The FX3G-40MR/ES-A is Mitsubishi Electric’s 40-point relay output base unit for the MELSEC FX3G compact PLC series, providing 24 digital inputs and 16 relay contact outputs in a self-contained AC-powered controller — the largest relay output base unit available in the FX3G entry-level compact PLC range, offering the highest I/O density of the FX3G family for standalone machine control applications requiring a comprehensive relay output point count at entry-level system cost without the additional capabilities and cost of the FX3U platform. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the FX3G-40MR/ES-A?
The FX3G-40MR/ES-A is a MELSEC FX3G series compact PLC base unit providing 24 input points (X0–X27, octal numbering) and 16 relay contact output points (Y0–Y17, octal), housed in the widest standard FX3G housing for DIN rail mounting with a built-in 100–240 VAC power supply. The relay outputs are organised in independent common groups, enabling different output groups to switch loads at different voltages simultaneously across the 16 contact points — useful in panels where some outputs control 230 VAC motor contactors and others control 24 VDC solenoid valves from the same PLC module. The FX3G CPU executes at 0.21 µs per basic instruction with a 32,000-step program memory, 6 built-in high-speed counter inputs at up to 10 kHz, and pulse output capability on Y0 and Y1 for single or dual-axis stepper positioning. The FX3G-40MR/ES-A expands to a maximum of 128 total I/O points via FX3G extension modules, with left-side special adapter support for analogue I/O and communication expansion — making it the top-tier specification within the FX3G range for applications not requiring the FX3U’s faster CPU, larger memory, or SSCNET III/H servo adapter.
Key Technical Specifications
- Model: FX3G-40MR/ES-A
- Total I/O Points: 40 (24 inputs + 16 outputs)
- Input Type: 24 VDC sink (X0–X27)
- 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: 32,000 steps
- Execution Speed: 0.21 µs per LD instruction
- Built-in High-Speed Counters: 6 inputs (10 kHz maximum)
- Built-in Pulse Outputs: Y0 (100 kHz) and Y1 (10 kHz)
- Communication: RS-422 (built-in)
- Real-Time Clock: Built-in
- Battery Backup: Yes
- Expansion: Up to 128 total I/O (base + extension modules)
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 150 mm × 90 mm × 75 mm
- Weight: Approx. 0.80 kg
Architecture & Design Overview
The FX3G-40MR/ES-A implements the same FX3G CPU architecture as the smaller 14-point and 24-point FX3G base units, with the increased physical housing width accommodating the additional I/O terminal capacity and the expanded relay output driver hardware for 16 contact points. The CPU executes a pre-compiled binary program stored in SRAM (battery-backed) at 0.21 µs per basic ladder instruction, with the program scan cycling continuously between input sampling, program execution, and output refresh. The FX3G’s simplified instruction set compared to the FX3U excludes some advanced motion and floating-point instructions available in the FX3U, but includes all standard relay ladder logic, timer/counter functions, data manipulation, and PID instructions required for the majority of compact machine control applications. The relay output driver circuit uses electromechanical relay contacts with separate common terminal groups — within each group of 8 outputs sharing a common terminal, the common connects to the external load supply, and each relay contact provides the switched return path for individual load circuits. This architecture requires that all outputs within a common group switch loads connected to the same voltage and polarity — outputs controlling 230 VAC loads and 24 VDC loads must be assigned to different common groups. The built-in high-speed counter architecture provides 6 input channels (X0–X5) configurable as single-phase or 2-phase AB quadrature counters at up to 10 kHz, with the counter values accessible in the FX3G’s high-speed counter register (C235–C255) for comparison and output triggering in the ladder program.
Expert Tips
When designing FX3G-40MR/ES-A applications that use the built-in high-speed counters (X0–X5 at up to 10 kHz) alongside normal input functions on the remaining input points, note that the high-speed counter input points (X0–X5) are processed by a dedicated high-speed input circuit operating at interrupt speed — these input points respond to input changes faster than the normal program scan cycle, but this means they cannot be used simultaneously as standard ladder rung contacts and high-speed counter inputs in the same application without careful program design. If X0 is configured as a high-speed counter input (C235 or C236), reading X0 as a standard input bit in the ladder program will reflect the last sampled state from the previous scan’s input refresh, not the current real-time state — use the corresponding high-speed counter’s current value register rather than the X0 contact for position-dependent ladder logic. For the relay output groups, assign outputs systematically to common groups based on load voltage — group all 230 VAC loads together in one common group and all 24 VDC loads in the other, and document this assignment clearly in the panel wiring schedule to prevent future maintenance personnel from inadvertently connecting a 24 VDC load to the 230 VAC common group during wiring changes. For applications using the FX3G-40MR/ES-A in environments with significant panel door vibration (mobile machinery, marine, vehicle-mounted), fit locking spring clamp ferrules on all terminal connections rather than standard crimp ferrules — spring clamp ferrules maintain clamping force under vibration without periodic re-torquing, reducing the risk of loose terminal connections developing over the service life of the installation.
Frequently Asked Questions
Q: Is the FX3G-40MR/ES-A a suitable replacement for the FX2N-40MR-ES/UL in a retrofit application?
A: Yes. The FX3G-40MR/ES-A is the direct replacement for the FX2N-40MR-ES/UL with identical I/O count (24 inputs, 16 relay outputs) and the same AC power supply input. The FX3G provides improved execution speed (0.21 µs versus 0.08 µs per basic instruction for FX2N, noting FX2N is faster in basic instructions but FX3G is faster in applied instructions) and double the built-in high-speed counter channels (6 versus 3 for FX2N-40MR). FX2N ladder programs transfer to the FX3G-40MR/ES-A with minor adaptation — GX Works2’s compatibility check identifies any instruction differences. FX2N extension I/O modules can be reused via the FX3G-CNV-ADP conversion adapter.
Q: How does the FX3G-40MR/ES-A compare to the FX3U-32MR/ES-A in terms of suitability for a 24-input, 16-output relay output application?
A: The FX3G-40MR/ES-A provides 24 inputs and 16 relay outputs — exactly matching the specified requirement — while the FX3U-32MR/ES-A provides only 16 inputs and 16 relay outputs (32 total versus 40 total). For applications requiring 24 inputs and 16 outputs specifically, the FX3G-40MR/ES-A is the more appropriate specification as it provides the required I/O without needing extension modules. The FX3U-32MR/ES-A would require an additional 8-point input extension module to reach 24 inputs, adding cost and complexity. The FX3G’s lower cost offsets its slower CPU speed and smaller memory for the majority of relay-output machine control applications.
Q: Can the FX3G-40MR/ES-A control a Mitsubishi FR-D740 inverter drive via the built-in RS-422 port?
A: Yes. The FX3G-40MR/ES-A’s built-in RS-422 port supports Mitsubishi’s dedicated inverter communication protocol (IVDR/IVRD instructions), enabling direct speed command, direction control, and status monitoring of FR-D740 and other FR-series inverters over RS-422 without separate analogue wiring. Connect the FX3G RS-422 port to the FR-D740’s RS-485 PU connector using a compatible cable (verify pin compatibility in both hardware manuals), configure the inverter for RS-485 communication mode via Pr.79, and use the FX3G’s IVDR instruction to send frequency setpoints and control commands directly from the ladder program.
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