Mitsubishi FX3U Series Modules: FX3U-128MR/ESS

Technical Dossier

Product Details And Specifications

Mitsubishi FX3U Series: Comprehensive Module Range and Technical Overview

The Mitsubishi Electric FX3U series represents the third-generation flagship of the MELSEC FX programmable logic controller family. Deployed across heavy industrial sectors including petrochemical refining, nuclear auxiliary systems, pharmaceutical batch processing, and steel mill automation, the FX3U platform holds a substantial global installed base estimated in the millions of units. Its 32-bit RISC CPU architecture, high-speed pulse output capability (up to 100 kHz on 3 axes), and native USB programming port made it the de facto standard for mid-range machine control from its introduction in 2004 through the 2020s. The FX3U-128MR/ESS specifically provides 64 relay inputs and 64 relay outputs in a compact base unit, with built-in RS-422 and RS-485 communication ports, supporting both standalone and networked configurations in demanding environments.

The Evolution of FX3U Architecture

The MELSEC FX lineage began with the FX0/FX0N series in the late 1980s, establishing a compact DIN-rail form factor that persisted through successive generations. The FX1S and FX1N introduced expanded I/O and analog capability in the 1990s. The FX2N (released 1998) became the dominant mid-range platform of its era, with a 16-bit CPU and a maximum of 256 I/O points via extension modules. The FX3U (2004) replaced the FX2N with a 32-bit CPU, tripling execution speed to 0.065 µs per basic instruction, and introduced high-speed counters up to 200 kHz. The FX3UC variant addressed space-constrained applications with a connector-type terminal block. The FX3G and FX3GE provided cost-reduced alternatives for simpler applications within the same programming environment (GX Works2/GX Developer). Mitsubishi Electric announced the FX3U series end-of-life production phase-out, with the FX5U series (iQ-F platform, released 2015) designated as the direct migration path. FX5U offers Ethernet as standard, structured programming in IEC 61131-3, and a 34 ns instruction cycle. Compatibility between FX3U and FX5U ladder programs requires migration using GX Works3 conversion tools; direct hardware substitution is not possible due to differing backplane and extension bus architectures.

FX3U Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly stocked models within the Mitsubishi FX3U series. Models are classified by functional category.

Base Units (CPU Modules)

FX3U-16MR/ES: 8 DC input / 8 relay output base unit, 100–240 VAC supply.
FX3U-32MR/ES: 16 DC input / 16 relay output, AC power, standard DIN rail mount.
FX3U-48MR/ES: 24 DC input / 24 relay output, AC supply, built-in RS-422.
FX3U-64MR/ES: 32 DC input / 32 relay output, AC power, 64-point base unit.
FX3U-80MR/ES: 40 DC input / 40 relay output, AC supply, expandable to 256 I/O.
FX3U-128MR/ES: 64 DC input / 64 relay output, AC power, maximum base I/O count.
FX3U-128MR/ESS: 64 DC input / 64 relay output, AC supply, with built-in RS-485 port.
FX3U-32MT/ES: 16 DC input / 16 transistor (sink) output, AC power, 100 kHz pulse output.
FX3U-64MT/ES: 32 DC input / 32 transistor output, AC supply, high-speed axis control.
FX3U-128MT/ES: 64 DC input / 64 transistor output, AC power, 3-axis pulse output.

Digital Extension Modules (I/O Expansion)

FX3U-16EX: 16-point DC input extension module, 24 VDC, sink/source compatible.
FX3U-16EYR: 16-point relay output extension module, 2A per point, 250 VAC rated.
FX3U-16EYT: 16-point transistor (sink) output extension, 0.5A per point, 5–30 VDC.

Communication & Special Function Modules

FX3U-232-BD: RS-232C communication board, mounts directly to FX3U base unit.
FX3U-485-BD: RS-485 communication board, supports MODBUS RTU and inverter protocol.
FX3U-USB-BD: USB-B programming interface board, replaces SC-09 cable requirement.
FX3U-ENET: Ethernet communication module, 10/100BASE-TX, SLMP/MC protocol support.
FX3U-4AD: 4-channel analog input module, 12-bit resolution, ±10V / 4–20mA selectable.
FX3U-4DA: 4-channel analog output module, 12-bit, voltage and current output modes.

Sourcing Hard-to-Find & Obsolete FX3U Parts

The FX3U series entered its end-of-life production phase, with Mitsubishi Electric progressively discontinuing base units and extension modules. For facilities operating FX3U-based control systems — particularly in chemical processing, water treatment, and discrete manufacturing — replacement procurement through the open market is the primary maintenance strategy. DriveKNMS maintains a dedicated inventory of FX3U base units, I/O extension modules, communication boards, and special function modules sourced from verified industrial surplus channels. All units are inspected prior to dispatch. For discontinued models such as the FX3U-128MR/ESS and associated extension modules, DriveKNMS provides lifecycle extension support including cross-reference to compatible FX3U variants and, where applicable, guidance on FX5U migration feasibility. Customers operating under long-term maintenance contracts for installed FX3U systems are advised to establish buffer stock for critical CPU base units, as lead times for new-old-stock units continue to extend as production wind-down progresses.

Quality Control for the FX3U Range

FX3U base units incorporate a multi-layer backplane bus connecting the CPU, power supply section, and extension I/O bus. Quality verification for used or refurbished FX3U units at DriveKNMS follows a structured protocol: (1) Visual inspection of terminal blocks, connector pins, and housing for mechanical damage or corrosion. (2) Power-on functional test with GX Works2 connection verification via USB-BD or SC-09 adapter, confirming firmware version and CPU status LEDs (RUN, ERR, BAT). (3) I/O point verification using a dedicated test harness cycling all input and output points individually, confirming relay contact integrity on MR-type units and transistor switching on MT-type units. (4) Battery voltage check for program retention (FX3U uses a CR2032 or equivalent lithium cell; units with low battery indication are replaced prior to shipment). (5) Communication port test on RS-422 and RS-485 interfaces using loopback verification. Units failing any stage are quarantined and not listed for sale. Test records are retained per unit serial number.

For procurement inquiries, cross-reference requests, or lifecycle support for Mitsubishi FX3U series modules:

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