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ANALOG • FX5U / GX WORKS3

Why is my FX5U analog value unstable?

First separate an electrical-noise problem from a real process fluctuation. Check shield grounding, cable routing, sensor supply, common wiring and the raw value before changing the program.

Practical explanation

A moving average can make a stable signal easier to read, but it cannot repair incorrect wiring or a noisy power supply.

Compare the signal with a calibrated meter at the PLC terminal.

Check in this order

  1. 1Measure the signal at the input terminal.
  2. 2Keep analog cable away from motor and VFD output cables.
  3. 3Ground the shield as specified for the installation.
  4. 4Apply filtering only after the electrical checks pass.

Last reviewed: 2 October 2026

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

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