What is the function of a Programmable Logic Controller (PLC) in gate systems?

• A. Mechanical interlock that locks gates permanently
• B. Electrical interlock that prevents both gates from being open at the same time
• C. Manual operation override only
• D. Video monitoring system

Answer: (B)

A Programmable Logic Controller in gate systems acts as the electronic brain that coordinates how gates move by continuously reading inputs from sensors and safety devices and then triggering the appropriate actuators. The key function is to enforce interlock sequencing so that the two gates cannot be open at the same time, preventing dangerous situations like pinch points or collisions. The PLC runs interlock logic: when one gate is commanded to open, it checks that the other gate is closed or in a safe state, then allows that gate to move and blocks the other from opening until it’s safe. It can also incorporate safety features such as emergency stops, obstacle detection, and timed delays, making operation automatic and reliable. This distinguishes the PLC from purely mechanical interlocks, manual override systems, or video monitoring, which serve different roles.