Question

A Programmable Logic Controller (PLC) is best suited for

• A. Continuous process control
• B. Batch reaction kinetics
• C. Discrete and sequential control operations
• D. Heat exchanger design

Hint:

Logic Tip: If a machine is doing a repetitive, step-by-step mechanical dance (like a robot arm welding a car frame, or an elevator opening and closing doors), a PLC is almost certainly the brain controlling it.

Answer 1

The Correct Option is C

Concept:
In industrial automation, different types of computer systems handle different types of tasks. While a DCS is built for continuous, smooth-flowing chemical processes, a PLC is designed for something else.

Step 1: PLCs were originally invented in the automotive industry to replace massive, complicated cabinets of physical electrical relays.

Step 2: Discrete means "on/off" or "true/false" states. A PLC excels at monitoring hundreds of simple switches, sensors, and buttons to instantly turn motors, lights, and pneumatic cylinders on or off.

Step 3: PLCs are programmed (often using "ladder logic") to execute rigid step-by-step sequences. (e.g.,
Step 1: Open door.
Step 2: Push box in.
Step 3: Close door.
Step 4: Start saw).

Step 4: While modern PLCs can do PID math for continuous temperatures or pressures, their primary, traditional strength is fast, reliable logic execution for assembly lines, packaging machines, and robotic cells.

Step 5: Therefore, PLCs are universally recognized as the best tool for discrete (on/off) and sequential (step-by-step) operations.