PLC systems are used to control two classifications of industrial electrical systems. Which statement best describes them?

• A. Discrete parts manufacturing and process manufacturing
• B. Only discrete parts manufacturing
• C. Only process manufacturing
• D. Neither classification applies

Answer: (A)

PLCs are versatile controllers that handle both discrete and process control tasks on the plant floor. In discrete manufacturing, control is about switching machines on and off, sequencing conveyors, and coordinating robots and sensors to move individual parts through a line. This uses digital (on/off) inputs and outputs, with logic that handles timers, counters, and interlocks to ensure correct sequencing and safety.

In process manufacturing, control focuses on keeping variables like temperature, pressure, flow, and level within tight ranges. This requires analog inputs and outputs and control algorithms such as PID to continuously regulate a process. Modern PLCs provide analog I/O, PID blocks, and batch control features, enabling them to monitor and adjust continuous or batch processes just as effectively as discrete systems.

Because PLCs can handle both digital and analog signals and implement both sequencing and continuous regulation, they are used across both types of manufacturing environments. The statement that best describes them is that they control discrete parts manufacturing and process manufacturing.

Other options would miss this breadth: limiting PLC use to only discrete, or only process, or suggesting they don’t apply to either, would ignore the real versatility of PLCs in industrial automation.