What is a loop diagram used for in commissioning and troubleshooting?

• A. A loop diagram maps all components in a control loop (sensor, transmitter, controller, actuator, final control element) and their wiring.
• B. A loop diagram shows only the plant layout.
• C. A loop diagram lists safety procedures.
• D. A loop diagram is used to plan maintenance budgets.

Answer: (A)

A loop diagram maps all components in a control loop and how they are wired together, showing the sensor, transmitter, controller, actuator, and final control element, along with the power supplies and grounding paths. This focuses on the signal path and electrical connections rather than physical layout or procedures. In commissioning, it lets you verify correct device connections, ensure the right signal types and terminations, and confirm the loop can be tested end-to-end before it goes live. In troubleshooting, you can trace the signal from the sensor to the final control element, spot where a fault or wiring error is changing the signal, and quickly isolate where the problem lies. The other options describe plant layout, safety procedures, or budgets, which don’t capture the wiring and signal-flow focus of a loop diagram.