The FX3G-24MR/ES-A is Mitsubishi Electric’s 24-point relay output base unit for the MELSEC FX3G compact PLC series, providing 14 digital inputs and 10 relay contact outputs in a self-contained AC-powered controller — the mid-range relay output model in the FX3G entry-level compact PLC family, offering significantly more I/O capacity than the 14-point FX3G-14MR/ES-A for standalone machine control applications requiring a moderate point count at entry-level system cost. With relay output flexibility for direct AC and DC load switching across 10 contact points, the FX3G-24MR/ES-A addresses the majority of small-to-mid-size standalone automation tasks where the extended capabilities of the FX3U are not required. The FX3G-24MR/ES-A is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the FX3G-24MR/ES-A?
The FX3G-24MR/ES-A is a MELSEC FX3G series compact PLC base unit providing 14 input points (X0–X15, octal numbering) and 10 relay contact output points (Y0–Y11, octal), powered from 100–240 VAC mains with a built-in power supply. The 24-point I/O count positions the FX3G-24MR/ES-A between the entry-level 14-point and the larger 40-point FX3G models, covering applications where 14 points is insufficient and 40 points would be oversized. The relay outputs are divided into common groups, with independent common terminals enabling different output groups to switch loads at different voltages simultaneously — a significant advantage for machine panels where some outputs control 230 VAC motor starters and others switch 24 VDC solenoid valves from the same PLC. The FX3G CPU provides 0.21 µs per basic instruction execution, 32,000-step program memory, real-time clock, RS-422 communication port, and 4 built-in high-speed counter inputs at up to 10 kHz — more counter channels than the 14-point FX3G models due to the increased hardware capacity of the wider housing. Built-in pulse output is available on Y0 and Y1 for stepper and servo positioning applications.
Key Technical Specifications
- Model: FX3G-24MR/ES-A
- Total I/O Points: 24 (14 inputs + 10 outputs)
- Input Type: 24 VDC sink (X0–X15)
- Output Type: Relay contact (Y0–Y11), 2 A per point, 240 VAC / 30 VDC
- Output Common Groups: 2 groups (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: 4 inputs (10 kHz maximum)
- Built-in Pulse Outputs: Y0 and Y1 (100 kHz and 10 kHz respectively)
- Communication: RS-422 (built-in)
- Real-Time Clock: Built-in
- Battery Backup: Yes
- Expansion: Up to 128 total I/O via FX3G extension modules
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 90 mm × 90 mm × 75 mm
- Weight: Approx. 0.55 kg
Compatibility & System Integration
The FX3G-24MR/ES-A integrates with the FX3G extension I/O module range connected to the right side of the base unit via the FX3G extension bus, expanding total I/O to a maximum of 128 points. FX3G-compatible left-side special adapter modules — including the FX3G-4AD-ADP analogue input adapter, FX3G-4DA-ADP analogue output adapter, and FX3G-485-BD RS-485 option board — provide analogue and communication expansion without consuming extension bus capacity. The built-in RS-422 port connects directly to Mitsubishi GOT1000 and GOT2000 HMI panels using standard GT-FX cables for operator interface, and to GX Works2 for programming via a USB-to-RS-422 cable adapter. For Modbus RTU SCADA integration, the FX3G-24MR/ES-A’s built-in RS-422 port supports Modbus RTU slave mode, enabling SCADA systems with Modbus master capability to read input states, output states, and data register values from the FX3G without additional communication hardware. The FX3G-485-BD option board, installed on the base unit’s option board slot, adds a second RS-485 port for inverter communication (controlling Mitsubishi FR-series inverters via the FX3G’s IVDR/IVRD instructions) or for connection to additional Modbus RTU devices while the built-in RS-422 port remains available for HMI or programming connection. For applications requiring CC-Link field network connectivity at the FX3G level, the FX3G-32CCL CC-Link local station module provides CC-Link Ver.1 compatibility, enabling the FX3G-24MR/ES-A to participate in Mitsubishi CC-Link networks managed by a MELSEC-Q or iQ-R master controller.
Maintenance Tips
The FX3G-24MR/ES-A relay outputs are rated for 200,000 operations at rated resistive load — for machines with high-frequency relay switching (10 or more operations per minute on the same output), calculate the expected service life and plan proactive base unit replacement rather than waiting for relay contact failure during production. A relay switching 15 times per minute on a single shift operation reaches 200,000 operations in approximately 278 hours — less than 35 eight-hour shifts. For outputs switching at this frequency, specify the transistor output FX3G-24MT/ES-A or FX3G-24MT/ESS to eliminate contact wear entirely. Inspect the relay output terminal block connections annually in vibration-prone environments — loose terminals cause intermittent output failures and localised heating at the terminal contact point that can degrade the terminal block housing. Re-torque all output terminal screws to the specified 0.5–0.8 N·m torque value (verify in FX3G hardware manual) during the annual inspection. The FX3G-24MR/ES-A’s lithium battery retains program and latch device data for approximately 5 years at 25°C ambient — replace the battery every 4–5 years before the low battery warning activates (special relay M8006 indicates low battery condition in the FX3G program). In high-temperature environments (above 40°C), reduce the battery replacement interval accordingly — battery life at 55°C is typically 30–40% of the rated life at 25°C. Always power down the FX3G-24MR/ES-A before replacing the battery, and replace the battery within 20 seconds to prevent loss of SRAM data during the battery-less period.
Frequently Asked Questions
Q: Can the FX3G-24MR/ES-A control a single-phase motor with forward and reverse direction via two relay outputs?
A: Yes. Standard FX3G interlocking instructions (RST interlock between Y0 and Y1, or mechanical/electrical interlock via the relay common wiring) prevent simultaneous activation of forward and reverse contactors, which would cause a line-to-line short circuit. The FX3G ladder program implements the interlock logic with a minimum 100 ms changeover time delay between deactivating one direction and activating the other, preventing capacitive residual voltage in the motor windings from causing inrush current at direction reversal.
Q: What is the difference in I/O count between the FX3G-24MR/ES-A and the FX3G-14MR/ES-A?
A: The FX3G-24MR/ES-A provides 14 inputs and 10 outputs (24 total), versus 8 inputs and 6 outputs (14 total) for the FX3G-14MR/ES-A. The additional 6 inputs and 4 outputs of the 24-point model are housed in the wider 90 mm housing (versus 60 mm for the 14-point model). The 24-point model also provides 4 built-in high-speed counter channels versus 2 on the 14-point model, and includes pulse output capability on both Y0 and Y1 versus Y0 only on the 14-point model.
Q: Can the FX3G-24MR/ES-A be used as a replacement for the legacy FX2N-24MR-ES/UL?
A: Yes. The FX3G-24MR/ES-A is the designated replacement for the FX2N-24MR-ES/UL with identical I/O point count and relay output specifications. FX2N ladder programs can be imported into GX Works2 and recompiled for the FX3G-24MR/ES-A — most FX2N programs transfer without modification, though GX Works2’s compatibility check should be run to identify any FX2N-specific instructions not supported on the FX3G. FX2N I/O expansion modules are compatible with the FX3G via the FX3G-CNV-ADP conversion adapter, allowing reuse of existing expansion hardware during the upgrade.
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