The FX3U-32MR/ES-A is Mitsubishi Electric’s 32-point relay output base unit for the MELSEC FX3U compact PLC series, providing 16 digital inputs and 16 relay contact outputs in a self-contained AC-powered controller — doubling the I/O capacity of the FX3U-16MR/ES-A while retaining the same FX3U CPU architecture, 64,000-step program memory, and relay output flexibility for direct AC and DC load switching in mid-size machine control applications. As the most widely specified relay output model in the FX3U range, the FX3U-32MR/ES-A addresses the majority of standalone machine control applications where relay output versatility and a 32-point I/O count provide complete coverage without requiring I/O expansion modules. The FX3U-32MR/ES-A is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the FX3U-32MR/ES-A?
The FX3U-32MR/ES-A is a MELSEC FX3U series compact PLC base unit providing 16 input points (X0–X17, octal numbering) and 16 relay contact output points (Y0–Y17), housed in a compact DIN rail mounting enclosure with the AC power supply built in. The relay outputs are organised in two common groups of 8 points each, with independent common terminals per group enabling the two output groups to switch loads at different voltages simultaneously — for example, group 1 (Y0–Y7) controlling 24 VDC solenoid valves and group 2 (Y10–Y17) controlling 230 VAC contactor coils from the same module without external interface relays. The FX3U CPU executes programs at 0.065 µs per basic instruction with a 64,000-step program memory — identical to all other FX3U base units regardless of I/O count — supporting ladder, SFC, structured text, and function block programming via GX Works2 and GX Works3. The base unit includes 6 built-in high-speed counter inputs (up to 100 kHz) and 3 pulse output points (up to 100 kHz on Y0 and Y1) for stepper and servo positioning without additional modules.
Key Technical Specifications
- Model: FX3U-32MR/ES-A
- Total I/O Points: 32 (16 inputs + 16 outputs)
- Input Type: 24 VDC sink (X0–X17)
- Output Type: Relay contact (Y0–Y17), 2 A per point, 240 VAC / 30 VDC
- Output Common Groups: 2 groups of 8 points (independent commons)
- 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)
- Built-in Pulse Outputs: 3 points (Y0, Y1: 100 kHz; Y2: 10 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): 150 mm × 90 mm × 87 mm
- Weight: Approx. 0.87 kg
Compatibility & System Integration
The FX3U-32MR/ES-A integrates with the full range of FX3U expansion I/O units (FX3U-16EX input expansion, FX3U-16EYR relay output expansion, FX3U-16EYT transistor output expansion) connected to the right side of the base unit via the FX3U extension bus. Up to 8 extension units can be connected, expanding the total I/O to a maximum of 256 points. FX3U special adapter modules (FX3U-4AD-ADP analogue input, FX3U-4DA-ADP analogue output, FX3U-4LC temperature control, FX3U-1PG pulse output) connect to the left side of the base unit, providing up to 4 additional special function channels without occupying extension bus capacity. For communication expansion, the FX3U-232-BD, FX3U-485-BD, and FX3U-422-BD option boards install directly onto the FX3U base unit’s built-in communication board slot, adding a second RS-232C, RS-485, or RS-422 port respectively for SCADA communication, inverter control via RS-485, or HMI connection. The FX3U-ENET-ADP Ethernet adapter provides Ethernet connectivity for the FX3U-32MR/ES-A, enabling MC protocol communication with GOT2000 HMIs, SCADA systems, and MES platforms via the plant LAN. Programming is performed using GX Works2 or GX Works3 via the built-in RS-422 port or via a FX3U-USB-BD USB option board.
Troubleshooting Guide
If the FX3U-32MR/ES-A fails to power up (no LED indicators illuminate), verify the AC supply voltage at the power input terminals using a multimeter — the module requires 100–240 VAC and will not power up below 85 VAC or above 264 VAC. Check that the power supply wiring is connected to the correct terminals (L and N for AC input, not to the 24 VDC sensor power output terminals which are labelled separately). If the POWER LED illuminates but the RUN LED does not, check that the RUN/STOP input (typically a hardware switch or a link between designated terminals) is in the RUN position — some FX3U installations use an external hardware RUN/STOP switch that may have been accidentally left in STOP position during maintenance. If specific output points fail to activate despite the corresponding Y output bit being ON in the program, use GX Works2’s device monitor to force the Y output ON and measure the voltage across the relay contact with a multimeter — a healthy closed relay contact should show less than 0.5 V drop at rated current; a contact showing over 1 V drop has reached end of life. For input points showing incorrect states, disconnect the field wiring from the affected input terminal and verify the input state with the terminal open — if the input reads ON with no wiring connected, the input circuit is faulty; if it reads OFF correctly, the fault is in the field device or wiring.
Frequently Asked Questions
Q: Can the FX3U-32MR/ES-A control a 3-phase motor starter directly without an intermediate contactor?
A: No. The FX3U-32MR/ES-A relay outputs are rated for single-phase loads at 2 A maximum per contact — they cannot switch 3-phase motor current directly. The relay outputs should be used to energise the coil of a 3-phase motor contactor or soft starter, with the relay contact in series with the contactor coil circuit. The contactor’s main contacts then switch the 3-phase motor power independently of the PLC output.
Q: How many relay output operations can the FX3U-32MR/ES-A relay contacts perform before replacement is needed?
A: The FX3U-32MR/ES-A relay contacts are rated for 200,000 operations at rated resistive load (2 A, 240 VAC). For inductive loads (contactor coils, solenoid valves) without arc suppression, contact life is significantly reduced — Mitsubishi recommends fitting varistors or RC snubbers across inductive loads to achieve contact life close to the 200,000-operation specification. In high-cycle applications exceeding 10 operations per minute, consider specifying the transistor output FX3U-32MT/ESS for the high-frequency outputs and using the relay model only for low-frequency AC load switching.
Q: Can the FX3U-32MR/ES-A be programmed with Mitsubishi’s GX Works3 software?
A: Yes. The FX3U-32MR/ES-A is supported by both GX Works2 and GX Works3. GX Works3 provides a modernised programming environment with enhanced structured programming features and a unified project format compatible with MELSEC iQ-R and iQ-F series controllers. For new FX3U projects, GX Works3 is recommended over GX Works2 to ensure long-term software compatibility as Mitsubishi transitions its toolchain to GX Works3 as the primary engineering environment.
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