The FX3U-128MT/ES-A is Mitsubishi Electric’s maximum-capacity base unit for the MELSEC FX3U compact PLC series, providing 64 digital inputs and 64 PNP source transistor outputs in a self-contained AC-powered controller — the largest I/O count available in any single FX3U base unit, combining the highest transistor output density with source (PNP) output polarity for European and Asian machine builders requiring maximum I/O integration in a single compact PLC enclosure. As the top-of-range FX3U base unit, the FX3U-128MT/ES-A addresses complex standalone machine control applications where 128-point I/O coverage from a single controller eliminates the wiring, cost, and reliability concerns of multi-unit expansion architectures. Atlantech Drives holds stock of the FX3U-128MT/ES-A. Contact us for fast worldwide delivery and competitive pricing.
What Is the FX3U-128MT/ES-A?
The FX3U-128MT/ES-A is a MELSEC FX3U series compact PLC base unit providing 64 input points (X0–X77, octal numbering) and 64 transistor source (PNP) output points (Y0–Y77). The 128-point total I/O count makes the FX3U-128MT/ES-A the largest compact PLC base unit in Mitsubishi’s FX3 series, covering applications that would otherwise require a 32-point or 48-point base unit with multiple expansion modules. The PNP source output topology is identical to the FX3U-80MT/ES-A — common terminal to 0 VDC, outputs push +24 VDC to load terminals on activation — and is compatible with NPN-input European field devices and safety relay input modules. The FX3U-128MT/ES-A shares the identical CPU, memory, and communication architecture as all other FX3U base units: 0.065 µs per basic instruction, 64,000-step program memory, 6 built-in high-speed counter inputs, and 100 kHz pulse output on Y0 and Y1 for stepper/servo positioning. Despite the 128-point I/O count, the base unit housing dimensions are only modestly wider than the 80-point models — a testament to Mitsubishi’s high-density terminal block design that maintains the compact FX3U form factor across the full I/O range.
Key Technical Specifications
- Model: FX3U-128MT/ES-A
- Total I/O Points: 128 (64 inputs + 64 outputs)
- Input Type: 24 VDC sink (X0–X77)
- Output Type: Transistor source/PNP (Y0–Y77), 0.5 A per point, 5–30 VDC
- Output Polarity: Source (PNP) — common terminal to 0 VDC negative
- High-Speed Pulse Output: Y0 and Y1 up to 100 kHz; Y2 up to 10 kHz
- Power Supply: 100–240 VAC, 50/60 Hz
- Program Memory: 64,000 steps
- Execution Speed: 0.065 µs per LD instruction
- Built-in High-Speed Counters: 6 inputs (100 kHz)
- Communication: RS-422 (built-in)
- Real-Time Clock: Built-in
- Battery Backup: Yes
- Expansion: Up to 8 extension units (max 256 total I/O), up to 4 special adapters
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 285 mm × 90 mm × 87 mm
- Weight: Approx. 1.55 kg
Replacement & Upgrade Notes
The FX3U-128MT/ES-A is the recommended upgrade path from FX2N-128MR-ES/UL or FX2N-128MT-ESS/UL installations where the 16,000-step FX2N program memory has been exhausted or where the additional communication and special adapter capabilities of the FX3U are required. The FX3U-128MT/ES-A provides four times the program memory (64,000 steps) and significantly faster execution (0.065 µs versus 0.08 µs) compared to the FX2N, enabling more complex control programs without upgrading to a modular MELSEC-Q system. FX2N ladder programs can be imported into GX Works2 and compiled for FX3U without modification in most cases — Mitsubishi’s compatibility check identifies any instruction differences. Extension I/O modules from the FX2N series (FX2N-8EX, FX2N-8EY) are compatible with the FX3U via the FX3U-CNV-BD conversion adapter when retention of existing expansion hardware is required. For applications currently using the FX3U-128MT/ES-A and requiring Ethernet connectivity, enhanced program memory (128,000 steps), or built-in SD card logging, the FX5U-32MR/ES with FX5U expansion units provides the direct iQ-F generation upgrade — the FX5U supports CC-Link IE Field Network natively and includes built-in Ethernet as standard, supporting the migration to Mitsubishi’s current compact PLC platform without requiring a step up to the MELSEC-Q modular platform. When migrating from FX3U-128MT/ES-A to FX5U, note that the FX5U uses a different device address scheme for some special relays and registers — verify the migration compatibility using Mitsubishi’s FX3U-to-FX5U migration guide before transferring programs.
Frequently Asked Questions
Q: Can the FX3U-128MT/ES-A expand to more than 128 I/O points using extension modules?
A: Yes. The FX3U-128MT/ES-A supports up to 8 FX3U extension I/O units connected to the right side of the base unit, expanding the total I/O beyond the base unit’s 128 points to a maximum of 256 total I/O points. However, expanding an already-large 128-point base unit with further extension modules is uncommon in practice — systems requiring more than 128 I/O points typically justify migration to the MELSEC-Q or MELSEC iQ-R modular platform for better maintainability and scalability.
Q: Does the FX3U-128MT/ES-A require a larger power supply or special mounting accessories compared to smaller FX3U models?
A: The FX3U-128MT/ES-A uses the same built-in AC power supply as all FX3U base units — no external power supply is required for the PLC itself. However, the 24 VDC external supply for the 64 transistor output load circuits must be rated for the total simultaneous output load current. At 0.5 A per output with 64 outputs, the theoretical maximum load supply demand is 32 A — in practice, not all 64 outputs will be simultaneously ON at maximum current, but the external 24 VDC supply should be rated for the actual simultaneous ON count multiplied by the average load current per point. A 10–15 A rated 24 VDC supply is typically sufficient for most installations with normal mixed-load duty cycles.
Q: Is the FX3U-128MT/ES-A discontinued, and should new designs specify the FX5U instead?
A: As of 2025, the FX3U-128MT/ES-A remains an active Mitsubishi product available for new orders, though Mitsubishi has been transitioning new design recommendations toward the FX5U (iQ-F) series for its built-in Ethernet, larger program memory, and CC-Link IE Field Network compatibility. For new machine designs initiated from 2024 onward, Mitsubishi recommends the FX5U series as the primary compact PLC specification — the FX3U-128MT/ES-A is recommended for retrofit, maintenance replacement, and applications where the existing FX3U program and expansion ecosystem must be preserved without platform migration.
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