What are ground loops and how are they eliminated in instrumentation?

Ground loops occur when multiple ground connections at different potentials create current flow through signal conductors, adding noise. They appear when equipment is grounded at multiple points with different ground voltages. Solutions include: single-point grounding (ground signal at one end only), galvanic isolation (isolators, transformers, optocouplers break ground loop), differential signaling (4-20 mA, balanced connections reject common-mode), proper shielding (ground shield at one end only), and using isolated power supplies. Isolation amplifiers provide 1000V+ isolation for industrial environments.