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SAFETY • FX5U / GX WORKS3

What should I check before an FX5U online program change?

Confirm authorization, the correct PLC, a current backup, machine safe state, the exact change scope and a recovery plan before transferring anything.

Practical explanation

Mitsubishi safety guidance warns that program changes, parameter changes, forced outputs and RUN/STOP operations can affect the controlled system.

The person making the change must understand both the program and the machine hazards.

Check in this order

  1. 1Identify the correct CPU and machine.
  2. 2Back up and compare the running project.
  3. 3Inform affected operators and obtain permission.
  4. 4Control stored energy and unexpected motion.
  5. 5Verify operation and save the final revision.

Safety: Follow site lockout/tagout, commissioning and change-control procedures. Never force an output without understanding the physical consequence.

Last reviewed: 2 October 2026

Official source: MELSEC iQ-F FX5 User's Manual (Application) — Safety Precautions

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