What is the purpose of a loop isolator and when is it required?

• A. Increases loop current to improve signal.
• B. Acts as a fuse for the loop.
• C. Breaks galvanic connection to prevent ground loops and common‑mode noise; used when different grounds exist or when isolating noisy devices.
• D. Changes the signal impedance but not grounding.

Answer: (C)

Loop isolators provide galvanic isolation between parts of a current loop, breaking the electrical connection that can carry unwanted ground currents. The main purpose is to prevent ground loops and reduce common‑mode noise, which occur when different equipment grounds sit at slightly different potentials. When the transmitter and the receiver have different grounds or when a noisy device is in the loop, stray currents can flow through the ground path and corrupt the measurement. An isolation barrier (such as a transformer or opto‑coupler) lets the signal pass while keeping the grounds separate, so those ground differences and noise sources don’t affect the loop current. This protects equipment, improves accuracy, and helps withstand transients.

It’s not about boosting the loop current, acting as a fuse, or primarily changing the signal impedance. Those are not the function of a loop isolator, whose core role is to electrically decouple the loop grounds to prevent ground loops and common‑mode interference.