FX3U MR vs MT: Relay Output or Transistor Output?

MR versus MT is not just a model suffix. It changes the physical output device, which affects switching speed, load compatibility and wiring.

MR uses contacts; MT uses semiconductor switching

In the FX3U family, MR generally denotes relay outputs and MT denotes transistor outputs. A relay physically opens and closes contacts, making it flexible for general AC/DC switching but subject to mechanical wear. A transistor has no contact wear and switches faster, but it is a DC device and requires correct polarity and output configuration.

High-speed pulse tasks point toward MT

Pulse trains for stepper or servo interfaces and frequently repeated outputs benefit from transistor switching. Lamps, interposing relays and low-frequency solenoids may be perfectly reasonable relay-output applications.

Check sink/source configuration on MT models

The exact FX3U suffix determines the transistor output arrangement. Verify COM terminals, polarity, external supply and load wiring against the manual instead of assuming every MT unit is wired the same way.

Selection checklist

• AC or DC load
• Required switching speed and repetition rate
• Per-point and common-group current limits
• Surge suppression for inductive loads
• Sink/source and supply direction for transistor outputs