MITSUBISHI FX3U-128MR/ESS PLC Logic Module | Replacement, Equivalent & Selection Guide
The MITSUBISHI FX3U-128MR/ESS is a high-performance compact PLC logic module from Mitsubishi Electric’s FX3U series — the flagship of the MELSEC FX family. Designed for demanding discrete and process control applications, it delivers 128 I/O points with relay output and built-in Ethernet (ESS), making it a preferred choice for procurement engineers upgrading legacy FX2N systems or specifying new automation cells.
Konmask.com supplies this module as genuine new stock, with full traceability documentation available on request. Whether you need an exact replacement, a compatible equivalent, or guidance on selecting the right FX3U variant, this page provides the complete engineering reference.
Technical Specifications
| Parameter | Specification |
|---|---|
| Model | FX3U-128MR/ESS |
| Brand | Mitsubishi Electric (MELSEC FX Series) |
| I/O Points | 128 total (64 inputs / 64 outputs) |
| Output Type | Relay (R) |
| Power Supply | AC 100–240 V |
| Communication | Built-in Ethernet (ESS) + RS-422 |
| Program Memory | 64,000 steps (with memory cassette) |
| Processing Speed | 0.065 µs / basic instruction |
| Expansion | Up to 8 extension modules |
| Special Function Modules | Up to 8 (analog, positioning, network) |
| Operating Temperature | 0 – 55 °C |
| Storage Temperature | -25 – 75 °C |
| Humidity | 5 – 95% RH (non-condensing) |
| Protection Class | IP20 |
| Dimensions (W×H×D) | Approx. 480 × 90 × 87 mm |
| Weight | Approx. 500 g (base unit) |
| Certifications | CE, UL, cUL |
Compatible Replacement & Equivalent Models
When the FX3U-128MR/ESS is unavailable or over-budget, the following models are engineering-validated alternatives. Always verify I/O count, output type, and communication requirements before substitution.
| Model | I/O | Output | Comms | Notes |
|---|---|---|---|---|
| FX3U-128MT/ESS | 128 | Transistor (sink) | Ethernet | Direct equivalent; use for high-speed pulse output applications |
| FX3U-128MT/ES | 128 | Transistor (sink) | RS-422 only | No built-in Ethernet; add FX3U-ENET if needed |
| FX3GE-40MR/ES | 40 | Relay | Ethernet | Smaller footprint; suitable for reduced I/O requirements |
| FX5U-128MR/ES | 128 | Relay | Ethernet + USB | Next-generation iQ-F platform; enhanced performance, different programming tool (GX Works3) |
| FX2N-128MR | 128 | Relay | RS-422 | Legacy predecessor; not recommended for new designs |
⚠ Note: FX5U series requires GX Works3 and is not backward-compatible with FX3U ladder programs without migration.
Why Choose the Original Model
- Proven FX3U platform — millions of units deployed globally across automotive, food & beverage, and packaging industries.
- Built-in Ethernet (ESS) — eliminates the need for a separate FX3U-ENET adapter, reducing BOM cost and panel space.
- Relay output reliability — ideal for mixed-voltage loads and inductive loads without external interface relays.
- Broad ecosystem — compatible with the full FX3U expansion library: analog, positioning, CC-Link, PROFIBUS, and more.
- GX Works2 compatibility — no toolchain migration required for existing FX2N/FX3U projects.
- Long service life — Mitsubishi Electric maintains parts availability and firmware support for the FX3U series through extended lifecycle commitments.
