The FX2N-2DA is Mitsubishi Electric’s 2-channel analogue output special function module for the MELSEC FX2N compact PLC series, providing two independent channels of 12-bit digital-to-analogue conversion for voltage and current output signals — the entry-level analogue output module in the FX2N special function module range, widely installed in FX2N-based speed control, valve positioning, and setpoint generation applications that remain in active industrial service. As a right-side extension bus module for the FX2N platform, the FX2N-2DA enables FX2N base units to generate precision analogue control signals for variable frequency drives, proportional valve controllers, and analogue-input process instruments without requiring separate signal generation hardware. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the FX2N-2DA?
The FX2N-2DA is a MELSEC FX2N series special function module providing two channels of 12-bit digital-to-analogue conversion. The module installs in the FX2N extension bus and communicates with the FX2N CPU via TO buffer memory write instructions — the FX2N ladder program writes digital output values to the FX2N-2DA’s buffer memory using TO instructions, and the module converts these digital values to the corresponding analogue output signals. Each channel independently generates either a voltage or current output in the configured range, with the output range selected via hardware rotary switches on the module front panel rather than software configuration — consistent with the FX2N-2AD’s hardware configuration approach. Channel 1 and channel 2 are independently configurable for voltage output (0–5 VDC, 0–10 VDC) or current output (4–20 mA) via the respective rotary switches, enabling different output types to be used on each channel from the same module. The FX2N-2DA’s 12-bit resolution provides 4,096 discrete output levels per channel — for a 0–10 VDC output range, this corresponds to a voltage resolution of approximately 2.4 mV per count, adequate for drive speed reference and valve position control applications.
Key Technical Specifications
- Model: FX2N-2DA
- Analogue Output Channels: 2
- Resolution: 12-bit (4,095 output levels)
- Output Range (Voltage): 0–5 VDC, 0–10 VDC (rotary switch selection per channel)
- Output Range (Current): 4–20 mA (rotary switch selection per channel)
- Maximum Output Current (Voltage Mode): 10 mA per channel
- Load Resistance (Current Mode): 600 Ω maximum
- Output Accuracy: ±1% of full scale at 25°C
- Output Response Time: 2 ms (both channels updated simultaneously)
- Extension Bus Occupation: 8 I/O points
- External Power Supply: 24 VDC ±10%, 85 mA (required)
- Operating Temperature: 0°C to 55°C
- Compatible FX2N base units: All FX2N models
- Weight: Approx. 0.15 kg
Architecture & Design Overview
The FX2N-2DA implements a TO buffer memory write architecture in which the FX2N CPU program writes digital output values directly to the module’s output data registers via TO instructions, and the module’s internal DAC circuit converts these values to the corresponding analogue output signals within 2 ms of the TO write. The 12-bit DAC uses an R-2R ladder network topology with precision resistors to generate the output voltage — the same fundamental architecture used in all FX2N analogue output modules, with accuracy determined by the resistor matching tolerance and the reference voltage stability. The output range selection via rotary switch determines the reference voltage and output amplifier gain applied to the DAC output — the 0–10 VDC range uses the full DAC reference voltage with unity gain, the 0–5 VDC range uses a ×0.5 output amplifier, and the 4–20 mA current output uses a voltage-to-current converter stage with 250 Ω shunt resistor compliance. The 2-channel architecture of the FX2N-2DA is functionally equivalent to one-half of the FX2N-4DA — both channels are updated simultaneously by the module’s output circuit, ensuring that in applications where both outputs must change together (such as generating XY position references for a 2-axis analogue-commanded system), the two channel outputs change in the same update cycle without inter-channel timing skew.
Expert Tips
For variable frequency drive speed control applications using the FX2N-2DA’s 0–10 VDC output, verify the drive’s analogue input impedance before connecting — most VFDs have analogue speed reference input impedances of 10 kΩ or higher, well within the FX2N-2DA’s 10 mA maximum voltage output current capacity. However, some older drives with lower input impedances (2–5 kΩ) draw more current than the FX2N-2DA can supply at full-scale voltage — calculate the required output current as Vmax ÷ Rinput and verify it is below 10 mA before connecting. For 4–20 mA current output applications, verify the total loop resistance including cable resistance does not exceed the FX2N-2DA’s 600 Ω maximum compliance resistance — a long cable run to a proportional valve with 250 Ω input resistance plus 50 Ω cable resistance totals 300 Ω, well within the 600 Ω limit, but multiple loads in series or very long cable runs can exceed this limit and cause the current output to saturate below 20 mA at full scale. For installations where the FX2N-2DA output must be calibrated to match the downstream device’s input span precisely (for example, adjusting the 4 mA and 20 mA calibration points to match a specific valve’s flow curve), use the FX2N-2DA’s built-in gain and offset adjustment registers in buffer memory — BFM#16 and BFM#17 for channel 1, BFM#18 and BFM#19 for channel 2 — rather than adjusting the receiving device’s input calibration. Calibrating at the source rather than the destination ensures that the FX2N program’s engineering unit values correspond accurately to the physical output, simplifying maintenance diagnostics.
Frequently Asked Questions
Q: Can the FX2N-2DA’s output range be changed from voltage to current (or vice versa) via software without physical module access?
A: No. The FX2N-2DA’s output range is selected via rotary switches on the module front panel — there is no software method to change the output type from the FX2N program. This differs from the FX2N-4DA which supports software output range configuration via buffer memory TO writes. To change the FX2N-2DA’s output range, the system must be powered down and the rotary switches adjusted physically. For applications requiring remote or software-selectable output range changes, specify the FX2N-4DA instead.
Q: What is the FX2N-2DA buffer memory address for writing channel 1’s digital output value?
A: The FX2N-2DA stores the channel 1 digital output value in buffer memory register BFM#0, and channel 2 in BFM#1. The TO instruction syntax for writing D10 to channel 1 is: TO K0 K0 D10 K1 — where K0 is the module number (position in extension bus), K0 is BFM#0 (channel 1 output register), D10 is the source data register, and K1 is the number of words to write. For 12-bit output, the digital value written to BFM#0 must be in the range 0–4095 for unipolar outputs (0–5 V, 0–10 V, 4–20 mA); values outside this range cause the output to clamp at the maximum output level.
Q: Can the FX2N-2DA be used with an FX3U base unit for replacement purposes?
A: No. The FX2N-2DA is an FX2N special function module and is incompatible with the FX3U extension bus interface. For FX3U systems requiring 2-channel analogue output, the FX3U-4DA-ADP left-side adapter provides four analogue output channels with software configuration, or the FX3U-2DA (if available as a separate module) provides 2-channel output. When migrating a complete FX2N system to FX3U, all FX2N special function modules including the FX2N-2DA must be replaced with FX3U-compatible equivalents.
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