Which diagram shows wiring between transmitters and controllers in a control loop?

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

Answer: (B)

Understanding how electrical signals move between transmitters and controllers clarifies why a loop diagram is used. A loop diagram specifically shows the wiring path of a control loop, including the transmitter output, the controller input, the power supply and return paths, and the interconnecting conductors. It’s designed to illustrate how the loop is wired from the field device to the controller and to highlight where to check connections, troubleshoot faults, and verify that the signal can flow properly (for example a 4-20 mA signal from transmitter through wiring to the controller input). This focus on the actual wiring and signal path distinguishes it from other diagrams. P&ID diagrams depict process streams, instrument tags, and interconnections at a high level without wiring details. A hydraulic schematic deals with fluid lines and components. A wiring diagram concentrates on internal device wiring or a harness and does not necessarily show how multiple devices are connected in a loop. Therefore, the diagram showing wiring between transmitters and controllers in a control loop is the loop diagram.