The FX3U-4DA is Mitsubishi Electric’s 4-channel analog output special function module for the MELSEC FX3U compact PLC series — providing 4 independent analog output channels with 12-bit resolution (4,096 counts) for voltage (0–10 VDC, ±10 VDC) and current (4–20 mA, 0–20 mA) signal generation, enabling the FX3U base unit to command variable-speed drives, control valves, setpoint transmitters, and other analog-controlled field devices from the FX3U PLC program. The FX3U-4DA is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the FX3U-4DA?
The FX3U-4DA is a MELSEC FX3U series special function module providing 4 analog output channels — the standard analog output module for FX3U PLC systems requiring multi-channel analog signal generation for field device control. The module connects to the FX3U base unit’s right-side extension bus and occupies one special function module position, with the FX3U CPU writing digital setpoint values to the FX3U-4DA’s buffer memory (BFM) using TO instructions (or auto-refresh from GX Works2 parameters), and the module converting those values to proportional analog output signals on each channel. Each of the 4 output channels can be individually configured for voltage output (0–10 VDC, ±10 VDC) or current output (4–20 mA, 0–20 mA) by parameter settings — a channel configured for 4–20 mA output converts the written digital value (0–4,095 counts) linearly to 4.0–20.0 mA, enabling the FX3U program to command a field device’s speed, position, or setpoint in engineering units by writing the appropriate scaled digital value to the channel’s BFM. The FX3U-4DA is the analog output counterpart to the FX3U-4AD analog input module — both use the same 12-bit resolution, the same buffer memory programming approach, and the same GX Works2 auto-refresh parameter capability, providing a consistent programming interface for analog I/O in FX3U systems. The module updates all 4 output channels with a conversion cycle of approximately 4 ms per channel (16 ms total) — faster update than the FX3U-4AD’s 15 ms per channel input conversion, enabling more responsive analog command generation for control applications.
Key Technical Specifications
- Model: FX3U-4DA
- Analog Output Channels: 4
- Output Signal Types: 0–10 VDC, ±10 VDC, 4–20 mA, 0–20 mA (per channel, selectable)
- Resolution: 12-bit (4,096 counts)
- Conversion Accuracy: ±0.5% of full scale (at 25°C)
- Output Update Time: Approx. 4 ms per channel (16 ms total for 4 channels)
- Voltage Output Drive Capability: Minimum 5 kΩ load (maximum 2 mA short-circuit protected)
- Current Output Drive Capability: Maximum 600 Ω load impedance
- Isolation: Between channels and FX3U internal bus (optical isolation)
- Extension Bus Occupation: 8 I/O points
- Power Supply: From FX3U base unit internal bus (no external supply required)
- Compatible Base Units: FX3U, FX3UC (via adapter)
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 40 mm × 90 mm × 87 mm
- Weight: Approx. 0.17 kg
Typical Industrial Applications
The FX3U-4DA is deployed in FX3U machine control applications requiring analog setpoint command signals to field devices — the most common application being frequency command to variable speed drives (FR-A800, FR-E700, FR-D700 series) for motor speed control from the FX3U ladder program. A single FX3U-4DA provides 4 independent 4–20 mA or 0–10 VDC speed reference channels to 4 inverter drives, enabling the FX3U to command independent motor speeds for 4 separate conveyor zones, 4 pump drives, or 4 fan speed axes from a single analog output module. In temperature control systems, the FX3U-4DA generates 4–20 mA output signals to control modulating heating valves, cooling water flow control valves, or electric heating element power controllers from PID loop calculations executed in the FX3U ladder program — the PID instruction output (percentage 0–100%) is scaled to the FX3U-4DA’s 0–4,095 count range and written to the appropriate channel for proportional valve control. Pressure and flow control in pneumatic and hydraulic systems uses the FX3U-4DA’s 0–10 VDC output to command proportional pressure regulators, proportional directional control valves, and electro-pneumatic positioners from the FX3U program. In laboratory and test equipment, the FX3U-4DA generates calibrated analog test signals (simulated sensor outputs, reference voltages) under FX3U program control for automated test sequences. Textile and printing machine tension control uses the FX3U-4DA’s 4–20 mA output to command dancer roll positioning actuators and web tension control brakes for web tension regulation in printing, laminating, and winding processes.
Troubleshooting Guide
For FX3U-4DA channels showing no output signal despite the FX3U program writing correct values to the buffer memory via TO instruction, verify the output type configuration parameter in BFM#0 — the default output type configuration may not match the required output type (voltage versus current) for the channel. Write the correct output type code to BFM#0 using a TO instruction in the FX3U initialisation sequence (a block executed once at PLC startup using the M8002 initial pulse contact) to configure the output type before any setpoint values are written. Confirm the BFM#0 write is executing by placing a SET M0 instruction after the TO instruction in the initialisation block and verifying M0 is set in GX Works2 device monitor after power-up. For FX3U-4DA current output channels reading 4 mA at minimum output (0 count) rather than 0 mA — this is correct behaviour for 4–20 mA configured channels, where 0 digital counts outputs 4.0 mA (the live-zero). If the field device requires 0 mA at minimum, configure the channel for 0–20 mA output mode rather than 4–20 mA. For FX3U-4DA voltage output channels showing voltage drift with temperature changes in the machine environment, verify the module’s ambient temperature remains within 0–55°C specification — temperature exceeding 55°C degrades the DAC’s reference voltage stability, causing output accuracy to exceed the ±0.5% specification. Install panel cooling or relocate heat-generating components away from the FX3U-4DA to maintain ambient temperature within specification.
Frequently Asked Questions
Q: Can the FX3U-4DA and FX3U-4AD be installed simultaneously in the same FX3U extension chain?
A: Yes. The FX3U-4AD (analog input) and FX3U-4DA (analog output) can coexist in the same FX3U extension chain with other FX3U special function modules, up to the 8-module maximum. Each module occupies one special function module position in the chain, and the FX3U CPU addresses each module independently by its position number (K0, K1, K2… from left to right in the extension chain) in the FROM/TO instructions. For systems requiring simultaneous analog input monitoring and analog output control, a common configuration is FX3U base unit + FX3U-4AD (in position 0) + FX3U-4DA (in position 1) — providing 4 analog inputs and 4 analog outputs in 2 special function module positions.
Q: What is the settling time for the FX3U-4DA’s voltage output after a digital value change, and does it affect closed-loop control stability?
A: The FX3U-4DA’s voltage output settles to within ±0.5% of the new setpoint within approximately 1 ms of the digital value update — significantly faster than the 4 ms per channel update cycle. For the FX3U PLC’s closed-loop control applications (PID loop), the 16 ms total output update cycle is the limiting factor for the analog output command update rate, not the DAC’s settling time. PID control cycles faster than 16 ms are not achievable with the FX3U-4DA’s standard update rate — for faster control cycles, a high-speed analog module with shorter conversion time must be specified.
Q: Can the FX3U-4DA’s current output drive a 250 Ω input impedance field device transmitter directly?
A: Yes. The FX3U-4DA’s 4–20 mA current output can drive load impedances up to 600 Ω — a 250 Ω input impedance field device is well within this limit. The current output maintains 4–20 mA constant current regardless of load impedance (within the 600 Ω maximum), so variations in cable resistance or input impedance tolerance do not affect the accuracy of the output signal at the field device. Verify the total series resistance in the current loop (cable resistance + field device input impedance) remains below 600 Ω to ensure the FX3U-4DA can maintain the specified output current range.
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