Which diagram shows physical connections between instruments in a process?

• A. Hydraulic schematic
• B. Loop diagram
• C. Wiring diagram
• D. P&ID

Answer: (B)

A loop diagram is used because it shows how the control loop’s instruments are wired together, mapping the signal path from the field device (sensor) through to the controller and final control element, including the power and interconnection wiring. This diagram specifically captures the physical connections between instruments within a process control loop, which is exactly what the question asks.

P&ID diagrams depict piping, equipment, and general instrument placement in the process, not the detailed wiring between instruments. Wiring diagrams focus on the electrical connections for a single device or panel, not the complete interinstrument loop. Hydraulic schematics illustrate fluid power connections, not instrument wiring.