Typical Applications
- Automotive body assembly lines and welding cell control
- Packaging machinery (filling, sealing, labeling)
- Conveyor and material handling systems
- HVAC and building automation panels
- Water treatment and pump station control
- Machine tool and CNC auxiliary control
- Food & beverage processing lines
- Elevator and escalator safety logic
System Compatibility
| Component | Compatible Items |
|---|---|
| Programming Software | GX Works2, GX Developer |
| Extension I/O Modules | FX3U-16EX, FX3U-16EYR, FX3U-32EX, FX3U-32EYR, etc. |
| Analog Modules | FX3U-4AD, FX3U-4DA, FX3U-4AD-PT, FX3U-4AD-TC |
| Positioning Modules | FX3U-1PG, FX3U-2HC |
| Network Adapters | FX3U-ENET (redundant), FX3U-PROFIBUS-DP, FX3U-64CCL |
| Memory Cassette | FX3U-FLROM-64L (extends to 64K steps) |
| HMI / GOT | GOT2000 series, GOT1000 series (GT Designer3) |
| SCADA / DCS | MC Protocol (Ethernet), SLMP, Modbus TCP (via adapter) |
Selection Guide
Use the decision matrix below to confirm the FX3U-128MR/ESS is the right choice for your application:
| Requirement | FX3U-128MR/ESS | Recommended Alternative |
|---|---|---|
| I/O ≥ 128 points | ✅ Yes | FX5U-128MR/ES (if upgrading platform) |
| Relay output required | ✅ Yes | FX3U-128MT/ESS (if high-speed pulse needed) |
| Built-in Ethernet required | ✅ Yes (ESS) | FX3U-128MT/ES + FX3U-ENET (if no ESS) |
| AC power supply | ✅ 100–240 VAC | FX3U-128MR/DS (DC 24V supply variant) |
| GX Works2 programming | ✅ Fully supported | FX5U requires GX Works3 |
| Budget-constrained project | Consider FX3GE series | FX3GE-40MR/ES (lower I/O, lower cost) |
Quality Assurance & Sourcing
- Genuine Mitsubishi Electric product — sourced through authorized industrial distribution channels.
- Batch traceability — date code and lot number documentation available upon request for MRO and OEM procurement.
- Pre-shipment inspection — each unit undergoes visual and packaging integrity checks before dispatch.
- Anti-counterfeit verification — holographic label and serial number cross-referenced against Mitsubishi Electric records.
- Warranty — 12-month warranty against manufacturing defects; DOA replacement within 7 days of receipt.
How to Order
- Confirm your exact model number: FX3U-128MR/ESS (relay output, built-in Ethernet, AC supply).
- Specify quantity and required delivery timeline.
- Request a formal quotation via support@konmask.com or add directly to cart.
- Provide your shipping address and preferred Incoterm (EXW / FOB Shenzhen / CIF).
- Payment: T/T, PayPal, or trade credit (approved accounts).
- Lead time: in-stock orders ship within 1–3 business days; ETA confirmed at order placement.
Replacement & Compatibility FAQ
Q: Can the FX3U-128MT/ESS replace the FX3U-128MR/ESS directly?
A: Electrically, yes — same I/O count and Ethernet. However, the MT variant uses transistor (sink) output instead of relay. Verify your load voltage and current requirements before substitution.
Q: Is the FX3U-128MR/ESS compatible with FX2N expansion modules?
A: No. FX3U uses its own expansion bus. FX2N extension modules are not electrically or mechanically compatible with FX3U.
Q: Can I use GX Developer instead of GX Works2?
A: GX Developer supports basic FX3U ladder programming, but GX Works2 is strongly recommended for full structured text, SFC, and function block support.
Q: What is the difference between FX3U-128MR/ESS and FX3U-128MR/ES?
A: The ESS suffix denotes built-in Ethernet (100BASE-TX). The ES suffix indicates RS-422 serial only — no built-in Ethernet port.
Q: Is the FX5U a drop-in replacement for the FX3U?
A: Not directly. The FX5U (iQ-F platform) requires GX Works3, has a different expansion bus, and programs are not directly portable. A migration project is required.
Q: Do you supply the FX3U-128MR/ESS with a warranty?
A: Yes — 12 months from shipment date, covering manufacturing defects. DOA units are replaced within 7 business days.
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