Which of the following is a disadvantage of a PLC?

• A. High initial cost
• B. Sensitive to dust, high temperature and high humidity
• C. Repair must be made by a qualified personnel
• D. No moving parts

Answer: (C)

Repair must be made by qualified personnel is the strongest disadvantage because PLCs are specialized controllers that require trained technicians to diagnose faults, understand ladder logic, and handle vendor-specific hardware and firmware. When a problem arises, downtime can be longer and service costs higher since skilled people are needed to troubleshoot, repair, and sometimes reprogram the system.

High initial cost is indeed a drawback, but it’s an upfront expense that can be justified by long-term gains in flexibility and reduced wiring. Being sensitive to dust, high temperature, and humidity is a concern, but with proper enclosure and environment control it can be mitigated. No moving parts is actually an advantage, contributing to reliability and lower mechanical wear.