is required, and it does not rely on an external DC or AC source. This two-wire arrangement is typical for loop-powered (two-wire) transmitters, where power and signal share the same pair of conductors. The loop must provide enough voltage headroom to power the transmitter and any load in the loop, but the current through the loop remains the output signal.