What is the primary purpose of a loop diagram in instrumentation?

• A. To show physical layout of piping
• B. To show wiring and electrical connections between transmitters, controllers, and actuators
• C. To show chemical composition of fluids
• D. To depict piping routes

Answer: (B)

Loop diagrams focus on the electrical signal path in a control system. They show how a sensor’s measurement becomes a signal that the controller uses, and how that signal drives the final control element, such as a valve or actuator. The diagram maps the wiring, loop power, grounding, and interconnections between transmitters, controllers, and actuators, so technicians can install, troubleshoot, and document the control loop accurately. This is different from diagrams that depict physical piping or fluid properties, which are shown in process or piping diagrams. By concentrating on the wiring and connections, the loop diagram provides a clear picture of how the control system actually operates and where failures or commissioning issues might arise.